This paper presents a method for solving optimal power flow (OPF) problems to restore solvability. The formulation of the proposed OPF is based on equivalent costs with respect to load demand scenario and constraint slacks. Since the proposed Equivalent Cost Based OPF (ECBOPF) in which load demand scenario parameter and constraint slacks are treated as decision variables, the information on unsolvability with respect to each load demand and each constraint can be obtained. In addition, since the proposed method whose objective function includes the equivalent costs of load demand error and constraint slacks, it is possible to do the strategic analysis from the viewpoint of costing on power system management. The feasibility and effectiveness of the proposed method are demonstrated on test problems with 49-bus and 2312-bus systems.

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Recently the wind power generation has attracted special interest and many wind ower stations are being in service in the world. In the wind power stations, in addition to normal induction machines, machines with special rotor structure, as double squirrel-cage rotor and deep-bar rotor induction generators, are also used as a generator. This paper presents a model of induction generators with special rotor structure, develops methods of power flow calculation and transient stability simulation of power system including the induction generators, and presents considerations on the characteristics of transient stability of the induction generators on the basis of numerical simulations. This paper also presents considerations on the effect of pitch control system of wind turbine on the transient stability of induction generators.

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Electric power industry trends towards deregulation all over the world. As the result, power markets are emerging in many countries. The nature of the power price and these behavior should be known to study and discuss adequately rules of power market or policies of the deregulation of electricity industry. Knowledge on characteristic of the power price and these behavior may be more important.
This paper presents a simulation method for analying the characteristic of power market. The proposerd method is based on time series simulation of artificial power market which consists of multi-economic agents such as power producers and customers. In this simulation, market clearing method is described, and more-over, behavior of the agent in the power market is modeled simply with the intention of lowering computing costs of simulation. In addition, equilibrium price of power which is calculated from time-series simulation using artificial power market is studied in order to discuss the validity of proposed method.

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The authors have proposed FRIENDS as a concept of future electric power system. In order to realize FRIENDS, it is necessary to design the concrete interior structure and control scheme of Quality Control Center (QCC) which is newly installed between distribution substation and customers. The hybrid-type transfer switches are assumed to be installed at the high voltage side of QCC for realizing the network reconfiguration. On the other hand, some devices for handling the power quality are also assumed to be installed at the low voltage side to realize the customized power quality.
In this paper, the novel control schme for turning off the thyristor switches by the power quality handling devices is proposed and the effectiveness of the proposed scheme is investigated through momentary analysis using PSCAD/EMTDC.

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In order to analyze arc behavior, a numerical calculation method combined with thermal radiation field and compressible gas dynamics has been developed. The method has following characteristics, (1) To analyze thermal radiation field, the radiation field is approximated by diffusion equation classified as Helmholtz equation and the equation is discretized by. FEM. (2) The electric field in an arc is calculated by FEM considering with the dependency of electric conductivity on temperature. The method has been applied to model arc generated between 20mm gap length, and we confirmed the method can predict arc behavior in account of thermal transport from arc to SF₆ gas around the arc, such as increase of arc resistance at current zero and dependency of arc radius on arc current to maintain constant arc current density.

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Focus was on the adjustment of voltage drop control, with a proposal for an advanced voltage control system, which can maintain Fly line voltage in an optimum condition by installing parallel capacitors dispersed on an HV line. In seeking a low cost, maintenance - free voltage control system, the authors clarified that several specific and advanced functions must be incorporated with conventionalvoltage control equipment.

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This paper presents a novel formulation for solving optimal power flow (OPF) problems with voltage stability constraints. The proposed Voltage Stability Constrained OPF (VSCOPF) formulation is based on a voltage sensitivity with respect to total load demand representing a gradient of P-V curve at an operating point. In the formulation, voltage constraints are given by a set of equality constraints which should be satisfied by the voltage sensitivity. Since the voltage stability constraints retain sparse matrix structure, the method based on the proposed OPF formulation may effectively solve large-scale problems. The feasibility and effectiveness of the proposed method are demonstrated on test problems with 2-bus, 49-bus and 2312-bus systems.

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In recent years wind power generation has developed tremendously and is growing up in Tohoku regions. On the other hand, because wind power output is influenced by natural phenomena, the fluctuation of wind power has come into question along with the increase of quantity of wind power connected to the power system. There are two issues, one is local area issue caused by the voltage fluctuation and protection, harmonics etc., another one is wide area issue caused by frequency fluctuation. The countermeasure of the former has become successful by a variety of guidelines, but the countermeasure of the latter has not been still realized. In general it's considered that wind power has smoothing effect caused by irregularity and asynchronizm, but the effect isn't still known clearly and in detail. So, in this paper, we report the analysis of the wind power fluctuation and a consideration of smoothing effect from the measuring data of the existing wind power site and the data of wind simulation.

