Voltage slope-based zero voltage switching detection method for wireless power transfer systems

Abstract

A zero voltage switching (ZVS) detection method, which relies on the half-bridge output voltage slopes during the MOSFET turn-on and turn-off transient processes, is proposed for the wireless power transfer (WPT) systems in this Letter. A voltage slope detection circuit and its active control method are also proposed to convert the nanosecond transient signal to a steady voltage level, which can be handled by the microcontroller easily. By having the information of the turn-on and turn-off voltage slopes, the state of ZVS can be evaluated to optimise the switching losses. A 500 kHz, three-coil resonant WPT system is built in order to evaluate the performance of the proposed detection method. Experimental results show that the ZVS state can be detected effectively. Also, the turn-off current can be controlled to a constant value to optimise the switching losses under the load and parameter variations.