A dual-side controlled inductive power transfer system optimized for large coupling factor variations

In this work, a 3kW inductive power transfer system is investigated, specifically intended for contactless vehicle charging. A series-series compensated topology with dual-side power control and a corresponding control strategy is proposed to significantly increase the overall efficiency, especially for systems with a large coupling factor variation and in partial load mode. A hardware prototype is built up and a peak DC-to-DC efficiency of 95.8% at 100mm air gap and a minimal efficiency of 92.1% at 170mm air gap is measured, including the power electronic components. The partial load efficiency at 500 W output power is still as high as 90.6% at 135mm air gap. All relevant loss mechanisms are modeled and the system is designed using a multi-objective optimization approach. An operating frequency of 35kHz was found to be the optimal tradeoff between the switching losses in the power electronics and the losses in the contactless transformer. Detailed measurement results are indicated showing an excellent agreement with the implemented simulation models.