Automatic Resonance Tuning With ON/OFF Soft Switching for Push-Pull Parallel-Resonant Inverter in Wireless Power Transfer

This letter proposes the tunable resonant tank and its control method for push-pull parallel-resonant inverter in wireless power transfer application. The parallel tuning capacitor is controlled using pulsewidth modulation, and its duty cycle is determined by the sensing of drain voltage waveshape. Soft switching is ensured at both the turn-on and turn-off for every switches in the proposed inverter: zero voltage turn-on and low dv/dt turn-off. The real-time tuning minimizes the voltage stress on switches and maximizes the output power, and guarantees soft switching regardless of detuning of parallel-resonant inverter. The voltage stress on the tunable element is lower than the stress on the main inverter part. Moreover, all the mosfets are connected to ground. Hence, the mosfets do not experience large resonant voltage swing across negative and positive levels. These also simplify the gate driving circuitry. The proposed tuning achieves higher efficiency than conventional switch-controlled capacitor due to the elimination of back-to-back two-series mosfets. The measurement verifies that the proposed method achieves maximum 1.96 times higher output power and 15.86% higher efficiency with the same voltage stress on switches.