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Although FRT capability is claimed in Japanese grid code for RE, DVS capability is not. In some European countries, not only FRT but also DVS is claimed. Whether this choice of our grid code is pragmatically adequate or not? To answer the question, it is necessary to evaluate FRT and DVS capabilities. But the past studies only evaluated qualitative merit of FRT and DVS, or evaluated quantitative merit on fictional system models. Since the authors intend to evaluate FRT and DVS capabilities in existing power system of Japan, some method for the evaluation must be invented. For the evaluation, values of FRT and DVS capabilities are evaluated by reduction amount of stabilizing equipment (i.e. SVC in the paper). The evaluation based on strict optimal SVC disposition is quite difficult, because existing power system must be adequately modeled, because number of SVCs is large and because every power flow conditions must be considered. However, semi‐optimal SVC disposition can be calculated as shown in the paper. As the result, value of FRT is quite larger than value of DVS. And then, our grid code is proved as pragmatically adequate, except some flaw in claimed FRT design that is introduced in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Recently, wind power generation are installed as a countermeasure for the environmental issue in Japan. However, wind power generation output is fluctuated due to wind condition. Moreover, it is some negative impact for system operation such as the economic load dispatching control and the load frequency control. In Japan, NEDO has started the project as a countermeasure for massive penetration of wind power generation in 2014, called “R&D Project on Grid Integration of Variable Renewable Energy.” In this paper, we proposed the output fluctuation suppression control method of wind power generation using the battery and forecast data of wind generation output. Specifically, the target value of wind power generation output is calculated to decrease the deviation output from fluctuation suppression code for ramp event using deterministic optimization method. The effectiveness of proposed method is evaluated through the computational simulation using forecast data and actual wind power generation output in Tohoku area. [ABSTRACT FROM AUTHOR]

SUMMARY This paper examines the influence of aggregated power output fluctuation of photovoltaic power generation system (PVS) on the power system frequency focusing on ramp events of aggregated PVS power output. A numerical simulation model of economic load dispatching control (EDC) and load frequency control (LFC) is used together with a PVS power output forecasting model and a unit commitment (UC) scheduling model developed in our preceding study. As a result, in the case of ramp event with long duration and high ramp rate, the frequency violation occurs when the power output of controllable generators with high load-following capability reaches to upper/lower limit even if the power output of low load-following capability generators is still available. If the load dispatching scheme is tentatively changed from the conventional EDC using an equal incremental fuel cost rule to, for example, a dispatching policy based on the capacity without the consideration of fuel cost, the aggregated load-following capability can be kept, avoiding the frequency violation. [ABSTRACT FROM AUTHOR]

SUMMARY In a distribution line, power system control and power equipment investment are planned based on a measured power system current. However, recently the mass introduction of photovoltaic (PV) make it difficult for us to precisely measure the demand curve that is a current consumed by electrical equipment because the reversal power flow from PV systems is superposed. Therefore, the prediction of demand curves of distribution line is indispensable for power system management. In addition, it is also necessary to estimate the reliability of the predicted values as well as predicted current itself. In this paper, we propose the estimation method of the prediction interval that is the index of reliability based on the past demand curve database. The feature of the proposed method based on Just-In-Time (JIT) modeling make it possible for us to accurately estimate the prediction interval by the normalized database of demand curve. In this paper, some numerical examples are presented, which demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

District Heating and Cooling (DHC) combined with a Cogeneration System (CGS) is one of the most efficient ways to supply energy to the commercial and residential sectors. This paper discusses the feasibility of introducting DHC from the viewpoint of the overall energy saving effect in Japan's energy system as a whole. Although DHC is efficient for congested areas such as urban business centers, these areas are limited in capacity and number. In our evaluation of the feasibility of introducing DHC, we consider the energy demand density profiles of Japan's commercial and residential sectors in order to determine the installed DHC capacity that is optimal for meeting the growth of energy demand. This paper also discusses operating patterns of CGS and of boilers in DHC. In order to improve the efficiency of individual DHC facilities, CGS should be operated so as to satisfy heating demand, resulting in a low annual load factor. On the other hand, the overall efficiency of the energy system requires an improvement of the overall load factor of CGS, which is achievable by combined use of CGS and boilers. Operation of CGS in this manner improves the feasibility of the introduction of DHC. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 31–42, 2000 [ABSTRACT FROM AUTHOR]

In the future, renewable energy (RE) generation systems will be constructed and interconnected to the power system by nonutility entities such as generation companies and residential customers. Therefore, generation expansion planning (GEP) should consider the effects of RE generation. The purpose of this paper is to discuss the best GEP from the economic, supply reliability, and environmental aspects considering the penetration of RE generation. For this purpose, this paper proposes a model of a utility's GEP process considering RE generation. The proposed method is based on stochastic dynamic programming (SDP) in which long-term uncertainties are modeled by geometric Brownian motion (GBM) and the binomial lattice process. The variation of RE generation output due to the weather conditions (short-term uncertainty) is also considered in the proposed method by means of the net load curve. [ABSTRACT FROM AUTHOR]

