Immediately after the Hanshin-Awaji earthquake, the areas affected by the outage of electric power represent about 2.6 million customers, we began to restore in no time, and the temporary restoration works were completed by just over six days after the earthquake hit.

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Active power filtering converter with discontinuous control scheme has already got widespread use for the application of single phase power source because this control scheme has large practical advantage, that is to say, it is very simple and cost-effective. But it has not been adopted practically for the application of three phase power source because the characteristics of this control scheme have some disadvantages for three phase main. We proposed a new circuit configuration with discontinuous control scheme which is suitable for three phase mains. This paper presents operation mode of the proposed topology and describes simulation results.

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The active PFCM ( Power Factor Correction Module), which is boosted type regulator, intended to apply on home- use inverter air conditioner for European market has been developed. This module has achieved the 1.5kW maximum output and the power factor of more than 99% at rated input. The performance meet the standard of IEC 1000-3-2 (specified on Power Line Harmonics) effective from 1996 and we may self-express “CE Declaration” on Sharp's air conditioner.

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The circulating current type cycloconverters have been applied to large capacity motor drive systems. A coupling of load current exists in the circulating current control loop, and deteriorates the control performance. In this paper, the circulating current control using rotational reference frame is proposed to suppress the coupling. The frequency of the fundamental component of the coupling is twice that of load. In addition, the circulating current is usually regulated to a constant do current. Authors have, therefore, applied the rotational reference frame synchronized with twice frequency of load to the circulating current control for a three-phase cycloconverter. The main component of the coupling can be compensated by the feedback control without the decoupling control. The effect of the proposed control scheme is confirmed by the digital simulation of an induction motor drive system.

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The next generation arc welding power source needs higher quality of welding. The present power source has only one output characteristic, but one characteristic is not always best becouse arc condition changes rapidly from arc to short. Therefore the arc welding power source that is able to change the output characteristic according to arc condition is required to achieve high quality welding. The other side, easy operation for arc welding power source is requested. So the arc welding power source that can improve welding quality by means of adjusting arc condition automaticaly with fuzzy logic and having programmable output characteristic is developed.

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Recent years have seen a spread of polyethylene pipe for gas and sewer. Several methods have been developed for joining of polyethylene pipe.
This paper presents an advanced method of polyethylene pipe joining system, which uses resonant inverter and special heater. This method, which combined the principles of Skin Effect, Curie Temperature and Resistance Heating, made it possible to make heaters that would self-regulate at a precise, designed temperature without the use of thermostats.

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An improved soft-switching PWM DC-DC converter operating under both low switching losses and low conduction losses is presented. The converter employs saturable reactors, which greatly help to achieve soft-switching with a low commutating current. The principle of operation and its steady-state analysis are illustrated. To demonstrate the effectiveness of the characteristic performances, key experiments are carried out with a 150W, 200kHz prototype converter.

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This paper presents two types of resonant DC link topology with synchronized PWM sheme, which are more suitable for voltage-fed inverter and converter using IGBT modules. The operation principles of two types of resonant DC link circuits are described including theoretical analysis. The circuit design concept of these resonant DC link are illustrated and simulating results are discussed in this paper.

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The soft-switching PWM converters are more attractive in the switched-mode power supplies and their related power application systems because their PWM converters have remarkable advantages such as lowered switching losses, reduced dynamic electrical stresses, constant frequency operation, simple control scheme and reduced EMI noise.
However, most of soft-switched quasi-resonant PWM converters developed so far including some inherent difficulties which have to be solved such as reduced power conversion efficiency due to significant circulating current generation. Further more, Zero Voltage Switching condition is more severely under the influence of circulating current.
To solve these problems, the authers propose a novel high-frequency transformer link soft-switching PWM DC-DC converter using active switches in rectifier circuit. This paper presents its operating principle and unique features as compared with the conventional soft-switching DC-DC converter. All switching devices in proposed DC-DC converter can be achieved soft-switching operation. Proposed DC-DC converter operation is illustrated and discussed by means of simulating results.

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The inverter-fed vector controlled induction motor with a speed sensor has been used in many industrial applications as actuating motors of variable speed servo-systems.
In this paper, many speed sensorless methods which determine the rotating speed of these induction motors by using the motor parameters, the instantaneous values of phase voltages and or phase currents sensing are collected. And the point at issue of the each sensorless systems are summarized put in order.

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Recently, silicon carbide (SiC) single crystal in the diameter of 3 inches have been developed and micropipes have been reduced to 3/cm² using the vaccum sublimation method. SiC JFET, MESFET and other devices operable at higher temperatures and higher power more than silicon devices have been realized in the research stage.
We report a feature of silicon cabide, the present state of device fabrication techniques and silicon carbide devices.

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Conventional DC-DC converters with transformer have some problems in case that they are designed to convert from low voltage to high voltage, e. g. large current in primary circuit, high surge voltage in secondary circuit, etc.
In this paper, a boosting forward converter with Power Source Bias is proposed. It is designed to be mounted on a small electric boat. It is important for such application to materialize compact, light and simple circuit configuration. Introduction of Power Source Bias is very easy and effective method to satisfy the above requisites. The idea of Power Source Bias is just the same as Boosting transformer in high voltage distribution lines.
A prototype circuit was made and tested by the authors, and it is showed that the boosting forward converter has not only higher efficiency but also higher output than conventional ones. In addition, it is possible to make the converter versatile with Power Source Bias ON/OFF switch.

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This paper describes a self-commutated type Static Var Compensator for suppressing voltage fluctuations caused by an ac electric railway. (Shinkansen, or New trunk line). The ac electric railway is a singlephase load with large changes of reactive power, and causes large voltage fluctuations and power unbalances among three phases. The authors have developed a new voltage fluctuation compensating system using a self-commutated Static Var Compensator. This system has functions of both reactive power compensation and negative-sequence current absorption and can suppress the rapidly changing voltage fluctuations caused by an ac electric railway, effectively. The system of 40MVA has been put into practical use, first in the world, in 1993. The test results at site showed that it has excellent performance characteristics.
In this paper, the theoretical analysis on the characteristics of voltage fluctuations with or without the compensating system and the evaluation of the test results are described.

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Power converters for superconducting magnet of DC use are of large current and low voltage because of the low resistance of a superconducting magnet. In case of quick change of magnet current, power converters of large current and high voltage, that is large capacity, are needed due to the large time constant of the magnet.
We have studied on power supplies for superconducting magnets which consists of a small power converter, a superconducting magnet for an energy storage, and an energy transfer circuit of inverter converter bridges (ICB). Energy change at a quick change of magnet current is supplied from the storage magnet through the energy transfer circuit.
We derived analytical solutions on the basic characteristics of ICB energy transfer circuits. From the analytical solutions, a new control method of ICB trannsfer circuit to reduce voltage ripples across a load superconducting magnet was proposed and discussed.
In this paper, the power supply of the proposed type which was designed and made is shown. The basic characteristics and the control methods of the test system are explained briefly. The results of fundamental tests using normal-conducting magnets are shown and discussed. Availabilities of the proposed control method were confirmed by the experimental studies.

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