A method for Selecting the Control Inputs for Zero Voltage Switching and Efficiency Optimization of Bidirectional Wireless Power Transfer System

The bidirectional wireless power transfer system (BD-WPT) system allows power flow in both directions between a source and a load. High frequency is required to increase the power transfer efficiency and reduce the size of the magnetic components. However, high frequency operation leads to an increase in switching losses of the converter. To reduce these losses, zero voltage switching (ZVS) operation of the converter is required. This paper presents a method of optimizing the coil-to-coil efficiency of the BD-WPT system whilst ensuring that ZVS is achieved. To achieve this goal, harmonic decomposition of the input voltages is used for the ZVS, which gives a better accuracy when compared to the fundamental harmonic approximation method and avoids the complexity of time domain analysis. Lagrange optimization was employed to optimize the efficiency of the coil for a given power requirements. It was shown that for optimum efficiency operation of the converter, the current in the primary and secondary coils should be equal.