Novel design theory for a three phase self commutated power conversion system (PCS) to perform as a AC current source is proposed. In this new AC current waveform control method termed error tracking mode, the switching instructions of main devices are decided only by the error function of AC current at every data sampling time which comes in constant period. The performance is theoretically evaluated. Simulation by SPICE is also executed and the characteristics are inspected.
Error tracking mode has following attractive features. It can treat arbitrary two current waveforms as target functions of arbitrary two phase AC currents. The error between actual AC current value and the objective function value can be controlled and guaranteed to be less than an arbitrary value which is given beforehand. All control components can get digitized. The minimum continuous on and off time of main devices is guaranteed in advance. No special starting control is necessary because actual AC currents are guaranteed to start tracking the target functions automatically. Error tracking mode surely makes contributions to improve precision in current control and to reduce current harmonics of self commutated voltage source power converters.

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The paper proposes a circuit for decreasing harmonic currents in the single phase rectifier. The circuit is a modified voltage tripler rectifier circuit which is composed of only passive devices such as capacitors, inductors and diodes. Accordingly the proposed circuit has the following merits;
1) High input power factor and small harmonic input currents,
2) High reliability and efficiency owing to the elimination of switching devices,
3) No switching noise generated by switching devices.
4) High capability for over load.
Using this circuit, 1200W (322V) dc power supply is constructed and the validity of the harmonic reduction is shown. The result fully satisfies the class-A restriction of harmonics.

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In this paper the authors have designed an experimental system to optimize the matching of a separately excited DC-motor interfaced to two PV arrays. Special emphasis has been placed on matching the load line of the field winding which, if directly connected to the PV array, intersects the V-I characteristics of the array at a voltage close to the open circuit voltage resulting in a very small excitation current and hence poor motor performance. Step-up choppers were used as impedance transformers to match the load lines of the field and armature windings to the maximum power lines of the PV arrays. The motor was coupled to a brake torque meter acting as a mechanical load and the step-up choppers were PWM controlled by a personal computer. The system efficiency defined as the ratio between the motor output mechanical power (calculated using the motor torque and speed) to the input power available from the PV arrays, was evaluated for four control modes as follows: applying no control, controlling only the armature winding, controlling only the field winding, and controlling both windings. The importance of controlling the field winding was clearly illustrated whereas controlling only the armature winding didn't significantly improve the system efficiency and this was because most of the input power was wasted in the form of heat in the armature winding due to the poor field excitation.

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This paper proposes system identification methods and an identified parameter-based vibration control of a 2-mass resonant system. First, it is described the proposed vibration control scheme which is the same as a disturbance observer-based two-degree-of-freedom control scheme. The key point of this vibration control is only optimum tuning of the disturbance observer gain according to a resonant mode of the 2-mass system, and it makes possible to suppress the torsion of the flexible shaft. Secondly, two methods of the system parameter identification for an adaptivevibration control is described. One is an initial identification method of unknown system parameters such as a load inertia and a spring constant. The other is an on-line identification method of a variable parameter such as the load inertia. Several simulation results are confirmed the validity of the vibration control, the system identification and the identifiedparameter-based adaptive vibration control.

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Frequency spectra of inverter output currents are one of the important factors to evaluate PWM methods. These spectra are, however, influenced not only by the PWM method itself but by the operating conditions of the inverter such as the switching frequency or load parameters. The harmonic distortion determining factor (HDDF) is considered to be a common quality index that represents the intrinsic spectral property of individual PWM methods. As it has a close relation to RMS values of the harmonic current or torque ripples of driven motors and, further, it is almost independent of the operating conditions, HDDF is quite useful for evaluating PWM methods. In this paper four typical carrier based PWM methods and two space vector based PWM methods are compared and evaluated based on the HDDF values.

