Time-sequential Coordination Based Collaborative Backup Protection and Control Scheme for Flexible DC Distribution network

The collaborative active fault control and primary protection scheme for flexible DC distribution networks can effectively overcome the limitations of traditional protection schemes, but its reliability is difficult to be guaranteed in extreme cases such as communication and isolation equipment failure. Thus, it is urgent to carry out the research on relevant backup protection theory. Therefore, by utilizing the fault active control of the converter, a backup protection scheme based on the polarity of the local current sudden-change is proposed. Based on the current sudden-change generated by the converter, the protections of load switches in the reverse fault direction are blocked by measuring the polarity of the sudden-change current. Then, according to the time-sequential coordination relationship, the faulty line can be isolated reliably. This scheme is independent of communication and DC circuit breakers. Through active control of the converter, fault isolation can be realized by only using load switches. Besides, an acceleration strategy for the backup protection is proposed, and its practicability is analyzed in combination with different topologies. Finally, a four-terminal flexible DC distribution network model is established in PSCAD/EMTDC. Simulation results show that the proposed scheme can realize fast and selective isolation of faulty lines only based on local information. © 2022 Automation of Electric Power Systems Press.