Showing papers on "Economic dispatch published in 1995"

CPFLOW: a practical tool for tracing power system steady-state stationary behavior due to load and generation variations

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. >

Large-scale economic dispatch by genetic algorithm

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.

Short-term generation scheduling with transmission and environmental constraints using an augmented Lagrangian relaxation

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. >

Refined genetic algorithm-economic dispatch example

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. >

Multi-area economic dispatch with tie line constraints

Abstract: This paper presents a new method for solving the multi-area power system economic dispatch (MAED) problem with tie line constraints. This formulation extends the traditional economic dispatch methods used in study applications such as unit commitment to include area demand constraints, area reserve constraints, and tie line capacity constraints between the modeled areas. The MAED is formulated as a capacitated nonlinear network flow problem which is solved using a high-speed network load flow code. The MAED determines the amount of power that can be economically generated in one area and transferred to another area to displace generation in the second area. The network flow model does not compute the actual power transfer between areas. The paper demonstrates that a significant number of the problem constraints may be formulated as network-type, and as a result, the method provides a robust, high-speed solution method for surprisingly large class of electric utility problems including the ability to analyze potential purchases and sales in a multi-area power system environment.

OPF for reactive pricing studies on the NGC system

Abstract: Retail transmission services like those being provided by the National Grid Company (NGC) in England and Wales pose new challenges for the pricing of reactive power supply. A reactive power market approach has been proposed by NGC and continues to be evaluated. Such an approach includes a novel requirement for transmission constrained economic dispatch of VAr, a problem in the security constrained optimal power flow (OPF) class. The problem formulations handled by the OPF package in use could not accommodate NGC's requirements. This paper describes the reactive pricing problem being addressed, the modeling requirements, and the resulting extensions made to the OPF formulation and package. It discusses the test results obtained to date on the NGC system.

A practical resource scheduling with OPF constraints

Abstract: This paper presents an efficient approach to short term power system resource scheduling based on the augmented Lagrangian relaxation method. The problem is divided into two stages, the commitment stage and the constrained economic dispatch stage. The proposed mathematical model incorporates optimal power flow (OPF) constraints in the unit commitment stage. By OPF constrains, the authors refer to the relevant active power constraints that are incorporated in the constrained economic dispatch stage (i.e. transmission capacity constraints, fuel and various regulated emission requirements). The inclusion of OPF constraints in the commitment stage will improve the feasibility of the constrained economic dispatch solution. Other unit commitment constraints such as spinning and operating reserve requirements, power balance as well as other relevant local constraints (i.e. unit ramping rates, upper and lower generation limits, minimum up and down times) are taken into account in the proposed model. As a larger number of constraints are dealt with, a more rigorous method is introduced for updating Lagrange multipliers to improve the solution convergence. A software package which addresses energy management systems requirements is developed and tested.

Clamped state solution of artificial neural network for real-time economic dispatch

Abstract: This paper presents a novel method for the real-time economic dispatch using clamped state variable formulation of the Kennedy, Chua and Lin (1988) artificial neural network (ANN). An efficient economic power dispatch algorithm must use real-time load conditions and the loss penalty-factor for representation of transmission losses in power system. The approach described in this paper assumes that an interface program will calculate the penalty factors for the current power flow state, as calculated by a state estimation program. The proposed method employs an ANN to enhance the speed and capability of algorithms which may use heuristics for online use. The ability of processing feedbacks in a collective parallel analog mode enables a neural network to simulate the dynamics that represent the optimization of an objective function subjected to its constraints for a given optimization model. Different techniques may be used to simulate the neural dynamic system. In this study, the authors propose a new method of simulation called the clamped state variable (CSV) technique. The new approach is very simple and it takes smaller computer time for the algorithm to converge than the complete circuit simulation. The results obtained by the CSV method are very close to that of numerical methods and are reported in this paper. >

Application of the fast Newton-Raphson economic dispatch and reactive power/voltage dispatch by sensitivity factors to optimal power flow

Abstract: This paper applies the sensitivity factor method to the reactive power/voltage dispatch problem and combines it with the fast Newton-Raphson economic dispatch to solve the optimal power flow problem. The advantage of this method is that it is fast and reliable. Firstly, the real power generalized generation shift distribution (GGSD) factors are used in economic dispatch to find the real power generation for every unit so that the fuel cost is minimum. During the process of solving the economic dispatch problem, the voltage magnitudes of load buses in a power system may be changed and may exceed the ranges of secure values. Therefore, reactive power sensitivity factors of bus voltage magnitudes are used to regulate the voltage magnitudes of load buses to the secure ranges. The process is repeated to find the optimal generation with all voltages staying within the secure ranges. Results show that the algorithm converges very fast. >

Systems and control theory for power systems

Abstract: Bifurcation-theoretic issues in the control of voltage collapse.- Reduced-order modeling of electric machines using integral manifolds.- The BCU method for direct stability analysis of electric power systems: theory and applications.- New algorithms for slow coherency aggregation of large power systems.- Computational complexity results in parametric robust stability analysis with power systems applications.- Damping and resonance in a high power switching circuit.- Dynamic analysis of voltage collapse in power systems.- Exact convergence of a parallel textured algorithm for constrained economic dispatch control problems.- Variable structure regulation of power plant drum level.- Analysis of mechanisms of voltage instability in electric power systems.- Structural stability in power systems.- Power system load modeling.- Parallel solutions of linear equations by overlapping epsilon decompositions.- Insects, fish and computer-based super-agents.- Application of real-time phasor measurements in power system control.- On the dynamics of differential-algebraic systems such as the balanced large electric power system.- Robust stabilization of controls in power systems.

