High Efficiency Buck LED Driver Using SiC

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2-4 March 2017, VIT University, Campus Energy Procedia 00 (2017) 1–12 Chennai 2-4 March 2017, VIT University, Energy Procedia 117 (2017) 224–235 Chennai Campus Energy Procedia 00 (2017) 000–000 1st International Conference on Power Engineering, Computing and Control, PECCON-2017, www.elsevier.com/locate/procedia 1st International Conference on Power Engineering, Computing and Control, PECCON-2017, 2-4 March 2017, VIT University, Chennai Campus 2-4 March 2017, VIT University, Chennai Campus 1st International Conference on Power Engineering, Computing and Control, High Efficiency Buck LED Driver Using SiC High Efficiency LEDComputing Driver Using SiCPECCON-2017, 1st International Conference on Power Engineering, and Control, PECCON-2017, 2-4 March 2017,Buck VIT University, Chennai Campus 2-4 March 2017, VIT University, Chennai Campus

High Efficiency Buck Driver Using a,∗ b a R.Srimathi Sitoke High Efficiency Buck LED LED Driver Using SiC SiC a,∗, Shubhendhu b , S.Hemamalini a R.Srimathi , Shubhendhu Sitoke , S.Hemamalini High Efficiency Buck LED Driver Using SiC The 15th International Symposium onChennai. District Heating and Cooling SELECT, VIT University, High Efficiency Buck LED Driver Using SiC a,∗ SELECT, b a VIT University, Chennai. NIT University, Warangal. R.Srimathi , Shubhendhu Sitoke , S.Hemamalini NIT University,Sitoke Warangal.b , S.Hemamalinia R.Srimathia,∗, Shubhendhu a,∗ SELECT,of b heat demand-outdoor AssessingR.Srimathi the feasibility using the VIT University, Chennai. , Shubhendhu Sitoke , S.Hemamaliniaa a,∗ SELECT, b VIT University, Chennai. NIT University, Warangal. R.Srimathi for , Shubhendhu Sitoke , S.Hemamalini University, Warangal. temperature function a NIT long-term district heat demand forecast SELECT, VIT University, Chennai. a a

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Abstract Abstract I.

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b NIT University, Warangal. a SELECT, VIT University, Chennai.

a NIT University, Warangal. b *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrièrec, O. Le Correc b

