Showing papers in "IEEE Transactions on Power Systems in 1993"
TL;DR: In this article, a genetic-based algorithm was proposed to solve an economic dispatch problem for valve point discontinuities, which utilizes payoff information of candidate solutions to evaluate their optimality.
Abstract: A genetics-based algorithm is proposed to solve an economic dispatch problem for valve point discontinuities. The algorithm utilizes payoff information of candidate solutions to evaluate their optimality. Thus, the constraints of classical LaGrangian techniques on unit curves are circumvented. The formulations of an economic dispatch computer program using genetic algorithms are presented and the program's performances using two different encoding techniques are compared. The results are verified for a sample problem using a dynamic programming technique. >
1,224 citations
Journal Article•
TL;DR: In this paper, the authors summarized the state of the art of representation of power system loads for dynamic performance analysis purposes, including definition of terminology, discussion of the importance of load modeling, important considerations for different types of loads and different kinds of analyses Typical load model data and methods for acquiring data are reviewed.
Abstract: This paper summarizes the state of the art of representation of power system loads for dynamic performance analysis purposes It includes definition of terminology, discussion of the importance of load modeling, important considerations for different types of loads and different types of analyses Typical load model data and methods for acquiring data are reviewed A list of recent references is included
749 citations
TL;DR: In this article, the placement of a minimal set of phasor measurement units (PMUs) so as to make the system measurement model observable, and thereby linear, is investigated.
Abstract: The placement of a minimal set of phasor measurement units (PMUs) so as to make the system measurement model observable, and thereby linear, is investigated. A PMU placed at a bus measures the voltage as well as all the current phasors at that bus, requiring the extension of the topological observability theory. In particular, the concept of spanning tree is extended to that of spanning measurement subgraph with an actual or a pseudomeasurement assigned to each of its branches. The minimal PMU set is found through a dual search algorithm which uses both a modified bisecting search and a simulated-annealing-based method. The former fixes the number of PMUs while the latter looks for a placement set that leads to an observable network for a fixed number of PMUs. In order to accelerate the procedure, an initial PMU placement is provided by a graph-theoretic procedure which builds a spanning measurement subgraph according to a depth-first search. From computer simulation results for various test systems it appears that only one fourth to one third of the system buses need to be provided with PMUs in order to make the system observable. >
728 citations
TL;DR: In this article, the implementation of both point of collapse (PoC) and continuation methods for the computation of voltage collapse points (saddle-node bifurcations) in large AC/DC power systems is described.
Abstract: The implementation of both point of collapse (PoC) methods and continuation methods for the computation of voltage collapse points (saddle-node bifurcations) in large AC/DC power systems is described. The performance of these methods is compared for real systems of up to 2158 buses. Computational details of the implementation of the PoC and continuation methods are detailed, and the unique problems encountered due to the presence of high-voltage direct-current (HVDC) transmission, area interchange power control, regulating transformers, and voltage and reactive power limits are discussed. The characteristics of a robust PoC power flow program are presented, and its application to detection and solution of voltage stability problems is demonstrated. >
614 citations
TL;DR: In this article, a simple dynamic load model is proposed which captures the usual nonlinear steady-state behavior plus load recovery and overshoot, and a simple but important dynamic voltage stability analysis is developed based on the model.
Abstract: Motivated by projects in Sweden on voltage stability analysis and associated load modeling, a simple dynamic load model is proposed which captures the usual nonlinear steady-state behavior plus load recovery and overshoot. The parameters of the model can be related to physical devices depending on the time zone following a disturbance. A simple but important dynamic voltage stability analysis is developed based on the model. >
450 citations
TL;DR: The proposed method was applied to practical 51-bus and 224-bus systems to show its feasibility and capabilities and the concept is quite promising and useful in the coming computer age.
Abstract: This paper presents a new approach to optimal reactive power planning based on a genetic algorithm. Many outstanding methods to this problem have been proposed in the past. However, most these approaches have the common defect of being caught to a local minimum solution. The integer problem which yields integer value solutions for discrete controllers/banks still remain as a difficult one. The genetic algorithm is a kind of search algorithm based on the mechanics of natural selection and genetics. This algorithm can search for a global solution using multiple paths and treat integer problems naturally. The proposed method was applied to practical 51-bus and 224-bus systems to show its feasibility and capabilities. Although this method is not as fast as sophisticated traditional methods, the concept is quite promising and useful in the coming computer age. >
444 citations
TL;DR: In this paper, a new algorithm using the primal-dual interior point method with the predictor-corrector for solving nonlinear optimal power flow (OPF) problems is presented.