There are some factors that render a power system network unbalanced: UHV transmission lines in which three-phase transmission lines are not transposed, an unbalanced transformer, unbalanced load as well as sustained unbalanced faults. On the other hand, the number of variable-speed generators used in pumping-up power stations has recently been increasing in Japan. This paper presents a new means of calculating unbalanced power flow of a power system which contains variable-speed pumping-up generators. This new technique is based on the phase coordinate method, because a power system which has elements of unsymmetrical impedance can easily be analyzed by using it. In this paper, phase coordinate models of the variable-speed generator and its secondary exciting circuit, composed of a GTO converter/inverter, are analyzed first. Procedures of power flow calculation of unbalanced power systems follow. © 2000 Scripta Technica, Electr Eng Jpn, 134(3): 34–43, 2001 [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the impact of an extensive introduction of electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs) on the energy supply mix in Japan. Energy consumption in Japan's transport sector has been dominated by petroleum, and CO2 emissions in this sector account for 20% of Japan's CO2 emissions. Therefore, the deployment of clean energy vehicles, such as EV and PHEV, is expected to play a significant role in tackling energy security and environmental concerns. In order to assess the energy and environmental benefits of EV and PHEV, we develop an energy system model integrating an optimal power generation mix model and a vehicle penetration model, with consideration of the optimal electricity charging profile of those advanced vehicles. The calculated results suggest that massive EV penetration serves as an energy saving measure in Japan's whole energy system due to significant petroleum reductions exceeding the growth of fuel input into the power generation sector derived from significant EV and PHEV penetration. Massive EV deployment is estimated to contribute to CO2 mitigation in the energy system as well. Evaluating CO2 emissions by mileage by automobile, however, carbon emissions by mileage for EVs is almost equivalent to that of gasoline hybrid vehicles (HEVs) in the case of decommissioning of nuclear power plants, which eventually causes a higher carbon intensity of the electricity supply. [ABSTRACT FROM AUTHOR]

This paper proposes a pole change generator for a windmill. Since micro windmill systems generate power from natural energy, power generation characteristics across a wide band are necessary. However, the conventional generator, in which the open voltage is simply proportional to the rotational velocity, encounters difficulty in generating power across a wide range of rotational velocities from low to high, because of the power generation characteristics. To develop a generator with a wide power band suitable for a micro windmill, this paper proposes a technique for switching the status of the generator coil connection. To demonstrate the effectiveness of pole changing, we use a pole-changing generator with 16 coils as an example. The coils can be connected using four patterns: 16-pole series, 8-pole 2-parallel, 4-pole 4-parallel, and 2-pole 8-parallel. Theoretical and experimental studies from this point of view demonstrate that this technique is effective. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(1): 28–36, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20873 [ABSTRACT FROM AUTHOR]

This paper proposes a high-speed reclosing operating method to improve the stability in a power system. The proposed method calculates the reclosing time, taking a standard case in which the reclosing is not done using the generator phase angle δ, and the angular velocity ω, and the field system voltage ed'. Also, the execution of reclosing time is calculated, while taking into consideration the acceleration/deceleration energy of the generator during a fault. It can be expected that δ is suppressed by this optimum reclosing operation. Therefore, the system stability can be expected to improve by carrying out high-speed reclosing when a fault occurs. At present, it has been set at a value which seems to be optimal considering various problems in the reclosing time. However, in those methods, the system stability improvement effect cannot be expected. It was demonstrated that the high-speed reclosing method serves to depress δ in the computer simulation. [ABSTRACT FROM AUTHOR]

In recent years, the trend has been toward factors (e.g., demand for load, energy cost) becoming more and more uncertain in power system expansion planning. Thus, it has become necessary to take this uncertainty into account in determining generation plans. In this paper, a robust generation plan is defined explicitly as a plan that ensures fixed performance (economy) despite deviations in these factors. In addition, a new formulation of the robust generation mix problem, whose purpose is to determine the most robust combination of plants in a target year, is proposed. It is generally difficult to solve the formulated problem with parameters. However, by analyzing a proposed formulation from the viewpoint of optimization, we show that the proposed formulation is transformed into the conventional optimization problem without parameters. The simulation results on a typical model show that the generation mix produced by the proposed formulation is more robust than that produced by the conventional formulation. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 26–35, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.2009 [ABSTRACT FROM AUTHOR]

