bluuebunny/crossref_metadata_2025 huggingface dataset:
Power‐system stabilizing control by SMES using fuzzy techniques and neural networks
Authors: Kawakita Yasuhiro , Ohsawa Yasuharu , Arai Kenji
Published: July 2007

It has been clarified that a superconducting magnetic energy storage (SMES) is very effective for power system stabilization. The control methods proposed for power system stabilization by SMES include the pole assignment, the optimum control, and so on, each of which, however, has its drawbacks. The application of fuzzy control is considered to overcome these drawbacks.

This paper considers the power system stabilization by fuzzy control of the active and reactive power of SMES. First, the adequate fuzzy control rules of an SMES for the model power system is derived. Then, to alleviate the dependence of the fuzzy control on the operating condition and the fault, a method is proposed which adjusts the fuzzy parameter according to the operating condition and the fault using a neural network. The validity of the proposed method is examined by computer simulations.
Multifault calculation method for dynamic stability study of electric power systems
Authors: Tanaka Kazuyuki
Published: July 2007

For the fault condition in dynamic stability study, balanced faults have mainly been utilized. Recently, however, with the progress of system protective control technologies such as the multiphase reclosing system for a faulted transmission line, the needs for stability software which would be able to calculate simultaneous faults without any restrictions on fault types, total numbers or location, have been increasing.

This report presents the newly developed multifault calculation method based on symmetrical components which is able to calculate simultaneous faults without any restrictions on combination of fault types, and total numbers or location. Fault types consist of balanced/ unbalanced ground fault, short‐circuit fault, line‐out of transmission lines, and short‐circuit of series condenser. The proposed method also allows for calculation of faults at an arbitrary location on the line without any topological changes of each symmetrical network even if the faults include line‐end faults with ensuring outages.

An example was shown to clarify the validity of the proposed method. Moreover, transient stability limits under the various fault conditions also were discussed.
Compensation characteristics of shunt active and series active power filters
Authors: Peng F. Z. , Kohata Masakazu , Akagi Hirofumi
Published: July 2007

Active power filters have been used in practice to suppress the harmonic interference in power systems. To compensate for harmonic currents of loads, active power filters usually are connected to power systems in parallel with the loads. These filters, which are called shunt active filters here, are very effective for loads that can be considered as current sources, such as thyristor rectifiers with large dc reactances. Many papers have covered the shunt active filters applied to these current‐source loads, however, none has discussed characteristics of the shunt active filters when they are applied to voltage‐source loads.

On the other hand, since more and more diode rectifiers with capacitive dc filters have recently been used, harmonics generated by them have become an issue. The diode rectifier with capacitive dc filters behaves as a voltage source rather than a current source. When a shunt active filter is applied to such a diode rectifier, the current injected from the shunt active filter may flow into the diode rectifier. As a result, harmonics of the source current cannot be reduced effectively, and harmonic current flowing into the diode rectifier increases greatly.

This paper presents the aforementioned problem of shunt active filters analytically and experimentally. Then a series active filter is proposed to suppress the harmonic current of the diode rectifiers. The features, operating conditions, and considerations of shunt active filters and series active filters are described analytically and demonstrated experimentally. Taking a diode rectifier with capacitive dc filter as a typical voltage‐source load, compensation characteristics of shunt active filters and series active filters are discussed by experiment and simulation. The validity of the series active filters is illustrated experimentally.
An expert system for switch operation planning on line dispatching
Authors: Haba Toshiaki , Maeda Shigeo , Watanabe Dai , Fukui Chihiro , Nomoto Masaaki
Published: July 2007

An expert system is presented that produces the operation sequence for disconnecting apparatus from a power system under normal operating conditions.

To maintain the reliability of power supply on the network during the operation, the operation sequence must be produced in due consideration of network states, such as load factors and routes of transmission line. Besides, since the network which the system manages includes many high‐voltage consumers, the operation sequence for each consumer should be divided into detailed switch operation sequence.

To produce a detailed switching operation sequence simultaneously with macronetwork operation sequence, we introduce the multilayered object‐oriented network model for the knowledge base of this expert system.

Each layer of this model represents network configuration in the different degree of detail, and the consistency between states of layers is maintained by an interlayer message‐passing mechanism. On the layer which represents apparatus and their connections in detail, the inference engine can generate the switching operation sequence. On another layer which represents control centers and consumers, the inference engine can search for routes of power supply and can generate the sequence of changing over the network. Therefore, by using each layer properly, the inference engine can produce various kinds of operation sequences.

