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Optimal location and control of a unified power flow controller (UPFC) along with transformer taps are tuned with a view to simultaneously optimize the real power losses and voltage stability limit (VSL) of a mesh power network. This issue is formulated as a nonlinear equality and inequality constrained optimization problem with an objective function incorporating both the real power loss and VSL. A new evolutionary algorithm known as bacteria foraging is applied for solving the multiobjective multivariable problem, with the UPFC location, its series injected voltage, and the transformer tap positions as the variables. For a single objective of only real power loss, the same problem is also solved with interior point successive linearization program (IPSLP) technique using the LINPROG command of MATLAB. A comparison between the two suggests the superiority of the proposed algorithm. A cost effectiveness analysis of UPFC installation vis-a-vis loss reduction is carried out to establish the benefit of investment in a UPFC. Index Terms--Bacteria foraging, continuation power flow, linear programming, optimal power flow (OPF).

This paper proposes a simple multiarea decentralized state estimation procedure. This procedure allows estimating the state of a multiarea electric energy system while preserving the independence of each area. Information interchange among area operators reduces to just border information. The proposed algorithm is both simple and robust. The procedure developed is illustrated through several case studies carried out using the IEEE Reliability Test System. Conclusions are duly drawn. Index Terms--Decomposition, large-scale optimization, multiarea power system, state estimation.

This paper presents a framework to implement supply and demand side contingency management in the reliability assessment of hybrid power markets. A model for the independent system operator (ISO) to coordinate reserve and load curtailment bids for contingency states is introduced to balance reliability worth and reliability cost. The load curtailments and generation re-dispatch for a contingency state are determined based on minimizing the market interruption cost using an optimization technique. A nousequential Monte Carlo simulation technique based on this framework has been proposed to evaluate the customer reliability of restructured power systems with the hybrid market model. The modified IEEE Reliability Test System (RTS) is used to illustrate the proposed technique. Index Terms--Contingency management, customer reliability, hybrid market, independent system operator (ISO), load curtailment bids, market interruption cost, Monte Carlo simulation, reliability assessment, reserve.

Harmonic resonance is closely related to the singularity of a network admittance matrix. The smallest eigenvalue of the matrix defines the mode of harmonic resonance. This paper applies this eigenvalue theory and proposes a method to determine which network components have significant contributions to a harmonic resonance phenomenon. The basic idea is to calculate the sensitivities of a resonance mode to the parameters of network components. The sensitivity results are then ranked to quantify the impact of each component. In this paper, the eigen-sensitivity theory as applied to harmonic resonance mode analysis is presented. Case studies are used to verify the theory. A practical example is given to illustrate the application of the proposed method. In addition, this paper further conducts extensive comparative analysis on three types of network-oriented modal analysis techniques. The results have clarified the similarities and differences among the techniques. Index Terms--Eigenvalue sensitivity, harmonic resonance, harmonics, modal analysis, power quality.

This paper describes a method for calculating energy losses in any system element assuming that the transmitted energy across it is known. The method identifies two components of losses: load variance and load mean. The load variance component can be neglected for large loads, but it is significant for small loads, which are dominant in low voltage networks. Needed parameters for loss calculation are determined by two load duration curves (LDCs) per load type. The formulae for loss calculation in transformers and distribution lines of various phase systems are given, including the formulae for energy losses and average current in the neutral conductor. A new algorithm for voltage calculation at network nodes is proposed and shown to provide high accuracy of calculated losses. The method enables loss calculation for compounded (nonhomogeneous) loads and gives the exact relationship between traditional loss factor and the load factor. Index Terms--Distribution networks, energy losses, load measurement, load variance, neutral conductor current.

We show how concepts from game theory can be used to find and evaluate strategies for defending an electric power system against antagonistic attacks. Consequently, the interaction between the antagonist and the defender of the system is envisaged as a game. In a numerical example, we study the performance of different defense strategies against a number of attack scenarios. Particularly, we study whether there is a dominant defense strategy and an optimal allocation of resources between protection of components and recovery. Index Terms--Blackout, game theory, homeland security.

This paper proposes a new version of the classical particle swarm optimization (PSO), namely, new PSO (NPSO), to solve nonconvex economic dispatch problems. In the classical PSO, the movement of a particle is governed by three behaviors, namely, inertial, cognitive, and social. The cognitive behavior helps the particle to remember its previously visited best position. This paper proposes a split-up in the cognitive behavior. That is, the particle is made to remember its worst position also. This modification helps to explore the search space very effectively. In order to well exploit the promising solution region, a simple local random search (LRS) procedure is integrated with NPSO. The resultant NPSO-LRS algorithm is very effective in solving the nonconvex economic dispatch problems. To validate the proposed NPSO-LRS method, it is applied to three test systems having nonconvex solution spaces, and better results are obtained when compared with previous approaches. Index Terms--Economic dispatch (ED), local search, nonconvex solution space, particle swarm optimization (PSO).

