Control strategy of transfer branch for reducing peak value of DCCB breaking current

Abstract

A high-voltage DC circuit breaker is one of the key equipment that constructs the DC power grid. Therefore, reducing the peak value of the breaking current and shortening the fault removal time are the main research directions for its performance optimization. This paper first analyzes the basic topology and the traditional breaking strategy of a hybrid high-voltage DC circuit breaker with forced current commutation. Then, the theoretical analysis of the fault current, voltage, and the relationship between the withstand voltage level of the fast mechanical switch and the exit time of the transfer branch, is conducted. A new breaking strategy is proposed, which can effectively reduce the peak value of the breaking current by turning off the transfer branch step by step. When a fast mechanical switch reaches the corresponding withstand voltage level, it sends the OFF signals to each sub-module of the transfer branch; thus, the energy consumption of the DC circuit breaker is reduced and the fault removal time is shortened. Finally, the PSCAD/EMTDC simulation platform is used to build the test system, which verified the effectiveness of current limiting and other functions of the proposed breaking control strategy.