Abstract: Existing HVDC circuit breakers are capable of interrupting HVDC currents within several tens of milliseconds, but this is too slow to fulfill the requirements of a reliable HVDC grid. HVDC breakers based on semiconductors can easily overcome the limitations of operating speed, but need large number of the series （parallel） connection of electronic switching devices； at the same time, it requires high technology and generates a lot of loss. To overcome these shortcomings, a topology of hybrid HVDC circuit breaker was introduced. Firstly, this paper described the principle of hybrid HVDC circuit breaker； then a control strategy of fault pretreatment was also proposed, that was the pre-action of the converter when fault occurred, in order to improve the breaking speed of the hybrid circuit breaker； at last the modeling and simulation were carried out on the hybrid HVDC circuit breaker by PSCAD, and unit prototype was made for the step-down experiments. The simulation and experimental results prove that: when a short circuit occurs, the hybrid HVDC circuit breaker can quickly break the short-circuit current| and the buffer circuit can be provided for the release of the stored energy circuit in DC circuit and load.

Key words: hybrid DC circuit break, control strategy, modeling and simulation, experiment study