In this paper, a Double Frequency Buck Driver (DFBD) using SiC diodes for LED lighting systems is presented.This topology In this paper, a for Double Frequency Buck Driver Buck (DFBD) using SiC diodes LED lighting systems is1049-001 presented.This topology a IN+ Center Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. the Rovisco Pais 1, losses Lisbon,diode. Portugal enhances the efficiency of the Double Frequency Converter (DFBC) byfor minimizing switching in power The Abstract b Double Frequency Buck Converter (DFBC) by minimizing the switching losses in power diode. The enhances the efficiency of the Abstract Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France design procedure, mathematical equations and efficiency calculations of the DFBD are discussed. A prototype of the Conventional design procedure, mathematical and efficiency calculations of the DFBD areAlfred A44300 prototype the Conventional In thisConverter paper,cDépartement a Double Frequency Buck Driver using diodes for LED lighting systems is Nantes, presented.This topology Systèmes et (DFBD) Environnement IMT Atlantique, 4 rue Kastler, France Buck (CBC) with Si equations andÉnergétiques SiC diode, with SiC-SiC diode and Si diode isdiscussed. implemented 10WofLED in hardware. Abstract In thisConverter paper, a Double Frequency Buck Driver DFBC (DFBD) using SiC diodes for LED lighting systemsfor is presented.This topology Buck (CBC) with Si and SiC diode, DFBC with SiC diode and Si diode is implemented for 10W LED indiode. hardware. enhances the efficiency of the Double Frequency Buck Converter (DFBC) by minimizing the switching losses in power The Abstract Experimental results are presented for the four different topologies to imply that the efficiency of the system increases with SiC enhances the efficiency of the Double Frequency Buck Converter (DFBC) by minimizing the switching losses in power diode. The In this procedure, paper, results a Double Frequency Buck Driver (DFBD)calculations using SiC to diodes for LED lighting systems is presented.This topology Experimental are presented for the four different topologies imply that the efficiency of the system increases with SiC design mathematical equations and efficiency of the DFBD are discussed. A prototype of the Conventional diodes. In addition, the cost analysis and energy savings for a multi-storeyed official building are estimated for the DFBC with SiC design procedure, mathematical equations and efficiency calculations of and thebyDFBD are A prototype of the Conventional In thisConverter paper, a Double Frequency Driver (DFBD) using SiC diodes for LED lighting systems is presented.This topology enhances the efficiency of theanalysis Double Frequency Buck Converter (DFBC) minimizing the switching losses power diodes. Inand addition, the with cost and energy savings for a SiC multi-storeyed official building are estimated forin the DFBC with The SiC Buck (CBC) with Si andBuck SiC diode, DFBC with diode Si diode isdiscussed. implemented for 10W LED indiode. hardware. topology validated the other topologies. Buck Converter (CBC) with Si andfor SiC DFBC with SiC (DFBC) diode and Si diode implemented for 10Win LED indiode. hardware. enhances the efficiency of thethe Double Frequency Buck Converter minimizing the switching losses power design procedure, mathematical equations and calculations thebyDFBD areis discussed. prototype of the Conventional topology and validated other topologies. Abstract Experimental results arewith presented thediode, fourefficiency different topologies toofimply that the efficiency ofAthe system increases with The SiC Experimental results are presented for the four different topologies to imply that the efficiency of the system increases with SiC design procedure, mathematical equations and efficiency calculations of the DFBD are discussed. A prototype of the Conventional Buck Converter (CBC) withanalysis SiBuck andElsevier SiC energy diode, DFBC with SiC diode and Si diodebuilding is implemented for 10W LED in hardware. Keywords: Double frequency Driver (DFBD); Silicon Diodes (SiC);Energy; Efficiency. © 2017 The Authors. Published by Ltd.savings diodes. In addition, the cost and for aCarbide multi-storeyed official are estimated for the DFBC with SiC Keywords: Double frequency Buck Driver (DFBD); Silicon Carbide Diodes (SiC);Energy; Efficiency. diodes. In addition, the cost analysis and energy savings for a multi-storeyed official building are estimated for the DFBC with SiC Buck Converter (CBC) with Si and SiC diode, DFBC with SiC diode and Si diode is implemented for 10W LED in hardware. Experimental results are presented for the four different topologies to imply that the efficiency of the system increases with Peer-review under responsibility of thetopologies. scientific committee the 1st International Conference on Power Engineering, topology validated with are the other District and heating networks commonly addressed in theofliterature as one of the most effective solutions for decreasingSiC the topology validated the other topologies. Experimental results arewith presented the foursector. different topologies torequire implyofficial that investments thebuilding efficiency of theare system increases with diodes. Inand addition, the cost analysis and energy savings for asystems multi-storeyed arewhich estimated for the DFBC Computing and CONtrol. greenhouse gas emissions from thefor building These high returned through theSiC heat 1. Introduction Keywords: Double frequency Buck (DFBD); Diodespolicies, (SiC);Energy; Efficiency. diodes. Inand addition, cost analysis and energy savings for aCarbide multi-storeyed official building are estimated the DFBC SiC topology validated with the otherDriver topologies. Due to the the changed climate conditions andSilicon building renovation heat demand in thefor future could with decrease, 1.sales. Introduction Keywords: Double frequency Buck Driver (DFBD); Silicon Carbide Diodes (SiC);Energy; Efficiency. topology and validated with the other topologies. prolonging the investment return period.as light source nowadays, as they replace the conventional incandescent lamps, The LEDs are frequency becoming popular Keywords: Double Buck Driver (DFBD); Silicon Carbide Diodes (SiC);Energy; Efficiency. The LEDs are becoming popular asthe light source as they replace theEfficiency. conventional incandescent The main scope of this paper is to feasibility ofnowadays, using the heat demand – outdoor temperature function for heatlamps, demand 1. Introduction Keywords:based Double frequency lamps Buckassess Driver (DFBD); Silicon Carbide (SiC);Energy; mercury fluorescent and halogen lamps[1, 2]. It Diodes has high luminous density, long life time, high power 1. Introduction forecast. The district of Alvalade, located in Lisbon (Portugal), used luminous as a case study. The district is consisted of 665 mercury based fluorescent lamps and halogen lamps[1, 2]. It was has high density, long life time, high power conversion efficiency and isconstruction compact inperiod size. and It has many applications such as display backlight, outdoor and indoor buildings that vary in both typology. Three weather scenarios (low, medium, high) and three district 1. Introduction The LEDs are becoming popular as light source nowadays, as they replace the conventional incandescent lamps, conversion efficiency and is compact in size. It has many applications such as display backlight, outdoor and indoor lighting andscenarios inare automobiles [3, 4]. A(shallow, single will have lowas output power. So to meet the heat desired lighting lumiThe LEDs becoming popular as light LED source nowadays, they replace the conventional incandescent lamps, 1. Introduction renovation were developed intermediate, deep). To estimate the error, obtained demand values were mercury based fluorescent lamps and halogen lamps[1, 2]. It has high luminous density, long life time, high power lighting and in automobiles [3, 4]. A single LED will have low output power. So to meet the desired lighting luminance, LEDs may bealamps connected in seriessource and parallel. About 1038% of the total energy bill globally is used for mercury based fluorescent and halogen lamps[1, 2].applications It has high luminous density, long life time, high power Themany LEDs are becoming popular as light nowadays, asdeveloped they replace the conventional incandescent lamps, compared with results from dynamic heat demand model, previously and validated by the authors. conversion efficiency and is compact in size. It has many such as display backlight, outdoor and indoor nance, many LEDs may be connected inlight seriessource and parallel. About 1038% of thethe total energy billincandescent globally is used for The LEDs are becoming popular as nowadays, as they replace conventional lamps, lighting applications. One report published in 2004 by USAID and The Energy Research Institute (TERI) estimated conversion efficiency and is compact in size. It has many applications such as display backlight, outdoor and indoor mercury based fluorescent lamps and halogen lamps[1, 2]. It has high luminous density, long life time, high power The results thatOne when only4].weather change is will considered, theand margin of error So could acceptable for some applications lighting andshowed in automobiles [3, A single LED have low output power. to be meet the desired lighting lumiapplications. report published in 2004 by USAID The Energy Research Institute (TERI) estimated mercury based fluorescent and halogen 2].applications hasoutput highconsidered). luminous density, life time, high power that cumulative lighting load4]. was approximately 42% ofIt the total energy consumed inlong India [5]. Therefore the lighting and in automobiles [3, A in single LED have low power. Sototal to meet the desired lighting lumi(the the error inefficiency annual demand was lower than 20% for all weather scenarios However, after introducing conversion andbeislamps compact size. Itlamps[1, haswill many such display backlight, outdoor and indoor nance, LEDs may connected in series and parallel. 1038% ofasthe energy bill globally is renovation used for that themany cumulative lighting load wasin approximately 42%applications ofAbout the total energy consumed in India [5]. Therefore the conversion efficiency and isconnected compact size. It(depending haswill many such asthe display backlight, outdoor and indoor scenarios, the error increased upAtosingle 59.5% on and renovation scenarios combination considered). electrical energy canvalue be saved by4]. increasing the efficiency of the the weather lighting systems. To increase the efficiency, the focus nance, many LEDs may be in series and parallel. About 1038% of total energy bill globally is used for lighting and in automobiles [3, LED have low output power. So to meet the desired lighting lumilighting applications. One report published in 2004 by USAID and The Energy Research Institute (TERI) estimated electrical energy cancoefficient be saved[3,by increasing the efficiency of low the lighting systems. To increase the efficiency, the lumifocus lighting and automobiles 4]. A (LED) single LED will have output power. to meet the desired lighting The value ofin slope increased onseries average within the About range of 3.8% uppower toSo 8% per decade, that corresponds tofor the should be on the electrical materials and driver circuits used. Low [6], low cost [7], high efficiency applications. One report published in 2004 by USAID and The Energy Research Institute (TERI) estimated nance, many LEDs may be connected in and parallel. 1038% of the total energy bill globally is used that thebe cumulative lighting load hours was (LED) approximately 42% ofheating theused. total energy consumed in combination India [5]. high Therefore the should the electrical materials and circuits Low(depending power [6], low cost efficiency decrease inon the number ofneed ofseries 22-139h during the season on the of is weather and nance, many LEDs beheating connected in anddriver parallel. About 1038% ofDC the total energy bill [7], globally used for LED drivers [8] aremay the for the day. For supplying these LED strings, current is needed. Henceforth many that the cumulative lighting load was approximately 42% of the total energy consumed in India [5]. Therefore the lighting applications. One report published in 2004 by USAID and The Energy Research Institute (TERI) estimated electrical energy canthe be saved byOn increasing the efficiency ofintercept theLED lighting systems. To increase the efficiency, the many focus LED drivers [8] are need for the day. For supplying these strings, DC current is Institute needed. Henceforth renovation scenarios considered). the other hand, function increased forconsumed 7.8-12.7% decade (depending onthe the lighting applications. report published in 2004 by42% USAID The Energy Research (TERI) estimated converter topologies inOne AC/DC DC/DC are developed. thetotal existing converter topologies can beTherefore classified as electrical energy can be saved byand increasing the efficiency ofofAll the lighting systems. To[6], increase the efficiency, the focus that thebe cumulative lighting load was approximately theand energy inperIndia [5]. should on the electrical materials (LED) and driver circuits used. Low power low cost [7], high efficiency converter topologies in AC/DC and DC/DC are developed. All the existing converter topologies can be classified as coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and that thestage cumulative lighting load was (LED) approximately 42% ofthe the[9] total energy consumed in India [5].inhigh Therefore the single two stage three stage topologies . Single stage driver topologies are low mostly domestic and should be on, [8] thecan electrical materials and driver circuits used. Low power cost [7], efficiency electrical energy be and saved by increasing the efficiency of lighting systems. To[6], increase theused efficiency, the many focus LED drivers the need for theestimations. day. For supplying LED strings, DC current needed. Henceforth single stage ,accuracy twoare stage and three stage topologies . Singlethese stage driver topologies are is mostly in domestic and improve the of demand electrical energy can beheat saved by increasing the efficiency of the [9] lighting systems. To increase theused efficiency, the focus

