Oscillation Suppressing Control Method Based on Impedance Optimization for Grid-Connected VSC-HVDC System

Broadband oscillation poses serious threat to voltage-sourced converter based high-voltage dc (VSC-HVDC) transmission systems. In this paper, a novel impedance optimization control method of grid-connected VSC-HVDC based modular multilevel converters (MMC) is proposed to suppressing broadband oscillation in this paper. Different from the previous control methods, the proposed method utilizes one first-order low pass filter in voltage feed-forward part to reduce resonant frequency of MMC and adopts one second-order filter, which is similar to a notch filter, in current feedback loop to modify impedance of very narrow frequency band to optimize impedance characteristics. By using the proposed impedance optimization method, both sub-synchronous oscillation(SSO) and high frequency oscillation can be suppressed in MMC based VSC-HVDC The presented control strategy is verified by simulations results based on HYPERSIM.