Synchronization Strategy Based on Resonant Current Detection for Bidirectional Wireless Charging System

Bidirectional wireless power transfer greatly improves the reliability of power supply. However, wireless communication between the primary and pickup controllers is usually required to transmit load information, which has time delay and is easily interfered by electromagnetic fields. Existing solutions to avoid the use of communication can be divided into three categories: additional dc/dc circuit, primary side bridge control, and secondary side bridge control. Compared with the other two methods, the secondary side bridge control has low loss and good robustness. But, it usually requires phase-locked loop (PLL) to eliminate the frequency error between primary and secondary side bridges, which increases the complexity. In this article, a constant current control strategy without communication is proposed. It is based on the secondary side bridge control and the switching sequence of the secondary side bridge is periodically synchronized according to the phase of the resonant current. It works robustly without the need for additional hardware such as PLL or Multiplier. The harmonic sensitivity analysis, parameter optimization design and stability analysis are carried out to improve the control efficiency. Experimental results based on a 1 kW prototype with dual LCC resonant network are presented to verify the effectiveness of the proposed control strategy.