Unit commitment in thermal power systems with long-term energy constraints

The authors describe a method for unit commitment, considering energy constraints obtained from a long-term optimization. In many electrical utilities, there exists the problem of fulfilling energy supply contracts with other utilities or with fuel suppliers. Furthermore, energy prices may change during the year or depend on the consumed electrical energy. The proposed method solves this complex task in two steps. The first step calculates a long-term, e.g., yearly, operation schedule with daily energies allocated to each unit. These daily energy constraints of the long-term optimization have to be incorporated in the second step, the daily unit commitment. The long-term optimization is solved by mixed integer programming, and the short-term is solved by a Lagrangian relaxation. Special attention is given to the coordination between long-term and short-term optimization.<>