A Control Strategy for Wireless EV Charging System to Improve Weak Coupling Output Based on Variable Inductor and Capacitor

The double-sided inductor capacitor capacitor topology has been proposed in some national standards for wireless charging systems. However, misalignment between the transmitting and receiving coils usually leads to detuning and weak coupling, resulting in low output power and inefficiency. To improve power output under weak coupling, this article proposes a control method based on the variable inductor and capacitor (VLC). First, it is deduced that the zero phase angle input and full output power can be achieved by VLC regulation under certain misalignment. Second, the variable inductor using an EE-shaped core and pulsewidth modulation controlled capacitor are applied to achieve VLC regulation, and the principles and implementation of VLC are analyzed. Third, as the coupling coefficient k can be identified through the primary electrical parameters, a convenient and accurate coupling coefficient identification method is utilized to help VLC regulation. Finally, a prototype with a 3.3 kW output power and an 87.5% maximum system efficiency (dc-dc) is built to validate the proposed method. The experimental results are consistent with the theoretical analysis, proving that the output power is almost constant when k varies from 0.08 to 0.18.