Furthermore the object‐oriented network model facilitates maintenance and extension of the system.
Overvoltage phenomena caused by disconnecting motor‐loads on power line with open‐phase
Authors: Himeno Takashi , Okamura Yukio , Asada Minoru , Nakamura Toshihiro
Published: July 2007

This paper describes overvoltage caused by disconnecting a lot of motor‐loads on a power distribution line with power‐factor‐correcting capacitors during a transmission line open‐phase. The overvoltage phenomena are studied by a field test, a steady‐state analysis and a transient analysis. Experimental results show that the line‐to‐line voltage on a 6.6 kV distribution line with an open‐phase 22 kV transmission line amounts to 1.7 per unit. The overvoltages are caused by two types of resonance. One is the linear circuit resonance between the power‐factor‐correcting capacitors and the secondary side impedance of motors. The difference between positive components and negative ones of the impedance produces the resonance. The other is the nonlinear circuit resonance between the power‐factor‐correcting capacitors and the saturated reactances of a transformer.
Effect of defects and moisture on insulation characteristics of XLPE insulated cable
Authors: Katsuta Ginzo , Toya Atsushi , Kanaoka Mamoru , Katakai Shoshi , Maruyama Yoshio , Muto Hideji
Published: July 2007

Sample cables having a few types of defects (such as voids, contaminants, and protrusions) with more volume than usual, were prepared intentionally to clarify how these defects affect separately insulation characteristics under the presence/nonpresence of moisture. In the case of void inclusion, insulation characteristics are even more susceptible to ac voltage than impulse voltage, and the distribution of lifetimes is classified into a wornout failure type due to discharge deterioration.

While protrusions and some other contaminants can greatly deteriorate original dielectric strength, these defects have a relatively slight effect on long‐term endurance in the atmosphere. Therefore, the distribution of lifetimes is classified into an early‐failure type. With reference to the influence of moisture, in a strong electric field (exceeding 15 kV/mm) and in a short‐term region, there is an increase in harmfulness around defects with water absorbed, thereby inducing electrical trees and resulting in a breakdown. In the light electric field (no more than 15 kV/mm) and in a long‐term region, harmfulness of defects will not deepen to a considerable extent, and the growth of water trees very possibly is influential.
Pulse switching characteristics of MAGTs for pulsed power applications
Authors: Endo Fumihiko , Atsumi Kaoru , Okamura Katsuya , Watanabe Yukio , Kaneko Eiji , Ohshima Iwao
Published: July 2007

For pulsed power systems such as lasers and accelerators, semiconductor switches with their longer service life have actively been developed as replacements for thyratrons. The MOS‐driven thyristors are suitable for pulsed power applications because they have high‐power handling and fast turn‐on capabilities. The MOS‐assisted gate‐triggered thyristor (MAGT), designed especially for pulsed power, is a promising candidate in this field.

This paper presents the results of an investigation into the performance of MAGTs. Using a pulse‐forming network (PEN), the pulse‐switching characteristics and the dynamic resistance characteristics during the current flow are investigated. A maximum current density of 21.8 kA/cm2anddi/dtof 106 kA/μs/cm2with 1550‐V anode voltage on a single‐shot basis were obtained. Furthermore, a life test with 109shots at a high repetition rate showed no degradation in the observed characteristics. Based on these experimental results, a carrier flow model of MAGT during turn‐on process is proposed and the turn‐on mechanism is considered.
Analysis of estimation error of observer for disturbance torque and velocity
Authors: Shimada Akira
Published: July 2007

This paper analyzes some features of estimation error of the observer which estimates disturbance torque and velocity. This observer inputs the information of driving torque and current position, and outputs the information of disturbance torque and velocity.

Although this observer is a practical tool to compose a robust control system, there has never been sufficient information to make the most of it. Thus the study to grasp some basic features of the observer is needed now. Also, it is very important to analyze the estimation error on it.

This paper considers the estimation error caused by disturbance torque and observation noise because these seem to be the most significant causes. The result of analysis provides a practical way to select the pole allocation of the observer. Finally, the simulation and the experimental results are shown.
Development of cable fault location method using fiber optic distributed temperature sensor
Authors: Takinami Naoki , Chino Takashi , Yoshida Shotaro , Miura Isao , Watanabe Kazuo , Amano Kazuo
Published: July 2007

When ground‐fault problems occur on a cable line, immediate fault location and restoration are required. Therefore, various new methods to locate the fault point instantaneously have been investigated to replace such conventional methods as the Murray loop method and the pulse radar method [1]. These methods require a long time to locate the fault point. One possible fault location method is to sense the temperature rise following a ground fault using a fiber optic distributed temperature sensor. Application of this method was found feasible through sensing the temperature rise at a ground‐fault test using a thermocouple as a temperature sensor with test cables [4].

