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Showing papers in "IEEE Transactions on Power Systems in 2008"


Journal ArticleDOI
TL;DR: In this article, a security-constrained unit commitment (SCUC) algorithm is proposed for managing the security of power system operation by taking into account the intermittency and volatility of wind power generation.
Abstract: This paper presents a security-constrained unit commitment (SCUC) algorithm which takes into account the intermittency and volatility of wind power generation. The UC problem is solved in the master problem with the forecasted intermittent wind power generation. Next, possible scenarios are simulated for representing the wind power volatility. The initial dispatch is checked in the subproblem and generation redispatch is considered for satisfying the hourly volatility of wind power in simulated scenarios. If the redispatch fails to mitigate violations, Benders cuts are created and added to the master problem to revise the commitment solution. The iterative process between the commitment problem and the feasibility check subproblem will continue until simulated wind power scenarios can be accommodated by redispatch. Numerical simulations indicate the effectiveness of the proposed SCUC algorithm for managing the security of power system operation by taking into account the intermittency and volatility of wind power generation.

869 citations


Journal ArticleDOI
TL;DR: In this article, an indirect algorithm based on the Beta pdf is proposed to obtain a more appropriate probability density function (pdf) of the wind power forecast error, which can be categorized as fat-tailed.
Abstract: Wind power forecast error usually has been assumed to have a near Gaussian distribution. With a simple statistical analysis, it can be shown that this is not valid. To obtain a more appropriate probability density function (pdf) of the wind power forecast error, an indirect algorithm based on the Beta pdf is proposed. Measured one-year time series from two different wind farms are used to generate the forecast data. Three different forecast scenarios are simulated based on the persistence approach. This makes the results comparable to other forecast methods. It is found that the forecast error pdf has a variable kurtosis ranging from 3 (like the Gaussian) to over 10, and therefore it can be categorized as fat-tailed. A new approximation function for the parameters of the Beta pdf is proposed because results from former publications could not be confirmed. Besides, a linear approximation is developed to describe the relationship between the persistence forecast and the related mean measured power. An energy storage system (ESS), which reduces the forecast error and smooths the wind power output, is considered. Results for this case show the usefulness of the proposed forecast error pdf for finding the optimum rated ESS power.

711 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the combined optimization of a wind farm and a pumped-storage facility from the point of view of a generation company in a market environment, and formulated the optimization model as a two-stage stochastic programming problem with two random parameters: market prices and wind generation.
Abstract: One of the main characteristics of wind power is the inherent variability and unpredictability of the generation source, even in the short-term. To cope with this drawback, hydro pumped-storage units have been proposed in the literature as a good complement to wind generation due to their ability to manage positive and negative energy imbalances over time. This paper investigates the combined optimization of a wind farm and a pumped-storage facility from the point of view of a generation company in a market environment. The optimization model is formulated as a two-stage stochastic programming problem with two random parameters: market prices and wind generation. The optimal bids for the day-ahead spot market are the ldquohere and nowrdquo decisions while the optimal operation of the facilities are the recourse variables. A joint configuration is modeled and compared with an uncoordinated operation. A realistic example case is presented where the developed models are tested with satisfactory results.

674 citations


Journal ArticleDOI
TL;DR: In this paper, a short-term forward electricity market-clearing problem with stochastic security is formulated to account for variable wind power generation sources, which allows greater wind power penetration without sacrificing security.
Abstract: In their attempt to cut down on greenhouse gas emissions from electricity generation, several countries are committed to install wind power generation up to and beyond the 10%-20% penetration mark. However, the large-scale integration of wind power represents a challenge for power system operations planning because wind power 1) cannot be dispatched in the classical sense; and 2) its output varies as weather conditions change. This warrants the investigation of alternative short-term power system operations planning methods capable of better coping with the nature of wind generation while maintaining or even improving the current reliability and economic performance of power systems. To this end, this paper formulates a short-term forward electricity market-clearing problem with stochastic security capable of accounting for nondispatchable and variable wind power generation sources. The principal benefit of this stochastic operation planning approach is that, when compared to a deterministic worst-case scenario planning philosophy, it allows greater wind power penetration without sacrificing security.