SUMMARY It is well known that the transient energy function (TEF) method is useful for an efficient transient stability assessment as represented by the estimation of the critical clearing time (CCT). However, there still remains an issue for practical use: most of the TEF methods adopt the classical model of a synchronous machine in which the internally generated voltage is assumed to be constant. Moreover, critical generated output can be a more practical stability index instead of the CCT used in the conventional TEF methods. In this paper, a conventional hybrid TEF method is developed in order to estimate the transient stable critical generated power by using an improved hybrid simulation. The proposed method can handle the detailed model for a synchronous machine and can estimate the critical generated power with higher accuracy. Experimental results for a large network model are given in order to verify the practicability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a new electric power network that makes it possible for many types of dispersed generation plants owned by nonutility organizations to participate in an electric power market without the disadvantages of existing power utility and customers. This power network is called an open electric energy network (OEEN) because the network is open to the many types of plants for the participation. For achieving such openness, electric power storage devices, load controller at each customer and data communication network are installed in OEEN; the flow of excess electric power generated by each plant is controlled autonomously and in a distributed way. That is, the control is done by transmitting the data on excess electric power such as generation and demand point, power quality, price, etc., from each dispersed generation plant to the power storage devices and the load controllers through the communication network. Since this data-driven power flow control is similar to the mail system for a packet with the addresses of sender and receiver, it is called packet electric power transportation. In OEEN the storage device plays a different role from load leveling. Therefore, the way to determine the storage capacity differs from the conventional approach. In this paper, the applicability of queuing theory for determining the capacity is also discussed. [ABSTRACT FROM AUTHOR]

A doubly fed induction generator is useful for a local-use water power plant. Setting it in nonconstant water flow, we can use it as a constant-frequency power generator. This paper shows how to control this generator system. This paper has two important points. One is that this generator system is always excited at primary winding. Another is that the control target in this study is secondary q axis current to obtain a constant voltage of primary generated power. [ABSTRACT FROM AUTHOR]

Numerous control methods based on modern control theory have been proposed to improve the load frequency control (LFC) characteristics of power systems. These control methods generally regard the load frequency control system as a linear system model. Furthermore, complicated mathematical equations have to be solved to determine control laws. However, realistic power systems are nonlinear, i.e., the nonlinearities of tie-lines connecting between the control areas and of generation rate constraints of power plants exist. Consequently, it is considered that the design of controllers is difficult. In this paper, the application of fuzzy control to the load frequency control system is proposed to solve the forementioned problems. The proposed control first, to satisfy the load frequency control requirements, estimates power demand variations of the control areas and uses them as the output set-point values of power plants, instead of using an integral-type controller. Next, to improve stability and optimality of the nonlinear load frequency control system using the forementioned output set-point control method, the proportional-type fuzzy control considering a computation time-delay is implemented. Parameters of the proposed fuzzy controller are determined by minimizing the integral square of the area control error (ACE) to ensure optimality of the system. [ABSTRACT FROM AUTHOR]

This paper first discusses in detail the Kakimoto method and PEBS method (Potential Energy Boundary method) proposed by Athay. It is pointed out that overly optimistic solutions are obtained to the presence of second swing and decelerating step-out as discussed. This paper also proposes a new method to determine the stability limit. Kakimoto's method gives an incorrect solution when the solution trajectory does not reach the critical energy curve and his method also fails to give the stability limit curve on the phase plane. A disadvantage of Athay's method is that the stability limit curve is approximated by PEBS method. The method proposed here gives a clearly defined stability limit curve. [ABSTRACT FROM AUTHOR]

This paper proposes a real‐time generation regulation system named as "on‐demand generation regulation control" system, which is suitable for small independent power grids with unstable renewable energy generators. It has been developed as a part of "robust demand and supply control manager" and plays an important role of flexible frequency control that includes vehicle to grid and generation restriction when necessary. The main feature of the system is the integrated framework to effectively deal with hard‐to‐predict control options in a flexible way by observing the unstable generator outputs and all generators/batteries status including electric vehicles. In addition, a feedback system is also proposed to flexibly adjust the regulation capacity in case unexpected disturbances occur. The performance of the proposed system is verified through numerical simulations based on an actual test site with successful results. [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the optimal power generation mix considering massive deployment of variable renewable energy and regional power interchange. Japan has initiated the feed-in-tariff (FIT) and expected the significant introduction of PV and wind power for energy self-sufficiency and climate change. However, wind power resources in Japan are concentrated mainly in Hokkaido and the Tohoku region, which are remote from electricity-consuming areas such as Tokyo, and facilitating the considerable deployment of wind power requires the establishment of inter-regional power transmission lines. Against these backgrounds, we develop an optimal power generation mix model including regional electricity exchange as a large-scale linear programming model with 10 million variables and 30 million constraints. The calculation results show that regional grid expansion encourages wind power installation in the Hokkaido and Tohoku regions for power supply to the Tokyo area, where PV power and stationary batteries are alternatively replaced. Grid expansion too promotes the shift of PV installation to the Kyushu and Shikoku regions, which have longer sunshine duration, and interchangeably mitigates PV deployment in other regions through the transport of PV power from those two regions. [ABSTRACT FROM AUTHOR]

