According to the rising concerns for environmental preservation and effective energy use, grid interconnections of distributed generation systems (DG) to the existing power systems are expected to increase in near future. It is important to evaluate the effect of DG on power quality and safety to cooperate with power system operation. This paper outlines the analysis models of DG and grid interconnection to simulate and evaluate interconnection characteristics.

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The tools for power system analysis should have at least a time-domain simulation program, a steady state analysis program, and data base system for those data. This paper introduces the process of development of these tools, which are being used by the Japanese electric power companies to perform their day-to-day analytical works.

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This paper presents a practical method for creating power system equivalents that can be used in power system stability analysis. The proposed method uses three branches to connect the boundary bus, generator, and load. The method is suitable to consider reactance from the boundary bus to the load for power system stability studies using a dynamic load model. Furthermore, this paper presents a practical procedure to determine the parameters of the aggregated generator, including control devices such as excitation systems, PSS (power system stabilizer), and speed governors. The quality of the various aggregation models is verified using power system stability simulations.

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Recently a lot of studies and developments about distributed generator such as photovoltaic generation system, wind turbine generation system and fuel cell have been performed under the background of the global environment issues and deregulation of the electricity market, and the technique of these distributed generators have progressed. Especially, micro grid which consists of several distributed generators, loads and storage battery is expected as one of the new operation system of distributed generator. However, since precipitous load fluctuation occurs in micro grid for the reason of its smaller capacity compared with conventional power system, high-accuracy load forecasting and control scheme to balance of supply and demand are needed. Namely, it is necessary to improve the precision of operation in micro grid by observing load fluctuation and correcting start-stop schedule and output of generators online. But it is not easy to determine the operation schedule of each generator in short time, because the problem to determine start-up, shut-down and output of each generator in micro grid is a mixed integer programming problem. In this paper, the authors propose an online optimization method for the optimal operation schedule of generators in micro grid. The proposed method is based on enumeration method and particle swarm optimization (PSO). In the proposed method, after picking up all unit commitment patterns of each generators satisfied with minimum up time and minimum down time constraint by using enumeration method, optimal schedule and output of generators are determined under the other operational constraints by using PSO. Numerical simulation is carried out for a micro grid model with five generators and photovoltaic generation system in order to examine the validity of the proposed method.

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Several new generation companies such as PPS (Power Producer and Supplier) and IPP (Independent Power Producer) are emerging due to the deregulation and liberalization of the power industry. One of the most important concerns after the deregulation is decline of investment for power plant construction due to uncertainties associated with the power market. Development of power stations should be planned considering short-term and long term trends of power market. This paper focuses on the power stations development issues under competitive environment and proposes a simulation method of power stations development. The developed simulation tool can deal the interactions among each player's both short-term and long-term strategies.

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The authors have been developing an estimation method of a dominant eigenvalue in large scale power systems using the measured data of the power system. A dominant eigenvalue means the eigenvalue due to long cycle oscillation mode between large scale power systems and has an important information on stability. This paper describes the basic principle of eigenvalue estimation method, the analysis of factors giving influence to accuracy and the accuracy improvement method. The result from the basic principle of eigenvalue estimation method shows that the estimated eigenvalue fluctuates in certain time domains and the accuracy is not satisfactory. The studies were made and it was clarified that frequencies lower than the frequency of the dominant eigenvalue are major sources for fluctuation and noise. In order to improve accuracy, a new method was proposed by applying maximum entropy method (MEM) to obtain power spectrum of maseaued data and by introducing new argorithm for descriminating signal from noise using MEM results. Results of applying the proposed method to dominant eigenvalue estimation show the accuracy was improved and the validity of the proposed method was verified.

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This paper describes an application of a neural network for forecasting to time variation of wind velocity. We discuss the forecasted results of wind velocity of 4m/s or more on the day as a case study. The neural network is used to forecast the wind velocity and the pattern matching is used to choose the training data of the neural network. It is found from our investigations that forecasting accuracy of the time series of wind velocity is improved by utilization the pattern matching of the weather map data. From the power generation simulation result, it is confirmed that the error of wind velocity greatly affects the power output. Therefore, the prediction accuracy of wind velocity is important.

