30 kW Bidirectional Inductive Power Transfer Charger With Intermediate Coil for EV Applications

High power, highly efficient, and robust bidirectional inductive power transfer (IPT) system based on three windings, used for automotive applications is considered in this article. Compensation strategies are revised, and benefits of three-coil system are outlined. A simple equivalent circuit model of the three-coil system is derived in order to improve the comprehension of the system. Tuning methodology for the compensation circuit of the three-coil IPT system, suitable for the considered application is proposed, together with the guidelines for its implementation. All of the coils were designed and optimized together with the proposed compensation circuitry, with the employed resonant dual active bridge (DAB) topology. IPT prototype for 30 kW has been realized according to the design proposal, and tested, transferring power levels between and 37.4 kW, with the varying air gap between and 150 mm, with the overall system efficiency ranging from 91.29% up to 96.72%. Behavior and efficiency of the system were tested using constant-power, constant-current, and constant-voltage charging methods, and both in grid-to-vehicle and vehicle-to-grid modes of operation.