Hybrid Modulation Technique of Series Resonant Inverter for Induction Heating Applications to Reduce Audible Noises and Switching Losses

Induction Heating (IH) is widely used in home and industrial applications due to its eco-friendly energy saving, high efficiency, and fast heating performance by direct heating mechanism. Series resonant inverters are generally used in the IH system to supply high-frequency electric power to an IH coil. The output power of the IH system is usually controlled by the variation of the operation frequency, which is called Pulse Frequency Modulation (PFM). It has the advantages of wider Zero Voltage Switching (ZVS) region and easier power control capability than other modulation techniques. However, in low-load conditions, high operating frequency is required to reduce the voltage gain of the IH system, which causes significant switching losses. In addition, multi-coil operations can induce audible noises due to operating frequency interference among the multiple IH coils. In this paper, hybrid modulation techniques are proposed, which combine PFM and Phase Shift Modulation (PSM), and PFM and Asymmetric Pulse Width Modulation (APWM) in the full-bridge and the half-bridge series resonant inverters, respectively. The proposed techniques reduce the operating frequency range, which can mitigate switching losses and avoid operating frequency interference in multiple IH coils. Finally, the proposed methods can improve efficiency and avoid audible noises in the IH system. The feasibility of the proposed methods is experimentally verified by 3.3 kW full-bridge and 2.0 kW half-bridge IH system prototypes.