bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the radial temperature distribution in the central part of an arc burning through a polyethylene tube
Authors: Takikawa Hirofumi , Sakakibara Tateki , Miyashita Mafumi , Kito Yukio , Sakuta Tadahiro
Published: July 2007

The radial temperature distributions in the central part of arcs burning through polyethylene (PE) tubes are estimated by measuring the half‐width of Hα line spectrum and using the electron density versus Stark half‐width and the electron density versus temperature characteristics. Estimation is carried out for various tube inner diameters (2 and 4 mm) and dc arc currents (5, 10 and 15 A). The result shows that the temperature at the arc center is around 10,000 K, and it tends to increase as the tube inner diameter becomes narrow and/or the arc current increases.

The overall temperature distributions from the arc axis to the tube wall are obtained by combining these inner temperature distributions with outer temperature distributions which have been derived from C2 spectra. They are found to take a form of typical two‐temperature distributions of ablation stabilized arcs.

The electric field strengths of PE arcs are evaluated from the temperature distributions and the electrical conductivity versus temperature characteristics of thermally decomposed polyethylene vapor gas. The results agree well with experimental values.
Development of railgun accelerator at the institute of space and astronautical science (ISAS)
Authors: Yamori Akra , Yanagisawa Masahisa , Kawasima Nobuki , Furukawa Suguru
Published: July 2007

This paper describes the current status of the development of electromagnetic launchers such as the railgun at ISAS. The railgun is the most improved accelerator of Electromagnetic Launchers (EML). EML offers a potential for accelerating a projectile to much greater velocities than achieved with conventional powder guns or light gas guns. However, there has been little progress in increasing the velocity of EMLs since the experiment by Rashleigh and Marshall. A few experiments have been reported achieving velocities greater than 6km/s.

The authors have achieved velocities greater than 6 km/s by reducing plasma leakage which is one of the factors limiting velocity.

In this paper a 6 km/s launch is reported, compared with the results of two other shots considered from the viewpoint of plasma leakage, and the effect of entrainment of eroded material into the armature by rail ablation was discussed on the basis of simulated numerical calculations.
Decentralized voltage control in multiarea power system
Authors: Iwase Noriyuki , Okada Kenji , Yasuda Keiichiro , Yokoyama Ryuichi
Published: July 2007

This paper discusses the feasibility of a decentralized voltage control scheme for large‐scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two‐point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation.

For a large‐scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large‐scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is presented.
Effect of applied voltage frequency on swarming pulsive microdischarges in closed voids
Authors: Hasegawa Taketoshi , Kimura Ken , Shibuya Yoshikazu
Published: July 2007

The extinction of the partial discharge (PD) pulse has frequently been observed in an epoxy specimen with a closed void during voltage endurance tests using a CIGRE Method‐II electrode. The individual discharge pulse becomes so small that the discharges cannot be detected by conventional pulse detection methods. Such discharges are known as “swarming pulsive microdischarges” (SPMD).

In this paper, the SPMD characteristics are investigated by varying the frequency of the applied voltage from 0.1 to 240 Hz. As a result, the SPMD are found to occur less frequently as the frequency is lowered. To seek this cause, one‐shot voltages were applied repeatedly at constant intervals. By varying the interval from 0.02 to 100 s, the PD off an electrically aged specimen was measured. It was revealed that the discharge magnitude increases as the interval becomes longer. The onset of SPMD was found to depend on the preceding discharge. The results explain the reason why swarming is harder to occur at lower frequency with a longer discharge interval. Hence, in the conventional pulse detection, it is useful to employ the very low frequency for diagnosis of machine insulation containing enclosed voids.
Stabilization of a fully superconducting, damperless generator by excitation control
Authors: Tsukamoto Osami , Chen Jianzhong , Morimoto Akihiro , Akita Shirabe
Published: July 2007

The development of ultrafine filaments superconductors for 50/60 Hz makes possible a fully superconducting generator which has superconducting field windings and armature windings. By omitting dampers and narrowing gaps between the field and the armature windings, the size and the weight of the fully superconducting generator can be drastically decreased. However, the damperless generator is inherently unstable and thus must be stablized by an appropriate method. We have investigated a method of stabilizing the generator in which the excitation voltage of the field winding is controlled by the state value feedback technique. The state values of the system are estimated by a state‐value observer and the feedback constants are determined according to optimal control theory. It is shown that this method is effective in stabilizing a fully superconducting, damperless generator.
Power‐generating performance of alkali metal thermoelectric converter
Authors: Masuda Toshihisa , Negishi Akira , Tanaka Kotaro , Honda Takeo , Fujii Takahiro
Published: July 2007

