Mechanism Analysis of Additional Damping Control Strategies for the High-frequency Resonance of MMC Connected to AC Grid

High-frequency resonance can occur when a modular multilevel converter (MMC) is inserted into an AC grid. Additional damping control is a relatively low-cost resonance suppression strategy compared to passive damping strategies. This paper analyzes the influences of a feed-forward voltage filter and feedback current filter for the inner controller for the high-frequency impedance characteristics of the MMC based on a model. Moreover, the mechanism, influencing factors, and limitations of the existing strategy including an additional low-pass filter in the voltage feed-forward stage are investigated. Secondly, a resonance suppression strategy for the inclusion of additional cascaded notch filters in the voltage feed-forward stage is proposed, and its parameter design method and applicable scenarios are analyzed. In addition, this paper analyzes the effects of the inclusion of an additional control in other stages for the inner controller of the MMC. Finally, the correctness of the theoretical analysis and the proposed strategy is verified based on the simulation of an actual project on PSCAD/EMTDC.