Microsoft Word - ETASR_V12_N4_pp9042-9047 Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9042 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … Transmitting Side Power Control for Dynamic Wireless Charging System of Electric Vehicles Nguyen Kien Trung School of Electrical and Electronic Engineering Hanoi University of Science and Technology Hanoi, Vietnam trung.nguyenkien1@hust.edu.vn Nguyen Thi Diep Faculty of Control and Automation Electric Power University Hanoi, Vietnam diepnt@epu.edu.vn Received: 17 April 2022 | Revised: 25 June 2022 | Accepted: 29 June 2022 Abstract-This paper proposes a new power control method in dynamic wireless charging systems for electric vehicles. A dual- loop controller is proposed to control charging power while the electric vehicle is moving without communication between the transmitting and receiving sides. The output power is estimated through the coupling coefficient estimation. However, the coupling coefficient varies with the position of the vehicle. Therefore, this paper also presents an easy-to-do practical estimation method from the transmitting side, in which the coupling coefficient value is continuously updated according to the vehicle's position. As a result, the output power is controlled according to the required level with an error of less than 5%. Keywords-electric vehicle; dynamic wireless charging; coupling coefficient estimation; LCC compensation; power control I. INTRODUCTION The use of Electric Vehicles (EVs) to reduce air pollution is globally rising. Much research on EVs is performed to make their use more convenient and safer [1-3]. One of the issues of interest to researchers is wireless charging technology for EVs [4, 5]. Wireless charging eliminates all charging cables, making charging safer and more flexible. Currently, Dynamic Wireless Charging (DWC) systems are preferred because EVs can be used on the road while charging [6, 7]. Therefore, the EVs can travel longer distances, the size and weight of the battery can be smaller, and the transportation efficiency is improved [8, 9]. In the DWC systems, output power pulses occur because coupling coefficients vary as the EVs move along the transmission lane. Moreover, output power sharply drops when the EV moves with lateral misalignment [10, 11]. This problem affects battery life. Many studies have been done to reduce the pulse of the output power by coil design [12, 13]. This solution may not be consistent for real EVs that have different sizes of receiver coil. In addition, these researches have not addressed the problem of EVs moving in lateral misalignment. Also, in a DWC system, many EVs of different types move and interact with the transmission lane and each EV type requires different levels of charging power [14]. Therefore, advanced control methods need to be applied in DWC systems to control the output power. Some studies perform power control for EVs in a wireless charging system [15]. In these studies, the output power is controlled using DC/DC converters on the receiving side. This solution increases the converters' number as well as increases the loss in the system. This paper proposes a new power control method on the transmitting side without additional DC/DC converters. However, to be able to perform control only at the transmitting side, it is necessary to know the output power on the receiving side. The output power can be known by using the wireless communication network [16]. This solution is not suitable for the DWC system where the EVs are always moving in a hard environment. In [17], the transmitting-side inverter is also used to control the output power in DWC systems. This study uses auxiliary coils to detect the position of the EV and determines lateral misalignment to control the output power. This system takes up a lot of space and is expensive. In [18], parameters are estimated based on high-frequency voltage, current, and phase angle measurements. However, the method of measuring these parameters at high frequency is a challenge in practice. In [19], a quadrature transformation algorithm is used to estimate power. This method requires a complex measuring circuit and signal conversion. To solve the above difficulties, the current paper proposes an easy-to-do practical power estimation method based on measuring the resonant current RMS value on transmitter coils and inverter input DC power. This new power control method provides stable output power to any EV position and provides multi-level output power for different EV types