649 citations


Journal ArticleDOI
TL;DR: In this paper, a distributed automatic control approach is proposed to alleviate the voltage rise caused by active power injection in distribution networks with distributed generation, where the objective is not to control bus voltage but to guarantee that generator injections alone do not cause significant voltage rise.
Abstract: This paper addresses the problem of voltage rise mitigation in distribution networks with distributed generation. A distributed automatic control approach is proposed to alleviate the voltage rise caused by active power injection. The objective of the proposed approach is not to control bus voltage but to guarantee that generator injections alone do not cause significant voltage rise: a solution in which distribution network operators (DNOs) are kept to their traditional task of voltage regulation for load demand. The approach is discussed in the perspective of effectiveness and adequacy. Its consequences to DNO control effort are evaluated. Illustration is provided for a single feeder with stochastic generation and transformer on-load tap-changing voltage regulation.

613 citations


Journal ArticleDOI
TL;DR: In this article, the problem of finding an optimal generation dispatch and transmission topology to meet a specific inflexible load was formulated as a mixed-integer linear program, which employs binary variables to represent the state of the equipment and linear relationships to describe the physical system.
Abstract: In this paper, we formulate the problem of finding an optimal generation dispatch and transmission topology to meet a specific inflexible load as a mixed integer program. Our model is a mixed-integer linear program because it employs binary variables to represent the state of the equipment and linear relationships to describe the physical system. We find that on the standard 118-bus IEEE test case a savings of 25% in system dispatch cost can be achieved.

585 citations


Journal ArticleDOI
TL;DR: A vulnerability assessment framework to systematically evaluate the vulnerabilities of SCADA systems at three levels: system, scenarios, and access points is proposed based on cyber systems embedded with the firewall and password models, the primary mode of protection in the power industry today.
Abstract: Vulnerability assessment is a requirement of NERC's cybersecurity standards for electric power systems. The purpose is to study the impact of a cyber attack on supervisory control and data acquisition (SCADA) systems. Compliance of the requirement to meet the standard has become increasingly challenging as the system becomes more dispersed in wide areas. Interdependencies between computer communication system and the physical infrastructure also become more complex as information technologies are further integrated into devices and networks. This paper proposes a vulnerability assessment framework to systematically evaluate the vulnerabilities of SCADA systems at three levels: system, scenarios, and access points. The proposed method is based on cyber systems embedded with the firewall and password models, the primary mode of protection in the power industry today. The impact of a potential electronic intrusion is evaluated by its potential loss of load in the power system. This capability is enabled by integration of a logic-based simulation method and a module for the power flow computation. The IEEE 30-bus system is used to evaluate the impact of attacks launched from outside or from within the substation networks. Countermeasures are identified for improvement of the cybersecurity.

523 citations


Journal ArticleDOI
TL;DR: In this article, a generalized integer linear programming (ILP) formulation for PMU placement was proposed for cases including redundant PMUs placement, full observability and incomplete observability. But the problem of optimal placement of PMU for the redundant PMU, full-observability, and incomplete observable analysis needs to be studied, for various purposes and considerations.
Abstract: Based on the integer linear programming formulation proposed for optimal PMU placement, this paper presents a generalized integer linear programming formulation for cases including redundant PMU placement, full observability and incomplete observability. Due to accurate voltage phasor measurement and current phasor measurements provided by PUM units, the accuracy, redundancy and thus the robustness of state estimation will be enhanced with the integration of PMU measurements. The problem of optimal placement of PMU for the redundant PMU placement, full observability and incomplete observability analysis needs to be studied, for various purposes and considerations. The proposed modeling approach by the author in another paper, which models PMU placement as an integer linear programming problem, is extended and generalized to satisfy different needs. Cases with and without zero injection measurements are considered. Simulation results on different power systems show that the proposed algorithm can be used in practice.

