A Monotonic and Continuous Frequency Control Method Covering Constant-Current and Constant-Voltage Charging Processes for Series-Series WPT Systems

In this paper, a monotonic and continuous frequency control method is proposed for series-series (SS) compensated wireless power transfer (WPT) systems with wide misalignment. The requirements for the operating frequency path through the whole constant-current (CC) and constant-voltage (CV) charging process and the whole coupling range are given as follows: (1) maintain a monotonic and continuous regulation; (2) maintain zero-voltage switching (ZVS) of the inverter; (3) the operating frequency of the CC mode should be closed to the resonant frequency for a higher power transfer efficiency. Based on mathematical derivations, the conditions for enabling an operating frequency path meeting the above requirements are visualized with graphical representations. Then, a comprehensive design framework and implementation steps are provided with the identified conditions. Finally, a prototype is designed with the proposed method, and then, it is built for experimental measurements with power ratings of 3.3 kW and 2.4 kW, respectively, and a coupling coefficient range of 0.1–0.3.