A Single-Stage Fault-Tolerant Three-Phase Bidirectional AC/DC Converter With Symmetric High-Frequency Y-Δ Connected Transformers

Abstract

This article presents a single-stage isolated three-phase bidirectional ac/dc converter with symmetric Y-Δ connected transformers, which implements ac/dc buck conversion, high-frequency electrical isolation, and high power factor for ac side (PF > 0.99). The converter can be utilized between the ac bus and the dc bus in ac–dc hybrid microgrid and in other applications where three-phase bidirectional ac/dc conversion is needed. With two operating modes available, the converter possesses the fault-tolerant ability and the improved light-load efficiency. When the converter works in the high power application with all the components operating normally, the transformers operate in the symmetric mode and share the power equally. Then, the switch current stress can be reduced. The converter can also operate in dual transformer mode for light-load conditions or with some abnormal components. The Y-Δ connected transformers provide an additional step-down conversion ratio and make the converter suitable for buck conversion. Furthermore, to guarantee the voltage-second balance of the transformers, the corresponding space vector pulse width modulation (SVPWM) algorithm is proposed. Experimental results based on a 2.4-kW prototype are presented in detail, which verify the theoretical analysis and demonstrate the converter's performance well.