SiC MOSFET Solid-State Circuit Breaker-Based Motor Control Center: Design Analysis, Novel Soft Start, and Soft Turn-Off Strategies

Solid-state circuit breaker (SSCB) has been identified as a potential game-changing technology for dc distribution systems. However, fewer SSCB research and applications have been reported in ac due to direct competition with mechanical CB (MCB), which has a proven record as ac circuit protection device. The proposed three-phase SSCB integrates the application-specific functions of soft starters, contactors, CBs, and thermal relays commonly present in motor control centers (MCCs). This article primarily discusses the current protection, soft start, and contactor functions of the proposed SSCB. Key design considerations for a 380-VAC/63-A three-phase SSCB are introduced, covering semiconductor device, metal oxide varistor (MOV), snubber, and heatsink selections, as well as MOV lifetime analysis. The current fault protection of the SSCB is verified at 200 A. Furthermore, novel soft start and soft turn-off strategies are proposed. The turn-off time of both strategies is determined by a grid voltage phase-locked loop (PLL) angle instead of current sensors. Finally, both simulation and experimental results using open- and closed-loop soft start strategies validate a significant reduction in motor inrush current. In addition, experimental results confirm that employing the novel soft turn-off strategy extends the lifetime of the SSCB when used as a contactor, as it does not activate MOVs. By combining the contactor, CB, and soft starter functions into one, SSCB can offer competitive advantages in MCC applications.