Abstract: A new algorithm using the primal-dual interior point method with the predictor-corrector for solving nonlinear optimal power flow (OPF) problems is presented. The formulation and the solution technique are new. Both equalities and inequalities in the OPF are considered and simultaneously solved in a nonlinear manner based on the Karush-Kuhn-Tucker (KKT) conditions. The major computational effort of the algorithm is solving a symmetrical system of equations, whose sparsity structure is fixed. Therefore only one optimal ordering and one symbolic factorization are involved. Numerical results of several test systems ranging in size from 9 to 2423 buses are presented and comparisons are made with the pure primal-dual interior point algorithm. The results show that the predictor-corrector primal-dual interior point algorithm for OPF is computationally more attractive than the pure primal-dual interior point algorithm in terms of speed and iteration count. >
422 citations
TL;DR: In this article, the authors presented a new method to solve the problem of economic power dispatch with piecewise quadratic cost function using the Hopfield neural network, which is much simpler and the results are very close to those of the numerical method.
Abstract: The authors present a new method to solve the problem of economic power dispatch with piecewise quadratic cost function using the Hopfield neural network. Traditionally one convex cost function for each generator is assumed. However, it is more realistic to represent the cost function as a piecewise quadratic function rather than one convex function. In this study, multiple intersecting cost functions are used for each unit. Through case studies, the possibility of the application of the Hopfield neural network to the economic load dispatch problem with general nonconvex cost functions was shown. The proposed approach is much simpler and the results are very close to those of the numerical method. >
422 citations
TL;DR: In this article, the authors proposed an algorithm to consider the ramp characteristics in starting up and shutting down the generating units as well as increasing and decreasing power generation, considering the inclusion of ramping constraints in both unit commitment and economic dispatch.
Abstract: The authors propose an algorithm to consider the ramp characteristics in starting up and shutting down the generating units as well as increasing and decreasing power generation. They consider the inclusion of ramping constraints in both unit commitment and economic dispatch. Since implementing ramp-rate constraints is a dynamic process, dynamic programming (DP) is a proper tool to treat this problem. To overcome the computational expense which is the main drawback of DP, this study initially employs artificial intelligence techniques to produce a unit commitment schedule which satisfies all system and unit operation constraints except unit ramp-rate limits. Then, a dynamic procedure is used to consider the ramp properties as units are started up and shut down. According to this adjustment, maximum generating capabilities of units will change the unit operation status instead of following a step function. Finally, a dynamic dispatch procedure is adopted to obtain a suitable power allocation which incorporates the unit generating capability information given by unit commitment and unit ramping constraints, as well as the economical considerations. Two examples are presented to demonstrate the efficiency of the method. >
395 citations
TL;DR: In this paper, the use of static voltage stability indices based on a singular value decomposition of the power flow Jacobian matrix and matrices derived from the Jacobian matrices is discussed.
Abstract: The use of static voltage stability indices based on a singular value decomposition of the power flow Jacobian matrix and matrices derived from the Jacobian matrix is discussed. It is shown that such indices, together with the singular vectors, contain substantial and important information about the proximity to voltage instability and also about critical buses and disturbances from a voltage instability point of view. This is done by a theoretical analysis of the linear power flow equations and an analysis from model power systems as well as realistic power systems (1033 nodes). It is argued that indices based on these matrices are useful for the system analyst in planning and operations planning. >
377 citations
TL;DR: In this paper, a new controller for the generator excitation system is described that uses a combination of feedback linearizing and the observation decoupled state space, which can be realistically implemented using only local measurements, and whose performance is consistent with respect to changes in network configuration, loading and power transfer conditions.
Abstract: A new controller for the generator excitation system is described that uses a combination of feedback linearizing and the observation decoupled state space. This creates a controller that can be realistically implemented using only local measurements, and whose performance is consistent with respect to changes in network configuration, loading and power transfer conditions. The control differs in this respect from linear constant-gain controllers such as power system stabilizers, whose characteristics can vary significantly with changes in operating conditions. The design is well-suited to a multimachine setting, in that it is not based on an infinite-bus approximation. Simulations were performed on a 38-bus reduced modelof the Northeast Power Coordinating Council system and benchmarked against simulations in which automatic voltage regulators with power system stabilizers were substituted in place of the nonlinear controls. >
TL;DR: In this paper, the relations between currents, voltages and power quantities are analyzed in the time domain using the FBD method and treatment in the frequency domain on the basis of Fourier series expansion of the time functions is also possible.