The alkali metal thermoelectric converter (AMTEC) utilizing the sodium ion conducting β‐alumina is a device to convert heat energy to electric energy directly. It is characterized by high conversion efficiencies, high power densities, no moving parts and low maintenance requirements. Because of these merits, AMTEC is one of the most promising candidates for aerospace power systems, remote power stations and dispersed small‐scale power stations.

In this paper, the experimental results of the series‐connected cells and the theoretical considerations about internal resistances have been reported. For the single cell, the open voltage of 1.37 V and the maximum power of 7.89 W and maximum power density of 0.40 W/cm2at the sodium temperature of 1077 K have been obtained. For the two series‐connected cells, the open voltage of 2.60 V and the maximum power of 12.3 W at the sodium temperature of 1016 K have been obtained. This power was about 90 percent of the sum power of two cells. This power decrease is due to the resistance of the current‐collecting busbar. It is necessary to optimize the current‐collecting busbar considering the electrical resistance and heat conductance.
An analysis of the field acceleration method and of vector control of induction motors
Authors: Tsuji Mineo , Yamada Eiji , Yamada Katsuhiro , Oyama Jun
Published: July 2007

The two‐axis theory and vector control based on this theory are well known. On the other hand, Yamamura has proposed the phase segregation method (spiral vector method) for the analysis of induction motors along with the field acceleration method (FAM). In this paper these analytical and control methods are compared.

We begin by analyzing the equations for phase segegation, which contain information derived from the three‐phase stator and rotor equations. We next demonstrate that the vector control system for constant rotor flux is obtained from the type T‐I type field acceleration method when the transient term is zero. By By using the equivalent circuit for a T‐I transient, we readily obtain the desired vector control system, because the circuit is identical to the steady‐state circuit when the rotor flux is constant. An analytical solution of the transient response for the vector control system is obtained for arbitrary initial conditions. Finally, the stability of type T‐II FAM is discussed, with special emphasis on the effect of changes in stator resistance, by computing the torque transfer function. When the stator resistance is correctly estimated, pole‐zero cancellation occurs on the imaginary axis.
Analysis of characteristics of half‐wave rectified brushless synchronous motor with permanent magnets
Authors: Oyama Jun , Higuchi Tsuyoshi , Abe Takashi , Yamada Eiji
Published: July 2007

Previously, the authors proposed a “half‐wave rectified brushless synchronous motor” as a novel servomotor. The rotor winding emf of the motor is induced by the stator current mmf which rotates at synchronous speed and pulsates at bias frequency. The field excitation is produced by the field current obtained from rectifying the emf with a diode inserted into the field winding. To improve the power factor and the efficiency, they also proposed a new‐type half‐wave rectified brushless synchronous motor with permanent magnets.

This paper analyzes the flux distribution and the torque characteristics of the new half‐wave rectified brushless synchronous motor using the finite element method. The computed torque characteristics are confirmed with the experimental results.

Furthermore, the steady‐state characteristic equations are derived and the effect of the modulation function waveforms on the motor performance is investigated. The theory also is confirmed by the experiments.
High‐power active filter using LC‐tuned filter
Authors: Takahashi Isao , Omura Yasushi
Published: July 2007

Usually, to eliminate the harmonics of transmission lines, LC tuned filters are employed to bypass these harmonic components. However, the elimination ability is limited by its damping resistance. Therefore, active filters composed of high‐frequency PWM converters are desirable. In comparison with the LC tuned filters, the cost would be very high even in high‐power systems.

