A Cosine Similarity-Based Centralized Protection Scheme for dc Microgrids

Unlike the phasor measurement-based protection in ac systems, the protection of dc systems deals with complex fault transients which mandate the isolation of the faulted segment within few milliseconds as continued fault current leads to overheating issue in power electronic converters. To this end, several works have been suggested-based on the unit and nonunit protections for dc microgrids. Threshold selection and protection coordination are the challenges associated with nonunit protection. Similarly, communication delay and link failure limit the application of unit protection. To address these issues, this article presents a robust centralized protection scheme for dc microgrids, which is resilient to communication delay and link failure. It uses the current of each line segment to compute the similarity of current change at both ends of the line segment to derive the protection decision. To overcome the communication failure from one end of the line segment or even from multiple segments, the proposed method uses data from adjacent segments to derive the protection decision correctly. Using power systems computer aided design (PSCAD)/electromagnetic transients and direct current (EMTDC) environment, the performance of the proposed method is evaluated for various cases and compared with available techniques. Finally, the accuracy of the protection algorithm is validated under experimental conditions.