The energy management technology has been occupying the attention due to the requests for the high-efficiency energy use. Especially, the electric power management is the key issue in order to achieve the high-efficiency energy generation, transmission, distribution, and consumption. Therefore, the progress in power electronics technology is very important, as the power electronics technology offers the function of efficient electric power control. The wide-gap semiconductor is the promising technology in the field of the power electronics which is now based on the Si devices. In this manuscript, the recent technical trend in the field of power electronics R&D is explained from the viewpoint of wide-gap semiconductor application.

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In this study, we evaluated the practical usability of so-called 1/√N rule, focusing on three factors, i.e. the geographical extent, the location of representative point, and the topological difference. First, by using the insolation data observed at 37 points mainly located in the Nobi Plain, we calculated the correlation diagram between two different standard deviations (STDs) of geographical average insolation fluctuation, i.e. STD of ensemble average insolation of N points (σ_e) and STD calculated with the representative point data by using 1/√N rule (σ_N). As the results of evaluating the slope and R² values of regression line of correlation diagram and the P-value of χ²-test regarding frequency distribution of σ_e and σ_N, the 1/√N rule would be applicable for the area of around 20km radius. The representative point for calculating σ_N should be carefully selected even within the area of 15km radius. Because the difference in weather condition is much larger in the Matsumoto Basin area than in the Nobi Plain area even if the area size is the same, the 1/√N rule should be applied to smaller area than the area of 20km radius available for the Nobi Plain area.

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The purpose of this study is to examine the influence of shape of cross-section of scramjet engine driven experimental DCW-MHD generator on generator performance by three-dimensional numerical analyses. We have designed the MHD generators with symmetric square and circular cross-section, based on the experimental MHD generator with asymmetric square cross-section. Under the optimum load condition, the electric power output becomes 26.6kW for the asymmetric square cross-section, 24.6kW for the symmetric square cross-section, and 22.4kW for the circular cross-section. The highest output is obtained for the experimental generator with asymmetric square cross-section. The difference of electric power output is induced by the difference of flow velocity and boundary layer thickness. For the generator with asymmetric square cross-section, the average flow velocity becomes the highest and the boundary layer becomes the thinnest. The compression wave is generated depending on the channel shape. The difference of flow velocity and boundary layer thickness is induced by the superposition of compression wave.

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Recent rapid introduction of photovoltaic power generations (PVs) causes several issues of power quality. First, reverse flow causes voltage rise of distribution lines. Second, since almost of residential PVs are connected to the distribution lines by single-phase, voltage imbalance is occurred by imbalance current of PVs. On the other hand, in Japan, almost high voltage consumers set up Static capacitors (SCs) to improve the power factor at their receiving points. However, the capacity of SC becomes excessive than required amount of capacity. Hence, the excessive amount of SCs may also cause voltage rise and harmonic voltage problems that is Ferranti Effect and harmonic resonance between SCs and inductance of lines.
Under these backgrounds, the purpose of this study is to propose the new control method of SCs not only improving power factor but also solving power quality problems. The major point of the proposed method is to determine the capacity of three-phase type SCs and single-phase type SCs so as to minimize power loss of distribution line in a limitation condition of each power quality.

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This paper proposes an application of a filter method in preprocessing stage for mid-term load demand forecasting to improve electricity load forecasting and to guarantee satisfactory forecasting accuracy. Case study employs the historical electricity consumption demand data in Thailand which were recorded in the 12 years of 1997 through to 2007. The load demand forecasted value is used for unit commitment and fuel reserve planning in the power system. This method consists of a trend component and a cyclical component decomposed from the original load demand using the Hodrick-Prescott (HP) filter in the preprocessing stage and the forecasting of each component using Double Neural Networks (DNNs) in the forecasting stage. Experimental results show that with preprocessing before forecasting can predict the load demand better than that without preprocessing.

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In this paper, an on-line deterioration prediction and residual life prediction method is proposed for maintenance of rotating equipment in thermal power plants. Condition of rotating equipment is inspected by vibration measurement. A mathematical model for the deterioration of the rotating equipment is derived in order to predict future condition of the rotating equipment. Residual life of the rotating equipment is predicted by deterioration prediction using on-line estimation of model parameters with forgetting factor. The effectiveness of the residual life prediction method is assured by applying it to actual vibration data of rotating equipment.

