A Method to Decrease the Submodule Capacitor Voltage Fluctuations in Voltage-Source Modular Multilevel Converter with Wide-Bandgap Power Devices

The Voltage-Source Modular Multilevel Converter (VMMC) improves conventional Modular Multilevel Converter (MMC) by reducing submodule count, offering a compact solution for grid-forming converters (GFCs) in high-voltage applications. This paper proposes a high-frequency energy balancing method to suppress submodule capacitor voltage fluctuations in VMMC, improving WBG performance and enabling a more efficient, lightweight design. It describes the operational principle of the topology, and analyses the submodule capacitor voltage fluctuation model in detail to reveal the impact mechanism between energy balancing frequency and the fluctuation. Analytical modeling and simulations validate its effectiveness, providing an opportunity to optimize WBG-based grid-forming converters in high-voltage applications.