Power electronics is an interdisciplinary area which is interstitial to all of the major disciplines of electrical engineering including “power (static and rotating equipment)”, “electronics (devices and circuits)” and “control (continuous and sampled-data)” as pointed out by Dr. W. E. Newell in 1973. Today, the covering field of power electronics has more widely spread out with the help of ever evolving micro electronics and computer science. For this reason, it has become a very important problem to find out “what are the truest essentials of power electronics? ” and “what is the efficient way in teaching them? ” from an educational point of view in universities and companies. This paper surveys the present status of the power electronics education in universities and companies, and try to point out some problems based on the discussions performed in the IEEI committee on power electronics education.

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If the mechanical load such as a pump is dirctly driven by solar power, CO₂ gas can be reduced considerably. It is necessary to interconnect the solar power system to the utility line so that a mechanical load can be driven stably and economically even in varying solar power.
This paper compares the loss between two interconnection systems which can generate the constant mechanical power from variable solar power. The first is named DC electric interconnection system in which DC power of photovoltaic arrays is connected to the output of a converter at the DC power line in a general-purpose inverter. The second is named a mechanical interconnection system which is composed of two coupled induction motors. One induction motor is driven by electric power of the photovoltaic arrays through a general-purpose inverter and the other induction machine is connected to the utility line. The loss of each system is represented as a function of the solar power of the photovoltaic arrays. As insolation varies randomly, a probability distribution function of the solar power is taken into consideration. Each average power loss is calculated from the distribution. It is shown from the comparison of two losses that a mechanical interconnection system is more efficient than a DC electric interconnection system.

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The immittance converter has an input impedance that is proportional to the admittance of a load connected across it's output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently a constant voltage source is converted into a constant current source and a constant current source into a constant voltage source. The immitance converters consist of only the passive elements reactor L and capacitor C are suitable to use in a high frequency link of power electronics.
We proposed some types of immittance converters and some applications to power electronics equipment. In this paper, we propose a new 3-phase immittance converter consist of each three L, C elements to obtain an alternating current source from a 3-phase voltage source without control.
This paper shows the configuration of the new 3-phase immittance converter that operates on either the anti-phase or the in-phase between the input voltage and the output voltage, and it's voltage-current transformation characteristics and efficiency characteristics.

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Widely distributed systems are constructed step-by-step over a long time. These systems are obliged critical timing check as a final test of newly added or modified real-time application programs in real environment. We propose an autonomous decentralized on-line test technique for verifying distributed and real-time control application programs. It enables testing during system operation without disturbing the operation. And it takes into consideration the difference of timing in on-line subsystems and test subsystem for the more precise verification. We apply the proposed technique to a validation tool for real distributed train traffic control systems and show its effectiveness.

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This paper proposes a new three-input and three-output characteristics-varying filter in the D-module for direct processing of three-phase signals, which are becoming indispensable for effective active-compensations in three-phase power systems such as harmonics current, negative phase current, reactive power and varying voltage compensations. The filter in the D-module can make distinction between positive and negative frequencies of three-phase signals and can allow direct processing of the signals based on frequency polarity. The filter in the D-module can also change dynamically its filtering characteristics by simply injecting a shift-signal to itself These filtering effects are obtained in a very simple manner using the D-module. A new unified analysis of attractive general characteristics of the proposed filter in the D-module is given for its easy designs and realizations as well. Effectiveness of the analysis and usefulness of the filter in the D-module are newly examined and confirmed through experiments. The newly proposed filter in the D-module has potential to a variety of three-phase signal filtering applications.

