Designing and Demonstration of Misalignment Reduction for Wireless Charging of Autonomous Electric Vehicle

Journal Pre-proof Designing and Demonstration of Misalignment Reduction for Wireless Charging of Autonomous Electric Vehicle Aqueel Ahmad, Mohammad Saad Alam, Yasser Rafat, Samit Shariff PII:

S2590-1168(20)30009-6

DOI:

https://doi.org/10.1016/j.etran.2020.100052

Reference:

ETRAN 100052

To appear in:

eTransportation

Received Date: 7 October 2019 Revised Date:

14 February 2020

Accepted Date: 15 February 2020

Please cite this article as: Ahmad, A., Alam, M.S., Rafat, Y., Shariff, S., Designing and Demonstration of Misalignment Reduction for Wireless Charging of Autonomous Electric Vehicle, eTransportation, https:// doi.org/10.1016/j.etran.2020.100052. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Elsevier B.V. All rights reserved.

Aqueel Ahmad: Conceptualization, Methodology, Software, Data curation, Writing- Original draft preparation. Mohammad Saad Alam: Supervision Yasser Rafat: Visualization, Investigation. Samir Shariff: Writing- Reviewing and Editing,

Designing and Demonstration of Misalignment Reduction for Wireless Charging of Autonomous Electric Vehicle 1

Aqueel Ahmad, 2Mohammad Saad Alam, 3Yasser Rafat, 4Samit Shariff

1,2,3

Center of Advanced Research in Electrified Transportation, Aligarh Muslim University, India, Department of Electric Engineering, Tayibah University, Al-Madinah, Kingdom of Saudi Arabia 1 [email protected], [email protected], [email protected], [email protected] 4

Abstract – One of the key challenges in the adoption of wireless charging for Electric Vehicles (EVs) is the misalignment between the power pads. This manuscript presents an intelligent alignment of the receiving coil to reduce the magnetic leakage between the coupling power pads. The proposed solution implicates sensors to detect the flux strength at the corners and the middle of the receiver coil. A two-dimensional control technique is used for positioning of the receiver coil controlled through the stepper motor driver and a controller circuit. An array of the Hall effect sensor is installed on the receiver to sense the flux, where sensor receiving the smallest flux will generate the least voltage. Further, the controller sends the command to shift the receiver coil to the direction of the sensor receiving highest flux. This manuscript evaluates and verifies the magnetic flux pattern at the maximum alignment position between the transmitter and the receiver using Finite Element Analysis (FEA) on Ansys Maxwell®. The proposed solution mitigates the flux leakage and improves the efficiency of the wireless power transfer. Theoretical analysis is performed and all the elements of the systems are briefly discussed and explained to develop the proposed system. The modeling and simulation results verify the advantage of proposed intelligent alignment.

Index Terms-- Sensor control; Misalignment; Receiver coil movement; Electric Vehicle; Wireless charging;

NOMENCLATURE AARS

Automatic Alignment Receiver System

AEV

Autonomous Electric Vehicle

IPT

Inductive Power Transfer

SCMR SS WPT

Strongly Coupled Magnetic Research Series Series Wireless Power Transfer

1

SWC

Static Wireless Charging


 ,


Primary and Secondary side inductance





 , 

Transmitter Inductance Receiver Inductance Primary and Secondary side Capacitance

M

Mutual Inductance



Primary side current



 , 

 ,  

 ,  k 

Secondary side current Primary and Secondary side Resistance Load Resistance Primary and Secondary side voltage Source Voltage Primary and Secondary quality factor Coupling Factor Resonant frequency

I.

INTRODUCTION

Autonomous Electric Vehicles are a potential solution to fossil fuel depletion and pollution control. Most of the automotive industries are ramping up to commercialize AEVs. The market share for EV is increasing exponentially but few drawbacks related to the technology limit the user’s attraction. AEV technology needs challenging research on the charging infrastructure to improve the driving range [1]. The available charging standards are merely for conductive charging. Conductive charging implicates deployment detriment of wiring, trip hazard, contact wear and tear, long charging time [2]. The wireless charging for AEV is showing the potential solutions to the changing detriments [3]. As compared to the conductive charging, the inductive charging is safe, convenient, automated and robust technology. The inductive charging for AEV entails some challenges which need to be encountered for commercialization. The design of the charging coil [4], compensation topology [5], [6], [7], misalignment [8], [9] and frequency of the wireless power transfer are the major factors which affect the charging seriously. The application of ferrite core has improved the coupling efficiency at a perfectly aligned position [10], [11]. A very 2