Future ship integrated power systems (IPSs) will be characterized by complex topologies of advanced power electronics and other evolving components. Advanced capabilities, such as intelligent reconfiguration of system function and connectivity will be possible; however, system level knowledge of component failure will be needed for intelligent power distribution under failure mode conditions. Diagnostic and prognostic coverage for sensors, components, and subsystems will be essential for achieving reliability goals. This paper will look at some diagnostic requirements and emerging technologies available for insertion into future ship IPSs. Index Terms--All-electric ship, diagnostics, distributed intelligence, integrated power systems (IPSs), intelligent software agents, knowledge management, prognostics.

This paper describes the control and parallel operation of two active power filters (APFs). Possible parallel operation situations of two APFs are investigated, and then the proposed topology is analyzed. The filters are coupled in a combined topology in which one filter is connected in a feedback loop and the other is in a feedforward loop for harmonic compensation. Thus, both active power filters bring their own characteristic advantages, i.e., the feedback filter improves the steady-state performance of the harmonic mitigation and the feedforward filter improves the dynamic response. Another characteristic of the proposed topology is the possibility of joint operation of both filters either as frequency-sharing or load-sharing, with or without redundancy. The frequency-sharing operation is possible due to the control algorithm, which is based on selective harmonic compensation using equivalent harmonic integrators. Implementation details and a discussion on the efficiency improvement for various switching frequencies are provided. The evaluation of the proposed topology concludes that this approach is very practical for achieving both low and high order harmonic compensation and stable grid operation. This is supported by extensive measurement results on a 15-kVA laboratory setup, indicating a reduction in total harmonic current distortion from the existing 30% to less than 2% for a typical adjustable speed drive application. Index Terms--Active filters, harmonic analysis, interconnected power systems, power system harmonic, pulse width modulated inverters.

Mathematical modeling for power dc-dc converters is a historical problem accompanying dc-dc conversion technology since the 1940s. The traditional mathematical modeling is not available for complex structure converters since the differential equation order increases very high. We have to search for other ways to establish mathematical modeling for power dc-dc converters. We have defined energy factor (EF) and new mathematical modeling for power dc--dc converters that have attracted much attention in recent years. This paper describes the small signal analysis of EF and mathematical modeling for power dc-dc converters in continuous conduction mode and discontinuous conduction mode. EF and the subsequential parameters can illustrate the unit-step response and interference recovery. This investigation may be helpful for system design and dc-dc converters characteristics. Two dc--dc converters: Buck converter and super-lift Luo-converter as the samples, are analyzed in this paper to demonstrate the applications of EF, pumping energy, stored energy (SE), capacitor/inductor SE ratio, energy losses, time constant r, and dumping time constant [[tau].sub.d]. Index Terms--Capacitor/inductor SE ratio (CIR), energy factor (EF), energy losses (EL), impulse response, mathematical modeling, pumping energy (PE), stored energy (SE), time constant [tau] and damping time constant [[tau].sub.d], unit-step response.

Nonsinusoidal voltage waveforms are quite common in high frequency power conversion magnetics. Low frequency nonsinusoidal waveforms are also common in ac motor applications with waveforms such as pulsewidth modulation and six-step. Previous attempts to model these losses, based on the Steinmetz equation, can work only in a limited range of frequencies, flux density excitations, and waveforms. In this paper, we present a very practical, yet very general and accurate model, for core loss calculations in case of nousinusoidal voltage waveforms. We show the model is equally applicable to low and high frequencies, metallic as well as nonmetallic (e.g., ferrites) core materials, by comparing the model prediction with measured data for various waveforms, frequencies, and flux densities. The model can be used for the design of high frequency transformers and inductors for use in switched mode power supplies. The model can also be used for ac motors where it is hard to estimate 'derating factor' and to avoid uncontrolled temperature rise. Index Terms--Pulsewidth modulation (PWM).

