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This paper proposes an optimization-based method of planning reactive power control for electric transmission systems to endow them with the capability of being reconfigured to a secure configuration under a list of contingencies. The overall objective function is to minimize the installation cost of new controls such as mechanically switched capacitors, while satisfying the requirements of voltage stability margin and voltage magnitude under a contingency list. The backward/forward search algorithm with linear complexity is used to select candidate locations for switched capacitors. Optimal locations and amounts of new switch controls are obtained by solving a sequence of mixed integer programming problems. The modified New England 39-bus system and a North American power system with 6358 buses are adopted to illustrate the effectiveness of the proposed method. Index Terms--Mixed integer programming, reactive power planning, reconfiguration, voltage stability.

To study the competitive behavior among individual generating companies (GENCOs), an incomplete information game model is proposed in this paper in which each GENCO is modeled as an agent. Each agent makes strategic generation capacity expansion decisions based on its incomplete information on other GENCOs. The formation of this game model falls into a bi-level optimization problem. The upper level of this problem is the GENCOs' own decision on optimal planning strategies and energy/reserve bidding strategies. The lower-level problem is the ISO's market clearing problem that minimizes the cost to supply the load, which yields price signals for GENCOs to calculate their own payoffs. A co-evolutionary algorithm combined with pattern search is proposed to optimize the search for the Nash equilibrium of the competition game with incomplete information. The Nash equilibrium is obtained if all GENCOs reach their maximum expected payoff assuming the planning strategies of other GENCOs' remain unchanged. The physical withholding of capacity is considered in the energy market and the Herfindahl-Hirschman Index is utilized to measure the market concentration. The competitive behaviors are analyzed in three policy scenarios based on different market rules for reserve procurement and compensation. Index Terms--agent modeling, generation expansion, market design, market power, noncooperative game, physical withholding, power system planning.

We propose a component model for the scheduling of combined-cycle gas turbine (CCGT) units by mixed-integer programming (MIP) in which combustion turbines (CTs) and steam turbines (STs) are modeled as individual units. The hourly schedule of CCGT based on the component model is compared with that of the mode model. The modeling of modes, which includes a combination of CTs and STs, would require certain approximations for representing fuel input-power output curves, ramping rate limits, minimum operating time limits, etc. The approximations can result in sub-optimal schedules. Furthermore, the commitment and dispatch of CCGTs based on the mode model will require a real-time dispatch to individual CT and ST components of CCGT. In comparison, the mode modeling approximations will no longer be required in the component model as individual CTs and STs are modeled and dispatched. The enhancement tools such as duct burners, foggers, and peak firing for increasing the CCGT output can be easily modeled in the component model. Case studies show that the proposed component model is effective for representing CCGTs, and verify that the proposed component model can potentially save CCGT operating costs. Numerical simulations in this paper also demonstrate the application of the component model of CCGT to schedule a cogeneration unit. Index Terms--Combined-cycle gas turbine, component model, mixed-integer programming, mode model, short-term unit commitment, state transition diagram.

In the framework of liberalized electricity markets, distributed generation and controllable demand have the opportunity to participate in the real-time operation of transmission and distribution networks. This may be done by using the virtual power plant (VPP) concept, which consists of aggregating the capacity of many distributed energy resources (DER) in order to make them more accessible and manageable across energy markets. This paper provides an optimization algorithm to manage a VPP composed of a large number of customers with thermostatically controlled appliances. The algorithm, based on a direct load control (DLC), determines the optimal control schedules that an aggregator should apply to the controllable devices of the VPP in order to optimize load reduction over a specified control period. The results define the load reduction bid that the aggregator can present in the electricity market, thus helping to minimize network congestion and deviations between generation and demand. The proposed model, which is valid for both transmission and distribution networks, is tested on a real power system to demonstrate its applicability. Index Terms--Air-conditioning, load management, optimal control.

Flexible ac Transmission Systems (FACTS) play an important role in improving the transfer capability and stability of a power system. In the application of voltage-sourced converter (VSC)-based FACTS controllers, it is important to study how a VSC impacts the flows in a power system. In this paper, we investigate this flow control problem using two sensitivity approaches, one using an injected voltage source formulation and the other an equivalent impedance formulation. The applications of sensitivity analysis for line active power redispatch and for new series VSC siting in a 1673-bus system are presented. Index Terms--Equivalent impedance, FACTS controllers, sensitivity analysis, voltage source model, voltage-sourced converter.