Abstract: Starting from the most general case of m-wire unbalanced multiphase power systems with unsymmetrical loads under nonsinusoidal conditions, it is explained how the relations between currents, voltages and power quantities are analyzed in the time domain using the FBD method. Treatment in the frequency domain on the basis of Fourier series expansion of the time functions is also possible. It is shown that components of the total nonactive currents may be compensated without any time delay and without changing the collective instantaneous power. Rules are given for deriving simple equivalent circuits with m-equally structured branches from given voltages and currents. >
TL;DR: In this article, the authors discuss voltage stability analysis of power systems using static and dynamic techniques, using a small test system, results of time domain simulations are presented to clarify the phenomenon of voltage instability and to better understand modeling requirements.
Abstract: The authors discuss voltage stability analysis of power systems using static and dynamic techniques. Using a small test system, results of time domain simulations are presented to clarify the phenomenon of voltage instability and to better understand modeling requirements. The same system is then analyzed using a static approach in which modal analysis is performed using system conditions, or snapshots, which approximate different stages along the time domain trajectory. The results obtained using the dynamic and static methods are compared and shown to be consistent. >
TL;DR: In this article, the results of a study to investigate whether the ANN model is system dependent, and/or case dependent, are presented and the effectiveness of a next 24 h ANN model in predicting 24-hour load profile at one time was compared with the traditional next 1-hour ANN model.
Abstract: The artificial neural network (ANN) technique for short-term load forecasting (STLF) has been proposed previously. In order to evaluate ANNs as a viable technique for STLF, one has to evaluate the performance of ANN methodology for practical considerations of STLF problems. The authors make an attempt to address these issues. The results of a study to investigate whether the ANN model is system dependent, and/or case dependent, are presented. Data from two utilities are used in modeling and forecasting. In addition, the effectiveness of a next 24 h ANN model in predicting 24 h load profile at one time was compared with the traditional next 1 h ANN model. >
TL;DR: In this paper, the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed.
Abstract: Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented. >
TL;DR: In this paper, a static VAr generator (SVG) using self-commutated inverters of 80 MVA capacity was developed and successfully applied to an annual 154 KV power system to stabilize the power system.
Abstract: A static VAr generator (SVG) using self-commutated inverters of 80 MVA capacity was developed and successfully applied to an annual 154 KV power system to stabilize the power system. The SVG consists of 48 pulse multiple inverters whereby gate turn-off (GTO) thyristors are applied. After installing it at a power system site, a field test was conducted to confirm the system stabilizing effect. The test results displayed the expected performance, and the SVG was proven to be effective power system stabilizer. The outline of the 80 MVA SVG, technical features, and the test results are described. >
TL;DR: In this paper, a nonconvex decision space is decomposition into a small number of subsets such that each of the associated dispatch problems is either infeasible or one that can be directly solved via the conventional Lagrangian relaxation approach.
Abstract: A method is described for solving the reserve constrained economic dispatch problem when some of the online generating units have prohibited operating zone(s). For a unit with prohibited zone(s), the zone(s) divide the operating region between the minimum generation limit (Pmin) and the maximum generation limit (Pmax) into disjoint convex subregions. These disjoint subregions form a nonconvex decisions space and the associated economic dispatch problem is thus a nonconvex optimization problem. As a result, the conventional Lagrangian relaxation (LR) approach (e.g. the lambda - delta iterative approach) cannot be applied directly. The method proposed decomposes the nonconvex decision space into a small number of subsets such that each of the associated dispatch problems is either infeasible or one that can be directly solved via the conventional LR approach. Based on the decomposition, the optimal solution is the least costly one among all the feasible solutions of the associated dispatch problems. Examples are also given to illustrate the proposed method. >
TL;DR: In this paper, the authors proposed new iterative and direct methods to compute load powers at which bifurcation occurs and which are locally closest to the current operating load powers.
Abstract: Voltage collapse and blackout can occur in an electric power system when load powers vary so that the system loses stability in a saddle node bifurcation. The authors propose new iterative and direct methods to compute load powers at which bifurcation occurs and which are locally closest to the current operating load powers. The distance in load power parameter space to this locally closest bifurcation is an index of voltage collapse. The pattern of load power increase need not be predicted; instead the index is a worst case load power margin. The computations are illustrated in the six-dimensional load power parameter space of a five bus power system. The normal vector and curvature of a hypersurface of critical load powers at which bifurcation occurs are also computed. The sensitivity of the index to parameters and controls is easily obtained from the normal vector. >
TL;DR: In this article, a generalized model for short-term load forecasting is proposed, which combines features from knowledge-based and statistical techniques, and it is based on a generalization model for the weather-load relationship.
