Dynamic performance of a current-phase control method for zone-control induction heating systems

This paper presents a phase angle control method of coil currents in a zone-control induction heating (ZCIH) system, which has split working coils on a work piece. The ZCIH system controls the amplitude of each coil current to make the temperature distribution on the work piece uniform. The coil currents should be adjusted to be in phase with each other to control the current amplitude in a wide range from 0 to 100%. This paper 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 with a two-zone ZCIH system, making it possible to adjust the current phase angle not only in steady states but also in transient states.