An Autonomous Impedance Adaptation Strategy for Wireless Power Transfer System Using Phase-Controlled Switched Capacitors

The values of the capacitance and inductance on the primary side of a wireless power transfer (WPT) system need to be appropriately designed and accurately tuned for the system to work in the resonant state. To achieve this, in this article, a novel autonomous impedance adaptation (AIA) strategy is proposed to realize adaptive impedance matching for WPT systems using a phase-controlled switched capacitor (PCSCap) to exert the highest possible power transfer efficiency. The relationship between the input impedance characteristics and operating conditions, resonant or nonresonant, is analytically and quantitatively established, using the complex \Gamma -plane. The input impedance angle is captured for the feedback control structure to adaptively adjust the equivalent capacitance of the PCSCap, so that the WPT system can operate in its resonant state, maximizing its power transfer efficiency. The proposed AIA method is designed to have a high impedance precision and large self-recovery margin. The effectiveness and advantages of the proposed PCSCap-based AIA mechanism are proven through simulation and experimentation, showing its great practicality and wide applicability in the WPT industry.