A Hybird Switching Modulation Method of Series Resonant Inverters to Reduce Operating Frequency Variations for Induction Heating

Induction heating (IH) is widely used in home appliances and industry applications due to its eco-friendly energy consumption, fast heating speed, and high efficiency via a direct heating mechanism. Series-resonant inverters are widely used in IH applications, and output power is typically controlled via pulse frequency modulation (PFM). PFM exhibits the advantage in which zero-voltage switching can be achieved by operating in the inductive region. However, a high switching frequency causes large switching losses under light load conditions. In addition, this wide operating frequency range may induce interference audible noises that can be generated by operating with multiple coils. In this study, a hybrid switching modulation method that combines PFM with phase shift modulation in a full-bridge series-resonant inverter is proposed. It allows IH inverters to operate at a relatively low switching frequency even under extremely light load conditions. The proposed method can obtain a narrow switching frequency range and suppress interference audible noise. The feasibility of the proposed method is verified through a 3.3 kW series resonant IH inverter system prototype.