In this paper, the optimal allocation of mega-solar is examined using data envelopment analysis (DEA). A great deal of attention is paid to photovoltaic power generation in Japan. Because such power generation can be freely used, it is attractive in Japan, which has few natural resources. The allocation of mega-solar, a large-scale photovoltaic power generation method, is an important problem for meeting the hope of efficient operation. We tried to apply DEA in Shizuoka Prefecture and to solve this issue. In this type of DEA application, some analyses often result in zero weighting factors in the parameters of some items to be studied, which implies that the corresponding items are not appropriately evaluated. The existing studies do not give special consideration to this situation. In this study, a new calculation scheme is proposed, the above-stated problems are successfully resolved, and the optimal candidate sites have been selected for the mega-solar allocation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 24-32, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22322 [ABSTRACT FROM AUTHOR]

This paper presents a combination system for wind power generation and hydrogen generation. In the proposed system, a doubly-fed synchronous generator (DFSG) is used as an adjustable speed wind generator, and an electrolyzer is connected to its terminals for hydrogen generation, which is controlled by power electronic converters. The output power from the wind generator is smoothed and supplied to the power system as well as to the electrolyzer to generate hydrogen under cooperative control between the wind generator and the electrolyzer. The performance of the proposed system is investigated by simulation analyses, in which simulations are performed using PSCAD/EMTDC. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(3): 27-36, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21003 [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a comprehensive congestion management scheme based on generator and FACTS device operations. To relieve congestion effectively and quickly, we use two indices based on the DC method. However, calculation errors using the DC method may become large due to its approximations. Thus, we also developed an improved DC method, which is a DC method considering transmission losses and transformer tap ratios, and performed simulations to confirm the validity of the improved DC method. Finally, we performed simulations by the proposed congestion management scheme using the IEEJ EAST 30-machine system. The simulation results indicate that congestion can be relieved effectively and quickly. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 28–36, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20893 [ABSTRACT FROM AUTHOR]

This paper proposes a brand-new method for transient stability analysis in power systems. The proposed method directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system. Although the method may be useful for general nonlinear dynamic systems, it is applied to the problem of obtaining a controlling UEP, unstable equilibrium point, which provides inevitable information for the energy function methods to assess transient stability. Namely, the proposed method effectively yields a critical trajectory on PEBS together with the controlling UEP, thus improving the conventional BCU method. The effectiveness of the proposed method is demonstrated in 3-machine 9-bus and 6-machine 30-bus systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 26–33, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20245 [ABSTRACT FROM AUTHOR]

It is indispensable to accurately perform short-term load forecasting of 10 minutes ahead in order to avoid undesirable disturbances in power system operations. The authors have so far developed such a forecasting method based on conventional chaos theory. However, this approach cannot give accurate forecasting results when the loads consecutively exceed the historical maximum or are less than the minimum. Electric furnace loads with steep fluctuations are another factor degrading the forecast accuracy. This paper presents an improved forecasting method based on chaos theory. In particular, the potential of the Local Fuzzy Reconstruction Method, a variant of the localized reconstruction methods, is fully exploited to realize accurate forecasting as much as possible. To resolve the forecast deterioration due to suddenly changing loads such as by electric furnaces, they are separated from the rest and smoothing operations are carried out afterwards. The separated loads are forecasted independently from the remaining components. Several error correction methods are incorporated to enhance the proposed forecasting method. Furthermore, a consistent measure of obtaining the optimal combination of parameters to be used in the forecasting method is presented. The effectiveness of the proposed methods is verified by using real load data for 1 year. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 55–63, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10322 [ABSTRACT FROM AUTHOR]

The integrated energy service system for a specific area is supposed to deliver electric and thermal energy in an integrated manner for the purpose of reducing cost, primary energy consumption, and CO2 emission. Under an assumption of the service system, this paper develops a multi-objective optimization model for determining urban energy systems. Considering the various energy system alternatives, such as photovoltaic generations for residential houses and fuel-cell cogenerations for business and commercial customers, the model determines the share of the energy system alternatives in order to minimize the above three indices. As numerical examples, this paper illustrates trade-off analyses in the case when the proposed model is applied to a 2 km × 2 km square area in Osaka. Finally, this paper illustrates the role of various energy system alternatives from CO2 reduction and fossil energy reduction points of view. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 20–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10275 [ABSTRACT FROM AUTHOR]

