Design Optimisation for an Efficient Wireless Power Transfer System for Electric Vehicles

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ScienceDirect ScienceDirect Energy Procedia 117 Energy Procedia 00(2017) (2017)1015–1023 000–000 www.elsevier.com/locate/procedia

1st International Conference on Power Engineering, Computing and CONtrol, PECCON-2017, 2-4 March 2017, VIT University, Chennai Campus 1st International Conference on Power Engineering, Computing and CONtrol, PECCON-2017, 1st International Conference on Power Engineering, Computing and CONtrol, PECCON-2017, 2-4 March 2017, VIT University, Chennai Campus Design Optimisation for an Efficient Wireless Power Transfer The 15th International Symposium on District Heating and Cooling 2-4 March 2017, VIT University, Chennai Campus

System for Efficient Electric Vehicles Design Optimisation for Wireless Power Assessing the feasibility of using the heat demand-outdoor Design Optimisation for an an Efficient Wireless Power Transfer Transfer 1 2for Electric3 Vehicles 4 5 System Soham Chatterjee , Archana Iyer for Bharatiraja Ishan Vaghasia Valiveti Rajesh temperature function for a, C.long-term district heat, demand forecast System Electric ,Vehicles

1, 2, 3 ,4 ,5

Department of Electrical and Electronics Engineering, Faculty of Engineering and Technology, SRM University, Chennai, India

2 3 4 5c a,b,c 1, Archana a a b c Soham Chatterjee Vaghasia Rajesh 1 A. Pina , Iyer 2, C. Bharatiraja 3, Ishan 4, Valiveti 5 I. Andrić *, P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre Soham Chatterjee , Archana Iyer , C. Bharatiraja , Ishan Vaghasia , Valiveti Rajesh __________________________________________________________________________ 1, 2, 3 ,4 ,5 Department of Electrical and Electronics Engineering, Faculty of Engineering and Technology, SRM University, Chennai, India 1, 2,a3IN+ ,4 ,5

Center for Innovation, and Policy ResearchFaculty - Instituto Superior Técnico, Av. Rovisco PaisUniversity, 1, 1049-001 Lisbon,India Portugal Department of ElectricalTechnology and Electronics Engineering, of Engineering and Technology, SRM Chennai,

b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract __________________________________________________________________________ c __________________________________________________________________________ Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France

Wireless AbstractPower Transfer (WPT) has been used to transfer small amounts of power over small distances to run smartphones, RFID tags, smart watches and even biomedical implants without any electrical contact. A popular application for this is the wireless charging of electric Abstract and hybrid electric vehicles. However, designing send amounts large amounts power over large distancestowhile maintaining appreciable Wireless Power Transfer (WPT) has been used tosystems transfertosmall of power over small distances run smartphones, RFID tags, Abstract efficiency is hard to do. In this paper, an overview of a typical WPT system has been given. Simple design equations have been to Wireless Power Transfer (WPT) has been used to transfer small amounts of power over small distances to run smartphones, RFID tags, smart watches and even biomedical implants without any electrical contact. A popular application for this is the wireless charging ofgiven electric calculate inductance, capacitance, power, quality factor and coupling coefficient to optimise coil design electric vehicle smarthybrid watches and even biomedical implants without any electrical contact. A popular application for this is for the wireless chargingapplication. of electric and electric vehicles. However, designing systems to send large amounts power over large distances while maintaining appreciable District heating networks are commonly in thelarge literature aspower one of most effective solutions forappreciable decreasing the Further, a comparison hasInbeen made theaddressed popular coil shapes the has effects ofgiven. the the change of coil parameters like number turns, and hybrid However, designing systems to send amounts over large distances while maintaining efficiency iselectric hard tovehicles. do. this paper,between an overview of a typical WPT and system been Simple design equations have been of given to greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat pitch and inner and outer radius on efficiency of the coil has been studied. efficiency is hard to do. In this paper, an overview of a typical WPT system has been given. Simple design equations have been given to calculate inductance, capacitance, power, quality factor and coupling coefficient to optimise coil design for electric vehicle application. sales. Due to the capacitance, changed climate conditions building renovation heatof demand in thelike future could decrease, calculate inductance, power, quality factorand and coupling coefficient topolicies, optimise coil design for electric vehicle application. Further, comparison has been made theLtd. popular coil shapes and the effects of the change coil parameters number of turns, © 2017 aThe Authors. Published bybetween Elsevier prolonging the investment return period. Further, a comparison has been made between the popular coil shapes and the effects of the change of coil parameters like number of turns, Keywords: Wireless Power Transfer, Electric Vehicles, Design Optimisation, Coil Shapes, Quality Factor, Coupling Coefficients. pitch and innerunder and outer radius on efficiency of the coilcommittee has been studied. Peer-review responsibility of the scientific of the 1st International Conference on Power Engineering, The and main scope thisradius paper to assessofthe ofstudied. using the heat demand – outdoor temperature function for heat demand pitch inner and of outer onisefficiency the feasibility coil has been

Computing and CONtrol. forecast. The district ofTransfer, Alvalade, located in Lisbon as Quality a caseFactor, study.Coupling The district is consisted of 665 1.Keywords: INTRODUCTION Wireless Power Electric Vehicles, Design (Portugal), Optimisation,was Coilused Shapes, Coefficients. buildings Wireless that varyPower in both construction period and typology. ThreeCoil weather (low,Coupling medium, high) and three district Keywords: Transfer, Electric Vehicles, Design Optimisation, Shapes,scenarios Quality Factor, Coefficients. scenariosPower were developed deep).magnetic To estimate the error, obtained heat over demand values Inductive Wireless Transfer (shallow, is the useintermediate, of time-varying fields to transfer power short and were 1.renovation INTRODUCTION 1.compared INTRODUCTION with results from a dynamic demand model, developed validated by the authors. and has since been medium distances to electric loads. Itheat was first used bypreviously Nikolai Tesla in theand early 20 th century The resultsWireless showed that when only change considered, themagnetic margin offields error could be acceptable for some applications developed prominently over the weather past three in research labs around the world [1]. It over has been used Inductive Power Transfer is the usedecades ofistime-varying to transfer power short and th toothbrushes (the errordistances in annual was lower fortime-varying allby weather However, after introducing renovation Inductive Wireless Power Transfer the 20% use electronics of magnetic fields to20 transfer power over short and prominently to transfer power to consumer likescenarios smartphones, electric andsince in audio century and has been medium todemand electric loads. Itisthan was first used Nikolai Tesla inconsidered). the early th scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). century and has since been medium distances to electric loads. It was first used by Nikolai Tesla in the early 20 systems ofprominently Apple iPhones WPTthree has decades also been used experimentally in world biomedical developed over [2]. the past in research labs around the [1]. Itimplants has beenwhere used The value ofhave slopebeen coefficient increased on average within range ofRFID 3.8% up toused 8%world per decade, that corresponds developed over past three decades in the research around the [1]. It has been used pacemakers powered WPT technologies [3], [4].labs tags in prisons and ID cards forto the prominentlyprominently to transfer powerthetousing consumer electronics like smartphones, electric toothbrushes and in audio decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather prominently to transfer power to consumer electronics like smartphones, electric toothbrushes and in audio identification use WPT systems gatherhas information and other remote sensors [5].implants WPT haswhere been and systems of Apple iPhones [2].toWPT also beenfrom usedtags experimentally in biomedical renovation scenarios considered). OnWPT the other hand, function intercept increased for 7.8-12.7% per decade (depending systems of Apple iPhones [2]. has also been used experimentally in biomedical implants where viewed as a viable alternative in consumer goods and in other applications like wireless sensor nodes iton the pacemakers have been powered using WPT technologies [3], [4]. RFID tags used in for prisons and ID considered, cardsasfor coupled scenarios). The values suggested could be used to modify the function parameters the scenarios pacemakers have been powered using WPT technologies [4].and RFID tags used in prisons and ID for and reduces the need wires, decreases the size required from for[3], charging apparatus in consumer goods andcards reduces identification use for WPT systems toestimations. gather information tags other remote sensors [5]. WPT has been improve the accuracy of heat demand identification use WPT systems to gather information from tags and other remote sensors [5]. WPT has been

the risk as to users duealternative to electrical In certain biomedicallike andwireless RFID, where is aasbig viewed a viable in shocks consumer goods applications and in otherlike applications sensor size nodes it viewed as aneed viable alternative in consumer goods and in other applications like wireless goods sensor and nodes as it concern, the use of WPT has helped engineers reduce the size of the devices [6]. reduces the for wires, decreases the size required for charging apparatus in consumer reduces © 2017 The Authors. Published by Elsevier Ltd. reduces theusers need for to wires, decreases theIn size required for charging apparatus inand consumer goods size and reduces the risk to electrical shocks certain applications like biomedical RFID, where is aand big Peer-review underdue responsibility of the Scientific Committee of The 15th International Symposium on District Heating the risk to users due to electrical shocks In certain applications like biomedical and RFID, where size is a big _____ the use of WPT has helped engineers reduce the size of the devices [6]. concern, Cooling. concern, the use of WPT has helped engineers reduce the size of the devices [6]. Soham Chatterjee. _____ Keywords: Heat demand; Forecast; Climate change _____ Tel.: +91-9176034273; Soham Chatterjee. Soham Chatterjee. Tel.: +91-9176034273; Tel.: +91-9176034273; 1876-6102 © 2017 The Authors. Published by Elsevier Ltd.by Elsevier Ltd. 1876-6102 © 2017 The Authors. Published

Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Publishedof bythe Elsevier Ltd. committee of the 1st International Conference on Peer-review under responsibility scientific Peer-review under responsibility of the scientific committee of the 1st International Conference on Power Engineering, Computing 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Power Engineering, Computing and CONtrol. and CONtrol. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 10.1016/j.egypro.2017.05.223 Peer-review under responsibility of the scientific committee of the 1st International Conference on

Peer-review under responsibility of the scientific committee of the 1st International Conference on Power Engineering, Computing and CONtrol. Power Engineering, Computing and CONtrol.

1016

Author name / Energy Procedia 00 (2017) 000–000 Author Author name name // Energy Energy Procedia Procedia 00 00 (2017) (2017) 000–000 000–000

