Showing papers on "Economic dispatch published in 1991"

Dispatch of direct load control using dynamic programming

Abstract: An approach based on dynamic programming is presented for the dispatch of direct load control (DLC). The objective is to coordinate DLC strategies with system unit commitment such that the system production cost is minimized. To achieve this goal, the DLC dispatch is first integrated into the unit commitment problem. An optimization technique based on dynamic programming is then developed to reach the optimal DLC dispatch strategy and system generation schedule. To demonstrate the effectiveness of the approach, results from a sample study performed on the Taiwan power system are described. >

Heuristic multi-area unit commitment with economic dispatch

Abstract: An improved multi-area unit commitment and economic dispatch algorithm is proposed. The approach supplements the traditional dynamic programming unit commitment with heuristic adjustments to refine the commitment schedule in each area. A global economic dispatch scheme coordinates the transactions between areas. A new tie-line constraint checking is included which is simple and effective. The overall algorithm can he implemented on an IBM-PC, which can process a fairly large system in a reasonable period of time. Experimental results show the application potential of this method to general multi-area power generation scheduling problems. >

A comprehensive approach for adequacy and security evaluation of bulk power systems

Abstract: A new approach is described for assessing the adequacy and security of bulk power systems. The method takes into account generation and transmission failures, load variation, generation economic dispatch, security limits, maintenance schedules, the control actions implemented in emergencies. and the impact of different operating schemes. Reliability indices for generation adequacy, transmission adequacy, and system security are defined. The proposed method is demonstrated by application to the IEEE Reliability Test System (RTS). >

Chronological probabilistic production costing and wheeling calculations with transmission network modeling

Abstract: The authors present an approach for the integrated analysis of generation and transmission system in terms of production costing and wheeling rate calculations. The methodology is based on the chronological simulation of system operation. Economic dispatch at each state is provided by linearized optimal power flow routines, which can represent network aspects and export/import contracts among utilities. Probabilistic aspects are represented by Monte Carlo sampling of generation capacities, load levels, etc. Marginal costs are calculated at bus level and serve as a basis for the evaluation of wheeling rates. This makes it possible to model complex utility situations for use in power system planning and operations, determination of interchange contracts, and regulatory applications. >

Improved cost functions for economic dispatch compensations (on power systems)

Abstract: Two polynomial curve fitting methods, Gram-Schmidt orthonormalization and the least-squares method, are evaluated for power system load dispatching economics analysis applications. It is shown that the Gram-Schmidt method, which does not require matrix inversion, gives more accurate fuel cost curves. Also, a constraint equation can be included in both methods to insure that incremental cost curves are monotonically increasing. Numerical examples are included to demonstrate the results. >

Auction markets for dispatchable power: How to score the bids

Abstract: Competitive bidding for electric generating capacity is becoming based on economic dispatch rather than the PURPA “must-take” norm. Incorporating economic dispatch into bidding requires different price scoring procedures. The “avoided cost” of a dispatchable project is determined by the energy price offered. Price scoring methods based on a “percentage of avoided cost” approach are uneconomically biased against baseload projects, because they neglect the duration effects of their dispatch. This bias is illustrated in a simple model of economic dispatch. A number of utilities use the “percentage of avoided cost” method for dispatchable capacity. They can correct the bias by using a net benefits per kW measure of economic value.

Transmission loss evaluation based on probabilistic power flow

Abstract: A simulation method for composite power systems is proposed for the purpose of evaluating the probability distribution function of transmission losses. The method accounts for the uncertainty of the electric load, availability of generating units, nonlinearities in the power flow equations, and major operating practices. The method is based on the following procedure. First, given the probabilistic electric load model, the probability distribution function of the power injection at generation buses is computed by taking into consideration the availability of generating units and economic dispatch practices. Next, transmission losses are expressed as a piecewise linear function of power injections at generation buses. Subsequently, the probability distribution function of transmission losses is computed. Validation of the method was performed via a Monte Carlo simulation. The method was applied to the 24-bus IEEE reliability test system, and the results are validated by comparing it to Monte Carlo simulation results. >

Improved cost functions for economic dispatch computations

Abstract: Representation of generator fuel cost curves by polynomials in real-time economic dispatch is standard industry practice. Two polynomial curve fitting methods, Gram-Schmidt orthonormalization and least-squares, are evaluated here. It is shown that the Gram-Schmidt method, which does require matrix inversion, gives more accurate fuel cost curves. Also, a constraint equation can be included in both methods to insure that incremental cost curves are monotonically increasing. Numerical examples are included to demonstrate the results.

