Adjustable High Frequency Quasi-Resonant Inverter for Induction Heating

Abstract

This paper presents the considerations of driving the Adjustable Frequency Quasi- Resonant Inverter Circuit in the high frequency. This inverter is requested to output frequency from 160kHz to 400kHz. Resonant inverter used for metalworking by the induction heating. In induction heating, high frequency can heat the shallow point, and low frequency can heat the deep point. So when heated depth is replaced, the frequency that inverter must output is different. It is necessary for the inverter to output two or more frequencies. In addition, in the heat-treatment called the hardening, only the metal surface must be heated. So, to heat-treat metal that a radius is small, it is necessary for the inverter to output high frequency. This inverter can output the frequency more than 100kHz by using Power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) as power device. The circuit includes the first resonant capacitor and second one with a one-way short-circuit switch. Because synthetic series capacitance is varied by manipulating the switch, this inverter can change a period during a half period. We confirmed this inverter can output an arbitrary frequency by the experiment.