Soham Chatterjee et al. / Energy Procedia 117 (2017) 1015–1023

Nomenclature Nomenclature Nomenclature L Inductance Vo Output Voltage/Secondary Coil Voltage N Number of Turns of Coil P Power L Inductance V Output L Inductance Voo Output Voltage/Secondary Voltage/Secondary Coil Coil Voltage Voltage D Inner Coil Diameter Q Quality Factor N Number of Turns of Coil P Power in N Number of Turns of Coil P Power Outer kQ Coupling Factor D Inner Q Quality out Inner Coil Coil Diameter Diameter Din Quality Factor Factor in w Width of Conductor R Outer Radius of Coil D Outer Coil Diameter k Coupling o out Outer Coil Diameter Dout k Coupling Factor Factor pw Pitch ofof Inner Radius w Width Conductor R Outer Radius of of Coil Coil Outer Radius of Coil Width ofCoil Conductor Roio Capacitance S Conductor Diameter pC Pitch of Coil R Inner Radius of Coil w Inner Radius of Coil Rii p Pitch of Coil fC Frequency ISow Output Current/Secondary Coil Current C Capacitance S Conductor Diameter Conductor Diameter Capacitance w Mutual Inductance fM Frequency I Output Current/Secondary Coil Current Current o Output Current/Secondary Coil Io f Frequency M Mutual M Mutual Inductance Inductance Recently, research has been going on in the use of WPT to transfer energy to static and dynamic Electric Vehicles [8]. Wireless charging of electric vehicles can increase theenergy ferry range of the vehicles andElectric reduce Recently, research has going in of to to and dynamic Recently,[7], research has been been going on on in the the use use of WPT WPT to transfer transfer energy to static static and dynamic Electric the size of battery packs, thus reducing the cost of the whole system. In this regard, Wang et. Al., has produced Vehicles [7], [8]. Wireless charging of electric vehicles can increase the ferry range of the vehicles and Vehicles [7], [8]. Wireless charging of electric vehicles can increase the ferry range of the vehicles and reduce reducea verysize efficient method forthus wireless transfer of power to stationary [9]. Research at universities the size of battery battery packs, thus reducing the cost cost of the the whole whole system.vehicles In this this regard, regard, Wang et. et.teams Al., has has produced aa the of packs, reducing the of system. In Wang Al., produced like University the California programvehicles have made lot of headway wireless very efficient method wireless transfer of to [9]. teams at universities veryKAIST, efficientAuckland method for for wirelessand transfer of power powerPATH to stationary stationary vehicles [9]. aResearch Research teams in at the universities charging of dynamic vehicles [10], [11], [14]. They have transferred power at various power levels and like KAIST, Auckland University and the California PATH program have made a lot of headway in the like KAIST, Auckland University and the California PATH program have made a lot of headway in the wireless wireless frequencies at efficiencies as high as 85% over distances of up to 1m. India is one of the largest importer of oil charging of dynamic vehicles [10], [11], [14]. They have transferred power at various power levels charging of dynamic vehicles [10], [11], [14]. They have transferred power at various power levels and and in the world, which it cannot afford to remain so, given the economic and environmental constraints. Electric frequencies at efficiencies as high as 85% over distances of up to 1m. India is one of the largest importer of frequencies at efficiencies as high as 85% over distances of up to 1m. India is one of the largest importer of oil oil scooters are popular the Indian markets, and so, it isgiven only athe matter of time before electric cars swarm theElectric Indian in which afford to economic and environmental constraints. in the the world, world, which it itin cannot cannot afford to remain remain so, given the economic and environmental constraints. Electric auto market too. Thein charging of and electric will make them more popular asswarm it givesthe user scooters are the markets, it only of before electric cars scooters are popular popular inwireless the Indian Indian markets, and it is is vehicles only aa matter matter of time time before electric cars swarm thetheIndian Indian portability and quick charging. The policy of electric vehicle progression has increased in the past few years in auto market too. The wireless charging of electric vehicles will make them more popular as it gives the auto market too. The wireless charging of electric vehicles will make them more popular as it gives the user user India. portability and quick charging. The policy of electric vehicle progression has increased in the past few years portability and quick charging. The policy of electric vehicle progression has increased in the past few years in in India. India. Among all the WPT technologies, the use of resonant inductive WPT has been seen to be the most efficient to transfer at medium distances EV‟s. The use of a resonance coupling Among all the technologies, the of inductive WPT has seen be most Among allpower the WPT WPT technologies, thetouse use of resonant resonant inductive WPTtopology has been beenincreases seen to to the be the the most between the coils and reduces the need to transfer power with higher current. Additionally, the power transfer efficient to transfer power at medium distances to EV‟s. The use of a resonance topology increases the coupling efficient to transfer power at medium distances to EV‟s. The use of a resonance topology increases the coupling method be asand efficient as the possible to deliver the required power to the In this between the reduces need to transfer power with higher Additionally, power betweenmust the coils coils and reduces the need to to reduce transferlosses powerand with higher current. current. Additionally, the vehicle. power transfer transfer paper, the procedure for design of resonant WPT losses has been and haveto made between method must be as to and to the required the In method must be as as efficient efficient as possible possible to reduce reduce losses andoutlined to deliver deliver thecomparisons required power power tobeen the vehicle. vehicle. In this this the various shapes of coils for WPT systems. Different parameters have been changed in each coil to find the paper, the procedure for design of resonant WPT has been outlined and comparisons have been made between paper, the procedure for design of resonant WPT has been outlined and comparisons have been made between optimum size and shape of the coil for a WPT system. the various shapes of coils for WPT systems. Different parameters have been changed in each coil to find the various shapes of coils for WPT systems. Different parameters have been changed in each coil to find the the optimum size shape coil aa WPT 2. Overview of Standard System optimum size and and shape of of the theWPT coil for for WPT system. system.

2. 2. Overview Overview of of Standard Standard WPT WPT System System

Fig 1: Structure of a Typical WPT System Fig Fig 1: 1: Structure Structure of of aa Typical Typical WPT WPT System System Any wireless power transfer system can be broadly divided into two parts- the transmitter and the receiver.A WPT system needs input power be given power DC sources. of AC Any power transfer system can broadly divided into two partsthe transmitter and the receiver.A Any wireless wireless power an transfer system which can be becan broadly divided intofrom two either parts- AC the or transmitter and In thecase receiver.A sources, the input power is first rectified. The rectifier stage may also contain a Power Factor correction module. WPT system needs an input power which can be given power from either AC or DC sources. In case WPT system needs an input power which can be given power from either AC or DC sources. In case of of AC AC The rectifier stagepower provides controlled power to the rest of the The next stageFactor is a boost converter that sources, the is rectified. The stage may also aa Power correction module. sources, the input input power is first first rectified. The rectifier rectifier stage maysystem. also contain contain Power Factor correction module. boosts the DC voltage to acontrolled higher value as to receiverThe stage. boost less than that 1.5, The stage provides power the of next stage is boost The rectifier rectifier stage provides controlled power torequired the rest rest by of the the system. system. The nextFor stage is aa ratios boost converter converter that switching losses are less in Z source converters as compared to conventional converters [12]. Hence the use of Z boosts the DC voltage to a higher value as required by the receiver stage. For boost ratios less than boosts the DC voltage to a higher value as required by the receiver stage. For boost ratios less than 1.5, 1.5, source network can also be employed. The inverter stage consists of a full-bridge switching network that switching losses are less in Z source converters as compared to conventional converters [12]. Hence the use of switching losses are less in Z source converters as compared to conventional converters [12]. Hence the use of Z Z converts the DCcan waveform a high The frequency Theof chosen is highnetwork to increase source also employed. inverter stage consists aa full-bridge switching that source network network can also be be into employed. The invertersquare stage wave. consists of frequency full-bridge switching network that efficiency andDC decrease losses in aathehigh transmitter stage.This stage converts the High Frequency wave converts waveform into frequency square The chosen is to converts the the DC waveform into high frequency square wave. wave. The frequency frequency chosen is high highSquare to increase increase output of the inverter stage to High Frequency Sine wave using passive components capacitors and inductors. efficiency and decrease losses in the transmitter stage.This stage converts the High Frequency Square efficiency and decrease losses in the transmitter stage.This stage converts the High Frequency Square wave wave The is matched in High both Frequency the transmitter and receiver stage components to increase capacitors the efficiency of power output of stage Sine using and outputfrequency of the the inverter inverter stage to to High Frequency Sine wave wave using passive passive components capacitors and inductors. inductors. transferred. The is incoming the pick-upand coil receiver is converted intoto again tothe the battery. The frequency frequency is matchedACin inpower both from the transmitter transmitter and receiver stage toDC increase thecharge efficiency of power power The matched both the stage increase efficiency of transferred. The incoming AC power from the pick-up coil is converted into DC again to charge transferred. The incoming AC power from the pick-up coil is converted into DC again to charge the the battery. battery. 3. Design of a WPT System 3. Design Design of of aa WPT WPT System System 3.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd.

3.1

Inductance 3.1 Inductance 3.1 Inductance 3.1 Inductance 3.1 Inductance

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Fig 2: Cross-sectional view of Circular Coil Fig 2: Cross-sectional view of Circular Coil Fig 2: Cross-sectional view of Circular Coil Figcalculated 2: Cross-sectional of Circular Coil The self-inductance of coils can be using the view Wheeler approximations for flat spiral coils [13]. The Figcalculated 2: Cross-sectional of Circular Coil The self-inductance of coils can be using the view Wheeler approximations for flat spiral coils [13]. The formula however is invalid incan cases where the using coil has few turns approximations and when the pitch is much thanThe the The self-inductance of coils be calculated the Wheeler for flat spiralsmaller coils [13]. formula however is invalid in cases where the coil has few turns and when the pitch is much smaller thanThe the The diameter. self-inductance of these coils boundary can be calculated using the Wheeler approximations for flat spiral coils [13]. coil In both conditions, the inductance is very lowtheand hence not suitable for WPT formula however is invalid in cases where the coil has few turns and when pitch is much smaller than the The self-inductance of coils can be calculated using the Wheeler approximations for flat spiral coils [13]. The coil diameter. In both these boundary conditions, the inductance is very low and hence not suitable for WPT formula however is invalid in cases where the coil has few turns andinwhen the pitch much smaller thanThe the applications. Knowing the value of inductance of athe coil is important the design of ais resonant topology. coil diameter. In both these boundary conditions, inductance is very low and hence not suitable for WPT formula however is invalid inboundary cases where the coil has few turns and theand pitch much smaller than the applications. Knowing the value of inductance of athe coil is important inwhen the design of ais resonant topology. The coil diameter. Insingle both these conditions, inductance is very low hence not suitable for WPT inductance of a layer helical coil is given by applications. the value ofcoil inductance coil is important in the design of a resonant topology. The coil diameter. both layer these boundary conditions, inductance is very low and hence not suitable for WPT inductance ofKnowing aInsingle helical is given of by aathe applications. Knowing the value of inductance of coil is important in the design of a resonant topology. The inductance of a single layer helical coil is given by applications. the value inductance a coil is important in the design of a resonant topology. The 2given of 2 inductance ofKnowing a single layer helicalofcoil is by (1) L = N2 (Dout – N (w + p))2 X 39.37 (Dout by – N (w + p))2 X 39.37 (1) L = is N2given inductance of a single layer helical coil 6 (16Dout) +N28N (w +2 p) X 10 6 (D – (w + p)) 39.37 (1) L=N 2 out (16Dout) + 28N (w + p) 10 (1) L = N2 (Dout – N (w + p))2 X 39.37 6 3.2 Capacitance (16Dout) + 28N (w + p) 10 6 (Dout – +N28N (w +(w p))+ p) X 10 39.37 (1) L=N 3.2 Capacitance (16Dout) 6 3.2 Capacitance (16Dout) + 28N (w + p) 10 3.2 TheCapacitance capacitance of a coil depends upon the number of turns and the pitch of the coil. The relative permittivity 3.2 TheCapacitance capacitance of a coil depends upon the number of turns and the pitch of the coil. The relative permittivity and the diameterofofathe also affects the capacitance thepitch coil.ofThe of capacitance becomes The capacitance coilconductor depends upon the number of turns andof thevalue coil. The relative permittivity and the diameterofofathe conductor also affects the capacitance ofthe thepitch coil.ofThe of capacitance becomes The capacitance coilthe depends the number of turns the thevalue coil. The relative permittivity harder todiameter calculate as numberupon of affects turns increases due and to ofadjacent winding capacitance. However, the and the of the conductor also the capacitance the coil. The value of capacitance becomes The the capacitance ofofaas coilthe depends the number of turns the pitch ofThe thevalue coil. The relative permittivity harder todiameter calculate numberupon of affects turns increases due and to ofadjacent winding capacitance. However, the and the conductor also the capacitance the coil. of capacitance becomes capacitance of the coil is small and of the order of a few pF and its effect on the design of a resonant topology is harder calculate as number of turns dueandtoits capacitance. However, the and the to diameter theisthe conductor also thea capacitance ofadjacent the coil. Thedesign value of acapacitance becomes capacitance of the of coil small and of theaffects orderincreases of few pF effect onwinding the of resonant topology is harder to calculate as the number of turns increases due to adjacent winding capacitance. However, the less. In general, the capacitance of a coil can be calculated as capacitance of the small and theturns order of a few pF its effect onwinding the design of a resonant topologythe is harder calculate asis number of due capacitance. However, less. In to general, thecoil capacitance of aof beincreases calculated asand capacitance of the coil isthe small and ofcoil thecan order of a few pF andtoitsadjacent effect on the design of a resonant topology is less. In general, thecoil capacitance of aofcoil can be of calculated asand its effect on the design of a resonant topology is capacitance of the is small and the order a few pF less. In general, the capacitance of a coil can be calculated C as =1/(2πf)2L (2) (2) less. In general, the capacitance of a coil can be calculated C as =1/(2πf)2L 3.3Mutual Inductance C =1/(2πf)2L (2) 3.3Mutual Inductance C =1/(2πf)2L (2) 3.3Mutual Inductance C =1/(2πf)2L (2) 3.3Mutual Inductance When two coils are under mutual inductance, the coupling coefficient, k, determines the strength of coupling 3.3Mutual When two Inductance coils are under mutual inductance, the coupling coefficient, k, determines the strength of coupling between thecoils coils. coupling fromcoefficient, 0 to 1, where 1 is perfectly 0 is no When two areThe under mutualcoefficient inductance,can therange coupling k, determines the coupled strength and of coupling between thecoils coils. The coupling coefficient can fromcoefficient, 0 to 1, where 1 is perfectly 0 is no When two are under mutual inductance, therange coupling k, determines the coupled strength and of coupling coupling. When k is between 0.5 and 1, the system is said to be tightly coupled. between the coils. The coupling coefficient can range from 0 to 1, where 1 is perfectly coupled and 0 is no When two coils under mutual inductance, therange coupling coefficient, k, determines the coupled strength and of coupling coupling. When kare isThe between 0.5 and 1, the system is saidfrom to be coupled. between the coils. coupling coefficient can 0 tightly to 1, where 1 is perfectly 0 is no coupling. When k is between 0.5 and 1, the system is said to be0 tightly coupled. between coils. coupling coefficient can range to 1, where 1 is perfectly coupled and 0 is no coupling.the When k isThe between 0.5 and 1, the system is saidfrom to be tightly coupled. coupling. When k is between 0.5 and 1, the system is said to be tightly coupled.

