bluuebunny/crossref_metadata_2025_split huggingface dataset:
H∞ control approach to a magnetic levitation system by 4‐point attraction with nonlinear characteristics
Authors: Qi Run‐De , Tsuji Teruo , Yang Zi‐Jiang , Oguro Ryuichi 
Published: July 2007

AbstractAn H∞ control system design for a magnetic levitation system by 4 points attraction is presented. In the levitation system, a vehicle which runs as the secondary in a reluctance‐type linear motor is levitated by four pairs of attraction forces and guided by two pairs of attraction forces. Because it has contactlessness, in the field of semiconductor products, its application is favorable for ultraclean environments in microscopic processing.In the control system design, the influence of both disturbances and uncertainties in the model is considered. The main disturbances stem from the position sensors. The uncertainties are divided into electromagnetic and mechanical ones: the former are due to the gain change in the current amplifier, the influence of leakage flux and linearization error in the magnetic circuit, and the latter are due to the changes of the mass and the moment of inertia of the vehicle. Therefore, the designed controller is indispensable to guarantee robustness of this system for both stability and performance. The controller design is based on the standard H∞‐optimal control problem.As the novel features in this paper, the low sensitivity and the robust stability for this system design is obtained. Further, there are two‐poles on jω‐axis in the controlled model, and an integrator is included in the controller so that equivalently there are three poles on the jω‐axis in the model. Finally, several experiments, comparisons and simulations are carried out to verify the low sensitivity and robustness of the designed control system.
Computer‐aided protective relay setting system for large power networks
Authors: Fujita Nobuo , Ichie Ryozo , Ogawa Shigeaki , Kudo Hiroyuki , Fukui Chihiro , Nakata Yuji 
Published: July 2007

AbstractThis paper introduces a protective relay setting system capable of handling a large network up to 10,000 buses. The remarkable features are such useful functions as network analysis (fault analysis, load flow calculation, zero‐sequence current calculation, etc.), relay operation simulation, and automated setting coordination tasks.Fault currents in the maximum and the minimum operation networks are calculated to examine the setting values. The protection zones are searched automatically along the network connection. Protection coordination tasks among the primary and the backup relays composed of different types of relays can be performed by the relay operation simulation.The system is built on an engineering workstation, which works in cooperation with other network operation support systems. Its graphical user interface helps every engineer to examine the relay setting using a variety of databases.
Nuclear reactor diagnostic system using genetic algorithm (GA)‐trained neural networks
Authors: Chen Yan , Narita Masakuni , Yamada Takayoshi 
Published: July 2007

AbstractSeveral nuclear reactor diagnostic systems using neural networks have been proposed in recent years. Neural networks trained by backpropagation, the standard training algorithm, have certain problems such as local minima and long training times.In this paper, neural networks trained by genetic algorithms are used in a nuclear reactor diagnostic system to solve these problems. The system is tested by simulated data modeled on the experimental fast reactor JOYO, and two categories of abnormality (abnormal control rod vibration and abnormal coolant flow) are identified. The comparisons to networks trained by back‐propagation also are discussed.
Giant magnetoresistance and magnetic anisotropy of Co9Fe/Cu/Co9Fe multilayer thin films on an MgO(110) substrate
Authors: Inomata Koichiro , Saito Yoshiaki 
Published: July 2007

AbstractMagnetoresistive effects have been investigated using Co9Fe/Cu/Co9Fe that were deposited on an MgO(110) substrate by ion beam sputtering with a 21‐A‐thick CU layer and with various thicknesses of the Co9Fe films. The influence of a 50‐A‐thick Fe buffer layer has also been investigated. In addition to a cubic symmetry anisotropy (K1), an in‐plane uniaxial magnetic anisotropy (Ku) was induced, which easy axis is parallel to the (110) plane of the MgO substrate and the (001) plane with and without the 50‐A‐thick Fe buffer layer, respectively. The magnetoresistance (MR) ratio decreased monotonically with increasing thickness of the Co9Fe films from 25 A to 70 A. A maximum MR ratio of 11.5 percent was obtained at room temperature. With increasing magnetic field, the MR ratio reached a plateau gradually after a steep drop at small magnetic fields without the Fe buffer layer. It reached a plateau rapidly at small magnetic fields with the Fe buffer layer. By considering both Ku and K1, these behaviors can be accounted for by the magnetization processes involved.
Application of parallel genetic algorithms to generation expansion planning using parallel processors
Authors: Fukuyama Yoshikazu , Ueki Yoshiteru 
Published: July 2007

