Wireless EV Charging System Using PWM-Controlled Variable Capacitor for Maximum Power Transfer under Severe Coil Misalignment

Transmitter (Tx) and receiver (Rx) coils of wireless electric vehicle charging systems are usually equipped with magnetic and conductive materials, which make the self-inductance of Tx and Rx coils sensitive to misalignment. When the coils are severely misaligned and the amplitude of the coil currents is regulated, the variation of the self-inductance reduces the power transferred to the vehicle. The system proposed in this paper adopts a PWM-controlled variable capacitor on the Rx circuit to compensate for the coil inductance variation and maximize the transferred power. The control scheme can autonomously adjust the variable capacitor without wireless communication between the road side and the vehicle side. A prototype of the proposed system is manufactured, and the control scheme is verified through experiments. The experimental results show that the proposed control scheme can compensate for the self-inductance variation and increase the transferred power.