Abstract: A recently developed algorithm for short-term load forecasting is generalized. The algorithm combines features from knowledge-based and statistical techniques. It is based on a generalized model for the weather-load relationship which makes it site-independent. Weather variables are investigated, and their relative effect on the load is reported. The algorithm is also fairly robust and inherently updatable, and it provides a systematic method for operator intervention if necessary. This property makes it especially suitable for application in conjunction with demand side management (DSM) programs. The algorithm uses pairwise comparison to quantify categorical variables, and then utilizes regression to obtain the least-squares estimation of the load. The technique has been tested using data from four different sites in Virginia, Massachusetts, Florida, and Washington. The average absolute weekday forecast errors range from 1.22% to 2.7% over all four seasons in a year. >
TL;DR: In this article, a methodology for expansion planning of power systems under uncertainty in factors such as demand growth, fuel cost, delay in project completion, and financial constraints is described, and case studies within the Brazilian system are presented.
Abstract: A methodology is described for expansion planning of power systems under uncertainty in factors such as demand growth, fuel cost, delay in project completion, and financial constraints The approach draws upon three classes of techniques: decomposition and stochastic optimization provide the basic framework, and allow an implicit representation of alternative investment strategies; decision analysis is used to represent the dynamic aspects of decision-making as uncertainties are resolved over time; and hedging objectives from tradeoff analysis help select flexible and resilient expansion strategies. Case studies within the Brazilian system are presented and discussed. >
TL;DR: In this paper, the existence of the strange attractor is confirmed by calculation of its Lyapunov exponents and by its broad-band spectrum, and some implications of this analysis are discussed.
Abstract: Chaotic behavior has been observed in computer simulations for a simple power system over a range of loading conditions. The existence of the chaos, also called a strange attractor, is confirmed by calculation of its Lyapunov exponents and by its broad-band spectrum. Some implications of this analysis are discussed. >
TL;DR: In this article, a slow-coherency based network partitioning technique which groups generators and load buses simultaneously into several coherent areas is presented, which is useful for system reduction and identification of weak links for calculations involving network decouplings.
Abstract: The authors present a slow-coherency based network partitioning technique which groups generators and load buses simultaneously into several coherent areas. The technique uses the slow eigenbasis matrix which is extended to include load buses. A simple method of calculating the closeness of each row eigenvector to the reference row eigenvectors is used for grouping the load buses with the respective reference machine. The grouping information is useful for system reduction and identification of weak links for calculations involving network decouplings. The grouping method is illustrated using test systems and large practical systems. >
TL;DR: In this paper, the authors conducted a study on the Alaskan railbelt system to examine the hydrothermal power system response after the hydroelectric power units at Bradley Lake are installed.
Abstract: Studies have been conducted on the Alaskan Railbelt System to examine the hydrothermal power system response after the hydroelectric power units at Bradley Lake are installed. The models and data for the generating units for the initial studies were not complete. Typical models were used, but their response appeared to be faster than judged by operating experience. A testing program was felt to be necessary so that accurate models could be obtained for the dynamic simulation studies. The testing method used for the combustion turbine governors, the models derived from tests, and comparison of those models with typical models are discussed. Simulation results revealed that the typical models were more optimistic. >
TL;DR: In this paper, a theory for analyzing power system damping enhancement by application of static VAr compensators (SVCs) has been developed using the equal area criterion, where the SVC reactive power output at discrete points is determined from the power deviation on a transmission line.
Abstract: A theory for analyzing power system damping enhancement by application of static VAr compensators (SVCs) has been developed using the equal area criterion. Some fundamental issues, such as the effect of SVCs on a power system, how to control an SVC to improve system damping, and the differences between continuous and discontinuous control of SVC reactive power to achieve the maximum damping improvement, are discussed. A discontinuous SVC reactive power output at discrete points is determined from the power deviation on a transmission line. Time-domain simulations of the application of this approach to a one-machine system to increase swing oscillation damping and to a four-machine system to increase the damping of an interarea oscillation mode demonstrate that the theory and method can be applied to solve practical power system damping problems. >
TL;DR: In this article, an interactive computer environment is used to estimate the parameters of a seasonal multiplicative autoregressive (AR) model encountered during power system load forecasting, which is applied to predict the Nova Scotia Power Corporation's 168 lead time hourly load.