Extensive studies on the performance of on-chip CMOS transformers with and without patterned ground shields (PGSs) at different temperatures are carried out in this paper. These transformers are fabricated using 0.18-[micro]m RF CMOS processes and are designed to have either interleaved or center-tapped interleaved geometries, respectively, but with the same inner dimensions, metal track widths, track spacings, and silicon substrate. Based on the two-port S-parameters measured at different temperatures, all performance parameters of these transformers, such as frequency- and temperature-dependent maximum available gain ([G.sub.max]), minimum noise figure ([NF.sub.min]), quality factor ([Q.sub.1]) of the primary or secondary coil, and power loss ([P.sub.loss]) are characterized and compared. It is found that: 1) the values of the [G.sub.max] and [Q.sub.1] factor usually decrease with the temperature; however, there may be reverse temperature effects on both [G.sub.max] and [Q.sub.1] factor beyond certain frequency; 2) with the same geometric parameters, interleaved transformers exhibit better low-frequency performance than center-tapped interleaved transformers, whereas the center-tapped configurations possess lower values of [NF.sub.min] at higher frequencies; and 3) with temperature rising, the degradation in performance of the interleaved transformers can be effectively compensated by the implementation of a PGS, while for center-tapped geometry, the shielding effectiveness of PGS on the performance improvement is ineffective. Index Terms--Interleaved and center-tapped transformers, maximum available gain, minimum noise figure, pattern ground shields (PGSs), power loss, quality (Q) factor, temperature.

The conventional method of obtaining the coefficients of proportional plus integral (PI) controllers for the active power filter utilizes a linear model of the PWM inverter. The values so obtained may not give satisfactory results for a wide variation in operating conditions. This paper presents a new algorithm based on the foraging behavior of E-coli Bacteria in the human intestine, to optimize the coefficients of the PI controller. Through the simulation results, it is observed that the dynamic response of the bacterial foraging PI (BF-PI) controller is quite satisfactory. The proposed BF technique is compared with the genetic algorithm (GA) and found to converge faster than GA to reach the global optimum solution. Index Terms--Bacterial foraging, power-quality improvement and dynamic behavior of the controller, shunt active power filter.

Power distribution network protection and restoration are significant issues in terms of quality and reliability of the supplied electrical energy. In this paper, an extended research in possible high-end protection and control methods is presented. The authors intend to show the efficiency of combining modern IT techniques with the equipment provided by distribution automation evolving technology. As a result, a flexible and versatile multiagent system (MAS) is proposed. The effected MAS is fault isolation and power restoration oriented, as shown in the case studies. The structure of the proposed system (software and hardware aspects) is introduced. Both microscopic and macroscopic procedures are revised. Power line communications technology is implemented. Results acquired from computer simulations are evaluated. Conclusions concerning the perspectives of implementing the proposed system are finally presented. Index Terms--Artificial intelligence, cooperative systems, power distribution protection, underground power distribution lines.

Transients caused by lightning in railway facilities have not received much attention. In this paper, we describe the measurements of lightning transients entering a Swedish railway facility during the summer of 2003. The measurements of the transients were made in a technical house that provides an uninterrupted power supply for telecommunication systems and the signal systems. An analysis of the data has shown that transients in excess of 7 kV (peak to peak) can appear across the line-to-neutral supply system due to an indirect lightning strike. Some typical characteristics of the line-to-neutral transient voltages in terms of stroke locations and stroke amplitudes are presented. Further, from the experimental data, an empirical relation for predicting the line-to-neutral transient voltage in terms of stroke location and stroke current amplitude is obtained. Simple induced voltage calculations are presented to identify the levels of induced voltages appearing at the input of the technical house. The influence of ground conductivity on those induced voltages is also presented. The information presented in the paper is an important electromagnetic-compatibility issue associated with the lightning protection for railway systems. Index Terms--Lightning, rail transportation power systems, rail transportation reliability, transients.

As power electronics are increasingly used in power-electric networks, there is an interest in the creation of time-domain simulation techniques that can model the diversity of the integrative power-electric and electronic system while achieving high accuracy and computational speed. In the proposed method, generation of electric network equivalents (GENE), this is supported through the nested structure of the overall simulation process. One or multiple parent simulations, in which the unknown voltages are calculated using nodal analysis, launch multiple child simulations concerned with diakoptic subdivisions of the system under study. The interfaces for information exchange between parent and child levels are designed to provide encapsulation. This makes the subdivisions appearing from outside in the form of network branches compatible with the nodal analysis approach. It also facilitates the use of diverse solution methods for different child simulations, as it is shown for the simultaneous solution of equations formulated with nodal analysis and state space methods. Computational efficiency is obtained through the coordinated application of sparsematrix methods, piecewise linear approximation of nonlinear characteristics, and precalculation of operations pertaining to recurring power-electronic switch statuses. The resulting overall solution process is simultaneous, distributed, and suitable for real-time simulation. The devised methodology is validated through simulation of the CIGRE HVdc benchmark model, comprising ac networks, twelve-pulse power-electronic converter stations, harmonic filters, and dc transmission. Index Terms--Algorithms, circuit simulation, cosimulation, diakoptics, electromagnetic transients program (EMTP), HVdc transmission, modeling, numerical methods, parallel processing, power electronics, power system simulation, real-time systems, sparse-matrix techniques.