Complexities of computer program codes for Newton--Raphson load flow (NRLF) analysis are usually enhanced during power flow modeling of an interline power flow controller (IPFC). This is due to the fact that the contributions of the series converters of the IPFC are needed to be accounted for while computing bus power injections and Jacobian matrix elements. Also, the IPFC real power injection term along with its associated Jacobian matrix call for new codes to be written. In this paper an advanced IPFC model is proposed to address this issue, wherein an existing power system installed with IPFC(s) is transformed into an augmented equivalent network without any IPFC. To obtain the solution of the original network containing IPFC(s), the augmented network can easily be solved by reusing the existing NRLF codes, as this network is now devoid of any IPFC. Consequently, the complexities of the computer program codes are reduced substantially. Various practical device limit constraints of the IPFC can also be taken into account by the proposed model. Index Terms--Flexible ac transmission systems (FACTS), interline power flow controller (IPFC), Newton power flow.

In order to be able to successfully apply interline power flow controllers (IPFCs) for power-system transient-stability improvement and for the damping of oscillations, proper control strategies should be applied to these devices. The basis for the implementation of such a strategy that is proposed in this paper is to know the energy function of a power system that includes IPFCs. Already-known energy functions that proved to be suitable for an electric-power system do not include such a device. Therefore, in this paper an energy function that considers the IPFC's action in the form of a supplement to the already-known structure-preserving energy functions was constructed. Furthermore, the strategy for implementing the newly developed IPFC energy functions in order to ensure a globally optimum control strategy in the Lyapunov sense is presented. The results of the numerical examples show that the magnitudes of the IPFC's series-injected voltages remain set to their maximum values and that only the angles of these voltages change, similar to the 'bang-bang' control strategies proposed for some other FACTS devices. Index Terms--FACTS devices, interline power flow controller (IPFC), Lyapunov energy function, power system control, power system dynamic stability.

In this paper, a robust sensor and actuator fault detection and isolation (FDI) method based on unknown input observers (UIO) is adopted and applied to the load frequency control loops of interconnected power systems. Changes in load demand are regarded as the unknown disturbances in the system and the designed UIOs and thus the proposed method are robust to these disturbances. Using selected different sets of measured variables in the UIO design, simulations are performed for the dynamical model of a power control system composed of two areas. As we distinguish the cases for successful and unsuccessful sensor and controller FDI, it is shown that the proposed scheme is able to detect and isolate sensor and controller faults for proper selections of measured variables. By using residuals generated by the UIOs, the designed 'fault detection and isolation logic' system shows the operator which sensor or controller is faulty. Hence the faulty sensor or controller can be replaced by a healthy one for a more reliable operation. Index Terms--Fault diagnosis, load frequency control, power system operation.

A new approach to improve the reconfiguration operations of distribution systems is presented in two papers. In this first part n economic dispatch (ED) through radialization method for medium voltage (MV) distribution networks with several alternative supply points and several energy prices is presented. The optimization criterion is based on energy purchase cost minimization to supply both the load and the loss. The ED through radialization (EDR) method assesses the economic impact of different energy prices for alternative supply points on the operative radial topology for a specific load level. Capacity limits of supply points and MV lines are considered, as well as the quality technical product using ac power flow calculations. The results obtained for a distribution network widely used in the literature show the effectiveness of the proposed methodology. The second part presents a methodology to determine the optimal reconfiguration plan for short and medium terms. This approach integrates purchase and switching costs associated to the reconfiguration plan. Index Terms--Ac power flow, economic dispatch, energy price, loss, minimization costs, network reconfiguration, radialization.

This paper presents a very efficient, two-stage method for the distribution system reconfiguration for loss minimization. The efficiency of the method stems from the use of real power loss sensitivity with respect to the impedances of the candidate branches. The proposed method uses these sensitivities in the first stage. A branch exchange procedure is used in the second stage to refine the solution. Results for five test systems have been obtained with the proposed method in order to demonstrate the effectiveness of the algorithm. Index Terms--Distribution system, loss minimization, network reconfiguration, sensitivity.

