MOSFET Inverter Type High - Frequency Power Supply

Induction heating is a typical application field for high-frequency power supplies whose operating frequencies range from one to several hundred kilohertz. Induction heating applies an alternating magnetic field generated from the current flow in a coil to the conductive matter to be heated. This induces eddy currents on the conductive matter, those currents generate joule loss due to the matter’s resistance and thus cause the matter to be heated. Steel sheet heating, hardening, and seam welding are some examples of the industrial applications of induction heating, and still now, there is much demand for the highfrequency power supplies used in these examples. In the past, vacuum tube oscillators were used for the high-frequency power supplies from one to several hundreds of kilohertz. In recent years, with the emergence of inverters using MOSFET (metal-oxidesemiconductor field effect transistor) devices suitable for high-speed switching, the volume of power supplies has been reduced to about 1/4, resulting in space savings. Also, efficiency has significantly increased to 96 % (during rated operation) from about 75 % previously, resulting in enhanced energy savings and productivity. Fuji Electric has previously commercialized flatpackaged 500 V, 240 A MOSFETs and high-frequency power supplies using 20 to 100 kW stacks which incorporated those MOSFETs. This paper will report the newly developed and commercialized flat-packaged large-power 500 V, 500 A MOSFET and the 125 kW stack containing those MOSFETs, both of which were applied to a 1,000 kW, 150 kHz high-frequency power supply for steel sheet heating in a steel production process. In addition, recent seam welding power supplies, application of high-frequency power supply for plasma heating, and surface treatment for metalizing film using high-frequency discharge, will also be introduced. 2. 1,000 kW, 150 kHz High-Frequency Power Supply