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Charging current and efficiency of a wireless power transfer system depend on the equivalent load resistance of supercapacitor load, which varies during charging. To achieve constant current (CC) charging and maximized efficiency under variable loads, control method that employs primary-side phase shift H-bridge inverter and secondary-side semiactive rectifier are proposed. The proposed secondary-side control method not only achieves CC charging, but also ensures no reactive impedance seen into the semiactive rectifier. Furthermore, the maximum efficiency tracking is based on searching the minimum system dc input current for any given output power. It is realized by phase shift H-bridge inverter that is controlled by the perturbation and observation algorithm. Simulation and experimental results validate the feasibility of the proposed control method. During CC charging of 3 A, the maximum efficiency is 81% and largest efficiency improvement is 15.2% at light load. The proposed control method improves the system performance and is suitable for the applications that require compact receiver and no wireless communication link between the transmitter and the receiver.
Li et al. (2018) studied this question.