commercial whereas twoday. stage and three stage topologies are usedlow inhigh not aefficiency concern, LED drivers [8] the need forand the For[10] supplying these strings, DC current iswhere needed. Henceforth many should be topologies onapplications, theare electrical materials (LED) and driver circuits used. Low[11] power [6], costcost [7], converter in AC/DC DC/DC are developed. AllLED the existing converter topologies can classified as commercial applications, whereas two stage [10] and three stage topologies [11] are [6], used where inbe not aefficiency concern, should be topologies on theare electrical materials (LED) and driver used. Lowthat power costcost [7], high ratherdrivers they focus on reliability and efficiency. The three circuits important factors should below considered while manufacconverter in AC/DC and DC/DC are developed. All the existing converter topologies can be classified as LED [8] the need for the day. For supplying these LED strings, DC current is needed. Henceforth many single stage , two stage and three stage topologies . Single stage [9] driver topologies are mostly used in domestic and © 2017 The Authors. Published by Elsevier Ltd. rather they focus on the reliability and efficiency. The three these important factors that should beisconsidered while manufacLED drivers [8] are need for the day. Forare supplying LED strings, DC current needed. Henceforth many turing LED Lighting System are LED driver, LED package and mechanical/thermal component. The main driving single stage , two stage and three stage topologies . Single stage [9] driver topologies are mostly used in domestic and converter topologies in AC/DC and DC/DC developed. All the existing converter topologies can be classified as Peer-review under responsibility of the Scientific Committee of stage Theand 15th International on District and commercial applications, whereas two stage [10] andpackage three topologies [11]Symposium are used where costThe inHeating not a concern, turing LED Lighting System are LED driver, LED mechanical/thermal component. main driving converter topologies in AC/DC and DC/DC are developed. All the existing converter topologies can be classified as technique used for LED drivers are PWM technique and amplitude mode driving technique. These drivers are mostly commercial applications, whereas two stage [10] and three stage topologies [11] are used where cost in not a concern, single stage , two stage and three stage topologies . Single stage [9] driver topologies are mostly used in domestic and Cooling. rather theyused focus reliability and efficiency. The three important mode factorsdriving that should be considered whileare manufactechnique foron LED drivers are PWM technique and amplitude technique. These drivers mostly single stagefocus ,applications, two stage and three stage topologies . three Single stage [9] driver topologies are mostly used in domestic and rather they on reliability and efficiency. The important factors that should be considered while manufaccommercial whereas two stage [10] and three stage topologies [11] are used where cost in not a concern, turing LED Lighting System are LED driver, LED package and mechanical/thermal component. The main driving commercial applications, whereas two stage [10] and three stage [11]should are used costThe inwhile not amanufacconcern, turing LED Lighting System are driver, LED package andtopologies mechanical/thermal component. main driving Keywords: Heat demand; Forecast; Climate change rather they focus reliability and efficiency. The three important factorsdriving that be where considered ∗ R.Srimathi technique used foronLED drivers areLED PWM technique and amplitude mode technique. These drivers are mostly ∗ R.Srimathi rather they focus on reliability and efficiency. The three important factors that should be considered while manufactechnique used for LED drivers are PWM technique and amplitude mode driving technique. These drivers are mostly turing LED Lighting System are LED driver, LED package and mechanical/thermal component. The main driving Email address: [email protected] (R.Srimathi) Email address: [email protected] (R.Srimathi) turing LED Lighting System areareLED driver, LED package and mechanical/thermal component. The main driving technique used for LED drivers PWM technique and amplitude mode driving technique. These drivers are mostly 1 ∗ R.Srimathi 1 technique used for LED drivers are PWM technique and amplitude mode driving technique. These drivers are mostly ∗

