Showing papers in "IEEE Transactions on Power Systems in 1995"
TL;DR: In this article, a three-phase power flow solution method for real-time analysis of primary distribution systems is presented, with the emphasis on modeling of dispersed generation (PV nodes), unbalanced and distributed loads, and voltage regulators and shunt capacitors with automatic local tap controls.
Abstract: This paper presents a three-phase power flow solution method for real-time analysis of primary distribution systems. This method is a direct extension of the compensation-based power flow method for weakly meshed distribution systems from single phase to three-phase, with the emphasis on modeling of dispersed generation (PV nodes), unbalanced and distributed loads, and voltage regulators and shunt capacitors with automatic local tap controls. The method proposed here is capable of addressing these modeling challenges while still maintaining a high execution speed required for real-time application in distribution automation systems. The paper also includes test results from the application of a computer program developed based on the proposed method to large primary electric distribution systems. >
818 citations
TL;DR: The main advantages of CPFLOW over repetitive power flow calculations are its computational speed and reliability as well as its wide applicability.
Abstract: In this paper, a computer package called CPFLOW, which is a comprehensive tool for tracing power system steady-state stationary behavior due to parameter variations, is presented. The variations include general bus real and/or reactive loads, area real and/or reactive loads, or system-wide real and/or reactive loads, and real generation at P-V buses (e.g. determined by economic dispatch or participation factor). The main advantages of CPFLOW over repetitive power flow calculations are its computational speed and reliability as well as its wide applicability. A detailed description of the implementation regarding the predictor, corrector, step-size control and parameterizations employed in CPFLOW is presented. CPFLOW has comprehensive modeling capability and can handle power systems up to 12000 buses. For an illustrative purpose, CPFLOW is applied to a 3500-bus power system with a comprehensive set of operational limits and controls. >
647 citations
TL;DR: In this article, a new genetic approach for solving the economic dispatch problem in large-scale power systems is presented, where the chromosome contains only an encoding of the normalized system incremental cost in this encoding technique.
Abstract: This paper presents a new genetic approach for solving the economic dispatch problem in large-scale power systems. A new encoding technique is developed. The chromosome contains only an encoding of the normalized system incremental cost in this encoding technique. Therefore, the total number of bits of chromosome is entirely independent of the number of units. The salient feature makes the proposed genetic approach attractive in large and complex systems which other methodologies may fail to achieve. Moreover, the approach can take network losses, ramp rate limits, and prohibited zone avoidance into account because of genetic algorithm's flexibility. Numerical results on an actual utility system of up to 40 units show that the proposed approach is faster and more robust than the well-known lambda-iteration method in large-scale systems.
583 citations
Journal Article•
TL;DR: The goal of this paper is to promote better load modeling and advanced load modeling, and to facilitate data exchange among users of various production-grade simulation programs.
Abstract: The authors recommend standard load models for power flow and dynamic simulation programs. The goal of this paper is to promote better load modeling and advanced load modeling, and to facilitate data exchange among users of various production-grade simulation programs. Flexibility of modeling is an important consideration. For transient stability, longer-term dynamics, and small-disturbance stability programs, the authors recommend the structure of multiple load types connected to a load bus. Load types are static including discharge lighting, induction motors, synchronous motors, and transformer saturation. For each load type, multiple models may be connected to the bus. For longer-term dynamics programs, a model for LTC transformers is also recommended.
561 citations
TL;DR: The augmented Lagrangian relaxation method enhanced by the decomposition and coordination techniques avoids oscillations associated with piece-wise linear cost functions and is fast and efficient in dealing with numerous power system constraints.
Abstract: This paper proposes a new approach based on augmented Lagrangian relaxation for short term generation scheduling problems with transmission and environmental constraints. In this method, the power system constraints, e.g. load demand, spinning reserve, transmission capacity and environmental constraints, are relaxed by using Lagrangian multipliers, and quadratic penalty terms associated with power system load demand balance are added to the Lagrangian objective function. Then, the decomposition and coordination technique is used, and nonseparable quadratic penalty terms are replaced by linearization around the solution obtained from the previous iteration. In order to improve the convergence property, the exactly convex quadratic terms of decision variables are added to the objective function as strongly convex, differentiable and separable auxiliary functions. The overall problem is decomposed into N subproblems, multipliers and penalty coefficients are updated in the dual problem and power system constraints are satisfied iteratively. The corresponding unit commitment subproblems are solved by dynamic programming, and the economic dispatch with transmission and environmental constraints is solved by an efficient network flow programming algorithm. The augmented Lagrangian relaxation method enhanced by the decomposition and coordination techniques avoids oscillations associated with piece-wise linear cost functions. Numerical results indicate that the proposed approach is fast and efficient in dealing with numerous power system constraints. >
484 citations
TL;DR: In this article, the authors presented a new algorithm for studying the load shedding and generation reallocation problem in emergencies where a portion of the transmission system is disabled and an AC power solution cannot be found for the overloaded system.