slight variation in the alignment of the charging coils decreases the efficiency. The nearby objects may damage owed to flux leakage and linking with near metal objects. Metal surface induces eddy current to generate heat. Fig.1 shows possible misalignment positions of receiver coil with respect to the transmitter coil. The horizontal and lateral misalignment critically affects the charging efficiency. Many researchers are working to reduce the misalignment, improve the coupling and designing a standard coupling resonant topology to increase the efficiency of the wireless charging system.

Fig. 1. Possible misalignments between the transmitter and receiver for static wireless charging [1]

M. Mohammad et al have proposed the various coils design along with ferrite core to improve the misalignment tolerance and minimize the losses in the core[12]. J. Chaw et al proposed a receiving coil with parallel and orthogonal winding to improve the wireless power transfer efficiency [13]. Multi-coil wave-type power pad system is proposed by J. Y. Lee et al to improve the angular, lateral and horizontal misalignment [14]. D. Ahn and S. Hong have worked on the analysis of the multiple-coil system to understand the effect of coupling [15]. S. Kong et al have analyzed and provided solutions for the protection of Electromagnetic emission for multi-coil power pad design[16]. Daerhan Liu et al proposed a Strongly Coupled Magnetic Research (SCMR) with less sensitive to the misalignment. Some of the improved topologies of compensation topology is being proposed by many to improve the misalignment tolerance[6][17]. The misalignment from all the directions affects the efficiency of the wireless power transfer [18]. The above-discussed methods are helpful, but for the deployment of wireless charging these applications are inadequate due to limited weight constraints and installation space. Even the above-discussed methods were implemented in the vehicle, the solution to misalignment still persist due to human parking error. In this manuscript, the solution is sensor-based where misalignment between transmitter and receiver is detected using sensor and the receiver is adjusted to with an autonomous control system until fully alignment is achieved. This method of magnetic tracking is the automatic alignment receiver system (AARS), which has been proposed by the authors of this paper in [9]. AARS is a novel method a similar method is already patented by R. Chabaan [19] but 3

with a different factor of control. R. Chabaan has used power transfer efficiency as a factor of control. This is the extended work of already conference paper published in the ITEC conference held in the USA as mentioned in the reference [9]. This manuscript has been organized into three major sections. Section II investigates the electrical circuit analysis, modeling and simulation results of the wireless charging system, to find the variation of efficiency due to the increase in the misalignment. Section III explains the hardware implementation methodology of the proposed system. Finally, section IV discusses the results and deployment challenges and solutions of the proposed AARS system. II.

MODELING AND SIMULATION OF THE AUTOMATIC ALIGNMENT RECEIVER SYSTEM

Inductive power transfer is a highly efficient technique of wireless power transfer for a limited air gap that operates at strong magnetic field coupling, therefore easy to adopt for low powered wireless charging but enormously challenging for high power wireless charging. However, a slight misalignment affects the power transfer efficiency which reduces drastically. In the following section II (A), electrical analysis has been performed to present the effect of misalignment on wireless power transfer efficiency. A. Analysis of wireless power transfer efficiency due to misalignment in static wireless charging of EV The fundamental principle of wireless power transfer is similar to the transformer, which is without core or air as a core [13]. In this section, a generalized analysis for compensation topology has been performed. The operating frequency   1/√
   is unique for the constant current operation, where
 and  are the primary side inductance and capacitance. This analysis has been performed to demonstrate the factors directly or indirectly related to the efficiency of the wireless power transfer. A generic block diagram of a wireless charging system for EV is shown in Fig. 2. The static wireless charging system consists of power supply, high-frequency converter, coupling coils, high-frequency rectifiers, and load.

AC

AC-DC Converter (Full Bridge Rectifier)

DC-Link

Magnetically Coupled Resonant Coils DC-AC Converter (High Frequency Inverter)

AC-DC Converter (On-board Rectifier) xEV Battery (Li-ion Battery Pack)

Fig. 2. A simple block diagram of a static wireless charging system

4

In this section, simple circuit analysis is performed to understand the relationship between the misalignments and the efficiency of the WPT [21]. Since the coupling coefficient changes by varying the alignment between the transmitter and the receiver. Hence, efficiency is directly related to the coupling coefficient.





