Three-leg inverter configuration for simultaneous dual-frequency induction hardening with independent control

Parts of certain objects need hardening. Hardening is a heat treatment process which can be achieved by induction heating. Certain objects like gears require alternating source with two different frequencies. Simultaneous application of dual frequencies is desirable for proper hardening of a gear. This study proposes a three-leg inverter topology with a load resonant circuit which can provide independent and simultaneous control of low-frequency (LF) and high-frequency (HF) currents through the load coil. The load circuit is a combination of two series resonant circuits which operates at the desired LF and HF. Power control is achieved with phase modulation and asymmetric duty cycle control techniques. A 240 W prototype of the proposed dual-frequency inverter is implemented and tested. Experimental results obtained are in good agreement with the simulation results.