Fig 3: Mutual Inductance of Coils Fig 3: Mutual Inductance of Coils Fig 3: Mutual Inductance of Coils Fig 3: Mutual of Coils In general, the output voltage on the secondary side ofInductance the WPT system is given by In general, the output voltage on the secondary side ofInductance the WPT system is given by Fig 3: Mutual of Coils 𝑉𝑉𝑜𝑜 =by𝑗𝑗𝜔𝜔𝑀𝑀𝐼𝐼 (3) In general, the output voltage on the secondary side of the WPT system is given 𝑉𝑉𝑜𝑜 =by𝑗𝑗𝜔𝜔𝑀𝑀𝐼𝐼 (3) In general, the the mutual output voltage on the sideusing of the system is given Therefore, inductance cansecondary be found by theWPT formula, 𝑉𝑉𝑜𝑜 = 𝑗𝑗𝜔𝜔𝑀𝑀𝐼𝐼 (3) In general, the mutual output voltage on the sideusing of the system is given by Therefore, inductance cansecondary be found by theWPT formula, 𝑉𝑉𝑜𝑜=𝑉𝑉𝑜𝑜/𝜔𝜔𝐼𝐼 = 𝑗𝑗𝜔𝜔𝑀𝑀𝐼𝐼 (3) 𝑀𝑀 (4) Therefore, the mutual inductance can be found by using the formula, 𝑉𝑉𝑜𝑜=𝑉𝑉𝑜𝑜/𝜔𝜔𝐼𝐼 = 𝑗𝑗𝜔𝜔𝑀𝑀𝐼𝐼 (3) 𝑀𝑀 (4) Therefore, the mutual inductance can be found by using the formula, The output current can be calculated by using the formula 𝑀𝑀 =𝑉𝑉𝑜𝑜/𝜔𝜔𝐼𝐼 (4) Therefore, mutual canby beusing foundthe byformula using the formula, The output the current caninductance be calculated 𝑀𝑀 =𝑉𝑉𝑜𝑜/𝜔𝜔𝐼𝐼 (4) 𝐼𝐼o = 𝑉𝑉𝑜𝑜/𝑗𝑗𝜔𝜔𝐿𝐿2 = 𝑀𝑀𝐼𝐼1/𝐿𝐿2 (5) The output current can be calculated by using the formula (4) 𝐼𝐼o = 𝑉𝑉𝑜𝑜/𝑗𝑗𝜔𝜔𝐿𝐿2𝑀𝑀 = =𝑉𝑉𝑜𝑜/𝜔𝜔𝐼𝐼 𝑀𝑀𝐼𝐼1/𝐿𝐿2 (5) ThePower output current can be calculated by using the formula 3.4 𝐼𝐼o = 𝑉𝑉𝑜𝑜/𝑗𝑗𝜔𝜔𝐿𝐿2 = 𝑀𝑀𝐼𝐼1/𝐿𝐿2 (5) The output current can be calculated by using the formula 3.4 Power 𝐼𝐼o = 𝑉𝑉𝑜𝑜/𝑗𝑗𝜔𝜔𝐿𝐿2 = 𝑀𝑀𝐼𝐼1/𝐿𝐿2 (5) 3.4 Power 𝐼𝐼o = 𝑉𝑉𝑜𝑜/𝑗𝑗𝜔𝜔𝐿𝐿2 = 𝑀𝑀𝐼𝐼1/𝐿𝐿2 (5) 3.4 ThePower power delivered to the receiver is the product of the formulas obtained above for the output voltage and ThePower power delivered to the receiver is the product of the formulas obtained above for the output voltage and 3.4 current. It isdelivered given by,to the receiver is the product of the formulas obtained above for the output voltage and The power current. It isdelivered given by,to the receiver is the product of the formulas obtained 2 The power for the output voltage and (6) = 𝜔𝜔𝐼𝐼122 𝑀𝑀above 2/𝐿𝐿2 current. It is given by,to the receiver is the product of the formulasP The power delivered for the output voltage and (6) P obtained = 𝜔𝜔𝐼𝐼12 𝑀𝑀above current. It is given by, 2/𝐿𝐿2 As can be seen, the maximum power that can be delivered is dependent largely on the mutual inductance 𝑀𝑀 /𝐿𝐿 (6) P = 𝜔𝜔𝐼𝐼1 2 2 2 current. giventhe by, maximum power that can be delivered is dependent As can It beisseen, largely on the mutual inductance 𝑀𝑀 /𝐿𝐿 (6) P = 𝜔𝜔𝐼𝐼1 between theseen, two coils and the primary side can current. The transmitted power also upon theinductance operating 2 largely 2 2 depends As can be the maximum power that be delivered is dependent on the mutual /𝐿𝐿2 depends (6) P = 𝜔𝜔𝐼𝐼1 between theseen, two coils and the primary side can current. The transmitted power𝑀𝑀largely also upon theinductance operating As can be the maximum power that be delivered is dependent on the mutual frequency. for coil design, power transmission can be increased by increasing the operating between theTherefore, two coils andaa given the primary side can current. The transmitted power also depends the As can be seen, the maximum power that be delivered is dependent largely onincreasing the upon mutual frequency. Therefore, for given coil design, power transmission can be increased by theinductance between the two coils and the primary side current. The transmitted power also depends upon the operating frequency or the coupling factor. The design, effects power of thesetransmission and using acan larger current has studiedtheinoperating the later frequency. Therefore, given coil be increased by been increasing between the two coilsfor andaafactor. the primary side current. The power also has depends upon the frequency or the coupling The design, effects of thesetransmission andtransmitted using acan larger current studied the later frequency. Therefore, for given coil power be increased by been increasing theinoperating operating sections. frequency or the coupling factor. The effects of these and using a larger current has been studied in the later frequency. Therefore, for a given coil design, power transmission can be increased by increasing the operating sections. frequency or the coupling factor. The effects of these and using a larger current has been studied in the later sections. frequency or the coupling factor. The effects of these and using a larger current has been studied in the later sections. 3.5 Frequency sections. 3.5 Frequency 3.5 Frequency 3.5 Frequency 3.5 Frequency

Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 The power is directly proportional to the /system increase000–000 the power transferred, a resonance Author name Energyfrequency. Procedia To 00 (2017) The power is directly proportional to the /system frequency. To increase000–000 the power transferred, a resonance Author name Energy Procedia 00 (2017) compensation used. The resonant topology makes both the transmitter and receiver resonate aatresonance the same The power is is directly proportional to the system frequency. To increase the powercoils transferred, Author name / Energy Procedia 00 (2017)and 000–000 compensation is used. The resonant topology makes both the transmitter receiver coils resonate at the same

The power 1018 frequency.