∗ R.Srimathi Email address: [email protected] (R.Srimathi) 1876-6102 © 2017 [email protected] The Authors. Published by(R.Srimathi) Elsevier Ltd. address: ∗ Email R.Srimathi 1 International Symposium on District Heating and Cooling. Peer-review under responsibility of the Scientific Committee of The 15th ∗ 1 Email address: [email protected] (R.Srimathi) 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. R.Srimathi Peer-review under [email protected] responsibility of the scientific committee of the 11st International Conference on Power Engineering, Computing Email address: (R.Srimathi) and CONtrol. 1 10.1016/j.egypro.2017.05.126



R. Srimathi et al. / Energy Procedia 117 (2017) 224–235 R.Srimathi / Energy Procedia 00 (2017) 1–12

225 2

operated with switches and power diodes. The reverse recovery current during turn-off of the diode in a conventional buck driver causes significant power dissipation in switches and increased EMI generation. Therefore buck driver is realized with SiC diodes so as to address the power dissipation in the diodes. Among the semiconductor devices, the power diode is the first commercialized device with SiC Technology. SiC diodes have zero reverse recovery current and high breakdown voltage [12]. Replacing conventional diodes with SiC diodes will increase the system efficiency and power density as well. In this paper, a low power DFBD with SiC diodes is proposed [13] as a single stage LED driver. The converter consists of two cells namely high frequency cell (HFC) and Low Frequency Cell (LFC). Each cell has a MOSFET, Inductor and Silicon Carbide Schottky Barrier Diodes (SiC SBD). Both cells are operated at distinct frequencies in Continuous Conduction Mode (CCM). The circuit is simulated in MATLAB Simulink and a prototype is implemented to imply efficiency. This paper is organised as follows: The operation and design of DFBC are described in Section 2, control strategy for DFBD is presented in Section 3, Simulation and Experimental results are shown in Section 4 and 5, and a case study for a multi-storey official building is given in Section 6. 2. Circuit Operation and Design of DFBC

Fig. 1. Conventional Buck Converter Circuit Diagram

The topology of the Conventional Buck Converter (CBC) is shown in Fig.1. The input Vin and the output Vo of the converter in steady sate is related by the equation Vo = DVin

(1)

Where, D is the duty ratio.

Fig. 2. Averaged Model of DFBC with the added CCS of DFBC.

Fig. 3. Block Diagram of DFBC.

