Low inertia power systems: Frequency response challenges and a possible solution

Abstract

In recent years, renewable energy sources like wind and solar photovoltaic (PV) are rapidly evolving in South Australia. Most of the new wind power plants in South Australia deploy variable speed wind machines, specifically type III and type IV wind turbine generators. These plants naturally do not provide any support in frequency regulation after a contingency. These ‘asynchronous’ machines together with rooftop PV units can result in substantial non-synchronous generation in South Australia. During high penetration of wind/PV and cheaper import from Victoria, the South Australian network may depend on a small number of synchronous generators to control frequency if separated from rest of the network. Such a low inertia grid could be potentially at a risk of experiencing excessive rate of change of frequency (ROCOF) after a contingency. A high ROCOF may initiate tripping of other synchronous generators. As a result, network frequency response may become more vulnerable and system may be subjected to significant under frequency load shedding or at a risk of blackout. To explore the above issue, this work investigates the effects of cascading failure on frequency response in a low inertia grid. A mitigation measure to avert such a failure is also presented.