This paper proposes a new connection for a unified power quality conditioner (UPQC) to improve the power quality of two feeders in a distribution system. A UPQC consists of a series voltage-source converter (VSC) and a shunt VSC both joined together by a common dc bus. It is demonstrated how this device is connected between two independent feeders to regulate the bus voltage of one of the feeders while regulating the voltage across a sensitive load in the other feeder. Since the UPQC is connected between two different feeders (fines), this connection of the UPQC will be called an interline UPQC (IUPQC). The structure, control and capability of the IUPQC are discussed in this paper. The efficacy of the proposed configuration has been verified through simulation studies using PSCAD/EMTDC. Index Terms--Distribution system, power quality, sensitive load, voltage sag, voltage-source converter (VSC).

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach. Index Terms--Load compensation, unbalanced and distorted voltages, voltage source inverter.

This paper introduces a new differential protection scheme based on zero-sequence voltages with 100% coverage for generator stator ground faults. Analysis shows that the A-fundamental zero-sequence voltages and the A-third-harmonic voltages at the generator neutral and the terminals will change simultaneously, and they present some similar characteristics. According to that, the new scheme that exploits the fault information of both the zero-sequence fundamental voltage and the third-harmonic voltage is described. As it combines the information of the zero-sequence fundamental voltage and the third-harmonic voltage, the scheme can detect the ground fault with high sensitivity in 100% coverage winding. Simulation and field test results show that the proposed scheme can obtain higher sensitivity than the traditional schemes. Index Terms--Fault contribution component, stator ground protection, third-harmonic voltage, zero-sequence fundamental voltage.

This paper presents a new method for an optimal measurement placement of phasor measurement units (PMUs) for power system state estimation. The proposed method considers two types of contingency conditions (i.e., single measurement loss and single-branch outage) in order to obtain a reliable measurement system. First, the minimum condition number of the normalized measurement matrix is used as the criteria in conjunction with the sequential elimination approach to obtain a completely determined condition. Next, a sequential addition approach is used to search for necessary candidates for single measurement loss and single-branch outage conditions. These redundant measurements are optimized by binary integer programming. Finally, in order to minimize the number of PMU placement sites, a heuristic technique to rearrange measurement positions is also proposed. Numerical results on the IEEE test systems are demonstrated. Index Terms--Contingency, measurement placement, phasor measurement units (PMUs), state estimation.

This paper presents a current-transformer (CT) model that is useful for low-frequency applications. To describe the iron-core magnetic behavior, a hysteresis model is proposed, which is able to generate minor asymmetric loops and remanent flux. The effects of classic eddy current losses and anomalous losses are represented by linear and nonlinear resistors, respectively. The obtained results are compared with those calculated by the Preisach's model and measured in the laboratory. This model may be applied in power system protection studies, as it is the case of numeric correction of distorted secondary currents in current transformers (CTs). Index Terms--Current transformers (CTs), hysteresis, magnetic losses, power system protection.

This paper presents an effective algorithm to protect unfused 22.9-kV shunt capacitor banks in grounded-wye connection by improving an existing voltage difference method-based algorithm. It has often been reported that it is difficult to detect ground faults with arc near the input points within the bank using existing algorithms that use only the magnitude of the differential voltage. In this paper, it is shown that ground faults with arc near the input point can be detected by fast Fourier transform (FFT) analysis of the differential voltage and that the proposed algorithm is not impacted by harmonics generated by nonlinear loads which have quantitative influence on the capacitor banks. Consequently, the proposed method using harmonics analysis can be applied as an extended version of the existing detection method. The proposed method is applied to a simplified 22.9-kV real-life Korea Electric Power Corporation system and it is verified that the proposed algorithm can clearly detect faults that are not easily detected by the existing method. Index Terms--Ground-wye connection, harmonics, protection algorithm, unfused shunt capacitor bank, voltage difference method (VDM).

In this paper, a study conducted to analyze the factors influencing the current transformer (CT) dimensioning for numerical relays is presented. The study identifies the factors contributing to the CT dimensioning. It analyzes the influence of system parameters on the dimensioning factor and also identifies the critical applications and conditions that determine the CT dimensioning. The errors introduced in phasor estimation of saturated current signals are also described in this study. Index Terms--Current transformer (CT), CT saturation, discrete Fourier transform (DFT), knee point voltage, numerical relays, phasor estimation, remanent flux, steady-state error, transient error.

This paper presents a new numerical algorithm suitable for determining adaptive dead time, and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined by the voltage signal of faulted and tripped line phase using the total harmonic distortion factor calculated by discrete Fourier transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of the presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of high-voltage lines with permanent fault. Index Terms--Adaptive autoreclosure, numerical protection, secondary arc, transmission lines.

