IEEJ Transactions on Power and Energy
Online ISSN : 1348-8147
Print ISSN : 0385-4213
ISSN-L : 0385-4213
Volume 127 , Issue 4
Showing 1-7 articles out of 7 articles from the selected issue
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Paper
  • Yoko Amano, Hiroyuki Kajiwara
    2007 Volume 127 Issue 4 Pages 559-565
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    This paper proposes a maximum output power control system of variable-speed small wind generators. Paying attention to an optimum rotational speed of a single phase AC wind generator which can obtain maximum output power according to natural wind speed, the proposed method adjusts the rotational speed of the single phase AC generator to the optimum rotational speed. Since this adjustment is realized on line so that it can be adapted for variable-speed wind, a generated power brake links directly with the single phase AC generator, and the rotational speed of the single phase AC generator is adjusted by controlling the current that flows the FET (Field-Effect Transistor) device as the generated power brake. In order to reduce heat loss of the FET device, the PWM (Pulse Width Modulation) controller is introduced. Moreover, the experimental system of the proposed method is constituted and the experiment is performed. Finally, the validity and the practicality of the proposed method are confirmed by experimental results.
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  • Eitaro Kurata, Hiroyuki Mori
    2007 Volume 127 Issue 4 Pages 566-572
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    In this paper, a novel method is proposed for short-term load forecasting. It is one of important tasks in power system operation and planning. The load behavior is so complicated that it is hard to predict the load. The deregulated power market is faced with a new aspect that the degree of uncertainty increases. Thus, power system operators are concerned with the significant level of load forecasting. Namely, probabilistic load forecasting is required to smooth power system operation and planning. In this paper, an IVM (Informative Vector Machine) based method is proposed for short-term load forecasting. IVM is a one of kernel machine techniques that are derived from SVM (Support Vector Machine). The Gaussian process (GP) satisfies the requirements that the prediction results are expressed in distribution rather than point. However, it is inclined to be overfitting for noise due to the basis function with N2 elements for N data. To overcome the problem, this paper makes use of IVM that selects necessary data for the model approximation with posteriori distribution of entropy. That has a useful function to suppress the overfitting. The proposed method is tested for real data of short-term load forecasting.
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  • Toshiyuki Sawa, Yuji Nakata, Mitsuo Tsurugai, Shigenari Sugiyama
    2007 Volume 127 Issue 4 Pages 573-580
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    We have developed a fast, innovative matching method for the spot power market, considering network constraints. In this method, buy and sell order bids are respectively divided into the aggregated volume of several band prices. Then the aggregated volume and the center of each band price are used to calculate a band clearing price, which contains the real clearing price. The dividing and calculating process is iterated until the band price is less than the tick size of the bidding price. We applied this method to a real problem in the Japanese power market with 9 areas, 10 area-connecting lines, and 9000 orders (volume/price pairs). Our simulation results show that the new method is ten times faster than conventional linear programming. This demonstrates the effectiveness of the developed method.
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  • Kiyoshi Aiba, Shigemitsu Okabe, Teru Miyazaki, Masahide Yoshikawa
    2007 Volume 127 Issue 4 Pages 581-588
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    Damages of home electric appliances from lightning surges through a distribution line have recently increased. Installation of SPDs (Surge Protective Devices) in indoor distribution line is one of countermeasures against the damages. However, installation of SPDs is not prevalent because the effect of it is uncertain and it is expensive.
    Therefore, to ascertain effects of the SPD, they were verified by means of experiments in various cases. As a result, an SPD in the switchboard wholly suppressed over-voltages in the indoor distribution line and an SPD installed near a home electric appliance did over-voltages in one indoor distribution branch line near the SPD. But the SPD for the appliance did not suppress over-voltages in the other indoor distribution branch lines. Installation of an SPD in the switchboard is one of effective methods to protect home electric appliances against lightning surges through a distribution line.
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  • Toshiyuki Takahashi, Yoh Yasuda, Shingo Ohmoto, Takehisa Hara
    2007 Volume 127 Issue 4 Pages 589-595
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    Independent distributed generations using small wind turbines are widely spread as increasing of wind power generation. Installation of small wind turbines in densely-populated urban area is not only useful from the viewpoint of digging up wind power source in weak-wind area but also for enlightenment of renewable energy due to closing power supplies to consumptions. From the point of view, the authors proposed “urban wind power generation" using collective system with a number of small vertical wind turbines and have developed a suitable generator for low-speed vertical wind turbines such as Savonius windmill.
    Standardized on a coreless generator, the proposed generator is designed to let direction of magnetic fluxes radial in order to install the magnets and coils on the outer end of the generator. The change of magnet composition and flux direction gives realization of maximized speed of flux change and output voltage in the limited space. With above composition, the power of the proposed one is independent on the diameter.
    In this report, we describe evaluated fundamental performance of a prototype of the proposed generator. As the result of the experiments, the maximum output power of 283W was obtained. The obtained starting torque is enough small to begin to rotate at weak wind condition of no more than 1m/s. Therefore, it is clear that the proposed “radial” coreless generator is suitable for self-starting and producing high power at low speed wind.
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Letter
  • Koji Michishita, Takaie Matsumoto, Toshiyuki Nagai, Yasuji Hongo
    2007 Volume 127 Issue 4 Pages 596-597
    Published: April 01, 2007
    Released: July 01, 2007
    JOURNALS FREE ACCESS
    The overvoltage waveforms on a medium-voltage (MV) line generated by lightning have a steep front and a short tail due to behavior of protection devices. To discuss the occurrence of sparkover on a MV line, it is necessary to estimate the insulation characteristics of the distribution instruments by using such waveforms. Therefore, it is of practical importance to develop an equivalent circuit of an impulse generator, applicable to the case of generation of such waveforms. In this letter, the authors verify the reproducibility of a steep and short-tailed lightning impulse voltage waveform by the detailed equivalent circuit.
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