The power–voltage and current–voltage characteristics of a PV array change with the variation of insolation and temperature. In particular, the output power of a PV-panel block consisting of series-PV modules inevitably goes down due to partial shading caused by peripheral obstacles. This results in a significant reduction of the total output power from the PV power generation system where a couple of PV blocks are parallel to the DC terminal of interactive inverter because of mismatch of the optimum operating voltages between the PV blocks. In this paper, we propose a power conversion system to compensate the output power of a partially shaded PV array. The proposed system can control the output power of the PV array on a PV block basis, which contributes to a more efficient and simpler implementation of the PV power compensation system than that by individual controls of PV modules using DC–DC converters. In addition, inverter DC voltage is appropriately controlled so that the maximum output power from the overall PV array can be obtained. Then, the feasibility of the system is investigated and verified from the simulation and experimental results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 74–82, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10203 [ABSTRACT FROM AUTHOR]

This paper proposes a multiagent system to power system unit commitment problems. Multiagent is a new paradigm for developing software applications. Coordinating the behavior of autonomous agents is a key issue in agent-oriented programming techniques today. Recently, agents are being used in an increasingly wide variety of applications, ranging from comparatively small systems such as E-mail filters to large, open, complex systems such as air traffic control. Though some agent frameworks have been proposed in the power system field, the number of studies is limited. In this paper, we developed a power system unit commitment application by multiagent architecture. Our multiagent system has the following characteristics: (1) The system consists of a single facilitator agent, two mobile agents, and one or more generator agents which are elements of power system network. (2) The facilitator agent is developed to act as a manager for the process by using the singleton design pattern. The mobile agents migrate to generator-agents to increase or decrease their power generations. The generator agents have their operational data. (3) Message object is developed to communicate between the agents using KQML-like object. The proposed approach is applied to a simple model system, and the results show that the multiagent system is an efficient decentralized approach for solving power system unit commitment problems. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 41–47, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10057 [ABSTRACT FROM AUTHOR]

The network of Chugoku Electric Power Co. is connected to the networks of other utilities, and a fault occurring in the network may cause loss of synchronism between the group of generators belonging to the western side of the network and that of the remaining generators. In order to prevent a wide-area blackout, a power system stabilizing controller is implemented which checks the results of numerous stability calculations, selects generators to be shed for stabilization if instability is predicted, and sheds them when a fault actually occurs. This paper describes the development and application of a new approach to the construction of an external equivalent for use by power system stabilizing controllers. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 1–9, 2001 [ABSTRACT FROM AUTHOR]

In Japan, electric power utilities purchase electricity from independent power producers (IPPs) through competitive bidding; the IPP evaluation is based on the avoided costs of corresponding generators of utilities. In this evaluation, however, nonpricing factors such as power flow constraints in the electric power system cannot be considered. In this paper, we propose a new approach to evaluate economic impacts of IPPs, the IPP electricity being priced on the basis of total generating costs of the electric power utilities. Such a price to purchase the electricity of IPPs is referred to as the “break-even cost.” The main results are summarized as follows: 1) Break-even cost depends on not only the power flow constraints in the system, but also various IPP factors such as generating pattern, location, and capacity, 2) Break-even cost for the base-type IPP is higher than the avoided cost of corresponding utility generators, because IPPs located on demand sides can reduce the transmission power loss in the electric power system, 3) Break-even cost is affected by available capacity of utility generators, especially for the peak-type IPP generating only during peak demand periods. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 20–30, 2000 [ABSTRACT FROM AUTHOR]

SUMMARY This paper demonstrates the electric power generator with both zero energy input and zero matter input and emission without violating the laws of thermodynamics. The hydrogen redox power generation system is a combined energy cycle consisting of the H2O reduction by the electrostatic induction hydrogen electrolytic cell for the synthesis of pure stoichiometric H2-O2 fuel and the H2 oxidation to H2O by the fuel cell. The electrostatic induction potential superposed hydrogen electrolytic cell works on the mechanism in which, on the theoretical base, power used is 17% of the total electrical energy required, while the remaining 83% can be provided by the electrostatic energy free of power. Part of the power delivered by the fuel cell is returned to the electrolytic cell, and the remainder represents the net power output. For high-power applications, the cycle power efficiency defined as the ratio of net power output outside the generator to power delivered by the H2-O2 fuel cell is of primary interest. According to calculations using the operational data of alkaline water electrolysis in industries, the cycle power efficiencies exceed 70%. [ABSTRACT FROM AUTHOR]

Many efforts towards a settlement of the CO2 problem have already been made through internationally organized meetings. It is not unlikely that some targets will be set for the reduction of CO2 emissions. If a stringent reduction target should be imposed on CO2 emitted from a national energy system, this cw possibly have as severe an impact upon electric power sectors as the oil price crises experienced in the seventies. It is, however, quite uncertain whether or not political muscles will be used specifically for tackling the CO2 problem in the near future. In such a context, this paper presents a new method for optimal power system planning under uncertain CO2 emissions control policies. The derived optimal expansion plan gives us the minimum expected value of the sum of the total system cost and the total amount of carbon taxes levied on net CO2 emissions from fossil fuel-fired power plants. The stochastic dynamic optimization problem discussed here is formulated as a linear programming problem decomposable into several small subproblems. The proposed method can take into account a specific future scenario of the magnitude of control policy uncertainties, which can be presumably resolved in the first half of the next century due to the increase in scientific wisdom. Ln order to evaluate the usefulness of the method proposed here, the authors also present a simple cue study with the Japanese national power system up to the year 2050. [ABSTRACT FROM AUTHOR]

