Tobias Diekhans

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

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.

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.

A systematic comparison of hard- and soft-switching topologies for inductive power transfer systems

This paper provides a comparison of four series-series compensated inductive power transfer systems for contact-less vehicle charging. A systematic comparison between hard-and soft-switching topologies, as well as different operating frequencies, is performed and the impacts on system efficiency and complexity are assessed in detail. In a holistic design process each system is individually optimized for a charging power of 3kW and a variable air gap from 100mm to 170mm at a coil diameter of 500mm. It is shown that the hard-switching topologies are highly attractive in the considered power range even with state of the art semiconductors. By introducing a dual-side controlled topology a superior system efficiency is demonstrated at an operating frequency of 35 kHz.

Compact 7 kW inductive charging system with circular coil design

A compact 7 kW inductive charging system for current automotive requirements is presented. The system is designed with the purpose of low hardware effort. Magnetic design incorporates asymmetric circular planar coils with a minimum of active materials. A new power electronics topology has been realized with dual-side power control that also uses minimum active and passive components and yields superior performance over a wide range of operational parameters. A position tolerance of > 150 mm in transversal and > 75 mm in longitudinal direction is demonstrated. Overall DC-to-DC efficiency is > 86 % for even worst coupling conditions. Due to low magnetic coupling factors, power losses are dominated by the transformer losses, which can be improved by an advanced magnetic design. The system is ready for bidirectional power transfer, enabling future vehicle-to-grid and smart home applications.