A Control-Oriented Voltage Tracking Design for Grid-Forming Based Modular Multilevel Converter

Modular multilevel converters (MMCs) based on grid-forming control as a converter-driven interface for renewable energy sources are the development trend of the future electronics-dominated power grids. MMC offers outstanding voltage quality without an AC filter, which is very distinct from the AC topology of conventional two-level converters (TLC). However, most literature that studies the grid-forming MMC directly follows the voltage tracking control (VTC) principle of TLC and does not involve the voltage controller specifically for the MMC topology. In this paper, the design of the voltage controller is step-by-step deduced based on the topological properties of MMC. According to the analysis findings, the proportional link of the voltage loop can result in high-frequency oscillation and the proposed VTC with a sole integral link cooperating with inner current-loop control presents excellent dynamic performance. Finally, the proposed VTC is realized robustly in the laboratory prototype.