It is important to make clear gas flow distribution in SF₆-gas insulated transformer windings because cooling performance of winding depends on gas velocity at each cooling ducts.
We try to measure velocity distribution in disc type winding by laser-doppler-velocimeter and make clear velocity distribution characteristics.
We estimate velocity distribution by calculation and clarify that difference for velocity distribution between air flow and SF gas flow is about 10_??_15% and that for improvement of inclination of velocity distribution, it is effective to arrange cooling duct size properly.

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The electromagnetic suspension system, which is a kind of magnetic levitation, can be divided into two groups; separate lift & guidance system and combined lift & guidance system. This paper deals with the latter system, in which lift and guidance forces are generated by a pair of staggered magnets with the inverted U-shaped rail. Although the above arrangement mentioned provides the lift and the guidance simultaneously, a separate control scheme over them is desirable.
In this work, a quasi-decoupled control method is presented, which reduces the coupling between guidance and lift over a substantially wide range of lateral displacement. Simulation showed that the lift control has a small effect on the guidance but the guidance control has a considerable effect on the lift. Therefore a parallel complementary controller on the lift controller is proposed to reduce the sensitivity for parameter variation and force disturbance.
In result, the lift system has robustness to parameter variation and force disturbance, while the guidance system is independently controllable with respect to lift system. Hence enabling to obtain adequate guidance force and to meet the ride quality standard related to the guidance of levitation vehicle.

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As reduction technique of speed ripple of small brushless motors, we developed two new speed control methods, using learning control theory. One is a ripple compensation control method which is canceled by motor torque ripple and compensating torque which is made by calculating the magnitude and phase of the torque ripple of arbitrary frequency in the speed ripple using Fourier transformation. The other is optimum gain control which searchs for the gain giving the minimum speed ripple. We applied them to motor control for audio-video and communications equipment. By applying the ripple compensating control methed to three frequency components, we could reduce speed ripple to 13_??_19 dB compared to values obtained when using no ripple compensating control method and we could cut the speed ripple magnitude in half. By applying the optimum gain control, we could reduce the speed ripple when a filter function was employed to calculate speed ripple. The speed ripple magnitude was reduced by half for these control method also.
By applying both system simultaneously, we could reduce speed ripple by one-third compared to that of ordinary systems, and it took 12_??_19 s to finish learning.

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Authors have developed a new type of motor composed of piezo-electric device and strain wave gearing, which is called piezo-electric motor, as a first stage to realize a low speed motor with small size and light-weight. The principle of the motor is that the traveling wave is produced by piezoelectric devices and displacement conversion devices without mechanical resonance and the torque to rotate the motor is generated by a mechanism of strain wave gearing (circular spline and flexspline) without using friction. The motor is operated in variable frequency and have its rotational position (angle) controlled in open-loop because it is basically a synchronous motor. In this paper, the structure and principle of the proposed motor are explained and the driving method and the mechanical characteristics of an experimental motor are also described.
The results are as follows;
(1) The proposed piezo-electric motor is experimentally verified realizable. The experimental motor operates in 2, 920 step per revolution, and its speed range is 0_??_960 pps _??_or 0_??_20 (rpm)_??_.
(2) The torque characteristics are clarified qualitatively.
(3) The generated torque of the experimental motor is small (less than 0.03 Nm) and therefore the improvement of the torque is an important subject here after.
(4) It is possible to construct the motor with nonmetallic material. This fact is considered to make a way to lighten the motor in weight in the future.

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A linear pulse motor is used for open loop position control with no position detection. However, in order to realize the more stable and higher speed control without hunting or pull-out, it is desirable to control the motor in closed loop with the position of the magnetic poles fed back to the phase of input voltages or input currents. It is necessary to derive an equivalent circuit to explain the steady-state and transient characteristics in order to find an adequate control rule for high performance control of the linear pulse motor.
In this paper, magnetic equivalent circuit is obtained, based on the structure of the motor, and then the equivalent circuit of the motor is derived by solving equations for the magnetic equivalent circuit.
Next, parameters of the equivalent circuit are determined from the frequency characteristics of impedance when the motor is locked and the relationships between terminal voltage and motor speed when the motor is not excited. Then, characteristics of the maximum thrust force of the motor and the phase between the speed e. m. f. of the motor and input voltages or input currents versus the motor speed to obtain the maximum thrust force are calculated using the equivalent circuit. Validity of equivalent circuit is confirmed by experiments.

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The voltage modulation factor of the magnetic flux control PWM method is discussed. The fundamental component of the inverter output voltage is proportional to the radius of the flux locus. The modulation factor is derived by the theoretical study on the length of the flux locus produced from inverter output voltage.
As a result, the modulation factor of the magnetic flux control PWM method is calculated by the portion of zero vectors in the PWM pattern. The modulation factor is proportional to the output voltage from zero to 12/π². By using proposed modulation factor, the magnetic flux control PWM method can control output voltage from zero to over-modulation.
Simulation results and experimental results are also shown.

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This is the first attempt of controlling the instantaneous output voltage of an AC/AC direct power converter. The AC chopper-type regulator has the potential ability of quick response to the control command. However, detecting the mean or effective value of the AC output voltage, as is commonly done in the conventional closed-loop AC regulators, greatly ruins the inherent fast response capability of the chopper circuit.
The proposed AC switching regulator adopts the _??_uk converter for the main circuit and an instantaneous voltage control technique. A practical state feedback scheme together with the integral control was devised to stabilize the system and also minimize the steady state error. The response speed is so fast (about 300μs with resistive load) that the converter can produce a sinusoidal output voltage even from a distorted source voltage. The four quadrant operation can handle any kind of AC load. A complete analytical description and relevant design data of this new regulator are provided with some experimental results.

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A software technique generation method using the space vector theory for PWM signals with superaudible frequencies was studied. This method is characterized by being able to obtain PWM signals of superaudible frequency without shortening the sampling time of the PWM control. This is achieved by dividing the duration times of voltage vectors which are obtained when the magnetic flux deviation vector of the primary magnetic flux references, generated between the n and (n+l) sampling times, is decomposed in the direction of the two voltage vectors which are closest to the direction of the magnetic flux deviation vector. In this PWM control, control is also excuted which suppresses the distortion of the primary currents due to the dead time of the PWM signals and the pulse dropping phenomena. The current distortion in the former is suppressed by correcting a rising or falling timing of the PWM signal on the basis of the primary current polarity got using the phases of their fundamental components. The current distortion in the latter is suppressed by controlling the limiting value of the amplitude of the magnetic flux deviation vector so as to ensure a minimum duration time of the zero vector, even if the phase of the primary magnetic flux is varied.
With the PWM control, a switching frequency of 16kHz was obtained with a sampling time of 120μs. The switching frequency could be kept constant at 16kHz, even if the inverter frequency was varied. Moreover, the current distortion factor was controlled to less than 6%, and the magnetic noise of a motor was also below the noise level of a motor driven by a commercial power source.

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