A Joint Control with Variable ZVS Angles for Dynamic Efficiency Optimization in Wireless Power Transfer System

Tight voltage regulation and high efficiency are fundamental objectives of wireless power transfer systems (WPTSs) as power supplies. Although the well-established impedance matching control attempts to achieve high efficiency, the associated extra dc-dc converters or hard switching of converters in WPTSs reduce the overall system efficiency, particularly for high-power applications. In this article, under zero voltage switching (ZVS) conditions, the minimum power loss point is derived and proved in detail with different ZVS angles. Moreover, a joint control with variable ZVS angles (JC-VZA) is proposed to ensure ZVS of all switches and achieve the required output, simultaneously. This control scheme is implemented by use of controllers in both sides of WPTSs, which adjust their respective ZVS angles for dynamic efficiency optimization. Under ZVS conditions, the proposed JC-VZA features an optimal amount of reactive power that achieves the minimum total power loss by significantly reducing the switching loss. As a result, the experimental results obtained from our WPTS prototype verify its superiority. With a coupling coefficient k of 0.2 or 0.15, the maximum efficiency reaches 96.8% or 95.0% under the power rating of 288 W (rated load) as well as 92.4% or 88.7% in the case of light load (9% of 288 W).