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A spot network (SNW) or a normal-stand-by distribution system is mainly applied to the present 22kV distribution lines. However, mixture of those systems on a same distribution line is not practicable, because reverse power flow may cause an undesirable interruption of the network protector. In addition, an in-house generator, which produces reverse power flow may not be connected to the SNW system. Therefore, if this problem is solved, 22kV distribution system will be more widely used. This paper proposes a new protection and control solution for the above problems and introduces a configuration of a proposed protection and control system, detection principle of each relay and protection coordination between the relays.

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The entry of Independent Power Producers (IPPs) and wheelings give various influences to electric power systems. IPPs may enter an electric power system selling surplus electric power to utilities. In this case, it is necessary to operate and control their own power plants appropriately, not breaching a contract with utilities. And now, customers who own non-utility generation facility and have the possibility of becoming IPPs use their own power plants for self-load buying the shortage from utilities. In this case, they must control their own power plants, keeping “demand contracts”. Therefore we can consider with same idea.
This paper focuses on the operation and control of non-utility generation facility considering demand contract. Specifically considering that production facilities consume power irregularly depending on the sequence of production, we investigate a load forecasting method using load pattern recognition. Also considering an error between forecasted load and actual load, this paper proposes a new generation control system to keep the demand within the contract made with a utility. Furthermore, the validity of the proposed control methods is confirmed through a simulation using actual load data.

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The photovoltaic power generation has a weak point that its power output is unstable according to the weather conditions. In order to realize the optimum control of a diesel-photovoltaic hybrid generation system, this paper describes a novel method to estimate daily/hourly amount of solar irradiation. The outline of the proposed method is as follows; (1) solar irradiance is observed and maximum and minimum values of “atmospheric transmittance” are obtained, (2) maximum and minimum values of daily/hourly solar irradiation are theoretically calculated using the values of the atmospheric transmittance, (3) a ratio of the sunshine time is also estimated by the observed solar irradiation, (4) the daily/hourly amount of solar irradiation is finally estimated using the ratio and the maximum and minimum values of the daily/hourly solar irradiation. The data of solar irradiance for one year, 355 days in 2000, were analyzed by the present method, and the values of daily (9 to 17 o'clock)/hourly (12 to 13 o'clock) solar irradiation were estimated. The result shows that the estimated values agree very well with the observed values on more than half of the days in 2000.

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This paper proposes a comprehensive model to examine potential CO₂ emission reduction in commercial and residential sectors through architectural enhancements and facility improvements considering long-term power generation best mix. The already proposed model of CO₂ reduction options on demand side enables the detailed evaluation taken into account of the regional characteristics, such as meteorological conditions and building distributions. This demand side model is integrated with a long-term power generation best mix model to assess long-term potential CO₂ emission reduction and the impact of demand side options on the power plant planning in electric power companies in the future. With this approach the prospective power generation structure is figured out and the economic efficiency and potential CO₂ emission reduction by options in the commercial and residential sectors of Tokyo are evaluated.

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The latest technological advancements in the field of power electronics, paved the way for the development of new type of frequency converters namely a self commutated type HDVC frequency converter, which is capable of controlling active power and reactive independently. As an another promising alternative, this paper, investigates a new type of Adjustable Speed Generator-motor based Frequency Converter (ASGFC), which is not only capable of controlling active power and reactive power independently, but also can absorb or release electric power energy.
Each of ASGFC and HVDC type frequency converters is placed in the model power system, and its dynamic performance is assessed during and after faults, during load shedding and generation shedding as well. On comparing the results, we observed that a self commutated type HVDC frequency converter and ASGFC have better performance than a line commutated type HVDC frequency converter, concerning the recovery of active power of load and voltage nearby the placement of the frequency converters, and so on. The electric power energy absorption and releasing feature of ASGFC was also clearly observed to have improved damping, and better voltage profile, etc.

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The Japanese power system is divided into 50Hz and 60Hz systems, which are interconnected by power electronics based frequency converter station. Frequency converter can be realized by using Adjustable Speed Generator/Motor(ASGM), which is excited by AC voltage. This frequency converter can also work as power system stabilizer. In this study, control systems for power interchange are designed based on eigenvalue control technique, and it is made clear that 300[MW] reverse power interchange can be achieved quickly and smoothly. Next, power system stabilizing control systems are also designed based on eigenvalue control technique or energy function, and control performances of these control systems are shown for a model system.

