The approaches to Smart Grid are characterized by the following three points. That is, 1) integration of electricity and information and communication technologies (ICT), 2) handling of large integration of renewable energy, 3) cooperation between supply side and demand side. Based on the above three points, this paper summarizes power system technologies to realize Smart Grid from the viewpoint of power supply chain. Also, recent research trend of related area is surveyed. Among the large integration technologies of renewable energy, researches on the areas of centralized generation and storage, distribution and distributed generation and storage in the supply chain are very active including peripheral technologies. Among the cooperation between supply side and demand side, most of the research faces to demand area in supply chain.
The 2011 Tohoku Earthquake had a great impact on the energy policy in Japan. It has so far been expected to install a large amount of generation from renewable energy sources such as wind power generation and photovoltaic generation. However, it causes some problems in power systems, e.g. imbalance between demand and supply, and Battery Energy Storage System (BESS) is one of the effective solutions to these problems. Due to a high cost of the BESS, applications of customers' appliances to the new power system control in replacement of a part of BESS have gained much attention. This paper proposes a power system control method by use of a number of Heat Pump Water Heaters (HPWHs) not only for Load Frequency Control (LFC) but also for Economic Dispatching Control (EDC). Considering the total LFC capacity which is required to regulate the system frequency, the operation of the HPWHs is scheduled by using tabu search to minimize the fuel cost and the start-up cost of thermal power plants. The effectiveness of the power consumption control of the HPWHs for the LFC during the period which is scheduled by the proposed method is evaluated by numerical simulations.
A new large-scale thermal power plant is planned to be located approximately 300km away from the main power grid. Existing transmission facilities is utilized for transmission of the power from the generating plant to the grid. In an effort to maximize the total transfer capability (TTC) of the existing lines and maintain security of the interconnection, a new special protection system (SPS) and STATCOM is introduced. This new SPS is developed as the Integrated Stability Control system (ISC) which can be applied to transient stability, voltage stability and frequency problems. In order to adopt merits of both pre-calculation method and post-fault real-time calculation method, the control function of ISC consists of primary control based on pre-calculation results and secondary control based on real-time calculation results. This paper describes the detailed algorithms of the ISC and the results of its verification test using prototype systems combined with RTDSTM or an analog-type simulator.
Measured data from IT switches are utilized in order to control voltage in distribution systems with photovoltaic generation systems. However, length of period from the data measurement to the data acquisition from IT switches affects voltage control ability in the distribution automation system. In this paper, a voltage control method by LRT and SVR with the periodic data from IT switches is proposed, and using the method, the effect of the length of the data acquisition period for voltage control is evaluated through numerical simulations in a distribution system model. Furthermore, the optimal length of the data acquisition period is determined according to PV penetration rate.
Voltages in distribution system are maintained within a proper voltage range by adjusting a tap position of Load Ratio control Transformer (LRT) and Step Voltage Regulator (SVR). In Japan, many voltage control methods have been researched. However, these conventional methods do not presuppose the bank fault restoration. Since the main purpose of voltage control of the conventional restoration approach is to reduce the amount of voltage violation in distribution system, the number of customers with voltage violation cannot be reduced to zero during a bank fault restoration. In this paper, the authors propose a cooperation voltage control method of LRT and SVR to minimize the number of customers with voltage violation corresponding to the bank fault restoration in distribution systems with PV systems. In the proposed method, the tap position of SVR is controlled after the control of LRT to avoid frequent tap changes and each tap position of voltage control devices is controlled to minimize the number of customers with voltage violation. In order to check the effectiveness of the proposed method, the simulation using distribution system model with PV systems is performed under various conditions.
Since residential photovoltaic systems trend to increase in low-voltage distribution feeders, it is becoming more important to estimate voltage profile including not only high and middle but low-voltage distribution network to operate distribution systems. In case of using the conventional power flow calculation method based on iterative calculation, it will be taken much time to get voltage values all over low-voltage distribution feeders. This paper presents a new method to calculate voltage quickly keeping the accuracy sufficient for practical operation. In order to check the validity of the proposed method, numerical results are shown by comparing its computation accuracy and time with those of the conventional one.