Abstract: This paper outlines the optimization problem of real and reactive power, and presents the new algorithm for studying the load shedding and generation reallocation problem in emergencies where a portion of the transmission system is disabled and an AC power solution cannot be found for the overloaded system. The paper describes a novel and efficient method and algorithm to obtain the optimal shift in power dispatch related to contingency states or overload situations in power system operation and planning phases under various objectives such as economy, reliability and environmental conditions. The optimization procedures basically utilize linear programming with bounded variables and it incorporates the techniques of the Section Reduction Method and the Third Simplex Method. The validity and effectiveness of the algorithm is verified by means of two examples: a 10-bus system and the IEEE 30-Bus, six generators system. >
442 citations
TL;DR: A three-phase distribution system state estimation algorithm is proposed in this paper, where the normal equation method is used to compute the real-time states of distribution systems modeled by their actual a-b-c phases.
Abstract: A three-phase distribution system state estimation algorithm is proposed in this paper. The normal equation method is used to compute the real-time states of distribution systems modeled by their actual a-b-c phases. A current based formulation is introduced and compared with other formulations. Observability analysis for the proposed distribution system state estimation is discussed. Test results indicate that the normal equation method is applicable to the distribution system state estimation and the current based rectangular form formulation is suitable for this application. >
432 citations
TL;DR: Concepts are described which provide design engineers with the insight to control performance and the understanding needed to ensure the secure operation of the bulk transmission system.
Abstract: The design of controllers sited in the transmission network for damping interarea power oscillations requires several types of analytical tools and field verification methods. Probably the most important aspect of such control design is the selection of proper feedback measurements from the network. This paper describes concepts which provide design engineers with the insight to control performance and the understanding needed to ensure the secure operation of the bulk transmission system. Specific attention is directed to procedures for selecting feedback signals. >
385 citations
TL;DR: A branch-current-based three-phase state estimation (SE) method for distribution systems is proposed and it is shown that distribution systems can be reduced without much loss of accuracy in SE.
Abstract: A branch-current-based three-phase state estimation (SE) method is proposed for distribution systems. The method is tailored for distribution feeders with a few loops. The method is computationally more efficient than the conventional node voltage-based SE methods. To further improve the computational efficiency, it is shown that distribution systems can be reduced without much loss of accuracy in SE. >
372 citations
TL;DR: In this article, an evolutionary programming (EP) method was applied to optimal reactive power dispatch and voltage control for large-scale power systems, and the proposed method has been evaluated on the IEEE 30-bus system.
Abstract: This paper is concerned with application of evolutionary programming (EP) to optimal reactive power dispatch and voltage control of power systems. Practical implementation of the EP for global optimization problems of large-scale power systems has been considered. The proposed EP method has been evaluated on the IEEE 30-bus system. Simulation results, compared with those obtained using a conventional gradient-based optimization method, are presented to show the potential of application of the proposed method to power system economical operations. >
340 citations
TL;DR: In this article, a simulated annealing approach to the long-term transmission expansion planning problem is presented, which is a hard, large scale combinatorial problem and is compared with a more conventional optimization technique based on mathematical decomposition with a zero-one implicit enumeration procedure.
Abstract: This paper presents a simulated annealing approach to the long term transmission expansion planning problem which is a hard, large scale combinatorial problem. The proposed approach has been compared with a more conventional optimization technique based on mathematical decomposition with a zero-one implicit enumeration procedure. Tests have been performed on three different systems. Two smaller systems for which optimal solutions are known have been used to tune the main parameters of the simulated annealing process. The simulated annealing method has then been applied to a larger example system for which no optimal solutions are known: as a result an entire family of interesting solutions have been obtained with costs about 7% less than the best solutions known for that particular example system.
TL;DR: In this article, the authors identify likely deregulation scenarios, identify the technical issues associated with load frequency control, and identify technical solutions, such as standards and algorithms, needed for the operation of this key component of national infrastructure in the face of profound structural changes.
