Renewable energy plays very important role for green-house gas emission reduction and energy security enhancement. More and more distributed generations (DGs) driven by renewable energies will be interconnected in future, however, their volatile and unpredictable generation output may disturb the demand and supply control of power system. Since most of DGs are installed and operated by customers, the demand and supply control should be discussed for both local network and bulk power system. This paper presents recent R&Ds on demand and supply control with massive DG installation.
Do you remember an expert system? I think there are various impressions about the system. For example, some might say “It reminds me of old days”. On the other hand, some might say “It was really troublesome”. About 25 years ago, from late 1980s to the middle of 1990s, when the Showa era was about to change into the Heisei Era, artificial intelligence boomed. Research and development for an expert system which was equipped with expertise and worked as smart as expert, was advanced in various fields. Our company also picked up the system as the new system which covered weak point of conventional computer technology. We started research and development in 1984, and installed an expert system in a SCADA system, which started operating in March 1990 in the Fukuoka Integrated Control Center. In this essay, as an electric power engineer who involved in development at that time, I introduce the situation and travail story about developing an expert system which support restorative actions from the outage and overload condition of power networks.
From depletion of energy resources and consideration to natural environment, dispersed power system such as wind power generator is scheduled for introduction. Additionally, all electrification apartment house or residence and electric vehicles are increase in recent years. However, due to the fluctuating power from renewable energy sources and loads, frequency fluctuation of power system become problematic. This paper presents a methodology for grid frequency control by distributed controllable loads. This system consists of diesel generator, wind farm, and loads. By applying power consumption controller with H∞ control theory, grid frequency fluctuation is maintained around rated value. In order to verify the effectiveness of the proposed system, MATLAB/Simulink is used in simulations.
A PV system output is not constant and varies depending on climate conditions. Varying PV power causes frequency deviations and decrease in reliability of the isolated power utility when large PV power from multiple PV systems is fed in the utility. In this paper, to overcome this problem, a simple coordinated control method based on fuzzy reasoning is proposed to reduce the frequency deviations. Here, the power command is formed in two steps: central and local. Fuzzy control is applied to produce the central power command considering average insolation, change of insolation, and frequency deviations. In the local step, a simple coordination is kept between the central power command and the local power commands by producing a common tuning factor. The proposed method is compared with the method where extracted maximum power is supplied to the utility without coordination. Simulation results show that the proposed method is feasible to reduce the frequency deviations of the isolated power utility and delivers PV power near the maximum PV power. Usually, to reduce frequency deviations, PV power is smoothed; however, propose method reduces the frequency deviation without smoothing of the PV power variations.
Recently, more and more renewable power plants are connecting into the power grids, and it becomes difficult for power system operators to grasp the system operating condition exactly. Therefore, a proper forecasting method is expected to predict the short-term power generation of the dispersed generators for use of short-term distributed control, short-term operating plan of dispersed generators and electric energy storage equipments, as well as economical employment. For this purpose, in this paper, we approach the forecasting precision enhancement method for the short-term wind power generation by use of an improved NN (Neural Network), which is only based on the real-time meteorological data. By the ways of properly selection of learning data and introduction of two types of improved NN methods called NARX and Ensemble Technique, we attempt to enhance the forecasting precision for the short-term wind power generation. The results from this study show that the Mean Absolute Percentage Errors and Maximum Errors are lower than that of the base model which is based on the generally used FNN method, and thus have verified the validity of these forecasting precision improving methods proposed in this work.
In this paper, the fast voltage stability contingency ranking method including unstable contingency cases is proposed. The proposed method provides the following three advantages at once: i) Reduction of the computation time for voltage stability contingencies using the concept of the power flow compensation, ii) Calculation of the voltage stability index for all load buses and assessment of the voltage stability for each N-1 contingency, iii) Estimation of the necessary amount of load shedding ΔPcut on condition that stabilizing the unstable load buses is required. The proposed method makes it possible to arrange contingency cases in descending order according to the severity of voltage stability index and the amount of load shedding, although unstable load buses are included in contingency cases. The performance of the method is validated using simple a 6-node test system and a modified IEEE 30 bus system.
In this paper we consider that there are two economical social behaviors when new technologies are introduced. One is on the short-term economic basis, the other one is on the long-tem economic basis. If we consider a learning curve on the technology, it is more economical than short-term behavior to accelerate the introduction of the technology much wider in the earlier term than that on short-term economic basis. The costs in the accelerated term are higher, but the introduction costs in the later terms are cheaper by learning curve. This paper focuses on the plug-in hybrid electric vehicles (PHEVs). The ways to derive the results on short-term economic basis and the results on long-term economic basis are shown. The result of short-term behaviors can be derived by using the iteration method in which the battery costs in every term are adjusted to the learning curve. The result of long-term behaviors can be derived by seeking to the way where the amount of battery capacity is increased. We also estimate that how much subsidy does it need to get close to results on the long-term economic basis when social behavior is on the short-term economic basis. We assume subsidy for PHEV's initial costs, which can be financed by charging fee on petroleum consumption. In that case, there is no additional cost in the system. We show that the greater the total amount of money to that subsidy is, the less the amount of both CO2 emissions and system costs.