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This paper discusses the conformation of micro co-generation system (μCGS) for the residential use. The evaluation is based on the observation of the hot-water load of 3 families which live in the same apartment house. We assumed DSS operation of μCGS. We evaluated the required capacity of μCGS, hot-water storage tank and supplementary heater to meet the daily hot-water load for each day in the observation period. The results are: 1) μCGS of 2 kW and hot-water storage tank of 350 ι are required in family-B when the supplementary heater is not installed, 2) the installation of the supplementary heater of 5 kW reduces the required capacity of hot-water storage tank by 50 ι, 3) the evaluation based on the hourly averaged hot-water load patterns underestimates the required capacity of hot-water storage tank, 4) the required capacity of hot-water storage tank is reduced by the smoothing effect of hot-water load pattern among 3 families.

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As the world wide deregulation in the electric power industry progresses, the basic structures of future power systems should change drastically. Particularly, in power distribution systems which are the closest to the demand side in a power system, higher flexibility and higher reliability are necessary. Flexible, Reliable and Intelligent Electric eNergy Delivery System (called “FRIENDS”) which has been proposed by the authors is a new concept for a future power distribution system. The most important idea of FRIENDS is to install the new facilities called Quality Control Center (QCC) between distribution substation and customers. QCC has dispersed generators, dispersed energy storage systems and many power electronics devices. By controlling those facilities appropriately, various purposes of FRIENDS can be achieved.
In Japan, power supply reliability is kept constant in high level, however, it will be difficult to keep the reliability level because Independent Power Producers (IPP) which have uncertainty will enter more and more into the electrical market if the deregulation makes progress and the market grows. If we want to keep the same level of reliability in the present system, we will need “useless” investment for expansion of equipment though some customers do not require the high reliability level. In other words, the present system cannot adopt to the deregulation. This paper proposes a new power supply system which has some advantages with in deregulation considering FRIENDS. In this system, a power system is divided into two parts and each part manages the reliability and the power rate independently. Further, this paper proposes two methods for evaluation of the system. First, by using the concept of value of service, we propose the method which decides the quantity of facilities in QCC and indicate that this system can allow a lower level of reliability. Second, by modeling a relation between power rate and load, we consider the construction of the proposed distribution system.

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This paper proposes to use a forced commutation current sourced converter with immitance conversion link (ICL) for HVdc transmission system. Immitance conversion link can convert the constant current characteristics to the constant voltage characteristics. For HVdc transmission, converter is operated in the mode of constant current control. On the other hand, ac transmission system is operated in the mode of constant ac voltage control. Therefore, some withdrawal occurs between HVdc system and ac system. We investigate ICL to eliminate this withdrawal. Some characterisitcs of ICL are remarkable and ideal for installation between HVdc and ac system.

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FRIENDS (Flexible, Reliable, and Intelligent Electrical eNergy Delivery System) is proposed as a new con-cept for a future power distribution system. One of the most important characteristics of FRIENDS is that QCC (Quality Control Center) as a power quality control facility is installed very closely to customers in order to supply several qualities of power and enables customers to choose the quality of power. The concept to supply multi-quality of power is called as unbundled power quality service.
As one of the configurations of QCCs, unbundled power quality supply system using an inverter with asymmetrical control and three-phase four-wire ac system is proposed by authors. In this paper, total characteristics and realization of proposed system are mentioned by showing experimental and simulation results. The capacity of inverter required to compensate load unbalance and harmonics current is also mentioned.

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This paper has two purposes. One is to validate subsidization programs in Japan by estimating and comparing cost-efficiencies of R&D on and subsidization to photovoltaics from the viewpoint of solar cell manufacturing cost reduction, The other is to demonstrate that cost-effectiveness analysis is helpful for rational and persuasive planning and effective and efficient promotion of technology development.
For estimating cost-efficiency of subsidization, the authors propose a definition of cost-efficiency which reflects manufacturing cost reduction through mass production effects and estimate cost reduction coefficients of mass production effects based on actual manufacturing costs of solar cells. On the other hand, the authors estimate cost-efficiencies of R&D from the viewpoints of present and future manufacturing cost reduction based on the actual and R&D goals of manufacturing costs, respectively.
These different cost-efficiencies of R&D give different results of analysis. Based on the former one, start of the subsidization programs are found to have been a little earlier, but they were well planned in terms of total amount of subsidy, On the contrary, based on the latter one, the subsidization programs should be found reasons for existence from other points of view, such as present manufacturing cost reduction or production increase of solar cells.