This paper proposes graphical representation methods of static and dynamic characteristics of power systems. The methods use the computed results of load flow calculation and dynamic stability calculation. This work develops three kinds of representation methods using maps and animation which are sequential graphical representation of maps based on dynamic stability calculation. Conventionally the results of load flow calculation and dynamic stability calculation are represented and comprehended using load flow maps or dynamic swing curve. However, quick and effective comprehension of power system characteristics by such conventional representation methods is becoming more difficult as power systems to be analyzed are becoming larger and more complicated, especially in power systems with many loops or grids. Graphical representation using the proposed methods makes it easy to understand the static and dynamic characteristics of power systems quickly and comprehensively. In addition to these methods, this paper proposes a heuristic logic that makes it possible to draw maps automatically. It is very convenient to apply these methods to arbitrary power systems even if their constitutions or characteristics are not well known. [ABSTRACT FROM AUTHOR]

This paper describes an optimal load-shedding policy based on quadratic programming using only some power system state variables after severe generation outages. When generation outage is severe, the imbalance between supply and demand causes a declining frequency. Utilities generators cannot be operated excessively at frequencies above normal. Some of the load must be shed to prevent system damage. Optimal load-shedding policies have been studies using all state variables of the power system. However, in real power system operations, it is difficult to obtain remote information in that fraction of a second following generation outages. An optimal load-shedding method is constructed in this research using quadratic programming (QP) under the assumption that all power system state variables can be available. However, these state variables cannot be easily accessible (as already mentioned). A suboptimal load-shedding scheme based on the local state variables is then studied. The proposed load-shedding method is based on the aforementioned optimal one. The change in line-power flows and the amount of generation power outage are used as accessible data at each load point. Incorporating this local information into the optimal load-shedding method based on the QP method, the proposed load-shedding method is established here. The effectiveness of this proposed method is illustrated by two examples and simulation results on a model power system show that the method is encouraging. [ABSTRACT FROM AUTHOR]

As the load in a power system continually changes, it is important to regulate the generator operating point. In this paper, assuming a suitable operating range for the generator the regulations for typical generator operating points within this range are selected and then fuzzy controllers are designed accordingly. To investigate the adaptation of each controller, many simulations are carried out for the various operating point changes. By quantitative investigation of the control performance of the adaptive controllers, a design method for fuzzy controllers for generator operating point regulation is proposed. Furthermore, a comparative estimation of the fuzzy control formula and optimal control formula with an observer is made using a common quantitative criterion. In addition, a one-machine infinite-bus system (including limits on the AVR and governor) is used as the control object model. [ABSTRACT FROM AUTHOR]

This paper proposes a new dynamic preventive control strategy to maintain power system security, in terms of both transient and midterm stabilities. While the authors have already presented preventive control strategies for transient stability, a new problem has arisen in midterm instability in which some generators lose synchronism after 10 seconds or more from a fault clearance. It is clear that the cause of the instability is mainly post-contingency dynamic steady-state instability. This paper first shows a preventive control strategy for improving midterm stability using a dominant eigenvalue of post-contingency equilibrium point. This paper also presents a unified dynamic preventive control algorithm that can maintain both stabilities together. In this algorithm, the time domain for each stability problem is considered appropriately and the difference between the classical model and the detailed model is analyzed in detail. The effectiveness of the proposed method is examined with numerical examples for a model system. [ABSTRACT FROM AUTHOR]

In general, electric power companies must prepare power supply capability for maximum electric load demand because it is very difficult at present to store electric power. It takes several years and requires a great amount of money to construct power generation and transmission facilities. Therefore, it is necessary to forecast long-term load demand exactly in order to plan or operate power systems efficiently. Several methods have been investigated so far for the long-term load forecasting. However, because the electric loads consist of many complex factors, good forecasting has been very difficult. This paper proposes a long-term load forecasting method using a recurrent neural network (RNN). This is a mutually connected network that has the ability of learning patterns and past records. In general, when interpolation is used for unlearned data sets, the neural network provides reasonably good outputs. However, when extrapolation is used, such as in long-term load forecasting, some kind of tunings have been necessary to obtain good results. Therefore, to solve the problem, a method is proposed in which growth rates are used as input and output data. Using the proposed method, successful results have been obtained and comparisons have been made with the conventional methods. [ABSTRACT FROM AUTHOR]