AbstractThis paper presents an application of parallel genetic algorithms (PGA) to the optimal long‐range generation expansion planning. The problem can be formulated as a combinatorial optimization problem that determines the order of introduced generation units at each interval of the year. The proposed method considers introduced power limits of each technology, maximum loads at each interval, and load duration curves at each interval. Appropriate string representation for the problem is presented. Binary and decimal coding and three selection methods are compared. The method is developed on a transputer that is one of the parallel processors. The feasibility of the proposed method is demonstrated using a typical expansion problem with four technologies and five intervals. The method is then compared with conventional dynamic programming and a simple genetic algorithm with promising results.
Analysis of high‐power factor AC‐DC boost converter
Authors: Nagao Michihiko , Nakakohara Takashi , Jinno Masahito , Harada Koosuke 
Published: July 2007

AbstractThis paper presents analysis of a high‐power factor ac‐dc converter with a boost converter operating in the discontinuous conduction mode (DCM) and the critical conduction mode (CRM). The converter can be expressed by a nonlinear differential equation for each mode. The equation in DCM is solved analytically by separating its variable (output voltage) into two terms of a ripple component and a direct component, and by linearizing the equation for the ripple component. On the other hand, the equation in CRM can be solved analytically. Furthermore, the source current waveform of the converter is expanded into the Fourier series. As a result, the output voltage, its ripple and the power factor of the converter in DCM and CRM are derived as a function of the circuit parameters, respectively, and verified experimentally. These equations exhibit clearly the effect of each circuit parameter of the converter and the difference between the converter in DCM and in CRM. The converter operating in CRM produces sinusoidal ac current with unity power factor.
Instantaneous value control of current vector of energy transfer circuit with inductor converter bridges between superconducting magnets
Authors: Shirai Yasuyuki , Nitta Tanzo , Suzuki Tomohiro , Yajima Syuichi , Okada Takao 
Published: July 2007

AbstractEnergy transfer circuits of inductor converter circuits (ICB), used for power supplies for superconducting magnets, are studied. Analytical solutions of steady‐state characteristics of ICB energy transfer circuits are analyzed. On the basis of these solutions, a discussion is presented regarding a new control method of ICB transfer circuit to reduce a voltage ripple across a load superconducting magnet. This paper will propose a new control for line‐commutated converters of ICB energy transfer circuit for quick changes in a transfer angle and a transfer frequency for the voltage ripple reduction control. Speeding‐up of the proposed controls is also discussed. Validity of the proposed controls is confirmed by computer simulations.
A study on the deterioration characteristics of power capacitors with oil‐impregnated paper
Authors: Okabe Shigemitsu , Koto Masanori , Fukuda Yoji , Hayashi Yoshinori , Nara Toshio , Takahashi Kunihiko 
Published: July 2007

AbstractPower capacitors are highly reliable due to their completely enclosed configuration. They are relatively trouble‐free over the long term. However, their dielectric strength can be reduced due to some stresses, including overvoltage application or thermal degradation of the insulation material during long periods of operation; these events can result in dielectric breakdown of capacitors in extreme cases.Since almost all power capacitors with oil‐impregnated paper have been operated for more than twenty years, some kind of failure should be expected. To prevent these incipient accidents, it is important to examine the insulation deterioration mechanism and evaluate the degree of deterioration before capacitor breakdown. To establish a diagnostic method of deterioration of the capacitors with oil‐impregnated paper, we have conducted thermally and electrically accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results we obtained, it can be concluded that the behavior of the oil‐dissolved gases can be used as a useful index to diagnose the insulation deterioration of these capacitors.
Assessment of transient voltage stability based on critical operating time of emergency control using neural networks
Authors: Maeda Tatsumi , Takigawa Kiyoshi , Minato Yoshinori , Yokoyama Akihiko 
Published: July 2007

