bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractElectric 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

AbstractThis 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

AbstractIn 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

AbstractThis 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

AbstractControl 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

AbstractAs 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.
Model evaluation of CO2 reduction technologies in the Asia‐pacific region
Authors: Nakata Hideki , Kaya Yoichi 
Published: July 2007

AbstractGlobal warming is one of the most serious issues in today's world. Various innovative technologies have been proposed for the reduction of CO2 emissions and the mitigation of global warming. They include (1) the WENET project, inaugurated in 1993 by the government of Japan, in which electricity produced by photovoltaic systems in vast areas such as the Sahara Desert, or by hydropower systems, is converted to hydrogen for transport to demand sites, and (2) Steinberg's Hydrocarb process, in which fossil fuels and biomass are coprocessed to produce carbon and methanol. While Japan is resource‐poor, it is located relatively close to Southeast Asia and Australia, which are large regions with abundant solar energy. This paper describes an investigation of the prospects for the adoption of these innovative technologies by Japan and surrounding resource regions in the next 30 to 40 years. An optimizing energy model is developed for the purpose, and the simulation results provide several interesting suggestions regarding Japan's future strategy for combatting global warming.
A control method to widen frequency bandwidth of switching regulator with two‐degrees‐of‐freedom control system based on coprime factorization description and its characteristics
Authors: Sugimoto Hidehiko , Morishima Yasuyuki 
Published: July 2007

AbstractThis paper describes a control method to widen the frequency bandwidth of a voltage control system for a switching regulator, which is based on a coprime factorization description of the system.First, this paper clarifies the control performance of a conventional voltage control method with a proportional‐integral control element and a phase lead element, which does not widen the frequency bandwidth enough. Next, a new voltage control method with a compensator based on the coprime factorization description of the system is proposed. The compensator employs a two‐degrees‐of‐freedom control system, and is made up of a stabilizing dynamic compensator and a reference signal response dynamic compensator. Furthermore, one possible design of the two dynamic compensators, and the simulation and experimental results for the test switching regulator are presented.
Photovoltaic system using buck‐boost PWM power inverter
Authors: Nagao Michihiko , Horikawa Hideo , Harada Koosuke 
Published: July 2007

AbstractThis paper presents a buck‐boost PWM power inverter and its application for the residential photovoltaic system. The PWM power inverter is realized by driving an inverter constructed with a high‐frequency buck‐boost chopper in the discontinuous conduction mode (DCM). The photovoltaic system with the power inverter has the following advantages: (1) the power generated by the photovoltaic array can be transferred to the load and the utility line under any array voltage; (2) isolation between the photovoltaic array and the utility line is performed by a small high‐frequency reactor operating as energy storage element; (3) there is no need of a reactor to link the utility line; (4) unity power factor operation is provided; and (5) the system configuration is very simple. the input‐output characteristics of the system are analyzed. As a result, the ripple component of the array current and the power flow between the interface and the utility line are derived and verified experimentally.
Instability of a static var compensator control system and its investigation based on the bifurcation theory
Authors: Ohtsuka Kei , Nishida Makoto , Hirano Takakazu 
Published: July 2007

AbstractThis paper deals with the instability of a static var compensator (SVC) control system, which compensates the reactive power of loads using measurements of voltage and reactive power of the loads. The SVC control system is characterized by its meeting a bifurcation point and its instability before the loads reach the so‐called nose point. This is proved by an investigation based on the bifurcation theory, and is also supported by stimulation studies of a power system. Motivated by the bifurcation theoretical investigation, an SVC control system using a reference voltage pattern is proposed which does not create such instability.
An approach for transmission expansion planning using neurocomputing hybridized with a genetic algorithm
Authors: Yoshimoto Katsuhisa , Yasuda Keiichiro , Yokoyama Ryuichi , Tanaka Hideo , Akimoto Yoshiakira 
Published: July 2007

