Multiple High-Frequency Resonances Analysis and Adaptive Virtual Impedance Control of MMC-Based System

In recent modular multilevel converter (MMC)-based projects, high-frequency resonance (HFR) incidents have posed a severe threat to the security of the power system. Existing HFR suppression methods mainly focus on specific operation conditions, and cannot be so effective when the grid impedance changes. The adaptive methods, however, still get limited to suppressing single HFR and cannot not deal with the multiple HFRs issue. To overcome these challenges, an adaptive virtual impedance (AVI) strategy is proposed to detect and mitigate the multiple HFRs. The proposed strategy consists of resonance detection and virtual impedance (VI)-based suppression method. Particularly, the parameter of the VI is designed to be adjusted adaptively, according to the detected resonance frequency in real time. The AVI control is configured in each HFR risk frequency band to achieve mitigation of multiple HFRs. Simulation and experimental results validate that the unpredictable HFRs can be effectively mitigated by the proposed method.