bluuebunny/crossref_metadata_2025 huggingface dataset:
Model evaluation of CO2 reduction technologies in the Asia‐pacific region
Authors: Nakata Hideki , Kaya Yoichi
Published: July 2007

Global 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

This 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

This 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

This 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

The 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

Global 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

It 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

A 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

In 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

This 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

The 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

Thermoplastic 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.
One‐day‐ through seven‐day‐ahead electrical load forecasting in consideration of uncertainties of weather information
Authors: Miyake Takashi , Murata Junichi , Hirasawa Koutaro
Published: July 2007

This paper proposes an approach to one‐day‐through seven‐day‐ahead electrical load forecasting based on a realistic problem formulation which should contribute to more reliable and economic weekly power stations operation. Generally, the load forecasting has the following problems:

(1) although the load is affected by various factors, such as temperatures, in the load forecasting, it is impossible to consider all of them;

(2) the relationships between the load and some factors are not clear, and often vary with time; and

(3) uncertainties in forecasts of the temperatures sometimes make the results of load forecasting worse.

They are very influential in the power station operation. While a number of methods have been proposed to solve the problems (1) and (2), there have been few attempts to solve the problem (3).

The following approach is proposed in this paper, taking these problems into consideration. First, concerning the problem (1), the focus is on such factors that have major influence on the load and whose values are obtainable on a weekly basis. The other factors are all regarded as stochastic and are not included in the forecasting model. Second, regarding the problem (2), a self‐organizing approach is used where the algorithm itself finds the optimal model structure or the optimal set of factors to be included in the model day by day. Finally, addressing the problem (3), a new performance index of model structures is proposed which can measure the balance between: i) improvement of the load‐forecasting accuracy due to inclusion of a factor in the model; and ii) degradation caused by uncertainty or error in the factor included. Using this index, a model is constructed which does not yield a large error in spite of errors in the temperature forecasts. Examples show that this approach improves the forecasted results when erroneous temperature forecasts are fed into the model, and verifies its effectiveness.
Power system stabilizing control by a superconducting magnetic energy storage with a high‐speed phase shifter
Authors: Uranaka Tsutomu , Mitani Yasunori , Tsuji Kiichiro
Published: July 2007

Electric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated.

On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously.

This paper proposes a combination of SMES with a high‐speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically.
A parametrization of the discrete‐time two‐degree‐of‐freedom integral controllers with computation delays and its applications
Authors: Guo Hia‐Jiao , Ishihara Tadashi , Takeda Hiroshi
Published: July 2007

Using the observer‐based integral controller proposed by Isihara et al. as a basic controller, a state‐space parametrization of discrete‐time two‐degree‐of‐freedom integral controllers of combined general computation delays. The proposed parametrization can easily be obtained by using the solution of an LQG problem for a plant but not for a higher‐order extended system. In addition, the parametrization does not require constraints on the two free parameters. The role of the free parameters is clarified in connection with the basic controller. As applications of the proposed parametrization, the loop transfer recovery and the pole assignment using the free parameters are considered. A numerical example is presented to show the effectiveness of the proposed methods.
Performance of a 3000/6000 V, 1000 kVA class superconducting transformer developed for a prospective power transmission model system integrated under superconducting environment (PROMISE)
Authors: Tang Yue‐Jin , Shimizu Hirotaka , Kato Takeyoshi , Hayakawa Naoki , Yokomizu Yasunobu , Matsumura Toshiro , Okubo Hitoshi , Kito Yukio , Miyake Seiichi , Kumano Tomoyuki , Hatano Masayuki , Satoh Kazuhiko , Satoh Wataru
Published: July 2007

