The Editorial Committee is working in planning and editing of the publication of Power and Energy Society. In this article, activities of the committee of last one-year are reported, and recent trend and future problems are also discussed. The process of planning and editing of the publication and the challenges to reduce the necessary months for reviewing papers and to increase the number of submitted papers are shown.

抄録全体を表示

本記事に「抄録」はありません。

抄録全体を表示

本記事に「抄録」はありません。

抄録全体を表示

本記事に「抄録」はありません。

抄録全体を表示

本記事に「抄録」はありません。

抄録全体を表示

本記事に「抄録」はありません。

抄録全体を表示

The first stage 600kW Photovoltaic (PV) system of Hokuto Mega-solar project was installed in Yamanashi Prefecture, Japan, in 2006-2007. And the second stage 1,200kW was finished construction considering the result of 1^st stage evaluation, and started measuring/evaluating the data The outline and the developing target of the project are introduced and some results provided so far are discussed in this paper.

抄録全体を表示

The photovoltaic power generation system (PV system) has been expected as a clean energy source. However, it is supposed that the system reliability is not so high. In this study, the operational performance on large-scale photovoltaic power generation system was evaluated by using 12 systems. The standard rated output of each system was 4kW. As the results of the evaluation analysis, the rate of output deviation of System4 decreased 25% or less, in comparison with estimated output and the operation efficiency was unstable. It was obtained that the decrease of operation efficiency was caused by String3. From the results of inspections of the module, the solar radiation and the power conditioner, there was difference in conversion ratio between a DC-DC converter of a normal string and that of String3. The conversion ratio affected on the output of the string. It was able to find malfunction. Moreover, the regression analysis was investigated by using the output data of the PV system and irradiance. Performance of the PV system was evaluated using the regression coefficient. Stability of the PV system was also investigated using the method of this study.

抄録全体を表示

For large-scale photovoltaic (PV) systems, we have developed a large capacity power conditioning system (PCS) with three functions: fault ride through function, harmonic reduction function and voltage control function. This paper deals with our new reactive power control method of the PCS for reducing voltage fluctuation in large-scale photovoltaic systems. The proposed method reduces the voltage fluctuation caused by the active power of PV by adjusting the power factor of the PCS automatically to the optimal value according to the conditions of power systems. In this paper, the control operation and the control effect of our proposed method were examined by numerical analysis and an experiment using small PCS models. We verified that the voltage fluctuation caused by output of PV at interconnecting point could be reducing by controlling reactive power at the optimal value according to the power system conditions. Then, we confirmed that there is no need to increase the PCS capacity by the adjusting the offset of the reactive power properly. Finally, we confirmed the voltage fluctuation could be reduced without biasing the reactive power to a specific PCS even if there is difference between outputs of plural PCSs operating in parallel.

抄録全体を表示

Power output fluctuation of photovoltaic power generation systems (PVSs) may cause negative impacts on the existing electric power system when the penetration of PVSs is quite large. A micro-grid consisting of clustered PVSs and a battery system would be one of the promising measures against negative impacts of clustered PVSs, while the capacity of battery system should be reduced as much as possible from the economic point of view. Because of the difference in output fluctuation among PVSs in the various locations, the total output fluctuations of PVSs would be relaxed due to the so-called “smoothing-effect”. By using data on solar irradiance simultaneously observed at five points, this study evaluates the total output fluctuation of several micro-grids and the required capacity of battery system, taking the smoothing effect into account. The main results are as follows. The balancing control is accomplished with the acceptable error by using the small capacity of battery system, while small output fluctuation still remains in each micro-grid. In such the situation, because the total fluctuation of five micro-grids is not so large, the acceptable error in balancing control can be increased by a few percentages, resulting in reduction in the required maximum power of battery system by a few ten percentages.

抄録全体を表示

Recently, a photovoltaic (PV) system has attracted attention because of serious environmental and energy problems. In near future, PV systems intensively connected to the grid will bring about the difficulties in the power system operation. As a countermeasure, this paper deals with the introduction of storage battery for making the unstable PV power controllable.
In this regard, when we introduce a storage battery into a PV system, we have to consider the advantages and disadvantages. In order to evaluate the system from various perspectives, we have carried out multi-objective optimization of battery operation in PV system design. However, as the number of objective functions increases, it becomes difficult to appropriately interpret the correlation among objective functions and design variables. With this background, in this paper, a novel computational method is proposed for data mining of PV system design, in which we make an attempt to effectively extract the design information of the battery system with the use of Self-Organizing Map (SOM).

抄録全体を表示

This paper presents an application of multi-objective optimization methods for voltage and reactive power control (VQC) taking account of an operation margin. Multi-objective optimization has been developed based on genetic algorithms (Gas) with the characteristic of multi points search. An operation margin is considered to minimize generator reactive outputs and tap potions difference from the neutral. To make clear usability of the proposed method, results of applying the proposed method to a 15 bus system model and a 118 bus system model are compared to result of studies using the conventional weighting coefficients, and effectiveness of the proposed method is discussed.

