Research and experiment of a current-limiting HVDC circuit breaker

Existing mechanical HVDC circuit breakers (CB) are capable of interrupting HVDC currents within several tens of milliseconds, but this is too slow to satisfy the requirements of a reliable HVDC grid. HVDC CB based on semiconductors can easily overcome the limitations of operating speed, but need large number of the series (parallel) connection of electronic switching devices. To overcome these shortcomings, this paper introduces a topology of hybrid CB; this paper first describes the principle of hybrid CB; then a control strategy of fault pre-treatment is also proposed, that is, the ‘pre-action and action (or recovery)’ of the switches, in order to improve the breaking speed of the hybrid CB and the equalising circuit of its solid-state switch has been designed. The proposed topology and control strategy do not produce loss in the normal operation of CB, and instantaneous trigger solid-state switch with quickly cutting short-circuit current during short-circuit faults; at last the simulation and experiment of the hybrid HVDC CB have also been done. The results turn out when a short circuit occurs, the hybrid HVDC CB can quickly break the short-circuit current; the buffer circuit can be provided for the release of the stored energy circuit.