A New Hybrid Power Control Technique for Induction Vessel Heating System

Recently, phase shifted control (PSC) and pulse density modulation control (PDM) have evolved as the most versatile schemes to control and regulate the output power for inverter based Induction Heating Systems. However, individually each one of these methods do not satisfy the requirement of wide power control range typically needed for vessel heating applications. This paper proposes a new hybrid power regulation and control technique for the IGBT/MOSFET based series resonant inverter for the induction vessel heating, combining both PSC and PDM. The inverter frequency is varied over a limited range to ensure the soft-switching ZVS mode of the inverter. The proposed scheme uses the PDM for coarse adjustment of power for heating vessels of different size and shapes with the same system without changing the hardware settings. The PSC is used for fine power control and regulation during the heating cycle to sustain the variation in load Q factor. The hardware implementation of the new scheme is discussed briefly. The qualitative performance is investigated through computer simulation. An experimental prototype to validate the system performance is build and successfully tested in an industrial environment over the entire load range and with induction coils for different vessels.