is directly proportional to theChatterjee system etfrequency. To the power transferred, capacitor a resonance al. / Energy Procedia 117be (2017) 1015–1023 are The two resonantSoham compensation topologies thatincrease can useda compensated in compensation used. resonant topology makesfrequency. both the transmitter and receiver coils resonate aatresonance the same The power There is is directly proportional to the system To increase the power transferred, frequency. There are two resonant compensation topologies that can be useda compensated capacitor in compensation is used. The resonant topology makes both the transmitter and receiver coils resonate at the same The power is directly proportional to the system frequency. To increase the power transferred, a resonance parallel or inThere series with theresonant transfer topology coils. Although increasing the frequency does increase the efficiency the frequency. are two resonant compensation topologies thatincrease can and be the useda compensated capacitor in compensation is used. The makesfrequency. both the transmitter receiver coils resonate atresonance theof same The power is directly proportional to the system To power transferred, a parallel or inThere series with theresonant transfer topology coils. Although increasing the frequency does increase the efficiency of the frequency. are two resonant compensation topologies that canSociety be the usedaAutomotive compensated capacitor in compensation is used. The makes both the transmitter and receiver coils resonate at the same The power is directly proportional to the system frequency. To increase power transferred, a resonance system and the amount of power transferred, guidelines set by the of Engineers and parallel or in series with the transfer coils. Although increasing the frequency does increase the efficiency of the frequency. There are The two resonant resonant topology compensation topologies that can and be useda compensated capacitor in compensation is used. makes both theset transmitter receiver coils resonate at theof same system and the amount of power transferred, guidelines by the Society of Automotive Engineers and parallel or in series with the transfer coils. Although increasing the frequency does increase the efficiency the frequency. There are two resonant compensation topologies that can be[16], usedaAutomotive compensated capacitor in compensation is used. The resonant topology makes both theset transmitter and receiver coils resonate at theof same International Electro-Technical Commission limit the frequency to 85 KHz [18]. system and the amount of power transferred, guidelines by the Society of Engineers and parallel or in series with the transfer coils. Although increasing the frequency does increase the efficiency the frequency. There are twoofresonant compensation that can be[16], usedaAutomotive compensated capacitorand in International Electro-Technical Commission limitguidelines thetopologies frequency to 85 KHz [18]. system and the amount power transferred, set the by the Society ofincrease Engineers parallel or in series with the transfer coils. Although increasing frequency does the efficiency of the frequency. There are two resonant compensation topologies that can be useda compensated capacitor in International Electro-Technical Commission limitguidelines theincreasing frequency to 85 [16], [18]. system and the amount of transfer power transferred, set the by theKHz Society ofincrease Automotive Engineersof and parallel or in series with the coils. Although frequency does the efficiency the International Electro-Technical Commission limit the frequency to 85 KHz [16], [18]. 3.6 Quality Factor system and the amount of power transferred, guidelines set by the Society of Automotive Engineers and parallel or in Electro-Technical series with the transfer coils. Although the frequency does increase the efficiency of the International Commission limitguidelines theincreasing frequency to 85 [16], [18]. 3.6 Quality system and Factor the amount of power transferred, set by theKHz Society of Automotive Engineers and 3.6 Quality International Electro-Technical Commission limitguidelines the frequency to 85 [16], [18]. system and Factor the amount of power transferred, set by theKHz Society of Automotive Engineers and International Electro-Technical limit the to 85 [16], the [18].resonance between the two 3.6 Quality The QualityFactor Factor, Q, is used Commission to further optimize thefrequency coil design andKHz improve 3.6 Quality Factor International Electro-Technical limit the frequency to 85 KHz [16], the [18].resonance between the two The Quality Factor, Q, is used Commission to further optimize the coil design and improve coils at the desired frequency. The quality factor is a ratio that characterises a resonators loss. The Quality Factor, Q, is used to further optimize the coil design and improve the resonance energy between the In twoaa 3.6 Quality Factor coilsQuality at compensation the Factor desired frequency. The quality factor the is capacitor acoil ratio that characterises a resonators energy 3.6 The Quality Factor, Q, is used to optimize design and improve the resonance between the In two parallel topology, a further parallel connected is used. In this case, the quality factorloss. between coils at the desired frequency. The quality factor is a ratio that characterises a resonators energy loss. In The Quality Factor, Q,topology, is used toa further optimize thecapacitor coil design and improve the resonance between the twoa 3.6 Quality Factor parallel compensation parallel connected is used. In this case, the quality factor between coils at the desired frequency. The quality factor is a ratio that characterises a resonators energy loss. In the two coils will be Q, astopology, follows, parallel compensation a further parallel connected is used. In this case, the quality factorloss. between The Quality Factor, is used to optimize design and improve the resonance between the In twoaa coils at coils the desired frequency. The quality factor the is capacitor acoil ratio that characterises a resonators energy the two will be Q, as follows, The Quality Factor, is used to further optimize the coil design and improve the resonance between the two parallel compensation topology, a parallel connected capacitor is used. In this case, the quality factor between =𝑅𝑅/𝜔𝜔𝐿𝐿 (7)a the will be Q, as follows, coils at coils the desired frequency. The quality factor the is𝑄𝑄𝑝𝑝 acoil ratio that characterises a resonators energy loss. In parallel compensation topology, a further parallel connected capacitor is used. In this case, the quality factorloss. between Thetwo Quality Factor, is used to optimize design and improve the resonance between the In two 𝑄𝑄𝑝𝑝 =𝑅𝑅/𝜔𝜔𝐿𝐿 (7) coils at the desired frequency. The quality factor is a ratio that characterises a resonators energy the two coils will be as follows, Whereas in the case of series compensation topology, the capacitor is connected in series. In this case, the Q isa 𝑄𝑄𝑝𝑝 =𝑅𝑅/𝜔𝜔𝐿𝐿 (7) parallel compensation topology, a parallel connected capacitor is used. In this case, the quality factor between the two coils will be as follows, coils at the desired frequency. The quality factor is a ratio that characterises a resonators energy loss. In Whereas in the case of series compensation topology, the capacitor is connected in series. In this case, the Q isa parallel compensation topology, a parallel connected capacitor is used. In this case, the quality factor between 𝑄𝑄𝑝𝑝 =𝑅𝑅/𝜔𝜔𝐿𝐿 (7) as follows Whereas in the case oftopology, series compensation topology,𝑄𝑄𝑝𝑝 the=𝑅𝑅/𝜔𝜔𝐿𝐿 capacitor is connected in series. In thisfactor case, between the Q(7) is the two coils will be as follows, parallel compensation a parallel connected capacitor is used. In this case, the quality as follows the two coils will be as Whereas in the case of follows, series compensation topology,𝑄𝑄𝑝𝑝 the=𝑅𝑅/𝜔𝜔𝐿𝐿 capacitor is connected in series. In this case, the Q(7) is as follows Whereas in the case of series compensation topology, the capacitor is connected in series. In this case, the Q is the two coils will be as follows, 𝑄𝑄𝑝𝑝 =𝑅𝑅/𝜔𝜔𝐿𝐿 (7) (8) 𝑄𝑄 as follows 𝑆𝑆 =𝜔𝜔𝐿𝐿/𝑅𝑅 Whereas in the case of series compensation topology,𝑄𝑄 the capacitor is connected in series. In this case, the Q is as follows 𝑄𝑄𝑝𝑝 =𝑅𝑅/𝜔𝜔𝐿𝐿 (7) =𝜔𝜔𝐿𝐿/𝑅𝑅 (8) 𝑆𝑆 Whereas in the case of series compensation topology,𝑄𝑄the capacitor is connected in series. In this case, the Q 3.8follows Current (8)is 𝑆𝑆 =𝜔𝜔𝐿𝐿/𝑅𝑅 as Whereas in the case of series compensation topology, the capacitor is connected in series. In this case, the Q 3.8 Current (8)is 𝑄𝑄𝑆𝑆 =𝜔𝜔𝐿𝐿/𝑅𝑅 as 3.8follows Current 𝑄𝑄 𝑆𝑆 =𝜔𝜔𝐿𝐿/𝑅𝑅 as follows TheCurrent value of power transferred depends on the square 𝑄𝑄 of the current in the primary coil. The primary current (8) can 3.8 =𝜔𝜔𝐿𝐿/𝑅𝑅 3.8 TheCurrent value of power transferred depends on the square 𝑄𝑄of𝑆𝑆 the current in the primary coil. The primary current (8) can =𝜔𝜔𝐿𝐿/𝑅𝑅 (8) 𝑆𝑆 be controlled and used to deliver rated power to the secondary. However, a larger supply current increases the TheCurrent value of power transferred depends on the square 𝑄𝑄 of the current in the primary coil. The primary current (8) can 3.8 =𝜔𝜔𝐿𝐿/𝑅𝑅 𝑆𝑆 the be controlled and used to deliver rated power to the secondary. However, a larger supply current increases the The value of power transferred depends on the square of current in the primary coil. The primary current can 3.8 Current copper losses on the transfer coils. Thispower brings changes frequency and decreases the efficiency be controlled and used to deliver rated the secondary. However, asystem largercoil. supply current increases the The value of power transferred depends on the to square of in thethe current in theofprimary The primary current can 3.8 Current copper losses on the transfer coils. This brings changes in the frequency of system and decreases the efficiency be controlled and used to deliver rated power to theofsecondary. a system largercoil. supply current increases the The value of power transferred depends on the square ofdamage thethe current theofprimary primary current of the system. A the high current can increase chances toHowever, theinwhole andThe increase the risk to can copper losses on transfer coils. This brings changes in frequency system and decreases the efficiency be controlled and used to deliver rated power to the secondary. However, a larger supply current increases the The value of power transferred depends on the square ofdamage thethe current theofprimary coil. primary current of the system. A the high current can increase chances ofsecondary. toHowever, theinwhole system andThe increase the risk to can the copper losses on transfer coils. This brings changes in frequency system and decreases the efficiency be controlled and used to deliver rated power to the a larger supply current increases the The value of power transferred depends on the square of the current in the primary coil. The primary current can users. For fast charging of Electric Vehicles, it is important that the output current be as high as possible and of the system. A high current can increase chances of damage to whole system and increase the risk to the copper losses and on the transfer coils.rated Thispower bringstochanges in the frequency ofasystem decreases the efficiency be controlled used toofdeliver the secondary. However, larger and supply current increases the users. For fast charging Electric Vehicles, it is important that the output current be as high as possible and of the system. A high current can increase chances of damage to whole system and increase the risk to the copper losses on the transfer coils. This brings changes in the frequency of system and decreases the efficiency be controlled and used to deliver rated power to the secondary. However, a larger supply current increases the within limits by the secondary ofbrings system and thedamage battery itself. users. fastset charging of Electric Vehicles, it is important that the output current and be as high asthe possible of the For system. A high current can side increase chances of to whole system increase risk to and the copper losses on the transfer coils. This in thethat frequency of system the efficiency within limits by the secondary ofbrings system and thedamage battery itself. users. fastset charging of Electric Vehicles, itchanges is important the currentand be decreases as high asthe possible of the For system. A high current can side increase chances of to the output whole system and increase risk to and the copper losses on the transfer coils. This changes in thethat frequency of system and decreases the efficiency within limits set by the secondary side of system and the battery itself. users. For fast charging of Electric Vehicles, it is important the output current be as high as possible and of the system. Aby high current can side increase chances of damage to the whole system and increase the risk to the within limits set the secondary of system and the battery itself. 3.9. Coupling Coefficient users. fastsetA charging of Electric Vehicles, it is important that current and be as high asthe possible of the For system. high can side increase chances of to the output whole system increase risk to and the within limits by thecurrent secondary of system and thedamage battery 3.9. Coupling users. For fastCoefficient charging of Electric Vehicles, it is important thatitself. the output current be as high as possible and 3.9. Coupling Coefficient within limits by the secondary side of system and the battery users. For fastset charging of Electric Vehicles, it is important thatitself. the output current be as high as possible and within limits set by the secondary of systemto and batteryofitself. 3.9. Coefficient The Coupling transmitted power is directlyside proportional thethesquare the mutual inductance between the two coils. 3.9. Coupling Coefficient within limits set by the secondary side of systemto and thesquare batteryofitself. The transmitted power is directly proportional the the mutual theby twomaking coils. Mutual inductance between the coils is the only factor in the formula thatinductance cannot bebetween increased The transmitted power is directly proportional to the square of the mutual inductance between theby twomaking coils. 3.9. Coupling Coefficient Mutual inductance between the coils is the only factor in the formula that cannot be increased 3.9. Coupling Coefficient The transmitted power isTherefore, directly proportional to the of the mutual inductance thethe twomaking coils. electronic adjustments. the isdesign has of square theinsystem must be such that be itbetween increases mutual Mutual inductance between the coils the only factor the formula that cannot increased by The transmitted power is directly proportional to the square of the mutual inductance between the two coils. 