Characteristics of quasi variable capacitors for induction heating

In this study, the diesel emission control system using induction heating is proposed as a method of reducing toxic substances included in exhaust gas. When the trapping filter of that system is heated by induction heating, ferromagnetic metals are suitable for that filter. However, they are transmuted to paramagnetic metals at high temperature more than Curie temperature. Therefore, automatic resonance tracking control is required to prevent breakdown of power supply because the equivalent circuit parameters of induction heating are rapidly changed at this temperature. Generally, although resonant frequency is tracked by PFM (Pulse Frequency Modulation), it is desirable to operate at constant frequency because the heating piece is changed in accordance with an operating frequency. Accordingly, we have proposed the quasi variable capacitor to maintain a resonance. This paper presents a comparison of the behavior of the proposed quasi variable capacitors. An analytical study of the proposed quasi variable capacitor is performed, and the main results are shown. The results derived from this analysis and the feasibility are verified through experimental prototype.