Heating method for ferromagnetic metal by power factor control

This paper presents a novel heating method for ferromagnetic metal and the power supply for induction heating. It is known that ferromagnetic metals are heated more easily than paramagnetic metals. However, when ferromagnetic metals are heated more than Curie temperature, their physical properties become the same as paramagnetic metals. In other words, a power supply may be destroyed because a soft switching cannot be maintained. Therefore the power supply and control method are newly proposed. This power supply always achieves a soft switching although metals are heated from low temperature to high temperature. In this power supply, not frequency control but power factor control is applied as new control method. A power factor is controlled with Pulse Width Modulation. It is realized with the simple circuit composition which is connecting one auxiliary switch and one capacitor to full bridge inverter.