This paper describes the application of the abrupt change detection technologies to detect the abrupt changes in the signals recorded during disturbances in the electrical power network of South Africa for disturbance analysis and relay performance monitoring. The aim is to estimate the time instants of the changes in the signal model parameters during the prefault condition, after initiation of fault, after the circuit-breaker opening and autoreclosure, etc. After these event-specific segmentations, the synchronization of the different digital fault recorder recordings are done based on the fault inception timings. The synchronized signals are segmented again. This synchronized segmentation is the first step toward automatic disturbance recognition, facilitating further complex feature vector analysis and pattern recognition. Besides, the synchronized, segmented recordings can be directly used to analyze certain kinds of disturbances and monitor the relay performance. This paper presents many practical examples from the power network in South Africa. Index Terms--Abrupt change detection, disturbance analysis, relay performance, wavelet transform (WT).

In this paper, proposed setting and response evaluations of power differential relay scheme for line protection are presented. Mathematical expressions describing the adaptive features of both active and reactive power settings are given. The union action of these two detectors is adopted to provide sensitive detection for high impedance internal faults and avoid maloperation for all power swings and external fault conditions. Response is computed for both active and reactive power detectors under different operation and fault conditions. The results corroborate the applicability and the immunity of the proposed relay scheme against the sampling misalignment and practical frequency drift. High sensitivity for high impedance internal faults is verified. Index Terms--Adaptive protection, high-impedance faults, line protection, power differential relay, relay setting.

Dynamic security region (DSR) for security assessment and preventive control is defined in terms of variables that are under the control of the dispatcher prior to a fault. The boundary of DSR can be expressed using the function describing the stable manifold of the controlling unstable equilibrium point. The function is shown to be the solution of a partial differential equation. Quadratic and linear approximations to the function characterizing the boundary of DSR are derived. Numerical tests of the approximations are conducted. Potential applications of the method are discussed. Index Terms--Direct method, dynamic security region (DSR), stability region, transient stability.

Medium-term electric energy demand forecasting is an essential tool for power system planning and operation, mainly in those countries whose power systems operate in a deregulated environment. This paper proposes a novel approach to monthly electric energy demand time series forecasting, in which it is split into two new series: the trend and the fluctuation around it. Then two neural networks are trained to forecast them separately. These predictions are added up to obtain an overall forecasting. Several methods have been tested to find out which of them provides the best performance in the trend extraction. The proposed technique has been applied to the Spanish peninsular monthly electric consumption. The results obtained are better than those reached when only one neural network was used to forecast the original consumption series and also than those obtained with the ARIMA method. Index Terms--Load forecasting, neural network applications, power system planning, time series.

We investigate the effect of fiber elongation on power loss as rays propagate along deformed polymer optical fibers (POFs). Variations in core diameter, incident angle, stress and strain distributions, and necking of the POFs during fiber elongation are studied. The power losses in the deformed POFs are analyzed both experimentally and numerically. Theoretical analysis based on an elastic--plastic finite-element and a planar waveguide assumption is proposed. It is found that fiber elongation significantly affects the power loss in POFs, particularly at higher values of elongation. Good agreement between the measured results and the results simulated from the proposed model is obtained. The maximum difference is less than 5%. Results indicate that the proposed theoretical analysis based on an elastic--plastic finite-element model and a planar waveguide assumption is feasible to predict the power loss variation introduced by elongated deformations. A curve-fitted equation is also proposed to estimate the power loss of POFs under different fiber elongation conditions. OCIS codes: 060.0060, 060.2270, 060.2300, 060.2310.

This paper addresses the emulation of linear and nonlinear loads using a vector-controller dynamometer for the position control of mechanical loads. The emulation strategy allows an electrical machine (dynamometer) to be controlled, so as to emulate both the static and dynamic characteristics of a load with a certain bandwidth. The approach can be used for the experimental validation and testing of the electrical drives and motion-control techniques. The dynamic structure of the emulated load is always preserved. High-order systems such as loads with flexible shafts and nonlinear effects can be emulated accurately. This paper presents the dynamometer-control design, its practical implementation, and experimental results for the position control of the linear and nonlinear emulated loads. Systems with stiff and flexible shafts are considered. Finally, the experimental results are compared with the corresponding simulated loads to validate the emulation strategy. Index Terms--Drive control, dynamic emulation, dynamometer, mechanical-load emulation.

This paper proposes an optimization procedure for generation expansion and placement considering generation reliability in multiarea power systems. The objective is to obtain a suitable tradeoff between system reliability and cost. In this process, reliability evaluation is performed using the concept of global decomposition. The prospective generation locations are preselected, but the magnitude of generation located in each area is determined by an optimization procedure. The structure of global decomposition is exploited to simplify the problem and solve it using dynamic programming. The method is illustrated by application to a three-area power system and also implemented for an actual twelve-area power system. Index Terms--Dynamic programming, generation adequacy, global decomposition, multiarea power system, power system optimization, reliability.

