Dynamic Behaviour of VSC-HVDC Systems under Different AC System Strengths

Operation of VSC with weak AC systems creates challenges such as ensuring stability after disturbances and proper selection of controller parameters, need to be addressed before physical implementations. This paper investigates the effect of controller parameters on the stability of a modular multilevel converter (MMC) VSC system. It was observed that d-q controller gains have greater influence on the stability compared to phase-locked loops (PLL) gains. It is demonstrated using time-domain simulation results obtained on the real-time digital simulator (RTDS) that a set of properly tuned controller gains could ensure small and large transient stabilities of the MMC-VSC system. Moreover, the negative effect of measurement delays in instantaneous currents and voltages is analyzed by performing small-signal stability assessment. The paper concludes with useful guidelines on selecting controller parameters for an MMC-VSC system connected to weak AC networks.