M Secondary Compensation

Primary Compensation

Vs



Fig. 4. The compensation topology of a wireless power transfer system

The power transfer from the primary side to the secondary side can be expressed by (1)    ! sin $

Where , ,  , ! %&' $

!

!

(1)

are the operating frequency of the circuit, Mutual inductance of the two coupling coils,

amplitude of primary coil current, amplitude of secondary coil current and phase difference between the primary and secondary current respectively. The power loss in the primary and secondary circuit caused by the primary resistance and secondary resistance ! . The power loss of the over all circuit can be evaluated approximately as (2)  (    + ! !

(2)

The efficiency * of wireless power transfer system can be evaluated approximately as (3) * 1−

 (   + ! !  1−   ! sin $ !

(3)

The general relationship between primary side inductance


inductance  can be presented as (4)   ,- 

and secondary side inductance
! and mutual

(4)

Further, the efficiency can be evaluated as (5)

5

*1−

 ! . . ! ! + 

,.



! . sin $ !

!

 1−

 ! . . ! ! + 

,- ! sin$ ! 

(5)

Where is the quality factor of primary side circuit, ! is the quality factor of the secondary side circuit and

 - !

However, applying Cauchy Inequality to the numerator of the (5) as shown by (6)  ! 0 + 0 ≥2 ! ! 

(6)

To maximize the efficiency, minimum value of the numerator is possible (7) satisfies. Which leads to the current balancing condition.

 ! 0  0 ! ! 

 !


! 0

(7)

Substituting (6) into (5), we can get * ≤ 1 −

2 2- ! ≤1− , sin$ !   sin $ !

(8)

From (8), it has been observed that the efficiency of WPT highly depends on the value of the mutual inductance between the transmitter and receiver coils and the operating frequency of power transfer. (8) also shows that the product of the coupling coefficient and quality factors of both the coils should be much higher than 1. Also, the coupling coefficient directly depends on the alignment between the transmitter and the receiver coils. Hence from the above analysis, the reduction in the misalignment can improve efficiency. However, the above analysis is generalized for any compensation topologies. The results of the above analysis are the motivation to develop a system with the automatic alignment of the transmitter and receiver coil structure.

6

B. Modeling and Simulation of the overall AEV Wireless Charging System In section II(A), the electrical power transfer analysis has been performed. The circuit analysis presented in section II(A), determined the dependency of overall efficiency on the misalignment. In this section, FEA analysis has been performed to analyze the results, where the 3D plots of FEA analysis help in understanding the practical impact of misalignment on the overall wireless charging system. A perfectly aligned system is considered for simplicity and the magnetic flux pattern has been analyzed at various positions and conditions. a) Design Parameter of the FEA simulation system In this section, the intensity of magnetic fields at different positions of transmitting and receiving coils have been analyzed. The modeling and simulation have been performed for WPT between transmitting and receiving coil separated by distance, d. The FEA model of the transmitter and receiver is shown in Fig. 5. The transmitter and receiver coils used in the model are considered with the same shape and size. Table 1 enlists the design parameters of the transmitter and receiver coils considered for modeling and simulation.

Fig. 5. A conceptual Simulation model for WPT

TABLE 1 DESIGN PARAMETERS OF SIMULATION Parameters

Symbol 4

Number of turns in the transmitter coil

4

Number of turns in the receiver coil

5

Conductor diameter

6(

The outer radius of the coil

7

Values 10 10 2mm 75mm

67

Internal radius of the coil

50mm

'

The air gap distance between the coils

100mm



Current in the transmitter coil

8A



Current in the receiver coil

8A

C. Simulation Results of Magnetic Field Plots under Perfect Alignment The coupling coefficient between the two coils is maximum when they are perfectly aligned with each other, along their axis [11]. Based on the design parameters in Table 2, the FEA analysis has been performed. From Fig. 6 to Fig. 12, the plots show the FEA results where Fig. 6 (a) shows the intensity of the magnetic flux density around the transmitter coil, which reveals the reduction in the intensity while moving far from the coil. Fig. 6 (b) shows the magnetic flux density on the receiver plane where flux density is maximum at the center and diminishes moving outward. The plot in Fig. 7 (a) shows the magnitude and direction of field intensity (8) around the transmitter coil and Fig. 7(b) shows the intensity of the magnetic field at the center of the transmitter coil along the vertical direction. Fig. 8 (a) shows the overall coupling system and variation in the magnetic field intensity near the system

