Accurate Soft-Switching Technique for Wireless Power Transfer System Based on State-Trajectory Analysis

Phase-shift modulation scheme, such as single-phase shift (SPS), is widely applied in wireless power transfer (WPT) system to regulate its output power and voltage transfer ratio. The ignored harmonic contents, however, inevitably affect the system soft-switching characteristics. This manuscript investigates the accurate zero voltage switching (ZVS) boundary for a SS (series-series) compensated inductive power transfer (IPT) system based on a state-plane trajectory. With the proposed state trajectory analysis, the IPT system is mapped into two decoupled and reduced sets of mathematical models and equivalent circuits. It allows to predict the ZVS state of any power devices and for any operating conditions with higher accuracy than the conventional fundamental harmonics analysis (FHA) based approach. The analysis is verified by a 200W extensive experimental prototype with the measured ZVS condition and state-plane trajectory. And the system peak efficiency is up to 94.2% at a transmission distance of 10cm.