In recent years, the research and development for the photovoltaic (PV) energy system are making rapidly progress around the world. In particular, the maximum power point tracking (MPPT) control attracts lots of attention, and our research group has already proposed the MPPT control method which use the fuzzy theory. However, if a small area of PV array is shaded, the characteristics and the maximum power point of PV array are changed, so the fuzzy control is difficult to extract the maximum power of PV array. To overcome this problem, this paper proposes a new control method using a fuzzy neural network (FNN) instead of fuzzy control. The FNN can be trained so that the MPPT controller is able to extract the maximum power under shading of small area of PV array. The usefulness and validity of the proposed control method are illustrated through MPPT control of PV array.

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Because of short of south-faced roof area of a building for PV array, PV array is often installed separately on multi surfaces of which azimuth or tilt angle is different. In this case, I-V curve of PV string on each surface is different each other. This causes reduction of output of PV array and a new system organization with multi string-inverter is proposed to solve this problem. The effect of new proposed system organization was studied by simulation. In this paper, the result of analysis on mismatch loss, stand-by loss, overload loss and loss of energy conversion by inverter was reported in detail. And it was concluded that an annual output energy of new system almost equals to that of a conventional PV system with a central inverter.

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In a network open access environment, various electricity transactions with different contract paths will occur, and which tend to result in parallel flows. In order to reduce such kinds of power flows, series types of FACTS devices suchasTCSC can be used. On the other hand, since the FACTS devices are effective means for stability enhancement, those devices will be utilized for the both purposes of power flow control and stabilizing control in the network open access environment.
This paper proposes a new concept of Transaction Path Filter (TPF) which can screen and order the electricity transactions from the viewpoint of parallel flow reduction and stabilizing ability of TCSC. In the TPF, first, the amount of compensation of TCSC is computed which is necessary for completely reducing the parallel flow of each transaction. Next, by using sensitivity analysis of eigenvalue, the effect of the compensation on stabilizing ability of TCSC is evaluated as the change in the real parts of eigenvalues corresponding to the focused oscillatory modes. Each transaction is classified into four ranks based on the necessary amount of compensation and the stabilizing ability, and then it is determined whether the transaction is accepted or not by system operators.

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The large-scale introduction of independent power producers (IPP's) which use coal and residual oil for economical electric power generation might influence the reduction in total CO₂ emission in Japan. In our previous study, we evaluated the potential capacity and the economic value of various types of IPP's considering the reduction in CO₂ emission in the electric power industry on basis of the optimal electric generation planning. This paper calculates fuel-and capacity-dependent maximum price of IPP's electricity for electric power utility under limitation of CO₂ emissions. This paper also proposes the fuel-dependent pricing of IPP's electricity considering the tender probability of IPP's for electric power market. As a result, the appropriate price of IPP's electricity for both utility and IPP was evaluated.

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This paper presents a simulation study on the transmission pricing method based on nodal pricing, which is theoretically expected to be an effective scheme for achieving efficient operation of power systems. Nodal price at each node is calculated as a short-term marginal cost reflected by generation and transmission cost and the opportunity cost related to congestion of the transmission network at the supply-demand balance, maximizing a social welfare consisted of customer's benefits and power generator's profits. In this study, transmission price (wheeling price) is obtained by using the nodal price difference between the points of the electric power wheeling. Feasibility of wheeling pricing including congestion cost is demonstrated numerically through simulation studies using a test system. Nodal pricing can be applied to achieve the efficient short-term operation. However, when congestion is occurred in the network, nodal prices and wheeling prices vary by location and extent of transmission congestion in the power systems. As results, congestion cost and loss of social welfare are increased due to network externality. When the network operator activates the strict constraint of transmission line intentionally, incentives for new entries of generators to the market are impeded by unstable market price and transmission congestion.

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The authors have proposed Flexible, Reliable, and Intelligent Electric eNergy Delivery System (FRIENDS) as a form of the future power delivery systems. The main idea of FRIENDS is to install Quality Control Centers (QCCs) in the vicinity of customers. These QCCs make a new power delivery network below power substations. Circuit breakers or switches using power electronics devices are also installed in the power delivery network so as to change the network configuration according to the system condition or the fault situation.
This paper investigates some functions of the network using solid state switches. In order to protect these switches, it is also examined the installation of current limiting devices to the network in FRIENDS.