A power/optical composite cable was prepared experimentally and after verifying its thermal mechanical performance, the temperature rise at an incidence of a fault was determined and the anticipated performance was demonstrated in a ground‐fault test. This article describes the outline of the test.
Real‐time digital simulator for power system analysis
Authors: Sato Nobuyuki , Nakazawa Taro , Yamazaki Akira , Taoka Hisao , Iyoda Isao , Noguchi Hideo
Published: July 2007

To understand a number of power system phenomena and to predict critical conditions in system operation, such as voltage collapse, a real‐time simulator able to model the dynamic behavior of large power systems has been needed for a long time. The need for real‐time simulations stems from the fact that in many practical situations it is desirable to test new equipment and analyze the dynamic behavior of a large power system using the actual pieces of equipment.

A new digital simulator was developed based on a hypercube‐type massively parallel computer to achieve this objective. The new simulator features: (1) real‐time simulation of a large power system which covers transient stability through long‐term behavior with constant accuracy level; (2) user‐friendly man‐machine interfaces which mimics an actual operating environment and realtime data presentation on a CRT; and (3) high‐speed digital/analog conversion interfaces which connect the digital simulator to actual equipment.
Protective system for a high‐power capacitor bank
Authors: Sato Yasuhiro , Hirano Yoichi , Yamaguchi Sataro
Published: July 2007

A new protection system for capacitor banks in the case of a short‐circuiting accident is described. A pulsed power system composed of many capacitor units and closing switches is well known for producing a controlled pulse current of high power as for the power source of a plasma experimental device, etc. According to the increase of capacity of a bank system, it becomes important to protect the whole bank system from a short‐circuiting accident in a capacitor unit.

Although some protective ideas have been proposed, these conventional ideas have not been sufficient to absorb the energy flowing into the failure unit from other normal units. Constructing the new 1‐MJ capacitor bank for a plasma experimental device, a newly conceived protective device is designed. The new protection system can absorb the bank energy and suppress the short‐circuiting current flowing into the failure capacitor units, and overcomes the defect in former protection systems. To confirm the utility of a new protection system, a test of a protection resistor imitating the actual bank circuit was made. The test result showed that absorbable energy for the unit ceramic resistor amounted to 1500 Joule/cc. The new system is adopted to the bank system of the TPE‐1RM15 plasma experimental device.
Intra‐aortic balloon pump driven by a linear pulse motor
Authors: Yamada Hajime , Wakiwaka Hiroyuki , Yano Takeshi , Watarai Akira , Karita Mitsuji , Morimoto Masami
Published: July 2007

The Intra‐Aortic Balloon Pump (IABP) is an effective device in assisting circulation. However, a small‐sized IABP is required in related fields.

This paper proposes a new small‐sized IABP which is driven by a Linear Pulse Motor (LPM) rather than an air‐driven motor. In general, the LPM has advantages of high thrust/input power and good controllability. The developed LPM for the IABP drive has high thrust/input power of 19.9 newtons/W. It also has kinetic thrust of 270 newtons at the range of speed from 100 to 140 mm/s. The IABP using the LPM has an extremely simple construction. As the result of mock testing, the IABP using an LPM not only gives the same performance as the ordinary air‐driven IABP, but the mass of the IABP will be reduced to half the size of the ordinary one.
Composite power systems reliability evaluation based on demand‐side reserve
Authors: Mottate Yasunori , Saitoh Hiroumi , Toyoda Junichi
Published: July 2007

This paper proposes new demand‐side reliability indices and useful computational methods for reliability evaluation of composite power systems. These new indices are based on the active power which can reach each demand spot under generating and transmission network constraints. This conception is defined as “reachable power,” and it leads the reserve margin on each demand spot, which is called as “demand‐side reserve.” If the reachable power is insufficient to satisfy the demand, load curtailment is required.

In the proposed approach, the conception of the load curtailment area is defined, and the estimate method of load curtailment area is indicated. In case the reachable power exceeds the demand, system reliability is evaluated by the demand‐side reserve, and the power system is divided into several reliability zones according to the demand‐side reserve levels. Small system examples are used to illustrate principles of the proposed approach, and middle system examples show the effectiveness and practicality.
Method for analyzing eddy currents in moving conductors
Authors: Muramatsu Kazuhiro , Nakata Takayoshi , Takahashi Norio , Fujiwara Koji
Published: July 2007

When magnetic fields in electrical machines with moving conductors such as linear induction motors are analyzed, eddy currents due to the movement of conductors should be taken into account. Although two kinds of coordinate systems (moving and fixed coordinate systems) can be applicable to the analysis of eddy currents in moving conductors, the advantages and disadvantages of both coordinate systems are obscure.

