Short-term hydropower scheduling via an optimization-simulation decomposition approach

This paper presents a decomposition approach based on an optimization-simulation approach to short-term hydropower scheduling. The problem is formulated as a mixed-integer nonlinear programming problem where the decision variables are the power output and the number of units committed at each hydro plant and hour of the day or week ahead. The goal consists of maximizing hydropower efficiency while reducing startup/shutdown costs and attaining system load, operational constraints, as well generation targets established by mid-term operation scheduling models. The approach proposed in this paper solves a relaxed version of the original problem in which hydraulic constraints are ignored. Eventual hydraulic infeasibilities are computed by a simulation step in order to either validate the solution or add violated constraints back into the problem. The approach is implemented and tested over the Brazilian power system for a study case comprised of 95 hydro plants, 447 generating units, and an average load of 41 GW for a week long horizon. Results confirm the approach to be very efficient in terms of computational costs, and both unit commitment and generation schedules.