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Photovoltaic (PV) systems have been introduced actively as a measure against green house effect etc. In the future it is considered that the amount of PV systems will increase more and more. Since the outputs of the PV systems are influenced by weather, they cannot be controlled easily. Therefore, energy storage systems are needed as a facility for giving a capacity credit to the PV systems with uncertain output characteristics. Further, when PV systems are introduced at the end of the network, it is expected that their fluctuation is absorbed at substation level (at a transformer substation). Therefore, the authors assume that energy storage systems are introduced at substation dispersively.
This paper evaluates the economic effect of PV system considering load leveling by dispersed-type energy storage (DES) systems. The calculation results by proposed method show some important relations between PV systems and DBS systems.

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There are some factors making the power system network unbalanced; i.e., UHV transmission lines in which three phase transmission lines are not transposed, 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 is recently increasing in Japan. This paper presents a new method of unbalanced power flow calculation of power system which contains variable speed pumping-up generators. The new method is based on the phase coordinate method, because a power system which has elements with unsymmetrical impedance can be easily analyzed by using the phase coordinate method.
In this paper, a phase coordinate models of the variable speed generators and its secondary exciting circuit composed of GTO converter/inverter are derived first. And then, procedures of power flow calculation of unbalanced power system are presented.

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This paper presents a practical algorithm for solving large-scale optimal power flow problems. The proposed algorithm is based on a successive approximation technique in which an original power system can be divided into a main-system and several sub-systems. In the proposed algorithm, approximate voltage characteristics of sub-systems can be derived from the results of OFF for sub-systems, and the OPF for the main-system in conjunction with the derived approximate voltage characteristics of sub-systems can be solved. Finally, the optimal solution of the original power system can be obtained by successively coordinating the approximate voltage characteristics of sub-systems. Since the dimensions of problems to be treated in OPF are reduced, the proposed algorithm can effectively solve large-scale OPF problems. Moreover, the optimal voltage characteristics of sub-systems can be derived. The feasibility and effectiveness of the proposed algorithm are demonstrated on a typical power system model.

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It is no doubt that an electric vehicle (EV) is going to be a main stream of the transportation resource for persons in the next century. The influence for EV, on the other hand, should be managed properly in accordance with the penetration revel. This is because that the influence caused by chargers seems to be an important issue for both the technique on the distribution level and the social aspect. For the time being, chargers are situated in the particular places, though appropriate installation is required to construct a convenient and accessible infrastructure for EV users. This is also important for the acceleration of EV penetration.
Besides, Voronoi mapping is well known method for the proper configuration of equipment geographically. We apply this method to arrange the chargers of electric vehicle in Tokyo metropolitan region properly. Under sufficient survey both of the gas station's market and the properties of the potential EV customers and geographical conditions, we use a weight table to evaluate these factors appropriately. Accordingly, we present an optimal installation technique for EV chargers using the weighted Voronoi mapping method. We also show the prospected shortest distance among the charges in case of 100 chargers situated in Tokyo area. Furthermore, we present a practical example for the proper configuration of chargers for EV in 2010.

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For solid round rotor body synchronous machines saturation effects are significant in both d- and q-axis, and because of this non linearity, the d- and q-axis magnetizing reactances are depressed to a considerable degree from their unsaturated values under both steady-state and transient operations. In this type of synchronous machine q-axis saturates appreciably more than that of the d-axis because of the presence of the rotor teeth in the magnetic path of the q-axis. This paper first presents a new method to calculate the q-axis saturation characteristic from the existing d-axis saturation characteristic. Next the effects of considering a separate q-axis saturation characteristic on the power system steady-state and transient stability have been presented.

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The paper presents an effective power flow controller design for a phase shifter used in parallel AC/DC links which interconnect power systems both by the phase shifter as an AC link and a BTB (back-to-back) as a DC link in parallel. An equivalent DC power flow model of the interconnected power systems is first introduced. Then, based on circuit theory, approximate equations are formulated to quantify the relation among phase-shifting angles of the phase shifter and power flows and impedances of the power systems. The validity of these equations are demonstrated through power flow studies and digital simulations. Finally, using the approximate equations, a power flow controller with feedback and feedforward structure is designed for the phase shifter. The effective control performance of the designed controller is also demonstrated through digital simulations.