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Signal processing based on frequency polarity has been attracting wide attentions due to its potential industrial-applications. It is popular to employ two vector-rotators for such signal processing. But, It was very recently reported that equivalent signal processing effect can be attained in a much simpler manner using two-input two-output filters in the D-module. This paper further investigates a class of characteristic-varying systems in the D-module, which contains the filters in the D-module as a special case, and gives new analytical results on their properties from viewpoints of existence, realization and stability. If the results are applied to filter problems, n-th order D-module filters in new forms can be easily and directly obtained, whose stability and response equivalent to the associated filters with vector-rotators are guaranteed. If the results are applied to AC motor modeling problems, dynamic models and block diagrams of AC motors in general reference frame are easily and directly obtained. Very general and useful analyses are given for newly proposed a class of characteristic-varying systems in the D-module that have potential usefulness in various industrial applications including control of magnetic bearing system, analyses and active compensations of power systems, and sensorless drives of AC motors.

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This paper proposes a new method of damping harmonic resonance at the dc-link of a large-capacity rectifier-inverter system such as in rapid-transit railways. A voltage-source PWM converter is connected in series to the dc capacitor of the rectifier through a matching transformer, acting as a damping resistor to the dc capacitor current. No filters are needed to extract harmonic components from the dc capacitor current. This results in a quick response and highly stable damping. The relationship between the control gain of the PWM converter and the required rating is theoretically discussed. We show that the required rating is less than one-thousandth of that previously proposed. In particular, regenerating the power consumed by the PWM converter is very important because of the large power in practical systems. Normally, an additional PWM inverter is connected to the dc bus of the PWM converter to regenerate the consumed power. The additional inverter regenerates the dc power to the ac source through a transformer. This method, however, makes the damping circuit complex, making the proposed method for the dc-link harmonic resonance less practicable. In this paper, a simple and novel scheme that utilizes the dc-link voltage of the rectifier as a dc source for the PWM converter is proposed. The excellent practicability of the proposed damping method with the novel regenerating scheme is confirmed using digital computer simulation.

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We proposed a searching system for wandering demented aged person using GPS (Global Positioning System), PHS (Personal Handyphone System) and mobile PC (Personal Computer). There were three subsystems: one base station and two mobile terminals carried by the aged and his family. We focused our system on reducing the mental stress of the family in the sense that, in using our system, the family does not need further assistance from others. The independence of the family is very important. In order to construct this user-friendly system, the mobile terminal for the family consisted of only the necessary input keys and the static station included a touch panel. Furthermore, to clarify intuitively the geometrical relationship between the aged and 'carer-person' in the family, the mobile terminal was able to show their loci on the same digital map in real time, and was automatically able to change the scale of the map using a GIS (Geographic Information System). We were encouraged by the results of the application of our system to a search for the wandering demented aged person.

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This paper presents a new prototype configuration of a single-phase voltage source soft switching inverter using IGBT power module packages in order to reduce switching power losses, electromagnetic noises. A single inductor-assisted resonant AC link snubber circuit as one of the resonant snubbers to achieve the zero voltage soft switching for the single-phase voltage source inverter is originally demonstrated, and its operation principle and unique features as well as the practical parameter design method of resonant AC link snubber circuit treated here is described on the basis of computer-aided simulation analysis. Furthermore, the practical operating performans of the single inductor-type resonant AC link snubber for the single-phase voltage source soft switching inverter using IGBTs are discussed and evaluated on the basis of switching power losses and electromagnetic conductive noise as compared with those of single-phase voltage source hard switching inverter from an experimental point of view.

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A converter without DC Link components needs snubber circuits, in order to assure the path of the load current during the dead-time period of the PWM rectifier section. In the snubber circuits, losses have been dissipated every time the switches of the rectifier section are turned on and turned off. During the zero voltage vector period of the inverter section, the load current does not flow in the PWM rectifier section. So if each switching operations of the PWM rectifier section are done in the zero voltage vector period, it is not necessary to assure the path of the load current. Therefore, snubber circuits are not necessary in the PWM rectifier section. In this paper, we describe a zero current switching strategy of the PWM rectifier section during zero voltage vector periods of the inverter section. The proposed strategy is verified by computer simulation and experimental test on an induction motor drive.