TABLE 2 CALCULATED PARAMETER

Parameters

Symbol 

Mutual Inductance




Self-Inductance of the Transmitter coil




Self-Inductance of the Receiver coil

,

Coupling Coefficient

$

Magnetic Flux of Transmitter

$

Magnetic Flux of Receiver

Values 1.025 µH 19.077 µH 19.130 µH 0.054 0.000145 Wb 0.000144 Wb

region. Fig. 8 (b) shows the field strength plot inside the conductor of the transmitter coil.

The flux density plot in Fig. 9 due to the transmitter coil in the space shows the reduction in the value of the magnetic field as the vertical distance increases from the center of the transmitter coil. The reduction in field density can be realized along the central line in Fig. 7 (b) along the z-axis. This reduction in flux density reduces the value of the coupling coefficient between the transmitter and receiver coils resulting in the reduction of WPT efficiency. Fig. 7 (b) shows the net magnetic field in the space emitted due to the interaction of receiver and transmitter 8

magnetic flux density. During wireless power transfer between the transmitter and receiver coils under the perfect alignment position, the flux density plot is shown in Fig. 8 (b). The ferrite material across the power pads restricts the outward magnetic field however the system becomes bulky [22]. Many researchers have optimized the use of the ferrite to make the coupling more efficient and protected [10], [11], [23], [24]. The high magnetic field affects near objects, however, the ferrite material plays an important role to restrict the magnetic field [25]. We have not introduced ferrite in the presented system to demonstrate an interrupted magnetic field pattern across the power pads.

Under perfect alignment condition, the field strength is high at the center of the receiver coil plane and starts decreasing as the receiver moves in an outward direction in the receiver coil plane which infers that the coupling coefficient is maximum at this position of coils. The magnetic field pattern on the bisector plane intersecting transmitter and receiver coils plane has been shown in Fig. 8 (b). As the Y-offset increases (zero in perfect alignment condition), the field strength at the receiver coil’s center decreases. The field plot in Fig.8(a) shows the flux density on the receiver coil plane due to the transmitter coil. Either X-offset or Y-offset of receiver coil with respect to transmitter coil results in a reduced value of flux density at the receiver coil center which reduces the coupling coefficient between the two coils and hence the WPT efficiency. The resulting values of self-inductance, mutual inductance, the coupling coefficient between the two coils and magnetic flux produced by the two coils obtained from the modeling and simulation in Ansys Maxwell® are tabulated in Table 2. Fig. 9 is a diagram depicting an example of the correlation between wireless power transfer efficiency and misalignment of transmitting and receiving coils [19]. According to Fig. 9, the efficiency of the wireless power transfer is maximum at the perfect alignment of power pads and diminished as the misalignment increases. However one more possible concept of misalignment detection of the efficiency which has already been patented by one of our coauthor Rakan Chabaan [19].

9

(a)

(b) Fig. 6. (a) The Flux density at a plane perpendicular to the transmitter coil (b) magnetic field at a plane 10 cm above the transmitter coil

(a)

10

(b)

Fig. 7. Vertical flux density around the transmitter coil and at the central line crossing through the middle of the transmitter.

9.1302e-001 4.0004e-001 1.7540e-001 7.7183e-002 5.3461e-002 1.9124e-002 8.1641e-003 6.3548e-003 4.1235e-003 2.3546e-003 9.1452e-004 7.3214e-004 5.1462e-005 3.1654e-005 2.1563e-005 9.1634e-006 6.1642e-006

(a)

(b) Fig. 8. Magnetic field distribution around the transmitter coil in the air as a medium (b) Magnetic field strength under perfect alignment on Receiver coil plane

11

Efficiency Vs Lateral Offset 100 99

Efficiency (%)

98 97 96 95 94 93 92 91 90 -25

-20

-15

-10

-5

0

5

10

15

20

25

Offset (cm)