In this paper, a low‐cost and high‐power active filters for a dc transmission system is proposed. It has active filter ability as well as low cost for high‐power uses. Its main circuit is composed of conventional LC filters in series with square‐wave voltage inverters. The voltage of the inverter is controlled to cancel the voltage drop of the internal resistance of the LC filter. Thus the Q‐factor of the filter can appear at infinity. Calculation of the harmonic and the control are done by DSP (TMS 32010). In the experimental system and simulations, two three‐phase tuned filters, 5th and 7th, are employed. Excellent results under 1 percent distortion voltage are obtained.
Coordinated stabilizing control for large‐scale interconnected power systems, by superconducting magnetic energy storage unit and power system stabilizers
Authors: Mitani Yasunori , Tsuji Kiichiro , Murakami Yoshishige
Published: July 2007

The purpose of large‐scale power system interconnection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators.

Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems.

In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so on.
A hypersimulation‐based learning environment for operator understanding of complex phenomena in power systems
Authors: Yoshizawa Junichi , Muto Syoichi , Ueda Takao , Nishida Shogo
Published: July 2007

This paper proposes a simulation‐based learning environment called hypersimulator, as a thinking tool to enhance operators' understanding of complex phenomena in power systems. The hypersimulator is literally a simulator fused with a concept of hypertext, a personal visual simulator with user interfaces viewing multiple aspects of the phenomena in power systems.

In the field of power system engineering, training simulators are used for operators to obtain the so‐called skill‐based and rule‐based expertise of an operation. However, the training simulators are not effective enough to provide knowledge‐based expertise based on deep understanding of a mechanism of complex phenomena. An aim of the hypersimulator is help the novice operator obtain such expertise through examining the phenomena and developing effective mental models (internal models formed in a person's mind) of them. The approach here to designing the system is a user‐centered one based on cognitive science and analysis of characteristics of power system phenomena and operators' ways of thinking.

In this paper, first, the characteristics of operators' ways of thinking are analyzed as the preliminary investigation to obtain a basic design concept. Second, the concept and the features of hypersimulator are discussed. Finally, the effectiveness of the system is demonstrated using simulation of phenomena in power systems.
Estimating power‐frequency characteristics in power systems by means of spectral analysis techniques
Authors: Hayashi Shigeo , Kawata Akira , Nagasawa Takashi , Yokoyama Naoto
Published: July 2007

This paper shows that normal power system operating data may be used to determine the power‐frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power‐frequency characteristics as transfer functions. The generator characteristics Kg are determined as a transfer function of the system in which input signals are frequency fluctuation ΔF and generator power setting signal ΔPg, and output signal is generator power output ΔPe, To estimate the load characteristics Kl, a difficulty arises. There is a relation ΔP/ = ΔLo + KlΔF between actual load ΔPl, ideal load under the state of nominal frequency ΔLo, and fluctuation of system frequency ΔF. Because it is impossible to measure ΔLo directly, ΔLo and KlΔF cannot be separated.

With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of ΔLo in a partial system to ΔF of the total system may be ignored, that is, ΔF and ΔLo are considered as independent phenomena. Thus the cross spectrum of ΔF and ΔLo decreases to zero according to the increase of data in number, and Kl of the partial system can be estimated.
Stabilizing control of variable impedance power systems: Applications to variable series capacitor systems
Authors: Okamoto Hiroshi , Yokoyama Akihiko , Sekine Yasuji
Published: July 2007

In future electric power systems, it will be very important to utilize existing ac networks more effectively with the help of power electronics technology. It has become clear that various types of apparatus utilizing such power electronics technologies as variable series capacitors (VSrC) and high‐speed phase shifters (HSPS) can improve transient stability and damping in one‐machine, infinite‐bus power systems. This paper presents a novel control scheme for variable impedance apparatus such as VSrC and HSPS devices in multi‐machine power systems.

First, this paper describes a comprehensive approach for control design of VSrC and HSPS apparatus. The proposed control scheme is based on the energy function of multi‐machine power systems. The controllers are designed so that the time derivative of the energy function has a smaller negative value than that without controllers. In this sense, the present method assures the improvement of first‐swing stability and damping.

Next, the proposed control scheme is applied to VSrC apparatus. Digital simulations and eigenvalue analysis are conducted for a three‐machine loop system and a five‐machine radial system to demonstrate the effectiveness of the proposed method. The results make it clear that the proposed controllers for VSrC can significantly improve both the transient stability and the steady‐state stability of power systems.
Use of permeance‐based air‐gap flux density analysis in the development of a synchronous generator model
Authors: Takase Fuyuto , Matsumura Toshiro , Ueda Yoshisuke
Published: July 2007

The magnetic flux inside a synchronous generator is regarded as a characteristic that dominates a generator operation. This paper develops a simple model of a synchronous generator by which it is possible to easily estimate an air‐gap flux as well as electrical characteristics. The air‐gap flux density can be related to a permeance and a magnetomotive force (mmf) along its magnetic path by the Ampere's laws. These relations are used in this paper.

