A Dual-Side Controlled Inductive Power Transfer System Optimized for Large Coupling Factor Variations and Partial Load

Abstract

In this study, a 3-kW 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 large coupling factor variations and in partial load mode. The topology, which is closely related to the dual-active bridge converter, enables the dual-side power control without adding additional dc/dc converters to the system, and thus keeping the additional hardware effort minimal. A detailed analysis of the proposed topology is provided, and the benefits of the dual-side control are demonstrated both theoretically and experimentally. A hardware prototype is built and a peak dc-to-dc efficiency of 95.8% at 100 mm air gap and a minimal efficiency of 92.1% at 170 mm 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 135 mm air gap. Overall, the proposed topology provides a practical method to overcome the main drawback of most single-side controlled inductive power transfer systems, which is a significant efficiency drop outside the nominal operating point.