Fig. 9 Efficiency vs. lateral offset

D. Concept of Automatic Alignment Receiver System (AARS) The proposed wireless charging system consists of the transmitter coil which is embedded inside the ground, the receiver coil is installed underneath the vehicle. To enhance the efficiency of WPT, the Hall-Effect sensors are incorporated with the receiver coil at a specific pattern as in Fig. 10, to detect the magnetic field intensity at various points of the horizontal plane of the receiver coil accordingly to get optimal alignment between the power pads. The overall system consists of five Hall effect sensors, a control circuit and two motor and rod-axle combinations. Four magnetic field sensors are placed at each corner of a square back-plate (Fig. 10). One sensor is placed at the center of the receiver coil (Fig.10). Since the transmitting coil has the maximum magnetic field at the center, hence, the sensor on the receiver coil placed at the center of the transmitter senses the maximum magnitude whereas the remaining sensors receive lower magnitudes of the magnetic field.

The motion of the receiver can be precisely controlled using two motor combination to perform a 2D motion of the receiver coil. The coil receives a signal from the control circuit to move in the direction of the sensor receiving a maximum magnetic field. Hence, the receiver coil starts moving in the direction of the sensor which has a higher magnetic field. Further, the receiver stops at a point where the magnetic field experienced by any two corresponding sensors become higher as compared to others in magnitude which signifies the position of the receiver coil is at one of the corners with respect to the transmitter coil, the receiver coil starts moving in the opposite direction i.e. towards the

12

y x Fig. 10 Position of sensors (white) on the ferrite plate. Diagrammatic presentation of the receiver and sensor position to evaluate sensor signal. Bottom view

13

Vehicle Body

Sensor 5

Sensor 4

Sensor 3

I1

Sensor 2

x x x x I1

Sensor 1

Sensor 4, 5

Receiver

Voltage Level

Sensor 3

Sensor 1, 2

(a) Sensor 3

Sensor 5

Sensor 4

I1

Sensor 3

x x x x I1

Sensor 2

Sensor 4, 5

Sensor 1

Sensor 1, 2

Voltage Level

Receiver

Vehicle Body

Sensor 5

Sensor 4

Sensor 3

Sensor 2

Sensor 1

Voltage Level

(b)

(c)

Sensor 5

Sensor 4

I1

Sensor 2

x x x x I1

Sensor 3

Sensor 4

Sensor 1

Sensor 1,3,5

Voltage Level

Receiver

Vehicle Body Sensor 2

(d)

Sensor 5

Sensor 4

I1

Sensor 3

x x x x I1

Sensor 2

Sensor 5

Sensor 1

Sensor 2,3,4

Voltage Level

Receiver

Vehicle Body Sensor 1

(e) Fig. 11. Sensor and magnetic field position variation with misalignment(a) Perfect alignment (b) Motion towards sensor 4 and 5 (c) Motion towards sensor 1 and 2 (d) 14 sensor 4 (e) Diagonally towards sensor 5 diagonally towards

sensors receiving lower magnetic fields. Finally, the receiver stops when all the four corner sensors receive the equal magnitude of the magnetic field. The following assumptions have been made: 1.

The angular misalignment between the transmitter and receiver coil is neglected.

2.

Transmitter and receiver coils are identical i.e., of the same shape and size.

3.

The magnetic field generated in the receiver coil has been neglected, due to an insignificant magnetic field from sensor activity.

The motion of the receiver coil can easily be programmed using Table 3, where sensor output has been discretized to digital form. When all the sensors receive output 1 the charging will start as shown in Table 3. However, when any of the four corner sensors receive ‘0’, the receiver starts moving to the opposite direction of the minimum receiving sensor.

START

All four corner sensors Detects same magnetic field At Low current

Yes

No Detection and comparison of all sensors voltage to find the direction of motion.

Starts high current for the power transfer

Receiver coil adjusted to move one step in the direction of maximum magnetic field No Receiver Coil Moves in required direction as Table 1

Battery Fully Charged Yes

Receiver coil stops when the all the four comer sensor senses the same magnetic field

STOP

Fig. 12. Flow chart for implementation of the proposed technique

Fig. 11 shows a 2D demonstration of the overall mechanism and Fig. 11 (a) shows a perfect alignment position, where each corner sensors are receiving the same magnetic field, whereas the central one receives the maximum magnetic field. Fig. 11 (b) shows the misalignment position of the receiver coil, where the transmitter is in front of 15

