電力用半導体素子の極低温特性と極低温動作電力変換器の構成

Abstract

In large superconducting coil applied systems, such as Superconducting Magnetic Energy Storage (SMES), nuclear fusion system and so on, large current leads for charging and discharging coils are needed, so that conduction heat through the leads may cause large heat losses and reduce efficiency of the system. Operating of a power supply (power converter) for a superconducting coil in the same cryostat together with the coil and converting the low voltage and high current power into high voltage and low current power in the cryostat, it will become possible to reduce the size of current leads and power losses of a power supply. Among existing power semiconductor devices such as thyristors and power transistors, power MOSFETs showed lower losses in low temperature region; they showed the minimum on-resistance value at around 70K. Utilizing this characteristic, a power converter using power MOSFETs and diodes was made and operated in a cryostat together with a superconducting coil. As a result, it was confirmed that the stable operation of a power converter in a cryostat is possible and that the size of current leads into a cryostat and power losses of a converter can be reduced.