In this paper, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings identified by the authors. In particular, the presence of a paradox in the classical loss partitioning approach, based on the use of the phase-by-phase difference between the input and output complex power, is highlighted. The conditions for performing effective loss partitioning without the occurrence of the paradox are thus established. The corresponding results are then used to extend the branch current decomposition loss allocation method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Several numerical examples on a three-phase line with grounded neutral and on the modified IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework. Index Terms--Distributed generation, distribution systems, loss allocation, loss partitioning, losses, paradox, unbalanced systems.

In this paper, two different approaches are applied to the Hydro-Quebec network in order to select the most effective signals to damp inter-area oscillations. The damping is obtained by static var compensator (SVC) and synchronous condenser (SC) modulation. The robustness analysis, the simulations, and statistical results show, unambiguously, that in the case of wide-area signals, the geometric approach is more reliable and useful than the residues approach. In fact, this study shows that the best robustness and performances are always obtained with the stabilizer configuration using the signals recommended by the geometric approach. In addition, the results confirm that wide-area control is more effective than local control for damping inter-area oscillations. Index Terms--Compensator, control loop selection, geometric measures, inter-area oscillations, power system stabilizer, residues, wide-area control.

A novel power system frequency control strategy is designed in this paper, which is mainly used to improve the stability of the islanding power system. Detecting the change of circuit breaker status, it is feasible to identify the serious accidents, for instance, a generator outage or disconnection from main grids, and so on. The balanceable power before disturbance and the capacity of the removed power can be used to calculate the power deficiency. Then, appropriate load can be shed adaptively. In the subsequent regulating process, adapting to the various stages of frequency variation, the concepts of rough-adjusting step and fine-adjusting step are proposed to obtain a balance between shedding loads quickly and refining the load shed in every step. The concept of proportional-integral-differential (PID) is introduced to design a closed-loop control strategy to trace frequency variation, with which a balance between restraining the sharp drop of frequency effectively and releasing the reserved system capacity thoroughly can be obtained. Moreover, the frequency recovery curve can be optimized and the dead zone of control during the frequency rising stage can be avoided. Compared with the conventional under-frequency loading shedding (UFLS) schemes, the effectiveness of the control strategy presented has been verified by EMTDC simulation tests. Index Terms--Emergency pick-up step, fine-adjusting step, proportional-integral-differential (PID) closed-loop control, rough-adjusting step, under-frequency loading shedding (UFLS).

State estimation uses measurements to obtain important power system operating information ('states'). This paper uses a tabular representation to quantify the effects of measurement failure (i.e., sensor failure or measurement communications failure). The concept of a measurement outage table is introduced to evaluate the state estimator performance under measurement failure conditions. The concept of a condition indicator is used and this includes a study of certain elements of the singular spectrum of the state estimator process matrix. Examples are shown to illustrate the concept. The analysis also shows that using condition indicators for measurement placement may improve the response of the state estimator under measurement failure conditions. Index Terms--Condition number, eigenvalues, phasor measurement unit (PMU), power system measurements, singular values, state estimation, synchrophasor.

In distribution systems, network reconfiguration and capacitor control, generally, are used to reduce real power losses and to improve voltage profiles. Since both capacitor control and network reconfiguration belong to the complicated combinatorial optimization problems, it is hard to combine them efficiently for better optimization results. In this paper, a joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. To achieve high performance and high efficiency of the proposed algorithm, an improved adaptive genetic algorithm (IAGA) is developed to optimize capacitor switching, and a simplified branch exchange algorithm is developed to find the optimal network structure for each genetic instance at each iteration of capacitor optimization algorithm. The solution algorithm has been implemented into a software package and tested on a 119-bus distribution system with very promising results. Index Terms--Capacitor control, genetic algorithm, joint optimization, loss minimum, network reconfiguration.

This paper deals with distribution network (DN) reconfiguration for loss minimization. To solve this combinatorial problem, a genetic algorithm (GA) is considered. In order to enhance its ability to explore the solution space, efficient genetic operators are developed. After a survey of the existing DN topology description methods, a theoretical approach based on the graph and matroid theories (graphic matroid in particular) is considered. These concepts are used in order to propose new intelligent and effective GA operators for efficient mutation and crossover well dedicated to the DN reconfiguration problem. All resulting individuals after GA operators are claimed to be feasible (radial) configurations. Moreover, the presented approach is valid for planar or nonplanar DN graph topologies and avoids tedious mesh checks for the topology constraint validation. The proposed method is finally compared to some previous topology coding techniques used by other authors. The results show smaller or at least equal power losses with considerably less computation effort. Index Terms--Distribution network (DN), genetic algorithm (GA), graph theory, matroid, minimal loss reconfiguration, planar graph, spanning tree.

