Abstract
This article presents the cryogenically cooled application for wide bandgap (WBG) semiconductor devices. Characteristics of silicon carbide (SiC) and gallium nitride (GaN) at cryogenic temperatures are illustrated. SiC MOSFETs exhibit increased on-state resistance and slower switching speed at cryogenic temperatures. However, cryogenic cooling provides low ambient temperature environment and thus enables the SiC converter to operate at lower junction temperature to achieve higher efficiency compared to room temperature cooling. A cryogenically cooled MW-level SiC inverter prototype is developed and demonstrated the feasibility of operating high-power SiC converter with cryogenic cooling. GaN HEMTs exhibit more than five times on-state resistance reduction and faster switching speed at cryogenic temperatures which makes GaN HEMTs an excellent candidate for cryogenic power electronics applications. The significantly reduced on-state resistance of GaN devices provides the possibility to operate them at a current level much higher than rated current at cryogenic temperatures. A GaN double pulse test (DPT) circuit is constructed and demonstrated that GaN HEMTs can operate at nearly four times of rated current at cryogenic temperatures. Challenges of utilizing WBG device with cryogenic cooling are discussed and summarized.
Highlights
wide bandgap (WBG) semiconductor devices, including silicon carbide (SiC) and gallium nitride (GaN), are attracting increasing attention due to their low specific onstate resistance, high-speed switching and high breakdown voltage
In some applications such as electric aircraft propulsion systems or other superconducting machine systems where cryogenic cooling is provided, it would be beneficial to the system if the power electronics can be integrated into the cryogenic cooled system
Cryogenic cooling may benefit general power electronics applications because it offers numerous benefits, including 1) several power semiconductor devices, such as Si and GaN, have improved performance at low temperature, with decreased specific on-state resistance and increased switching speed; 2) power semiconductor devices can be operated at higher switching frequencies and reducing the weight and size of passive components at cryogenic temperature; 3) less cooling requirement due to low ambient temperature provided by cryogenic cooling; 4) light and/or efficient conductors such as busbar and inductor winding components due to low resistivity of copper/aluminum at low temperature
Summary
WBG semiconductor devices, including SiC and GaN, are attracting increasing attention due to their low specific onstate resistance, high-speed switching and high breakdown voltage. CHEN AND WANG: SIC AND GAN DEVICES WITH CRYOGENIC COOLING decreases due to the increase of carrier mobility. A 1 MW cryogenically cooled SiC power module based three-level inverter for electric aircraft propulsion applications is presented by the authors [25]. Both Si MOSFET and GaN HEMT show significantly reduced specific on-state resistance at cryogenic temperatures. At very low temperature (< 100 K), the specific on-state-resistance of Si MOSFETs begin to increase due to carrier freeze out but that of GaN HEMT keeps decreasing. DEMONSTRATION OF MW-LEVEL SIC CONVERTER OPERATION WITH CRYOGENIC COOLING This section presents a MW-level SiC power module based inverter using cryogenic cooling for electric aircraft propulsion applications. Transient analysis, harmonics analysis, busbar design, and filter design of paralleled 3L-ANPC inverters can be referred in [26]–[32]
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