An Improved Virtual Impedance Control Based Oscillation Suppression Method for MMC DC System

The oscillation phenomenon has detrimental effects on the stable operation of the module multilevel converter (MMC)-based high voltage DC (MMC-HVDC) transmission system. The virtual inductance or resistance control can be used as the oscillation suppression method to limit the system instability. To improve the oscillation suppression effectiveness based on the existing virtual impedance control methods. This paper first analyzes the DC output impedance of the MMC-HVDC system and verify the correctness of the DC output impedance. Then an improved virtual impedance control (IVIC) method is presented based on the traditional virtual resistance control (TVRC) and the phase lag compensation control (PLCC) method. Under the same conditions, the Nyquist stability analysis is presented to verify the MMC system stability can be more improved by using the IVIC method compared with the TVRC and PLCC. In PSCAD/EMTDC, the simulation results verify that the IVIC can suppress the MMC DC system oscillation and can improve the oscillation suppression effectiveness compared with the TVRC and PLCC. The stability analysis and simulation results verify that the proposed IVIC method can help to mitigate the detri-mental effects caused by system instabilities and oscillations.