in the DWC system. II. THE POWER CONTROL PROBLEM A. Structure of the Proposed System The structure of the designed system is shown in Figure 1. On the transmitting side, transmitters are designed modular. Each module includes a full-bridge inverter that provides power to three transmitting coils through LCC compensation circuits. At the receiving side, the induced AC voltage on the receiving coil is also fed through the LCC compensation circuit to the impedance matching circuit, the battery management converter, and the battery. The transmitting coils are placed under the roadway to form a DWC lane for the EVs. In Figure 1, at the transmitting side: S1 ~ S4 is the SiC MOSFET; DC AB U ,U are input and output voltages of the inverter Corresponding author: Nguyen Thi Diep Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9043 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … respectively, fi fr fi fr i r L , L ,C ,C ,C ,C are the inductances, lower branch capacitors, and upper branch capacitors of double LCC compensation circuit respectively, i Li I , I are the input current to LCC compensation circuits and the resonant current on the transmitting coils (i=1,2,3) respectively, Lr r ab I ,I ,u are the resonant current on the receiving coil, the output current/voltage of the compensation circuit, and i r L ,L are the coil inductances. The issue of switching between modules has not been considered in this paper. Proposed transmitting side controller D W C la n e Lf1 Cf1 C1 L1 i1 iL1 Lf2 Cf2 C2 L2 i2 iL2 Lf3 Cf3 C3 L3 i3 iL3 UDC A B S1 S3 S4 S2 uAB I DC iAB Lr Cr Cfr Lfri Lr ir Ub IbRL Impedance matching circuit A DWC module ZLi Cin a b u ab Battery management converter Fig. 1. The structure of the proposed DWC system. B. Characteristics of the Coupling Coefficient According to the EV’s Position Figure 2 shows the FEA simulation model of a design system's magnetic coupler. The design of the transmitter and receiver is described in [20]. It is assumed that during dynamic charging, the transfer distance is always 150mm. Receiver's positions in the x and y directions are defined as dx and dy respectively. When the receiver is centered with the first transmitter (T1), dx is zero and dy is zero. Figure 3 shows the FEA simulation result of the total coupling coefficient. This result is obtained in case dx increases from 0 to 800mm and dy increases from 0 to ±60mm, where the total coupling coefficient of the receiver with the transmitters is performed as follows: 3 1 r ir i k k = =  (1) where ir k is the coupling coefficient of the ith transmitting coil (Ti) with the receiving coil (R). The results show that the coupling coefficient ir k is the greatest when the receiving coil is centered with the transmitting coils. The FEA simulation result in Figure 3 (solid lines) shows that when dy is 0mm (case 1-red line), the average value of the total coupling coefficient is 0.143. When dy is 40mm (case 2- blue line), the average value of the total coupling coefficient is 0.111. In case 3 (black line), the dy is 60mm and the average value of the total coupling coefficient is 0.078. These show that during dynamic charging, the total coupling coefficient is varied and is significantly reduced when lateral misalignment increases. Fig. 2. The FEA model of the proposed magnetic coupler. Fig. 3. FEA simulation/estimation coupling coefficients result. C. Analysis of Power Control Capability The fundamental harmonic approximation method was used to give an equivalent circuit as shown in Figure 4. AB U is Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9044 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … approximated as a sinusoidal source. For simplicity in circuit analysis, the losses on the compensation circuit and inverter are ignored. i r R ,R are the resistances of the transmitting and receiving coils respectively, L R is the equivalent load impedance seen from the impedance matching circuit input to the load, 1 2 3 i L L L L= = = are the transmitting coils which are designed the same, i M is the total mutual inductance of transmitting coil (Li) with other transmitting coils ( 3 1 i ij j , j i M M = ≠ =  ), and irM is the mutual inductance of the transmitting coil (Li) with the receiving coil (R). UAB IAB jωM1rILr jωM1ILi 0 Lf1 Cf1 C1 R1 L1 0 jωM2rILr jωM3rILr jωM2ILi jωM3ILi Lf2 Cf2 C2 R2 L2 Lf3 Cf3 C3 0 R3 L3 jωM1rIL1 jωM2rIL2 jωM3rIL3 Lr Rr Cr Lfr Cfr RL IL1 IL2 IL3 I1 I2 I3 ILr Ir Zp1 Zp2 Zp3 ZM3 ZM2 ZM1 Zs ZL1 ZL3 ZL3 Fig. 4. Equivalent resonant circuit. Fig. 5. The PWM