In this paper, methods for analyzing magnetic circuits with moving conductors are classified systematically, and the moving and fixed coordinate systems are compared with each other from the standpoints of accuracy, memory requirement, and CPU time. It is shown that the moving coordinate system is superior to the fixed coordinate system for transient analysis.
Steady‐state characteristics of matrix converter
Authors: Oyama Jun , Higuchi Tsuyoshi , Tsukamoto Ryuta , Haraguchi Takehisa , Yamada Eiji , Koga Takashi
Published: July 2007

The matrix converter proposed by Venturini is very simple in structure and has powerful controllability. However, there are few applications especially in power electronics fields. This seems to be caused mainly by the fact that such power devices that were fast enough to suppress ringing oscillations in the supply lines and large enough to pay for more devices and more complicated control circuits than in conventional dc‐link converter‐inverter systems were not available. At present, static induction thyristors (SIThs) have been introduced and a new possibility for the matrix converter has been raised.

This paper describes a new control strategy which is simple and practical and allows the output voltage of 0.866 times the supply voltage to be generated. Also, the new firing sequences which eliminate voltage and current spikes are proposed. Steady‐state and distortion characteristics of the prototype PWM matrix converter with SITh are shown.
Neural‐network steering control of an automated guided vehicle
Authors: Funabiki Shigeyuki , Mino Michio
Published: July 2007

With the progress in factory automation in industry has come the demand for higher speed drive and performance for an AGV (automated guided vehicle). A new steering control of the AGV by fuzzy control has been proposed to replace the PI control. However, much time is required to investigate the regulations and to adjust the scaling factors for excellent performance in the fuzzy control.

In this paper, a new steering control for an AGV based on the neural network using the backpropagation method is proposed. The good steering control results by the fuzzy control are adopted for the teaching signal of the neural network. First, the effect of the number of learning and the learning errors on the steering control results are discussed by computer simulation using the AGV model. Further, the ability of generalization in the turning radius and the traveling speed also are investigated. It becomes clear that the AGV can travel along a designated route provided the neural network learns both the right and left turning at the maximum traveling speed and the minimum turning radius. Then it is proved by an experiment using the AGV constructed for the test that the proposed steering control method is very affective.
Performance evaluation of solar‐powered air conditioner
Authors: Tanaka Kuniho , Ding Lu , Makino Yasuhiro , Sakoguchi Etsuo , Takeoka Akio , Yamada Eiji
Published: July 2007

With present‐day global environmental and energy problems, high expectations exist for solar power generation to reduce carbon dioxide generated by the consumption of fossil fuels.

On the other hand, power consumption in residential homes is increasing every year. Among the many household appliances, the power demand for air conditioners increases dramatically during the summer, particularly in the afternoons. Since this pattern closely matches the output pattern of solar cells, it should be possible to combine a photovoltaic array with an air conditioner to decrease the energy consumption within the home.

In this paper a residential solar‐powered air conditioner is developed that operates through a combination of photovoltaic array and commercial power. Also, the configuration and specification of the solar‐powered air conditioner are described, and its performance characteristics are examined by analysis of the characteristics of the solar cell.
Long‐term load forecasting using improved recurrent neural network
Authors: Hayashi Yasuhiro , Iwamoto Shinichi
Published: July 2007

In general, electric power companies must prepare power supply capability for maximum electric load demand because it is very difficult at present to store electric power. It takes several years and requires a great amount of money to construct power generation and transmission facilities. Therefore, it is necessary to forecast long‐term load demand exactly in order to plan or operate power systems efficiently. Several methods have been investigated so far for the long‐term load forecasting. However, because the electric loads consist of many complex factors, good forecasting has been very difficult.

This paper proposes a long‐term load forecasting method using a recurrent neural network (RNN). This is a mutually connected network that has the ability of learning patterns and past records. In general, when interpolation is used for unlearned data sets, the neural network provides reasonably good outputs. However, when extrapolation is used, such as in long‐term load forecasting, some kind of tunings have been necessary to obtain good results. Therefore, to solve the problem, a method is proposed in which growth rates are used as input and output data. Using the proposed method, successful results have been obtained and comparisons have been made with the conventional methods.
Characteristics analysis of superconducting power transformer without iron core
Authors: Yamaguchi Hiroshi , Sato Yukihiko , Kataoka Teruo
Published: July 2007

With the progress of superconducting wires for ac power use, research on superconducting power transformers is increasing. These transformers can be divided into two types: the iron‐core type [1, 2]; and the air‐core type [3–9]. The latter type has such advantages as absence of iron losses and magnetic saturation, and greater possibility of reduction of size and weight. However, the air‐core transformer has a large magnetizing current due to the absence of iron core. Hence, research has been carried out on the possibility of using the air‐core transformer also as a shunt reactor in a power transmission system. However, the operating characteristics of the air‐core transformer, such as voltage regulation and reactance voltage, are not clear at present.