A method of calculating the communication delay (latency) for measurements and control signals in a power system is shown. The basis of the calculation is a dedicated communication channel for control signals. The time delay calculation is examined using a dynamic equivalent of the Western Electricity Coordinating Council transmission system. The impact on control system response is discussed. The application given is a wide area control system for interarea mode damping. Results demonstrate that control signal latency can degrade the performance of controls in a wide area control system. Index Terms--Damping, latency, network delay, power system control, power system stabilizer, queuing, wide area control systems, wide area measurement systems.

A load model is one of the most important elements in power system simulation and control. Recently, the constant impedance, constant current, and constant power load in combination with the induction motor load have been widely used as the composite load model, whose parameters are all identified from the field measurements in measurement-based load modeling practices so far. However, there is virtually no research conducted on whether all these parameters could really be identified. This paper investigates the possibility on reducing the number of composite load model parameters to be identified from field measurements. This paper first shows that direct application of the IEEE load motor parameters in the composite load model may be inadequate on describing the load dynamics over different operating status. Then the perturbation method is used to derive the trajectory sensitivities of the equivalent motor parameters, based on which the reduction on the identified parameters of the composite load model is presented. Two cases of measurement-based load modeling in North China and Northeast China are studied to illustrate the validity of the reduction method. It is shown that the reduction does not lose the model's capability on describing the load dynamics. The reduction on the number of identified parameters not only provides a possible way to solve the multi-valued load model problem based on the current practices on measurement-based load modeling, but it also facilitates building of the load model with more components included in it. Meanwhile, reducing the identified parameters reduces the identification time; thus, the proposed strategy significantly enhances the efficiency of the load modeling work. Index Terms--Composite load model, field measurements, power system stability, trajectory sensitivity.

This paper presents a new method for transmission loss allocation. The method is based on tracing the complex power flow through the network and determining the share of each load on the flow and losses through each line. Transmission losses are taken into consideration during power flow tracing. Unbundling line losses is carried out using an equation, which has a physical basis, and considers the coupling between active and reactive power flows as well as the cross effects of active and reactive power on active and reactive losses. A tracing algorithm which can be considered direct to a good extent, as there is no need for exhaustive search to determine the flow paths as these are determined in a systematic way during the course of tracing. Results of application of the proposed method are also presented. Index Terms--Deregulation, open access transmission, power flow tracing, transmission loss allocation.

This paper first investigates a local voltage and reactive power control (local control) in a distribution system based on local control of on-load tap-changer (OLTC), substation capacitors, and feeder capacitors, and how the presence of induction machine based distributed generation (DG) affects it. A proper coordination among those available voltage and reactive power control equipment to minimize losses in the distribution system, with and without DG, is formulated. Secondly, a combined local and remote voltage and reactive power control (local-remote control), which is based on automated remote adjustment to the local control in order to minimize the losses even more, is proposed. The automated remote adjustment in the local-remote control is also intended to keep the operating constraints fulfilled all the time, which cannot be achieved by using the local control when DG is present in the system. The OLTC and substation capacitors are assumed to be remotely controllable, while the feeder capacitors are not. DG with both constant power and varying power are investigated. Index Terms--Capacitor, distributed generation, distribution system, induction machine, losses, on-load tap-changer, reactive power control, voltage control.

The aim of the Spanish voltage control ancillary service is the minimization of the transmission losses while keeping the system away from voltage instability. The latter target can be achieved maintaining an adequate voltage profile in normal operating condition and assuring that generators exhibit enough reactive margins that guarantee that the system voltages will remain under acceptable values in case of contingencies. The service has been designed in Spain to be partially mandatory and partially subject to payment based on market-driven rules and performance evaluation. In the annual time scope, the optional reactive offers submitted by the service suppliers are selected analyzing a number of forecasted scenarios. This paper explains the implementation of the Spanish voltage control ancillary service (VCAS) that is provided by generators in the annual time scope. For this purpose, a mixed-integer linear programming optimal power flow (OPF) is used. Reactive bids of generators are modeled within each scenario by modifying the reactive limits of the generators. The use of the proposed OPF in the assignment of the voltage control ancillary service is explained and illustrated using actual scenarios of the Spanish power system. Index Terms--Ancillary services (AS), linear programming (LP), optimal power flow (OPF), power loss reduction, reactive power dispatch, VAR/voltage control.

