Design and analysis of hybrid DC circuit breaker for LVDC grid systems

The emerging interconnections of renewable energy sources that generate DC power have resulted in demands on DC grid systems. In this situation, a low-voltage DC (LVDC) grid system could be a solution for these DC power sources. For the reliable operation of a LVDC grid, DC faults are an issue and DC circuit breakers (DC CBs) are appropriate devices to clear fault current. However, there are some difficulties in terms of breaking DC faults such as the absence of zero crossing of the current and voltage, and the high di/dt of the fault current. This paper proposes a hybrid circuit breaker (HCB) with a new structure for a LVDC grid system. The main switch consists of a vacuum interrupter (VI) and a permanent magnetic actuator (PMA). Some improvements are proposed to enhance the performance of the PMA. A bi-directional commutation loop consisting of a minimum number of power electronic devices is suggested. To absorb fault energy, a capacitor and a diode loop are applied. The principle of the proposed HCB and the design methods for all of the components are analyzed. Through a simulation model, the designed components are selected and verified. Experimental results with a realized prototype (750 V/300A) verify the design method and its performance.