A Bridgeless AC/DC High Voltage Gain Converter With Three-Phase Modular Series-Output Connected Configuration for MVDC Grid Applications

In this article, a novel power factor correction, soft-switched, bridgeless ac-dc converter is presented for step-up voltage conversion in medium voltage dc grid applications. To reduce the number of conversion stages, the proposed bridgeless boost rectifier is integrated with isolated high-frequency step-up resonant converter with voltage multiplier modules to form a single-stage ac-dc step-up converter. Almost sinusoidal input currents with near unity power factor are achieved at the three-phase ac input side, while at the same time, the converter achieves a very high voltage gain at the output. The proposed converter is able to reduce the number of lossy diodes required for the front-end rectifier, and to achieve soft switching for all the Silicon Carbide (SiC) mosfets and SiC diodes, thus enhancing the converter efficiency. Simulation results on a 100-kW, 1-kVac/15-kVdc design, and experimental results on a laboratory scale proof-of-concept 2-kW, 250-Vac/4-kVdc medium voltage prototype are presented to verify with the proposed converter's performance.