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# 9291_c018 - 18 Generation Control Economic Dispatch and...

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18 Generation Control: Economic Dispatch and Unit Commitment Charles W. Richter, Jr. AREVA T&D Corporation 18.1 Economic Dispatch ......................................................... 18 -1 Economic Dispatch Defined . Factors to Consider in the EDC . EDC and System Limitations . The Objective of EDC . The Traditional EDC Mathematical Formulation . EDC Solution Techniques . An Example of Cost Minimizing EDC . EDC and Auctions 18.2 The Unit Commitment Problem ................................... 18 -7 Unit Commitment Defined . Factors to Consider in Solving the UC Problem . Mathematical Formulation for UC . The Importance of EDC to the UC Solution . Solution Methods . A Genetic-Based UC Algorithm . Unit Commitment and Auctions 18.3 Summary of Economical Generation Operation ........ 18 -17 An area of power system control having a large impact on cost and profit is the optimal scheduling of generating units. A good schedule identifies which units to operate, and the amount to generate at each online unit in order to achieve a set of economic goals. These are the problems commonly referred to as the unit commitment (UC) problem, and the economic dispatch calculation, respectively. The goal is to choose a control strategy that minimizes losses (or maximizes profits), subject to meeting a certain demand and other system constraints. The following sections define EDC, the UC problem, and discuss methods that have been used to solve these problems. Realizing that electric power grids are complex interconnected systems that must be carefully controlled if they are to remain stable and secure, it should be mentioned that the tools described in this chapter are intended for steady-state operation. Short-term (less than a few seconds) changes to the system are handled by dynamic and transient system controls, which maintain secure and stable operation, and are beyond the scope of this discussion. 18.1 Economic Dispatch 18.1.1 Economic Dispatch Defined An economic dispatch calculation (EDC) is performed to dispatch , or schedule, a set of online generating units to collectively produce electricity at a level that satisfies a specified demand in an economical manner. Each online generating unit may have many characteristics that make it unique, and which must be considered in the calculation. The amount of electricity demanded can vary quickly and the ß 2006 by Taylor & Francis Group, LLC.

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schedule produced by an EDC should leave units able to respond and adapt without major implications to cost or profit. The electric system may have limits (e.g., voltage, transmission, etc.) that impact the EDC and hence should be considered. Generating units may have prohibited generation levels at which resonant frequencies may cause damage or other problems to the system. The impact of transmission losses, congestion, and limits that may inhibit the ability to serve the load in a particular region from a particular generator (e.g., a low-cost generator) should be considered. The market structure within an operating region and its associated regulations must be considered in determining the specified demand, and in determining what constitutes economical operation. An independent system operator (ISO)
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9291_c018 - 18 Generation Control Economic Dispatch and...

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