Isolated Modular Multilevel Matrix Converter (I-M3C) Based Novel Solid-State Transformer (SST) With Low-Frequency Medium-Voltage AC Port

This article proposes a novel solid-state transformer (SST) having a low-frequency medium-voltage ac (LF-MVac) port distinctively, which can be the key equipment for smart distribution networks based on LF-MVac interconnection. The proposed SST has four ports of power-frequency medium-voltage ac (MVac), LF-MVac, low-voltage dc (LVdc), and low-voltage ac (LVac). In addition to the two-level low-voltage dc/ac converter, the proposed SST is mainly composed of an isolated modular multilevel matrix converter (I-M3C), which can achieve single-stage three-port power conversion. First, the topology of the I-M3C is introduced. Then, a simple modulation scheme is provided to achieve single-stage three-port power conversion, and the operating principles of the I-M3C are given in detail. In addition, a control strategy based on dual-dq coordinate system is designed, which can achieve stable operation without the complex multistage coordinated control and voltage-balancing control strategies. Finally, the effectiveness of the proposed control strategy is verified through a 10-kV/2-MW full-power simulation platform, and a 100-V/1-kW scaled-down experimental prototype is built to further demonstrate the correctness of the proposed I-M3C.