Damping control strategy research for MMC Based HVDC system

Abstract

The resonant frequency and peak value of DC current in the flexible HVDC system are related to the parameters of the main circuit, smoothing reactor, cable length, steady operational points and the adopted control strategy. To study the resonant characteristics of DC current and its damping control strategies, a small signal model for MMC- HVDC considering the parameters of main circuit, smoothing reactor, arm reactor, cable length, steady operating points and the adopted control strategy based on simplified equivalent model of MMC was established, and the resonant features of actual MMC based HVDC system were studied. Secondly, a damping control strategy for MMC based HVDC to suppress the resonant DC current was designed. The impact of additional damping control strategy on system dynamic performance was researched and the calculating expressions for choosing the parameters were derived. Finally, the effectiveness and correctness of the additional damping control strategy were validated in the numeric simulation model.