AbstractSince unstable phenomena that load bus voltages collapse rapidly after a large disturbance occurred in a bulk power system, it is becoming necessary to develop a fast and precise evaluation method of what is called transient voltage stability. Although many indices have so far been proposed for static voltage stability assessment, there are few evaluation methods, digital simulation analysis for example, for the transient voltage stability assessment that deals with the dynamic characteristics of generators, loads, etc.This paper presents the transient voltage stability evaluation system that consists of two artificial neural networks (NNs). The first NN judges whether the system is stable or not under a given operating condition, load composition and fault location from the viewpoint of the transient voltage stability. If it is judged to be unstable, the second NN estimates critical operating time of emergency control action as a severity index of the transient voltage instability. Here, closing of a bus tie that is switched off in the normal state is adopted as the emergency control for voltage stabilization. Numerical examples for a 26‐bus model system are shown in order to check the effectiveness of the proposed evaluation system.
Optimal planning for introducing dispersed generating sources in power systems based on an economical viewpoint
Authors: Nishiya Ken‐Ichi , Kita Hiroyuki , Hasegawa Jun , Haga Yoshihiro , Minagawa Kazushi , Simazu Kenji , Nakamura Hideo 
Published: July 2007

AbstractThis paper discusses optimal planning problems for dispersed generating sources so as to provide a guideline for their introduction to power systems. First, a recursive method is developed from the viewpoint of supplying electric power only where solutions for one unit are superposed. The computational loads are decreased by selecting alternatives of buses based on the so‐called penalty factor. However, for effective utilization of dispersed generating sources, it is indispensable to consider their thermal merits in addition to electric power. After applying the Kuhn‐Tucker theory to the optimal dispatching problem including boiler fuel costs, thermal values of the dispersed generating units are evaluated quantitatively. Finally, the above‐mentioned technique for the optimal planning basically is also effective and is extended into this case. The validity of the proposed algorithms are demonstrated using a real‐scale model system.
Some factors for the space charge formation in polyethylene
Authors: Takahashi Tohru , Miyata Hiroyuki , Nakatuka Tohru , Yokoyama Ayako 
Published: July 2007

AbstractInformation on space‐charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer‐insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm‐thick polyethylene (PE). The following results were obtained.For measurement factors:(1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE.(2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space‐charge decay.(3) The space‐charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness.For insulating material factors:(1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low‐density PE (base of XLPE).The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours.(2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).
Stability of large‐scale coal‐fired MHD channels
Authors: Ishikawa Motoo , Kyogoku Akihiro , Umoto Juro 
Published: July 2007

AbstractStability of large‐scale coal‐fired MHD channels is studied by (1) linearized stability analysis, and (2) time‐dependent 1‐D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current.Time‐dependent one‐dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u ‐ a and u waves are unstable.
Flexible generator maintenance scheduling based on subjective relaxation of constraints
Authors: Miao Zhiyong , Yasuda Keiichiro , Yokoyama Ryuichi 
Published: July 2007

AbstractThis paper presents a fuzzy‐based method for determining a flexible generator maintenance scheduling by means of subjective relaxation of constraints imposed on the maintenance scheduling problem. The constraints are divided into hard (crisp) constraint set and soft (fuzzy) constraint set according to reflecting conditions which surround power systems. The problem is formulated as a fuzzy mathematical programming problem and solved with the fuzzy branch‐and‐bound method using Bellman‐Zadeh maximizing decision. The proposed approach provides not only a new flexible concept of planning problems in power systems, but also natural expansion of conventional approaches based on crisp set theory. The effectiveness and feasibility of the proposed approach are demonstrated on two typical power system models which consist of 15 generators and 60 generators, respectively.
ADTR‐motor drive for electric vehicle
Authors: Kawamura Atsuo , Yokoyama Tomoki , Kume Tsuneo 
Published: July 2007

AbstractA new motor (ADTR‐motor: Anti‐Directional Twin Rotary Motor) for electric vehicle drive is proposed. A stator in a conventional motor is reformed to be movable, and the stator (outer rotor) and the rotor (inner rotor) rotate in anti‐directions. The IM‐type ADTR‐motor and the SM‐type ADTR‐motor are considered, and in this paper a prototype of the IM‐type ADTR‐motor is constructed experimentally. When the ADTR‐motor is used for an EV drive, the direction of one of the rotors should be reversed. Both rotors, when rotated in the same direction, propel the two wheels of EV. The torque of the wheels can be balanced without differential gear. The fundamental characteristics of ADTR‐motor are clarified. The characteristics are the structure of ADTR‐motor, the equivalent circuit parameters, the torque balance theory, the torque‐speed characteristics, the rotor speed transient characteristics, and the transient response under the speed sensorless torque control.
Revolving magnet wheels with permanent magnets
Authors: Fujii Nobuo , Ogawa Kokichi , Matsumoto Toshio 
Published: July 2007