In this paper, the equivalent circuit without losses is proposed first. Since this equivalent circuit is expressed by means of the magnetic coupling factor and self‐inductances of windings, the effect of these parameters on the transformer characteristics can easily be investigated. Then, based on this equivalent circuit, the per‐unit expressions for the air‐core transformer characteristics are derived and the characteristics are analyzed in detail. The validity of the theoretical results are confirmed by experimental results obtained by the use of an experimental superconducting transformer.
Low torque pulsation and high‐power control of permanent magnet motor with distributed electromotive force
Authors: Osawa Hiroshi , Hashii Makoto , Matsuda Naotaka , Endoh Kenji
Published: July 2007

This paper describes low torque pulsation and high‐power control of permanent magnet synchronous motor (PM motor) with distorted electromotive force (emf).

The experimental model of PM motor is a 40‐kW, 190 r/min, salient‐pole, six‐phase machine. An individual single‐phase transistor inverter is connected to each phase of PM motor as a power source. By adopting full pitch and concentrated winding in the armature of the motor, the rate of flux utilization and output torque per mass can be increased. This winding causes trapezoidal distortion in the phase voltage waveform at no load. For realization of high‐performance control of PM motor, the current waveform should be determined so as to minimize torque pulsation and to maximize the output torque of the motor under the rated current.

This paper proposes also the method to determine the optimum current waveform. The currents and emfs are expressed as N‐dimensional vectors (N: the number of phases). Due to the characteristics of the particular structure of the motor, the armature reaction is small enough to be neglected. In this case, the optimum current vector can be derived under two conditions: (1) the direction of the current vector always agrees with that of the emf vector; and (2) the scalar product of the two vectors is held constant. Supplying the optimum current vector provides no torque pulsation and the nearly maximum output torque under the rated current. This method also can derive the new optimum current corresponding to open‐phase operation.

The validity of the method is confirmed experimentally. The characteristics of the experimental model of PM motor also are described in this paper.
Chaotic behavior in parametric oscillations
Authors: Tatsuta Fujio , Tadokoro Mutsuo
Published: July 2007

Parametric oscillations which occur in a nonlinear two‐phase circuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light load, the output voltage of these devices exhibits unstable oscillations, i.e., subharmonic oscillations, quasi‐periodic oscillations or chaotic oscillations. This paper analyzes the abnormal oscillations and confirms the validity of the analysis experimentally.

In this paper, new circuit equations are presented that can be applied to the analysis of a two‐phase nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi‐periodic with the existence of resistances of the power supply side. Also, when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations in addition to the aforementioned oscillations.
A numerical integration method for long‐term power system dynamic simulation
Authors: Inoue Toshio , Taniguchi Haruhito , Ichikawa Tatsumi
Published: July 2007

Large power system frequency/voltage fluctuations due to severe faults in trunk transmission lines or major generating units may trip‐off other facilities and result in large‐scale power system blackout. To prevent such blackout, development of an accurate and fast long‐term power system dynamic simulation tool is required. With respect to the development stage, selection of a numerical integration method available for step‐size adjustment, and the development of a scheme for the adjustment are principal subjects.

The trapezoidal and the second‐order Gear methods were selected as possible candidates for the step‐size adjustment from the viewpoint of numerical stability. The trapezoidal method is selected from the viewpoint of accuracy and applicability to power system dynamic simulations.

A new scheme for the automatic step‐size adjustment is proposed for the trapezoidal method to achieve fast simulation of the long‐term power system dynamics. The validity of the proposed scheme is verified through simulation studies on a single‐machine‐to‐infinite bus system.
Improvement in stabilization of launching performance and launching velocity using linear accelerator
Authors: Ebihara Daiki , Watada Masaya , Nagashima Kenji
Published: July 2007

This paper describes the improvements in launching stability and launching velocity of the linear accelerator (LAC).

The authors have designed and produced a railgun using the LAC for weaving loom shuttles. The LAC is an electromagnetic launcher which enables a projectile to be launched at a speed of more than 50 m/s. Basically, it consists of a unipole linear dc motor and operates the same principle as dc rotary motors, the most difficult problem in this system being the stabilization of the current collection on the projectile.

Then, various launch experiments have been conducted. As a result, the carbon projectile was launched at a speed of 73 m/s using double‐state‐type LAC.
Gas discrimination method for detecting transformer faults by neural network
Authors: Nogami Takeki , Yokoi Yoshihide , Ichiba Hideo , Atsumi Yoshihiro
Published: July 2007

This paper describes a method available for early detection of abnormality in an oil‐filled transformer. In this method, four gas sensors having different characteristics and neural network are used to identify gas species (H2, CH4, C2H4, C2H2 and mixture of two species). To improve the selectivity of gas sensors, the time response patterns induced by changing sensor temperature and the stationary sensor output are identified by neural network. Furthermore, the mixture ratio of gases is derived by using the stationary sensor output in response to the changing sensor temperature.

