This paper deals with an efficient treatment of a periodic boundary condition in parallel environments for a three-dimensional electromagnetic analysis. To reduce computation time, analysis domain is often reduced using the periodic boundary condition. In general, high efficiency in parallel computing using the hierarchical domain decomposition method (HDDM) with the periodic boundary condition is difficult to achieve. The HDDM is known as an efficient parallel finite element method for an analysis of a rotating machine including moving bodies. In this paper, a new domain decomposition technique for the HDDM that enables us to achieve efficient scalability on massively parallel computers is proposed.
This paper proposes an efficient method to perform a finite-element analysis (FEA) of soft magnetic composites (SMC) by using a dynamic hysteresis modeling based on Cauer circuit representation for eddy-current fields. The FEA coupling with the equivalent circuit requires additional unknown variables, which results in large computational cost. To overcome the difficulty, we propose two approaches: one is the elimination of unknown variables corresponding to the equivalent circuit with the help of the Schur complement, and the other is the direct incorporation of the equivalent circuit into the finite-element formulation considering magnetic hysteresis. To demonstrate the effectiveness of the proposed methods, numerical results of a practical SMC-core reactor are presented.
A 3-D eddy current analysis based on the A-ϕ method with a domain decomposition method (DDM) has been proposed. In the 3-D eddy current analysis with the DDM, the conjugate orthogonal conjugate gradient with incomplete Cholesky factorization (ICCOCG) method is generally applied to solve subdomain problems because the coefficient matrices become singular. However, it is difficult to obtain high-accuracy solutions by using iterative methods because the solutions contain truncation errors. Regularization methods such as to fix gauges deteriorate the convergence of the iterative method. Therefore, we propose an improvement method of the convergence applying a direct method based on a singular value decomposition (SVD-direct method) as the subdomain solver. This proposed method has a merit that the A-ϕ method can be formulated. The improvement of convergence can be obtained with the SVD-direct method. In this paper, the algorithm of the proposed method is described, and improvement effects are shown through several experiments.
Though installation of photovoltaic (PV) systems already exceeds 40GW, more and more PV will be needed for de-carbonization. The capacity of PV will be several times of the load or more, especially in rural area distribution feeders. This paper proposes integrated measures for such PV installations which combine grid reinforcement and PV power factor control. The reinforcement includes not only replacing to heavier lines, but also using 22kV lines partially. Hosting capacities are analyzed stochastically to evaluate and compare the impact of these measures.
In order to maintain the electricity supply and demand balancing of an electric power system with high penetration photovoltaic (PV) power generation, the improvement of unit commitment (UC) scheduling based on a highly accurate and reliable forecasting of PV power generation is essentially important. Considering the wide variety of PV power generation depending on the change in weather conditions, the probabilistic forecast of PV power generation should be applied to UC scheduling. When the larger confidence interval is used in UC scheduling, the power supply reliability can be improved although the operation cost would be increased. In order to improve the power supply reliability while avoiding the increase in operation cost as much as possible, the proper confidence interval should be used. For this purpose, this paper proposes a novel UC scheduling method based on the adaptive confidence interval, which is selected so that the power supply flexibility (or reserve capacity) exceeds the predetermined level. As a first step of developing such a UC scheduling method, this paper demonstrates the effect of adaptive confidence interval for several different situations in terms of price of electricity purchased for compensating for the shortage of electricity supply and PV penetration level. The results suggest that the proposed method is useful when the PV penetration is huge but acceptable level, and the electricity price for shortage compensation is not expensive so much.
Increase of photovoltaics (PV) penetration and concentration of electric vehicle (EV) charging may cause voltage violation in distribution lines. One measure for voltage violation in distribution lines is reactive power control. In this research, to reduce additional installation cost of reactive power control equipment, reactive power control by use of power factor correction converters in consumer loads was proposed. In this paper, voltage control ability of the proposed method was evaluated from the point of additional increase of PV generation and EV charging. Distribution voltage distortion caused by harmonic currents from consumer loads to which the proposed method were applied was also evaluated from the point of maximum reactive power output from loads within allowable voltage distortion level.
The installed capacity of photovoltaic (PV) systems has been increasing rapidly due to the enforcement of the feed-in tariff scheme in Japan. However, reverse power flows from the roof-mounted PV systems cause voltage-rises in distribution networks. As for the voltage stabilization with reactive power compensation, SVC (Static Var Compensator) has been installed in the high-voltage distribution network until now. On the other hand, reactive power compensation from the low-voltage side using demand side equipment is proposed as a promising alternative with its cost-effectiveness. This paper proposes a method for evaluating the cost-effectiveness of the demand side equipment. We assumed following four installation schemes: (1) the demand side equipment is installed in the same order as PVs (2) the demand side equipment is installed with no relation to PVs (3) the demand side equipment is installed in reverse order of PVs (4) the demand side equipment is optimally installed so that the total capacity is minimized. The proposed method reveals a cost-boundary-value of the demand side equipment where those are widely used, and analyze the changes in the cost-boundary-value under various power system conditions.
Recently, the penetration of renewable energy such as photovoltaic generation (PV) and wind turbine generation is rapidly increased. However, large-scale PV output power fluctuation is caused negative impact on power grid. Therefore, the fluctuation of PV must be smoothed using energy storage system such as a battery. Generally, moving average method is used to stabilize the power fluctuation, but there is a problem that it is difficult to be compatible PV power stabilization and reduction of battery capacity. This paper proposes a new algorithm for stabilizing fluctuation in PV system, DFC (De-trended Fluctuation Component) method, which stabilizes only short-term fluctuation of PV. We calculated battery capacity to stabilize PV output power fluctuation using moving average method and DFC method. The result shows that the DFC method can reduce maximum battery capacity by 7.6% compared to moving average method.
This paper describes improvements of current breaking performance in fuse-link by controlling the temperature distribution of the fuse element during pre-arcing process. The fuse element is designed and produced to obtain the simultaneous arc-forming of several interrupting points in the fuse element by controlling the temperature of the interruption point in consideration of the heat generation by current flowing and heat radiation to the surrounding media. The interruption test was carried out to evaluate the current breaking performance. It was confirmed that the current breaking performance of the fuse which controlled temperature distribution was improved in comparison with common structure fuses without temperature controls. Also, it was found that this control method can be applied to fuses of different pattern and thicknesses. In addition, the interruption performance could be improved for different currents conditions used for calculation.