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Deblock of AC-DC interconnected system with externally commutated converters generally adopts soft start which makes trigger delay angle about 90 degrees and starts DC voltage from about 0kV. High DC voltage, however, is possibly caused by relation between the deblock signal and AC voltage phase at the commutation start of converter, resulting to overdue current. Consequently, overshoot of DC current is generated and transient AC voltage sag is caused especially under the condition of relatively weak AC system.
We resolved the generation mechanism of DC current overshoot at deblock. In addition, we reflected the mechanism in the control system of Higashi-Shimizu FC, and drew up overshoot damping control by EMTP simulation. Furthermore, we checked the effect of overshoot damping control at the commissioning test period and verified that result of measurement corresponded with EMTP simulation.

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Photovoltaic (PV) and Wind Turbine (WT) generation systems are expected to offer solutions to reduce green house gases and become more widely used in the future. However, the chief technical drawback of using these kinds of weather-dependent generators is the difficulty of forecasting their output, which can have negative impacts on commercial grids if a large number of them are introduced. Thus, this problem may hinder the wider application of PV and WT generation systems. The Regional Power Grid with Renewable Energy Resources Project was launched to seek a solution to this problem.
The scope of the project is to develop, operate, and evaluate a Dispersed Renewable Energy Supply System with the ability to adapt the total energy output in response to changes in weather and demand. Such a system would reduce the impact that PV and WT generation systems have on commercial grids and allow the interconnection of more Dispersed Energy Resources (DER). In other words, the main objective of this project is to demonstrate an integrated energy management system, or a type of microgrid [1], as a new way of introducing DERs. The system has been in operation since October 2005 and will continue operation until March 2008. Through the project period, the data on power quality, system efficiency, operation cost, and environmental burden will be gathered and a cost-benefit analysis of the system will be undertaken.
In this paper, firstly we introduce the concept of microgrid for reducing negative impact of natural energy, and secondly illustrate the structure of electric and thermal supply control system for Microgrid, especially for the Hachinohe demonstration project. The control system consists of four stages; weekly operation planning, economic dispatching control, tie-line control and local frequency control. And finally demonstration results and evaluation results are shown.

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On designing and developing products, the finite element analysis of three dimensional eddy current-thermal problems is very useful. This paper shows effectiveness of a large scale eddy current-thermal analysis for a transformer tank using the domain decomposition method.

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In order to verify a non-destructive method of measuring permittivity in multi-dielectric media using a long-distance small parallel-plate air capacitor with additional electrodes, we have proposed a novel technique to draw electric lines of force that applies the average of the electric field vectors to the drawing of perpendicular lines to the equipotential lines. Squared deviations of the electric field lines of force between the analytical and calculated values are estimated for three different discretized domains.

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The introduction of PEFC (polymer electrolyte fuel cell) μCGS (micro cogeneration system) into apartment is expected from the viewpoint of the energy saving effect in the home section. To introduce this system, the optimization of the equipment capacity of the fuel cell and the examination of its control method are indispensable. In this paper, therefore, the authors suppose a PEFC μCGS and examine its operation method based on the measured results of the electricity and hot water loads of an apartment in Fukuoka. At first, using the measured load patterns, the authors numerically determine the optimum operation schedule that maximizes the energy saving rate for various values of PEFC capacity and reveal the PEFC capacity suitable for the μCGS in both cases of each house installation and central installation. The relation between the seasonal change and the operation pattern of the PEFC in the case of central installation is also investigated. Next, the authors assume the central installation of the PEFC with the above suitable capacity, and propose a practically applicable prediction control method. The energy saving rate of the proposed control method is only a little lower than that of the optimum operation, indicating that the proposed control method has sufficiently high performance.

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The authors have already developed the simulation codes for the one channel region and the single cell plate in the cell stack of planar type solid oxide fuel cell (SOFC). To accurately calculate the effect of radiation heat transfer from and to the cell stack surfaces, however, a code that can treat the whole cell stack is necessary. In the present study, therefore, the authors newly develop a three-dimensional simulation code of the planar SOFC stack, and detailed effect of radiation heat transfer is investigated. It is made clear that sufficiently high temperature for power generation can be maintained at the central part of the cell stack even under low ambient temperature condition. This is because the thermal conductivity of the cell materials made of ceramics is very small and the central part of the cell stack is almost free from the influence of radiation heat transfer. The stack simulation is needed to accurately calculate the cell stack voltage, because the radiation heat transfer from the cell top and bottom surfaces reduces it when the ambient temperature is low. The bad influence of the low ambient temperature on the voltage is, however, small and relatively high cell stack voltage is obtained even when the ambient temperature is very low.