The DFBC is operated in CCM and can be considered as Controlled Current Source (CCS). Fig.2 shows the averaged model of DFBC with the CCS (IL1 ). This added current source enhances the transient and steady state operation when compared to a conventional buck converter. Fig. 3 shows the circuit diagram of DFBC. This converter has two cells namely HFC and LFC. The HFC consists of S 1 , D1 , L1 components and the LFC has S 2 , D2 , L2 . Under 2

226

R. Srimathi et al. / Energy Procedia 117 (2017) 224–235 R.Srimathi / Energy Procedia 00 (2017) 1–12 R.Srimathi Energy00 Procedia 00(2017) (2017)1–12 1–12 R.SrimathiR.Srimathi / Energy Procedia / / Energy Procedia (2017) 00 1–12

3

3 33

steady the current main switch and by (2) steady state, thethrough currentthrough through the mainand switch andthe the diode are given by(3). (2)and and(3). (3). steady state, steady thestate, state, current the current through the mainthe the switch main switch the diode and the arediode diode givenare are bygiven given (2) and by (2) and (3). IIID1 = L1 − −=D(I D(I ID(I −− I IIIL2 )))= ==III111 ID1 = D(I DD L111 = L2 )LL= 11 1 LL22 ==(1 −− (1 D)(I I s1 = (1 I− IIss1s1D)(I −D)(I D)(I IL2 )LLL111 − −−IIILLL222))) L1− 1 = (1

(2) (3)

(2) (2) (2) (3) (3) (3)

main switch IL1 and IIIL2 current are current the ,,,IIIDcurrent is the current IS 1 =I 1 is 1 is the =Imain isthe the maincurrent, switchcurrent, andthe arethe thethrough currentthrough through theinductors inductors thethrough currentthrough through Where, the switch main switch current, Icurrent, and the current through the inductors the inductors , ID1 is the current through Where, IWhere, Where, S11=I S 1 =I1 isIISthe 11 is L1 and IILIL2L11are LL22 are DD11 is the main diode. From equation (2) and (3) it is visible that when both the currents are equal the current the mainFrom diode. From equation equation (2)itand and (3) itit isisthat visible that when both the currents currents are equal thethrough currentthrough throughthe the the mainthe diode. main diode. equation From (2) and (3) (2) is visible (3) visible when that both when theboth currents the are equalare theequal current the current through the the main switch and diode zero. itititis to the at frequencies. The mainand switch and diode are zero. Therefore Therefore mandatory tooperate operate both theswitches switches atdifferent different frequencies. The main switch main switch diode and are diode zero.are are Therefore zero. Therefore it is mandatory isismandatory mandatory to operate to both operate theboth both switches the switches at different at different frequencies. frequencies. The The and SSS2 are at low ,,, F high is switches andoperated areoperated operated at high highfrequency frequency ,F111 and and lowfrequency frequency respectively. The high frequency frequency switchesswitches switches S 1 and SSSS2111are and operated at high frequency at high frequency ,F1 and ,F ,F low and frequency low frequency , F2 respectively. FF222 respectively. respectively. The highThe The frequency high frequency is isis 22 are chosen to be the integral multiple of low frequency as given in (4). chosen to be the the integral integral multiple multiple of low low frequency frequency as given in in (4). (4). chosen to chosen be theto integral be multiple of low frequency of as givenas in given (4). =N ∗FF11F1 = NN∗∗∗F FF222 F1 = N F 2=

Fig. 4. Mode 1 (S 1 -ON and S 2 -ON). Fig.14.4. 1(S (S1S1-ON -ON andSS22-ON). -ON). Fig. 4. Mode Fig. (SMode -ON 1and and 1Mode 2 -ON).

Fig. 6. Mode 3 (S 1 OFF and S 2 -ON). Fig.36.6. (S11SOFF OFF andSS22-ON). -ON). Fig. 6. Mode Fig. (SMode (S OFF33and and 1Mode 2 -ON).

(4)

(4) (4) (4)

Fig. 5. Mode 2 (S 1 ON and S 2 -OFF). Fig.25.5. (SS112ON ON andSS22-OFF). -OFF). Fig. 5. Mode Fig. (SMode ON and 22(S -OFF). and 1Mode

Fig. 7. Mode 4 (S 1 -OFF and S 2 -OFF). Fig.47.7. (S11-OFF andSS22-OFF). -OFF). Fig. 7. Mode Fig. (SMode -OFF44and (S S-OFF and 1Mode 2 -OFF).

cell the cell the output The power is The LFC cellenhances enhances theefficiency efficiency and HFC cellimproves improves the outputperformance. performance. The power circuit operated The LFCThe The cellLFC LFC enhances cell enhances the efficiency the efficiency and HFCand and cellHFC HFC improves cell improves the output the performance. output performance. The power The circuit power iscircuit circuit operated isisoperated operated in four different modes. The equivalent circuit for each mode is given in Fig.4 to Fig.7. The averaged model in four four different different modes. The equivalent equivalent circuit for each mode is is given given in Fig.4 Fig.4 to toThe Fig.7. The averaged averaged model forthe the in four different in modes. The modes. equivalent The circuit for circuit eachfor mode each is mode given in Fig.4 in to Fig.7. Fig.7. averaged The model for model the for for the controller design is derived from the differential equations of switching states as given from Fig.4 to Fig.7. This model controller design derived from thedifferential differential equations ofswitching switching statesas asgiven given from Fig.4to to Fig.7. Thismodel model controller controller design isdesign derived isisfrom derived thefrom differential the equations equations of switching of states asstates given from Fig.4 from to Fig.4 Fig.7. This Fig.7. model This is used design the and The as usedto tothe design theconverter converter andthe thecontroller. controller. Theaveraged averaged model isgiven given asfollows follows is used to isisdesign used to design converter the converter and the controller. and the controller. The averaged The averaged model ismodel model given is is as given follows as follows di diL1 diL1 L1 di L1 L1 (5) (5) L1 =LL1v1 indt− d= ==ivvvinin− −−ddd111iioioo (5) (5) dt 1 o in dt dt di diL2 diL2 L2 di L2 = (d1 − d2 )io L2 (6) (6) (d1 −−dd22)i)ioo L2 (6) (6) =LL2(d ==)i (d 2 dt 1−d dt 2 o1 dt dt v dv dvooo + vvooo = (iL2 − iL1 )d1 − iL2 d2 dvo Cvodv (7) (7) + CC dt= (i ++ − =i=L1(i(i )d − iiL1 d)d211 −−iiL2 (7) (7) C L2 L1)d L2dd22 L2 1− L2 dt L2R dt R dt RR The steady state are from by time Thestate steady stateequations equations arederived derived from(5)to(7) (5)to(7) byequating equating the timederivatives derivatives tozero. zero. The steady The steady equations state equations are derived are from derived (5)to(7) from (5)to(7) by equating by equating the timethe the derivatives time derivatives to zero. to to zero. o = =DV DVininin DV Vo = DVV VV inoo = D=111 = =D D222 = D D1 = D2D D = D D ==D D D i = i 1 L1 o D i = D1 iL1 = D io11iL1 L1 = iioo 3 3 33

