Half-bridge series resonant inverter for induction heating applications with load-adaptive PFM control strategy

This paper presents an effective control scheme incorporated in a voltage-fed half-bridge series resonant inverter for induction heating applications, which is based upon a load-adaptive tuned frequency tracking control strategy using a PLL (phase locked loop) and its peripheral control circuit. The proposed control strategy ensures stable operation characteristics of the overall inverter system and ZVS (zero voltage switching) operation in spite of sensitive load parameters variations as well as power regulation, especially for nonmagnetic heating loads. The operating principle and the design procedure of the inverter system with the proposed control scheme are described. Also, simulation results and performance characteristics in the steady-state are shown as compared with experimental results for a prototype induction cooking system rated at 1.2 kW.