ABSTRACT

Rapid Fault Isolation (RFI) in legacy and/or emerging AC and DC power systems has emerged as an extremely important issue from the reliability, stability, power quality, and capacity utilization viewpoints. This project seeks to develop a silicon-carbide based optically-activated gate-turn-off thyristor (SiC OA-GTO) that is expected to be a game changer in RFI, with clear device and system level benefits based on radically new innovations. The SiC OA-GTO will also have clear benefits for several major applications including pulsed-power systems, transfer switches, high-voltage power electronic converters for medium-voltage drives, energy storage, step-up-transformerless integration of solar and wind energy, and flexible AC transmission systems (FACTS), to name a few. This National Science Foundation (NSF) project will provide graduate- and undergraduate-level research and education opportunities, including a significant representation of minority and cross-disciplinary students. Guidance will be provided to one middle-school student each summer. The results of the research will be integrated into the course ECE 442 (Power semiconductor devices and integrated circuits). The PI will leverage his demonstrated mechanisms of research dissemination (for his ongoing and prior NSF projects) to support this NSF project.

The technical objectives of this project are as follows: 1) To synthesize a high-gain monolithic SiC based optically-activated (OA) gate-turn-off thyristor (i.e., SiC OA-GTO) for realization of a Rapid Fault Isolation Device (RFID) (i.e., SiC OA-RFID). The SiC OA-RFID is expected to support high breakdown voltage, high rated and surge currents, high slew rate, low on-state forward drop, high junction temperature, and operation using low average optical triggering power; 2) To design an optimal photonic package for the SiC OA-GTO and then using it realize a SiC OA-RFID to address reduced parasitic inductance given the presence of large di/dt, thermal robustness, and uniform and efficient triggering and mitigation of current filamentation by optimal beam localization; and 3) Experimental I-V and switching characterizations of the fabricated prototype device at package levels for performance validations. The SiC OA-GTO device for the OA-RFID incorporates several key features: a) a monolithic SiC device structure that mitigates parasitic inductances yielding high di/dt; b) rapid turn-on and turn-off due to novel optical excitation and unity-gain turn off; c) very low optical power requirement due to thyristor action and conductivity modulation; d) low forward drop; e) seamless voltage and current scaling; f) high-voltage blocking and current conduction; g) high thermal conductivity; h) novel optical triggering that simplifies switching; and i) no dependence on oxide layer. The new optical single-bias device, unlike leading high voltage Si and SiC based devices yields immunity against noise, enhanced reliability, and reduced delay due to direct photogeneration. Additionally, optical triggering eliminates complexity associated with negative gate referencing. The optical device enhances isolation between the SiC OA-GTO power stage and the low-voltage control stage. Photonic modulation of the device enables dynamic control of device dynamics of the SiC OA-GTO yielding reduced delay and improved on-state and off-state characteristics.

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