Abstract: Open transmission access is a legal requirement in the United States, but is not fully implemented. Discussion of deregulation has so far focused principally on the tariff structure for transmission access, but operating the power system in this new environment will present significant problems of an almost purely technical nature. Something as simple as frequency control becomes challenging when implemented in the competitive, distributed control environment that true third party wheeling creates. This paper seeks to identify likely deregulation scenarios, identify the technical issues associated with load frequency control, and identify technical solutions, such as standards and algorithms, needed for the operation of this key component of national infrastructure in the face of profound structural changes.
TL;DR: In this article, the authors describe the application of marginal cost based pricing in the Chilean power system and the difficulties faced in allocating the supplement among parties involved, and formulate alternative methods for defining the allocation.
Abstract: The application of marginal costing to transmission pricing in open access schemes requires the collection of a supplement to finance the transmission systems. The paper describes the application of marginal cost based pricing in the Chilean power system and the difficulties faced in allocating the supplement among parties involved. Alternative methods for defining the allocation are formulated. Generalized generation and load distribution factors for cost allocation are formulated and implemented. The methods are applied to allocate payments for transmission services provided by the transmission network and by a distribution company. >
TL;DR: In this article, a generalized version of the unit commitment problem is formulated, which can treat minimum up-and down-time constraints, power flow constraints, line flow limits, voltage limits, reserve constraints, ramp limits, and total fuel and energy limits on hydro and thermal power generating units.
Abstract: The authors formulate a generalized version of the unit commitment problem that can treat minimum up- and down-time constraints, power flow constraints, line flow limits, voltage limits, reserve constraints, ramp limits, and total fuel and energy limits on hydro and thermal power generating units. They propose an algorithm for this problem, based on Lagrangian decomposition, and demonstrate the algorithm with reference to a simple model system. >
TL;DR: In this paper, a genetic-based algorithm is used to solve a power system economic dispatch (ED) problem, which utilizes payoff information of perspective solutions to evaluate optimality, and the constraints of classical LaGrangian techniques on unit curves are eliminated.
Abstract: A genetic-based algorithm is used to solve a power system economic dispatch (ED) problem. The algorithm utilizes payoff information of perspective solutions to evaluate optimality. Thus, the constraints of classical LaGrangian techniques on unit curves are eliminated. Using an economic dispatch problem as a basis for comparison, several different techniques which enhance program efficiency and accuracy, such as mutation prediction, elitism, interval approximation and penalty factors, are explored. Two unique genetic algorithms are also compared. The results are verified for a sample problem using a classical technique. >
TL;DR: In this article, the development and utilization of an annual chronological load curve for each load bus in a composite generation and transmission system and a sequential Monte Carlo simulation approach for composite system reliability assessment are presented.
Abstract: The paper illustrates the development and utilization of an annual chronological load curve for each load bus in a composite generation and transmission system and a sequential Monte Carlo simulation approach for composite system reliability assessment. Antithetic variates as a variance reduction technique has been applied to the simulation model to increase the efficiency of the simulation. An approximate method using a load duration curve of the system load and an enumeration process have been applied to the developed load model and the results are compared in this paper. >
TL;DR: New aggregation algorithms for obtaining reduced order power networks when coherent generators are aggregated will decrease the stiffening effect and produce, for the same coherent machine groups, aggregate networks with improved inter-area mode approximations.
Abstract: This paper presents new aggregation algorithms for obtaining reduced order power networks when coherent generators are aggregated. The generation terminal bus aggregation algorithm in the EPRI DYNRED software tends to stiffen the reduced order network during the aggregation process, thus increasing the frequencies of inter-area modes. The inertial and slow coherency aggregations will decrease the stiffening effect and produce, for the same coherent machine groups, aggregate networks with improved inter-area mode approximations. This paper contains new procedures to construct these aggregate networks and demonstrates the benefits of these new aggregate networks on a 48-machine power system using eigenvalues and nonlinear simulations. >
TL;DR: In this paper, the authors present an in-depth analysis of network revenues computed with marginal pricing, and in particular they investigate the reasons why marginal prices fail to recover the total incurred network costs in actual power systems.
Abstract: This paper presents an in-depth analysis of network revenues computed with marginal pricing, and in particular it investigates the reasons why marginal prices fail to recover the total incurred network costs in actual power systems. The basic theoretical results are presented and the major causes of the mismatch between network costs and marginal revenues are identified and illustrated with numerical examples, some tutorial and others of realistic size. The regulatory implications of marginal network pricing in the context of competitive electricity markets are analyzed, and suggestions are provided for the meaningful allocation of the costs of the network among its users. >
TL;DR: A survey of publications on applications of fuzzy set theory to power systems and the basic procedures for fuzzy set based methods to solve specific power systems problems is presented.