This paper describes a new algorithm to compute the dominant poles of a high-order scalar transfer function. The algorithm, called the subspace accelerated dominant pole algorithm (SADPA), is more robust than existing methods in finding both real and complex dominant poles and faster because of subspace acceleration. SADPA is able to compute the full set of dominant poles and produce good modal equivalents automatically, without any human interaction. Index Terms--Dominant pole spectrum, large-scale systems, modal equivalents, model reduction, poorly-damped oscillations, power system dynamics, small-signal stability, sparse eigenanaiysis, system poles, transfer function.

In this paper, a new approach to adaptive underfrequency load shedding (UFLS), a procedure for protecting electric power systems from dynamic instability and frequency collapse, is presented. It consists of two main stages. In the first stage, the frequency and the rate of frequency change are estimated by the nonrecursive Newton-type algorithm. By using the simplest expression of the generator swing equation, in the second algorithm stage, the magnitude of the disturbance is determined. The UFLS plan is adapted to the magnitude estimated, obtaining in this way a more efficient system operation during emergency conditions. Results of procedure testing are demonstrated through the dynamic simulations by using: 1) a simple three-machine test system and 2) a ten-machine New England system. Index Terms--Adaptive control, dynamic simulation, nonlinear estimation, underfrequency load shedding (UFLS).

In this paper, a new gain-scheduling control design approach is applied to a supplementary damping controller (SDC) design for a FACTS device in the IEEE 50-machine system. The power system model with the FACTS device is linearized at different operating points to obtain an LPV open-loop model, whose state-space entries depend continuously on a time-varying parameter vector. A synthesis procedure for an improved LPV controller using multiple parameter-dependent Lyapunov functions and an interpolation scheme is presented and applied to the static VAr compensator (SVC) SDC design. Comparisons from simulation results are presented among the interpolated LPV controller designed using multiple parameter-dependent Lyapunov functions (MLPV SDC), the LPV controller designed using a single parameter-dependent Lyapunov function (SLPV SDC), and a conventional controller designed using the Root-locus method (RL SDC), which show that with an interpolated MLPV SDC for the SVC device, the system can achieve better robustness in an extended operating range. Index Terms--Damping controller, FACTS, gain-scheduling, IEEE 50-machine test system, linear parameter varying (LPV), Lyapunov function,

This paper analyzes the effect of the coordination of optimal reclosing and fuzzy logic-controlled braking resistor on the transient stability of a multimachine power system in case of an unsuccessful reclosing of circuit breakers. The transient stability performance of the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is compared to that of the coordinated operation of conventional auto-reclosing and fuzzy controlled braking resistor. The effectiveness of the proposed method is confirmed by simulations in case of a nine-bus power system model as well as a ten-machine system. Simulation results of both balanced and unbalanced faults at different points in the power systems show that the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is able to stabilize the systems well in case of an unsuccessful reclosing. Moreover, the transient stability performance of the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is better than that of the coordinated operation of conventional auto-reclosing and fuzzy controlled braking resistor. Index Terms--Balanced fault, braking resistor (BR), fuzzy controller, global positioning system (GPS), optimal reclosing, power system transient stability, unbalanced faults, unsuccessful reclosing.

Series compensation of transmission lines is one of the most effective means to increase the loading margin of an inter-connected power system. In this paper, a methodology is proposed for the identification of the critical transmission lines and their proper compensation rate with respect to voltage stability using decision trees (DTs) methodology. This methodology is applied to the Hellenic interconnected transmission system in normal operation and in (N-1) configurations, taking into account its future expansion plans. Results are validated by comparison with sensitivity analysis. Index Terms--Available transfer capability (ATC), decision trees (DTs), loading margin, sensitivity analysis, series compensation, thyristor controlled series capacitor (TCSC), voltage stability.

This paper presents the solution approach for simulation of control systems and nonlinearities used in UBC's Object Virtual Network Integrator (OVNI) power system simulator. OVNI is aimed at simulation of full-size power system networks in real time using integrated software/hardware solutions. The software solution is based on the Multiarea Thevenin Equivalent (MATE) network partitioning framework. Multilevel MATE expands the concept of MATE to a subsystem level, allowing for the efficient inclusion of controllers' equations and nonlinearities. Index Terms--Controllers, diakoptics, EMTP solution, Multi-level Muitiarea Thevenin Equivalent (MATE), nonlinear elements.

