A single-phase diode bridge rectifier with a filter capacitor on the DC side is often employed to convert AC input into a DC voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e. non-zero DC side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.
This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the AC and DC side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulation.

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This paper reports the method of electric power generation from tidal currents and test results of the system which is specially designed for this purpose. The system consists of a vertical axis turbine, a accelerator, an electric generator, and a control unit. The turbine is vertical axis Darrieus rotor, and has three blades. The real test in tidal currents was conducted from 1983 to 1988, at Kurushima straits, and its results are discussed.

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We propose the instantaneous speed observer for high performance control of servomotors which use inexpensive low precision shaft encoders. Due to the recent development of DSP (Digital Signal Processors), we have been able to control servomotors with a very short sampling period. We usually obtain the speed information from the increased pulse number of a shaft encoder in a sampling period. However, in this simple method, we lose the speed resolution easily. If we get accurate speed information by clocking the period of encoder pulse, the system will be easily unstable in the lower speed range because a long deadtime is inserted in the feedback loop. To overcome these problems, we propose the novel estimation technique of the instantaneous speed by utilizing the armature current together with the encoder information. As this observer inherently includes the disturbance observer. We can use it for the effective disturbance rejection control. We implement this system by using a DSP, and prove through laboratory experiments that it can greatly improve the system stability and achieves the excellent disturbance rejection performance.

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High frequency link DC/AC converters for UPS are characterized by small size and weight of the isolation transformers. Two types are considered in the high frequency link DC/AC converters. One is called a DC/DC converter type, and the other is a cycloconverter type. The DC/DC converter type can be constructed easily, but the efficiency is low because of many steps of power conversion The system configuration for the cycloconverter type with a single phase output has been proposed, but the cycloconverter type which directly converts high frequency voltage into three phase line voltages is not studied.
In this paper, the system configuration and the control method of the high frequency link DC/AC converter with three-phase output voltages using the PWM cycloconverter are proposed. This system can control flow of power bidirectionally, and charge the DC power supply and compensate instantaneous reactive power. Simulations and experiments are carried out to confirm the feasibility of the proposed system.

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Pulse width modulated inverters using GTOs are aptly used high quality AC motor drives. A nuetral point clamped (NPC) inverter with three level output voltage is of great advantages to large capacity AC motor drives: lower ripple currents and higher output voltages.
GTOs in inverters call for the minimum on-time to discharge the capacitive energy of snubber circuits. The NPC inverter cannot control the pulse-wise voltage for a small reference on account of the minimum on-time.
This paper describes the details of control characteristics of the NPC inverter and proposes a new PWM control to cover the whole operating ranges. The digital simulations and the experimental results are described to clear the effects of new control methods.
Finally, the NPC inverter is compared with the conventional bridge inverter at the point of applying to AC moter drives.

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Various kinds of materials and methods that are used to print the characters on industrial parts often produce printed letters with differences in color, blurs and other characteristics. Those differences cause individual developments of recognition systems depending object characters. Therefore, the improvement of system productivity becomes a strong requirement.
To answer that requirement, we have developed a character recognition system using a neural network which functions automatic extraction of pattern features. This system uses a core network which is matched to the characteristics of the object characters, so that the system can reduce a leaning time. The core network is generated by a design module which contains knowledge on the applicable range of character recognition algorithms. The design module first selects an algorithm that is suitable for object characters and then outputs parameters that present the core network with functions equal to the selected algorithm.
This system was implemented on a workstation and an image processor, and used in the development of a reconsition system for the low-contrast laser marking characters that are hard to recognize with conventional binary image-processing method.

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This paper describes principles together analytic and experimental studies of an exciterless, brushless, and self-excited three-phase synchronous generator which was devised by authors. As traditonal brushless and DC self-excited three-phase synchronous generators without exciter didn't have the self-exciting function by series characteristic component proportional to the load current inside the generator, they need auto-voltage regulating equipment or together a transformer with three windings and condensers in order to get constant voltage characteristics. It has also the following problem in the case of two-pole traditional generator: Oscillatory tension is generated at the shaft of the rotor causing by the magnetic force between magnetic poles of stator and rotor windings; it causes mechanical vibration and noise.
This paper proposes a new brushless and self-excited three-phase generator solving the above-problems: the ratio of poles of the windings for providing power to load (armature and field windings) to the windings for supplying exciting power (stator and rotor exciting windings) is 1 to 5, then oscillatory tension does not generated theoretically. Furthermore, a self-exciting using the 5th-harmonic component of armature reaction which makes series characteristic component proportional to the load current, is available.
In this paper, the winding construction, the electric circuit, and the principle of the above stated generator are described. and the experimental results of the trial producted generator show that the three-phase terminal voltage wave forms are almost sinusoidal and are also balanced, and the voltage can be kept near constant for the change of load. This generator has high reliability because of simple construction.

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