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To estimate characteristics of electric machines that have conductors with complex form, it is effective to analyze the surface charge concerned with eddy current phenomena. However, the eddy current field is generally treated as quasi-static field in which the displacement current is neglected and the electric field is not defined in the non-conductive region in the calculating process. Therefore, when we adopt only the A-φ FE method as a field analysis method, it is difficult to directly calculate the surface charge at the interface between conductive and non-conductive regions. In this paper, with this background, we propose a novel analysis method of the surface charge based both on the A-φ formulation of 3D edge FE method and on the integral equation. This approach enables us to precisely calculate the surface charge. Some numerical results, which demonstrate the validity of the proposed method, are also presented, e. g., the surface charge analysis of linear induction motors for evaluating the relationships among the surface charge, eddy current, and conductor shape.

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The high reliable timer is required in a synchronous measurement and in a distributed processing that uses the network computers. The precision of it is expressed with the stability of the frequency. The easiness of embedding, the low cost and down sizing are requested to the timer that is required in these various fields in addition to its precision. In this paper we propose a technique that realizes a high precision timer, which enables the synchronization in a many point with the low cost and with the small size. The proposed technique adopts a general PI control of VCO (Voltage Controlled Oscillator) based on GPS (Global Posi-tioning System). Also the controller of the timer that was developed is realized by software by using a DSP (Digital Signal Processor). The frequency stability that was obtained by the timer that was developed was 2.3×10^-13

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The operating characteristics of the sensorless vector-controlled induction motors are generally affected by motor parameters. Starting from the basic concept, the paper presents the practical self-commissioning techniques of electrical motor parameters of sensorless vector-controlled induction motors. By using the proposed method, the control accuracy is improved up to ±0.5% in peed and ±5% in torque, respectively.

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Advanced safety vehicle (ASV) assists drivers' manipulations to avoid traffic accidents. In this paper, a control system for ASV is designed to avoid obstacles using an automated steering system. The control system is based on a visual feedback and the system model is built in consideration of dynamics of the lane and vehicle using an LFT description. The controller is designed by μ-synthesis such that the control system is robust against uncertainties for vehicle parameters. The performance of the designed control system is examined by numerical experiments for obstacle avoidance.

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The objective of this paper is to find out optimum stator core structure for high performance in three-phase hybrid stepping motors. Output torques of various polyphase hybrid stepping motors are evaluated by using the methods of the previous paper (7). Inductances between terminals having an effect on high speed behavior are estimated. Also, arrangements of stator teeth for reducing cogging torque and linkage flux distortion are investigated on the basis of the method in the other previous paper (5). Finally, the results above mentioned are verified by FEM simulation of the hybrid steppinng motors using two-dimensional model.
In conclusion: (1) Three-phase motor with six winding poles is best regarding the output torque. (2) Terminal inductances are almost the same in the various motors. (3) The vernier arrangements of stator teeth are effective on reduction of cogging torque and flux distortion in three-phase hybrid motors. Totally, the three-phase motor with six poles composed of vernier teeth balanced on 6th harmonic plane accomplishes highest characteristics.

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This paper presents an alternative water-purifying facility. This facility uses only the iron-electrolysis as coagulants under the high-oxygen condition. Any chemical coagulants are not required to remove pollutants in the water. So we can provide a peaceful water-purifying facility for the environment of the earth. A prototype model is constructed and tested to verify the excellent practicability of the proposed water-purifying facility. We also develop a pilot plant for the proposed facility. The experimental results demonstrate that the proposed water-purifying facility is most suitable as a coagulator for the water polluted by red clay in Okinawa prefecture.

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Transformers are miniaturized by a high-frequency link. High-frequency transformers, with simultaneous reversing of both polarities of input and output, are shown to have equivalent load-characteristics as conventional transformers. Low-frequency input of arbitrary waveform is multiplied by square-wave of ±1. The same waveform of voltage is induced in the secondary coil, and is coincidentally reversed again. So, the high-frequency component vanishes and the output is exactly the same as input waveform. High-frequency currents of no-load need filters. A reversing of c times as frequent as conventional transforms miniaturizes their volumes by c^-3/4.

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