A Single-Stage Fault-Tolerant Nine-Bridge Isolated Three-Phase Bidirectional AC/DC Converter and Its SVPWM Algorithm

The three-phase bidirectional ac/dc converter is an important interface for bus voltage matching in microgrid and power conversion in energy storage system. This article proposes a fault-tolerant nine-bridge single-stage isolated three-phase bidirectional ac/dc converter with three operation modes: triple-transformer symmetrical operation mode for normal operation (3T), as well as dual-transformer operation mode (2T) and triple-transformer asymmetrical operation mode (A3T) for open-circuit fault-tolerant operation. With the modified space vector pulse width modulation algorithm (SVPWM), the converter can achieve 1) single-stage power conversion, enhancing efficiency and power density; 2) symmetrical operation of three transformers, sharing the total power equally; 3) inherent fault-tolerant ability, improving reliability; 4) dual-transformer (2T) operation mode, improving light-load efficiency; 5) Y-Δ connection of three transformers, providing an additional voltage ratio for buck-boost ac/dc conversion; 6) topology optimization, reducing the number of switches. This article presents a detailed analysis of the operation principles, as well as the experimental results based on a 2.8 kW prototype, which demonstrates the circuit performance well.