signals for S1, S2, S3, S4, and voltage waveform. The relationship of compensation circuit parameters is shown in (2) [20]: 2 2 2 2 1 1 1 1 fi fi i i fi i fr fr r r fr C L C ( L L M ) C L C L L ω ω ω ω  =   = − +   =    =   −  (2) ω = 2πfsw The resonant current in transmitting coils is the same and is expressed as [20]: 1 2 3L L L Li fi AB I I I I j C U= = = = − ω (3) Analyzing the circuit of Figure 4 and combining it with (2)- (3) the output power can be expressed as: 2 2 2 2 L i r out r Li r L fr fr R L L P k I R R L L =   +    ω (4) In designed DWC systems, the resonant frequency is usually kept constant, and the designed parameters of coils and compensation circuits are constant. It is assumed that at the receiving side the equivalent load impedance value is maintained constant and equal to the optimal load value for maximum transfer efficiency. Equation (4) shows that if the coupling coefficient ( r k ) is estimated, then the output power could be controlled by regulating the resonant current of transmitting coils ( Li I ). Further, (3) shows that this resonant current can be controlled by controlling the inverter output voltage value ( AB U ). The output voltage of the inverters is adjusted by the phase-shift method. The signals for S1~S4 and the inverter output voltage waveform are shown in Figure 5. The RMS of the inverter’s output voltage can be expressed as [21]: 2 2 2 AB DC U U cos α π = (5) From (3), (4), and (5) it is shown that the output power can be adjusted by adjusting the phase-shift angle α. D. Estimated Output Power Given the circuit of Figure 4 at resonant point, the derivatives of the equations are shown below. The equivalent reflected impedance of transmitting coils to each other is: i Li Mi i Li j M I Z j M I = = ω ω ; with i = 1,2,3 (6) The receiving side impedance ( s Z ) can be represented by the ratio between the coupled voltage r Li j M Iω and the receiver resonant current Lr I as follows: 1 1 2 2 3 3 3 2 2 1 r L r L r L s Lr ir Li fri r Li r Lr Lr L j M I j M I j M I Z I j M I Lj M I R I I R = + + =       = = = +  ω ω ω ω ωω (7) The equivalent reflected impedance of the receiving coil to each transmitting coil can be expressed as: 2 ir Lr ir r pi Li s j M I M M Z I Z ω ω = = (8) Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9045 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … The equivalent impedance of each transmitting coil is calculated as: Li i pi i i Z R Z j L j Mω ω= + + + (9) At the resonance condition, the reflected impedance pi Z can be calculated as: { } 2 Li pi Li i i Li .RMS P Z Re Z R R I = − = − (10) Approximately, ignoring the power loss on the inverter, the total impedance reflected from the secondary to the transmitting side is shown in (11): 3 3 1 2 2 1 3 3 Li i DC pi i i i Li .RMS Li .RMS P P Z R R I I = = = − = −   (11) where DC P is the input power of the inverter. From (8) and (11), the coupling coefficient is given by: 2 2 2 1 3 fr DCr r i i r L Li .RMS L PR k R L L R Iω     = + −         (12) When the DWC system is designed, the system parameters, such as coils, compensator, and resonant angular frequency are assumed to be constant. When DC P and Li .RMS P are measured by sensors, the equivalent load impedance ( L R ) is maintained constant and r k is estimated according to (12). Therefore, the output power is estimated according to (4). E. The Proposed Power Controller The block diagram of the proposed power controller is shown in Figure 6. Pout.ref - - ILi kr.est Pout.est I*Li α Estimate output power (4) Power Controller Current Controller Estimate coupling coefficient (12) PDC ILi IDC UDC Voltage/ current measurement Giα(s) Fig. 6. Power control block diagram. The inner loop is the current loop which is important for the estimated results to have high accuracy. The outer loop is a power control loop according to the load. At the transmitting side, the RMS value of resonant current ( Li I ) and the value of the inverter input voltage/current ( DC DC U / I ) are measured. Then, (12) is used to estimate the coupling coefficient, and (4) is used to estimate the output power. The reference output power ( out .ref P ) is compared with the estimated output power ( out .est P ), then the error is taken to the power controller to determine the referent current value ( Li I * ). The error between the referent and the measured current is passed to the current controller. The current controller determines the phase shift angle to control the inverter. III. SIMULATION AND EXPERIMENTAL RESULTS A simulation model was built on PSIM simulation software to verify the proposed method. The system parameters are shown in Table I. TABLE I. PARAMETERS OF THE DWC SYSTEM Parameter Values Parameter Values out P 1.5kW fiL 52.6μH DC U 310V fiC 66.5nF ab U 400V 1 C 93.7nF r k 0.14 2 C 123.2nF sw f 85kHz 3 C 95nF i L 102μH frL 28.9μH i R 0.13Ω frC 120.9nF r L 120μH r C 38.5nF r R 0.115Ω Fig. 7. Simulation characteristic of the output power according to the reference power. Fig. 8. The experimental DWC system setup. Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9046 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … The total coupling coefficient estimation results are shown in Figure 3(b) (dot lines). In case 1, dy is 0mm and the average value of the estimated total coupling coefficient (Kr.est) is equal to 0.138. In case 2, dy is 40mm and Kr.est is equal to 0.108. In case 3, dy is 60mm and Kr.est is equal to 0.074. The estimation error is less than 5.3%. Figure 7 shows the simulation result of power control when the reference power changes from 0.8kW to 1.2kW. It shows that the value of the estimated power ( out .est P ) and the load power ( out .load P ) grip to the reference value ( out .ref P ) with a response time of 1.1ms and an error of 0.5%. Figure 8 shows the experimental model of the proposed DWC system. PE40 ferrite bars were used to increase magnetic conductivity. Polypropylene film capacitors were used for their small loss and high ability to withstand high currents at high frequencies. MOSFETs SiC (C3M0280090D) was used for the inverter. Stranded wire was used in building the coils. The impedance matching circuit and battery were replaced by an equivalent load. The experimental waveforms when the receiver position dx and dy are zero and 310 DC U V= are presented in Figure 9. The results show that the resonant frequency is 85kHz and the ZVS condition for SiC is achieved in both cases of phase shift angle (α) equal to 0 and 60 0 . Figure 9(a) shows the resonant current 10 6 Li I . A= , output power equal to 1.32kW, and the system efficiency reaching 89.6% in the case of α =0 0 . Figure 9(b) shows that when α=60 0 , 9 2 Li I . A= , the output power is equal to 1.2kW and the system efficiency reaches 89.2%. Fig. 9. Experimental waveforms: inverter output voltage/current and resonant currents. The following tests were performed to demonstrate the operation of the dual-loop controller in two cases. The DC voltage ( DC U ) was set to 250V and the equivalent load L R to 53.3Ω. In case 1, when the position of the receiver is dx = 0mm to 800mm and dy = 0mm, the required output power changes from 600W to 400W. The experimental results of the reference/ estimation/measured output power, phase shift angle α, the inverter output voltage waveform ( AB u - red color), and resonant current ( Li I - blue color) are presented in Figure 10. The results show that the angle α increased from 41.6 to 51.4 0 , Li.RMS I decreased from 6.34A to 5.21A, and the output power responds to the preset value. In case 2, when the position of the receiver is a lateral misalignment in the y-direction from 0mm to 40mm, the reference output power is 400W. The experimental results are presented in Figure 11. In this case, the coupling coefficient reduces, the phase shift angle α decreased from 52.6 to 36.7 0 , the r.m.s value of Li I increased from 5.18A to 6.9A, and the output power was constant. Fig. 10. Experimental results when the reference output power changes from 600W to 400W. Fig. 11. Experimental results when the reference output power is 400W. These results show that the proposed control method could control the output power with a response time of 0.01s and an error less than 5%. The output power estimation method could continuously estimate the output power. The proposed system responds well when the vehicle speed is below 40km/h. Figure 12 shows the system's efficiency experimental result when the Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 9042-9047 9047 www.etasr.com Diep & Trung: Transmitting Side Power Control for Dynamic Wireless Charging System of Electric … receiver moves along the transmission lane without any lateral misalignment. The average system efficiency is 80.7%. Fig. 12. Experimental efficiency characteristics. IV. CONCLUSION This paper proposes a new method of controlling the output power in the DWC system for EVs. The transmitting side inverter has been used to control power without using an additional boost/buck inverter. 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