Power circuit for induction heating

Abstract

A power circuit for use in billet heating, surface heat treating and melting and protective circuitry associated therewith. The power circuit generally comprises a source of potential in series with a pair of inductances and an inverter module. The inverter module has two sections each comprised of a thyristor in parallel with a diode. A pair of series connected charging capacitors are connected across the source of potential and a load is connected from between the capacitors to between the two sections of the inverter module. Current flows through one thyristor, through the load and charges the capacitors. The capacitors discharge and a reverse current flows through the load and through the corresponding diode. This cycle is repeated then with the opposite section of the inverter module. A commutation failure protection circuit is provided which detects the voltage collapse condition accompanying a short circuit through the inverter module and when this occurs, it acts to shut off the thyristors. An open load detect circuit is provided which senses the voltage build up which occurs when the load is open, and this circuit also acts to shut off the thyristors should this happen. The power circuit also has a peak power detect circuit which compares the phasing of the voltage and current and enables the circuit to maintain operation at maximum power by inhibiting any frequency increase when resonance operation is achieved.