(8) (9) (10)

(8) (8) (8) (9) (9) (9)

(10) (10) (10)



R. Srimathi et al. / Energy Procedia 117 (2017) 224–235 R.Srimathi / Energy Procedia 00 (2017) 1–12

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Where, Vin is the input voltage, R is the load, L is the inductor, C is the filter capacitor, Vo is the output voltage. D1 and D2 are the duty ratios of HFC and LFC respectively. The steady state equations derived is similar to conventional buck converter. Therefore the design equations for DFBC are similar to conventional buck converter and are given in Table 1. For calculating these values, the desired current (IL ) and voltage ripple (Vo ) are taken as 0.204 A and 0.349 V .Whereas, N = 1 for HFC and 2 for LFC respectively. Table 1. Specifications of DFBC LED Driver

Inductor L=

Capacitor

D∗(Vin −Vo ) IL ∗F N

C=

IL 8∗F N ∗Vo

3. Design of Converter and PID Compensator The Small Signal modelling (SSM) and the compensator design for the closed loop control for the DFBC is presented in this section. 3.1. Small Signal Modelling Small Signal modelling (SSM) [14, 15] is required to design the closed loop control to achieve the desired performance. The first order small signal linearization is applied from (5)(7) to derive the state space model. The state space representation for the converter is given as x = Ax + Bd + Cvin

(11)

Where,x= [iL1 ,iL2 ,vo ] and d =[d1 ,d2 ] respectively. The state matrices respectively A, B and C are given below       1   −1  L   0 0 L  1   1           A =  0 0 0  ; C = 0 0 1 ; B =  0             1 0 −1  0 C RC

The transfer functions are derived by applying Laplace transform in (11).

X(s) = (sI − A)−1 Bd(s) + (sI − A)−1CVin (s)

(12)

From (12), I is a 3X3 identity matrix. Substituting the steady equations from (8) to (10) in (12) yields the following transfer functions in continuous domain.  Vin  1 + sCR (13) GiL1 d1 (s) = R 1 + s L1 + s2 L1C R  1 Vin  GiL2 d2 (s) = (14) RL1C 1 + s L1 + s2 L1C R  1 Vin  Gvo d1 (s) = (15) L1C 1 + s L1 + s2 L1C R  Vin  s (16) Gvo d2 (s) = RC 1 + s L1 + s2 L1C R   s Gvo vin (s) = D (17) 1 + s LR1 + s2 L1C GiL2 Vo (s) = 0

4

(18)

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The inductor L2 of LFC is not involved in any of the transfer functions from (13) - (17). The inclusion of LFC cell diverts the current from the main switch S 1 in HFC to LFC and thereby reduces the conduction losses in main switch. 3.2. Compensator Design

Fig. 8. Current Mode Control of DFBC

The closed loop control of DFBC converter using dual loop control strategy is given in Fig.8. The control of the DFBC is done to meet out the desired voltage and current output. The output voltage from the converter is fed to PIC16F877Abwhere it is compared with the reference signal. The error signal is processed by the PID controller. The sensed current waveforms of both the inductors are in turn compared with the outputs of PID controller. The resultant outputs are the PWM signals generated by the microcontroller for power switches S 1 and S 2 . The closed loop performance of the converter is veried by designing a suitable digital PID controller for the DFBC. The discrete control transfer function of the converter is derived using direct digital design approach. The control transfer function G vd (s) is discretized using Zero Order Hold (ZOH) and computational delay and given in (18).