A 3000/6000V, 1000 kVA class superconducting transformer (SC‐Tr) was developed for a Prospective Power Transmission Model System Integrated under Superconducting Environment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC‐Tr. Fundamental characteristics of the SC‐Tr are obtained through no‐load, short‐circuit tests and quench experiments. The results of the no‐load test have verified that the SC‐Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short‐circuit tests have proved that the SC‐Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real‐load experiment with the PROMISE, electric power of 3800 V‐460 kVA of 50 Hz in high‐voltage side is transmitted through this SC‐Tr.
Coordinated fuzzy logic control between SVC and PSS to enhance stability of power systems
Authors: Kihara Hidemi , Hiyama Takashi , Miyauchi Hajime , Ortmeyer Thomas H.
Published: July 2007

This paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. The PSSs are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region.
Forecasting daily peak load by a deterministic prediction method employing Gram‐Schmidt orthonormalization
Authors: Mizukami Yuichi , Nishimori Toshiro , Okamoto Junko , Aihara Kazuyuki
Published: July 2007

A technique for forecasting daily peak load in a utility power system is presented. After embedding time series data of daily peak load into a reconstructed state space, a nonlinear mapping is constructed by a local approximation method based on the orthonormal Gram‐Schmidt bases. This method utilizes only the past load data for short‐term prediction of the daily peak load, while many conventional methods make predictions with various kinds of data such as temperature and weather. The quality of prediction by the proposed method is as good as those with other prediction methods. Moreover, the results of short‐term prediction by this method are satisfactory even with data as small as 250 points.
Eddy current testing by upgraded microloop magnetic sensor array
Authors: Uesaka Mitsuru , Hakuta Kazumi , Miya Kenzo , Aoki Kazuhiko , Takahashi Ayumu
Published: July 2007

A micro‐eddy current testing (ECT) probe, which consists of a planar microloop inductive magnetic sensor array and a pancake‐type exciting coil, was developed to upgrade the ECT technology, especially as it is used for inspecting steam generator tubing in a pressurized nuclear power plant (PWR). Eddy currents and resultant magnetic fields are perturbed due to a flaw in a conductor. The flaw is detected via perturbation of the electromotive force (EMF) and phase from the array. Flaws manufactured by electric discharge machining in INCONEL 600 planar specimens, the thickness of which was 1.25 mm, were detected and reconstructed by using stacked database and simplified algorithm. Even an outer‐edged 10 percent flaw could be detected. Measured EMF and phase signals were compared with numerical results obtained by using a three‐dimensional eddy current and field analysis code and then verified. The experiment confirmed that the spatial resolution of detection of the micro‐ECT probe is superior to that of the conventional pancake‐type ECT probe. Finally, it was demonstrated that it is possible to establish the same measurement speed using the micro‐ECT probe as it is by using the pancake‐type ECT probe.
Heating and acceleration processes of high melting point ceramic particles in pulsed plasma
Authors: Miyamoto Masahiro , Hikosaka Tomoyuki , Yamada Mamoru , Sakuta Tadahiro , Tago Masanari
Published: July 2007

Plasma spraying is gradually becoming an important technique in the materials processing field, its primary feature being the ease by which the area or thickness of the deposited film can be controlled. High‐temperature plasmas to heat ceramic particles with a high melting point have in the past been generated by dc power sources. Applying a pulsed plasma using a high current of the order of tens of kA is proposed for the plasma spraying of refractory materials.

Numerical analysis of the short‐time heating and acceleration of the particles showed that alumina particles 20 μ in diameter reach the complete melting state after a residence time of 83 and 9.6 μs and a flying distance of 5.8 and 0.5 mm, when the temperature of the pulsed plasma is assumed to be 10,000 and 20,000, respectively, with a constant plasma velocity of 200 m/s.

