Novel power supply for induction heating with power factor control using phase shift

An induction heating is used in various fields because it has many merits. Especially ferromagnetic metals are efficiently heated. However, when these metals are heated more than Curie temperature, they are transmuted into paramagnetic ones. Simultaneously, an induction heating load is changed suddenly. If an operation of power supply is not controlled securely, power supply is broken down. Though highly precise resonant frequency tracking control is applied generally to prevent a power supply failure, the heating piece is also changed by changing the penetration depth. Therefore, the new heating control method is proposed for the purpose of heating a ferromagnetic metal efficiently. In this method, a power factor is controlled at constant frequency by phase shift control instead of PFM (Pulse Frequency Modulation) to maintain a soft switching. In this paper, it is proved that the proposed control method is useful to heat a ferromagnetic metal.