A Simplified Three-Order Small-Signal Model for Capacitive Power Transfer System Using Series Compensation

Capacitive power transfer is promising for high-efficiency wireless charging. A small-signal model is required to evaluate the system stability under different control approaches. This letter focuses on the modeling and simplification of the high-order system using series compensation. Based on the extended describing function method, this letter proposes a series of model transformation and approximation to effectively reduce the circuit order of the resonant tank. The number of resonant components is reduced from ten to two. Combining with the inverter and rectifier model, a third-order equivalent circuit model is first derived for the whole system with clear physical meaning and explicit transfer function. The experiment results show the model is accurate up to 1/5 of the switching frequency.