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

This paper proposes a novel solid-state transformer (SST) having a low-frequency medium-voltage AC (LF-MVAC) port distinctively, which can be as 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 lowvoltage 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. Additionally, a control strategy based on dual-dq coordinate system is designed, which can achieve stable operation without the complex multi-stage coordinated control and voltagebalancing 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.