We estimate the distribution of the permeance along the air‐gap and the mmf profiles of the stator and the rotor of a 6 kVA scaled‐down tested synchronous generator. From these estimated profiles, the relations among the air‐gap flux, field current, and armature current are represented by a linear equation system. Consequently, the static electrical and magnetic characteristics of a synchronous generator can be estimated by giving only field exciting voltage and load impedance. The distributions of the air‐gap flux density and waveforms of the field and armature currents are simulated for various unbalanced‐load conditions. The simulated results well agree with experimental ones not only for fundamental components but also for higher harmonic components. Therefore, our method, based on the permeance profile, is available to calculate the static characteristics of synchronous generators.
Prevention of reignition overvoltages by phase‐angle‐controlled switching of a gas circuit breaker at shunt reactor current interruption
Authors: Yamagata Yoshifumi , Kumagai Tsutomu , Nishiwaki Susumu , Toda Hiroaki , Ishikawa Masayuki , Yokota Takeshi
Published: July 2007

Shunt reactors installed at gas‐insulated switchgear substations (GIS‐substations) are switched relatively frequently by large‐capacity gas circuit breakers (GCBs). Surge voltages appear at such switching operations through various mechanisms. Among them, high‐frequency current interruption and subsequent multiple reignition might cause the highest overvoltage and may be harmful to the insulation of the components of the substation.

In this paper, shunt reactor current‐interrupting tests are conducted in high‐power laboratory. The existence of critical arcing time above which reignitions never occur is shown through these tests. From this fact, a phase‐angle‐controlled‐interruption system is proposed. With this system, arcing time is set artificially so that reignitions should be prevented. The reliability of this system is confirmed through the reactor current‐interrupting test in the laboratory as well. Afterward the phase‐angle‐controlled‐interruption system is applied to the shunt reactor switching at an actual 275‐kV substation. The switching performance of this system is measured over three months. Reignition‐free interruption is shown to be attained with this system.
Experimental study on hunting phenomena in synchronous generators
Authors: Matsuki Junya , Okada Takao , Tamaishi Zen'ichi , Kotsuji Akihiro
Published: July 2007

Numerous studies have been made on the hunting phenomena of synchronous machines. However. most of them have been concerned with the mathematical analysis based on equivalent‐circuit models of machine and system, and experimental studies are quite rare. However, few papers have treated the phenomena from the viewpoint of internal air‐gap fluxes which actually govern the machine behaviors.

This paper describes the experimental results on hunting phenomena of synchronous generators caused by a fast‐acting AVR (Automatic Voltage Regulator) in a laboratory‐model one‐machine/infinite‐bus power system. Changes of air‐gap fluxes in the process of hunting phenomena are measured by a search coil wound around a stator tooth on top of the tested synchronous generator and are examined. The interaction is made clear between field fluxes and quadrature‐axis fluxes both of which directly influence the hunting phenomena. The results obtained are confirmed by simulation studies. Thus, the relationship between system stability and machine fluxes is given a clearer understanding than before.
A PWM‐controlled rectifier step up/down output voltage with a high power factor
Authors: Funabiki Shigeyuki , Toita Noriyuki
Published: July 2007

It is desirable that the rectifier that is an ac‐to‐dc converter, have the characteristics of fast response and the wide range of the output voltage control, and the sinusoidal source current waveform. In this paper, a step up/down output voltage PWM‐controlled rectifier is proposed. The features of the proposed rectifier are as follows.

(1) The calculation of pulsewidth is based on the geometrical technique and the source current can be inphase with the source voltage.

(2) The output voltage is controlled from about zero to more than the maximum value of the source voltage.