AbstractA new type of actuator with both magnetic levitation and linear drive is proposed. The actuator, called magnet wheel, has a rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive‐type magnetic lift force with self‐stabilization can be obtained by linking the rotating flux to a conducting plate. The induced simultaneous drag torque, which causes power loss, is used to obtain thrust in two proposed ways. These are called “tilt type” and “partial overlap type,” respectively. In the tilt type, the magnet wheel is tilted against the surface of a conducting plate. In the partial overlap type, the magnet wheel operates near the edge of a conducting plate.In this paper, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three‐dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in tilt type and partial overlap type magnet wheel are proved by experiments, respectively.
A method of predicting transient constants of synchronous machines
Authors: Ara Takahiro , Akima Tsunaki , Oda Shoichi 
Published: July 2007

AbstractIt is difficult to determine the subtransient (transient) reactance and subtransient (transient) short‐circuit time constants of medium and large synchronous machines by the sudden three‐phase short‐circuit test because large‐capacity equipment is required.This paper describes a new method of measuring these constants by means of a simple test using a small dc power supply.The key points of this method are as follows.(1) A dc voltage is applied to the armature winding (two terminals with the third one open) of a stationary synchronous machine through a resistance. When the two terminals are closed, the winding is short‐circuited and the current in the armature winding decays. The whole process of decaying current is recorded.(2) The value of the transient phenomena of the winding calculated from circuit equations (armature, field winding and damper winding circuits) is compared with actual data, and the unknown equivalent circuit constants are identified by the least squares method.(3) Transient phenomena of the sudden three‐phase short‐circuit are calculated by the two‐reaction theory using identified constants, and, hence, these constants are calculated.The transient constants of synchronous machines obtained by the new method agree closely with the observed values.
Tan δ of ethylene‐propylene rubber in cryogenic temperature region–effects of additives and sample thickness
Authors: Mizuno Yukio , Mitsuyama Yasuichi , Minoda Atsushi , Nagao Masayuki , Kosaki Masamitsu 
Published: July 2007

AbstractThe authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene‐propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown.The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.
Optimal load‐shedding using local information
Authors: Fujita Goro , Shirai Goro 
Published: July 2007

AbstractThis paper describes an optimal load‐shedding policy based on quadratic programming using only some power system state variables after severe generation outages. When generation outage is severe, the imbalance between supply and demand causes a declining frequency. Utilities generators cannot be operated excessively at frequencies above normal. Some of the load must be shed to prevent system damage. Optimal load‐shedding policies have been studied using all state variables of the power system. However, in real power system operations, it is difficult to obtain remote information in that fraction of a second following generation outages.An optimal load‐shedding method is constructed in this research using quadratic programming (QP) under the assumption that all power system state variables can be available. However, these state variables cannot be easily accessible (as already mentioned). A suboptimal load‐shedding scheme based on the local state variables is then studied. The proposed load‐shedding method is based on the aforementioned optimal one. The change in line‐power flows and the amount of generation power outage are used as accessible data at each load point. Incorporating this local information into the optimal loadshedding method based on the QP method, the proposed load‐shedding method is established here.The effectiveness of this proposed method is illustrated by two examples and simulation results on a model power system show that the method is encouraging.
Assessment of dynamic stability of large‐scale power system by Rayleigh's quotient
Authors: Kakimoto Naoto , Sugano Keiji 
Published: July 2007

AbstractA method of assessing dynamic stability of large‐scale power system by Rayleigh's quotient is proposed. One‐machine infinite‐bus systems show damping torque characteristics similar to diagonal components of operational transfer matrices for original multimachine systems, which means that design of PSS with one‐machine systems controls those components. An expression for damping constants of oscillation modes is derived based on an energy function and its time derivative for a simplified system representation. This expression demonstrates that oscillations do not necessarily become unstable even if there are some generators with negative damping; and the effect of damping torque is determined by eigenvectors. The expression is generalized with Rayleigh's quotient, and a method of estimating eigenvalues of large‐scale power systems is proposed. With this method, approximate eigenvalues are refined to accurate eigenvalues. Only a specified number of eigenvalue analyses are required irrespective of the number of generators, hence much calculation is saved. Finally, this method is applied to a 107‐machine system to verify its effectiveness.