Impact of DC voltage control parameters on AC/DC system dynamics under faulted conditions

This paper discusses the influence of dynamics within a multi-terminal offshore DC grid (MTDC) on the onshore AC power system stability under faulted conditions. An AC-fault occurring at the HVDC converter station terminals may propagate via the offshore MTDC grid to the undisturbed asynchronously connected AC power system. This disturbance manifests itself as additional active power overshoot at the remotely connected converters. It is shown that the severity of this disturbance propagation is sensitive to the parameters of the DC voltage droop control employed for voltage regulation in the MTDC scheme. Furthermore, the effect of the MTDC grid topology on these dynamic interactions is illustrated by comparing a meshed with a radial topology. The analysis has been performed with phasor-mode time domain simulations, augmented with a user-defined state-space model for the MTDC grid. The AC system dynamics are based on available models of benchmark power systems in the stability simulation software PSS®E.