A 4-state unit definition for the unit commitment problem

This paper proposes a new state definition for the thermal generator units. Being different from the classic On/Off state definition, a model that considers four possible states in order to commit a unit is proposed. The main difference in the classic UC is that in the on-state mode, the unit can be committed to a maximum or minimum power according to its technical generation limits, but it can be also committed without giving power to the system in synchronism (banking state). Therefore, the unit commitment problem is formulated as a combinatorial optimisation problem with four variables. A more complete and necessary state definition is considered according to the electric energy non-regulated market’s characteristics and particularly because of the Chilean energy market’s characteristics. The new UC problem formulation is then solved using the Simulated Annealing technique and several examples show the effectiveness and robustness of the proposed method.