This paper proposes new demand-side reliability indices and useful computational methods for reliability evaluation of composite power systems. These new indices are based on the active power which can reach each demand spot under generating and transmission network constraints. This conception is defined as ‘reachable power’' and it leads the reserve margin on each demand spot. which is called as ‘demand-side reserve’. If the reachable power is insufficient to satisfy the demand, load curtailment is required. In the proposed approach, the conception of the load curtailment area is defined, and the estimate method of load curtailment area is indicated. In case the reachable power exceeds the demand, system reliability is evaluated by the demand-side reserve, and the power system is divided into several reliability zones according to the demand-side reserve levels. Small system examples are used to illustrate principles of the proposed approach, and middle system examples show the effectiveness and practicality. [ABSTRACT FROM AUTHOR]

This paper investigates the voltage stability in a single OLTC (On-Load Tap Changer) system, which consists of a single OLTC and multiple generators as well as loads. It is shown that the sensitivity of the load voltage to tap position dV/dn = (I1 = exact value) plays an important role, independently of the existence of the equilibrium of the tap position. That is, when the equilibrium exists, the region where I1 > 0 is in the stability region; if the equilibrium disappears, the stability region also disappears but the voltage is still recovering in the region where I1 > 0. Based on these results, the region of reverse control action of OLTC is defined as the region where I1 < O. It is proved that another sensitivity I2, which is defined as dV/dn when constant power characteristics are assumed for loads, can be used to estimate the region of reverse control action when the exact load characteristics are not available. [ABSTRACT FROM AUTHOR]

To cope with the high rate of increase of power demand in the main industrialized districts in Japan, 550-Kv transmission systems covering the distrits have been reinforced, with most of the main power plants connected directy tro these systems.Throught 550-/300-kV substations, the majority of power to the districts is supplied by 300-+kV systems. To limit the excess short-circuit capacity in the 300-*kV systems, they tend to be reconstructed as so-called radia; networks. in radial networks with high short-circuit capacity and relatively small number of transmission lines connected to the substation busbars, the rate of rise of TRV can be far higher than standard value. This paper analyzes the transient recovery. this paper analyzes the transient recovery voltages (TRV) in such extra-high-voltage radial networks in Japan, together with the relevant stress to circuit-breakers during clearing. future system conditions have also beeen introduced. As the typical rate of rise of the TRV values, more than twice that of today's standard ones are probable. [ABSTRACT FROM AUTHOR]

Recently, a demand for small-capacity generators has been increasing as electric sources in small ships and automobiles or as portable electric sources driven by engines. It is desired that the structure of small-capacity generators be simple and robust, and that the generators be highly reliable, easily maintained and controlled. This paper describes an analysis of the original brushless synchronous generator without exciter. The output voltage can be adjusted in the wide range by controlling the stator de current. The analyze the characteristics of this generator, the finite element method is applied. It is found that the results of theoretical analysis agree well with the experimental results. [ABSTRACT FROM AUTHOR]

The purpose of large-scale power system inter-connection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators. Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems. In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so on. [ABSTRACT FROM AUTHOR]

This paper discusses an optimal short-range scheduling of multireservoir hydrothermal power systems considering runoff prediction. Using Prasad's rainfall-runoff model and the Kalman filter-based, second-order filtering technique, the hour-by-hour characteristic is estimated for a given short-range forecasted rainfall pattern. Unlike the usual hydroscheduling problem in which a single-reservoir operating condition is specified at the end point conditions are examined to deal with the predicted runoff characteristic and to avoid possible water spillages from reservoirs. [ABSTRACT FROM AUTHOR]

Evaluation of the system state is becoming imperative in supervising and controlling huge systems such as power generation and transmission systems and industrial plants. This paper discusses two methods of building the neural networks: one is based upon backpropagation, and the other is a new method proposed herein. Unlike backpropagation which forms the completely distributed activation structure of neurons, the proposed method enables self-organization of the modules which are activated selectively to an input pattern. The new method not only makes a biologically natural structure of neural network but also shortens considerably the learning time by localizing the links to be updated In the learning process. [ABSTRACT FROM AUTHOR]

This paper presents the results of the analysis of three-dimensional mutual interaction between electromagnetic field and fluid of the subsonic Faraday-type MHD generator. [ABSTRACT FROM AUTHOR]

This paper derives a generalized Lyapunov function (Lur´-type function) for multi-machine power systems which include load characteristics and generator flux decays, by using the construction technique developed by Moore and Anderson. Essentially, the system model is based on the system preserving model introduced by Bergen and Hill. In our model, a power system in which each generator is connected to a large power consumption area via a long transmission line is considered. We assume that the system disturbance occurs only on the transmission lines and the effects of disturbance on the load-bus voltage magnitudes are negligibly small. Under these assumptions, the system preserving concept has good application to our system. Furthermore, to incorporate the effects of flux decays, generator terminals are assumed to have no loads and thus are free of disturbances. Although we assume first that the product-type nonlinear functions satisfy Desoer-Wu's condition, well-defined sectors for the nonlinear functions are established later. Under these sectors, it is shown that the obtained Lyapunov function satisfies Lyapunov's criteria and the generalized Lyapunov function can be derived. [ABSTRACT FROM AUTHOR]

