Dual-Phase-Shift Control Strategy with Switch-Controlled Capacitor for Overall Efficiency Optimization in Wireless Power Transfer System

In this paper, a dual-phase-shift control strategy combining with a switch-controlled capacitor (SCC) is proposed to realize efficiency maximization while realizing zero voltage switching (ZVS) for a LCC-LCC compensated wireless power transfer (WPT) system. The dual-phase-shift control is employed with a semi-active rectifier (SAR) to reduce the current stress in the resonant network. To realize accurate ZVS operation, both the SCC control angle and the SAR phase-shift angle are used as the control variables. First, the conditions of ZVS operation and circulating reactive power minimization are derived based on the time-domain model. Then, the power losses in the resonant network, inverter and semi-active rectifier are analyzed and optimized under the constant voltage output. An optimal control strategy is further proposed to maintain the constant voltage output while maximizing overall system efficiency. It is worth mentioning that the proposed control strategy allows the decoupling of the ZVS control and the power regulation. Finally, the performance of the proposed control strategy is examined based on a 6.6-kW WPT prototype. The results show that all switches realize ZVS operation within the entire power range with a peak system efficiency of 95.1%, which exhibits a good agreement with the theoretical analysis.