A high power factor of a Class-D LLC resonant inverter for multi-coil induction hardening application

This paper presented a high power factor Class-D LLC resonant inverter for multi-coils induction hardening application. The main function of the Class-D resonant inverter is to provide high frequency AC from bridge rectifier and LC filter input voltage. The advantages of this technique, the power switched are operated under the zero voltage switching condition and the transformer leakage inductance the LLC resonant can be used. A prototype Class-D operating at a 102 kHz fixed frequency, 730 W maximum input power. Experimental results, induction hardening had a nearly unity power factor, total harmonic distortion of the input current THDi 6.5 %, it can be heat up 2 work pieces a same size diameter 9.5-mm from room temperature to 400 °C within about 1 minutes and 92% efficiency at full power and simulation result confirmed by experimental result.