Comparison of two heuristic approaches to hydro unit commitment

This paper is concerned with the unit commitment of hydro generating units on an hourly basis throughout a single day. The performance criterion to be optimized includes the efficiency of hydro conversion, which depends on variations in tailrace elevation, penstock head losses and turbine-generator efficiency, as well as the cost of startup/shutdown of the hydro generating units. The paper presents a comparison of two heuristic approaches for solving the optimization problem. One heuristic is based on decomposing the problem into Generation Scheduling (GS) and Unit Scheduling (US) sub-problems, and solving the sub-problems by Lagrangian Relaxation and Dynamic Programming, respectively. The other heuristic makes use of a Genetic Algorithm combined with Lagrangian Relaxation to solve the original problem. The two heuristics were tested on a system composed of sixteen hydro plants, one hundred generating units, and an installed capacity of 21,933 MW in the Brazilian power system. The actual scheduling of generation actual for a typical day was used for comparison with the solutions proposed by the two heuristics. The results of both heuristics show significant savings in terms of hydro conversion efficiency and startup/shutdown costs.