499 citations


Journal ArticleDOI
TL;DR: In this paper, the authors quantified the capability of providing a short-term excess active power support of a commercial multi-megawatt variable speed wind turbine and generalized the findings by considering different wind turbine (WT) physical parameters in a wider range from the example case.
Abstract: This paper quantifies the capability of providing a short-term excess active power support of a commercial multi-megawatt variable speed wind turbine (VSWT) and generalizes the findings by considering different wind turbine (WT) physical parameters in a wider range from the example case. The paper also identifies some possible applications of it, in particular, in a hydro dominated system. To be able to quantify the system characteristic, a delay model of the studied hydro system is developed. Due to the fact that the initial power surge of a hydro turbine is opposite to that desired, the short-term extra active power support from a wind farm (WF) could be beneficial for a hydro dominated system in arresting the initial frequency fall, which corresponds to an improvement in the system temporary minimum frequency (TMF). The improvements in the TMF are calculated by using both the developed delay model and a detailed model, and the results show good agreement. It is shown that the WT under consideration can provide a 0.1 pu extra active power support for 10 s quite easily which is twice the Hydro-Quebec requirement.

494 citations


Journal ArticleDOI
TL;DR: This paper proposes to apply a novel self-organizing hierarchical particle swarm optimization (SOH_PSO) for the nonconvex economic dispatch (NCED) and shows that the proposed approach outperforms previous methods for NCED.
Abstract: The economic dispatch has the objective of generation allocation to the power generators in such a manner that the total fuel cost is minimized while all operating constraints are satisfied. Conventional optimization methods assume generator cost curves to be continuous and monotonically increasing, but modern generators have a variety of nonlinearities in their cost curves making this assumption inaccurate, and the resulting approximate dispatches cause a lot of revenue loss. Evolutionary methods like particle swarm optimization perform better for such problems as no convexity assumptions are imposed, but these methods converge to sub-optimum solutions prematurely, particularly for multimodal problems. To handle the problem of premature convergence, this paper proposes to apply a novel self-organizing hierarchical particle swarm optimization (SOH_PSO) for the nonconvex economic dispatch (NCED). The performance further improves when time-varying acceleration coefficients are included. The results show that the proposed approach outperforms previous methods for NCED.

484 citations


Journal ArticleDOI
TL;DR: In this paper, a method for optimal placement of phasor measurement units (PMUs) for complete observability of a power system for normal operating conditions, as well as for single branch outages is proposed.
Abstract: This paper proposes a method for optimal placement of phasor measurement units (PMUs) for complete observability of a power system for normal operating conditions, as well as for single branch outages. A binary search algorithm is used to determine the minimum number of PMUs needed to make the system observable. In case of more than one solution, a strategy is proposed to select the solution resulting in the most preferred pattern of measurement redundancy. The proposed method is used to benchmark the optimal PMU placement solutions for the IEEE 14-bus, IEEE 24-bus, IEEE 30-bus and New England 39-bus test systems. The proposed method is applied on a 298-bus system to determine the optimal placement of PMUs when conventional measurements are available.

Journal ArticleDOI
TL;DR: In this article, a voltage-power droop/frequency-reactive power boost (VPD/FQB) control scheme was proposed to allow multiple voltage source converters (VSCs) to operate in parallel in a VSC fed microgrid.
Abstract: This paper presents a voltage-power droop/frequency-reactive power boost (VPD/FQB) control scheme that allows multiple voltage source converters (VSCs) to operate in parallel in a VSC fed microgrid Each current controlled VSC in such a microgrid has its own VPD/FQB controller that sets its current references to regulate the voltage and frequency of a common microgrid bus By drooping the voltage reference of each controller against its real power output, multiple VPD/FQB controllers jointly regulate the microgrid voltage while sharing a common load power in proportion to a predetermined ratio Similarly, by boosting the frequency reference of each controller against its reactive power output, multiple VPD/FQB controllers jointly regulate the microgrid frequency while sharing the reactive load in proportion to a predetermined ratio The proposed control scheme can also operate in grid connected mode Experimental results are provided to validate the VPD/FQB control scheme

Journal ArticleDOI
Zhang Yun1, Zhou Quan1, Sun Cai-xin1, Lei Shaolan, Liu Yu-ming1, Song Yang1 
TL;DR: A model to forecast short-term load is established by combining the radial basis function (RBF) neural network with the adaptive neural fuzzy inference system (ANFIS) to improve forecasting accuracy and overcome the defects of the RBF network.
Abstract: With the appearance of electricity markets, the variation of the price of electricity will influence usage custom of electric energy. This will complicate short-term load forecasting and challenge the existing forecasting methods that are applied to a fixed-price environment. In regard to the influence of real-time electricity prices on short-term load, a model to forecast short-term load is established by combining the radial basis function (RBF) neural network with the adaptive neural fuzzy inference system (ANFIS). The model first makes use of the nonlinear approaching capacity of the RBF network to forecast the load on the prediction day with no account of the factor of electricity price, and then, based on the recent changes of the real-time price, it uses the ANFIS system to adjust the results of load forecasting obtained by RBF network. This system integration will improve forecasting accuracy and overcome the defects of the RBF network. As shown in this paper by the results of an example of factual forecasting, the model presented can work effectively.