AbstractThe aim of transmission expansion planning is to determine which right‐of‐way to use when constructing new lines in order to meet a forecasted load in the most economical way. This problem has been solved previously by mathematical sensitivity analysis (which finds a single nonoptimal solution). It is difficult to plan for economical and reliable expansion due to its discrete and combinatorial nature. Although another method that has efficiency for combinatorial problems is neurocomputing, this approach saves computational efforts but obtains poor solutions. The most desirable approach for this planning problem is one in which many good solutions are found in reasonable time, because planning experts will then be able to plan economical and reliable expansion according to these solutions.This paper presents an approach for solving transmission expansion planning based on neurocomputing hybridized with a genetic algorithm. This approach generates suitable initial states, which include past information, of neural networks utilizing genetic algorithm. Mingling neurocomputing and a genetic algorithm, the proposed approach can find many good solutions in reasonable time making full use of their merits. Computational examples show the effectiveness of the proposed approach by comparison with conventional approaches.
Effect of fluctuation of surface sea water temperature and ambient pressure on evaporation rate of evaporator in barometric type OC‐OTEC system
Authors: Amano Masatsugu , Takazawa Hiroyuki , Tanaka Tadayoshi 
Published: July 2007

AbstractGlobal environmental problems, such as global warming and the effects of acid rain, are expected to become more serious in the future. One methodology for solving this problem uses harmless energy resources. Ocean energy is one of such energy resources. This research involves a study of the OC‐OTEC system, which is one type of ocean thermal energy conversion technology. In this system, the steam that drives a turbine is generated in an evaporator and condenses in a condenser after passing through a turbine. However, the steam evaporating rate in an evaporator is affected by the fluctuations of surface sea water temperature and ambient pressure. Therefore, it is necessary to define the dynamic characteristics of the evaporator in order to gain constant power output. This paper presents an analysis as to how evaporation rate is affected when surface sea water temperature and ambient pressure change. Further, we clarify that the dynamic characteristics of the evaporator are more affected by fluctuations in the ambient pressure than in surface sea water temperature.
A dynamic load model for analysis of power system voltage
Authors: Yamamoto Masato 
Published: July 2007

AbstractIt has become important in recent years that power systems be protected from voltage instability caused, in part, by heavy loads and the concentration of air conditioning loads during certain hours. Many studies have explored the problems and possible countermeasures. However, the load representations used in these studies are based on power values, i.e., P and Q; therefore, these analytic models are insufficient to express load responses and, thus, investigation is somewhat limited.This paper introduces a load model expressing load admittance responses by a first‐order delay differential equation and uses this model in tandem with power network solutions to analyze power system voltage stability. This load model is shown to work reliably and effectively. Using this model, it is possible to investigate more precisely and widely than before the power system voltage stability phenomenon of arbitrary characteristic loads in lower voltage ranges and on propagations of instability through the networks.
Multiobjective dynamic load‐dispatching method for optimal operation of power systems
Authors: Yoshikawa Motonobu , Nakajima Hiroshi , Inada Takeshi , Harada Yasushi , Amano Masahiko , Nakata Yuji 
Published: July 2007

AbstractA new practical method is proposed which gives a quasi‐optimal solution of the dynamic load‐dispatching problem formulated by a multiconstraint multiobjective optimization problem. Here, the multiple constraints are rate reserve constraints and power flow ones, and the multiple objectives are fuel cost and CO2 emission.The proposed method is an integration of the following three techniques: (1) “Group Dispatch Scheme,” which is developed by the authors, is used to satisfy a violated constraint easily. This scheme consists of three steps. The first step is to classify all generators into two groups. One is the group which should be more loaded to satisfy the violated constraint, and the other is the should‐be less loaded group. The second step is to add some load to the former group, and to subtract the same load from the latter. The third step is to dispatch each group load to each groups generators, respectively; (2) the dynamic load‐dispatching algorithm is used which provides, in practical time, quasi‐optimal generation trajectories; (3) the conventional weighting parametric method is used to obtain a Pareto optimal solution of multiobjective problems.The effectiveness of the method is clarified by a computer simulation on the actual power system of Kansai Electric Power Company.
Application of catastrophe theory to power systems
Authors: Huang Yu , Tsukao Shigeyuki , Tamura Yasuo , Iwamoto Shinichi 
Published: July 2007