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A synchronous-induction motor has a feature of both synchronous motor and wound-rotor induction motor, and far excels other synchronous motors in starting characteristic. However, a major drawback of the synchronous-induction motor is to need an excitation power supply with a power rating of low-voltage and large-current. For this reason, its driving equipment becomes large, and increases the overall cost.
In this paper we propose a new synchronous-induction motor, which has no problem described above by making the motor of self-excited type. It employs the second space harmonic component of armature reaction field to obtain the self-excitation of field system, and installs a harmonic winding, which is used for extraction of an excitation power, in the rotor. This new self-excited motor has following advantages. (1) The driving equipment is small, since no excitation power supply is involved. (2) Due to the effect of the series characteristic by which the field current varies in proportion to the load current automatically, the motor can be operated with a good power factor.
In the present paper the structure and operating principle of the new motor are explained, and the basic characteristics are also investigated by means of a simple analysis and experimental results with a 1.5-kW trial machine.

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When a given plant has poles on the jω axis in the two block mixed sensitivity problem setting, they become the zeros of G₁₂ or G₂₁ in the generalized plant, and the H_∞ control problem becomes a nonstandard one. To circumvent this problem on zeros, the authors introduce a loop transforming technique and the extended H_∞ control theory, previously proposed by authors, and derive an H_∞ controller. The results include a design method of a servo system where the poles of the plant or/and the designed controller play a role of the internal model. This particularly is useful in designing motion control systems because one often models actuators to have single or double integlators when the damping coefficient and/or the spring coefficient are small but uncertain.

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The authors have been developing a high speed hydraulic servo valve (Linear Servo Valve, LSV), which has a dynamic response of a 90° phase lag at 500Hz and the rated flow of 40L/min, with a high response linear DC motor to improve the accuracy and the productivity of sheet metal machines. This paper describes a large capacity and high speed two-stage LSV used the LSV as a pilot valve and its application to a hydraulic turret punch press. The following points are obtained:
(1) The two-stage LSV exhibits a dynamic response of a 90° phase lag at 100Hz. It is clarified that the dynamic response of the two-stage LSV is 25% higher than that of the conventional three-stage hydraulic valves.
(2) High ram speed of the hydraulic turret punch press, 2times higher than that of the conventional machine using the three-stage hydraulic servo valve, has been realized by adopting the two-stage LSV.
(3) The hydraulic turret punch press using the two-stage LSV is able to reduce the power consumption to 91% in comparison with the conventional machine using the three-stage hydraulic servo valve.

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A liquid He free conduction cooled NbTi superconducting magnet for X-band klystron was designed, fabricated, and tested successfully. The magnet has a room temperature bore of 190 mm. The rated field is 0.7T. In order to meet the requested magnetic field distribution, the NbTi coil is separated to three parts and a return yoke is set. The coil is cooled by a two-stage Gifford-McMahon cycle refrigerator. The refrigeration capacity is 1.1 W at 6K and 30W at 40K for each stage. Current leads are made of 2223 Bi-based oxide superconductor. The coil was cooled down to superconducting state from room temperature in 85 hours. The ultimate temperature of the coil was below 4K, and the coil was energized without quench to 18.5 A which was 105% of rated current. The power consumption of 6kW is 1/8 of the normal conducting magnet. The thermal leak of 0.2W into the coil was measured, which was the same value of the design.

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High-temperature superconductor Y Ba₂Cu₃O_7-x with strong pinning force has allowed the realization of stable magnetic suspension with no control. Two type superconducting magnetic bearings (SMB) using YBCO and permanent magnet were assembled. There were a radial type and an axial type. Dynamic stiffness of each SMB, while being cooled down under a magnetic field by liquid nitrogen, was measured both in radial and axial directions. As a result, it was found that the spring constants of these SMBs were almost as large as a practically desirable value but their damping coefficients were lower than the practical level. These findings are useful as one of the data bases for development of an optimum SMB design to support the weight of rotors in an axial direction.

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A thyristor converter is superior to GTO converter from a view point of weight and efficiency. Therefore, the thyristor converter is the best answer for AC inverter rolling stock, especially for commuter and interurban trains, in the next several years. For a thyristor converter, it is very important to prevent the commutation failure even when the catenary voltage decreases, in order to continue regenerating operation to sustain the brake torque. In a conventional system, a series resistance is inserted between the thyristor bridge and LC filter where the DC stage voltage is decreased enough to keep the regenerating power. The conventional thyristor enables regenerating braking in the whole operational region, but result in low power factor and efficiency. This paper proposes a new regenerating method to improve the power factor and efficiency, which keep regenerating power with no series resistance and higher DC stage voltage. Simulation results show the effectiveness of the method.

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