A Hopfield network approach to economic dispatch with prohibited operating zones

Abstract: This paper presents a Hopfield model to solve the power system economic dispatch (ED) problem with some of the units having prohibited operating zones. In the proposed method, the authors introduce an equilibrium point, lying in the interior of a prohibited zone, which will divide the prohibited zone into the left and the right prohibited zones referred to this point. In this way, in order to prevent the unit from operating into prohibited zone, they incorporate the novel countermeasures into the proposed Hopfield model. Through case studies of a system with 15 units, they prove the possibility of application of the Hopfield model to a practical ED problem mentioned above. Computer simulations manifest that not only this proposed model itself is much simpler but also its computation results are very close to those of the conventional methods.

Economic dispatch with non-monotonically increasing incremental cost units and transmission system losses

Abstract: Economic dispatch problems, in the presence of nonmonotonically increasing incremental cost generating units, is solved by use of the Newton approach. A linear transmission loss model, which is based on load flow solutions, is established and incorporated into the economic dispatch problem. Test results show that a fast convergence can be achieved by using this approach. >

Advanced generation control with economic dispatch

Abstract: A new approach for the automatic generation control (AGC) of electric power networks is introduced. This approach also supports an economic dispatch feature which operates at a slower time scale and interacts with the AGC frequency stabilization function. AGC is separated into two subtasks: frequency regulation and tie-line flow control, and a hierarchy of controls are formulated to realize these two functions. The frequency regulation level, called secondary control, is decentralized, and optimized with respect to both frequency offset and change in generator governor controls. The tie-line flow control level, called tertiary control, is centralized, and works on a slower time scale than secondary control. Tertiary control compensates for inadvertent flows between areas by momentarily offsetting generator frequencies. These frequency offsets shift the phase angles found at tie-line terminals, and eventually realize the desired line flows. The role of economic dispatch (ED) is to reschedule the entire system to minimize overall generation cost. The proposed version of ED is centralized, and invoked at an even slower rate than tertiary tie-line regulation.

Polynomial loss models for economic dispatch and error estimation

Abstract: Polynomial loss models are introduced for the economic dispatch problem. The models are based on interpolations of load flow solutions. An approximate error estimation method for the loss models is also presented. The effect of approximate loss models on the economic dispatch is evaluated according to the deterioration of total generation cost in addition to the relative values of the coefficients of the loss formula. Case study shows that loss expressions have characteristics which have not been considered previously. Comparisons between the proposed models and the generalized generation distribution factor (GGDF) based models show the advantages of the proposed models. >

Multiobjective decision making in stochastic economic dispatch

Abstract: Recently, multiple objective decision making has been well established as a practical approach to seek satisfactory solutions to decision making problems in limited resources, information and cognitive ability of the Decision Maker (DM). In the past, it was normal to assume well behaved and deterministic system data. Now the trend is to assume them variable and uncertain for more realistic approach. This paper deals with decision making methodology based on fuzzy set theory in order to determine the optimal generation dispatch with due consideration of uncertainties in system production cost and randomness of load demand. The classical economic dispatch problem is formulated as stochastic multiobjective optimisation problem where operating cost and variance of generation mismatch are two non-commensurable objectives. Such problems are solved to generate non-inferior solutions. Weighted sum technique is used to simulate trade_off relation among the conflicting objectives in the non-inferior domain...

Short-term energy and emission trading analysis

Abstract: This paper presents four different methods to compute the cost of a power system short-term transaction with environmental constraints. The transaction to be analyzed can be either an energy or emission transaction. The advantages and disadvantages of these methods are discussed. An efficient method based on an incremental analysis is proposed to calculate the cost of a transaction. The method proposed can be efficiently used to screen a very large number of transactions. This paper demonstrates that once the emission constraints are introduced, normal economic dispatch cannot be used to perform even an energy transaction. The need for current Economy A to include emission constraints is presented. Different test results for a sample test system are presented. >

Optimal compensation of variable series capacitors for improved economic dispatch in power systems

Abstract: This paper presents the development of a mathematical model representation of variable series capacitors which are also known as flexible AC transmission systems (FACTS) in power system economic dispatch. The objective of this research is to find the optimal locations of FACTS devices for improved economic dispatch. The proposed approach is based on the decomposition-coordination method and the network compensation technique. Taking the advantages of accumulated experience in power system optimization and the existence of the optimal power flow (OFF) software, the software development cost for implementing the proposed algorithm is reduced. In this paper, digital simulation studies on small power systems with and without variable series capacitors were conducted respectively. The purpose of these simulation studies is to assess the effectiveness of the proposed algorithm in minimizing the operating cost and enhancing the system performance. The results of the simulation studies and the proposed algorithm are presented and discussed in greater detail.

