In this paper, the authors develop a model and technique for solving the combined hydro and thermal unit commitment problem, taking into full account the hydro unit dynamic constraints in achieving overall economy of power system operation. The combined hydrothermal unit commitment problem is solved by a decomposition and coordination approach. Thermal unit commitment is solved using a conventional Lagrangian relaxation technique. The hydro system is divided into watersheds, which are further broken down into reservoirs. The watersheds are optimized by network flow programming (NFP). Priority-list-based dynamic programming is used to solve the hydro unit commitment (HUC) problem at the reservoir level. A successive approximation method is used for updating the marginal water values (Lagrange multipliers) to improve the hydro unit commitment convergence, due to the large size and multiple couplings of water conservation constraints. The integration of the hydro unit commitment into the existing hydro-thermal optimization (HTO) package greatly improves the quality of its solution in the PG&E power system.


Engineering Management and Systems Engineering

Keywords and Phrases

Lagrange multipliers; dynamic constraints; dynamic programming; economic operation; hydro unit commitment; hydro-thermal power system optimization; hydrothermal power systems; load dispatching; load distribution; marginal water values; network flow programming; power system planning; priority list-based dynamic programming; reservoir; successive approximation method

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

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© 1997 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.