Cascading contingencies in low inertia power systems: Frequency response challenges and a potential solution

South Australia has the highest level of combined wind and rooftop solar photovoltaic (PV) generation capacity of any states in Australia. Most of the recent wind farms in South Australia use variable speed machines, namely, type III and IV wind turbine generators. Unlike synchronous generators, type III and IV wind machines usually do not participate in frequency regulation. In addition, PV sources do not provide any frequency support after a contingency. Under high penetration of the above non-synchronous generation and cheaper interconnection import from the adjacent state, a few synchronous generators may be committed in the South Australian grid. During such operating conditions, network frequency response following the loss of interconnection may become a concern. Moreover, the default under frequency protection setting of some existing PV units in South Australia could be higher than the under frequency load shedding (UFLS) threshold. Hence, the loss of interconnection may cause a substantial ‘secondary PV trip’. Consequently, the frequency response may further deteriorate and the network may experience a considerable amount of load shedding. To address the above issues, this research work investigates the frequency response of the equivalent low inertia South Australian power system by considering the cascading PV trip phenomenon. Then, a countermeasure to prevent the subsequent PV trip is explored by activating emulated inertia and active power control from variable speed wind machines.