Abstract: An induction heating system having at least one power supply switching network is disclosed to provide selective power control to multiple zones of an induction heating coil to achieve a desired heat distribution in a workpiece. The power supply switching network includes a number of bidirectional switches, each connected in series with one another, and each connected in parallel with a portion, or zone, of an induction heating coil. The bidirectional switches are controlled by a computer that supplies a control signal having a duty cycle as determined by the computer and a multi-zone feedback circuit. By splitting the coils and inserting a switch in parallel with each coil, and each switch in series with one another, the coil is effectively split into multiple series connected coils, thereby being more effectively controllable while avoiding physical alterations to the heating coil.

Abstract: A solid state radio frequency high power generator for induction heating applications uses MOSFET devices controlled at radio frequency by a current loop which is automatically corrected against the possible occurrence of a leading phase shift by a voltage-current phase shift detection loop which responds to digital signals corrected against inherent time delays.

Abstract: A high frequency current-fed inverter of the series/parallel compensated type is started directly with the main thyristors of the inverter by charging the series capacitor through the input inductor of the DC supply during a first time interval with one pole, by discharging the same during a second time interval with the other pole, then passing to free-running operation at an initial frequency from which load operation can begin. The first and second time intervals are established while a constant DC voltage is being applied so that commutation of the outgoing thyristor is insured. DC voltage regulation is eliminated as soon as the free-running operation has been initiated.