A nearly unity power factor isolated Class-D resonant inverter for series multi-coil induction hardening

This paper presented a nearly unity power factor isolated Class-D resonant inverter for series multi-coil induction hardening. The main switch are operated under the zero voltage switching condition and used leakage inductance and magnetite inductance of high frequency transformer apply to LLC resonant tank. A prototype was Class-D resonant operating 102-110 kHz variable frequency, when as heat up is 1 coil and heat up are 2 coil 800 and 730 W maximum input power. Experimental results, in a heat up each coil induction hardening had a nearly unity power factor, it can be heat up work pieces a size diameter 9.5-mm from room temperature to 400 oC within time about 50 second, 1 minutes and 94%, 92% efficiency at maximum full power.