Research on the High Frequency Oscillation of MMC-HVDC Integrated into Renewable Energy System

Abstract

The high frequency oscillation (HFO) of renewable energy integrated into MMC brings serious challenges to the stable operation of power system. This article proposes the mathematical impedance model of MMC with considering control system time delay, sequence component separation, control system. Besides time delay, the main factors of HFO such as SCS, virtual filter of voltage and current, inner-loop controller are derivate in this article. It is proved that SCS may lead to the fluctuation of phase character of MMC high frequency impedance and lead to low damping character of MMC system. Virtual filter of voltage and current can enhance the damping ratio of MMC system. Lower proportional gain of inner-loop control lead to a higher damping character of MMC system. The solutions of HFO are validated in Zhangbei project. The 1550Hz HFO in the project is suppressed by the optimization of control system.