The aforementioned features are clarified by simulation and the steady‐state characteristics are discussed. Further, these results are verified in experiment using the microprocessor‐based control system.
Structure of a simulated muscle system
Authors: Murakami Toshiyuki , Ishibashi Hirozumi , Ohnishi Kouhei
Published: July 2007

This paper describes a network system designed to realize the motion of a muscle. First, the motion of the network system is analyzed by a model system which consists of many electromagnets. Second, the control strategy of the network motion system, implemented with microactuators, is described. In the proposed network motion system, the total system consists of many force transmission lines and the superposition of the force signals propagated by the lines acts on the final actuator. The proposed motion control method is therefore called the Delay Superposition Method (DSM). Several experimental and numerical results confirm the validity of the proposed method.
Suppression control of speed variation in an induction motor with fluctuating load by repetitive learning control
Authors: Ishda Muneaki , Hori Takamasa , Ohno Masaharu
Published: July 2007

Induction motors are robust and inexpensive machines and are used widely for variable speed control because of the recent development of electronic technique. In the case where loads of the motors are compressors, pumps, and so on, the constant V/F control of the induction motors usually is employed because it is difficult to install speed sensors and accurate speed control is not required. In such loads, the rotational speed of the motors fluctuates considerably because the load torque is pulsated. When the frequency of the torque pulsation is close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced especially in the low‐frequency region.

This paper proposes a method to suppress the variation of the rotational speed of the V/F controlled induction motor with a fluctuated load by feedforward compensation using a timing sensor of 1 pulse/rev, considering that the load torque varies periodically. The feedforward data by a period for the compensation is obtained by the learning control based on the repetitive control in which the motor speed is controlled by periodically reflecting the past speed error on the present V/F input to the inverter. Effectiveness of the proposed method is confirmed by approximate analysis, simulations and experiments.
Magnetic core properties and their thermal stability in a BCC Fe‐Zr‐B‐Cu alloy with nanoscale grain size
Authors: Makino Akihiro , Suzuki Kiyonori , Inoue Akihisa , Masumoto Tsuyosi
Published: July 2007

A mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe‐Zr‐B, Fe‐Hf‐B and Fe‐M‐B‐Cu (M = Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μe) combined with high saturation magnetization (Bs).

Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe86Zr7B6Cu1 alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe86Si9B13 alloy and Fe‐3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co70.5Fe4.5Si10B15 alloy with zero magnetostriction.

In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high‐frequency transformers. Furthermore, the core losses of the nanocrystalline Fe86Zr7B6Cu1 alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe‐Zr‐B‐Cu alloys with the advantages of high Bs, high μe, and low core loss is expected to be used as a core material in various transformers.
Cluster pulse criteria for recognition of partial discharge
Authors: Tsutsumi Yasuyuki , Yonekura Tatuhiro , Kikuchi Tsuyoshi
Published: July 2007

Statistical calculating programs simulating partial discharge appearance are developed and applied to evaluations of criteria for discrimination of the partial discharges from noises. According to the simulation, clusters of sequential pulses appear at the partial discharge inception voltage, and have never been utilized at the usual pattern recognition of the partial discharges. Two original indexes that are a pair pulse rate and a maximum sequential pulse rate are defined to describe the time sequential features of the partial discharge and their signal distinguishable capabilities from noises are evaluated. A new logical index describing the signal distinguishable capability of the usual ø‐q pattern of the partial discharges from the noises also is proposed and compared with those of cluster pulses. The maximum sequential pulse rate gives most sensitive criteria in the bounds of calculating conditions.

A 66‐kV cross‐linked polyethylene cable with an artificial defect is used to detect cluster pulses. By adding twice as many noise pulses as measured partial discharge pulses, the usual ø‐q pattern criteria becomes powerless, but cluster pulse criteria are still informative for the recognition of the partial discharges.
Approach and structure of stabilizing control system preventing an extension of synchronism loss
Authors: Ōura Yoshifumi , Suzuki Mamoru , Yanagihashi Ken , Sato Masihiro , Tsukui Ryouichi , Matsushima Tetsuro , Omata Kazuya
Published: July 2007

Recently, large‐capacity power stations have been built far from load centers with long‐distance transmission lines. Therefore, if a fault occurs at the line, generators in the large‐capacity power station may lose synchronism from the remaining generators [1, 3]. To prevent an extension of loss of synchronism to other generators, fast shedding of some generators is an effective measure.

The following methods have been proposed so far: A method [3] based on energy function approach; and a method [2] which estimates and predicts the relative swing among generators using data measured on‐line at each generator and proposes shedding some generators for stabilization. This method requires a large communication network for an exchange of data between power stations.

