A Dual-Phase-Shift Control Method for MMC-H Solid State Transformer with Current Stress Suppression Effect

MMC-H is a novel solid-state transformer that can significantly reduce the number of transformers and increase power density. However, traditional single-phase-shift (SPS) control methods result in excessively large inner currents of the system. This paper proposed a dual-phase-shift (DPS) control method based on sine modulation, which can significantly reduce transmitting current and MMC bridge arm current. First, the mathematical relationships between system power/current and phase-shift angles were revealed. Then, the optimum combinations of two phase-shift angles were obtained. Finally, a comprehensive closed-loop control method with the optimum phase angles was proposed to control the overall system. Simulation results show that the proposed method reduces the system transmitting current and MMC bridge arm current by more than 60% under light load, significantly improving system efficiency.