TABLE 3 LOGIC TABLE FOR DIAGONAL MOTION OF RECEIVER Sensors

Digital output combination from the sensor to start charge

Motion towards sensor 5

Motion towards sensor 4

Motion towards sensor 2

Motion towards sensor 1

Sensor 1

1

0

1

1

1

Sensor 2

1

1

0

1

1

Sensor 3

1

1

1

1

1

Sensor 4

1

1

1

0

1

Sensor 5

1

1

1

1

0

sensor 4, sensor 5, and sensor 1, sensor 2 is receiving a minimum magnetic field. Fig. 11 (c) is the mirror position of the case shown in Fig. 11 (b) where sensor 4 and sensor 5 are receiving the least magnetic field. Fig. 11 (d) presents the diagonal position of the receiver coil, where sensor 2 is receiving the least magnetic field whereas Fig. 11 (e) second diagonal position in which sensor 1 is receiving the least magnetic field. Similarly, the remaining two diagonal positions can be analyzed. The overall mechanism of the proposed method has been explained as follows:

Step 1: Before starting the main charging, a test magnetic field is generated from the transmitter to verify the position of the receiver coil. The receiver coil detects the magnetic field in the vicinity. The receiver sensors detect the magnetic field of the transmitter. The voltage received from the sensors is fed to the comparator. The controller shall calculate the position of the receiver on the basis of voltages received from the sensors. Then the controller would send the signal to move the receiver along the required direction as already discussed in Fig. 11. The charging starts at the condition when all the four corner sensors receive an equal magnetic field and the central one receives the highest as shown in Fig. 11(a). Step 2: The conditions mentioned in Fig. 11 (b, c, d, e) will drive the receiver to the directions shown in Table 3. The motion of the receiver is stepwise controlled. After each step, the controller will test the condition. Step 3: The receiving coil moves in the opposite direction to the maximum experienced magnetic field by the sensor. Simultaneously, data is taken up by the controller to detect whether the receiver coil is moving in the correct direction or not. The receiver coil stops moving/aligning when all four corner placed sensors start experiencing the same magnetic field (Fig.11(a)). Step 4: The direction of motion of the receiver coil has been decided by the controller as shown in Fig. 11 (b) and Fig.11 (c). The diagonal motion condition is shown in Fig. 11 (d) and Fig. 11 (e).

16

The overall systems operating procedure of AARS has been presented as the flow chart is shown in Fig. 12. This mechanism aids in reducing the coil misalignment. Further, a simulation study has been performed to analyze the magnetic field intensity at various positions of the receiver coil. Fig. 13 shows the three-dimensional FEA model, where the arrangement of the transmitter and receiver coil and sensors simulated on Ansys Maxwell® and Figure 14 shows the resultant plot of magnetic field intensity distribution on the receiving plane of receiving coil at the perfect alignment position.

Fig. 13. The placement of sensors on their respective position for the perfect alignment.

In Fig. 13, the origin is taken as the receiver’s center and the transmitter is underneath the receiver showing the negative z-axis. Further, the modeling and simulation have been performed using the same parameters as presented in Table 1 with a reduced current of 1 Ampere. In Fig. 14, the three-dimensional field plot shows the resultant magnetic field intensity over the receiving plane generated from the transmitter. Furthermore, the sensors at each corner are receiving the same magnetic field as it is the case of a zero misalignment. The central sensor is receiving a higher magnetic field as compared to the other sensors. The simulation results prove the effectiveness of the proposed method.

17

Fig. 14. Magnetic field intensity at the four sensor positions and the center of the receiving coil at low current

III.

HARDWARE IMPLEMENTATION OF AUTOMATIC ALIGNMENT OF THE RECEIVER COIL

AARS has been proposed to solve the problem of misalignment between the transmitter and receiver. Since the misalignment reduces the WPT efficiency severely due to enormous flux leakage and poor coupling coefficient which has already been discussed earlier in section III. In this section, the hardware implementation of the proposed AARS has been explained. The advantages of using AARS are autonomous, smart adaptive, improved efficiency and reduces user anxiety which occurs due to manual alignment of home wireless charging. The practical implementation of AARS can be performed on any wireless charging system. Fig. 15 shows the generic block diagram of the proposed system, where the three major blocks of the proposed system are (a) Sensor signal detection block (b) determine the position from sensed signals (c) command to the receiver for motion using fuzzy decision. The block diagram shows a feedback control loop system that senses the magnetic field through the sensor to control the receiver motion. The system has both settings manual as well as automatic alignment, which means the user can manually align or set to the automatic system.