Gas species are well discriminated, and the mixture ratio derived from the sensor output agrees well with the measurement by gas chromatography. Therefore, it is confirmed that our method is applicable to the transformer diagnostic technology.
Three‐phase and zero‐phase current sensors using hall ICs
Authors: Hara Kazuhiro , Kawamorita Satoshi
Published: July 2007

Three‐phase current sensors are required in power‐line distribution systems to monitor currents and protect systems from possible failures. Zero‐phase current sensors also are required to detect leakage currents between power lines and the earth, thus preventing accidents such as a fire.

This paper describes new three‐phase and zero‐phase current sensors which are based on a zero method. The sensors consist of Hall ICs, coils, and electronic circuits; no magnetic cores are used. The three‐phase current sensor provides measurements of currents from 0.8 A to 720 A with excellent accuracy, while the zero‐phase current sensor provides measurements from 90 mA to 20 A. The output signal levels are suitable for microprocessor‐based metering and control systems. The sensors are relatively small and lightweight compared to a conventional current transformer (CT). Moreover, they withstand excess currents and do not yield burning or deterioration. They do not require expensive components so they have an advantage in cost compared to an optical‐fiber current transformer.
Fundamental design and electrical characteristics of superconducting commutatorless motor
Authors: Muta Itsuya , Hoshino Tsutomu , Hayashi Kenichiroh
Published: July 2007

Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than those of conventional motors. Thus the low synchronous reactance would be expected to improve the torque‐ampere ratio stability and the overload capacity in case of the variable‐speed drive system of a load‐commutated inverter due to the small armature reaction. Moreover, the low subtransient reactance may contribute to lessen the voltage stress during the shortened commutating period, especially in current source‐type inverter (CSI) systems.

In this paper, after presenting analytical formulas needed for a machine design, one design algorithm is described, citing one example of an experimental CSI‐fed superconducting motor of 30 kVA which will be fabricated. Further, the distinguished features in its operation, as expected in the foregoing, are verified by the computer simulation study in comparison with a conventional machine in terms of a high specific power density, an extension of stable power limit, and so on.
Expert system for dispatch control in restoration of ehv power system after complete blackout
Authors: Kakimoto Naoto , Lin Bunpin , Sugihara Hiroaki
Published: July 2007

Present‐day power systems operate with high reliability, and it is rare that a blackout will extend over an entire system swiftly and securely.

This paper considers automatic power supply to loads after a complete blackout of a system. First, taking into account characteristics of generators, loads, and initial power sources, a method is proposed of allocating several generators to each load in parallel to the system and supplying power to the load sequentially. Second, to remove the imbalance between supply and demand of power, a method is proposed of adjusting the amount of supply and generation according to a present imbalance and the sum of past ones. Third, to automatically issue orders for start‐up, parallel, follow‐up, stand‐by, and stoppage of generators, several rules for each power station are set and an expert system is made based on them. Finally, the expert system is applied to a model power system, and it is verified that it can restore loads without any trouble for a complete blackout which occur at any time of a day and in any restoration pattern.
Application of genetic algorithms to service restoration in distribution systems
Authors: Fukuyama Yoshikazu , Ueki Yoshiteru
Published: July 2007

Service restoration in distribution systems can be formulated as a combinatorial optimization problem to determine power sources for each load considering radial network constraints and power source limits. Until now, the problem has been considered using conventional methods, e.g., the branch‐and‐bounds method, expert system, neural networks, and fuzzy reasoning.

Recently, Genetic Algorithms (GA) have been recognized as one of the efficient methods for solving large combinatorial optimization problems. The method can perform parallel search, and can more easily search optimal solutions.

This paper presents an application of GA to service restoration in distribution systems. The feasibility of the proposed method is demonstrated on a typical distribution system model. The result shows that the method can solve the problem efficiently, and this tendency becomes dominant by increasing problem dimensions.
Loop power system control by high‐speed phase shifter
Authors: Fujita Hideki , Kurebayashi Hisayuki , Nohara Haruo , Goto Masuo , Kito Yukio
Published: July 2007

Recently, power systems have become larger and more complex. Particularly, the looping of power systems is becoming highly desirable to improve the stability. The main features of such looped power systems are: (i) comparatively fewer losses; and (ii) improved angle stability as well as voltage stability. However, these systems have demerits, such as, in case of route off fault in a loop power system, power disturbances increase more and more, etc. If these demerits are overcome, the loop power systems are going to be more beneficial. In an attempt to obtain a solution to such problems, this paper describes several results of applying a high‐speed phase shifter in the control system of a loop power system.
Technology for highly dependable large capacity uninterruptible power supply system
Authors: Matsuzaki Kaoru
Published: July 2007

Powerful information networks comprising computers and communication equipment are a modern fact of life. Our dependence upon them requires that they function with no problems. System safety is crucial. Uninterruptible power supply (UPS) systems are commonly equipped to supply stable power regarding critical loads, e.g., large computer centers, telephone and telecommunication centers, aviation control systems, etc. Several types of UPS systems are now used in many of these important fields. However, there has been to date little numerical evaluation vis‐a‐vis system reliability.