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Trouble due to harmonics rapidly increases after 1990. A ratio of troubled equipment caused by the harmonics shows a series reactor and a power capacitor account for 65% and 26%, respectively. A modified JIS recommends allowance 5th harmonic current of 55% in the series reactor, and standardize to a 6% series reactor for a capacitor. However, to install the capacitor with the 6% series reactor due to harmonic current is sometimes the temperature rise in observed. The authors clarify a combination of capacitor and reactor to reduce harmonic current efficiently. A Capacitor based on the combination is applied to customer substations of 6.6kV and 33kV. This paper describes the capacitor, which is named Tough Var, and test results at the substations.

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A rule based economic load dispatch (ELD) has been proposed for the daily and weekly operation planning of thermal units. The proposed ELD scheme is based on the well known equal incremental cost method. To determine the load dispatch among thermal units in the study system, most of the actual constraints has been considered. A simple rule base has also been proposed for the unit commitment according to a ranking considering the startup cost of each thermal unit. To demonstratethe efficiency of the proposed ELD scheme, a weekly planning of 23 thermal unitshas been performed with significant reduction of the total operation cost compared with that in the actual operation.

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The power system simulator is convenient for understanding the system characteristics, foreseeing the difficulty and conducting countermeasures, but the conventional analog type model is not flexible to evaluate the progressing apparatus, such as FACTS (Flexible AC Transmission System), DESS (Dispersed Energy Storage System), etc. This paper develops the real time digital simulation model of the voltage sourced converter, which is sufficiently flexible to evaluate the power electronics apparatus. This paper also discusses about the relation between the accuracy of the output of the model and the calculation time-step, which become restriction in real time calculation. The evaluation of the accuracy is performed not only by the waveform itself but also by the frequency characteristics of the harmonics generated from the converter model. Moreover, this paper proposed to use Wavelet-transform to evaluate the accuracy of the output of the proposed model in the time-frequency domain. The obtained results show that the proposed real time digital simulation model can give appropriate output with high accuracy to the objective frequency area.

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Power system stabilizers (PSS) are designed to reduce oscillations in power systems. Since PSS cannot ab-sorb energy by itself, surplus energy is consumed by damper windings and loads. On the other hand, if turbine governor which can absorbsurplus energy directly is operated pertinently, it will be considered to be effective in recovery of energy balance. We have proposed the Governor-PSS Co-Operative control method, which utilizes mechanical torque supplied by turbines in addition to electrical torque handled by PSS.
However, since operation of governorhas influence on turbine wings, it cannot be operated by the same frequency bandas PSS. In order to take in such complicated specification, the H₂ control theory in which delicate adjustment is possi-ble was adopted.
This paper shows a H₂ controller design procedure consulting conventional PSS properties and the performance of this me-thod through simulation results with widely varied power systems.

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Two systems of the same structure and of the same parameter values can be synchronized by supplying the signal from one to the other even when they behave chaotically. This phenomenon is called synchronization of chaos. In this paper we investigate the fundamental aspects of the method to identify the parameter values of a generator model utilizing the chaos synchronization. Letting the system that includes the target generator be chaotic and making up the virtual identical system simulated in a computer, we check the synchronization between the two systems for the purpose of parameter value identification.

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In this paper, a new method is presented to determine the location and parameters of UPFCs. In recent years, they plays a key role as FACTS devices to control power flows in deregulated power systems. From a standpoint of power system operation and planning, it is important to optimize the location and the parameters of UPFCs. The problem formulation may be described as a nonlinear mixed integer programming problem. In practice, it is not easy to solve the formulation efficiently. This paper proposes parallel tabu search (PTS) with hybrid coding that includes both continuous and integer variables. The conventional methods find out better solutions with two phases or double loops in determining the location and parameters of UPFCs. The proposed method evaluates better solutions through a single loop rather than double loops in PTS. The effectiveness of the proposed method is demonstrated in a sample system.

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This paper proposes a hybrid method of the fuzzy optimal regression tree (FORT) and the multi-layer perceptron (MLP) of an artificial neural net for short-term load forecasting. The regression tree (RT) is useful in discovering meaningful rules and classifying data so that the relationship between input and output variables is clarified. In this paper, a couple of strategies is developed to improve the performance of RT. One is to make use of tabu search to determine the globally optimal tree structure. The other is to introduce simplified fuzzy inference into RT to enhance the accuracy of the split value. As a prefiltering technique, FORT is used to classify data into one of clusters. MLP is constructed to forecast one-step ahead daily maximum loads for each cluster. The proposed method is successfully applied to real data.

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This paper presents the real-time detection method of power system frequency. The method is based on the RDFT(Recursive Discrete Fourier Transform) applied in the PMU(Phasor Measurement Unit). It is described that the dynamic performance of the power system frequency can be evaluated with high accuracy.

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