Abstract: Increasing interest has been seen in applying fuzzy set theory to power systems problems from the number of publications on this topic. As a relatively new research topic a need is felt to pay more attention to the understanding of the basic principles of the theory and the identification of problems suitable for solving by this method. This paper presents a survey of publications on applications of fuzzy set theory to power systems and the basic procedures for fuzzy set based methods to solve specific power systems problems. Simple numerical examples are used to show the practical procedures of problem formulation and solution. Theses examples are: generator maintenance scheduling, dynamic programming, and power system stabiliser. >
TL;DR: In this article, a new problem formulation of three-phase distribution power flow equations taking into account the radial structure of the distribution network is presented, and an effective solution method for general unbalanced radial distribution systems is presented.
Abstract: This paper presents a novel power flow formulation and an effective solution method for general unbalanced radial distribution systems. Comprehensive models are considered including lines, switches, transformers, shunt capacitors, cogenerators, and several types of loads. A new problem formulation of three-phase distribution power flow equations taking into account the radial structure of the distribution network is presented. A distinguishing feature of the new problem formulation is that it significantly reduces the number of power flow equations, as compared with the conventional formulation. The numerical properties as well as the structural properties of distribution systems are exploited resulting in a fast decoupled solution algorithm. The proposed solution algorithm is evaluated on three-phase unbalanced 292-bus and 394-bus test systems with very promising results.
TL;DR: Test results show that the FNN can forecast future loads with an accuracy comparable to that of neural networks, while its training is much faster than that of Neural networks.
Abstract: This paper presents the development of a fuzzy system for short term load forecasting. The fuzzy system has the network structure and the training procedure of a neural network and is called a fuzzy neural network (FNN). An FNN initially creates a rule base from existing historical load data. The parameters of the rule base are then tuned through a training process, so that the output of the FNN adequately matches the available historical load data. Once trained, the FNN can be used to forecast future loads. Test results show that the FNN can forecast future loads with an accuracy comparable to that of neural networks, while its training is much faster than that of neural networks. >
TL;DR: In this article, a modular artificial neural network (ANN) based hourly load forecaster which has already been implemented at 20 electric utilities across the US and is being used on-line by several of them.
Abstract: This paper describes a modular artificial neural network (ANN) based hourly load forecaster which has already been implemented at 20 electric utilities across the US and is being used on-line by several of them. The behavior or the load and its correlation with parameters affecting it (e.g. weather variables) are decomposed into three distinct trends of weekly, daily, and hourly. Each trend is modeled by a separate module containing several multi-layer feed-forward ANNs trained by the back-propagation learning rule. The forecasts produced by each module are then combined by adaptive filters to arrive at the final forecast. During the forecasting phase, the parameters of the ANNs within each module are adaptively changed in response to the system's latest forecast accuracy. The performance of the forecaster has been tested on data from these 20 utilities with excellent results. The on-line performance of the system has also been quite satisfactory and superior to other forecasting packages used by the utilities. Moreover, the forecaster is robust, easy to use, and produces accurate results in the case of rapid weather changes. >
TL;DR: In this paper, the design of an H/sub /spl infin controller for a series VAr compensator to enhance the damping of an inter-area oscillations in a large power system is presented.
Abstract: The design of an H/sub /spl infin controller for a thyristor controlled series VAr compensator to enhance the damping of an inter-area oscillations in a large power system is presented. The paper describes a comprehensive and systematic method of applying the H/sub /spl infin control design algorithm in power systems. Two methods to obtain a satisfactory reduced order system model, which is crucial to the success of the design, are described. >
TL;DR: In the test case of 1994 for implementation in the short term load forecasting expert system of Korea Electric Power Corporation (KEPCO), the proposed hybrid model provided good forecasting accuracy of the mean absolute percentage errors below 1.3%.
Abstract: In this paper, a hybrid model for short-term load forecast that integrates artificial neural networks and fuzzy expert systems is presented. The forecasted load is obtained by passing through two steps. In the first procedure, the artificial neural networks are trained with the load patterns corresponding to the forecasting hour, and the provisional forecasted load is obtained by the trained artificial neural networks. In the second procedure, the fuzzy expert systems modify the provisional forecasted load considering the possibility of load variation due to changes in temperature and the load behavior of holiday. In the test case of 1994 for implementation in the short term load forecasting expert system of Korea Electric Power Corporation (KEPCO), the proposed hybrid model provided good forecasting accuracy of the mean absolute percentage errors below 1.3%. The comparison results with exponential smoothing method showed the efficiency and accuracy of the hybrid model. >
TL;DR: An improved simple genetic algorithm developed for reactive power system planning and a new population selection and generation method which makes the use of Benders' cut is presented.
