Series resonant frequency tracking-based high-frequency inverter using static induction power transistors for electromagnetic industrial induction metal surface heating and feasible evaluations

This paper describes the advanced developments of the voltage-fed series load resonant high-frequency high-power inverter using static induction transistors (SITs) for industrial induction-heating and melting power supply. The load-adaptive variable frequency tuned-controller using PLL, the AC/DC converter for PAM, and protective control schemes are described from a practical viewpoint. In particular, the practical short circuit test of this SIT inverter developed for induction heat treatments are demonstrated to obtain the various basic data relating to switching characteristics of large capacity SITs incorporated into this inverter circuit and to design the cost-effective protective circuits of SITs and their optimum snubber circuits for SIT switching-legs