In recent years, a lot of equipments have been made using the inverter technology from home electric appliances to office automation apparatuses and industrial equipments with the development of power electronics technology. The voltage distortion of a distribution system has increased due to the harmonic currents generated from these apparatuses, and the increase in harmonics continues to be expected. In addition, the distribution system forms the circuit of harmonic distortion expansion by the prevalence of static capacitor without L for power factor improvement. Moreover, the voltage imbalance occurs by diversification of loads or imbalanced connection of single-phase loads. The deterioration of power quality in the distribution system causes various problems such as the overheating of equipments and malfunction of rotating machines. Since the power quality changes according to air temperature and date, it is desirable to measure the voltages and currents continuously for a long time. In this study, the authors focus attention on the distribution system in the University of Fukui campus, and the authors have measured the voltages and currents in the distribution system for a long period with WAMS (Wide Area Measurement System) using NCT (Network Computing Terminal). Based on the obtained data, the authors analyzed the power quality of the campus distribution system from viewpoints of voltage imbalance, current imbalance, voltage THD (Total Harmonic Distortion), and current THD. Furthermore, the improvement effect of power quality of the campus distribution system by exchange of single-phase load connection is described.
Many of the electric power apparatuses that were installed at the period of high economic growth in Japan are reaching their supposed lifetime. Therefore, an important issue is how to effectively maintain, manage, and replace the many aged electric power apparatuses. Hence, it is necessary to develop a condition diagnosis technique and a method of confirming the healthy condition of an aged power apparatus. Consequently, the establishment of a maintenance standard for such aged power apparatuses, which is helpful for judging the possibility of prolonged operation with satisfactory reliability and the replacement time, is required. From the above-stated viewpoint, we have aimed to establish a method of judging the condition of aged power apparatuses by executing on-site insulation tests. If an insulation test of the aged power apparatus is executed, it is important to estimate the risk (increase in the cumulative insulation fault probability) considering the background (life-stress) of the voltage application, including the on-site insulation test. In this paper, we discuss the influence of the insulation test of aged power apparatus on the cumulative insulation fault probability using a Weibull distribution.
This paper describes the phenomenon of internal pressure-rise due to arcs in the air. The electrodes used were made of aluminum, copper and iron. The arcs were ignited in a closed chamber with current of 12.5kA and duration of 0.1s. Firstly, the internal pressure-rises were measured with changing the gap length between electrodes in the range of 5 to 75mm. As a result of the evaluations of the efficiency factor, which was defined as the amount of the maximum pressure-rise divided by the total arc energy, it was clarified that the efficiency factor in the case of the aluminum was strongly influenced by the gap length. This was presumably caused by the change in the oxidation reaction energy of the vaporized electrodes with the gap length. Secondly, the internal pressure-rises were measured with changing the size of the chamber in the range of 0.32 to 0.71m3 in volume. Consequently, it was proved that maximum pressure-rise at a certain size of the chamber exceeded the one estimated with taking into account only the volume change of the chamber. This was presumably attributable to the resonance effect.
In this technical note, electromagnetic models of the lightning return stroke proposed as of today are reviewed and evaluated. In this class of models, using a numerical technique, Maxwell's equations are solved to yield the distribution of current along a vertical wire that represents the lightning return-stroke channel. Here, it is shown that a current wave necessarily suffers attenuation as it propagates upward along a vertical non-zero-thickness wire above perfectly conducting ground excited at its bottom by a lumped source, even if the wire has no ohmic losses, which is a distinctive feature of this class of models. Then, electromagnetic models proposed as of today are classified into six types depending on lightning-channel representation, and channel-current distributions and resultant electromagnetic fields calculated for these different channel representations are presented. Furthermore, methods of excitation, representative numerical techniques for solving Maxwell's equations, and applications of lightning return-stroke electromagnetic models are reviewed.
This letter describes a parallel solution method of power system transient stability analysis on a multi-core PC cluster system. We use a cash blocking method for solving differential equations and simultaneous equations. This method can use multi-core PC cluster efficiently by dividing matrix calculation of differential equations and simultaneous equations of power system simulation into cash size of each core.
In a concentrator photovoltaic (PV) system, high concentration causes a decrease of electrical output, since the temperature of the PV cell increases. A linear-array photovoltaic system (LAPS) with a relatively low concentration using a cylindrical mirror was developed. In this system, the sunlight was concentrated on a linearly-arrayed PV system with 7 mono-crystalline silicon PV modules. The LAPS was mounted on a two-axis sun-tracker system. The electrical efficiency was approximately 11% under typical operating conditions.