HYDRO UNIT COMMITMENT IN HYDROTHERMAL OPTIMIZATION

In this paper we develop a model and technique for solving the combine d hydro and thermal unit commitment problem, taking into full account the hydro unit dynamic constraints in achieving overall economy of pow er 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 techni que. The hydro system is divided into watersheds, which are further br oken down into reservoirs. The watersheds are optimized by Network Flo w Programming (NFP). Priority-list-based Dynamic Programming is used t o 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 commitme nt 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 im proves the quality of its solution in the PG&E power system.