Journal ArticleDOI
TL;DR: In this paper, the authors developed a systematic procedure of designing a centralized damping control system for power grid interarea oscillations putting emphasis on the signal selection and control system structure assignment.
Abstract: This paper develops a systematic procedure of designing a centralized damping control system for power grid interarea oscillations putting emphasis on the signal selection and control system structure assignment. Geometric measures of controllability/observability are used to select the most effective stabilizing signals and control locations. Line power flows and currents are found to be the most effective input signals. The synthesis of the controller is defined as a problem of mixed H 2/H infin output-feedback control with regional pole placement and is resolved by the linear matrix inequality (LMI) approach. A tuning process and nonlinear simulations are then used to modify the controller parameters to ensure the performance and robustness of the controller designed with linear techniques. The design process is tested on the New England 39-bus ten-machine system.

Journal ArticleDOI
TL;DR: In this paper, the authors presented an optimization approach to choose such systems and their operating schedules using Berkeley Lab's Distributed Energy Resources Customer Adoption Model (DER-CAM), extended to incorporate electrical and thermal storage options.
Abstract: The deployment of small ( < 1-2 MW ) clusters of generators, heat and electrical storage, efficiency investments, and combined heat and power (CHP) applications (particularly involving heat-activated cooling) in commercial buildings promises significant benefits but poses many technical and financial challenges, both in system choice and its operation; if successful, such systems may be precursors to widespread microgrid deployment. The presented optimization approach to choosing such systems and their operating schedules uses Berkeley Lab's Distributed Energy Resources Customer Adoption Model (DER-CAM), extended to incorporate electrical and thermal storage options. DER-CAM chooses annual energy bill minimizing systems in a fully technology-neutral manner. An illustrative example for a hypothetical San Francisco hotel is reported. The chosen system includes one large reciprocating engine and an absorption chiller providing an estimated 11% cost savings and 8% carbon emission reductions under idealized circumstances.

Journal ArticleDOI
TL;DR: In this article, the frequency response capability of the full converter variable speed wind turbine generator (FCWTG) with permanent magnet synchronous generator (PMSG) is investigated and a control scheme is developed that improves the frequency control performance.
Abstract: With an increased number of wind turbine generators (WTGs) connected to an electricity network the system operator may request that they participate in frequency control in the event of a sudden unbalancing of power generated and consumed on the system. In this paper the frequency response capability of the full converter variable speed wind turbine generator (FCWTG) with permanent magnet synchronous generator (PMSG) is investigated. A control scheme is developed that improves the frequency control performance, illustrating the importance of the initial active power output of the FCWTG. A method of carefully ending the frequency support of a wind farm is proposed and simulated. The resulting frequency control performance compares favorably to that of a conventional synchronous generator plant.

Journal ArticleDOI
TL;DR: In this paper, the authors developed an algorithm which uses known system topology information, together with PMU phasor angle measurements, to detect system line outages and provide an estimate of the pre-outage flow on the outaged line.
Abstract: Although phasor measurement units (PMUs) have become increasingly widespread throughout power networks, the buses monitored by PMUs still constitute a very small percentage of the total number of system buses. Our research explores methods to derive useful information from PMU data in spite of this limited coverage. In particular, we have developed an algorithm which uses known system topology information, together with PMU phasor angle measurements, to detect system line outages. In addition to determining the outaged line, the algorithm also provides an estimate of the pre-outage flow on the outaged line. To demonstrate the effectiveness of our approach, the algorithm is demonstrated using simulated and real PMU data from two systems - a 37-bus study case and the TVA control area.