This paper considers the day-ahead market with batteries and accumulators to level power generation. First, we model consumers with batteries, generators with batteries, and accumulators, all of whom strive to maximize their own profit. An optimal pricing algorithm based on dual decomposition and the steepest descent method is derived and shown to be stable. Finally, the effectiveness of the algorithm is demonstrated by means of numerical simulations which indicate that it achieves demand-supply balance. [ABSTRACT FROM AUTHOR]

SUMMARY Several approaches have been proposed for evaluating the capacity value of intermittent generation. In this paper, we assume that the uncertainty included in demand, existing generation, and intermittent generation, can be treated by means of a normal distribution model. Using a newly developed approximation method similar to the Garver approximation, and the Z-stochastic approach, the effective load carrying capability method is comprehensively surveyed. The percentile method adopted in the higher demand level is also discussed in connection with the probabilistic properties of intermittent generation. Numerical examples and a simulation illustrating the probabilistic approach are included. [ABSTRACT FROM AUTHOR]

SUMMARY The electrical double layer capacitor-electrostatic induction electric power generation system (EDLC-ESIG) undergoes an electric cycle consisting of three steps: energy storage by electrostatic induction, power generation, and initialization by electromechanical coupling. An internally self-sustaining electric power can be generated by repetition of cycles with periods of the order of seconds. The objective of this paper is to show the design of EDLC-cell configuration for practical use to produce constant power output. On the basis of energy densities of the conventional EDLCs for energy storage, the volumetric power density has been estimated to be 450 W/L for the discharge time of 10 s. Possibilities of commercial applications of the EDLC-ESIG system to vehicles and high power generations in central station have been considered with respect to the power densities of the EDLC-cells consolidated into a generation system. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the impact of extensive introduction of photovoltaic (PV) systems and stationary battery technology into the optimal power gen-eration mix in the Kanto and Kinki regions. The introduc-tion of solar PV systems is expected to be extensively deployed in the Japanese household sector and utility com-panies in order to address the concerns of energy security and climate change. Considering this expected large-scale deployment of PV systems in electric power systems, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accom-modating the intermittent output-power fluctuations inher-ent in PV systems. Against this background, we develop both a solar photovoltaic power generation model and an optimal power generation mix model, including stationary battery technology, which can be used to explicitly analyze the impact of PV output fluctuations at a detailed time interval resolution such as 10 minutes for 365 consecutive days. Simulation results reveal that PV introduction does not necessarily increase battery technology due to the cost competitiveness of thermal power plants in the load-follow-ing requirement caused by PV systems. Additionally, on the basis of sensitivity analysis on PV system cost, dramatic cost reduction proves to be indispensable for PV to supply bulk electricity similarly to thermal and nuclear power plants. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 9-19, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). [ABSTRACT FROM AUTHOR]

Verification test results of the isolated operation of a microgrid configured with some new energy generators at Aichi EXPO 2005 showed stable controllability without a rotating machine. However, improvement of voltage fluctuation with changing reactive power of loads had been hoped for. Some improvements of system voltage control had been implemented on the microgrid moved to Central Japan Airport City. This paper presents the results of verification testing of the improvement of voltage fluctuation in isolated operation with PAFC output power compensation control by NaS batteries, and also presents a simulation study of further improvement of the voltage control strategies of PAFC inverters. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 41-52, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21096 [ABSTRACT FROM AUTHOR]

The plug-in hybrid electric vehicle (PHEV) is a technology intended to reduce CO emissions in the transport sector. This paper presents scenarios that show how widely used PHEVs will be in the future, how much CO emissions will be reduced by the introduction of PHEVs, and whether there will be serious effects on the power supply system. PHEVs can run on both gasoline and electricity, and therefore we evaluate CO emissions not only from gasoline consumption but also from electricity consumption. Consideration of the distribution of daily trip distances is important for evaluating the economical benefits and CO emissions resulting from the introduction of PHEVs. Also, future battery costs are very important in constructing PHEV growth scenarios. The growth of the number of PHEVs will make battery costs lower. Thus, we formulate an overall model that combines the passenger car sector and power supply sector, taking account of the distribution of daily trip distances and incorporating a learning curve for battery costs. We use the iteration method to provide a learning curve that is nonlinear. Therefore, we set the battery cost only in the first year of the simulation: battery costs in the later years are calculated in the model. We focus on a 25-year time period in Japan, starting from 2010, and divided into 5 parts (1st to 5th). The model selects the most economical combinations of car types and power sources. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 31-40, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21098 [ABSTRACT FROM AUTHOR]