A high efficiency of a Class-D resonant inverter high power factor for induction heating multi-coils hardening application

This paper presented a high efficiency Class-D resonant inverter high power factor for induction heating multi-coils 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 leakage inductance of transformer can be used the LLC resonant. A prototype Class-D operating at a 102 kHz fixed frequency, 730 W maximum input power. Experimental results, induction hardening had a near unity power factor, total harmonic distortion of the input current THD_i 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.