This paper presents a derivation of a new quadratic expression for the transmission loss in a power system. The main advantage of this expression is the improvement in accuracy over the other existing approximations. Furthermore, this improved quadratic form allows the transmission loss to be expressed in terms of nodal power injections. This paper builds on the derived loss expression and proposes a bus-loss matrix. This matrix is useful in quantifying the interactions among different bus power injections and establishing a loss allocation scheme for individual buses. Numerical examples are used to illustrate the accuracy of the derived quadratic form and its use in loss allocation. Index Terms--Loss allocation, power flow, Taylor series, transmission loss.

The allocation of the system losses to suppliers and consumers is a challenging issue for the restructured electricity business. Meaningful loss allocation techniques have to be adopted to set up appropriate economic penalties or rewards. The allocation factors should depend on size, location, and time evolution of the resources connected to the system. In the presence of distributed generation, the variety of the power flows in distribution systems calls for adopting mechanisms able to discriminate among the contributions that increase or reduce the total losses. Some loss allocation techniques already developed in the literature have shown consistent behavior. However, their application requires computing a set of additional quantities with respect to those provided by the distribution system power flow solved with the backward/forward sweep approach. This paper presents a new circuit-based loss allocation technique, based on the decomposition of the branch currents, specifically developed for radial distribution systems with distributed generation. The proposed technique is simple and effective and is only based on the information provided by the network data and by the power flow solution. Examples of application are shown to confirm its effectiveness. Index Terms--Branch current decomposition, distributed generation (DG), distribution systems, losses, loss allocation.

In this paper, we examine auction-based electricity markets from the viewpoint of a power company in order to evaluate the market design. Optimal trading strategies under uncertainty are developed by abolishing the widespread assumption that a single company has no influence on the market price. The resulting trading strategies explain the high prices and the high volatility observed in real electricity auction markets and show to what extent power companies can manipulate the market price. From these trading strategies, we derive critical points in market design and formulate necessary and sufficient conditions that characterize a competitive electricity auction market. Unfortunately, these conditions are far from being realizable in practice, from which follows that electricity auction markets cannot be competitive. Index Terms--Competition, double-sided auctions, electricity market, market design, market power, oligopoly, trading strategies, uniform-price auctions.

This paper derives appropriate decisions for load transfer among distribution feeders by switching operations to improve system operating performance by combining the load characteristics and the variations among customers as a result of temperature increases using a switching operation decision inference mechanism based on a colored Petri net (CPN) approach. A practical distribution system with 19 feeders, daily load profiles, and corresponding data on temperature sensitivity (TS) is used to perform computer simulations to demonstrate the effectiveness of the proposed methodology. It is concluded that the proposed CPN inference mechanism can enhance the system operating performance with the proper switching operation by considering the TS of customer power consumption served in each service zone of distribution feeders. Index Terms--Colored Petri net (CPN), feeder reconfiguration, load balance, load transfer, service restoration, switching operation, temperature sensitivity.

By integrating a genetic algorithm (GA) with a nonlinear interior point method (IPM), a novel hybrid method for the optimal reactive power flow (ORPF) problem is proposed in this paper. The proposed method can be mainly divided into two parts. The first part is to solve the ORPF with the IPM by relaxing the discrete variables. The second part is to decompose the original ORPF into two sub-problems: continuous optimization and discrete optimization. The GA is used to solve the discrete optimization with the continuous variables being fixed, whereas the IPM solves the continuous optimization with the discrete variables being constant. The optimal solution can be obtained by solving the two sub-problems alternately. A dynamic adjustment strategy is also proposed to make the GA and the IPM to complement each other and to enhance the efficiency of the hybrid proposed method. Numerical simulations on the IEEE 30-bus, IEEE 118-bus and Chongqing 161-bus test systems illustrate that the proposed hybrid method is efficient for the ORPF problem. Index Terms--Genetic algorithm (GA), interior point method (IPM), nonlinear programming, optimal reactive power flow (ORPF).

The modern power infrastructure has evolved from small isolated circuits into an expansive interconnected system that is dependant on multiple supporting infrastructures. One of the most significant and potentially detrimental supporting infrastructures to interact with power systems is telecommunications. Currently, there are no established analytic techniques that enable system operators or planners to analyze the interactions that occur at the seam between these two infrastructures. This paper presents a method for analyzing and assessing events that occur at the interface of the power and telecommunications infrastructures. Index Terms--Petri nets (PNs), power system communication, power system modeling, power systems.

A probabilistic method for a pool-based combined energy and reserve market, which considers both generators and interruptible loads (ILs), is proposed in this paper. We minimize generation production cost together with the cost associated with expected energy not supplied (EENS) due to outages of generating units and failures of ILs to supply the reserve when required. The proposed settlement scheme allocates equitably cost of reserve among generators and ILs. Given that the method takes into account reliability of individual generators and ILs, the proposed scheme provides incentives for all market participants to improve their performance. A number of case studies are carried out to illustrate the impact of participant's characteristics on the reserve cost allocation. Index Terms--Expected energy not supplied (EENS), interruptible load, probabilistic reserve, system risk.

