Power control of an adjustable frequency quasi-resonant inverter for dual frequency induction heating

When such an uneven workpiece as a gear is hardened by induction heating, it is desirable that the workpiece is heated at both a higher frequency and a lower frequency. Thus, we report a novel adjustable frequency quasi-resonant inverter and alternative dual frequency induction heating which becomes possible. The heat-treated depth depends on not only output frequency of the inverter but also supplied power to the work. Therefore, we propose a new power control method of the reported inverter. The resistor of the circuit is divided into an equivalent loss resistor and an equivalent output resistor where the equivalent output resistance varies in accordance with the supplied current. The input DC voltage of the inverter is manipulated so that the calculated output power may be equal to the desired variable after the output frequency was controlled to the desired variable.