Novel Control Strategy for Modular Multilevel Resonant Converter based Solid-State Transformer

Abstract:
This paper presents a new control methodology for Modular Multilevel Resonant (MMR) converters in Solid-State Transformer (SST) systems, targeting medium-voltage conversion for hydrogen electrolysis applications. The study begins by analyzing various existing control strategies for MMR, assessing their working principles, regulation effectiveness, and influence on efficiency. To enhance control simplicity and effectiveness, a continuous modulation index method is introduced, reducing the number of control variables to one while maintaining stable operation. The proposed scheme effectively reduces harmonic distortion in the resonant current and limits magnetizing current in the transformer, by fixing a small phase shift angle among MMC submodules and setting operation at the resonant frequency. A 10% reduction in overall power losses compared to phase shift control is indicated by thermal modeling, leading to improved efficiency and potential cost savings in cooling systems. The effectiveness of the proposed method is confirmed through Simulink-based simulations.