Analysis and Design of a Dual-Coupled LCC-S Compensated IPT System Considering Air Gap Variation

In inductive power transfer (IPT) systems, variations in the air gap can affect the self-inductance and mutual inductance of the loosely coupled transformer (LCT). As the resonant frequency is primarily determined by the self-inductance and the compensation capacitance, any variation in self-inductance can cause the resonant frequency to deviate from its designed value, resulting in reduced output gain and efficiency. To address this issue, a dual-coupled LCC-S compensated IPT system with a three-coil LCT is proposed. The key idea is to utilize the additional degree of freedom provided by the coupling between the compensation coil and the secondary coil to adjust the system’s resonant frequency. By introducing a compensation coupling factor and determining its optimal value through a cost function, the frequency for zero phase angle (ZPA) input can be converged into a minimal range across the predetermined air gap range. Based on this, by selecting an appropriate operating frequency near the resonant frequency range, zero-voltage switching (ZVS) can be achieved, leading to a reduction in reactive current and switching loss. Subsequently, the parametric design process of the LCT with an optimal compensation coupling factor is elaborated. A 4.5-kW prototype was built and the experimental results have verified the theoretical analysis. The system operates at 85.5 kHz with a maximum input impedance angle of 12.2° across the air gap range of 40–120 mm while the self-inductance varies by 17.5% and mutual inductance by 245%, respectively. The peak efficiency of the system is 95.2%.