A Large-scale Wireless Charging Station for Electric Vehicles

This paper proposes a large-scale, high-power, transformerless, multilevel wireless charging station for electric vehicles (EVs) using a multilevel rectifier, resonant inverters, and excitation coils. The multilevel rectifier converts the medium voltage (MV, 22.9 kVrms in S.Korea) of the electrical grid to 42 levels of 1 kV. Forty-two resonant inverters and excitation coils generate synchronized magnetic fields and induce voltage and current to a transmitter coil. Then, the transmitter coil induces voltages on receiver coils mounted on EVs. The proposed topology has the advantage of balancing the cell voltages of the multilevel converter for arbitrary load conditions. The input impedance seen from each converter is balanced regardless of the load numbers and their conditions. Circuit analysis of the multilevel inductive power transfer (IPT) system with multiple loads is presented to achieve load-independent output voltages. In addition, a novel dq synchronous reference frame controller for the multilevel rectifier is proposed. A 42-level IPT system with ten receiver coils was evaluated with simulation results. The cell balancing of the multilevel converter and the load-independent output voltages were achieved.