This paper presents a new stabilizing method and a newly developed stabilizing control system which does not require a large communication network because it utilizes generator output, voltage and current measured on‐line in the vicinity of the large‐capacity power station. Using these measured data, the system estimates and predicts the relative swing between generators in the large‐capacity power station and the remaining generators. Finally, the number of generators to be shed for stabilization is decided and shedding is performed. Configuration and characteristics of the developed stabilizing control system are shown. The validity of this method is confirmed by simulation and testing using an artificial power system.
Economical preventive control of power flow after disturbances in the decentralized power system
Authors: Uriu Yoshihisa , Koyanagi Fumiko , Yokoyama Kiyoshi
Published: July 2007

This paper discusses the preventive controls of the generator outputs to improve security in the decentralized power system. Preventive controls of the power system can improve security level. However, the preventive control requires too much computation time because of too many considerable faults in the power system. Multiarea decentralization can be considered to reduce computation time of the power flow calculation. It is assumed that the effects of disturbances in the external systems are relatively smaller than the effects of disturbances in the study area.

Linearized sensitivity analysis is used to evaluate the effects of the external systems to reduce computation time. Linear programming is used to determine the control signals of generators considering the incremental cost of generators. The New England 38 buses system is used as an example system to check the validity of the algorithm in this paper. The calculations of the example system show satisfactory results.
Ripple compensation of a single‐phase rectifier by two‐quadrant chopper and auxiliary capacitor
Authors: Irie Hisaichi , Takemoto Nobuyuki , Yamashita Takeshi
Published: July 2007

The single‐phase converter or rectifier always has a voltage ripple in the output dc voltage because the instantaneous power of the single‐phase ac line varies on the double frequency of the line. To obtain a smooth dc voltage, an energy‐storing element is necessary. The smoothing capacitor is used to reduce the ripple voltage in the dc output. Usually, it has much larger capacitance than that needed to absorb the ripple energy.

This paper discusses the required capacitance to absorb the ripple energy, and represents a ripple‐compensation circuit with a small auxiliary capacitor controlled by a 2‐quadrant chopper connected in parallel to the smoothing capacitor. The appended capacitor works under large ripple voltage and efficiently absorbs the ripple energy. The ripple‐compensation circuit works as an equivalent capacitor with a large capacitance.
Structure and operation mechanism of a friction‐type piezoelectric motor utilizing the principle of strain‐wave gearing
Authors: Ishida Muneaki , Shirasuka Keiichi , Hori Takamasa
Published: July 2007

This paper proposes a new type of motor which utilizes multilayer piezoelectric devices for electromechanical power conversion and the mechanism of the strain‐wave gearing to generate traveling waves and motive force. The construction and basic operation of the motor are described. The motor can be operated in variable frequency because piezodevices are operated in the nonresonant mode. Approximate analysis is performed to clarify the operating mechanism of the motor and to obtain characteristics on the rotational speed in the case of no‐load. Experimental results on rotational speed of the prototype motor made of metals except for the piezoelectric devices also are presented, which verifies the feasibility of the proposed motor.
A sinusoidal PAM‐PWM inverter
Authors: Inoue Masakazu , Taniguchi Katsunori
Published: July 2007

A new strategy, using both PAM (pulse amplitude modulation) and PWM (pulsewidth modulation) in combination for a power inverter is described. The output waveforms in the proposed PAM‐PWM inverter are investigated both theoretically and experimentally. The line‐to‐line voltage waveform includes the fundamental component and the sidebands of the carrier frequency. Lower‐order harmonics are not included in the output waveform. The amplitude of the fundamental component increases 15 percent more than that of a conventional sine‐wave inverter. Since each inverter arm does not operate during two‐thirds of the period, the heat generated in the devices is reduced, i.e., the size of the inverter system can be minimized because of the reduction in the heat dissipating equipment.
Harmonic analysis of a single‐phase rectifier with a DC filter capacitor
Authors: Sakui Masaaki , Kitamura Toshihiro , Fujita Hiroshi
Published: July 2007

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.
Suppression of electrical treeing by addition of lithium carbonate to low‐density polyethylene
Authors: Hoshimura Yoshikazu , Yamamoto Shigeru
Published: July 2007

Low‐density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added.

