Phase-lock loop operated load-resonance inverter using static induction power transistors and its practical characteristic evaluations

This paper deals with the advanced feasible development technology of the voltage-fed type series load-resonant high-frequency high-power inverter circuit using static induction transistors (SITs) for industrial induction-heating and melting power supply system. The load-adaptive variable frequency tuned-controller using PLL-IC, the DC power regulator of phase controlled AC/DC thyristor converter, and inverter protective control schemes for overvoltage and/or overcurrent generation are demonstrated from a practical viewpoint. In particular, the practically shorted circuit test of this SIT inverter developed for an induction heated treatment plant is implemented in order to obtain the various basic design data relating to switching characteristics of large capacity SITs incorporated into the bridge arms of this inverter circuit, with design of the cost-effective protective circuits of SITs with their optimum snubber circuits for high-power SIT switching-legs