Inverter Configuration for Simultaneous Dual Frequency Induction Hardening with Independent Control

Induction hardening is a heat treatment process which selectively heats parts of work-piece with different size and shape. Components like gears require different frequencies with inner core requiring low frequency and outer surface requiring high frequency. Simultaneous application of low and high frequency currents is desirable for proper hardening of gear This paper proposes a two inverter topology with a load resonant circuit which can provide independent and simultaneous control of low and high frequency currents through the load coil. The load circuit is a combination of two series resonant circuits which operates at the desired low and high frequencies. Power control is achieved with phase modulation of low and high frequency inverters.