High-Frequency Oscillation Mechanism Analysis and Suppression Strategy of Grid-Forming Control MMC-HVDC

Recently, several high-frequency oscillation (HFO) events have occurred in the modular multilevel converter (MMC) based HVDC (MMC-HVDC) projects, threatening the safety and reliability of power systems. Existing studies only focus on the HFO of MMC-HVDC with grid-following control (GFWC) but less on the HFO of MMC-HVDC with grid-forming control (GFMC). Therefore, this paper establishes the small-signal model of MMC-HVDC with GFMC through the dynamic phasor method. Then, the impact of different parameters on the HFO is discussed. Unlike MMC-HVDC with GFWC, the outer loop control of MMC-HVDC with GFMC has a great influence on HFO. Meanwhile, the existing HFO suppression strategies by adding a low-pass filter (LPF) to feedforward control of terminal voltage for MMC-HVDC with GFWC will increase the HFO risk of MMC-HVDC with GFMC. Further, the HFO suppression strategies suitable for MMC-HVDC with GFMC are proposed based on the mechanism analysis results. Finally, the obtained results are verified by the time-domain simulation of the studied system in RT-LAB.