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Nowadays, the power industry is in transition to a fully competitive scenario. Under this situation, some power system controls such as frequency control will be served as ancillary services. Then, it is important to consider how the system frequency should be controlled. In this paper, a robust frequency stabilization controller design method of solid-state phase shifter is proposed. The frequency controller of phase shifter located in series with a tie line between two areas, is designed based on the idea of enhancing the damping of inter-area oscillation mode. The method of Overlapping Decompositions for system reduction and the Η_∞ control via Normalized Coprime Factorization (NCP) approach are used to achieve the proposed design idea. By NCF approach, the weighting selection in Η_∞ control design is simplified. Simulation results confirm the performance and robustness of the proposed control against load disturbance and system uncertainties.

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This paper presents the stability enhance method of power system with VSrC (Variable Series Capacitor) using adaptive fuzzy controller. The adaptive fuzzy controller is systematically constructed on the basis of control process with the system stability considered by sliding-mode control. Moreover, the proposed control scheme introduces the on-line adjustment system in this fuzzy controller. This on-line adjustment system adaptively adjusts the coefficients for the operation part of the fuzzy rules so as to damp a oscillation of generators. The simulation results show that the proposed controller is robust to the variations of the system parameters, system operating conditions, and fault points.

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This paper proposes a new distributed autonomous control method for tap change under load (TCUL) transformers. Using a fuzzy control scheme, we realize advantageous control characteristics which inherit both the reliability of the conventional control scheme and the optimality of the control actions of distributed controllers, where the index derived from the optimization problem is used to minimize the voltage deviations and the number of tap operations. To increase the performance of control, a voltage prediction algorithm in each controller and then the data exchange scheme among controllers is adopted to consist an adaptive control scheme. Effectiveness of the proposed method is demonstrated through numerical simulations using an equivalent system made from a real system data.

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This paper presents a particle swarm optimization for reactive power and voltage control (VQC) problem formulated as a mixed integer nonlinear optimization problem (MINLP) considering voltage security assessment. The proposed method realizes loss minimization and determines VQC strategy with continuous and discrete control variables such as AYR operating values, OLTC tap positions, and amount of reactive power compensation equipment. The method also considers voltage security assessment using a continuation power flow and voltage contingency analysis technique when determining the control strategy. The feasibility of the proposed method for the problem is demonstrated and compared with reactive tabu search and enumeration method on practical power system models with promising results.

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It is a common practice that the synchronous machines, induction machines and the other rotating machines are modeled in dqO reference frame when we analyze their transient hehaviors. However, external network (transmission lines, etc) is mostly modeled in phase-domain reference frame. Therefore, if rotating machine can be modeled in phase-domain reference frame, we can construct the electric network model without reference frame transformation. In this paper, we derive the phase-domain model of an induction generator in terms of instantaneous values, and its validity is analyzed based on numerical simulations.

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This paper describes a new algorithm for transformer protection relays to discriminate between internal faults and inrush currents by estimating the magnetizing curve of a transformer core regardless of the ratio of the second harmonic components.
Every transformer core has its own magnetizing characteristic, called the B-H curve. Even immediately after energizing or an external fault, this curve remains unchanged. The newly developed algorithm incorpo- rates a model B-H curve as a reference, and trackes the locus of (H, B) calculated from the instantaneous values of voltage and current at each terminal of the transformer. Because of the difficulty of obtaining the initial flux density, this algorithm determines the relative values of flux density instead of the absolute values.
The magnetic flux density (B) and magnetic field intensity (H) are calculated as B=B_r+B_d=B_r+K₁ ∫ Vdt, H=K₂I_d=K₂∑I_i where B_r is the initial flux density, B_d is the flux density caused by magnetizing voltage V, I_d is the magnetizing current, I_i, the is instantaneous current of each terminal of the transformer, and K₁ and K₂ are constants. When the sum of the currents reaches a threshold I_r, this algorithm assumes B_r=0 and starts integration of the voltage to track the locus of (H, B_d). The locus follows the reference curve if there is no internal fault.

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In order to control large and complex power system, more flexible decentralized control scheme is desired. Since the system configuration is changing continuously, the system must be controlled based on uncertain and inadequate information. The control scheme should provide robustness.
The sliding mode control based on the variable structure system theory is paid attention as one of the promising robust control scheme. In the sliding mode control, the structure of the control system is changed across the hyperplane (switching plane) in state space so that the state variables of the system are kept on the hyperplane.
In this paper, applications of the sliding mode control to power system stabilization are discussed. The sliding mode control is applied to the control of the thyristor controlled SDR (System Damping Resistor). Since the SDR is operated discretely (on or off), it is impossible to keep the state variables on the switching plane all the time. Therefore, the “partial” sliding mode control is introduced. A new practical switching plane for the sliding mode control is developed. Using the plane, the system can be stabilized effectively.

