Optimal Reliable Operation of Hydrothermal Power Systems with Random Unit Outages

A new model for long-term operation of hydrothermal power systems is introduced, and a method for obtaining an optimal solution is developed. We assume both reservoir inflows and energy demand are stochastic and all units are exposed to random outages. The objective is to minimize the total cost of the system as well as the expected interruption cost of energy (EIC) during a given planning horizon. This goal is reached through simultaneous determination of hydro plant discharges, thermal units energy output, and the system reliability level. Long-term hydrothermal system operation planning and system reliability determination are integrated in a unified model. Since the resulting model is a large-scale stochastic nonlinear program, an algorithm is especially developed to solve it. This algorithm, which includes decomposition technique, Lagrangian relaxation, nonlinear and dynamic programming, finds an optimal solution within three stages. To test the method, it is implemented for the Khuzestan power system in Iran, and the results are analyzed.