Experiments are then performed using a specially developed plasma torch with a pulsed discharged current of 24 kA peak and a duration of 400 μs. This current is provided from a capacitor with a maximum stored energy of 14 kJ. The simultaneous, in‐flight measurements of the temperature, velocity, and size were taken for alumina particles injected into the pulsed plasma. Results show that the surface temperature of the alumina particles reached values as high as 2700 to 3300 K, which was considerably higher than the melting point. Particle velocity was found to be around 200 m/s, which is comparable to that of dc plasma. The experimental results confirmed the applicability of pulsed plasma for the spraying of refractory materials.
Power control of coupled nonequilibrium disk MHD generator and line‐commutated inverter system
Authors: Inui Yoshitaka , Ishikawa Motoo , Umoto Juro
Published: July 2007

A new power control method is proposed which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line‐commutated inverter. The thermal input of the generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method can realize both high performance for part load operation and fast output power control of which the time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance.
Transient analysis of converter‐fed adjustable‐speed generator‐motor for the pumped storage power plant
Authors: Yanagisawa Tadahiro , Kageyama Takahisa , Okamura Kazuhiko , Kusunoki Kiyoshi , Taguchi Tadashi , Abe Michiyuki , Kaneko Hirokazu
Published: July 2007

A converter‐fed adjustable‐speed generator‐motor for a pumped storage power plant has been developed in order to contribute to the automatic frequency control on an electric power system during pumping operations, as well as to improve the efficiency of turbines during generating operations together with stability. This system consists of a reversible pump turbine, a generator motor, cycloconverter and control units. The rotor of the generator motor, which is coupled directly with the turbine runner, normally is operated at a rotating speed which is equal to the difference between the frequency of the electric power system and that of the rotor current. In the state that a fault has occurred in the primary circuit of the generator motor, the adjustable‐speed generator‐motor fault current differs from that of a conventional synchronous generator motor.

This paper describes the fault current analysis results for the condition when a sudden short‐circuit is made on the primary side of the generator motor, and collates the results with the field test and EMTP simulation results.
An efficient faults calculation method taking into account mutually coupled lines of power systems
Authors: Tanaka Kazuyuki
Published: July 2007

It is necessary to take into account the effects of mutual couplings when unbalanced faults are to be calculated in transient stability study.

When the method based on symmetrical coordinates is applied to faults calculation, it has been necessary in the conventional method to construct the zero sequence network, the configuration of which is more complex than other networks so far. Then, the application of faults calculation including mutual couplings to the analysis on the bulk power system model has been considerably difficult for a long time.

This report presents a newly developed method to calculate the effects of mutual coupling in multifaults calculation under the same configuration and with no change for all sequence networks. The validity of the proposed method was verified through the application of transient stability analysis for power system models.
Genetic algorithm‐based method for contingency screening in power systems
Authors: Saitoh Hiroumi , Takano Yutaka , Toyoda Junichi
Published: July 2007

This paper proposes an application of genetic algorithm (GA) to contingency screening in power systems. The contingency selected by the GA‐based screening method is the double line outage which has the risk of causing transient instability. Generally, the contingency screening problem including multiple outage can be interpreted as the combinatorial optimization one for searching the combination of single outages which makes the system insecure. Therefore, GA which is one of the probabilistic searches for combinatorial problems, is applicable for such contingency screening problems. In the GA‐based contingency screening method, a double line outage is represented as a chromosome. The fitness of the chromosome for environment is defined by using the transient energy function of power systems. The new procedure for avoiding the loss of important outage during contingency screening is developed and embedded in the proposed method by using the theorem of schema for GA. The validity of the proposed method is confirmed by applying it to a 6‐machine 30‐bus 40‐line system. The result shows that the GA‐based contingency screening has the potential for practical use.
Evaluation of influence of external magnetic disturbance on superconducting magnet taking conservation of linkage flux into account
Authors: Takechi Moriaki , Kuroda Sigenori
Published: July 2007

External magnetic disturbance influences the quality of the image obtained with a magnetic resonance imaging (MRI) system because it causes magnetic resonance frequency drift. When a superconducting magnet in persistent current mode operation is exposed to external magnetic disturbance coil current varies to keep linkage flux constant. Conventional analysis is usually formulated with constant current and does not provide correct evaluation of drift of magnetic field in the magnet. This paper proposes a method of numerical analysis of magnetic field considering conservation of linkage flux in a superconducting magnet under a persistent current mode operation. This method is applied to evaluate drift of the magnetic field in a superconducting magnet for magnetic resonance imaging due to external magnetic disturbance. Analysis results show good agreement with the experimental results.
Multiple single‐phase PWM inverter by means of combination control
Authors: Ohnishi Tokuo
Published: July 2007

