Design Metrics of Compensation Methods for Contactless Charging of Electric Vehicles

Contactless power transfer (CPT) is an emerging topic which relies in high frequency resonant inverters to transfer power from a transmitter to a physically separated receiver inductively. Capacitive compensations on both the primary and secondary sides of a loosely coupled transformer are usually employed in recent researches in order to enhance the power transfer capability and the system efficiency. Achieving high efficiency, high power transfer and control capability of the output voltage and current of a compensated CPT circuit are conflicting criteria under variable loads and coupling coefficients. This paper studies the most important design metrics to choose the appropriate compensation method for high power applications. Series-series (SS) and series-parallel (SP) topologies as the two most economical configurations are focused in this paper and their main characteristics are extracted. It is investigated how to select the source frequency and compensation capacitors appropriately to achieve the best ideal functionality of the CPT system independent of output load and coupling coefficient variations, while providing the maximum efficiency. The design procedures are proposed and experimentally verified by a 3 kW prototype. Based on the results, SS configuration demonstrates as the best suited topology for charging the battery of electric vehicles (EVs).