Bidirectional Solid-State Circuit Breaker using Super Cascode for MV SST and Energy Storage Systems

Solid State Transformers (SSTs) are developing as highly efficient interfaces in renewable energy, transport, and energy storage systems. However, performance limitations, such as overvoltage sensitivity and fault handling capabilities, have slowed widespread adoption. Though SSTs are developing added capabilities for fault management, the required response speed and overdesign introduces added costs, particularly in protection of in ultra-low inductance systems, such as those sourced by energy storage systems (ESSs). With increased use of power electronics, the power distribution systems are speeding up having shorter fault propagation delays and higher fault currents. This creates a need for alternative approaches to MV system protection. This paper describes a Bidirectional Solid-State Circuit Breaker (BSSCB) based on a new SiC SuperCascode power switch, and a multi-layered transient absorption network. The paper studies transient heat transfer in the switch and provides a redefinition of the fuse curve as applied to the BSSCB suitable for digital control. The paper identifies critical fault issues, discusses the impact on critical design points of the SuperCascode for a BSSCB, and provides design calculations for a complete 10kV/300A/3X breaker, including the SuperCascode module. A scaled 6kV/10A/7X SuperCascode is fabricated and tested to demonstrate switch response of <60 ns with fault isolation in 200ns.