High Current Medium Voltage Bidirectional Solid State Circuit Breaker using SiC JFET Super Cascode
Utkarsh Mehrotra, Bahji Ballard, Douglas C. Hopkins
Abstract
DC power systems found in electric transport, data centers and residential microgrid applications maintain a demand for fast, reliable and efficient power electronics in the Medium Voltage (MV) range. DC systems are inherently more sensitive to faults due to low system impedance and voltage sensitivity of accompanying power electronics creating a need for a fast all Solid State approach to system protection. This paper proposes a Bidirectional Solid State Circuit Breaker (BSSCB) utilizing the SuperCascode topology as the breaking element and has parallel transient energy absorption circuitry comprising of MOVs and snubbers to denergize the line upon fault. The paper discusses critical design points in breaker design, advantages of SuperCascode switch for breaker applications and power stage scaling calculations of the transient absorption circuitry. For packaging, a novel Epoxy Resin Composite Dielectric (ERCD) is considered as an alternative to metal-clad ceramic (DBC) substrate for higher reliability. The paper studies transient heat transfer in the power module using finite element analysis (FEA) and proposes a thermally defined and digitally controlled fuse curve for breakers. A design example of 10kV/100 A BSSCB is provided which holds 10x rated current for a 5ms dwell. A scaled-down 6kV/10A SSCB prototype using TO-247 packaged dies is demonstrated and is capable of withstanding 7x over-current for 1μs and short circuit interruption in approximately 60 ns.