A parallel HAD-textured algorithm for constrained economic dispatch control problems

Abstract: In our earlier papers we developed a parallel textured algorithm to solve the constrained economic dispatch control (CEDC) problems. The exact convergence theorem and its proof were provided to guarantee the convergence of the algorithm to the true solution; and some examples were given to show the impact of exact convergence conditions. In this paper, we incorporate the hierarchical aggregation-disaggregation (HAD) concept and the textured concept to solve the CEDC. The algorithm is then implemented on an nCUBE2 machine and tested on a modified IEEE 14-bus system, a modified IEEE 57-bus system, a 114-bus system, and a 228-bus system. Some test results are given to show the speedup advantage of the proposed algorithm over the one without textured decomposition. Even when the proposed algorithm is executed sequentially, the speedup is still essential. >

Optimization of unit commitment using parallel structures of genetic algorithm

Abstract: This paper proposes an innovative genetic algorithm (GA) approach to solving the thermal unit commitment (UC) problem using a constraint satisfaction technique. Minimum up-time and down-time constraints on the generating units are embedded in the delicately designed binary strings to represent the on-off states of the units. Ramp rate constraints on the units being started up or shut down are tackled in the economic dispatch subprogram by limiting the associated maximum available capacities for generating. Violations of the other constraints are considered by integrating penalty factors into the cost function. The developed algorithm is further paralleled on an 8-processor transputer network, processors of which are arranged in master-slave and dual-direction ring structures, respectively. The proposed approach is tested on the simple 4 thermal units system and the practical Taiwan Power system of 38 thermal units. Speed-up and efficiency for each structure with different number of processors are compared to those of the sequential GA approach. The proposed approach is shown to be well amenable to parallel implementation.

Distributed price-directive decomposition applications in power systems operations

Abstract: A number of important problems in the area of power systems operations and planning can be modeled as optimization problems that are amenable to solution by decomposition techniques. A major drawback on large problems, however, is that computer run times are often long, thereby limiting the utility of this approach for real-time operations. Using the constrained economic dispatch model as a case study, this paper demonstrates that distributed decomposition on a hypercube multiprocessor can be extremely effective in controlling the growth in run times as problem size is increased. >

Real-time hydro coordination and economic hydro optimization

Abstract: This paper addresses the real-time aspects of the hydro-thermal coordination problem. It describes the real-time modeling and monitoring of hydro resources, and the use of the resulting real-time hydraulic data in the online economic dispatch algorithm. A variable head, hydro loss model is incorporated that allows for online changes to the hydro topology. The method presented provides the operator with a current view of the available water resources, enables the validation of the real-time hydro data received from the field, and enables real-time optimization of the hydro-thermal unit commitment plan. The implementation of this approach on the Iberdrola system in Spain is described.

Expected Cost Penalty due to Deviation from Economic Dispatch for interconnected power systems

Abstract: This paper introduces and evaluates a new index called "Expected Cost Penalty due to Deviation from the Economic Dispatch" (EPDED) for interconnected power systems. This index represents the cost penalties associated with uncertainties such as random failure of generating units, load growth, and fuel costs in interconnected power systems. The significance of this index is that it represents common events such as operating problems that can be observed over short periods (e.g., one or two years) rather than the rare events such as load curtailment which is currently used for reliability evaluation of power systems. This paper presents two techniques to evaluate this index. Monte-Carlo simulation and a tree structured state enumeration. System studies are performed to determine the variation of expected cost penalty with respect to changes in load values and probability of failure of generating units. >

A strategic approach for dispatch

Abstract: The increase of the average transport distances and number of trips, the decrease of equipment productivity and the specialisation of services and vehicles are the most important repercussions of the current economic context on the goods transport industry. Dispatch is highly affected by those constraints in so far as it realizes the "goods-drivers-trucks-trips" allocation. The dispatch strategy has direct repercussions on the profitability of the company. In fact, if the dispatch strategy is supply-oriented and aimed to increase equipment productivity, the company will be limited by its own capacities and resources. On the other hand, if the strategy is demand-oriented with regard to satisfy the maximum of it, the company must strive to find resources in order to satisfy its immediate needs. Therefore, which strategy would be the best with regard to the new economic context? The authors present a strategic approach for dispatch as one which can contribute significant competitive advantages to goods haulage companies. They also propose dispatch strategies which can be implemented by these companies in order to better manage operating costs and service differentiation.

A partially decoupled HAD OPF algorithm for constrained power economic dispatch

Abstract: A partially decoupled hierarchical aggregation/disaggregation (HAD) optimal power flow (OPF) algorithm is developed for the constrained power economic dispatch. The effects of the new partially decoupled real power OPF are investigated. The test results show that the proposed method has acceptable accuracy, and efficiently speeds up the computation process.