This paper evaluates mean time between failures (MTBF) of parallel redundant UPS systems, and reports that the MTBF of two sets of parallel redundant UPS systems is lower than that of 3 sets of parallel redundant UPS systems under some circumstances. Continuous power supply reliability of the UPS system with bypass and uninterruptible transfer switch is much higher than is the case for other UPS systems lacking bypass circuit and uninterruptible transfer switch. Highly reliable parallel operation technology is also shown.
A suitable single‐phase pulse width modulation current source inverter for utility interactive photovoltaic generation system
Authors: Nonaka Sakutaro
Published: July 2007

A suitable single‐phase inverter for the utility interactive photovoltaic generation system is proposed. The single‐phase Pulse Width Modulation (PWM) current source inverter has a novel circuit configuration in which an auxiliary branch is added to the normal single‐phase bridge circuit. To reduce the size and weight of the dc reactor, a double frequency parallel resonance circuit (LC tank circuit) is inserted in the dc side of the inverter. As a result, the double frequency voltage appearing in the dc side of the inverter due to the pulsation of the single‐phase instantaneous power is perfectly suppressed by the tank circuit. The constant dc current without pulsation is supplied from PV array to the inverter. The inverter provides a sinusoidal ac current for domestic loads and the utility line with unity power factor.

The virtual maximum power of the PV array can be obtained without any feedback control. In the system, the PV array can play an important role as a current‐limiter due to itsV‐Icharacteristics. Computed waveforms by simulation are shown. Excellent inverter equipment will be realized that is smaller in size and lighter in weight than is usual for a conventional inverter.
Dynamic preventive control strategies for power systems considering transient and midterm stabilities
Authors: Kita Hiroyuki , Hasegawa Jun , Sato Naohiro , Nishiya Ken‐Ichi
Published: July 2007

This paper proposes a new dynamic preventive control strategy to maintain power system security, in terms of both transient and midterm stabilities. While the authors have already presented preventive control strategies for transient stability, a new problem has arisen in midterm instability in which some generators lose synchronism after 10 seconds or more from a fault clearance. It is clear that the cause of the instability is mainly post‐contingency dynamic steady‐state instability.

This paper first shows a preventive control strategy for improving midterm stability using a dominant eigenvalue of post‐contingency equilibrium point. This paper also presents a unified dynamic preventive control algorithm that can maintain both stabilities together. In this algorithm, the time domain for each stability problem is considered appropriately and the difference between the classical model and the detailed model is analyzed in detail. The effectiveness of the proposed method is examined with numerical examples for a model system.
Study of 1000‐kV network protection
Authors: Suzuki Mamoru , Matsuda Takayuki , Inagaki Keizou , Sasaki Hiroshi , Usui Masaji , Hori Masao
Published: July 2007

Electric power systems in Japan are developing due to economic growth. Especially, recent demand for electrical power in metropolitan areas has increased by more than 250 percent since 1973 when the 50‐kV system was first used. Increasing power demands will continue in the future. To satisfy this demand, utilities developed new transmission lines to make networks substantial with stable and efficient operation of the power system. However, this countermeasure causes extremely large fault currents at the substations where large power sources are concentrated. Problems such as large fault currents beyond interrupting the capacity of a circuit breaker or electromagnetic interference have become more severe. To solve these difficulties, Tokyo Electric Power Company is going to develop 1000‐kV networks. These increase the capacity of transmitted power and suppress the fault current level by splitting the 500‐kV system into several parts. Considering the associated difficulties of 1000‐kV networks (such as increasing capacitive current on transmission line), prolonged dc time constants due to large diameter conductors and other electrical characteristics of 1000‐kV networks, we examine the applications of a reliable protection system. The results are summarized as follows:

1) To adopt multiple phase autoreclosing with highspeed grounding switches to suppress secondary arcing on faulted phases.

2) To adopt air‐core type CT for 1000‐kV busbar protection as a countermeasure against CT saturation.

3) To adopt the current comparison scheme to realize sensitive protection for paralleled transformer bank.

