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This paper deal 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 tunedcontroller 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 induction heated treatment plant is implemented in order to btain the various basic design data relating to switching Characteristics of large capacity SlTs incorporated into the bridge arms of this inverter circuit with design of the costeffective protective circuits of SITS with their optimum snubber circuits for high-power SIT switching-legs.

Thispaper describes the schematicreview o f Travelling-wave type Ultrasonic Motor (T-USM) and a newly-proposed weigt-quality speed tracking controller of T-USM on the basics o f the computer software-based varia ble-gain adjustm en t stra tegy.Its speed tracking characteristics capable o f improving speed ripple, speed regulation and speed tracking characteristics are feasibly demonstrated i n experiment as compared with a previously-developed fuzzy-logic speed controller of T-USM actuated servo drive system. I t is proved that T-USMspeed control scheme developed herein i s practically acceptable for direct-drivespeed servo system.

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Buck-Type high-power-factor PWM active converter topology is not only sufficiently capable of the effective elimination of input current harmonics, but also its characteristics include high efficiency, absence of inrush current, the capability to obtain low DC output voltage, ability to protect against short circuit, and so force. The buck-type high-power-factor converter has the inherent capability to become attractive power supplies for telecommunications energy systems. On the other hand, because this type of converter must employ high-inductance reactors, these tend to increase equipment in size and weight, and this has prevented their widespread use.This paper presents a new control strategy for Buck-type high-power-factor PWM converter which can reduce the size and weight of reactor and also eliminate the ripple component included into output voltage. The operating principle and simulation results are described.