Fig. 9. Uncompensated and Compensated Bode Plots for DFBC

To derive the controller transfer function in Z domain, Single Input Single Output (SISO) tool of MATLAB is used. The control transfer functions as in (15) and (16) are given as inputs to SISO tool. The general discrete PID 5



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controller structure is given in (19).  1 − e−sT s

Gvd (z) = z



e−sT s Gvd (s)

(19)

s z − 1 Ts + Kd Gc (z) = K p + Ki z−1 z

(20)

The bode plots for compensated and uncompensated control (Gvd(z)) transfer functions are given in Fig.9. From the plot, it is observed that voltage loop gain has a crossover frequency of 7.14 kHz with a phase margin of 53.2◦ . This ensures that the system is stable for any change in load or input voltage. 4. Simulation Results 4.1. Transient and Steady State Analysis The DFBC is simulated in MATLAB/Simulink environment with the specifications given in Table 2. Table 2. Specifications of DFBC LED Driver

Parameters

Value

Parameters

Input Voltage (Vin )

48 V

Inductor (L1 andL2 )

L2 =3900 µH

Output Voltage (Vo )

12 V

C (µF)

220

Input Current (Iin )

0.208 A

Inductor current Ripple (I)

0.204 A

Duty Ratio (D)

0.25 A

Output Power (Po )

10 W

14.4 Ω

Frequency

Load (R)

(F1 andF2 )

Value L1 =390 µH

F1 =100 kHz F2 =10 kHz

The transient performance of DFBC is analysed for variations in load and input voltage as shown in the Fig. 10 respectively. The transient performance is observed for a change of load (step down) from 14Ω to 12Ω during 0.1 ms to 0.15 ms and from 14Ω to 16Ω (step up) during 0.2 to 0.25 ms respectively as shown in Fig.10. Similarly it can be seen from Fig.11, that there is a change in the input voltage from 48V to 40V (step down) during 0.1 to 0.15ms and from 48V to 58V (step up) during 0.2 to 0.25 ms. It is evident from Fig. 10 and 11, the output voltage is regulated with the designed control circuit for any kind of disturbances in the system. 4.2. Efficiency Calculation The efficiency of DFBC [16] is computed by calculating the conduction and switching losses of the power semiconductor devices. Based on the specification given in Table 2 suitable Si and SiC diodes are selected. The key parameters used for calculating the losses are given in Table 3. The static characteristics are used to calculate the conduction losses. The static characteristics from datasheets of the devices clearly indicate that the MOSFET is strongly dependent on temperature. Hence heat sink is to be properly designed to improve its performance. Moreover the Si diodes have negative temperature coefficient and SiC diodes have positive temperature coefficient. This clearly indicates that the conduction losses of Si diodes will be lesser than SiC diodes. The dynamic characteristics are used to calculate the switching losses of the device. The MOSFET/Si Diode and MOSFET/SiC diode do not have any difference in the turn-off process as it has similar turn-off waveforms. But the 6

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(b) Fig. 10. Dynamic load change and input voltage change.

turn-on process is different for both the topologies.This is because of the large reverse recovery current of Si diode and ultimately zero reverse recovery current for SiC diodes. Hence the turn-off losses will be similar for both diodes and turn-on losses will be quite dissimilar because of large reverse recovery current. The total semiconductor losses are calculated for the two topologies and are given in Fig.11 for a particular input and output condition. Table 3. Parameters of the Semiconductor Devices

Parameter

Symbol

Devices Si Diode GME MUR405G Superfast 50

SiC Diode Vishay UF5400 SiC Schotkhy 50

Breakdown Voltage ,V

VBD

CoolMOS Vishay IRF530 Cool MOS 100

Rated Current, A

ID

9.2

4

3

Junction Temperature,◦ C

T jmax

175

175

150

R◦jA

62

28

8.5

TO-220-3

DO-201AD

DO-201AD

Manufacturer Part No Type

Thermal

Resistance,◦ CW

Package

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5

5

Losses (%)

4 3

4

4

3

3

2 1

1

1

8

4

P scon P sssw PDcon PDrr

2

2

1 0.5

1 0.5 iC D

D

FB C

FB C

/S

/S i

C Si C/ CB

CB

C/ Si

0

Fig. 11. Fig.12. Distributed Power Loss (Vin = 20V, Vout =5V and D=0.25) 100

100

95

95 90 Efficiency[%]

Efficiency[%]

90 85 80 75

CBC/Si CBC/SiC DFBC/Si DFBC/SiC

70 65 60

0

4

8

85 80 75 70 CBC/Si CBC/SiC DFBC/Si DFBC/SiC

65 60 55 50

12 16 20 24 28 32 36 Load Resistance [Ω]

Fig. 12. Load change Vs Efficiency

0

10

20

30

40 50 60 Input Voltage [V]

70

80

90

Fig. 13. Input Voltage Vs Efficiency

Efficiency is calculated for all the topologies namely CBC,CBC with SiC diode, DFBC with Si diode and DFBC with SiC diode for change in duty ratio and input voltage. The efficiency for the four different topologies are plotted as shown in Fig. 12 and 13 for variation in load change and input voltage change. It is evident from the plots that DFBC with SiC has higher efficiency than other topologies. 5. Experimental Results The hardware prototype is developed for Conventional Buck Converter and Double Frequency Buck Converter. Both the converters are realized using Si and SiC diodes. The converters are designed and developed for 10W. The simulation parameters and the experimental prototype parameters are the same. The part No’s of the components used in hardware prototype are listed in Table 4. The specifications of the LED light used herein are described as follows. The LED’s are made with 10W, with a Forward Voltage (VF ) of DC 9-12V and Forward current (IF ) of 1050mA. Other details of the specified LED includes Output Lumens of 600-700 Lm,Color and Temperature as White(6000-6500K),Beam Angle - 140 degrees and with a life span greater than 50,000 hours. The experimental setup and prototype of the converters is shown in Fig. 14 (a), (b) and (c) respectively.

