This paper proposes a thyristor-based hybrid DC circuit breaker (HDCCB), which is composed of a fast mechanical circuit breaker and an LC resonant
circuit with thyristor switches. The proposed HDCCB provides a zero-crossing point of fault current by injecting a resonant current to the reverse
direction of the fault current. The proposed HDCCB has a low conduction loss in normal operation by using the mechanical circuit breaker and it
offers advantages of low cost, high reliability, and large capacity by using thyristor switches instead of IGBT switches. It also has a design flexibility to
adjust the magnitude of injection current depending on the fault current level. A bidirectional HDCCB is also proposed by adding several components
to the developed unidirectional HDCCB, which can offer compact system size and low system cost. The design considerations are discussed. The
validity of the proposed HDCCB is verified by simulation results and experimental results.