User Input

Automatic Receiver Coil Alignment System Sensor Unit

Position Detection Unit

Fuzzy Receiver coil control

Manual Adjustment Setting

Position Detection

Fig.15. Block diagram for the position detection unit

18

A. Automatic Alignment Receiver System (AARS) sensors unit

According to the (9), at resonance, the voltage drop on the load can be expressed as  

9  : 1 9
 + + : 9 

(14)

Where  is the constant current source at the primary coil, and  is the most dominant parameter for varying the receiver voltage. Since mutual inductance directly depends on the alignment between the transmitter and the receiver coil. Hence, it is very important to detect misalignment. This is a challenging design problem for WPT, which has been addressed and resolved in this section. To detect the misalignment, a system with five Hall Effect sensor is proposed. As discussed in section III (B), the sensor receiving the least magnetic field will generate the smallest voltage and will be far from the center of the transmitter. However, initially, a low magnetic field would be generated through the transmitter for the perfect alignment of the power pads. The Hall Effect sensors may not disrupt the magnetic coupling while charging EV. Further, the Hall Effect sensor detects the variation in the magnetic field and the variation in the sensor reading has been used as detection of the position of the receiver coil.

Receiver Coil

Sensor Signals

Digital Voltmete r

Voltage Comparator

Logic Decision

Position Estimator (y)

Position Estimator (x)

Receiving coil control

Receiving coil control

Fig. 16. Block diagram of AARS

Fig. 16 is showing the block diagram of the sensor detector for position control. The control is along the x-axis and y-axis. A voltage comparator is used to find the least voltage level of the sensors and converted it to a digital signal.

A logic decision block consists of an XOR gate that is implemented to decide the axis motion and the motion of the 19

receiver stepwise. The logic used in controlling the motion of the receiver coil has already been presented in Table 3. The complete schematic circuit diagram of the proposed system at 20 kHz is explained in Fig. 17, where the system consists of a sensor unit where all the five sensors are installed at their respective positions. To eliminate the noise generated during the wireless coupling a non-inverting lowpass filter block is designed to adjust between the sensor assembly and voltage comparator unit. The voltage comparator sends the sensor's digital signal to the microcontroller unit for decision making and driving the receiving coil. For experimental verification, the values of the parameters are shown in Table 4.

Fig. 17. Complete schematic circuit for the practical implementation

TABLE 4 THE EXPERIMENTAL COMPONENT PARAMETERS OF THE POWER TRANSFER SYSTEM ALONG WITH THE PROPOSED ALIGNMENT SYSTEM.

Component

Symbol




107.55 &>



238.33 ;>



 ?((:@7AB

Smoothing Capacitor



C  C

Load Resistance Low Pass filter 20

165 <Ω




Coupling resonance @20 kHz

Value 595 ;8 185 ;8 10 Ω

3200 ;> 10 Ω 919 Ω 9.8 nF

TABLE 5 EFFECT OF VARIATION OF ALIGNMENT AND CHANGE IN THE COUPLING COEFFICIENT AND MUTUAL INDUCTANCE

Variation of receiver coil position

Misalignment (mm) '  −15

Along x variation

Along y variation

Diagonal variation

'  −10

'  −5

'0

'5

'  10

'  15

Coupling coefficient

0.038

0.041

0.043

0.093

0.043

0.041

0.039

Mutual Inductance (&8)

101.23

108.031

112.00

113.50

112.24

109.75

103.15

Coupling coefficient

0.030

0.043

0.054

0.095

0.056

0.044

0.032

Mutual Inductance (&8)

70.47

119.68

151.35

188.70

158.21

124.86

89.04

Coupling coefficient

0.034

0.043

0.065

0.095

0.083

0.056

0.038

Mutual Inductance (&8)

131.65

168.47

203.69

245.98

213.65

197.37

146.78

0.150

Along x direction Along y direction Diagonally

Coupling Coefficient

0.125

0.100

0.075

0.050

0.025

0.000 -20

-15

-10

-5

0

5

10

15

20

Misalignmnet (mm)

Fig. 18 Variation of coupling coefficient with respect to the change in the alignment.

IV.

