Analysis and enhanced topologies of active-resonance DC circuit breaker

DC circuit breakers are needed in future HVDC grids to provide selectivity in clearing DC faults and to achieve continuous operation of the healthy part of the grid. Standard mechanical circuit breakers as used in AC systems cannot be used in HVDC applications due to the lack of current zero-crossing, which is essential for arc extinction. To use mechanical interrupters for fault current interruption in DC applications, resonant circuits are used to create artificial current zero-crossings, by superimposing the resonant current on the DC current in the circuit breaker. Although the resonant current creates the zero-crossing, it introduces stresses on the mechanical circuit breaker and limits its rating, since the superimposed resonant current possibly introduces large peaks before current interruption. This paper proposes an improved active-resonance DC circuit breaker topology which aims to increase breaker ratings by avoiding these peaks. The improved topology is able to control the direction of resonant current injection, limit internal circuit breaker currents and allows for multiple interruption attempts. The principle of operation and advantages over presently proposed topologies have been verified by simulation results.