Microgrid protection using system observer and minimum measurement set

Microgrids work in two modes, grid connected and islanded. Short circuit levels in islanded mode tend to be small compared to those in grid-connected mode. Moreover, power flows in microgrids are not always unidirectional. For these reasons, it is difficult to protect microgrids using relaying strategies traditionally used in distribution systems. In this paper, a new technique is presented which uses a state observer to detect and identify faults that occur within the zone of protection, regardless of whether the microgrid is islanded or grid connected. The proposed system can be centralized or decentralized. In addition, based on system observability, the required number of measurements can be reduced, thereby reducing the cost of the proposed protection system. It is possible to devise a low-cost protection system using the proposed approach. The performance of the proposed method in protecting IEEE 34 node test feeder is demonstrated on an Alternative Transient Program (ATP). The proposed approach is shown to be effective in grid-connected and islanded modes. Copyright © 2014 John Wiley & Sons, Ltd.