3.9. Coupling Coefficient electronic adjustments. Therefore, the design has of theinsystem must be such that it increased increases the mutual Mutual inductance between the the only factor formula thatinductance be by making inductance between the isTherefore, two coils.coils The mutual inductance isthe directly related tocannot the coupling between the two electronic adjustments. the is design has of square theinsystem must be such that itbetween increases mutual The transmitted power directly proportional to the of the mutual thethe two coils. Mutual inductance between the coils is the only factor the formula that cannot be increased by making inductance between the two coils. The mutual inductance is directly related to the coupling between the two The isTherefore, directly proportional to the of the mutual inductance thethe two coils. electronic adjustments. the isdesign has of square theinsystem must be such that itbetween increases mutual coils transmitted given by thepower formula, inductance between the two coils. The mutual inductance is directly related to the coupling between the two Mutual inductance between the coils the only factor the formula that cannot be increased by making electronic adjustments. Therefore, the design has of the system must be such that it increases the mutual The transmitted power is directly proportional to the square of the mutual inductance between the two coils. coils given by the formula, Mutual inductance between the 𝑘𝑘only factor formula thatsuch be by the making inductance between the Therefore, two the coils.coils The mutual inductance isthe directly related tocannot the coupling between two (9) =𝑀𝑀/√𝐿𝐿 2 insystem coils given by the formula, electronic adjustments. the is has of 1𝐿𝐿 must be that it increased increases the mutual inductance between the Therefore, two the coils.coils The mutual inductance isthe directly related tocannot the coupling between two Mutual inductance between isdesign the 𝑘𝑘only factor insystem formula thatsuch be increased by the making 𝐿𝐿the (9) =𝑀𝑀/√𝐿𝐿 1in 2 the electronic adjustments. the design has of the must be that it increases the mutual coils given by the formula, Coupling depends upon the distance between the coils vertical axis. Any misalignment between the coils 𝐿𝐿 (9) 𝑘𝑘 =𝑀𝑀/√𝐿𝐿 inductance between the two coils. The mutual inductance is directly related to the coupling between the two 1 2 coils given by the formula, electronic adjustments. Therefore, the design has of the system must be such that it increases the mutual Coupling depends upon the distance between the coils in the vertical axis. Any misalignment between the coils inductance between the two coils. the The mutual inductance is vertical directly related tomisalignment the coupling between thecoils two 𝐿𝐿2 the (9) 𝑘𝑘the =𝑀𝑀/√𝐿𝐿 in thegiven horizontal axis also reduces mutual inductance between theaxis. twoAny coils. It has been seen that the specific 1in Coupling depends upon the distance between coils between coils by the formula, (9) 𝑘𝑘inductance =𝑀𝑀/√𝐿𝐿 inductance between the two coils. the Themutual mutual inductance is directly related to the coupling between the two 1𝐿𝐿2 between in thestructures horizontal axis also reduces theaxis. two coils. ItThat has been seen that the specific coils given by the formula, Coupling depends upon the distance between the coils in the vertical Any misalignment between coils coil increases the tolerance of WPT systems in only one direction. is, a coil with greater in thestructures horizontal axis also reduces the mutual inductance between theaxis. two coils. ItThat has is, been seen that the specific 𝐿𝐿2 the (9) 𝑘𝑘the =𝑀𝑀/√𝐿𝐿 1in Coupling depends upon the distance between coils vertical Any misalignment between coils coils given by the formula, coil increases the tolerance of WPT systems in only one direction. a coil with greater 𝐿𝐿in (9) 𝑘𝑘 =𝑀𝑀/√𝐿𝐿 in thestructures horizontal axis also reduces the mutual inductance between theaxis. two coils. ItThat has is, been that the specific tolerance for distance will have decreased tolerance misalignment. Large variations inseen coupling iscoils not 1in 2 the coil increases the tolerance of WPT systems in only one direction. a coil with greater Coupling depends upon the distance between the coils vertical Any misalignment between in the horizontal axis also reduces the mutual inductance between the two coils. It has been seen that specific 𝐿𝐿 (9) 𝑘𝑘 =𝑀𝑀/√𝐿𝐿 tolerance forWPT distance will have decreased tolerance in misalignment. Large variations inbetween coupling iscoils not 1in 2 the Coupling depends upon the distance between the coils vertical axis. Any misalignment the coil structures increases the tolerance of WPT systems in only one direction. That is, a coil with greater desirable in system as frequent changes in current can damage power electronic components. In resonant tolerance for distance will have decreased tolerance in misalignment. Large variations in coupling is not in the horizontal axis also reduces the mutual inductance between the two coils. It has been seen that specific coil structures increases the tolerance of WPT systems in only one direction. That is, a coil with greater Coupling depends upon the distance between the coils in the vertical axis. Any misalignment between the coils desirable in system asreduces frequent changes in current can damage power electronic components. In resonant in horizontal axis also the mutual inductance between the two coils. ItThat hasis been seen that specific tolerance forWPT distance will have decreased tolerance misalignment. Large variations coupling is 0.1 not power transfer system, the coupling factor between the in transmitter and receiver coils generally between desirable in system asreduces frequent changes in current can damage power electronic components. In resonant coilthe increases the tolerance of WPT systems in only one direction. is, ain coil with greater tolerance forWPT distance will have decreased tolerance in misalignment. Large variations inseen coupling is 0.1 not in thestructures horizontal axis also the mutual inductance between the two coils. ItThat hasis been that specific power transfer system, the coupling factor between the transmitter and receiver coils generally between coil structures increases the tolerance of WPT systems in only one direction. is, a coil with greater desirable in WPT system as frequent changes in current can damage power electronic components. In resonant and 0.4.transfer This low coupling coefficient is due to the high leakage flux between thecoils coilsisdue to the large air gap power system, the coupling factor between the transmitter and receiver generally between 0.1 tolerance for distance will have decreased tolerance in misalignment. Large variations in coupling is not desirable in WPT system as frequent changes in current can damage power electronic components. In resonant coil structures increases the tolerance of WPT systems in only one direction. That is, a coil with greater and 0.4. This low coupling coefficient is due to the high leakage flux between the coils due to the large air gap tolerance forWPT distance will have tolerance in misalignment. Large variations in coupling is not power transfer system, the coupling factor between thein transmitter and receiver is generally between 0.1 between the two coils. Making the decreased value of k to large can turn reduce the value ofcoils supply current and the losses and 0.4. This low coupling coefficient is due the high leakage flux between the coils due to the large air gap desirable in system as frequent changes in current can damage power electronic components. In resonant power transfer system, the coupling factor between thein transmitter and receiver coils is generally between 0.1 tolerance forWPT distance will have tolerance in misalignment. Large variations in coupling is not between the two coils. Making the decreased value of kbeto large can turn reduce the value of supply current and the losses desirable in system as frequent changes in current can damage power electronic components. In resonant and 0.4. This low coupling coefficient is due the high leakage flux between the coils due to the large air gap associated with it. Further research needs to done in improving coil design to increase the value of k. In some between the two coils. Making the value of kbeto large can intransmitter turndamage reduce the value of supply current and the losses power transfer system, theas coupling factor between theimproving and receiver coils is generally between 0.1 and 0.4. This low coupling coefficient is due the high leakage flux between the coils due to the large air gap desirable in WPT system frequent changes in current can power electronic components. In resonant associated with it. Further research needs to done in coil design to increase the value of k. In some power system, theresearch coupling factor the and receiver coils isdue generally between 0.1 between thewith two coils. Making the value kbeto large can intransmitter turnfor reduce the value of supply current losses cases, ittransfer has also seen that a high coupling isthe not suitable WPT systems [15]. The various coil structures associated it.been Further needs to between done in improving coil design tothe increase the value of k.the Inair some and 0.4. This low coupling coefficient is of due high leakage flux between coils to theand large gap between the also two coils. Making the value of k to large can intransmitter turnfor reduce the value of supply current and the losses power system, theresearch coupling factor between the and receiver coils isdue generally between 0.1 cases, ittransfer has been seen that aofhigh coupling isthe not suitable WPT systems [15]. The various coil structures and 0.4. This low coupling coefficient is due high leakage flux between the coils to the large air gap associated with it. Further needs to be done in improving coil design to increase the value of k. In some have been studied in a later part the paper. cases, it has also been seen that aofhigh coupling isthe not suitable WPT systems [15]. Thedue various coil structures between the two coils. Making the value of kbeto large can inleakage turnfor reduce the value of supply current and the losses associated with it. Further research needs to done in improving coil design to increase the value of k. In some and 0.4. This low coupling coefficient is due high flux between the coils to the large air gap have been studied in a later part the paper. between the twoit.been coils. Making value of can in turnfor reduce value of supply current cases, it has also that aofhigh coupling is not WPT systems Thethe various coil structures have been studied in a seen later partthe the paper. associated with Further research needs to kkbelarge done insuitable improving coil the design to [15]. increase valueand of k.the Inlosses some cases, it has also seen that a high coupling is not suitable WPT systems [15]. Thethe various coil structures between the twoit.been coils. Making the value of large can in turnfor reduce the value of supply current and the associated with Further research needs to be done in improving coil design to increase value of k. Inlosses some have been studied in a later part of the paper. 3.10 Leakage Flux cases, it has also been seen that a high coupling is not suitable for WPT systems [15]. The various coil structures have been studied in a later part of the paper. associated with it. Further research needs to be done in improving coil design to increase the value of k. In some 3.10 Leakage Flux cases, it has also been seen that a high coupling is not suitable for WPT systems [15]. The various coil structures 3.10 Leakage Flux have been studied in a seen later that part aofhigh the paper. cases, it has also been coupling is not suitable for WPT systems [15]. The various coil structures have beenflux studied in flux a later part has of the 3.10 Leakage Flux Leakage is that which notpaper. been captured by the secondary coil. As coupling between the two coils 3.10 Leakage Flux have beenflux studied in flux a later part has of the Leakage is that which notpaper. beenbiggest captured by thereducing secondary As coupling twoiscoils decreases, theis leakage flux increases. The factors thecoil. coupling betweenbetween the twothe coils the Leakage flux that flux which has not beenbiggest captured by thereducing secondary coil. As coupling between the twoiscoils 3.10 Leakage Flux decreases, the leakage flux increases. The factors the coupling between the two coils the 3.10 Leakage Flux Leakage flux is that fluxflux which hasand notThe been captured by thereducing secondary coil. As coupling between the two coils vertical distance between theincreases. coils the horizontal misalignment. As the leakage flux increases with increase decreases, the leakage biggest factors the coupling between the two coils is the Leakage flux is that flux which hasand not the been capturedmisalignment. by the secondary coil. As coupling between with the two coils 3.10 Leakage Flux vertical distance between the coils horizontal As the leakage flux increases increase decreases, leakage flux increases. The biggest factors reducing thecoil. coupling between the two coils iscoils in height, athe difference of even ahas few centimetres between the two coils can reduce the coupling and hence the vertical distance between the coils and the horizontal misalignment. As the leakage flux increases with increase Leakage flux is that flux which not been captured by the secondary As coupling between the two decreases, the flux increases. The biggest factors reducing thecoil. coupling between the two coils iscoils in height, aof difference of even adecreases few centimetres between the twoflux coils can reduce thecoupling coupling and hence the Leakage flux isleakage that flux which has not been captured by the secondary As to coupling between the two vertical distance between the coils and the horizontal misalignment. As leakage flux increases with increase efficiency the overall system drastically. The leakage isthe related the as follows in height, aof difference of even adecreases few centimetres between the twoflux coils can reduce thecoupling coupling and hence the decreases, the leakage flux increases. The biggest factors reducing the coupling between the as two coils iscoils vertical distance between the coils and the horizontal misalignment. As the leakage flux increases with increase Leakage flux is that flux which has not been captured by the secondary coil. As coupling between the two efficiency the overall system drastically. The leakage is related to the follows decreases, the flux increases. The biggest factors reducing the coupling between the as two coils is(10) in height, aof difference of even adecreases few between the twoflux coils can reduce thecoupling coupling and hence the (1 − 𝑘𝑘) ∝The Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 efficiency theleakage overall system leakage is related to the follows vertical distance between the coils andcentimetres thedrastically. horizontal misalignment. As the leakage flux increases with increase in height, a difference of even a few centimetres between the two coils can reduce the coupling and hence the decreases, the leakage flux increases. The biggest factors reducing the coupling between the two coils is (10) (1 − 𝑘𝑘) ∝The Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 vertical distance between the andcentimetres thedrastically. horizontal misalignment. Asisthe leakage flux increases withhence increase efficiency the overall leakage related to the asand follows (10) (1 − 𝑘𝑘) ∝The Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 in height, aof ofsystem evencoils adecreases few between the twoflux coils can reduce thecoupling coupling the efficiency ofasdifference the overall system decreases leakage flux related to the coupling asand follows vertical distance between the coils andcentimetres thedrastically. horizontal misalignment. Asisthe leakage flux increases withhence increase Therefore, the coupling decreases, the leakage flux increases. Moreover, with a decrease in coupling, in height, a difference of even a few between the two coils can reduce the coupling the (10) (1 − 𝑘𝑘) ∝The Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 efficiency ofasdifference the overall system decreases drastically. leakage flux is can related to the coupling asand follows (10) (1 − 𝑘𝑘) ∝ Ψ Therefore, the coupling decreases, the leakage flux increases. Moreover, with a decrease in coupling, in height, a of even a few centimetres between the two coils reduce the coupling hence the 𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 current should be increased to deliver the required power to the secondary side. This increase in current will lead efficiency of the overall system decreases drastically. The leakage flux is related to the coupling as follows Therefore, asthe the coupling decreases, therequired leakage flux increases. Moreover, with aincrease decrease in coupling, the (10) (1 − 𝑘𝑘)power ∝The Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 current should be increased to deliver the to the secondary side. This in current will lead efficiency of overall system decreases drastically. leakage flux is related to the coupling as follows Therefore, as the coupling decreases, the leakage flux increases. Moreover, with aincrease decrease in coupling, the to a further increase in leakage flux. Athe large supply current alsosecondary increases the copper losses in the primary side. (10) (1 − 𝑘𝑘)power ∝ Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 current should be increased to deliver required to the side. This in current will lead Therefore, as the coupling decreases, the leakage flux increases. Moreover, with a losses decrease in coupling, the to a further increase in leakage flux. Athe large supply current alsosecondary increases the copper in the primary side. (10) (1 − 𝑘𝑘)power ∝ Ψ𝑙𝑙𝑒𝑒𝑎𝑎𝑘𝑘𝑎𝑎𝑔𝑔𝑒𝑒 current should be increased to deliver required to the side. This increase in current will lead 1876-6102 ©the 2017 Authors. bypower Elsevier Ltd.secondary to a further increase inThe leakage flux. Published Athe large supply current also increases the copper losses in the primary side. Therefore, as coupling decreases, the leakage flux increases. Moreover, with aincrease decrease in coupling, the current should be increased to deliver required to the side. This in current will lead 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Therefore, as the coupling decreases, the leakage flux increases. Moreover, with decrease in coupling, the to a further increase in leakage flux. Athe large supply current alsosecondary increases the copper losses in the primary side. current should be increased to deliver required to the This aaincrease in current willon lead Peer-review responsibility of the scientific committee of the side. 1st International Conference 1876-6102 ©under 2017 The Authors. bypower Elsevier Ltd. increases to a further increase in leakage flux. Published A the large supply current also the copper losses in the primary side. Therefore, as the coupling decreases, leakage flux increases. Moreover, with decrease in coupling, the

