Local Power Controller Based Load Shedding Scheme in Islanded Microgrids

To decrease the blackout risk due to the large disturbances, it is recommended to intentionally create islanded conditions in power systems. In this event, system elements will be insulated and the supply for creating the islands can be preserved. To do so, resources and generations in the islands are discharged and loads should be shed in case it is required. In this condition, voltage and frequency stay in their limits. In this paper, a priority-based load shedding technique is proposed using a Local Power Controller (LPC) for islanded microgrids. The suggested method utilizes frequency and rate of change of frequency (ROCOF) based approaches to activate the shedding procedure. Moreover, the proposed approach controls the islanded microgrids for developing a support for the main grid in the case of frequency deviation events whereas supplying the local critical loads is mandatory. The advantages of method are minimum equipment requirement and suitability for end-users with critical loads. In the proposed methodology, a load addition mechanism is also considered. This mechanism automatically switches the shed loads when the system frequency recovers to a certain level. The proposed method scheme is verified and validated in a laboratory microgrid test bench under two operation modes, specifically allowing load shedding procedure in advance of and consequent to the islanded situation. In both cases, the results demonstrate that the scheme is able to sustain the islands.