A new protection system will be field‐tested in 1995.
A computer method for formal linearization of nonlinear systems by the discrete fourier expansion and its applications
Authors: Komatsu Kazuo , Takata Hitoshi , Tsuji Teruo
Published: July 2007

This paper proposes a numerical computer method for formal linearization of nonlinear systems by using the discrete Fourier expansion. A nonlinear system is described by a system of nonlinear ordinary differential equations. A linearizing function is given by a sequence of trigonometric functions. The nonlinear terms of the differential equations are expanded into finite sums of trigonometric functions by the method of the discrete Fourier expansion. As a result, a formal linear system is derived from the given nonlinear system.

A computer algorithm of the linearization is acquired and numerical computation is easily carried out with the aid of computers. Further, as the application of the linearization, both a nonlinear observer and a nonlinear filter are synthesized in this paper. Examples show that the accuracy of the method is improved as the order of the trigonometric functions increases.
Characteristics of LSM combined propulsion, levitation and guidance
Authors: Murai Toshiaki
Published: July 2007

In commercializing the superconducting maglev system, it is important to reduce the cost, especially that of ground coils installed all along the guideway. The ground coils designed for Yamanashi test track under construction are composed of both octagonal‐shaped null‐flux coils for EDS (Electrodynamic Suspension) and double‐layered armature coils of LSM (Linear Synchronous Motor). The former reduces the magnetic drag of the running resistance, and the latter reduces the electromagnetic fluctuation in the superconducting coils.

In addition, the octagonal‐shaped coils can generate propulsion force by being connected to the power supply. This system can generate levitation force, guidance force and propulsion force by the same ground coils. Therefore this system is expected to reduce the cost of ground coils, the number of which is decreased.

This paper presents the principle and analytical formula of the combined propulsion, levitation and guidance system (PLG system), including one for angles. In addition, using numerical examples, the characteristics of this system are expressed.
New current differential protection and fault‐location scheme for multiterminal lines
Authors: Nagasawa Takashi , Deno Kenichi , Yoshimi Masashi , Matsunaga Kanzo , Itou Kenji
Published: July 2007

This paper presents a new scheme of protection and fault location in multiterminal high‐voltage lines. The new protection scheme is PCM (Pulse Code Modulation) current differential protection using OPGW (Optical Fiber Ground Wire). This scheme can be applied to protection up to 8‐terminal transmission lines. This scheme has coped with the miss trip in the cause of CT‐saturation. But this may have an opposite result, i.e., obstruction of trip during 4‐cycle. Then, the index to cope with the miss trip for CT‐saturation is proposed.

The aforementioned system obtains various information at each terminal (e.g., current data and CB‐condition, et al.). Then, a fault location scheme is developed using this information. It has two kinds of techniques using the synchronized current data of multi‐terminal lines. One technique is to measure the current diversion ratio with current of each terminal. The other technique is to measure impedance using current of each terminal and voltage. This scheme can automatically choose between the two technique at fault type. The equipment using this scheme has obtained a good result in the field.
Synchronous generator control using neural network‐based nonlinear adaptive regulator
Authors: Kobayashi Takenori , Yokoyama Akihiko , Morioka Yasuo
Published: July 2007

Control equipment of synchronous generators such as automatic voltage regulators, speed governors and power system stabilizers have been developed to maintain stability and to improve damping of power systems. When an operating condition changes greatly, however, such controllers may become less effective because of nonlinearity of the power system.

In this paper, a nonlinear adaptive generator control system using neural networks is proposed. The proposed neurocontrol system consists of two neural networks which work as an identifier and a controller, respectively, and generates supplementary control signals to the conventional controllers. An essential feature of the proposed system is that the internal connection weights of both neural networks are adjusted adaptively so as to generate appropriate control signals for transient stability and damping enhancement in response to changes of the operating conditions and the network configuration.

To investigate the control performance of the proposed neurocontrol system, digital time simulations are carried out for a one‐machine infinite bus model system. As a result, it is clarified that the proposed adaptive neurocontrol system effectively improves the system damping and shows adaptability against the wide changes of the operating conditions.
A study of generator operating point regulation based on fuzzy control
Authors: Guo Bin , Tanaka Eiichi , Hasegawa Jun
Published: July 2007

As the load in a power system continually changes, it is important to regulate the generator operating point. In this paper, assuming a suitable operating range for the generator the regulations for typical generator operating points within this range are selected and then fuzzy controllers are designed accordingly. To investigate the adaptation of each controller, many simulations are carried out for the various operating point changes. By quantitative investigation of the control performance of the adaptive controllers, a design method for fuzzy controllers for generator operating point regulation is proposed. Furthermore, a comparative estimation of the fuzzy control formula and optimal control formula with an observer is made using a common quantitative criterion. In addition, a one‐machine infinite‐bus system (including limits on the AVR and governor) is used as the control object model.