Research on a Low Switching Loss Bidirectional Hybrid DC Circuit Breaker Topology

The hybrid DC circuit breaker is a key device to ensure the safe operation of the flexible DC grid, and is used to realize the disconnection of the fault current on the DC side. The existing hybrid circuit breaker mainly uses IGBTs (Insulated Gate Bipolar Transistor) as the switching component, and the series-parallel connection of multiple IGBTs leads to static imbalance. Long-term operation leads to large conduction loss and high heat production, which seriously affects the response speed of IGBT, even makes IGBTs fail, and the circuit breaker cannot disconnect the fault current normally. To solve this problem, this paper proposes a topology of a hybrid DC circuit breaker with low switching loss. During the normal conduction process of the circuit breaker, the IGBT has no loss because it is bypassed by the mechanical switch, which solves the static imbalance problem of multiple IGBTs in series and parallel. In addition, the hybrid circuit breaker has a bidirectional blocking function, which reduces the number of hybrid circuit breaker in large-scale application of bidirectional transmission by half compared with unidirectional DC circuit breakers. In this paper, the fracture process of this topology is theoretically analyzed. By optimizing the component parameters of the buffer branch, the extreme voltage at both ends of the buffer branch is reduced. Finally, a DC simulation platform was established to verify the feasibility of the topology and the reliability of the theory in this paper.