Journal ArticleDOI
TL;DR: This paper presents a new approach to nontechnical loss (NTL) analysis for utilities using the modern computational technique extreme learning machine (ELM) and online sequential-ELM (OS- ELM) algorithms are both used to achieve an improved classification performance and to increase accuracy of results.
Abstract: This paper presents a new approach to nontechnical loss (NTL) analysis for utilities using the modern computational technique extreme learning machine (ELM). Nontechnical losses represent a significant proportion of electricity losses in both developing and developed countries. The ELM-based approach presented here uses customer load-profile information to expose abnormal behavior that is known to be highly correlated with NTL activities. This approach provides a method of data mining for this purpose, and it involves extracting patterns of customer behavior from historical kWh consumption data. The results yield classification classes that are used to reveal whether any significant behavior that emerges is due to irregularities in consumption. In this paper, ELM and online sequential-ELM (OS-ELM) algorithms are both used to achieve an improved classification performance and to increase accuracy of results. A comparison of this approach with other classification techniques, such as the support vector machine (SVM) algorithm, is also undertaken and the ELM performance and accuracy in NTL analysis is shown to be superior.

Journal ArticleDOI
TL;DR: Computational results show that simultaneously taking into account both feeder reconfiguration and capacitor placement is more effective than considering them separately.
Abstract: This paper aims to study distribution system operations by the ant colony search algorithm (ACSA). The objective of this study is to present new algorithms for solving the optimal feeder reconfiguration problem, the optimal capacitor placement problem, and the problem of a combination of the two. The ACSA is a relatively new and powerful swarm intelligence method for solving optimization problems. It is a population-based approach that uses exploration of positive feedback as well as ldquogreedyrdquo search. The ACSA was inspired from the natural behavior of ants in locating food sources and bring them back to their colony by the formation of unique trails. Therefore, through a collection of cooperative agents called ldquoants,rdquo the near-optimal solution to the feeder reconfiguration and capacitor placement problems can be effectively achieved. In addition, the ACSA applies the state transition, local pheromone-updating, and global pheromone-updating rules to facilitate the computation. Through simultaneous operation of population agents, process stagnation can be effectively prevented. Optimization capability can be significantly enhanced. The proposed approach is demonstrated using two example systems from the literature. Computational results show that simultaneously taking into account both feeder reconfiguration and capacitor placement is more effective than considering them separately.

Journal ArticleDOI
TL;DR: In this paper, a simple optimal placement algorithm of phasor measurement units (PMU) by using integer linear programming is presented, where the measurement placement problems under both conventional power flow and injection measurements are formulated as an integer linear program which saves the CPU computation time greatly.
Abstract: This letter presents a simple optimal placement algorithm of phasor measurement units (PMU) by using integer linear programming. Cases with and without conventional power flow and injection measurements are considered. The measurement placement problems under those cases are formulated as an integer linear programming which saves the CPU computation time greatly. Simulation results show that the proposed algorithm can be used in practice.

Journal ArticleDOI
TL;DR: A model is presented that takes into account the head effects on power production through an enhanced linearization technique, and turns out to be more general and efficient than those available in the literature.
Abstract: The paper deals with a unit commitment problem of a generation company whose aim is to find the optimal scheduling of a multiunit pump-storage hydro power station, for a short term period in which the electricity prices are forecasted. The problem has a mixed-integer nonlinear structure, which makes very hard to handle the corresponding mathematical models. However, modern mixed-integer linear programming (MILP) software tools have reached a high efficiency, both in terms of solution accuracy and computing time. Hence we introduce MILP models of increasing complexity, which allow to accurately represent most of the hydroelectric system characteristics, and turn out to be computationally solvable. In particular we present a model that takes into account the head effects on power production through an enhanced linearization technique, and turns out to be more general and efficient than those available in the literature. The practical behavior of the models is analyzed through computational experiments on real-world data.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed an integrated model for assessing the impact of interdependency of electricity and natural gas networks on power system security, which incorporates the natural gas network constraints into the optimal solution of security-constrained unit commitment.
Abstract: This paper proposes an integrated model for assessing the impact of interdependency of electricity and natural gas networks on power system security. The integrated model incorporates the natural gas network constraints into the optimal solution of security-constrained unit commitment. The natural gas network is modeled by daily and hourly limits on pipelines, sub-areas, plants, and generating units. The application of fuel diversity (e.g., generating units with fuel switching capability) is presented as an effective peak shaving strategy for natural gas demand which could hedge price volatilities of natural gas and electric power. The proposed model can be used by a vertically integrated utility for the commitment and dispatch of generating units and the allocation of natural gas for the next day utilization. The proposed model can also be used for measuring the security of social services by modeling the interdependency of natural gas and electric power system infrastructures. If the proposed model is used by GENCOs, gas constraints will be submitted to electricity markets as energy constraints. Illustrative examples show the impact of natural gas supply infrastructure on the economic operation of a vertically integrated utility. The examples also discuss the impact of generating units with fuel switching capability on the power system security when the supply of natural gas is limited.