This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate‐added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz‐added LDPE and even at elevated temperatures lithium carbonate‐added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate‐added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz‐added LDPE, which showed improvement in heat resistance of LDPE.
Magnetic properties of melt‐spun Nd‐Fe‐Co‐B‐Cu‐Nb system alloys and their bonded magnets
Authors: Yamamoto Hiroshi , Katagiri Eito
Published: July 2007

Melt‐spun ribbons of Nd‐Fe‐Co‐B‐Cu‐Nb system alloys were prepared by the single roller rapid‐quenching method. The effects of composition, wheel velocity and heat‐treatment on the magnetic properties were investigated. The magnetic properties of bonded magnets prepared by compression molding of optimally annealed ribbons were also measured. A maximum energy product of 152.1 kJ/m3 was obtained for the Nd11Fe72Co8B7.5Cu0.5Nb1.0 alloy ribbon prepared at a wheel velocity of 17.1 m/s.

From the TEM observation on the above Nd11Fe72Co8B7.5Cu0.5Nb1.0 ribbon, the particle size of these ribbons was determined to be between 10 and 40 nm. It is conjectured that the high remanence is observed by the magnetic interaction of these fine particles, and it was found that these fine particles were achieved by Nd‐Fe‐Co‐B compound in addition with Nb and Cu at the same time.

The amorphous Nd11Fe72Co8B7.5Cu0.5Nb1.0 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 15 min. Its corresponding value of (BH)max is 144.5 kJ/m3. A maximum energy product of 88.1 kJ/m3 was achieved with Nd11Fe72Co8B7.5Cu0.5Nb1.0 bonded magnets made from the optimally prepared ribbons.
Stability analysis of a controlled‐current source‐fed induction motor vector control system without a speed sensor
Authors: Tsuji Mineo , Yamada Eiji , Izumi Katsuhiro , Oyama Jun
Published: July 2007

One of the representative vector‐controlled induction motor drive systems without a speed sensor is composed of a rotor flux estimator, a PI torque current controller and a conventional vector‐controlled current source. However, the stability analysis of this system has not been reported.

In this paper, the flux estimator is interpreted as a flux observer. Then a linear model of the system is proposed by deriving the equations of the flux estimator in a synchronously rotating reference frame. By computing the trajectories of the poles and zeros and the transient responses, the following results are obtained.

(1) If the rotor flux is estimated using only the stator equations (voltage model), the system becomes unstable when the actuator stator resistance is smaller than the value used by the controller.

(2) By choosing a small time constant of the first‐order lag element in the flux estimator (reciprocal number of observer gain), the poles and zeros on the imaginary axis move to the stable region. However, another pair of poles has reverse performance.

(3) From the viewpoint of stability, the gain of the PI torque current controller should be chosen as large as possible and the stator and rotor resistances in the controller should be set to values smaller than their actual values.
Practical design of superconducting generator—electrical characteristics equations
Authors: Maki Naoki
Published: July 2007

A superconducting generator (SCG) consists of a nonmagnetic cryogenic rotor, which contains a super‐conducting field winding cooled by liquid helium, and an airgap armature winding, which makes it possible to obtain a high magnetic field in the airgap. Since the SCG construction differs from that of the conventional generator, practical application requires that its electrical and mechanical design methods be established.

This paper describes electrical characteristics equations of the SCG, electromagnetic shield characteristics of double dampers and proof test results of a 50‐MVA experimental SCG. Equations for the generator parameters (voltages, output capacity, reactances, time constants, flux densities), which are useful for the practical design of the SCG, are derived from two‐dimensional electromagnetic analysis considering winding thickness and the edge effect. From comparison with measured and calculated values of no‐load, sudden 1–3 phase short‐circuit and slip extended tests, these equations were confirmed as valid.
A new voltage control equipment using fuzzy inference
Authors: Takahashi Tsuyoshi , Kitou Masahito , Asai Michio , Kido Mitsuyasu , Chiba Tomio , Kawakami Junzou , Matsui Yoshiaki
Published: July 2007

Power system control equipment needs higher sensitivity and operational reliability. Advanced voltage control equipment is needed for reducing the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage to meet today's power system requirements. However, these objectives are in a trade‐off relationship. Studies of voltage control derived from a knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Compared with corresponding conventional equipment, the new equipment improved the deviation of 30 min average voltage of 30 percent.

