The indirect field oriented control of an induction motor is widely used. This methbd has a disadvantage which is sensitivity to the motor parameter variation. Especially, resistance depends on the motor temperature. On the other hand, the direct field oriented control method is robust against the motor parameter variation because the measured motor flux is fed back to the reference. The disadvantage of this method is that the installation of a flux sensor is necessary. Therefore, flux estimation from the terminal variables is usually used instead of the flux measurement. However, flux estimation is also sensitive to the motor parameter variation.
Recently, flux observers have been proposed for flux estimation. The sensitivity of the flux observers to the rotor resistance variation is much lower than that of the conventional flux, estimator. However, the sensitivity of these observers cannot be completely zero.
To solve these problems, a new rotor flux observer with parameter adaption scheme is proposed in this paper. Parameters identified adaptively are the stator and rotor resistance which are dependent upon the motor temperature. A stability of the proposed adaptive flux observer is proved by the Lyapunov's theorem.

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In recent years, fuzzy control has found significant applications in many engineering fields. However, the design method of fuzzy control systems has not been established yet, and it is difficult to realize a precise control because control signals are derived from fuzzy scheme of inferences. On the other hand, it is well known that a conventional PD linear control can offer a precise control.
In this paper, a new hybrid control scheme is proposed, which is attempt to combine the advantages of PD control and a fuzzy control. In the points which are close to the reference point, a PD control is mainly used to obtain the precision, and in other points a fuzzy contol is mainly used to improve the transient response and to cope with the nonlinearity of systems. From the experimental results on position control of DC servomotor, it is confirmed that the proposed hybrid controller performes better than either PD or fuzzy control.

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The forced commutated cycloconverters (PWM-controlled cycloconverters) have no energy storage components except for small ac filters for elimination of switching ripples. Therefore, the PWM-controlled cycloconverters can be made compact and highly reliable compared with the conventional rectifier-inverter systems. The PWM-controlled cycloconverters, however, directly connect the input terminals to the output terminals by the switching devices. Therefore, if the source voltages contain asymmetrical and/or harmonic components, the influences directly appear on the output terminals. This problem may be a major obstacle for the PWM-controlled cycloconverters to be used in place of the conventional converter-inverter systems. We have already reported a real time control method based on a coordinate transformation. The method realizes sinusoidal output voltages and sinusoidal input currents with controllable input displacement factors regardless of the load power factors. But the control functions of this control method need complex calculations to compensate the distortion of the input source voltages and are difficult to comprehend physically.
In this paper, we propose a novel control method using a new control function with a clear physical meaning. By this control method, the compensation of the asymmetrical and harmonic components of the input source voltages is easily realized. Feasibility of the proposed control method is confirmed by simulations and experiments.

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In the field of robotics, especially locomotion robotics, ‘power to weight ratio’ gathers a lot of attentions but we have had no remarkable improvement on this problem. Usual actuator system i.e., ‘motor and battery’ or ‘piston-cylinder and compressor’ have poor ‘power to weight ratio’, thus it is not possible to employ them for such purpose, to use as actuators for walking robots with multi-legs, robots for constructing buildings and so on. On this viewpoint, we try to construct a servo system by using gasoline engine as an actuator. Though engines can not stop or rotate reversely, the weight of engine with gasoline tank is far lighter than the weight of motor and battery. To overcome the defect of gasoline engine, we employ a computer controlled clutch system, and bang-bang regulator technique.

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Some energy storage devices, such as inductors or capacitors, are needed in single-phase AC to DC converter because instantaneous power flow of input single-phase AC is inherently pulsating and output DC power is required to have as little ripple as possible. Energy storage devices are usually used at the DC side, such as smoothing inductors or capacitors. In those converters, energy storage ability of the devices can not be used effectively, especially when DC power ripple is required to be very small.
To solve such a problem, this paper presents novel single-phase AC/DC conversion circuits, in which the energy storage devices are used at the AC side rather than at the DC side. That is, after converting single-phase AC into balanced (rectangular) two-phase AC using variable reactance element, re-conversion of it into DC is carried out.
This paper presents control method of the converters and the variable reactance devices, and performance of the proposed circuits are confirmed using computer simulation.

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There have been many approaches in the field of stabilizing control of inverted pendulum system. In many cases, however, linealization technique for small deviation from equilibrium point has been adopted to apply LQ theory or MRACS to the inverted pendulum system. These algorithms are not necessarily satisfactory for a class of non-linear and time-varying systems such as the inverted pendulum system.
In this paper, we propose a new MRACS technique with predictor network which is applicable for the non-linear and time-varying system, inverted pendulum system. This predictor-network-based MRACS can also achieve any convergence characteristics.

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A novel and simple control scheme of the interior type permanent magnet synchronous motor having high efficiency and good dynamic response was described. The prominent feature of the control scheme is to always keep the MMF phase angle φ at a constant value, which was derived on basis of the theory using φ instead of the interior phase angle δ as a parameter. The φ constant control is implemented by the control of only the current phase, and its amplitude is used to control the instantaneous torque. Such a decoupled control of both the phase and the amplitude of armature current results in very simple control scheme. The value of φ to be kept constant was determined after studying the performance variation dependent on φ. The experimental results showed superior steady state performance and excellent four quadrant operation.

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Auto-transformer feeding system is standard equipment for power supply to high-speed trains on the AC electrified Shinkansen lines in Japan.
Feeder side voltage of feeding transformer is 60kV on Shinkansen lines, and power supply to vehicle by an auto-transformer is stepped down from 60kV to 30kV. In the present autotransformer feeding system in which the feeder side of the feeding transformer is not grounded, the insulation level on the feeder side of the substation is set at class 60.
For the purpose of economy on the substation power system, it is effective to adopt a three-winding transformer which makes the insulation level on the feeder side equal to 1/2 of the present value. Therefore, authors propose a new three-winding transformer connection that permits neutral direct grounding for the substation receiving extra-high voltage.
This paper describes a theoretical study and results of a test on a mini-model of the proposed new type transformer connection. According to the result of examination, impedance characteristics of the transformer satisfy the terms of insulation level reduction. There are good prospects that the new type transformer can be introduced in practical use.

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