This material presents first the short history of abnormal oscillations such as the undamped and subharmonic oscillations occurred in transmission lines in Japan. It also focuses on the dynamics of subharmonic oscillations of order 1/3 in a nonlinear three-phase circuit which is the model of the series-capacitor-compensated transmission line. The analytical methods employed are the asymptotic and shooting-homotopy methods. The results are compared with the real experimental circuit. The shooting-homotopy method gives the features of several bifurcations such as saddle-node, period doubling, Neimark-Sacker bifurcations and so on. The experiment reveals the existence of eleven kinds including chaotic 1/3-subharmonic oscillations.

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An HVDC project of ±500kV and 2800MW bipolar system is planned to interconnect AC 500kV net-works of Shikoku Electric Power Company and The Kansai Electric Power Company. At the first stage, the HVDC system will be commissioned at ±250kV and 1400MW in 2000. The HVDC system links between the two 500kV systems in parallel with existing AC 500kV interconnection lines and mainly transmits power from a coal power station to Kansai area as well as reinforces the existing interconnection.
This paper describes the planning of the HVDC project and technical innovation involved with this project.

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Voltage fed single-ended resonant-type inverters are commonly used for induction-heating cookers because of their relatively small device switching losses, low cost and compactness.
This paper presents a performance evaluation of the 4th generation IGBT when used in voltage-fed single-ended inverter for induction-heating cookers as the switching device.
A total loss reduction of 11% was observed with the 4th generation IGBT as compared with the 3rd generation one. Moreover, its chip size could be successfully made smaller by the approach or increasing the current density.

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This paper describes the results of an experimental study on the steady-state impedance characteristics and instability of a thyristor controlled series capacitor (TCSC). A laboratory-scale TCSC was produced and installed in a laboratory power system. The impedance characteristics for various combinations of circuit components were measured and analyzed. Instability caused by harmonics was also investigated.

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Single-phase PWM current source inverter has attracted special interest recently especially in utility-interactive system. But this type of inverter has a disadvantage, that is to say, output current of inverter has large harmonic component when its smoothing reactor is not large enough to eliminate the ripple component of its current. This paper presents a new control strategy to reduce the harmonic component of the single-phase PWM current source inverter sufficiently. Operation principles of the proposed control circuit and simulation results are described.

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The soft-switching high-frequency AC link converters are more suitable for cogeneration systems using new energies such as solar batteries because of the downsized transformer, lowered switching losses, reduced EMI noise and so on. However, most of the soft-switching quasi-resonant PWM converters cause an increase of conduction losses due to a circulating current generation. Furthermore their resonant circuits are influenced by the load current. This paper presents a novel high-frequency AC link three-phase cycloinverter which can solve these problems. Its operation principle is illustrated and evaluated by means of simulated results.

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This paper presents new methods of current control and active prevention of islanding operation for utility interactive inverter with high-frequency link, which has been developed at the residential power level of 3kw. Firstly the algorithm of the current feed-back control is described using adaptive FIR (finite impulse response) filter with improved synchronized filtered-X LMS (SFX) algorithm which has been popularly used for the periodic sound and vibration control. Secondly an active prevention method of islanding operation is presented, which detects the islanding by the frequency shift control using small distortion on the output current of the inverter.
These control have been implemented using DSP (TMS320C209), and tested. Experimental results show that presented method dose not have a dead-band of sensibility for islanding operation. Furthermore, it has been achieved that the total harmonic current distortion is less than 1% on the rated output power of the inverter.

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This paper presents a Multiple Bridges Power Conversion Circuit (MBPCC) for the switchmode gradient power amplifiers in the magnetic resonance imaging (MRI) systems. The MBPCC is connected in parallel with the conventional 4-switch full-bridge circuits using insulated gate bipolar transistors (IGBTs) at their inputs/outputs in order to realize further high-power density. A unique digital control scheme for MBPCC, which requires minimized the ripple and improved the rise/fall response characteristics of the current in the gradient coil, is proposed and described here. The MBPCC as overall system is perfectly suited to the gradient power amplifier for advanced MRI because the output current waves are not restricted to ramped-squarewaves and can assume any arbitrary forms. It is expected that the proposed techniques will highly enlarge the diagnostic target and improve the image quality of MRI.

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Device simulation is an important way to design new devices and predict their characteristics. Using the FEM, we analyzed switching characteristics of GTO. In this paper we simulate the carrier life-time control proposed recently to realize fast turn-off of GTO. The influences of intensity of irradiation and irradiated point for the local life-time control on switching characteristics were studied. The results show that the local life-time control has the possibility to reduce turn-off time of GTO keeping low on-state voltage.

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Although the Pulse-Width-Modulation has been widely applied to several power converters to obtain high performance, it requires a smoothing do voltage or current. Thus, the PWM causes bulky and costly reactive components connected in the do-side of the converters to reduce the voltage or current ripples. To overcome the problem, the authors have proposed a new modulation scheme where time-integral-value in each modulation period of the modulated voltage or current is controlled to follow the variation of a reference signal. Thus, the ripples of the dc voltage or current do not cause modulation errors in Pulse Integral-value Modulated power converters, and a small dc smoothing inductor or capacitor is applicable to the converters.
The PIM (Pulse Integral-value Modulation) is applied to a single-phase buck-boost high-power-factor rectifier first. Then, several modified or extended versions to apply it to different power converters have been developed by referring the application of the conventional PWM.
This paper introduces the principle of the PIM and reviews operation, modulation mechanism and experimental result in different Pulse Integral-value Modulated power converters. The relation between the PIM and other control/modulation schemes and remaining subjects on the study of the PIM are briefly described.

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We generally use isolated power supply circuits to drive switching devices of power frequency changers.
In this paper, we show the usefulness of the isolated power supply circuit consisting of capacitor and diode.
We formulate the equation to calculate the adequate value of this capacitor, and express the safty operation domain of the inverter circuit on the capacitance-frequency plane.

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This paper proposes a current fed type multi-level inverter and its PWM method which allows a great reduction in the DC reactor values. This PWM method based on closed-loop regulation of the instantaneous current vector. The suitable current vector is carefully selected to reduce the output current waveform distortion. Moreover by using the suitable load connection among several connection which give same output vector, it is possible to reduce the unbalance of currents in the DC reactors.

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The Transfer Supporting Equipment lifts the sick and disabled from beds, and transports them to the bathroom, toilet or elsewhere. At present, such nursing tasks are almost always manually performed, but the awkward positions involved put tremendous physical strain on the attendants. This equipment not only takes the load off nurses, but restores the mobility of the sick and handicapped. It's superb nursing capability will become invaluable to our aged society in Japan.
We developed the Patient-Care Robot under a joint commission from the NEDO and the AIST-MITI. And now, to advance the reliability and simplification of this robot system, we are developing a Transfer Supporting Equipment for a popular utility.

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