Journal ArticleDOI
TL;DR: In this paper, an adaptive wavelet neural network (AWNN) was proposed for short-term price forecasting in the electricity markets, where a commonly used Mexican hat wavelet has been chosen as the activation function for hidden-layer neurons of feed-forward neural network.
Abstract: In a competitive electricity market, an accurate forecasting of energy prices is an important activity for all the market participants either for developing bidding strategies or for making investment decisions. An adaptive wavelet neural network (AWNN) is proposed in this paper for short-term price forecasting (STPF) in the electricity markets. A commonly used Mexican hat wavelet has been chosen as the activation function for hidden-layer neurons of feed-forward neural network (FFNN). To demonstrate the effectiveness of the proposed approach, day-ahead prediction of market clearing price (MCP) of Spain market, which is a duopoly market with a dominant player, and locational marginal price (LMP) forecasting in PJM electricity market, are considered. The forecasted results clearly show that AWNN has good prediction properties compared to other forecasting techniques, such as wavelet-ARIMA, multi-layer perceptron (MLP) and radial basis function (RBF) neural networks as well as recently proposed fuzzy neural network (FNN).

Journal ArticleDOI
TL;DR: An algorithm based on particle swarm optimization (PSO) which minimizes the deviations of rescheduled values of generator power outputs from scheduled levels and handles the binding constraints by a technique different from the traditional penalty function method is proposed.
Abstract: Power system congestion is a major problem that the system operator (SO) would face in the post-deregulated era. Therefore, investigation of techniques for congestion-free wheeling of power is of paramount interest. One of the most practiced and an obvious technique of congestion management is rescheduling the power outputs of generators in the system. However, all generators in the system need not take part in congestion management. Development of sound formulation and appropriate solution technique for this problem is aimed in this paper. Contributions made in the present paper are twofold. Firstly a technique for optimum selection of participating generators has been introduced using generator sensitivities to the power flow on congested lines. Secondly this paper proposes an algorithm based on particle swarm optimization (PSO) which minimizes the deviations of rescheduled values of generator power outputs from scheduled levels. The PSO algorithm, reported in this paper, handles the binding constraints by a technique different from the traditional penalty function method. The effectiveness of the proposed methodology has been analyzed on IEEE 30-bus and 118-bus systems and the 39 -bus New England system.

Journal ArticleDOI
TL;DR: In this paper, an economic analysis of the inclusion of pumped storage in a small island system that has abundant renewable energy available but that at times cannot accept all of this power because of limits imposed by security criteria is presented.
Abstract: This work describes an economic analysis of the inclusion of pumped storage in a small island system that has abundant renewable energy available but that at times cannot accept all of this power because of limits imposed by security criteria. The question of whether or how much pumped storage to include is addressed by formulating a linear programming optimization problem. The stochastic nature of load and renewable production is addressed using scenarios developed through fuzzy clustering. Both the unit capacity in MW and the reservoir storage capacity in MWh are optimized, and optimal operating strategies for the scenarios are produced. Results showed that including pumped storage can be an effective means of allowing larger penetration of intermittent renewable energy sources, improving both the dynamic security and the economic operation of a test system. Including the dynamic security criteria in the economic question of dimensioning the pumped storage unit proved to make a significant difference in the optimal pumped storage capacity.

