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Frontiers in Energy

Front. Energy    2020, Vol. 14 Issue (1) : 152-165
Analysis of resonant coupling coil configurations of EV wireless charging system: a simulation study
Electrical and Computer Engineering Department, Nazarbayev University, Astana 010000, Kazakhstan
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Nowadays, internal combustion engine vehicles are considered as one of the major contributors to air pollution. To make transportation more environmentally friendly, plug-in electric vehicles (PEVs) have been proposed. However, with an increase in the number of PEVs, the drawbacks associated with the cost and size, as well as charging cables of batteries have arisen. To address these challenges, a novel technology named wireless charging system has been recently recommended. This technology rapidly evolves and becomes very attractive for charging operations of electric vehicles. Currently, wireless charging systems offer highly efficient power transfer over the distances ranging from several millimeters to several hundred millimeters. This paper is focused on analyzing electromagnetically coupled resonant wireless technique used for the charging of EVs. The resonant wireless charging system for EVs is modeled, simulated, and then examined by changing different key parameters to evaluate how transfer distance, load, and coil’s geometry, precisely number of coin’s turns, coin’s shape, and inter-turn distance, influence the efficiency of the charging process. The simulation results are analyzed and critical dimensions are discussed. It is revealed that a proper choice of the dimensions, inter-turn distance, and transfer distance between the coils can result in a significant improvement in charging efficiency. Furthermore, the influence of the transfer distance, frequency, load, as well as the number of the turns of the coil on the performance of wireless charging system is the main focus of this paper.

Keywords electromagnetically coupled resonator      near-field power transfer      wireless power transfer (WPT)     
Corresponding Authors: M. BAGHERI   
Online First Date: 04 March 2019    Issue Date: 16 March 2020
 Cite this article:   
M. LU,A. JUNUSSOV,M. BAGHERI. Analysis of resonant coupling coil configurations of EV wireless charging system: a simulation study[J]. Front. Energy, 2020, 14(1): 152-165.
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Fig.1  Layout of a typical wireless charging system
Advantages Disadvantages
Cables, towers, substations are removed Cost of charging infrastructure is high
Energy can be transmitted to places, where wired transmission is impossible Radiation received is potentially dangerous for humans’ health
Peak efficiency is high Efficiency decays as the transfer distance increases
Tab.1  Advantages and disadvantages of WPT [1316]
Fig.2  Layout of a typical wireless EV charging system
Fig.3  Two-coil WPT system 9
Microwave power transfer Capacitive power transfer Resonant IPT
Distance Long Short Short
Frequency 1–30 MHz 1 kHz–20 MHz 20–200 kHz
Power level Low/Medium Low High
Cost Medium Low Medium
Efficiency Medium Low Medium
Tab.2  A comparative summary of WPT systems [23]
Fig.4  Model of a two-coil wireless charging system
Fig.5  ANSYS model for two coils situated at a variable distance from each other
Fig.6  Proposed WPT system
Fig.7  Schematic of H-bridge inverter
0 cm 10 cm 20 cm 30 cm
L1/mH 112.34 118.69 119.33 119.45
L2/mH 112.27 118.76 119.21 119.33
M/mH 111.77 47.99 25.472 14.863
k 0.995 0.404 0.214 0.124
Tab.3  Simulation results for the change in distance
5 7 9 11 13 15
L1/mH 22.11 41.62 67.44 99.88 139.4 186.5
L2/mH 31.09 41.63 67.43 99.91 139.4 186.6
M/mH 6.025 13.05 23.59 38.16 57.33 81.60
k 0.273 0.31 0.349 0.382 0.411 0.437
Tab.4  Simulation results for the change in number of turns
3 mm 5 mm 7 mm 9 mm 10 mm
L1/mH 118.89 118.3 118.2 118.4 118.7
L2/mH 118.86 118.3 118.2 118.5 118.7
M/mH 37.618 40.46 43.18 45.84 47.14
k 0.316 0.342 0.365 0.386 0.396
Tab.5  Simulation results for the change in spacing between turns
0 cm 10 cm 20 cm 30 cm
L1/mH 108.96 119.27 119.51 119.90
L2/mH 113.78 118.86 119.21 119.33
M/mH 98.325 45.955 25.372 15.16
k 0.883 0.386 0.212 0.127
Tab.6  D-shaped receiver simulation results
Fig.8  Effect of distance change on the efficiency of WPT (circular receiver)
Fig.9  Changing number of the turns of the coil versus the efficiency of WPT
Fig.10  Inter-turn distance variation versus the efficiency of WPT
Spacing/mm Transmitter radius/mm Receiver radius/mm Area/mm2 Coupling coefficient
7 385.8 385.8 308556.67 0.859
10 421.8 421.8 399894.08 0.8797
Percentage change/% 9.33 9.33 29.6 2.41
Tab.7  Comparison of coupling coefficient change due to increase of space between turns
Transmitting coil type Receiving coil type Par. 0 cm 10 cm 20 cm 30 cm
Circular coil Circular coil M/mH 111.7 47.99 25.472 16.863
k 0.995 0.404 0.214 0.128
Circular coil D-shaped coil M/mH 98.32 45.955 25.372 15.16
k 0.883 0.386 0.212 0.127
Tab.8  Comparison between circular and D-shaped coils
Spacing/mm Inner radius/mm Outer radius/mm Area/mm2 Efficiency/%
7 225 385.8 308556.67 76.4
10 225 421.8 399894.08 77.5
Percentage of change/% 29.6 1.4
Tab.9  Comparison of efficiency change due to increase of space between turns
Fig.11  Relation between load and efficiency
RL Distance/cm Turns Spacing between turns/mm
25 15 14 10
Tab.10  Realistic practical parameters for the WPT system retrieved from the parametric studies
I*1, I*2 Current in the transmitting and receiving coils, respectively
I1, I2 Root-mean square value of currents flowing through the coils
U12, U21 Voltage induced by the transmitting coil into the receiving one and vice versa
S12, S21 Apparent power values transferred from the transmitting circuit to the receiving one and vice versa
j12 Phase difference between I1and I2
M Mutual inductance between the coils
w Angular frequency
P12 Active power transfer between two coils (from 1 to 2)
S Total complex power
Q1, Q2 Quality factors of transmitting and receiving coils, respectively
L1, L2 Self-inductances of primary and secondary coils, respectively
R1, R2 Resistances of primary and secondary coils, respectively
k Coupling coefficient between L1and L2
VS Voltage source
RS Internal resistance of a voltage source
C1, C2 Resonant capacitors
RL Active load
η Power transfer efficiency
D Distance between two coils
r1, r2 Transmitting and receiving coils’ radii, respectively
S1, S2, S3, S4 Switches of the H-bridge inverter
R11, L11, C11 Compensation resistance, self-inductance and capacitance, respectively
A Surface area of the circular coil
Rout, Rin Outer and inner radii of the coils, respectively
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