A new multilevel inverter with simple circuit configuration and control is proposed here. The inverter is composed of a series connection of individual single‐phase inverters. The number of the output voltage levels depends on the number of the individual inverters in series and their output voltage level. The switching devices in the new circuit configuration can be reduced by using a common switching‐leg for the individual inverters. In this inverter circuit, the number of the levels is equal to 2m‐1 or 2m where m is the number of switching‐legs used.

In the paper, a 15 level inverter using four switching legs (m = 4) is introduced. If the number of voltage levels is increased, smoother sinusoidal waveforms can be obtained directly and it is possible to control the output voltage almost continuously from zero to maximum without generating high‐voltage step changes as pulsewidth modulation techniques.

The control principle, the circuit configuration and the characteristics of the output voltage control are discussed. The feasibility of the circuit is demonstrated by simulation and experimental results.
A basic study on power storage capacitor systems
Authors: Okamura Michio
Published: July 2007

Storage batteries or pumped hydraulic power stations have been used to store electric energy. However, there are problems with storage batteries, e.g., long charging time, limited cycle life, low Coulomb efficiency, and inaccurate residual power meters. Because of these problems, practical power applications have not been achieved.

To solve these problems, a complex system of capacitors and electronic circuits called the ECS (Energy Capacitor System) is proposed. The capacitor part of the ECS is a group of electric double‐layer capacitors of increased energy density. The circuits part is built around switching regulators. Although the capacitors alone are not capable of delivering stable output, the accompanying circuits compensate for various characteristics throughout the charge and discharge cycle.

This combination of capacitors and electronic circuits increases the energy density by about 16 times that of the conventional electric double‐layer capacitors, close to the level of lead‐acid batteries but with lower output resistance and better voltage stability. The ECS inherently features short charging time, very long cycle life, and good Coulomb efficiency. The cells are completely sealed and made from materials which are not harmful to the environment.
Characteristics of flow and plasma under high MHD interaction in nonequilibrium disk MHD generator using argon
Authors: Tsuji Kiyoshi , Okubo Masaaki , Yamasaki Hiroyuki , Niwa Yoshimitsu , Kaneko Tetsuya
Published: July 2007

Results of experimental studies on behavior of a supersonic flow and of a nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the disk MHD channel were investigated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and, at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5 percent was achieved for cesium seeded argon. However, adiabatic efficiencies remained still low due to large pressure losses.
Measurement method using coupled transmission lines for voltage transients on the distribution line
Authors: Kawamata Ken , Minegishi Shigeki , Haga Akira , Sato Risaburo
Published: July 2007

It is well known that voltage transients are caused by the operation of switchgears in a power system. The voltage transients travel along the power line as a traveling wave, and cause malfunction of electrical devices, communication systems, and the operational error of a control system.

The voltage transients at the making operation of switchgear were examined to obtain the fundamental data for considering the immunity of communication systems used on a power system. However, it was difficult to observe the voltage transients using the potential transformer and the capacitance potential device because the transients were very rapid.

Therefore, a measurement method using the coupled transmission line system is proposed to measure the high‐speed and high‐voltage transients, and the actual experimental results on the 6.9‐kV power system are presented. This method enables the measurement of high‐speed voltage transients in out of contact with the power system.
Discharge luminescence and discharge magnitude in treeing degradation
Authors: Ehara Yoshiyasu , Ito Tairo , Kishida Haruo , Sakai Takao
Published: July 2007

This paper describes results of the discharge luminescence and discharge magnitude measurements performed on the insulation materials exposed to partial discharge. Polymethyl methacrylate (PMMA) with an artificial needle shape void were used as the treeing specimens. The discharge luminescence is observed by image intensifier, and the luminous image is processed by computer. At the same time, the discharge magnitude distribution in relation to phase angle of the applied voltage was measured by a partial discharge measuring system. The mechanism of electric treeing was discussed by not only the measurement of the discharge pulses but also the local luminescence intensity of partial discharge.

