Characterization and Application of GaN-HEMTs at Cryogenic Temperatures

• Applicant: Professor Dr.-Ing. Marc Hiller
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546257378

This project aims to investigate the suitability of GaN HEMTs for applications in which the power semiconductors are operated at temperatures far below the usual temperature range. These applications are characterized by the combination of superconducting technologies and power electronics, e.g. in a drive system for electric airplanes, in superconducting wind generators or systems for energy transmission and distribution. Previous work has shown that GaN HEMTs are characterized by an extremely low on-resistance at cryogenic temperatures. In addition, reduced switching losses have also been shown. These advantageous properties can be exploited if, for example, the vaporization energy of liquid nitrogen is used in applications with high-temperature superconductors to cool the power semiconductors. This allows the power semiconductors to be operated in a temperature range that is far below the usual operating temperatures. As a result, the efficiency of the energy conversion can be significantly improved. This is particularly true when GaN HEMTs are used to construct a solid state transformer in which the galvanically isolating transformer can simultaneously act as a thermal insulator between the cold and hot parts of the system. The heat transfer to the cold part can thus be significantly reduced, which in consideration of the poor thermodynamic efficiency of cooling units means a significant reduction in losses. In order to design and operate such circuits, a suitable model of the GaN devices is required. For this purpose, the switching and conduction behavior of various GaN devices must be characterized by measurement in the complete temperature range. This characterization includes in particular the investigation of trapping effects and the resulting dynamic on-resistance. In the proposed project, suitable test setups will be designed and set up to characterize the devices. Reference measurements in the usual temperature range will also be carried out for comparison purposes. These detailed measurements of the behavior of the GaN devices at low temperatures, including the dynamic transfer and output characteristics, are not yet known from the literature. Based on these results, it will be investigated how the overall efficiency of a power electronic circuit is affected by operation at low temperatures compared to normal operating temperatures. Particular attention will be paid to the influence of the dynamic on-resistance. In addition, investigations in a specific application enable the validation of the newly developed loss models.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2312: Energy Efficient Power Electronics "GaNius"