The introduction of distributed generation (DG) is leading to a fundamental change in how distribution networks are utilized and viewed. Distribution networks are now used as a means to connect geographically dispersed energy sources to the electricity system, thereby converting what were originally energy delivery networks, to networks used both for the delivery and harvesting of energy. This paper presents a methodology which maximizes the amount of energy that may be reaped from a given area, while taking account of the available energy resources, connection costs, losses, frequency of constraint breaches, and other technical constraints. The optimal energy allocation is determined for a sample section of network, illustrating the implementation of the methodology and the scope for non firm access to the distribution network. Index Terms--Dispersed storage and generation, energy resources, linear programming, losses, power distribution planning.

In rural power systems, the automatic voltage regulators (AVRs) help to reduce energy losses and to improve the energy quality of electric utilities, compensating the voltage drops through distribution fines. In order to help electric companies in the decision-making process, this paper presents a method to define the optimal location of a set of AVRs in electric distribution networks. The optimization process is treated as a multiobjective problem considering the total power losses and the voltage drops in the system as the objectives to be optimized. A novel technique called micro genetic algorithm ([micro]GA) is used to solve the multiobjective problem. This technique is capable of finding, in a very efficient way, the Pareto optimal solutions, giving the decision maker a set of possible (trade-off) solutions from which to choose. Index Terms--Evolutionary algorithms, losses, micro genetic algorithms, multiobjective optimization, optimization methods, power distribution, voltage control, voltage regulators.

The accuracy of the load model has great effects on power system stability analysis and control. Based on our practice in China on modeling load from field measurements, this paper systematically develops a measurement-based composite load model. Principles guiding the load modeling practice are discussed based on detailed analysis on stochastic characteristics of the modeling procedure. The structure of the measurement-based composite load model is presented. A multicurve identification technique is described to derive parameters. The generalization capability of this built load model is also investigated in this paper. Two cases are studied to illustrate the accuracy of the developed load model on describing the load dynamic characteristics in the actual power system. Index Terms--Load modeling, measurement approach, power system stability.

The representation of load dynamic characteristics remains an area of great uncertainty and has become a limiting factor for power system analysis and control. The random nature of the load makes load modeling a very difficult problem, which becomes even more challenging when the field measurements increase and the recorded dataset becomes large. This paper proposes a novel concept of modeling load based on support vectors (SVs) of load data. A three-stage procedure to find SVs of the recorded load dataset is presented. Then the load model is built on the SVs. Although the model is derived from only a small subset of the original dataset, it has a strong generalization capability to describe dynamics of the whole dataset. However, the computational burden on the modeling process is much relieved since only a small subset of data is involved. The proposed method also answers the question on how data should be grouped and how many load models should be built as data are accumulated. This paper infers that, although the data space where the load varies seems indefinite and big, its characteristic can be captured and modeled in a much smaller subspace. The presented method is shown to be effective by the case study on Hushitai substation. Index Terms--Load modeling, measurement approach, support vectors (SVs).

This paper is a system study guide for the correction of voltage dips due to large motor startups with Static Var Compensators (SVCs). The method utilizes time simulations, which are an important aid in the equipment design and specification. The paper illustrates the process of setting-up a computer model and performing time simulations. The study process is demonstrated through an example, the Shawnee feeder in the Niagara Mohawk Power Corporation service area.

This paper addresses the control problem of a power system which is operating in a restorative state, i.e., a power system that has 109t some of its load and/or has separated into electrical islands as a result of a major system disturbance. By means of a hierarchical interactive approach, this control problem is decomposed here into three layers or time-hierarchies (i.e., adaptive, optimizing, and direct); restorative control actions are then determined and executed by the appropriate layer according to the time frame available for doing so. The paper describes the restoration control problem in power systems, and provides the conceptual details of the hierarchical interactive approach proposed for its solution.

In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its dc link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC- network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly.

In this letter, we point out an ambiguity in the mathematical formulation of the optimization problem for the system loss using loss sensitivities treated in a recent IEEE publication and provide a concrete mathematical interpretation of the optimization procedure to clear up the ambiguity. Index Terms--Mathematical formulation, optimization, system loss.