Ching-Hsiang Yang

This letter proposes an indirect power detection based short-circuit protection (SCP) method for gallium nitride high-electron-mobility transistors (GaN HEMTs). The proposed method requires sensing only v_ds of a GaN HEMT, similar to the widely used desaturation protection method. However, unlike desaturation protection, the proposed method directly monitors v_ds after a predefined delay without a diode, enabling faster short circuit detection and improved noise immunity. Experimental results show that the short-circuit detection time is significantly shorter than that of the desaturation protection. In addition, the proposed method is evaluated over a wide temperature range, from room temperature to cryogenic temperatures, verifying its effectiveness for GaN HEMTs in cryogenic applications.

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.

As a crucial component of the direct current (DC) electrified aircraft propulsion (EAP) systems, the DC solid-state circuit breaker (DC-SSCB) has been extensively studied at the breaker level, including topology, energy absorption circuit, gate driver, and control. However, system-level considerations are also crucial but have received limited attention. This paper presents a comprehensive solution with integrated circuitries functioning as fault detectors, actuators for regulating semiconductor operating status, and coordinated control to seamlessly transition between modes (e.g., the normal mode, precaution mode, i2t mode, and instantaneous trip mode). This design enables the developed SSCB to limit system fault currents within the short-circuit current rating (SCCR) and respond appropriately to various fault scenarios. First, two improved fault detection circuits are introduced to enhance SSCB applications. Second, four operation modes are proposed to achieve optimal system functionality. Third, leveraging these four operation modes, a control strategy is demonstrated to execute different actions based on the fault scenarios. Finally, the feasibility and effectiveness of the proposed comprehensive SSCB are validated through experimental results.

Solid-state circuit breaker (SSCB) with high efficiency and high gravimetric power density is required for electrified aircraft propulsion (EAP). A cryogenically cooled gallium nitride (GaN) device-based SSCB module is developed for the EAP system to achieve a higher power density than existing SSCBs. The SSCB module is suitable for medium voltage direct current (MVdc) applications and is designed with low-weight modular cold plates. Each module is rated for 750 V, 100 A, and can interrupt a fault current of 1 kA at cryogenic temperature. The SSCB module structure design, thermal interface design, modular cold plate design, and insulation design are discussed. The developed SSCB module prototype achieves a power density of 329 kW/kg and an efficiency of 99.93%. Experimental results of interrupting a fault of 1 kA and insulation test of the SSCB module are provided to validate its operation.