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The six utilities in the western region from the Chubu area to the Kyushu area have a maximum total power demand of some 94 GW. The power transmission distance from the Chubu area to the Kyushu area is some 1000 km, and the east-ward power flow is increasing. When a power failure occurs in such a large-scale power transmission system, the result is not only a power oscillation with a cycle of about 0.7-1.2 seconds but also other power oscillations with a cycle of about 2-6 seconds. The latter has become a problem of increasing magnitude in recent years.
This paper describes a PSS that can damp system power modes of a wide band more effectively than the currently available PSS and which has been developed as part of an improvement of an excitation control system with relatively low cost. The feature of this PSS is that it includes an element operating in parallel with the (ΔP+Δω)-PSS with the ability to damp long-cycle oscillations. This PSS is referred to as a parallel PSS.
To verify that the parallel PSS has the originally expected damping capability, simulations on the real power system were conducted.

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A method for PSS parameter tuning under restriction of robustness is proposed. In the design procedure, the proposed method uses a low-order linearized model which reprepsents dominant dynamics of the power system. The ignored higher order modes and pertuabation of the low frequency modes are considered as multiplicative perturbations. The controller with high performance and high robustness can be derived by solving a nonlinear optimization problem.
Because of the non-convexity of the optimization problem, gradient methods are not suitable for solving the problem. For this reason, the present paper proposes utilization of genetic algorithm (GA) for solving the nonlinear programming problem.
The present paper makes it clear through digital simulations using a simple three-machine power system model that the designed controller is effective for damping interarea modes and achieves higher robustness against change of load flow condition than the well tuned conventional controller.

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Power systems are becoming larger and larger for meeting electric power demand. In that regard, as fault currents occuring in a power system tend to increase, measures against generator stability problems are expected to be more serious. On the other hand, in recent years researches and developments on superconducting fault current limiter (SFCL) are moving forward in accordance with the advancement of superconducting technology, which are hoped to be applied in practical power systems. This paper describes results of analysis about stabilizations of synchronous generators under balanced and unbalanced faults by SFCL.

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Comparative studies were carried out on cycle efficiencies of five coal synthesized gas driven combined power plants. In the top gasification scheme, where the coal is gasified separately from the power generation units, we considered an oxygen combustion MHD topping cycle (Case I), a 40% oxygen enriched air combustion (Case II), a high temperature preheated air combustion (Case III) and a gas turbine topping cycle (Case V). The bottoming is a steam cycle in these four cases. The fifth case (Case IV) was a tail gasification scheme with oxygen combustion plasma MHD as the topper and a combined gas turbine and steam turbine system as the bottoming system, where the coal was synthesized by the high temperature MHD exhaust gas and both of the top and bottom units were driven by the synthetic fuel. Assuming the same enthalpy extraction for the MHD generator, the gas turbine cycle and the steam turbine cycle, the same inlet and outlet temperature at the wall separated type regenerator and the same exhaust temperature at the stack in five cases, we showed that the Case IV exhibited the highest plant efficiency of 62.5% which was higher than that of the Case V by about 10%.

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The paper deals with the method of insulation design for reactor tap windings. Surges entering a reactor cause resonance voltages in reactor windings and overvoltages appear between tap windings. New design method for evaluation of overvoltages is experimentally confirmed. We are applied this method to AC SOOkV filter reactor.

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This paper develops experimentally a simulation model for a single corona pulse using a short line electrode. The model consists of a resistor, a capacitor and a switch. An integration method is introduced into control of the switch for expressing dispersion of formative time lag, which has been ignored in conventional models. The proposed method does not require a charge versus voltage curve, which is indispensable for a conventional numerical analysis. Corona discharges generated on a long electrode are expressed by cascaded single pulse models. Corona discharge current for a long electrode is satisfactorily represented by this method. The proposed model expresses length-dependence of the corona discharge current which has been neglected in a conventional analysis. The simple structure of the proposed model enables a numerical simulation using Electro-Magnetic Transients Program (EMTP).

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A feasibility study for development of a non-contacting voltage presence detector was performed. This detector is intended to be used for maintenance of the overhead transmission lines. A detection method by measurement of electric field on the surface of the tower post was proposed and investigated by means of electric field measurements at the transmission test line and numerical calculations. The results showed good performance to realize the non-contacting voltage presence detection.

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