As a result, the luminescence intensity analysis showed the relation between tree growing length and void length when maximum luminescence intensity moved from the void area to the tree area. Both tree growth and maximum luminescence intensity at the tree area increase with constant ratio. The discharge luminescence intensity at the tree area increases significantly depending on the discharge magnitude in the specific phase angle area in positive and negative.
Operation of power distribution systems by using a section management method
Authors: Sano Tsuneyo , Tatsumi Mitsunobu
Published: July 2007

High‐voltage power distribution systems are connected in a branch configuration so as to meet the need for highly reliable power service. When service is interrupted the faulty section is automatically isolated and the power supply is rerouted from an adjacent power distribution system thereby minimizing the service interruption area. The faulty section in the power distribution system is quickly located by means of time relays installed in the switchgears. The settings of those time relays, however, must be monitored constantly.

For this reason, we have proposed a “section management method” which can supervise each section of the power distribution system. From this method, we developed a prototype automated distribution system for overall management of time relays through the use of internal software, facilities and customer feedback.

This paper describes the section management of power distribution systems.
Estimation of breakdown voltages of surface flashovers initiated from triple junction in SF6 gas
Authors: Hama Hiroyuki , Inami Kiyoshi , Yoshimura Manabu , Nakanishi Koichiro
Published: July 2007

In this paper, a method is proposed to estimate the minimum breakdown voltages of surface flashovers initiated from the triple junction at which a solid insulator, SF6 gas, and a metal electrode come in contact.

Using four kinds of test samples, the flashover voltages Vf are measured. The voltages Vf become lower than the theoretical voltages Vs of streamer inception in the case of the test sample with the large electrode area at the triple junction. To understand the phenomena quantitatively, we estimated the real partial discharge voltages Vc from the voltages Vf, and investigated the relationship between the voltages Vc and the theoretical values Vs. The values of Vs/Vc, which characterize the properties of the partial discharges, can be shown by the product λS90%Eav P of the following parameters: (1) coefficient λ representing the surface roughness of electrode at the triple junction; (2) effective area S90% of the electrode; (3) average field Eav at the area S90%; and (4) gas pressure p. The minimum surface flashover voltages in the insulators for coaxial electrode systems can be estimated precisely, considering the properties of Vs/Vc.
Daily peak electric load forecasting using an artificial neural network and an improvement method for reducing the forecasting errors
Authors: Makino Kyoko , Shimada Tsuyoshi , Ichikawa Ryoichi , Ono Masaya , Endo Tsunekazu
Published: July 2007

This paper proposes a forecasting method for shortterm peak electric loads using a 3‐layer neural network of locally active units. Each unit in the hidden layer of the neural network is activated only by input vectors in a bounded domain of vector space. This characteristic enables additional learning. Furthermore, it is supposed to provide the network structure with information that helps to improve forecasting accuracy. The neural network is applied to daily peak load forecasting simulations in summer. The results show that the proposed method is superior to a conventional neural network with the backpropagation algorithm. To make the best use of the neural network, an error‐oriented method of parameter modification is also examined.
Proposal and characteristics evaluation of a CO2‐recovering hybrid power generation system utilizing solar thermal energy
Authors: Pak Pyong Sik , Hachikawa Takeshi , Suzuki Yutaka
Published: July 2007

A CO2‐recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO2 is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO2 can be recovered by using an oxygen combustion method, so that a high CO2 capturing ratio of near 100 percent as well as no thermal NOx emission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 220°C.
Theory and characteristics of novel variable reluctance 1X resolver
Authors: Ishizaki Akira , Takasaki Kazuhiko , Shimomura Shoji , Masaki Kouichi , Kitazawa Kanji
Published: July 2007

Although brushless resolvers have been used widely as angular position transducers, they are expensive due to their intricate construction, involving a rotary transformer to supply the exciting coils wound on the rotor poles with the current.

