Improvement in the Hydro Plants Production Function for the Mid-Term Operation Planning Model in Hydrothermal Systems

1. Abstract In Brazil, the operation planning of the Interconnected hydrothermal system is coordinated by the National System Operator (ONS), with the support of a chain of models designed by the Brazilian Electrical Power Research Center (CEPEL). In this chain, whose objective is to minimize system operation costs, the mid-term optimization model is called DECOMP. The power generation of a hydro plant is described by a Hydro Production Function (HPF), which is a non-linear function that relates the energy produced by the power plant with the water storage level of the reservoir, the turbined outflow, and sometimes, also with the spillage. The paper proposes an improvement in the piecewise linear model for the HPF that has been used in the DECOMP model. The main contribution of this work is to formulate spillage and turbined outflows as separated variables, instead of only representing the total water discharge of the plant, as in the previous model. Both formulations are assessed and compared based on the deviations of each model from the real HPF (e.g., the difference between the power generation given by the model and the generation obtained from the real HPF). The study cases comprise 18 PMO’s (Monthly Operation Program), from February 2003 to July 2004. The results showed a much better performance of the proposed formulation as compared to the previous formulation. 2. Keywords: hydro power generation, hydrothermal coordination, linear programming.