Stability Enhancement by VSC-HVDC With a Supplementary Frequency Control Strategy in Case of System Splits

Within the interconnected European power system power outages up to 3 GW can be handled without load shedding due to the load-frequency control design. Transient faults may cause system splits dividing it into weaker asynchronous subsystems. These possible fault events may result in power deficits exceeding the incident of dimensioning, which ultimately cause high gradients in the subsystems' frequency. Emerging HVDC links may contribute towards maintaining system stability. Due to their ability to transmit power between asynchronous systems a supplementary frequency control may be applied to support either of the connected systems. In this paper a suitable frequency controller for such events is implemented and the resulting system's behavior is analyzed. It is shown that the applied controller design successfully supports frequency stability of the system. In addition the effects of various input signals and the available transfer capacity of the HVDC is evaluated.