AbstractIn recent publications dealing with nonlinear systems, nonlinearities existing in the systems under study have drawn much attention. Studies on the effects of nonlinearities in power systems are becoming an increasingly important part of the research on system stability. It is probable that heretofore undiscovered phenomena caused by the nonlinearities involved in load flow equations, generator swing equations and characteristics of control equipments and loads, etc., may be found.This paper presents a new Catastrophe Theory application to nonlinear power systems. Making use of the concept of Duffing's equation, it is shown that a Catastrophe Theory analogy can be used to interpret unstable phenomena caused by system nonlinearities from the viewpoint of oscillations. When considering system nonlinearities due to poor combinations of system parameters and periodic disturbances, there may exist the characteristic “jumps” in system ates that correspond to slow (quasi‐dynamic) changes of the frequencies of periodic disturbances. With this Catastrophe Theory approach, a system bifurcation set can be identified to assess the unstable phenomena of power systems.
Steady‐state torque control system with secondary‐current feedback for three‐phase squirrel‐cage induction motors
Authors: Inuzuka Katsumi , Matsui Hiromu , Mohri Kaneo 
Published: July 2007

AbstractThis paper presents a highly stable steady‐state torque control system with a feedback of a secondary current signal.The torque control system is constructed with a feedback of the secondary current (I2) signal using a quick response magnetic‐field sensor constructed with an amorphous core multivibrator bridge, which can solve the secondary resistance change problem for temperature variation in the IM. Moreover, we added a state feedback to the system to improve the response speed for the unit step function of a torque order.The I2 sensor method has advantages especially at a low‐speed range, in which conventional method using an integrator shows control errors.
Stability of the multistrand superconducting cables under partial current distribution
Authors: Ono Michitaka , Wachi Yoshihiro , Shimadai Mamoru , Hanawa Shinichi , Hamajima Takataro , Yamaguchi Mitsugi , Yamamoto Keichi , Fujioka Tsutomu 
Published: July 2007

AbstractThe stability of the multistrand cables under partial current distribution among strands is discussed. The stability is influenced by a current sharing process among the strands. Stability tests under controlled current distribution are carried out for some test samples that had various electric resistance among strands. Then numerical analysis of the stability is carried out with a simplified electric circuit model that simulates current sharing process among strands. The results of the numerical calculations had good agreement with the experimental data. For stability of the multistrand cables, the electrical resistance among strands, which is the key parameter, is required to be lower than the normal resistance. This corresponds to the length of the heated region.
Electrical and mechanical properties of thermoplastic polyimide‐insulated coaxial cable for use under high‐temperature and radioactive conditions
Authors: Mitsui Hisayasu , Shiono Takeo , Ushiki Masataka , Sato Yoshimi , Sudo Shigeaki , Ono Shin‐Ichi , Murase Tomotaka 
Published: July 2007

AbstractThermoplastic polyimide‐insulated coaxial cable for use under high‐temperature and radioactive conditions was developed and its electrical and mechanical properties were evaluated in comparison with cable insulated with polyetheretherketone which is known for its superior heat‐ and radiation‐resistant characteristics. According to experiments, the electrical properties of thermoplastic polyimide‐insulated cable are stable over a wider temperature range in comparison with polyetheretherketone‐insulated cable even after 1.2 MGy of γ‐ray irradiation and 6‐months heat aging at 220°C, indicating that thermoplastic polyimide is superior for use as a heat‐ and radiation‐resistant cable‐covering material. The electrical properties of TPI cable observed, were within actual use requirements, even under γ‐ray irradiation up to 1000 Gy/h.