抄録全体を表示

By the development of industry, in recent years; dependence to electric energy is growing year by year. Therefore, reliable electric power supply is in need. However, to stock a huge amount of electric energy is very difficult. Also, there is a necessity to keep balance between the demand and supply, which changes hour after hour. Consequently, to supply the high quality and highly dependable electric power supply, economically, and with high efficiency, there is a need to forecast the movement of the electric power demand carefully in advance. And using that forecast as the source, supply and demand management plan should be made. Thus load forecasting is said to be an important job among demand investment of electric power companies. So far, forecasting method using Fuzzy logic, Neural Net Work, Regression model has been suggested for the development of forecasting accuracy. Those forecasting accuracy is in a high level. But to invest electric power in higher accuracy more economically, a new forecasting method with higher accuracy is needed. In this paper, to develop the forecasting accuracy of the former methods, the daily peak load forecasting method using the weather distribution of highest and lowest temperatures, and comparison value of each nearby date data is suggested.

抄録全体を表示

Considering the interconnection of a large capacity of wind power generation to the utility grid, it is of great concern that its output power change has adverse influences, e.g. frequency fluctuation. There have so far been some research works on the installation of battery energy storage systems (BESS), as a solution to these problems. However, owing to very high cost of the BESS, its capacity should be as small as possible. In this paper, not only the installation of the BESS as one of the measures for suppressing the frequency fluctuation caused by wind power generation, but also heat pump water heater, one of the demand load, is considered. This paper proposes a coordinated control method of the BESS and the heat pump water heater, and evaluates reduction of the required BESS capacity.

抄録全体を表示

The variable speed drives of the power electronics application are the most sensitive to the voltage dip that is caused by power system fault. Variable speed drives are composed by the converter, the voltage source inverter and induction motor. They could fall into operation failure by wrong control in the converter when degree of the voltage dip exceeds 15% and 10ms. Therefore, important loads are equipped with the voltage dip compensation.
Since the load characteristic of the converter equals nearly the impedance load, the induction motors connected directly to power supply are more sensitive to the output voltage waveform of the compensator than the converter. Thus, the induction motors are used as the important load (compensated load) on the simulation. The simulations of the compensation performance to the induction motors are carried out by using simulation tool PSCAD/EMTDC. It is confirmed that the goal of the compensation performance is able to be achieved.

抄録全体を表示

Many alternative energy power generation systems create dc electricity. Also, many devices consume dc converted from ac. Therefore, it may be possible to reduce conversion losses and CO₂ emissions by adopting dc distribution. We assume that superconducting cables will be used for dc distribution because their electrical resistance is almost zero. However, if a superconducting cable is adopted, it is of great concern that if an excessive current flows because of, for instance, a short circuit, there is a possibility that this current cannot be interrupted by a circuit breaker alone. We propose that the fault current is limited by a Superconducting Fault Current Limiter (SFCL), and that this limited current is then interrupted by a dc circuit breaker. In this paper, we have separately investigated the SFCL and dc breaker, and their use in combination.

抄録全体を表示

With the worldwide spread of wind turbine installations, various problems such as landscape issues, bird strikes and grid connections have arisen. Protection of wind turbines from lightning is cited as one of the main problems. Wind turbines are often struck by lightning because of their open-air locations, such as in mountainous areas, and their special configuration and very-high construction. Especially, low-voltage and control circuits can fail or suffer burnout while blades can incur serious damage if struck by lightning. Wind turbine failures caused by lightning strikes account for approximately 25% of all failures. The problem is regarded as a global one that needs immediate resolution.
It is important to understand the impedance characteristics of wind turbine earthing systems from the viewpoint of lightning protection. A report from IEC TR61400-24 recommends a “ring earth electrode”. This was originally defined in IEC 61024 (currently revised and re-numbered as IEC 62305), where such an electrode is recommended to reduce touch and step voltages in households and buildings. IEC TR61400-24 also recommended additional electrodes of vertical or horizontal rods. However, these concepts have not been fully discussed from the viewpoint of its application to wind turbines.
To confirm the effect of a combination of a ring earth electrode and additional vertical rods for protection of a wind turbine, this report uses the Finite Difference Time Domain (FDTD) method to present an electromagnetic transient analysis on such a wind turbine earthing system. The results show that an optimal combination can be arranged from viewpoints of lightning protection and construction cost. Thus, this report discusses how to establish a quantitative design methodology of the wind turbine earthing system to provide effective lightning protection.

抄録全体を表示

Recently, the FDTD (Finite Difference Time Domain) method, which directly solves Maxwell's equations, has been applied to lightning surge problems involving electrical wires in three-dimensional arrangements, such as power and telecommunication circuits. Lightning arresters are installed to protect the circuits from abnormal voltages due to lightning, for example. We have already proposed a technique for representing a lightning arrester in the FDTD method. However, this technique simply represents the V-I characteristics of the arrester using just three parameters and requires a method for avoiding the numerical oscillation due to the nonlinear characteristics of the arrester.
In this paper, we propose a new technique for representing the V-I characteristics of the arrester in detail using the piecewise linear function defined by several points and for improving the numerical stability without the method for avoiding the numerical oscillation. Using a test circuit, the proposed technique is validated by comparing the results calculated by the FDTD method with those by the EMTP (ElectroMagnetic Transients Program) which is a circuit-theory-based simulation program. Finally, as an example of applying the proposed technique, we calculate lightning-induced voltages on a distribution line with a lightning arrester. The calculated results by the FDTD method agree well with those by a conventional method based on circuit theroy.

抄録全体を表示

In electric power system operation and dam management, it is important that we forecast the rainfall depth in the rainy season. This paper studies the technique using neural network in order to forecast the amount of rainfall in rainy season on upper district of dam for hydro power plant. A case study was carried out on Central Japan. We were able to confirm the effectiveness of the information obtained from El Nino and La Nina data.

抄録全体を表示