In Poland, the expansion of the introduction of wind power generation has been recently accelerating as a global warming countermeasure mainly in the area of northern Poland along the Baltic Sea. The transmission company (PSE-Operator, “PSE”) and the distribution company in the northern area (ENERGA-Operator, “ENERGA”) have faced an urgent issue of reinforcement in transmission lines to tackle with such expansion. Moreover, concerns have been increasing about negative impacts on the supply-demand balance and the power quality due to fluctuations in wind power generation output. We have analyzed and examined power system stabilization measures such as special protection scheme (SPS) with a minimum cost for expanding the introduction volume of wind power generation in order to address such concerns. In addition, we have examined measures for stable operation of the power system through the application of smart grid technologies such as storage batteries for the power system, and studied the possible commercialization of such measures. Through the analysis we confirmed the effect of introduction of SPS or decision support system for operators which conduct a control of the power system such as generation shedding against overload which could be caused in the event of N-1 fault when the introduction volume of wind power generation is expanded. And we also confirmed the effect of introduction of storage batteries that suppress extra area flow fluctuations of wind power generation and shave a peak of demand.
In this paper, the use of heat pump air-conditioning system (HPACS) for power fluctuation compensation is focused. Verification experiments have been carried out using a model microgrid system with gas engine, battery energy storage system (BESS), HPACS, photovoltaic cells, and loads. The BESS's necessary energy capacity for power fluctuation compensation and the microgrid system's ability to suppress power fluctuation is analysed by use of experimental results. It is clarified from the analysis that control of HPACS is effective for reduction of BESS's necessary energy capacity without deterioration of microgrid's ability to suppress power fluctuation. Furthermore, the temperature of the rooms that use the HPACS is calculated by a room temperature calculation model. The results show that the temperature fluctuation caused by control of HPACS is negligible small.
Until now, Itochu Techno-Solutions Corporation (CTC) and Tohoku Electric Power Co., Inc. have developed the system which predicts the wind power output in the control area of electric power system in order to contribute to demand and supply control of the power system. The official operation of the system has been started after experimental operation during three years. Currently, the forecast information is used as reference information for the electric power system operation in Tohoku Electric Power Co., Inc. In this paper, we describe the outline, operational status and forecast accuracy of the system. We verified stable operation of the system and forecast accuracy that is about 8% (Intraday forecast) and 10% (Day ahead forecast) by RMSE during experimental and official operation.
For the impact assessment of high-penetration photovoltaic power generation systems (PVS) on the electric power system, the proper estimation of total power output fluctuation of PVS is essential, considering the so-called smoothing effect among a number of PVSs. By using the irradiance data observed at 61 points for a year, this study statistically evaluated the fluctuation characteristics of spatial average irradiance in the Chubu region, Japan. The smoothing effect around individual observation point was taken into account by using a low-pass filter developed based on the so-called transfer-hypothesis. Main results are as follows. The absolute value of the maximum fluctuation width (MFW) calculated with 120min window is around 350W/m2 on many days due to the sunrise or sunset. The MFW of sun-position independent spatial average irradiance is sometimes larger than 300W/m2 and occurs before or after the noon due to the coherent change of weather condition over the region. The MFW of spatial average irradiance tends to be large in the summer season, while the MFW of clearness index tends to be large in winter season. The hourly standard deviation of fluctuation including cycles shorter than 32min is a few percentage of hourly average irradiance.
Distribution system has huge number of configuration candidates because the network configuration is determined by state of many sectionalizing switches (SW: opened or closed) installed in terms of keeping power quality, reliability and so on. Transmission system also has huge number of configuration candidates and circuit breakers (CB: opened or closed) as same objective as distribution system. Since feeder current and voltage depend on the network configuration, losses of transmission and distribution systems can be reduced by controlling states of CB and SW. So far, various methods to determine the loss minimum configuration of transmission and distribution systems have been researched. However, a method that hierarchically determines the loss minimum configuration of transmission and distribution system with PV has not been proposed. In addition, power flow of whole system is changed by various PV penetration distribution patterns. Therefore, transmission and distribution losses must be evaluated in various PV penetration cases. In this paper, a hierarchy control method to determine a transmission and distribution loss minimum network configuration by controlling on-off states of CB and SW is proposed. The validity of the proposed method is evaluated to calculate the reduction of whole network loss in a transmission and distribution model with 48 CB and 1404 SW in two kinds of PV penetration cases.
This paper describes dynamic voltage control method using SVC with controllable dead band that changes dynamically to a node voltage in a distribution system installed SVC. Proposed method consists of three systems. First system detects probability of voltage deviation from proper range of node voltage. Second system is used to stabilize output of SVC based on changing dead band. Third system expect voltage trend. In order to verify the validity of the proposed method in comparison with conventional methods, numerical simulation and experiment were carried out using a distribution system model with RES.