It is shown theoretically in this paper that the resolver without rotary transformer or brushes can be realized by simple construction, which consists of the stator core with both 4‐poles exciting windings and 2‐poles output ones and the rotor core carrying no windings. In this resolver the rotor core has minimum gap at one side and a maximum gap at another side of the diameter. It is characterized by an outer surface form that makes the fluctuation part of gap permeance very in proportion to cos θ, where θ represents the angular position of a point in the air gap with respect to the origin on the rotor, the point of minimum air gap. The method determining the rotor form to embody the aforementioned gap permeance variation is also shown.

It has been confirmed not only by simulation but also experiment that the 2‐phase output voltages of a model designed based on the theory have sinusoidal waveforms with very small harmonic contents. Moreover, the rotor position detected by processing the output voltages through the conventional resolver/digital converter was within acceptable engineering accuracy.
A three‐degrees‐of‐freedom Maglev system with actuators and permanent magnets
Authors: Oka Koichi , Higuchi Toshiro
Published: July 2007

A magnetic suspension system with linear actuators and permanent magnets (instead of electromagnets) has been developed. In this system the bearing forces are controlled by adjusting the air gaps between permanent magnets and the levitated object (a circular disk). This system uses less energy and exhibits none of the overheating of coils typical of systems employing electromagnets. This paper describes a disk suspension system with three degrees of freedom. The system can operate either with a decentralized (distributed) feedback control system or with a centralized (lumped) one. Feedback gain matrices are calculated for each type of control system. The performances of the two types of control systems are compared by numerical simulations and experiment. This work is part of an effort to develop a magnetic levitation conveyer system.
Experimental studies on a structure of eddy current probe for detection of magnetic flux distorted by a flaw
Authors: Ebine Noriya , Takeuchi Shinjiro , Ara Katsuyuki
Published: July 2007

Bobbin‐coil‐type eddy current probes, which are conventionally used for nondestructive inspection of steam generator tubes in pressurized‐water‐type nuclear power plants, have poor detection sensitivity to circumferential flaws. Hence a new type of eddy current probe was proposed to effectively detect the magnetic flux component that is indicative of a flaw and thus to eliminate the dependency on sensitivity in flaw detection. In the course of development of the proposed method, probe structures were investigated based on the measurement of magnetic fields induced by variously‐shaped excitation flat coils. The new type of probe proposed here consists of differential pick‐up coils detecting magnetic flux and excitation coils having a parallelogrammic shape. The structure of the coils was fabricated in order to detect flaws independently of their directions in trial. Nondestructive flaw detection tests were then conducted with the probe. The results obtained concrete evidence showing that both the horizontal, the vertical slit‐flaws and even the small hole of 0.5 mm in diameter can be detected successfully.
Switching characteristics of a triggered vacuum gap employing a trigger electrode in the respective main electrodes
Authors: Sugawara Akira , Samaulah Hazairin , Itagaki Kouichi , Kitamura Hiroshi
Published: July 2007

Both switching time and minimum firing voltage of a triggered vacuum gap employing a trigger electrode in the cathode and anode (double triggered vacuum gap) were measured. The double triggered vacuum gap was operated below 100 V independent of the high voltage main electrode polarity (positive or negative). This minimum firing voltage was lower than that of the conventional triggered vacuum gap. The switching time is approximately 0.5 μs in the range 3 to 18 kV.

The conventional triggered vacuum gap has a trigger electrode that is placed at the center of the grounded main electrode. The polarity of the main electrode affected switching time characteristics. A trigger electrode was added to the high voltage main electrode. The double triggered vacuum gap was only slightly influenced by the polarity of the high voltage main electrode when both main electrodes were triggered at the same time.