Phase Angle Control of High-Frequency Resonant Currents in a Multiple Inverter System for Zone-Control Induction Heating

This paper presents a phase angle control method of high-frequency resonant currents in a zone-control induction heating (ZCIH) system, which consists of split working coils and multiple inverters. The ZCIH system controls the amplitude of each coil current to make the temperature distribution on the workpiece uniform. The amplitude of the coil current can be controlled in a wide range when its phase angle is adjusted to be the same with other coil currents. This paper theoretically derives the phase-angle change of the coil current in transient states, and reveals that the phase-angle change can be considered as a first-order response. A phase-angle controller was designed and examined in experiments using a two-zone ZCIH system. It is clarified that the phase angle control makes it possible to adjust the current phase angle not only in steady states but also in transient states.