State-Plane-Based Frequency Domain Analysis and Optimal Design for SS Compensated IPT Systems

When modeling series-series (SS) compensated inductive power transfer (IPT) systems, conventional frequency-domain methods focus on output characteristics while neglecting the time-domain information of the current. To improve the model accuracy, we propose a state-plane-based frequency domain analysis method. It integrates both time and frequency information, providing a more comprehensive analysis. By decoupling the coupling coil model, two independent equivalent circuits and their corresponding state-plane diagrams are developed. Hence, the amplitude and phase of each harmonic component can be accurately determined. Additionally, the proposed model allows for the precise calculation of the switch turn-off currents. The study also depicts the zero-voltage-switching (ZVS) ranges under various output conditions. An optimal modulation strategy is developed to minimize the condition losses while ensuring ZVS of all MOSFETs over the entire power range. A 400 W laboratory prototype is built and tested. The experiment results effectively validate the model’s accuracy. A 95.61% peak efficiency is recorded with improved performance throughout its operational power range.