90°-Phase-Shift-Based Soft Switching Analysis in Strong-Coupling Bidirectional Wireless Power Transfer Systems

Increasing the coupling coefficient can enhance the power density of a wireless power transfer (WPT) system, but it also leads to the current waveform distortion, resulting in hard switching in the inverter. Based on prior research, this paper analyzes the soft-switching conditions of the strong-coupling se-ries-series bidirectional WPT (SC-SS-BWPT) system with the full power range under dual asymmetric modulation by adjusting the rectifier duty cycle to vary the system output power. Through time-domain analysis, the variation of system power with respect to the rectifier duty cycle under a 90° phase shift is examined. It is revealed that, during bidirectional power transfer under a 90° phase shift, the inverter can achieve soft switching regardless of changes in the rectifier duty cycle, and the conditions for achieving soft switching on the rectifier side are derived. The simulation shows that from 150 W to 3 kW under a 90° dual-phase shift, as the secondary rectifier duty cycle varies from 10 % to 90 %, the pri-mary-side current remains constant at $\pm 1.34 ~\mathrm{A}$ during voltage transitions, satisfying ZVS conditions, while the secondary side achieves ZVS over a wide operating range.