Efficient economic dispatch algorithm for thermal unit commitment

Abstract: The paper presents a simple and efficient economic dispatch algorithm suitable for unit commitment. It also caters for any combination of polynomial cost functions. The algorithm reduces the economic dispatch into an equivalent lossless problem from which solutions are easily obtained and analytically. The equivalent lossless problem enables the generators whose outputs violate their limit constraints to be handled efficiently and correctly. The algorithm can cater for both the B matrix and Jacobian matrix loss formulation. Case studies with various test systems are presented and discussed.

An approximate reasoning approach for optimal dynamic dispatch of thermal generating units including auxiliary control

Abstract: Fuzzy set theory is applied to decision-making in the optimal generation dispatch of thermal generating units. Operational requirements such as unit auxiliary start-up and shutdown create discrete zones of generation output. Plant operators are required to switch units dynamically from one output zone to another in order to keep track of the changing load. The problem arises when making the decision to switch zones for dynamic load dispatch, because of complicated operational conditions. The authors apply approximate reasoning in order to coordinate multiple system requirements and to make effective zone-switching decisions. Membership functions are introduced to measure generation-load balance, fuel cost, and time to stay in a zone. Approximate reasoning using these indices yields information concerning compatibility of output zones. Model analysis is used to demonstrate the flexibility and improved man-machine interface of the approach. >

Power generation scheduling through use of generalised network flow programming

Abstract: The economic dispatch problem is important in both power system planning and operation. Although there have been major advances in defining and solving more complete optimal power flow (OPF) problems, there exists a need for constrained economic dispatch (CED) techniques which, though not as rigorous or as exact as an OPF, are fast enough to be used on desktop computers. The authors present a CED formulation that is based upon generalised network flow programming (GNFP). The methodology for applying GNFP to the CED problem is developed and illustrated in this paper using four examples: 5, 39, 264, and 515-bus systems. Starting with a solved loadflow case, execution times for the CED are shown to be about the same as for a Newton-Raphson loadflow, and memory requirements are approximately 75% of the loadflow. Salient features of the CED-GNFP method include the ability to minimise generation cost while meeting constraints on line flows and area interchange. Network location of loads and generators is automatically considered without need of penalty factors, and transmission line flow limits do not affect solution times significantly. The authors believe that, owing to its simplicity of application, robustness, and ease of implementation on desktop computers, the CED-GNFP procedure is an important adjunct to the group of techniques and algorithms currently available for solving the overall economic dispatch/OPF problem.

Application of the Homotopy MLthod to Finding Economic Dispatch Solutions

Abstract: The functions of the cost curve and transmission losses are existing nonlinear, simultaneous subject to equality and inequality constraints. Mathematically, the solutions of the nonlinear equations of economic dispatch problems may result in multiple solutions, singal solution or no solution. Conventional methods may fail to find all the multiple solutions if the initial guess values are not appropriately located within the convergency region. To overcome this difficulty the homotopy method is suggested for the solution technique. In this paper the homotopy theorem is incorporated with the B-coefficient method to solve the economic dispatch problem. Not only the initial value is easily obtained but also all the multiple solutions can be obtained. So the exact least cost of economic dispatch can be derived.

Integration of the optimal power flow into generation control and dispatch

Abstract: A close interaction of automatic generation control (AGC), reserve monitor (RM), and economic dispatch (ED) is prerequisite of economic and reliable operation. In power systems where network limitations frequently constrain pure economic dispatch an integration of optimal power flow (OPF) is necessary. The primary practical requirements are best met by applying a general purpose OPF package using a full AC network model and unit models originating from the generation control and dispatch subsystem, including piecewise quadratic cost curves. The authors describe a closed-loop OPF based on a general-purpose, nonspecialized OPF package. All functions described form an integrated part of an EMS package. >

Dispatch of spinning reserve

Abstract: Maintaining system frequency within operational and statutory limits following generation infeed losses requires sufficient active power reserves. An enhanced dispatch algorithm is presented in which generator loading and operating pressure are instructed to provide spinning reserve in the most economical way. A power system simulation is also presented to illustrate the benefits of adopting such an algorithm. >

Application Of The Homotopy Method To Finding Dispatch Solutions

Abstract: The functions of the cost curve and transmission losses are existing nonlinear, simultaneous subject to equality and inequality constraints. Mathematically, the solutions of the nonlinear equations of economic dispatch problem may result in multiple solutions, singal solution or no solution. Conventional methods may fail to find all the multiple solutions if the initial guess values are not appropriately located within the convergency region. To overcome this difficulty te homotopy method is suggested for the solution technique. In this paper the homotopy theorem is incorporated with the B-coefficient method to solve the economic dispatch problem. Not only the initial value is easily obtained but also all the multiple solutions can be obtained. So the next exact least cost of economic dispatch can be derived.