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Many approaches have been developing for energy conversion throughout the world. However, it is difficult to achieve the global warming countermeasure based on “The Kyoto protocol”. Until now effective utilization of low temperature thermal energy (under 300°C) is not advancing one. For example, effective utilization method has not been established for waste heat energy which arise from industry machine tools, automobiles, internal combustion engines and thermal energy from natural environment, etc.
In this paper, we reported the experiment for effective utilizing of low temperature (under 300°C) thermal energy conversion. The device used for the measurement is a copper thermo device. Thermo electromotive force of 150mW/cm² was obtained at 200°C. The obtained thermo electromotive force is about 15 times higher in comparison with generally used alumal-chromal thermocouple. Our aim is that utilizes low temperature thermal energy effectively by converting into electricity.

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Current distribution and overvoltages in a structure of a seismic isolated building struck by lightning are analyzed by a Finite-Difference Time-Domain (FDTD) method and by the Electromagnetic Transients Program (EMTP). The simulated results by the FDTD method show that the voltage at the first floor, which is an important factor of a design of building installation, shows a damped oscillatory wave. The transient overvoltage is caused by the multiple reflections within the structures and the resonance between a stray capacitance of the structure and an equivalent inductance of the bonding wire, which electrically shunts a rubber insulator installed for dumping earthquake tremor. The investigation shows that the transient response can be expressed by a lumped-parameter equivalent circuit. Two numerical models for circuit analysis method are proposed in this paper. A multiphase model reproduces a distribution of currents flowing through vertical pillars by mutual couplings between the pillars. A single phase model is obtained by a simplification of the multiphase model and gives the voltage at the first floor. The calculation time is remarkably reduced compared to that by the FDTD method. The accuracy of the models is discussed in comparison with the results obtained by the FDTD method.

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In the present work, effect of CO₂+H₂ gas mixture inclusion on shrinkage of plasma was numerically investigated on high power Ar inductively coupled thermal plasmas at atmospheric pressure. The gas mixture of CO₂+H₂ has many reactions in wide temperature range of 300-20000K which may cause some performance in thermal plasmas. Simulation has been carried out solving a two-dimensional local thermodynamic equilibrium (LTE) code. The active plasma power and input fundamental frequency were fixed at 27kW and 450kHz respectively. The main variable parameter was the admixture ratio of secondary gas (CO₂+H₂ gas mixture) and it has been found that the injection of excess dissociative molecular gases shrink the plasma in radius keeping the center temperature about 10,000K by investigating the plasma radius having temperature beyond 5,000K for each of the case. The result also shows that increasing the inclusion (admixture ratio) of CO₂+H₂ molecular gas raises the plasma peak temperature. The result is also compared with that of Ar-CO₂ and Ar-H₂ thermal plasma and finally a comparative study and conclusions have been made.

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Fault current limiter (FCL) is expected as an apparatus not only suppressing an overcurrent caused by short-circuit fault but also improving an instantaneous voltage drop. In this paper, the improvement effect of fault current limiter on the instantaneous bus voltage drop was investigated based on circuit theory. We assumed that an FCL was installed at a bus exit and a three-phase short-circuit fault occurred. Two types of FCL were considered, i.e., an inductive FCL and resistive one. In case that the relatively large limiting impedance is used, the bus voltage can be kept higher level by the resistive FCL than the inductive FCL which has the same magnitude of limiting impedance as the resistive one. The limiting impedance required to keep the bus voltage a specified level by the resistive FCL is smaller than that by the inductive one. From the results obtained in this paper, it is found that the resistive FCL is more desirable for the improvement in the bus voltage drop.

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A two dimensional large eddy simulation has been carried out to study and compare the performance of two disk MHD generators with different wall profiles under high magnetic flux densities. One disk MHD generator has the commonly used straight disk walls and the other has newly proposed contoured disk walls. The numerical results clearly show that the generator with contoured disk walls achieves higher performance than the generator with straight disk walls, because of the improvements in the flow behavior and plasma conditions in the generator channel. For high magnetic flux densities, the flow becomes subsonic in the generator with straight disk walls and its performance tends to saturate with increasing in magnetic flux density. In the generator with contoured disk walls, on the other hand, the supersonic flow is maintained in the entire generator region and its performance increases with increasing in magnetic flux density even under the same working conditions.

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