A Cyber Resilient Protection Scheme for Bipolar DC Microgrids Using Symmetrical Component Decomposition

This article presents a unit protection scheme for bipolar dc microgrids, which is resilient to cyber attacks. The proposed method uses current measurement of both ends of the protected line segment for distinguishing the internal faults and cyber attacks. For any change in current, the disturbance index exceeds the threshold value, subsequently, the proposed protection algorithm is triggered. Being a bipolar dc system, the concept of symmetrical component decomposition is used to obtain the bias, unbalance, and balance components during an unbalance condition. The superimposed balance component of both ends of the line on a four-quadrant plane acts as a decisive discriminator between internal and external faults. The correct faulted pole is identified by analyzing the superimposed unbalanced component. By comparing the superimposed bias component with the local pole domain currents, the cyber attack is correctly identified. The proposed protection scheme is validated on a ring-type bipolar dc microgrid, simulated in real-time digital simulator, for different internal and external faults and cyber attacks. The performance of the proposed method is tested for various conditions, including the detection of internal and external high resistance faults, fault type classification, change in load, distinguishing between different faults, and cyber attacks. A comparative assessment of the proposed method with the available techniques confirms its strength.