RESULTS AND DISCUSSION

For a WPT system, the value of the coupling coefficient between the coils and their mutual inductances are the two main factors that largely affect its power transfer efficiency. However, the value of the coupling coefficient, k, and mutual inductance, M depend upon the positioning of two coils. Hence, the misalignment between the coils reduces the value of k and M. Table 5 shows the results of changing the coil position and variation in mutual inductance and coupling coefficient. In static WPT systems for EVs, lateral misalignment is a major issue that can be fixed by the perfect alignment of the transmitter and receiver coils and thereby, increasing wireless power transfer efficiency to its peak. An auto-alignment WPT system for EVs in which the receiver coil moves automatically in response to the 21

magnetic field due to transmitter coil sensed by the sensors placed on the receiver to align perfectly with the transmitter would prove to have optimum performance. However, some other factors such as parameters of compensation topology, quality factor and resonant frequency, which can affect the power transfer efficiency for wireless systems [10].

The proposed system is feasible for residential charging, charging stations as well as dynamic wireless charging with some modification in the control circuit. The reliability of the Hall Effect sensors is the primary factor to decide the practicality of the system. Further, the operation of the receiver’s motion can be compared with the motion of extruders in 3D printers. In this case, a similar framework for the motion of the receiver can be designed, however, the controller will drive the receiver coil according to the input from Hall Effect sensors. Fig. 18 shows a graphical presentation of the simulation results and Table 4 shows the values of the parameters for the wireless power transfer at 20 kHz. The deployment of the proposed system modifies only the receiver side of the WPT system. However, the transmitter would have been installed inside the ground. Fig. 19 shows the typical wireless charging infrastructure layout for potential deployment in a parking lot at the Center of Advanced Research in Electrified Transportation (CARET), Aligarh Muslim University, Aligarh, INDIA.

Fig. 19 A typical wireless charging infrastructure

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V.

DEPLOYMENT AND THE HARDWARE DEVELOPMENT OF THE PROPOSED SYSTEM

The presented chapter provides the technique which automates the alignment between the transmitter and receiver for the wireless charging application, thereby improving the wireless power transfer efficiency. The Hall Effect sensors were used to measure the magnetic field intensity. However, the motion of the receiver coil can be controlled by a linear actuator mechanism, as, discussed in the patent [19]. The five signals received from the five sensors installed underneath the receiver will be used to evaluate the direction of the receiver’s motion. Further motion of the receiver coil can be designed using the principle of operation of 3D printer’s extruder.

VI.

CONCLUSION

In this manuscript, an AARS for the static wireless charging of AEVs has been proposed to improve the efficiency of the power transfer. AARS is a very simple and smart technique to align the power pads mechanically using a twodimensional control technique. The power delivery has been analyzed and verified through the FEA simulation on Ansys Maxwell. Simulation results confirm that the magnetic field is maximum at the vertical positions of the transmitter coil which reduces while moving far from the transmitter. The perfect alignment between the charging pads produces the maximum efficiency due to maximum flux linkage. AARS utilized the Hall Effect sensors to sense the magnetic field intensity and determines the direction of motion. The overall implementation methodology has been discussed in detail. The variation in the mutual inductance due to misalignment has been verified through FEA and resulted in the maximum mutual inductance at the zero-misalignment position.

VII. FUTURE WORK The proposed Automatic Alignment Receiver System has been introduced solely to improve the efficiency of the power transfer. In the future, we intend to include the PCB based control system to make the system economical and feasible. The number of Hall Effect sensors can be reduced by some optimization techniques. The other aspect of the proposed technique is to move the transmitter instead of the receiver. To make the system more efficient and reliable, we would restrict the motion of the receiver. Some other methods could be introduced such as a multi-coil system, which can be logically aligned to the most coupled coil. In the future, many challenges need to be addressed to increase the efficiency of the wireless charging system.

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VIII. ACKNOWLEDGEMENT The authors would like to acknowledge financial support provided by Department of Heavy Industries, Government of India and IMPRINT-II IMP/2018/001267.

IX. [1]

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Highlights

1. Power pad misalignment is a foremost challenge for EV Wireless Charging 2. Proposed a solution to improve efficiency by reducing misalignment. 3. Automatic misalignment reduction through Hall Effect sensor-based detection. 4. Verification through Finite Element Analysis. 5.

Described hardware prototype development.