Author name / Energy Procedia 00 (2017) 000–000



Soham Chatterjee et al. / Energy Procedia 117 (2017) 1015–1023

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Horizontal misalignment between the coils also reduces the coupling and increases the leakage flux. As it is impossible for a driver to park the vehicle directly over the transmitter coil, the coupling between the coils will further decrease. Guidelines set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) a maximum of 27 𝜇𝜇𝑇𝑇 is the magnetic field exposure limit for humans.

3.11 Efficiency

The transmission efficiency of a WPT system is the ratio of the output power to the input power. It has been shown that the efficiency of a WPT system can be given by (11) Therefore, k and Q must be increased as much as possible. Further, it has been shown that the maximum transmission efficiency for both series and parallel transmission topologies is given by (

(

√

)

(

) )

(12)

The value of coupling between the two coils can be increased by increasing the mutual inductance between two coils and designing more misalignment tolerant coils. The quality factor of the transmission coils is the geometric average of the quality factor of the two coils. The Quality factor is given by 𝑄𝑄

(13)

Angular frequency can be increased by increasing the frequency. W is the stored energy of the coil and P is the power loss in the inductor. 3.12 Material of the Coil Materials that are generally used in WPT applications must have less DC resistance, low AC losses and be capable of handling high fluctuating currents and voltages.For high frequency conductors, Litz wires are the preferred materials. Litz wire are individually insulated and twisted together to make one single conductor. They have been designed to reduce skin effects and proximity effects that are significant in high frequencies. The DC resistance of Litz wires are insignificant making them the perfect material for making conductors. The low electrical conductivity prevents eddy current loss too. Common ferrite materials used in cores up to a frequency of 5 MHz is Manganese Zinc Ferrite. It has a low coercivity which means that losses due to hysteresis is less. Magnetic shielding is required to protect the various power electronic components below the coils from magnetic flux. Ferrite materials provide low reluctance to the magnetic field than the surrounding air. Thus, the magnetic flux can be concentrated in them. However, some ferrite materials have more hysteresis and Eddy current losses. These losses are converted to heat which may cause again harm sensitive components. 4. COMMON COIL STRUCTURES Coils shapes have been most extensively researched for low power applications [17]. In these cases, the angle, power and air gap of the devices can vary significantly. Coils for WPT can be classified into three types based on the polarity of the flux distribution: Unipolar [19], polarised [20] and Double polarised [7]. The four most popular coil structures that have been studied extensively for EV charging are the circular, square, rectangular and double coils. Each coil structure has its own advantages and are suitable for different applications. Each structure has been explained in detail and they have been compared to find the optimum shape for Electric Vehicle charging. 4.1 CIRCULAR COIL

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Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author Soham nameChatterjee / Energyet Procedia 00 (2017) 000–000 al. / Energy Procedia 117 (2017) 1015–1023

Fig 4: Circular coils Fig 4: Circular coils Fig flux 4: Circular coils kind. The circular coil has the advantage of Circular coils are of the non-polarised or unipolar distribution Fig 4: Circular coils Fig 4: Circular coilsresults Circulara coils are of thedistribution. non-polarised unipolar flux distribution kind. from The circular coil has the advantage of having uniform flux Theoruniform flux distribution the symmetrical geometry of the Fig flux 4: Circular coils kind. The circular coil has the advantage of Circular coils areflux of the non-polarised or unipolar distribution having a uniform flux distribution. The uniform flux distribution results from the symmetrical geometry of the coil. A uniform distribution helps the coupling be uniform and helps the power transferred be similar in all Fig flux 4: Circular coils kind. The circular coil has the advantage of Circulara coils are of thedistribution. non-polarised unipolar distribution having uniform flux Theor uniform flux distribution results from the part symmetrical geometry ofinthe Circular coils are of the non-polarised or unipolar flux distribution kind. The circular coil hassecondary the advantage of coil. A uniform flux distribution helps the coupling be uniform and helps the power transferred be similar all direction. This uniform power transfer reduces the stress on the power electronic of the side of having a coils uniform flux distribution. Theor uniform flux results from the symmetrical geometry ofinthe Circular areflux of the non-polarised unipolar flux distribution kind. The circular coil has the of coil. A uniform distribution helps the coupling bedistribution uniform and helps the power transferred beadvantage similar all having a coils uniform flux distribution. Theor uniform flux distribution results from the part symmetrical geometry of the direction. This uniform power transfer reduces the stress on the power electronic of the secondary side of the system. Circular are of the non-polarised unipolar flux distribution kind. The circular coil has the advantage of coil. A uniform flux helps coupling bedistribution uniform and helps the power transferred be similar all having a uniform fluxdistribution distribution. Thethe uniform flux results from the part symmetrical geometry ofinthe direction. This uniform power transfer reduces the stress on the power electronic of the secondary side of coil. A uniform flux helps coupling bedistribution uniform and helpsfrom the power transferredgeometry be similarofinthe all the system. having a uniform fluxdistribution distribution. Thethe uniform flux results the part symmetrical direction. This uniform power transfer reduces the stress on the power electronic of the secondary side of coil. A uniform flux distribution helps the coupling be uniform and helps the power transferred be similar in all the system. For circular coils, thedistribution quality is given by the stress direction. This uniform powerfactor transfer reduces on the and power electronic parttransferred of the secondary sideinofall coil. A uniform flux helps the coupling be uniform helps the power be similar the system.This uniform power transfer reduces the stress on the power electronic part of the secondary side of direction. For circular coils, the quality is given by the stress on the power electronic part of the secondary side of the system. direction. This uniform powerfactor transfer reduces the system. For circular coils, the quality factor is given by (14) 𝑄𝑄C=𝜔𝜔𝐿𝐿/𝑅𝑅 the system. For circular coils, the quality factor is given by (14) As increase in the valueby of Q can𝑄𝑄increase be For shown circularpreviously, coils, the quality factor is given C=𝜔𝜔𝐿𝐿/𝑅𝑅 the power delivered. The quality factor can For shown circular coils, the quality factor is𝜔𝜔.given by (14) 𝑄𝑄increase C=𝜔𝜔𝐿𝐿/𝑅𝑅 As previously, increase in the value of Q can the power delivered. The quality factor can be increased by increasing the value of However, in cases where 𝜔𝜔 is constant, the value of Q can be increased For circular coils, the quality factor is given by =𝜔𝜔𝐿𝐿/𝑅𝑅 the power delivered. The quality factor can (14) 𝑄𝑄increase As shownby previously, increase inthe the𝜔𝜔. value of Q in cancases be =𝜔𝜔𝐿𝐿/𝑅𝑅 (14) 𝑄𝑄CCthe increased increasing the value of However, where 𝜔𝜔 is constant, the value of Q can be increased by increasing the inductance of coil or decreasing value of resistance. When using conductors of low As shownby previously, increase inofthe𝜔𝜔.value of Q in cancases the power delivered. The of quality factor can be (14) 𝑄𝑄increase C=𝜔𝜔𝐿𝐿/𝑅𝑅 increased increasing theturns value However, where 𝜔𝜔 is constant, the value Q can be increased As shown previously, increase inthe the value of Qby can increase the power delivered. The quality factor can be by increasing the inductance of coil or decreasing the value of resistance. When using conductors of low resistance, the number of can be increased reducing the pitch of the coils, without significant increase =𝜔𝜔𝐿𝐿/𝑅𝑅 (14) 𝑄𝑄 C increased by increasing the value of 𝜔𝜔. However, in cases where 𝜔𝜔 is constant, the value of Q can be increased As shown previously, increaseofinthethecoil value of Q can increase theofpower delivered. The quality factor of canlow be by increasing the inductance orordecreasing thewhere value When using conductors increased by value ofthe 𝜔𝜔.value However, in cases 𝜔𝜔 power isresistance. constant, the value of Q canfactor be increased resistance, theincreasing number ofthe turns be increased reducing thethe pitch of the coils, without significant increase in resistance. The use of ferrite spokes a ferrite centre can significantly increase the coupling between the As shown previously, increase inthe of Qby can increase delivered. The quality canlow be by the increasing the inductance ofcan coil or decreasing thewhere value of isresistance. When using conductors of increased by increasing theturns value ofbe 𝜔𝜔. However, in cases 𝜔𝜔 constant, the value of Q can be increased resistance, the number of can increased by reducing the pitch of the coils, without significant increase by increasing thespoke inductance ofa low the coil orordecreasing value of isresistance. When using conductors ofoflow in the resistance. The use of ferrite a ferrite can significantly increase the coupling between coils. The ferrite acts as reluctance path tocentre the where magnetic field which increases the inductance the increased by increasing the value ofspokes 𝜔𝜔. However, in reducing cases 𝜔𝜔 constant, the value of Q can be increased resistance, the number of turns can be increased by the pitch of the coils, without significant increase by increasing the inductance of the coil or decreasing the value of resistance. When using conductors of low in resistance. The use of ferrite a ferrite centre can increase the between the resistance, the number of turns can be increased bytoreducing thesignificantly pitch of the coils, without significant increase coils. The spoke acts as low reluctance path to the magnetic field which increases the inductance the coilthe and theferrite quality factor. The coils need be shielded using ferrite materials to coupling protect the electronic by increasing inductance ofacircular thespokes coil oror the value of resistance. When using conductors ofoflow in the resistance. The use of ferrite spokes ordecreasing a ferrite centre can increase the coupling between the resistance, the the number of turns can be increased by reducing thesignificantly pitch of the coils, without significant increase coils. The ferrite spoke acts as a low reluctance path to the magnetic field which increases the inductance of the in theand resistance. The use ferrite spokes or need aleakage ferrite centre can significantly the coupling between coil theferrite quality factor. The circular coils be shielded using ferrite materials towidely protect the electronic parts from damage due toof flux and to reduce flux. The coil isincrease the most researched and resistance, the number of turns can bereluctance increased bytoreducing thecircular pitch of the coils, without significant increase coils. The spoke acts as a low path to the magnetic field which increases the inductance of the in the resistance. The use of ferrite spokes or a ferrite centre can significantly increase the coupling between coil and theferrite quality factor. The circular coils need to to be shielded using ferrite materials towidely protect the electronic coils. The spoke acts as aand lowspokes reluctance path the magnetic field which increases the inductance ofboth the parts from damage due toofflux to reduce flux. The coil isincrease the most researched and commonly used coil. Circular coils provide best misalignment tolerance. These coils work best when in resistance. The use ferrite orthe aleakage ferrite centre can circular significantly the coupling between the coiltheand theferrite quality factor. The circular coils need to to be shielded using ferrite materials towidely protect the electronic coils. The spoke acts as aand lowtoreluctance path the magnetic field which increases the inductance of and the parts from damage due to flux reduce leakage flux. The circular coil is the most researched coil and the quality factor. The circular coils need to be shielded using ferrite materials to protect the electronic commonly used coil. Circular coils provide the best misalignment tolerance. These coils work best when both the coils are of the same size. Power transferred increases as the outer radius is increased. coils. The ferrite spoke acts as a low reluctance path to the magnetic field which increases the inductance of the partsand from due to flux and to reduce leakage flux. The circular coil ismaterials the most researched and coil thedamage quality factor. Thecoils circular coils the need to be shielded using ferrite towidely protectbest thewhen electronic commonly used coil. Circular provide best misalignment tolerance. coils work both parts from due to flux and to reduce leakage flux. circular coilisisThese the most researched and the coils aredamage of the same size. Power transferred increases as The the outer radius increased. coil and the quality factor. The circular coils the need to be shielded using ferrite materials towidely protectbest thewhen electronic commonly used coil. Circular coils provide best misalignment tolerance. These coils work both parts from damage due to flux and to reduce leakage flux. The circular coil is the most widely researched and the coils areused of the same size. Power transferred increases as the outer radius isisThese increased. 4.2 RECTANGULAR COILS commonly coil. Circular coils provide best misalignment tolerance. coilswidely work best when both partscoils from due to fluxPower and to reducethe leakage flux. circular coilis the most researched and the aredamage of the same size. transferred increases as The the outer radius increased. commonly used coil. Circular coils provide the best misalignment tolerance. These coils work best when both 4.2 RECTANGULAR COILS the coils are of the same size. Power transferred increases as the outer radius is increased. commonly used coil. Circular coils provide the best misalignment tolerance. These coils work best when both the coils are of same size. Power the outerbut radius increased. 4.2 RECTANGULAR COILS Rectangular andthe square shaped coils transferred have almostincreases the sameas theyis hugely in performance.They the coils are of the same size. Power transferred increases asstructure, the outer radius isdiffer increased. 4.2 RECTANGULAR COILS 4.2 RECTANGULAR COILS Rectangular and square shaped coils haveadvantage almost theissame structure, but is they differashugely in performance.They form a polarised flux distribution. Their that the flux path higher compared to circular coils. 4.2 RECTANGULAR COILS Rectangular and square shaped coils haveadvantage almost theissame structure, but is they differashugely in performance.They form a polarised flux distribution. Their that the flux path higher compared toofcircular coils. 4.2 RECTANGULAR COILS However, the coil being two sided has half the leakage flux in the bottom direction. This type coil has the Rectangular and square shaped coils have almost the same structure, but they differ hugely in performance.They form a polarised flux distribution. Their advantage thatflux the flux path higher compared toofcircular coils. Rectangular and square shaped coils have almost theissame structure, but is they differashugely intype performance.They However, the coil being two sided has half the leakage in the bottom direction. This coil has the highest leakage is hence not suitable for the efficient in EV. being a polarised type ofcoils. coil, Rectangular andflux square shaped coils have almost structure, butHowever, they differas hugely in performance.They form a polarised fluxand distribution. Their advantage issame that WPT the flux path is higher compared to circular However, theand coil being two sided has half the leakage in theEV. bottom direction. This type coil has the form a polarised flux distribution. Their advantage issame thatflux the flux path is higher as compared toofcircular coils. Rectangular square shaped coils have almost the structure, but they differ hugely in performance.They highest leakage flux and is hence not suitable for efficient WPT in However, being a polarised type of coil, they have the highest coupling among thethe other types ofthecoils. coupling reduces greatly when coils form a polarised distribution. Their advantage is thatflux flux path is higher as compared circular coils. However, coilflux being two sided hasall half leakage in theThis bottom direction. This typetoof coilthe has the highest leakage flux and is hence not suitable forleakage efficient WPT in EV. However, being a polarised type ofcoils. coil, However, the highest coil being two sided has half the in theThis bottom direction. This typetoof coilthe has the form a polarised flux distribution. Their advantage is thatflux the flux path is higher as circular theymisaligned. have the coupling among all the other types of coils. coupling reduces when coils are Rectangular coils have the best tolerance in vertical displacement. Tocompared make atype rectangular coil of However, the coil two sided has half the leakage flux in in theEV. bottom direction. This of coil has the highest leakage fluxbeing and is hence not suitable for efficient WPT However, being a greatly polarised type of coil, they have the highest coupling among all the other types of coils. This coupling reduces greatly when the coils highest leakage flux and is hence not suitable for efficient WPT in EV. However, being a polarised type of coil, However, coil being two sided has half the leakage flux in the bottom direction. This type of coil has the are misaligned. Rectangular coils have the best tolerance in vertical displacement. To make a rectangular coil of the same area that and ofcoupling a iscircular coil, the oftypes Litz wire required also more. highest leakage flux hence not suitable for efficient WPT in This EV. is However, being a greatly polarised typethe of coils coil, they have the as highest among all amount the other of coils. coupling reduces when are misaligned. Rectangular coils havesuitable the amount bestother tolerance in vertical displacement. To make a rectangular coil of they have the as highest coupling among all the types of coils. coupling reduces when coils highest leakage flux and iscircular hence not for efficient WPT in This EV. However, being a greatly polarised typethe of coil, the same area that of a coil, the of Litz wire required is also more. theymisaligned. have the highest coupling among types in ofvertical coils. This coupling reduces greatly when thecoil coils are Rectangular coils have all the the bestother tolerance displacement. To make a rectangular of the same that ofcoupling a circular coil, oftypes Litz in wire required is also more. are misaligned. Rectangular coils have the the amount bestother tolerance displacement. To make a rectangular of they havearea the as highest among all the ofvertical coils. This coupling reduces greatly when thecoil coils are same misaligned. coils coil, have the the amount best tolerance vertical displacement. To make a rectangular coil of the area asRectangular that of a circular of Litz in wire required is also more. the same area asRectangular that of a circular of Litz in wire required is also more. are misaligned. coils coil, have the the amount best tolerance vertical displacement. To make a rectangular coil of the same area as that of a circular coil, the amount of Litz wire required is also more. the same area as that of a circular coil, the amount of Litz wire required is also more.