In this paper, a technique based on interval arithmetic is presented for considering the uncertainties of the input parameters in the power flow solution of three-phase unbalanced radial distribution systems. The uncertainties in both the load demand and the feeder parameters have been considered. The results obtained from an interval arithmetic-based power flow solution have been compared with those obtained from repeated load flow simulations. Index Terms--Interval arithmetic, power flow, three-phase distribution system.

A cost-based approach is developed to study the economics of operation of the proton exchange membrane (PEM) fuel cell power plants (FCPP). This paper includes the operational cost, thermal recovery, power trade with the local grid, and hydrogen production. The cost-based approach is used to determine the optimal operational strategy that yields a minimum operating cost. The optimal operational strategy is achieved through the estimation of the hourly generated power, the amount of thermal power recovered from the FCPP to satisfy the thermal load, the amount of power trade with the local grid, and the amount of hydrogen that can be generated from the FCPP. An evolutionary programming-based technique is used to determine the optimal operational strategy. The strategy is tested using electrical and thermal load profiles. Results are encouraging and indicate the effectiveness of the proposed approach. Index Terms--Evolutionary programming, fuel cell, fuel cell cost-based approach, proton exchange membrane (PEM) fuel cell.

In this paper, an adaptive preconditioner is constructed for Jacobian-free Newton-GMRES(m) [JFNG(m)] methods, which is devised for solving coordination equations in distributed simulations of power systems. The preconditioner is updated during both Newton iterations and GMRES iterations by means of a rank-one update algorithm. The proposed preconditioned JFNG(m) is applied to power flow calculations for test. The results show that the adaptive preconditioner can enhance convergence of Newton-GMRES(m) iteration schemes greatly and has stronger robustness compared with other precondition methods. Moreover, the proposed method has strong parallelism and scalability, which makes it feasible to solve distributed simulation problems of power systems. Index Terms--Newton-GMRES(m), precondition, power flow.

As far as the electricity market is considered, both governments and private sector are interested in energy supply industry and so consider it essential to predict energy demand. Solution of the problem depends on availability of a model. This paper proposes a systematically developed model. It is based on a previously performed exogeneity investigation of various quantified variables. A certain nonlinear model among a collection of 100 models with different inputs is chosen as the most appropriate model. Structure of all nonlinear competing models is established according to logical conjunctive and disjunctive relationships between variables. Different combinations of the exogenous variables generate these models. At first, unacceptable models are put away applying coefficient sign significance criterion and error validity. An automated fuzzy decision-making process determines the winner model, which is a hybrid nonlinear model, among the other remaining models. Index Terms--Decision-making, dynamics, energy models, fuzzy systems, modeling, nonlinear systems, power demand, smoothing methods.

This paper investigates the use of the constraint reactive implicit coupling (CRIC) method for the engine of a continuation power flow program. Full Newton continuation power flow methods are robust and accurate but are computationally expensive. Fast decoupled methods provide accurate results and require less computational time, but their performance worsens at heavy loading conditions, where the system active/reactive power decoupling characteristics are lost. This paper makes use of the CRIC method, which preserves the decoupled power flow solution structure but better models the active/reactive coupling. Effective stopping criteria are proposed for the continuation method, which helps to speed up computation. Such stopping criteria are also applied for tracing QV curves for some practical Brazilian power systems, with all operating limits considered. Index Terms--Constraint reactive implicit coupling (CRIC) method, continuation methods, Newton method, power flow, QV curves, stopping criteria, voltage collapse.

This paper presents a systematic methodology to analyze the power loss of whole distribution system in Taipower. The total power delivered to the distribution system has been calculated according to the total power generation and power loss of transmission system. To enhance the efficiency for power loss analysis of voluminous distribution feeders, the artificial neural network (ANN)-based simplified power loss models have been developed for the overhead feeders and underground feeders, respectively. The three-phase load flow analysis is executed to find the sensitivity of feeder loss with the variation of power loading, conductor length, and total capacity of distribution transformers. By this way, the data set for neural network training is prepared to derive the ANN-based simplified power loss model. The power loss of each distribution feeder can be derived easily according to the key factors of hourly loading, feeder length, and transformer capacity. By integrating the power loss of all feeders, the power loss of whole distribution system is therefore obtained to estimate the operation efficiency of Taipower system. Index Terms--Artificial neural network (ANN) power loss model, automated mapping and facility management (AM/FM) system, distribution feeder loss analysis, load profile synthesis.