Adaptive Damping Control of MMC to Suppress High-Frequency Resonance

High-frequency resonances (HFRs) between modular multilevel converters (MMCs) and power system are developed due to the delay-induced negative damping of MMCs. Because the resonance frequencies are unknown and dependent on the ac network configuration, system operating condition and MMC control modes, the efficacy of applying a pre-designed damping control in advance is limited. To overcome this limitation, this article presents an adaptive damping control scheme that employs online resonance detection to identify HFRs from voltage and current measurements and then automatically program narrowband damping control for the mitigation of HFRs. By continuously monitoring system resonance conditions (e.g., disappearance of resonances, frequency change of resonances, emergence of new resonances), it automatically adjusts the number of damping controllers being used, the value of damping gain for each damping controller, and the width of the damping band designed for each damping controller. The results of the Electromagnetic Transient (EMT) simulation validate the effectiveness of the proposed method in different MMC-based systems.