Fig 5: Rectangular Coils Fig 5: Rectangular Coils Fig 5: Rectangular Coils 4.3 DOUBLE COILS Fig 5: Rectangular Coils Fig 5: Rectangular Coils 4.3 DOUBLE COILS 5: Rectangular Coils 4.3 DOUBLE COILS coils that are attachedFig They are two circular in parallel to eachCoils other and have reduced leakage flux and form a Fig 5: Rectangular 4.3 DOUBLE COILS 4.3 DOUBLE COILS They are two circular coils that are attached in parallel to each other and have reducedand leakage fluxpower and form polarised flux COILS distribution in the middle. This structure has a high coupling efficiency a better factora 4.3 DOUBLE They are two circular coils that are attached in parallel to each other and have reduced leakage flux and form a polarised flux distribution in the middle. This structure has a high coupling efficiency and a better power factor 4.3 COILS thanDOUBLE the coils. However, takes up more and a lotand more Litz wire toleakage make. The coila They areother two circular coils thatit are attached in space parallel torequires each other have reduced flux double and form polarised flux circular distribution the middle. This has a high coupling efficiency and a better factor They areother two coilsinthat attached instructure parallel torequires each other have reduced fluxpower and form than the coils. However, it are takes more space and acoupling lotand more Litz wire toleakage make. The double coilaa has better misalignment tolerance anduphas one sided flux similar to theand circular coil andform have They are two circular coils are attached in parallel to each other and have reduced leakage flux and polarised flux distribution inthat the middle. This structure has a distribution high efficiency a better power factor than the other coils. However, it takes up more space and requires a lot more Litz wire to make. The double coil polarised flux distribution in the middle. This structure has a high coupling efficiency and a better power factor They are two circular coils that are attached in parallel to each other and have reduced leakage flux and form has better misalignment andupof has one sided flux similar theand circular coil have reduced flux.However, For tolerance ainsimilar size double coiland and circular coil, the double coil asand much asa polarised flux distribution the middle. This structure has a distribution high acoupling efficiency a achieve better power factor than the leakage other coils. it takes more space requires lot more Litz to wire tocan make. The double coil has better misalignment tolerance and has one sided flux distribution similar to the circular coil and have than the other coils. However, it takes up more space and requires a lot more Litz wire to make. The double coil polarised fluxcoupling distribution the middle. This structure has circular a high coupling efficiency and a achieve better power factor reduced flux.However, For ain similar size double coiland and the double coil asand much as 1.5 times the of atolerance circular coil. than the leakage other coils. it takes more space requires a coil, lot more Litz to wire make. The coil has better misalignment andupof has one sided flux distribution similar thetocan circular coildouble have reduced leakage flux. For a similar size of double coil and circular coil, the double coil can achieve as much as has better misalignment tolerance and has one sided flux distribution similar to the circular coil and have than the other coils. However, it takes up more space and requires a lot more Litz wire to make. The double coil 1.5 times the coupling of atolerance has better misalignment and hasdouble onebysided fluxcircular distribution similar to coil the can circular coilasand have reduced leakage flux. The For acircular similar coil. size of coil and coil, the double achieve much as 1876-6102 © 2017 Authors. Published Elsevier Ltd. 1.5 times the coupling of atolerance reduced leakage flux. For acircular similar coil. size of coil and coil, the double achieve much as has better misalignment and hasdouble one sided fluxcircular distribution similar to coil the can circular coilasand have reduced flux. The For acircular similar coil. size of double and circular 1.5 timesleakage the© coupling of aAuthors. 1876-6102 2017 Published bycoil Elsevier Ltd. coil, the double coil can achieve as much as

Author name / Energy Procedia 00 (2017) 000–000 5. 5. DISCUSSION DISCUSSION

Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000

Soham Chatterjee et al. / Energy Procedia 117 (2017)has 1015–1023misalignment tolerance 1021 The The circular circular coil coil occupies occupies the the least least space space and and requires requires the the least least material. material. It It also also has more more misalignment tolerance 5. DISCUSSION and and less less leakage leakage flux. flux. However, However, even even when when the the coils coils are are aligned, aligned, it it has has the the least least coupling coupling coefficient. coefficient. On On the the other hand, the rectangular coil has better coupling coefficient at great distances. The changes in coupling are 5. DISCUSSION other hand, the rectangular coil has better coupling coefficient at great distances. The changes in coupling are The circular coil occupies the least space and requires the least material. It also has more misalignment tolerance significantly lesser when the between the coils increase. However, almost half the flux is significantly lesser when the distance distance between the coils However, almost half of of coefficient. the leakage leakage On fluxthe is and less leakage flux. However, even when the coils areincrease. aligned, it hasIt the least coupling The circular coil occupies the least space and requires the least material. also has more misalignment tolerance lost the of This type of also wide in coupling the misaligned lost in inhand, the bottom bottom of the the coil. coil.coil This type of coil coil also has has wide variation variation in distances. coupling when when the coils coilsinare arecoupling misaligned other the rectangular has better coupling coefficient at great The changes are and less leakage flux. However, even when the coils are aligned, itithas the least coupling coefficient. On The the horizontally and requires more material for its Hence, not for WPT applications. horizontally and requires material forcoupling its construction. construction. Hence, it is is distances. not suitable suitable for WPT applications. The significantly lesser when more thecoil distance between the coils increase. However, almost half of the leakage flux is other hand, the rectangular has better coefficient at great The changes in coupling are double coils have the best misalignment tolerance and less leakage flux. However, it occupies more space and double coils have the best misalignment tolerance and less leakage flux. However, it occupies more space and lost in the bottom of the coil. This type of coil also has wide variation in coupling when the coils are misaligned significantly lesser when As the circular distance coils between thebeen coilsseen increase. However, almost half of the power leakagetransfer flux is requires more material. have to optimum for requires more As circular coils have been seenHence, to be be itthe the optimum forforwireless wireless power transfer horizontally andmaterial. requires more material forcoil its construction. is coupling not suitable WPT applications. The lost in the bottom of the coil. This type of also has wide variation in when the coils are misaligned applications, we have discussed more in detail about the effects of the different parameters in the circular coil, to applications, we have discussed more in detail about the effects of the different parameters in the circular coil, to double coils and haverequires the bestmore misalignment tolerance and less leakage However, occupies more space The and horizontally materialcoil. for its construction. Hence, itflux. is not suitableitfor WPT applications. find the optimum design of the circular find the optimum design of the circular coil. requires more material. circular coils have been seenleakage to be flux. the optimum wireless more powerspace transfer double coils have the bestAs misalignment tolerance and less However,for it occupies and applications, we have discussed more in detail about the effects of the different parameters in the circular coil, to requires more material. As circular coils have been seen to be the optimum for wireless power transfer find the optimum design of the circular applications, we have discussed moreCircular incoil. detail about the effects of the different parameters in the circular coil, to Parameter Rectangular Double Parameter Circular Coil Coil Rectangular Coil Coil Double Coil Coil find the optimum design of the circular coil. Polarity Unipolar Polarised Unipolar Polarity Unipolar Polarised Unipolar Flux Distribution Uniform Non-Uniform Non-Uniform Flux Distribution Uniform Non-Uniform Non-Uniform Parameter Circular Coil Rectangular Coil Double Coil Horizontal More Less More Horizontal Tolerance Tolerance More Less More Polarity Unipolar Polarised Unipolar Parameter Circular Coil Rectangular Coil Double Coil Vertical Tolerance Less More Less Vertical Tolerance Less More Less Flux Polarity Distribution Uniform Non-Uniform Non-Uniform Material Required Least Moderate Most Unipolar Polarised Unipolar Material Required Least Moderate Most Horizontal Tolerance More Less More Leakage Flux In Horizontal In Direction Reduced Flux Distribution Non-Uniform Non-Uniform Leakage Flux In Uniform Horizontal In Bottom Bottom Direction Reduced Vertical Tolerance Less More Less Direction Horizontal Tolerance More Less More Direction Material Required Least Moderate Most Table 1: Comparison of Different Vertical Tolerance Less of More Less of Characteristics Characteristics ofDirection Different Coils Coils Reduced Leakage Flux Table 1: Comparison In Horizontal In Bottom Material Required Least Moderate Most Leakage Flux InDirection Horizontal In Bottom Direction Reduced Table 1: Comparison Direction of Characteristics of Different Coils

