Smart load shedding strategy for minimized supply interruption

Following large system disturbances, one of the solutions to limit the potential risk of occurrence and/or extent of the blackout is to intentionally create system islands such that the disturbed system elements are isolated and the supply to the created islands can be maintained. In order to sustain the created islands, generations within the islands are dispatched and if necessary local loads are shed to ensure that frequency and voltage remain within required limits. This paper presents a priority-based load shedding scheme implemented within a Local Power Controller (LPC) to assist the management of islanded microgrids so as to provide support to the main network during frequency deviation events while maintaining high level of security of supply to local critical loads. The load shedding scheme requires minimum instrumentation and uses frequency and rate of change of frequency (ROCOF) measurements to trigger the shedding processes, and it is most suitable for end-users with critical loads such as hospitals and data centers. The scheme is also equipped with a load addition mechanism that allows automatically switching on the shed loads when the system frequency recovers to a certain level. The scheme is tested and demonstrated in a laboratory microgrid environment under two operation modes, i.e. enabling load shedding process in advance of and subsequent to the islanded condition. The results show that the scheme is capable of sustaining the islands in both cases. Potential improvements to the scheme to incorporate demand-side information for a smarter and faster algorithm to minimize the interruption of supply are presented, and future activities to investigate the communication requirements to support the practical implementation of such a scheme are also discussed.