High reliable, low voltage and high current converter technologies for information equipment using high speed CPU are described in this paper. Recently, 1.1-2.7V, 60A, 1A/ns output converter using multiphase regulator topology was developed. However, higher requirements (lower voltage and higher current ) are requested from information equipment. New solutions are needed to achieve the converter, and high efficiency, miniaturized technologies are also desired.

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The immittance converter has an input impedance that is proportional to the admittance of a load connected across output terminals. Therefore, in this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant voltage source into a constant current source and a constant current source into a constant voltage source.
It is well known that the quarter-wavelength transmission line shows immittance conversion characteristics. However, it has very long line length for the switching frequency of converters and is not suitable for power electronics application. So we proposed five types of immittance converters that consist of lumped elements L. C and showed improved immittance conversion characteristics at a resonant frequency.
The output characteristics and efficiency characteristics of an immittance converter is the most important parameter when it is used in practical applications in a high frequency link. In this paper we show voltage-current transformation characteristics, current-voltage transformation characteristics and efficiency characteristics of a Hybrid type immittance converter compared with a T-LCL type one.

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This paper presents a method to compensate voltage sags with minimum energy injection for a series connected voltage restorer using a μ-SMES as energy storage device. A circuit for extracting the fundamental symmetrical components from sagged voltages and a minimum energy injection algorithm is described. Voltage sags compensation simulations are carried out using PSCAD/EMTDC for various types of fault. The simulation results confirm the validity of the proposed method and show the possibility to reduce the size of energy storage device.

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This paper presents a driving method of the motor with concentrated windings for the refrigeration compressor. In resent years, power-saving has been demanded more strongly for domestic refrigerators. Under such a background, we have developed a motor with concentrated windings for a refrigeration compressor. And we have developed the high efficiency driving method, the control of current wave and the control of 2 level voltage, of this motor. This driving method can reduce the input power by approximately 3%.

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This paper presents a sensorless control of IPMSM using an estimated axis error on the basis of an extended emf. In the sensorless control method using a rotational axis model, the approximated model is generally used, thus some problems exist in the sensorless control at IPMSM with a large saliency ratio. In this paper the use of a rotational axis model using an extended emf can accomplish a sensorless control on the basis of an IPMSM model without any approximation. Moreover to confirm the effectiveness of the proposed method this paper shows simulation results of some kinds of drive situations and IPMSMs with various saliency ratios.

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The ultrasonic motor (USM) is a new actuator used ultrasonic vibration and frictional driving force. The mechanical resonance is utilized for generating the ultrasonic vibration, however, the mechanical resonant state is changeable. It is necessary to control the driving frequency of applied voltage on the USM in order to keep the driving performance of the USM.
This paper describes a variable frequency resonant inverter for the USM. The proposed resonant inverter includes the transformer which is able to control the resonant frequency of inverter by changing the secondary current. The operating waves are provided to demonstrate the effectiveness of the proposed resonant inverter.

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In order to stabilize voltage fluctuations in electric power systems, TCR-SVC is widely used. Recently an unstable switching behavior of TCR-SVC was found according to the change of the firing angle of thyristor.
In this paper, the switching operation are discussed based on the experimental and simulated results for the single-phase equivalent circuit of TCR-SVC. Moreover, the similar discussion is extended to a three-phase system.

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I spent half a year as a visiting researcher at the University of Toronto. In this period, I had chances to visit two research institutes developing the real time simulator in Canada. This paper describes what I saw and heard about the research of the power system and power electronic circuit simulation in Canada while my stay from April to September in 2000.

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In recent years, many vector control methods with a flux observer for the induction motors have been developed. These methods are assumed to be robustness to the stator and rotor resistance deviation. In this paper, we give the method of steady analysis about the torque control characteristics and show deterioration when an induction motor is driven at low speeds with resistance deviations.

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[in Japanese]

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