An Approach for Selecting Compensation Capacitances in Resonance-Based EV Wireless Power Transfer Systems With Switched Capacitors

Wireless chargers for electric vehicles (EVs) can achieve high power-transfer efficiency by utilizing magnetic resonance. However, the efficiency depends on the position of the receiver coil on board the EV relative to the charging pad, which may present a challenge in some coil topologies. In multi-coil topologies, the additional auxiliary coils increase the magnetic coupling between the primary transmitter and receiver coil, helping to improve the misalignment tolerance of a wireless power transfer (WPT) system. In this paper, an approach is presented for selecting compensation capacitances in resonance based multi-coil WPT systems that utilize switched capacitor compensation. The approach for selecting the compensation capacitors is based on maintaining operation within the split resonant frequency region while misaligned. In this paper, the compensation capacitor design approach is applied to a four-coil WPT system with overlapping auxiliary coils with switched capacitors on each auxiliary coil. Experimental results are presented which show that with the selected compensation capacitances the power factor is maintained above 0.9 from 0- to 20-cm misalignment compared to a power factor that decreases to 0.34 at 20 cm when the compensation capacitors are not retuned based on misalignment.