This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, field test results are described along with rules of fuzzy inference, membership functions, and the deviation of 30 min average voltage through detailed simulation.
A rapid solution for the maximum loading point of a power system
Authors: Kataoka Yoshihiko
Published: July 2007

This paper presents a new solution method for computing the maximum loading point of a bulk power system under the condition where the loads of the nodes can be parameterized by a scalar which is the loading level of the system.

A special loading model, in which the loading level of the system depends on the voltage magnitude of a loading node, is adopted for the purpose of releasing the load‐flow computation from the ill‐condition near and at the maximum loading point. The loading level of the system is unknown in the aforementioned loading model. The maximum loading point is obtained by adjusting the operating parameter so as to achieve the maximum loading.

The operating parameter is adjusted in the converging process of the Newton‐Raphson iterative computation. The adjustment is computed based on the least squares estimation using the data set which is obtained from its own iteration process.

It is shown in numerical examples that the proposed method is satisfactorily rapid, stable, and accurate.
IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias
Authors: Fukushima Toshihiro , Kato Kazuaki , Ohsumi Shuzo , Takenaka Tadashi
Published: July 2007

Recently, one type of thermal‐type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature Tc for stable responsivity to temperature. Electric field induced‐type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Sc1/2Ta1/2)O3 (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor.

This paper describes the sensor properties of electric field induced‐type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high‐response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced‐type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.
Design of single‐sided linear induction motors using a nonlinear optimization technique
Authors: Higuchi Tsuyoshi , Nonaka Sakutaro
Published: July 2007

Both low‐speed wheel‐on‐rail and the medium‐speed Maglev transport system with single‐sided linear induction motor (SLIM) propulsion have been in practical application.

This paper presents the method of optimizing the design parameters of SLIMs using the nonlinear optimization method. The optimization problem is formulated by the use of the design formulas taking into account the end effect, skin effect and airgap leakage, and the transformation method and the simplex method are applied to solve the problem.

Seven parameters, such as the number of poles, the pole pitch and the stack height, are chosen as the independent variables. The output kW/input kVA, the maximum flux density in the core teeth, the temperature increase, the primary length, the stack height and the maximum thrust are selected as the constraint functions. The performance characteristics are estimated using space harmonic analysis as well as the approximate equations.

The method is applied to the SLIM design for urban transit, and the maximum speed is about 70 km/h. As the transformation methods, the interior point transformation and the exterior point transformation are compared from the viewpoints of accuracy and CPU time. The design is analyzed under several objective functions, the primary weight, the input kVA and the cost of secondary materials.
Realization of the powering/regenerative operation of the induction motor by the parallel resonant power converter and proposal of a novel circuit topology
Authors: Yang Seung Hak , Harashima Fumio , Takizawa Satoki , Kondo Seiji
Published: July 2007

A resonant power converter for the low switching loss power conversion must be achieved for high‐frequency zero voltage switching or zero current switching. The important matters of the continuation of resonant phenomena are the control strategy of resonant initial current and the clamp circuit for suppressing the resonant link voltage.

The control strategy of the resonant initial current is discussed and the powering and regenerative operation are shown successfully in the steady state and transient state by experimental test.

Finally, a new resonant dc link dual converter system is proposed and it is confirmed that the voltage stress of the resonant capacitor and the rms value of electrolytic capacitor current are decreased with experimental test also.
Effect of the stator slot opening on the electromagnetic vibration in a squirrel‐cage induction motor
Authors: Onodera Satoru , Yamasawa Kiyohito
Published: July 2007

Field harmonics produce a radial electromagnetic force in a squirrel‐cage induction motor with a particular number of rotor slots corresponding to the number of poles. The radial force causes vibration and acoustic noise.

In this paper, a simplified equation for the radial force at no‐load is introduced, and the relation between the width of the stator slot opening and the radial force is discussed quantitatively. The field harmonic component produced by the interaction between the fundamental magnetomotive force due to the stator current and the pulsation of air‐gap permeance dominates for the radial force.

Furthermore, the vibration of the stator core due to the radial force is calculated under a simple assumption. The calculated results are verified by experiments.