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Table 4. Part Nos of Components used In Prototype

Devices MOSFET Diode Inductors Capacitor Driver LED

CBC

CBC with SiC diode

DFBC with Si diode

DFBC with SiC diode

IRF530 IRF530

UF5400 L1 =1140-222K-RC MSS1278T-394 L2 =1130-212K-RC SKR221M2AK25M TLP250 SMD LED (10W, 12V)

(a)

(b)

(c) Fig. 14. (a) Experimental setup (b) Prototype Board for CBC and DFBC (c)Topology as LED Driver

All the converter topologies are subjected to load change and input voltage change to study the dynamic performance. However, the dynamic performance of DFBC with SiC is shown in Fig. 15 (a) and (b) respectively. The converter load is changed from 14Ω to 12 Ω and 12 Ω to 14 Ω as shown in Fig. 15 (a). It is also subjected to an input voltage change of 48V to 58V and from 48V to 38V for input voltage change and is shown in Fig. 15 (b). In both the cases, it is observed that the output voltage Vo is regulated irrespective of the disturbances due to the closed loop control. The experimentation is also done with LED for change in input voltage and load. The luminous intensity is measured for all the fout topologies in open loop using digital Lux Meter MS6610 and is given in Table 5. The input and output currents and voltages are measured to calculate the efficiency.

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(b) Fig. 15. Dynamic :oad and Input Voltage Change of DFBC Table 5. Actual Output Measured from Prototype For Vin = 47.5V ,Iin = 0.22A, d = 0.25 Load Change

Parameters

For Vin = 47.10V, Iin = 0.22A, d = 0.25 Input voltage change

CBC

CBC with SiC diode

DFBC with Si diode

DFBC with SiC diode

CBC

CBC with Si diode

DFBC with Si diode

DFBC with SiC diode

Output Power (W)

8.2

8.96

9.2

9.45

8.15

8.35

8.62

8.9

Output Lumens (Lm)

510

553

570

581

505

515

530

548

The hardware efficiency plots for the converters are given in Fig. 16 and 17. It can be seen from the plots that the efficiency has been increased for DFBC with SiC diodes when compared to other topologies. The input and output currents and voltages are measured to calculate the efficiency. The hardware efficiency plots 100

100

95

95 90 Efficiency[%]

Efficiency[%]

90 85 80 75

CBC/Si CBC/SiC DFBC/Si DFBC/SiC

70 65 60

0

4

8

85 80 75 70 CBC/Si CBC/SiC DFBC/Si DFBC/SiC

65 60 55 50

12 16 20 24 28 32 36 Load resistance [Ω]

0

10

20

30

40

50

60

70

80

90

Input Voltage [V]

Fig. 16. Load change Vs Efficiency

Fig. 17. Input Voltage Vs Efficiency

for the converters are given in Fig. 16 and 17. It can be seen from the plots that the efficiency has been increased for DFBC with SiC diodes when compared to other topologies. From Table 5, it is clear that the output power of DFBC with SiC diode is higher than other topologies. Consider the case for Input voltage change in Table 5. To deliver same output power as like CBC with Si diode the input power can be reduced by a factor of 1.1 for DFBC with SiC diode. 10

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6. Case Study for a VIT University Office Building Energy and efficiency in buildings [17] are of major concern nowadays. If the topologies are developed and implemented as retrofit in an official VIT University building, then the energy saved is estimated in this section. The lighting loads for the official building are fed by a separate feeder I, which consumes 8124 units/month. The number of 18W fluorescent tube lights with T12 fixtures connected to feeder I is 508. Assuming each light consumes power for 8 hours/day, the total power consumed/month by lighting load is nearly 30% i.e. 73.15kWhr. The tariff for energy consumed id Rs.5.50/unit. The estimated energy consumed and energy saved for an official multistorey building with 508 lamps is tabulated in Table 6. From Table 8, it is clear that the topology with DFBC/SiC diode saves energy of 1370 Kw-hr and cost/30 days of Rs.7536. The installation cost and payback period are also estimated and shown in Fig 18. The LED and the driver have longer life time. If it serves for nearly 14 years, the amount saved after the payback period is Rs. 1,63,224. Table 6. Estimated Cost and Energy Savings

Components

Fluorescent tube and T12 fixture

CBC with Si

CBC with SiC

DFBC with Si

DFBC with SiC

Total Installation Cost (Rs)

2,23,520

4,52,628

4,51,668

6,01,472

5,99,948

Power consumed / bill (Kw-hr)

2194

1097

998

906

824

Bill amount (Rs)

12070

6035

5486

4987

4534

Payback Period (years)

1.5

6.3

6.8

10

11

Installation Cost [lakhs]

7 CBC/Si CBC/SiC DFBC/Si DFBC/SiC

5 4 3 2 1 0

0

2

4

6

8

10

12

Period [yrs]

Fig. 18. Installation Cost Vs Payback period of converters

7. Conclusion A DFBC based LED driver with Si and SiC diodes is implemented and presented in this paper. The efficiency is calculated for all the four combinations in software and in hardware. The dynamic performance of the converter is analyzed for load change and input voltage change. To validate the simulation results, hardware prototype of 10W is developed and tested. Results showed that in terms of efficiency and output lumens, the converter using the SiC diodes performed better than the converter using the Si diodes. Likewise energy saving and cost savings are achieved using converter with SiC diodes. References

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