A Cryogenically-Cooled GaN-Based Solid-State Circuit Breaker for Electrified Aircraft

Future electrified aircraft propulsion (EAP) requires solid-state circuit breaker (SSCB) to be: 1) extremely light, efficient, fast and reliable; 2) suitable for both longer-term higher voltage (>10 kV dc) or shorter-term lower voltage (1 to 2 kV dc) systems; 3) suitable for cryogenic cooling enabled by liquified natural gas or liquid hydrogen fuel; and 4) highly flexible, intelligent and easy for protection coordination. This article summarizes the research effort led by the University of Tennessee team of applying gallium nitride (GaN) devices to a cryogenically-cooled SSCB for EAP applications. With the careful device selection, characterization, packaging and system-level integration and control, the developed SSCB reached an extremely high efficiency ( $>99.96$ % in a 40kft altitude chamber with liquid nitrogen cooling), high density (>336 kW/kg for a 750V/100A rating per module), high scalability (able to be configured in the range of 1kV to 10kV and 100A to 1000A), and intelligent and coordinated fault protections, e.g., $10\times $ fault current interruption and i2t protection, polarity-sensitive and voltage-dependent fault detection, and current limiting functions.