Closed-Loop Current Components Control Strategy of Operational Test System for MMC Valves

Operational test system for modular multilevel converter (MMC) valves is a commonly used method for assessing the critical stress tolerance of MMC submodules. In addition to the DC and fundamental frequency components, the actual current borne by MMC during operation also needs to consider the second harmonic current component under the failure of circulating current suppression. It is extremely necessary to accurately reproduce these three current components in the operational test system. In this article, the basic operation principle of the operational test system for MMC valves is analyzed firstly. Then, a convenient and accurate method for extracting the DC, fundamental, and second harmonic components of the test current is designed, and a closed-loop control strategy is proposed to effectively control these three current components. Finally, a simulation model of the system is established in PSCAD/EMTDC, and simulation results verify the effectiveness of the proposed current component extraction method and the closed-loop current components control strategy.