He Zhiyuan

A hybrid circuit breaker for DC-application

The development of large scale DC microgrid and high voltage direct current (HVDC) power grid requires a reliable, fast and low-loss circuit breaker. In spite of the advantages of DC gird such as low loss and no reactive power, DC grid has major disadvantages concerning control and switch actions. A new hybrid breaker with forced commutation is proposed in this paper, which is able to interrupt the fault current in several milliseconds. Furthermore, zero-current open of mechanical switch is achieved in this topology, and the breaker could be maintained in conducting state even if the gate driver of the semiconductor devices suddenly experiences blackout. The breaker can be applied in both VSC-HVDC system and DC micro grid. The design principles of the proposed hybrid breaker are presented and verified by simulation results.

Control strategy of the full-bridge based hybrid DC breaker

A reliable, fast and low conduction losses DC breaker plays an significant role in the development of the DC grid. This paper presents the control strategy of the hybrid DC breaker based on series combination of full bridge Sub-modules (FBSM). The topology and operation principle of the full-bridge based hybrid DC breaker is illustrated. Compared with the topology that utilize directly IGBTs in series connection, the voltage balance is easier to achieve for connecting FBSM in series. For a DC line fault close to the DC switchyard, the fault current could rise to a large value in a short time. In order to get a quick response to the DC grid fault, the rapid fault detection method and the pre-transferring strategy are introduced. A low voltage physical dynamic model has been built to verify the operation and control strategy.