Abstract: Suboptimal least squares or iteratively reweighted least-squares (IRWLS) procedures for estimating the parameters of a seasonal multiplicative autoregressive (AR) model encountered during power system load forecasting are proposed. The method involves using an interactive computer environment to estimate the parameters of a seasonal multiplicative AR process. The method comprises five major computational steps. The first determines the order of the seasonal multiplicative AR process, and the second uses the least squares or the IRWLS to estimate the optimal nonseasonal AR model parameters. In the third step one obtains the intermediate series by back forecast, which is followed by using the least squares or the IRWLS to estimate the optimal seasonal AR parameters. The final step uses the estimated parameters to forecast future load. The method is applied to predict the Nova Scotia Power Corporation's 168 lead time hourly load. The results obtained are documented and compared with results based on the Box and Jenkins method. >
TL;DR: In this article, a tool based on the determination of critical modes is proposed to determine the most suitable sites for system reinforcement in the vicinity of the point of collapse, which does not rely on base case linearizations.
Abstract: The location of SVC (static VAr compensators) and other types of shunt compensation devices for voltage support is an important practical question. This paper considers a tool based on the determination of critical modes. Critical modes are computed by studying the system modes in the vicinity of the point of collapse. System participation factors for the critical mode are used to determine the most suitable sites for system reinforcement. Because the method does not rely on base case linearizations, the method is able to properly consider all system limits and nonlinear effects. The paper tests the proposed method by performing an assessment of the impact of the addition of static VAr compensators to a 1380 bus model of the BC Hydro system. >
TL;DR: In this paper, a model for short-term operation planning for a hydrothermal power system is supplemented with a wind power model and the results include an estimation of whether there is a deficit or excess of instantaneous, fast, or slow reserves during each hour of the planning period.
Abstract: A method for studying the effect of wind power on power system reserve margins, need of extra resources, etc. is presented. A conventional model for short-term operation planning for a hydrothermal power system is supplemented with a wind power model. The wind power model includes the forecast of total wind power generation and the uncertainty of the forecast. The conventional hydro-thermal model is extended to take into account load forecast uncertainty and reserve margins of the generation units. The requirements of instantaneous, fast, and slow reserves, depending on possible forced outages of thermal units and uncertain load and wind speed forecasts etc., are calculated together with the available capacities of the corresponding reserve type. The results include an estimation of whether there is a deficit or excess of instantaneous, fast, or slow reserves during each hour of the planning period. A numerical example shows an application of the method to the Swedish power system. >
TL;DR: In this paper, a probabilistic model for the active power produced and the reactive power absorbed by wind turbines equipped with induction generators is developed which takes into account the probability of short-term wind velocity forecasts.
Abstract: A probabilistic model for the active power produced and the reactive power absorbed by wind turbines (WTs) equipped with induction generators is developed which takes into account the probabilistic nature of short-term wind velocity forecasts. The model is incorporated in a radial distribution load flow program which allows probabilistic modeling of loads at the MV/LV substation level and of voltage regulator effects at the beginning of the MV distribution feeder. Using this program probabilistic short- and medium-term predictions of the power flows at the various sections of the feeder and of voltage profiles at all nodes of the network are obtained. >
TL;DR: In this paper, the development of dynamic load models using the measurement approach for the Taipower system is described. But the authors focus on the use of the measured data from an online transient recording system to develop dynamic load model structures.
Abstract: Accurate dynamic load models allow more precise calculations of power system controls and stability limits, which are critical in the planning and operation of power systems. The development of dynamic load models using the measurement approach for the Taipower system are described. Two dynamic load model structures are developed. A procedure for applying a set of measured data from an online transient recording system to develop dynamic load models for the Taipower system is described. A technique based on the concept of confidence interval is used to validate the developed high-order load model structure. Case studies are also presented. >
TL;DR: In this article, the authors deal with the use of successive linear programming (SLP) for the solution of the security-constrained economic dispatch (SCED) problem.
Abstract: The authors deal with the use of successive linear programming (SLP) for the solution of the security-constrained economic dispatch (SCED) problem. They tutorially describe an interior point method (IPM) for the solution of linear programming (LP) problems, discussing important implementation issues that really make this method far superior to the simplex method. A study of the convergence of the SLP technique and a practical criterion to avoid oscillatory behavior in the iteration process are also proposed. A comparison of the proposed method with an efficient simplex code (MINOS) is carried out by solving SCED problems on two standard IEEE systems. The results show that the interior point technique is reliable, accurate, and more than two times as fast as the simplex algorithm. >