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 the last term 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.
This paper presents a frequency control method by a coordinated control of a wind turbine generator (WTG) and a battery energy storage system (BESS) using load estimation in an isolated power system. The load variation is assumed as a disturbance to the power system and can be estimated by using a disturbance observer. For the load estimation, H∞ control theory and parameter identification are applied to achieve robust control performance. Each output power command of the WTG and the BESS is determined by using the estimated load. Low frequency component in the load variation is reduced by the WTG with pitch angle control, while high frequency component in the load variation is reduced by the BESS with charge/discharge operation, respectively. In addition to the frequency control, a capacity reduction technique for BESS is proposed. The effectiveness of the proposed method is verified by numerical simulations.
Wind power generation is expected as one of countermeasures for the environmental issues and energy security crisis. However, uncertain and volatile fluctuations in wind power generation output may disturb the system frequency control. This paper proposes a fluctuation stabilization method utilizing a controllable distributed generator (CDG) and a battery system considering the actual technical requirement for a wind power generation system set by the Tohoku Electric Power Co. In the proposed method, the CDG plays a role of main compensator and the battery is used to support the slow dynamic response of CDG. In this paper, the validity of proposed method is ascertained and the necessary capacity of battery system is evaluated through some computational simulations.
This paper proposes a new method for transmission network expansion planning (TNEP) with Multi-objective Memetic Algorithm (MOMA) in consideration of a probabilistic reliability index. Recently, power networks increase the degree of the uncertainties due to the new environment of power network liberations, the emergences of renewable energy, etc. As a result, the importance of improving power supply reliability with probabilistic approaches has been recognized in power system operation and planning. This paper formulates TNEP as a multi-objective optimization problem that optimizes a probabilistic reliability index as well as the construction cost to obtain a set of the Pareto solutions in Monte Carlo Simulation (MCS). This paper proposes a new method for TNEP with MOMA that combines Multi-objective meta-heuristics (MOMH) with Tabu Search (TS) to obtain better solution sets. MOMH is useful for evaluating a set of the Pareto solutions systematically while TS plays a key role to improve the solution quality. The effectiveness of the proposed method is successfully demonstrated in the IEEE 24-bus system.
This paper proposes a novel searching method for radial distribution network to maximize outputs of PV generators. When a lot of PV generators are connected to distribution network, it is necessary to control PV outputs to keep the voltage within the regulated range of power quality. The aim of the paper is to find the optimal topology, that is the state of section switches so as to maximize the total PV outputs. This problem becomes a combinatorial optimization one and the exhaustive search results in enormous computation time. In this paper, a novel searching method is proposed which is based on the replacement of the complex combinatorial optimization problem with a minimization problem regarding with voltage profile of distribution network. The features of the proposed method are to utilize the relation between the total outputs of PV generators and the voltage profile, the superposition of radial electric circuit and a sequential algorithm for search in an optimal topology. In order to verify the proposed method, the comparison study has been done by using two distribution network models. As the result, there is possibility that the proposed method can find sub optimal topology in a short time compared with tabu search approach.
Multi-core CPU is widely used for PC now. PC cluster, which is composed of many PC's, can easily get its high performance using multi-core CPU's. It is named as a multi-core cluster. In this paper, we propose hierarchical parallel solution methods of power system transient stability analysis on a multi-core cluster. In a multi-core cluster, there are two level layers in communication system. One is the communication among cores in a CPU, and the other is the communication among CPU's in the multi-core cluster. To communicate between cores in a CPU, there are two ways. One is the communication through cache, and the other is the communication through bus in a CPU. The speed of the former one through cache is higher than that through bus. In addition, to get maximum speed of communication through cache, the size of data to process should be kept within the size of each cache used in each calculation step. A long development term is necessary to optimize software for two communication ways. We developed an optimization technique of matrix operations and a hierarchical parallel processing method for a multi-core cluster, and applied them to solve differential equations and simultaneous equations in power system simulation. We obtained 1.5 times speedup using two cores in a PC, which communicate through shared memory and 1.39 times speedup using two PCs with single core which communicate through bus.
This paper presents a new efficient method for network reconfigurations with step voltage regulators (SVRs) in distribution networks. Recently, the power market becomes more deregulated, competitive and complex. Therefore, the conventional methods are insufficient because of simple objective problem. This paper defines the network reconfiguration as a multi-objective optimization problem (MOP). Furthermore, this paper considers SVRs to improving the voltage deviation in distribution networks. Multi-objective meta-heuristics (MOMH efficiently) solves MOP. This paper makes use of a new MOMH that combines with REX* and TS-based method. The proposed MOMH has higher performance in comparison with MOMH. Therefore, the proposed method provides system operators with the better solution candidates in consideration of trade-off. The proposed method is successfully applied to a sample system.