Abstract: This paper presents an improved simple genetic algorithm developed for reactive power system planning. Successive linear programming is used to solve operational optimization sub-problems. A new population selection and generation method which makes the use of Benders' cut is presented in this paper. It is desirable to find the optimal solution in few iterations, especially in some test cases where the optimal results are expected to be obtained easily. However, the simple genetic algorithm has failed in finding the solution except through an extensive number of iterations. Different population generation and crossover methods are also tested and discussed. The method has been tested for 6 bus and 30 bus power systems to show its effectiveness. Further improvement for the method is also discussed.
TL;DR: Numerical experiments show suitable performance of the proposed method with regard to estimation accuracy, convergence robustness and computational efficiency, and indicate the decoupled nature of the state estimation problem.
Abstract: The need for higher frequency in state estimation execution covering larger supervised networks has led to the investigation of faster and numerically more stable state estimation algorithms. However, technical developments in distributed Energy Management Systems, based on fast data communication networks, open up the possibility of parallel or distributed state estimation implementation. In this paper, this possibility is exploited to derive a solution methodology based on conventional state estimation algorithms and a coupling constraints optimization technique. Numerical experiments show suitable performance of the proposed method with regard to estimation accuracy, convergence robustness and computational efficiency. The results of these experiments also indicate the decoupled nature of the state estimation problem. >
TL;DR: In this article, the authors identify features underlying restoration processes that are common to almost all utilities and that can serve as guides for preparing and evaluating restoration plans, for developing expert system programs that will be widely useful, and ultimately for improving the effectiveness of restoration practices.
Abstract: The results presented here reflect work, extending over several years, to identify features underlying restoration processes that are common to almost all utilities and that can serve as guides for preparing and evaluating restoration plans, for developing expert system programs that will be widely useful, and ultimately for improving the effectiveness of restoration practices. Generality is achieved by identifying constituent elements of the process, namely a "target system", "restoration building blocks (RBBs)", "generic restoration actions (GRAs)", and process constraints, and the factors that distinguish among three clearly demarcated stages. This distillation of the constituent elements of the restoration process provides a basis for development of a comprehensive, knowledge-based restoration expert system appropriate to a broad spectrum of power system utilities. >
TL;DR: In this article, the relation between bifurcations and power systems stability through a thorough analysis of several examples, to clarify some ideas regarding the usefulness and limitations of Bifurcation theory in network studies and operation, particularly in voltage stability related issues.
Abstract: This paper discusses the relation between bifurcations and power systems stability through a thorough analysis of several examples, to clarify some ideas regarding the usefulness and limitations of bifurcation theory in network studies and operation, particularly in voltage stability related issues. Different types of load models are used in a sample system to analyze their effect on system stability and bifurcation. Finally, the Ecuadorian National Interconnected System is used to depict and discuss the effect of load modeling in saddle-node bifurcation analysis of real power systems. >
TL;DR: This paper presents a practical method to account for security constraints when scheduling electric generating units and indicates that this method obtains lower-cost solutions faster than if the security constraints are considered retroactively.
Abstract: Secure operation is an enduring concern to electric utilities. Several factors oblige utilities to operate their systems-particularly transmission systems-at or close to their capacities. Few methods for scheduling electric generating units, however, take security into account. Utilities, therefore, may inadvertently risk overloading critical transmission lines if units are not rescheduled. Without advance planning a utility may incur significant costs if it must reschedule generation retroactively. This paper presents a practical method to account for security constraints when scheduling electric generating units. The results indicate that this method obtains lower-cost solutions faster than if the security constraints are considered retroactively. >
TL;DR: The VVC algorithm is based on the oriented discrete coordinate descent method and takes into account all the optimization objectives of interest in distribution system analysis: minimum power loss, power demand or the number of control steps to keep the system within constraints.
Abstract: In this paper, a centralized volt/VAr control (VVC) algorithm for a distribution management system is presented. The algorithm is based on the oriented discrete coordinate descent method and takes into account all the optimization objectives of interest in distribution system analysis: minimum power loss, power demand or the number of control steps to keep the system within constraints. Although the optimization method used belongs to the traditional class of combinatorial integer programming, the algorithm provides good speed for real-time application. Numerical examples illustrate how well the VVC algorithm works for the different types of objective functions and it's advantages in comparison with other possible optimization strategies. >