Journal ArticleDOI
TL;DR: In this paper, a new voltage instability risk indicator based on local phasor measurements at fast sampling rate is proposed, based on real-time computation of the Thevenin equivalent impedance of the classic electrical circuit given by an equivalent generator connected to an equivalent load impedance through an equivalent connecting impedance.
Abstract: This paper proposes a new voltage instability risk indicator based on local phasor measurements at fast sampling rate. The effectiveness of the indicator is analyzed at EHV load and ldquotransitrdquo buses. The risk criterion is based on the real-time computation of the Thevenin equivalent impedance of the classic electrical circuit given by an equivalent generator connected to an equivalent load impedance through an equivalent connecting impedance. The main contribution of the paper is the innovating algorithm utilized on the real-time adaptive identification of the Thevenin voltage and impedance equivalents. The algorithm performance is shown through a detailed sensitivity analysis. The paper presents important numerical results from the actual Italian EHV network.

Journal ArticleDOI
TL;DR: In this paper, the authors developed a new framework for designing and assessing such an advanced direct load control program with the objective of minimizing end-user discomfort and is formulated as an optimization problem.
Abstract: The advent of advanced sensor technology and the breakthroughs in telecommunication open up several new possibilities for demand-side management. More recently, there has been greater interest from utilities as well as system operators in utilizing load as a system resource through the application of new technologies. With the wider application of demand-side management, there is an increasing emphasis on control of loads with minimum disruption. This paper develops a new framework for designing as well as assessing such an advanced direct load control program with the objective of minimizing end-user discomfort and is formulated as an optimization problem. With a fairly general setup for demand-side management, a simulation-based framework is developed for the stochastic optimization problem. Next, using this framework, insights into the effect of different parameters and constraints in the model on load control are developed.

Journal ArticleDOI
TL;DR: In this paper, a robust and efficient method for solving TSCOPF problems based on differential evolution (DE) is developed, which is a new branch of evolutionary algorithms with strong ability in searching global optimal solutions of highly nonlinear and nonconvex problems.
Abstract: Consideration of transient stability constraints in optimal power flow (OPF) problems is increasingly important because modern power systems tend to operate closer to stability boundaries due to the rapid increase of electricity demand and the deregulation of electricity markets. Transient stability constrained OPF (TSCOPF) is however a nonlinear optimization problem with both algebraic and differential equations, which is difficult to be solved even for small power systems. This paper develops a robust and efficient method for solving TSCOPF problems based on differential evolution (DE), which is a new branch of evolutionary algorithms with strong ability in searching global optimal solutions of highly nonlinear and nonconvex problems. Due to the flexible properties of DE mechanism, the hybrid method for transient stability assessment, which combines time-domain simulation and transient energy function method, can be employed in DE so that the detailed dynamic models of the system can be incorporated. To reduce the computational burden, several strategies are proposed for the initialization, assessment and selection of solution individuals in evolution process of DE. Numerical tests on the WSCC three-generator, nine-bus system and New England ten-generator, 39-bus system have demonstrated the robustness and effectiveness of the proposed approach. Finally, in order to deal with the large-scale system and speed up the computation, DE is parallelized and implemented on a Beowulf PC-cluster. The effectiveness of the parallel DE approach is demonstrated by simulations on the 17-generator, 162-bus system.

Journal ArticleDOI
TL;DR: In this article, a mixed-integer linear programming (LP) formulation for the long-term transmission expansion planning problem in a competitive pool-based electricity market is presented, where investment and operating costs, transmission losses and generator offers, and demand bids are considered.
Abstract: This paper presents a mixed-integer linear programming (LP) formulation for the long-term transmission expansion planning problem in a competitive pool-based electricity market. To achieve optimal expansion planning while modeling market functioning, we define a number of scenarios based on the future demand in the system and we simulate the maximization of the aggregate social welfare. Investment and operating costs, transmission losses and generator offers, and demand bids are considered. We propose to use a set of metrics to rate the effect of the expansion on the generators, demands, and the system as a whole. The proposed model is applied to the Garver six-bus system and to the IEEE 24-bus reliability test system. Simulation results can be interpreted in economic terms based on the values of the metrics obtained for different scenarios, parameters, and topologies.

Journal ArticleDOI
TL;DR: In this paper, a method of calculating the communication delay (latency) for measurements and control signals in a power system is shown, based on a dedicated communication channel for control signals.
Abstract: 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.