Analysis and control of series/series-parallel compensated resonant converter for contactless power transfer

Series/series (S/S) and series/parallel (S/P) compensations are widely used in contactless power transfer systems. However, the inductive input impedance of the S/S compensated converter operating at an output voltage gain intersection point impairs the system's efficiency, and the output voltage of the S/P compensated converter operating at resonant frequency is quite sensitive to variation of transformer's parameters caused by air gap change or misalignment. This paper proposes a novel series/series-parallel (S/SP) compensation topology to achieve both high efficiency and good output controllability. The frequency-domain and time-domain analyses of the proposed resonant converter are performed in this paper. Similar to the conventional resonant converters, both phase-locked-loop (PLL) control and fixed-frequency control can be employed. A 60-W prototype with PLL control and a 1.5-kW prototype with fixed-frequency control are built to verify the theoretical analysis. To perform the input-to-output voltage gain comparison, an S/P compensated converter is also fabricated. Experimental results verify the effectiveness of the proposed compensation method. The efficiency of the fabricated S/SP prototype reaches 95.2% at an output power of 1.5 kW with a 10-cm air gap between windings.