Medium frequency combined inverter for electroheat with improved starting arrangements

Current-fed parallel inverters used for induction heating sometimes fail to start. Simulation and measurements show the importance of the turn-off angle during start up. An auxiliary voltage-fed inverter operated in parallel with the main current-fed inverter obviates the difficulty and provides reliable starting behaviour. On the basis of the results a new model of the thyristor frequency converter (1 60 kW 4.0 kHz) has been projected for industrial induction heating and melting applications.