Design and Operation of Bi-Directional Hybrid Circuit Breaker Based on Transient Commutation Current Injection

Fault protection represents a major technical challenge in the emerging DC transmission and distribution power networks. This paper reports on the design and operation of a new bidirectional DC hybrid circuit breaker (HCB) based on a transient commutation current injection (TCCI) concept. The TCCI-based HCB conducts a normal current through its mechanical path with an ultra-high efficiency (>99.9%), but commutates a fault current to a parallel power electronic path by the TCCI circuit before turning off. The TCCI circuit is essentially a dual-input current source buck converter which quickly reduces the current through the mechanical switch to zero within 10-20 µs and then maintains a near-zero high frequency AC ripple current until the mechanical switch opens. In comparison to the previously reported unidirectional TCCI-based HCB, the new bidirectional HCB adopts an H-bridge circuit of four low-voltage MOSFETs to conduct the commutation current in either direction. An additional current sensor is used to detect the direction of the load current and subsequently control the H-bridge. A 600V/20A bidirectional HCB prototype using a commercial vacuum relay as the mechanical switch is built and tested. The HCB experimentally demonstrates interruption of a fault current up to 148A within 570 µs.