Single-Phase Bidirectional ZVZCS AC-DC Converter for MVConnected Ultra-fast Chargers

Abstract:
A single-phase bidirectional converter fed by a Modular Multilevel Converter (MMC) through a Medium-Frequency Transformer (MFT) is a promising solution for medium-voltage-connected chargers of Electric Vehicles (EV). An operating scheme is developed for the converter to realize Zero-Voltage Switching (ZVS) and nearly Zero-Current Switching (ZCS) over the full load range. In comparison with conventional Phase Shift Control (PSC), the proposed scheme significantly reduces the reactive power through the AC-DC converter, thereby decreasing turn-off switching losses and the RMS current through the output capacitor. A trade-off between RMS current stresses and the required minimum number of sub-modules in the MMC side is found and studied to provide insights on how the proposed method affects the overall performance of the system. Simulations results are provided to verify the analytical findings.