Operation of power electronic converters at cryogenic temperatures for utility energy conditioning applications

The operation of power MOSFET devices at cryogenic temperatures has been shown to offer potential advantages in large conversion systems, due primarily to a major drop in on-resistance. This paper investigates the use of high frequency switch mode power electronics converters based on available commercial devices operating at cryogenic temperatures, particularly in relation to electricity supply applications. Efficiency, transient response and power density are all important characteristics which show potential improvement over state of the art room temperature implementations. These characteristics are discussed in relation to both simulation and experimental measurements of a half bridge inverter configuration, and the initial results from tests on an experimental 50 kW three phase inverter are reported. A comparison is made between the circuit performance predicted using standard power electronics simulation tools, applied to modelling switching characteristics at 77 K, and results derived from measured values. The simulations show general full cycle waveform agreement with the experimental model, but there is considerable discrepancy when focusing on the switch transitions. This can result in an inaccurate estimate of overall converter switching power loss which must be accurately defined, since it is the dominant loss mechanism at cryogenic temperatures. Application areas where cryogenic power electronic converter systems may be used in the future are identified, and where, in combination with high temperature superconductor (HTS) power systems equipment, synergistic benefits may result.