This paper describes the development of a new islanding detection system based on the change ratio of harmonic admittances, voltages and currents of the power system between the response measured when the main utility supply is connected to the distributed generation site and that measured when the distributed generation site is operating in islanding. The results of verification tests conducted at the Akagi Test Center of CRIEPI and at several hydroelectric power plants of Kansai Electric Power are also described. No disturbance to the grid is caused through this mechanism because it uses only harmonics characteristics without injecting any active influence to the grid. In addition, the islanding condition can be detected accurately regardless of the grid state even when the local generation power and the loads in the islanding system are perfectly balanced.
This paper presents an adaptive evolutionary programming incorporating neural network for solving transient stability constrained optimal power flow (TSCOPF). The proposed AEP method is an evolutionary programming (EP)-based algorithm, which adjusts its population size automatically during an optimization process. The artificial neural network, which classifies the AEP individual based on its stability degrees, is embedded into the search template to reduce the computational load caused by transient stability constraints. The fuel cost minimization is selected as the objective function of TSCOPF. The proposed method is tested on the IEEE 30-bus system with two types of the fuel cost functions, i.e. the conventional quadratic function and the quadratic function superimposed by sine component to model the cost curves without and with valve-point loading effect respectively. The numerical examples show that AEP is more effective than conventional EP in terms of computational speed, and when the neural network is incorporated into AEP, it can significantly reduce the computational time of TSCOPF. A study of the architecture of the neural network is also conducted and discussed. In addition, the effectiveness of the proposed method for solving TSCOPF with the consideration of multiple contingencies is manifested.
For energy conservation and CO2 reduction, cogeneration systems may be useful. This paper shows the effectiveness of the cogeneration system, used in a residential area and designed to supply heat by hot water pipelines. The cogeneration system consists of a micro gas turbine (MGT) generator and a boiler. Entire heat load is supplied by the MGT or boiler, while an electric load may be supplied by an electric power company. Optimal diameter of the hot water pipeline becomes large when the load density becomes low. Total heat supply loss is less then 10% for moderate temperature region. However, it exceeds 20% for a sparse load in the cold region. The MGT should generates heat just required by the load for the primary energy or cost minimum operation. In the moderate temperature region, primary energy reduction ratio is positive in almost all cases, while it becomes negative in the cold region. On the other hand, CO2 emission almost always decreases in some extent. In the warm or moderate temperature region, MGT cogeneration systems are effective for energy conservation. They are also effective for CO2 reduction in almost all cases.
This article presents a numerical model of streamer breakdown of sphere gap in air at atmospheric pressure. The streamer propagation is described by a system of equations, including charge continuity equation and Poisson equation. In addition, the photoionization effect is simplified and integrated into the model. The numerical results was performed and compared with the measurement of breakdown current. From the results, the increase of discharge current before the gap breakdown could be divided into three stages according to the development of each type of streamer. We propose that the sphere gap will breakdown when positive streamer reaches the cathode and the rate of increase of discharge current is about 1.4A/ns.
Power fluctuations of the rolling mill may cause the instability of electric power systems, and increase the cost of the electric power facility and electricity charges. Therefore, in order to compensate the power fluctuations, the development of the electric power-leveling systems (EPLS) is very important in the future electric power system. The EPLS with a SMES has been proposed as one of the countermeasures for the electric power quality improvement. However, the SMES is very expensive and it is difficult to decide the gains of the controller. It is essential in the practical use that the reduction of SMES capacity is realized. This paper proposes a new optimization method of the EPLS. The proposed algorithm is Cluster-Structured GA with Masking (CSGA). The optimization of the EPLS can be achieved by the proposed CSGA compared to the GA.
Spectrum analysis has been carried out based on the spatial structure model of wind. Power fluctuation from nine wind turbines arranged in 3 × 3 manner is less than that from a single turbine, regardless of wind direction. The increased distance between two turbines slightly reduces power fluctuation. In case of an inline arrangement, power fluctuation caused by the wind perpendicular to the turbine line is lower than that by the wind parallel to the turbine line, because the coherence of wind perpendicular to the wind direction decays sharply. For double line arrangement, fluctuation will be almost the same for the 3 × 3 arrangement.