Yuzhou Yao received the B.S. degree from University of Plymouth, Plymouth, United Kingdom, in June 2019. He is currently working towards the Ph.D. degree in electrical and computer engineering at the Ohio State University. His current research interests are mainly on high power density converter design.
NASA’s Watts on the Moon Challenge is seeking solutions to transfer at least 1.065 kW power from a 120 V dc source to a 24-32 V dc load over 3 km distance under the same environmental conditions as the Lunar surface (i.e., 77 K temperature and 1 mTorr pressure). The selected solution from the author’s team proposed utilizing two modular multilevel GaN based isolated dc-dc converters to connect the 120 V dc source with the 24-32 V dc load bank via 1.5 kV rated dc transmission lines. The modular multilevel converters feature frequency multiplication, high step-down voltage ratio and low device voltage stress. In the converters, GaN GIT and GaN HEMT devices are chosen as switching devices, due to the merits of lower power loss, radiation hardness and ability to work under cryogenic temperature. In addition, LiFePO4 battery based energy storage with power condition system is added in parallel with the load to provide uninterrupted power. Active heating units and passive multi-layer insulation are designed to manage the proper operation of the battery under cryogenic and vacuum conditions. Furthermore, the hardware design for the power converters has been validated at 1.5 kV/1.5 kW condition. The operation of submodules in the developed converter has been demonstrated at 77 K temperature and less than 10-6 Torr pressure. The efficiency of the designed converter can achieve 97.42%. In total, the proposed power conversion and transmission system has a mass of 98.7 kg, which is significantly lower than 150 kg limit from the competition.
This paper is mainly about the power conversion and transmission system design for the lunar surface. The total mass of the system can be less than 100 kg, and the Modular Multilevel GaN Based dcdc converter can achieve 97.42% efficiency, The system has the ability to work at cryogenic and vacuum.
