Optimal Bivariate Control Strategy of Multistage Constant Current Charging for IPT-Based Wireless Electric Vehicle Charging

Wireless inductive power transfer (IPT) charging has the potential to improve the user experience of electric vehicle (EV) charging by eliminating the cost and effort of physical connections. Unlike the conventional constant-current and constant-voltage (CC-CV) charging profile of the Li-ion battery, our focus is on the multistage constant current (MSCC) charging profile, which consists of different constant current (CC) output stages, as a means of improving charging rates and prolonging the lifetime of EV batteries. To provide a load-independent current output, the inductor-capacitor–capacitor-series (LCC-S)-compensated IPT converter exhibits a CC output with a constant operating frequency. Yet its overall transfer efficiency can deteriorate noticeably due to the wide equivalent load variation during the battery charging process. To address this issue, we propose an optimal bivariate control strategy for the LCC-S-compensated IPT converter. This strategy uses a variable inductance at the primary side to achieve different CC output stages, while a voltage-controlled semi-active rectifier (VCSAR) at the secondary side ensures efficiency optimization. Furthermore, zero-voltage switching (ZVS) can be achieved at both the inverter and the VCSAR. Finally, we build a downscaled 1.1 kW experimental platform to validate the effectiveness of the bivariate control strategy and MSCC charging for the LCC-S-compensated IPT converter.