Implementing Symmetrical Structure in MOV-RCD Snubber-Based DC Solid-State Circuit Breakers
Shuyan Zhao, Reza Kheirollahi, Yao Wang, Hua Zhang, Fei Lu
Abstract
This article deals with metal-oxide varistor (MOV) and resistor–capacitor–diode (RCD) snubber-based solid-state circuit breakers (SSCBs). There are two main contributions. First, a design methodology of MOV-RCD snubber parameters is proposed by considering thermal dissipation and snubber charging time for the first time. The thermal profile of the main conduction switches determines nominal current under passive cooling. Based on the nominal current, the fault current magnitude is derived, and a design method of key parameters of an MOV-RCD snubber is proposed. Four snubbers are designed with different fault currents and dc voltages. Second, symmetrical layouts with distributed parallel cells are proposed for high current capability, which enables scalability. Q3D simulations facilitate the evenly distributed stray inductances among paralleled branches. Both low- and medium-voltage SSCBs are implemented, ranging from 500 V/300 A to 2 kV/1 kA. The power density achieves 37.8 kW/L at 500 V/1 kA. Experiments demonstrate that the reverse voltage reaches 4.88 kV with an ultrafast interruption speed of 24 μs for 2 kV/1.144 kA fault current including the MOV conduction time interval.