Table 1: Comparison of Characteristics ofIN Different Coils COIL 6.EFFECTS 6.EFFECTS OF OF PARAMETERS PARAMETERS ON ON POWER POWER TRANSFERRED TRANSFERRED IN CIRCULAR CIRCULAR COIL 6.1 Outer Outer Radius Radius 6.1 6.EFFECTS OF PARAMETERS ON POWER TRANSFERRED IN CIRCULAR COIL If the the outer outer radius radius is increased increased while whileON keeping the other other parameters constant, constant, then the the coupling coupling will increase. increase. The The 6.EFFECTS OF PARAMETERS POWER TRANSFERRED IN CIRCULAR COIL will If is keeping the parameters then 6.1 Outer Radius tolerance in the vertical direction will increase in this case. The effect of increasing outer diameter of the tolerance in the vertical direction will increase in this case. The effect of increasing outer diameter of the 6.1 Outercoil, Radius circular by increasing increasing the the number number of of turns turns while while keeping keeping the the other other parameters parameters constant constant has has been been studied. studied. circular coil,radius by If the outer is increased while keeping the other parameters constant, then the coupling will increase. The This will increase the inductance and hence the quality factor of the coils will increase. The mutual inductance This will increase the inductance and hence the quality factor the effect coils will increase. The mutual inductance tolerance in the vertical direction will increase in this case. ofThe of increasing outer diameter of the If the outer is increased while other parameters between theradius two coils coils is aa function function ofkeeping couplingthe which will increase.constant, then the coupling will increase. The between the two is of coupling which will increase. circular coil, by increasing the number of turns while keeping the other parameters constant has been studied. tolerance in the vertical direction will increase in this case. The effect of increasing outer diameter of the ThisInner willcoil, increase the inductance and hence the quality factor ofthe theother coilsparameters will increase. The mutual inductance circular by increasing the number of turns while keeping constant has been studied. 6.2 Radius 6.2 Inner Radius between the two coils is a function of coupling which will increase. This will increase the inductance and hence the quality factor of the coils will increase. The mutual inductance To study studythe thetwo effects ofis inner inner coil radius, radius, the outer outer coil radius was kept kept constant constant and and the the inner inner coil coil radius radius was was between coilsof a function of coupling which willradius increase. To the effects coil the coil was 6.2 Inner Radius varied while keeping the radius of the coils and the thickness of the conductor constant. The inner coil radius varied while keeping the radius of the coils and the thickness of the conductor constant. The inner coil radius 6.2 has Inner veryRadius significant effect effect on the the coupling coupling between between the two two coils. coils. The The coils coils having having lesser lesser inner inner radius radius have has aa very significant To study the effects of inner on coil radius, the outer coilthe radius was kept constant and the inner coil radiushave was better coupling. coupling. When When designing designing aa coil, coil, the the inner inner radius radius must must be be kept kept as as small small as as possible. possible. better varied while keeping the radius of the coils and the thickness of the conductor constant. The inner coil radius To study the effects of inner coil radius, the outer coil radius was kept constant and the inner coil radius was has Pitch a very effect on the coupling between the two of coils. coils having lesser have varied whilesignificant keeping the radius of the coils and the thickness the The conductor constant. Theinner innerradius coil radius 6.3 6.3 Pitch better coupling. When designing a coil, the inner radius must be kept as small as possible. has a very significant effect on the coupling between the two coils. The coils having lesser inner radius have The pitch pitch of the the When coil can can be varied varieda by by increasing the space between two adjacent turns while while keeping keeping the the number number better coupling. designing coil, the inner the radius must be kepttwo as adjacent small as possible. The of coil be increasing space between turns 6.3 Pitch of turns turns same. same. For For an an increased increased pitch, pitch, if if the the inner inner and and outer outer radius radius remains remains the the same, same, the the number number of of turns turns will will of 6.3 Pitch This will reduce the inductance of the coil and coupling will decrease. A smaller pitch will allow for a decrease. decrease. inductance of the coil and coupling A smaller will the allow for a The pitch This of thewill coilreduce can bethe varied by increasing the space betweenwill twodecrease. adjacent turns whilepitch keeping number smaller flux flux lost lost between between the the windings windings which which will will increase increase the the coil coil inductance. inductance. With With higher higher inductance, inductance, the the smaller of turns same. ancan increased pitch, if the inner outer radiustwo remains the turns same,while the number turns will The pitch of theFor coil be varied by increasing theand space between adjacent keepingofthe number mutual inductance will rise. mutual rise.the inductance decrease. This will reduce of the coiland andouter coupling will decrease. smaller willofallow of turnsinductance same. For will an increased pitch, if the inner radius remains the A same, the pitch number turnsfor willa smaller flux between the inductance windings which will and increase the will coil decrease. inductance. With higher inductance, decrease. This will reduce the of the coil coupling A smaller pitch will allow forthea 6.4 Number Number oflost Turns 6.4 of Turns mutual inductance will rise. smaller flux lost between the windings which will increase the coil inductance. With higher inductance, the With an aninductance increase in in the number of of turns, turns, the the magnetic magnetic coupling coupling increases increases dramatically. dramatically. However, However, with with an an mutual willthe rise. With increase number 6.4 Number of turns, Turns the resistance also increases. To keep the outer radius constant while increasing the number increase in the increase in the turns, the resistance also increases. To keep the outer radius constant while increasing the number 6.4 Number of Turns With an increase in The the number turns, the by magnetic increases dramatically. However, with an 1876-6102 © Authors. Elsevier Ltd. 1876-6102 © 2017 2017 The Authors.ofPublished Published by Elseviercoupling Ltd. increase in theunder turns, the resistance also increases. To keep the outerofradius constant while increasing the number Peer-review responsibility of the scientific committee the 1st International Conference on

Author Author name name // Energy Energy Procedia Procedia 00 00 (2017) (2017) 000–000 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000 Author name / Energy Procedia 00 (2017) 000–000

Soham Chatterjee et al. / Energy Procedia 117 (2017) 1015–1023 of of turns, turns, the the diameter diameter of of the the conductor conductor should should be be decreased. decreased. However, However, with with aa decrease decrease in in the the conductor conductor of turns, the diameter of the conductor should be decreased. However, withreduces a decrease in thefactor conductor diameter, there is an increase in the parasitic capacitance in the coil. This in turn the quality of diameter, is an increase the parasiticshould capacitance in the coil. This in turn the quality of the the of turns, there the diameter of thein conductor be decreased. However, withreduces a decrease in thefactor conductor diameter, there isof an the increase the parasitic capacitance inhas theacoil. This in turn the quality of the of turns, the diameter of thein conductor should be decreased. However, withreduces a decrease in voltage thefactor conductor coil. The effect change in the number of turns more significant effect on the on coil. The there effectisof change in parasitic the number of turns inhas more significant effect the on quality the voltage diameter, an the increase in the capacitance theacoil. This in turn reduces factoron of the coil. The there effect the change in the number of turns acoil. more significant effect on thepronounced voltage the diameter, isof an increase in the parasitic capacitance inhas the This ineffect turn reduces the quality factoron ofthan secondary side the ratio of primary to turns changes. This much more secondary side as asof thethe ratio of the the in primary to secondary secondary turns effect is iseffect much on more coil. The effect change the number of turns haschanges. a more This significant thepronounced voltage onthan the secondary side as the ratio of the primary to secondary turns changes. This effect is much more pronounced than coil. The effect of the change in the number of turns has a more significant effect on the voltage on the effects to capacitances or in of and coupling. effects due dueside to parasitic parasitic capacitances or changes changes in the the values values of inductance inductance coupling. secondary as the ratio of the primary to secondary turns changes. This and effect is much more pronounced than effects dueside to parasitic capacitances or changes in the values of inductance coupling. secondary as the ratio of the primary to secondary turns changes. This and effect is much more pronounced than effects due to parasitic capacitances or changes in the values of inductance and coupling. 6.5 Conductor Diameter effects due to parasitic capacitances or changes in the values of inductance and coupling. 6.5 Conductor Diameter 6.5 Conductor Diameter 6.5 Conductor Diameter When the diameter 6.5 Conductor Diameter When the conductor conductor diameter is is decreased decreased keeping keeping the the other other values values constant, constant, there there is is an an increase increase in in parasitic parasitic When the conductor diameter is decreased keeping the other values constant, there is an increase in value parasitic capacitance in between the adjacent turns. A decrease in conductor diameter also decreases the of capacitance in between the adjacent turns.keeping A decrease in conductor diameter alsois decreases of When the conductor diameter is decreased the other values constant, there an increasethe in value parasitic capacitance in between the adjacent turns.keeping A decrease in conductor diameter alsois decreases of When the conductor diameter is decreased the other values constant, there an increasethe in value parasitic inductance which reduces coupling. inductance which reducesthe coupling. capacitance in between adjacent turns. A decrease in conductor diameter also decreases the value of inductance which reducesthe coupling. capacitance in between adjacent turns. A decrease in conductor diameter also decreases the value of inductance which reduces coupling. 7. inductance which reduces coupling. 7. CONCLUSION CONCLUSION 7. CONCLUSION 7. CONCLUSION In this 7. In CONCLUSION this paper, paper, aa Wireless Wireless Power Power Transfer Transfer System System for for wireless wireless charging charging of of Electric Electric Vehicles Vehicles have have been been studied. studied. In this paper, a Wireless Power Transfer System for The wireless charging of parameters Electric Vehicles have beenofstudied. Simple equations to design a coil has been given. effects of these on the amount power Simple equations to design a coil has been given. effects of these on thehave amount power In this paper, a Wireless Power Transfer System for The wireless charging of parameters Electric Vehicles beenofstudied. Simple equations to design a The coil has been given. effects of these on the amount power In this paper, a Wireless Power Transfer System for The wireless charging of parameters Electric Vehicles have beenof studied. transferred has been studied. materials generally used in WPT systems have been given. The different transferred has been studied. The materials generally used in WPT systems have been given. The different Simple equations to design a coil has been given. The effects of these parameters on the amount of power transferred has been studied. The materials generally used in WPT systems have been given. The different Simple equations to design a coil has been given. The effects of these parameters on the amount of power popular structures have presented. It has that the with best coupling coefficient and popular coil coilhas structures have been been has been been found found thatWPT the coil coil with the the best coupling and transferred been studied. Thepresented. materialsItgenerally used in systems have been given.coefficient The different popular coil structures have been presented. It has been found that the coil with the best coupling coefficient anda transferred has been studied. The materials generally used in WPT systems have been given. The different misalignment tolerance is the circular coil. The effect on the efficiency on changing the different parameters in misalignment tolerancehave is thebeen circular coil. The effect onfound the efficiency on changing the different popular coil structures presented. It has been that the coil with the best coupling parameters coefficient in anda misalignment tolerance is the circular coil. The effect on the efficiency on changing thehave different parameters in popular coil structures have been presented. It has been found that the coil withthat the best coupling coefficient anda circular been studied. Further work must be done to better misalignment circular coil has has been also also studied. Further workeffect muston bethe done to design designoncoils coils that can can betterparameters misalignment misalignment tolerance is the circular coil. The efficiency changing thehave different in a circular coil has been coupling also studied. Further work must bethe done to design that can have better misalignment misalignment tolerance is the circular coil. The effect on efficiency oncoils changing theparasitic different parameters in a tolerance and better coefficients. Design changes can be made to reduce capacitance and tolerancecoil andhasbetter coefficients. Design changes be made to that reduce capacitance and circular been coupling also studied. Further work must be donecan to design coils can parasitic have better misalignment tolerance and better coupling coefficients. Design changes can be made to reduce parasitic capacitance and circular coil has been also studied. Further work must be done to design coils that can have better misalignment increase inductance to coupling. increase coil coil to increase increase coupling.Design changes can be made to reduce parasitic capacitance and tolerance andinductance better coupling coefficients. increase coil to increase coupling.Design changes can be made to reduce parasitic capacitance and tolerance andinductance better coupling coefficients. increase coil inductance to increase coupling. References increase coil inductance to increase coupling. References References References [1] Nikola Nikola Tesla, Tesla, "Apparatus "Apparatus for for transmitting transmitting electrical electrical energy.," energy.," US1119732 US1119732 A, A, May May 4, 4, 1907. 1907. References [1] [1] Nikola Tesla, "Apparatus for transmitting electrical energy.," US1119732 A, May 4, 1907. [2] E. Waffenschmidt and T. 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