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Recent wind farm grid codes require wind generators to ride through voltage sags, which means that normal power production should be re-initiated once the nominal grid voltage is recovered. However, fixed speed wind turbine generator system using induction generator (IG) has the stability problem similar to the step-out phenomenon of a synchronous generator. On the other hand, doubly fed induction generator (DFIG) can control its real and reactive powers independently while being operated in variable speed mode. This paper proposes a new control strategy using DFIGs for stabilizing a wind farm composed of DFIGs and IGs, without incorporating additional FACTS devices. A new current controlled voltage source converter (CC-VSC) scheme is proposed to control the converters of DFIG and the performance is verified by comparing the results with those of voltage controlled voltage source converter (VC-VSC) scheme. Another salient feature of this study is to reduce the number of proportionate integral (PI) controllers used in the rotor side converter without degrading dynamic and transient performances. Moreover, DC-link protection scheme during grid fault can be omitted in the proposed scheme which reduces overall cost of the system. Extensive simulation analyses by using PSCAD/EMTDC are carried out to clarify the effectiveness of the proposed CC-VSC based control scheme of DFIGs.

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In this paper, the authors propose an improved identification method of the magnetizing inrush current phenomena. A first improvement is the development of determinant method about the transformer connection, which gives a calculation method of magnetic flux, using with theoretical pattern of inrush current ratio. And then, since the Aitken's Δ²-process, which uses the estimation of the saturation on/off time, has many extrema, it is difficult to determinate the saturation on/off time. Therefore, using the pattern of derivative current, a new determinant method of the saturation on/off time is developed.

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Micro discharges (MDs) such as spark or partial discharges on distribution lines, which occur by degradation of insulators, insulated wires, bushings, etc., may cause television interference or ground fault. A technique for locating MDs using differences in arrival time of electromagnetic pulses radiated from the MDs has been investigated recently. However, the technique requires a large and expensive apparatus such as a digital storage oscilloscope able to record the received pulse signals very fast. We investigated a new technique to estimate the direction of arrival (DOA) of the electromagnetic pulses using analogue signal processing, and produced a prototype of a MD locator. In order to evaluate the estimation error of DOA, we performed several experiments to locate spark discharges about 50nC/pulse on testing distribution line by using the MD locator. The average estimation error was about 5 degree, and the error of azimuth was several times larger than that of elevation in most cases. This reason is considered that resolving power of azimuth became lower than that of elevation owing to configuration of receiving antennas. We also tried to locate MDs on real distribution lines, and confirmed that there was no significant influence of reflected or carrier waves on DOA estimation.

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CFRP (Carbon Fiber Reinforced Plastic) is widely used in the structures of aircrafts, automobiles, wing turbines, and rockets because of its qualities of high mechanical strength, low weight, fatigue resistance, and dimensional stability. However, these structures are often at risk of being struck by lightning. When lightning strikes such structures and lightning current flows through the CFRP, it may be structurally damaged because of the impact of the lightning strike or ignitions between layers. If there are electronic systems near the CFRP, they may break down or malfunction because of the resulting electromagnetic disturbance. In fact, the generation mechanisms of these breakdowns and malfunctions depend on the current distribution in the CFRP. Hence, it is critical to clarify the current distribution in various kinds of CFRPs. In this study, two kinds of CFRP panels—one composed of quasi-isotropic lamination layers and the other composed of 0°/90° lamination layers of unidirectional CFRP prepregs—are used to investigate the dependence of current distribution on the nature of the lamination layers. The current distribution measurements and simulations for CFRP panels are compared with those for a same-sized aluminum plate. The knowledge of these current distribution characteristics would be very useful for designing the CFRP structures of aircrafts, automobiles, wing turbines, rockets, etc. in the future.

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This paper investigates grounding impedance reduction with various shapes of grounding electrodes in comparison with a conventional vertical rod based on field measurements and FDTD simulations. It is found that a vertical rectangular conducting plate is effective to reduce the transient and steady-state impedance less than a half of that of the vertical rod. A circular conducting plate parallel to the earth surface is also effective to reduce the steady-state impedance, but the transient impedance is nearly the same as that of the vertical rod. The rate of the reduction is somehow proportional to the surface area of the electrode, but tends to saturate as the area increases. The transient impedance is rather independent of the earth resistivity and permittivity, but tends to inversely proportional to the wavefront duration of an applied current.

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Structures on mountainous area have more lightning incidence than those on the flat ground. In order to evaluate lightning striking characteristics to such structures, a concept of ‘Effective height’ has been proposed. The value of the effective height of a structure has been estimated from the number of lightning or ratio of upward flashes of the structure. In this letter, a method to calculate the effective height is proposed. The calculated values agree with field experiences very well.

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Cumulative distributions of charge amount and specific energy of upward winter lightning flashes, observed by Rogowski coils instrumented on wind turbines in the coastal area of the Sea of Japan, were analyzed. Among 284 current data recorded at 16 measuring sites, the transferred charge of 13 lightning flashes exceeded 300C, and the specific energy of 2 flashes exceeded 10MJ/Ω. The medians of transferred charge are about 60% higher than those observed at Nikaho wind farm in winter for the three types of current, negative, positive and bipolar. Importance of observation at multiple sites is manifest.

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