Solving Unit Commitment by a Unit Decommitment Method

A problem that must be frequently solved by a power utility is to economically determine a schedule of what units will be used to meet the forecast demand, and operating constraints such as spinning reserve requirements, over a short time horizon. This problem is commonly referred to as the unit commitment (UC) problem. The UC problem is in the class of NP-hard problems. Many optimization methods have been proposed to solve the UC problem. Among them, the Lagrangian relaxation (LR) methods are the most widely used approaches for solving such a problem. In this paper, we present an alternative method for solving the UC problem, which can be regarded as an approximate implementation of the LR approach. The basic idea is to employ a unit decommitment method. This method starts with a solution having all available units on-line at all hours in the planning horizon and determines an optimal strategy for decommitting units, one at a time. We show that the number of iterations required by the method is bounded by the number of units. Empirical tests suggest that the proposed method is more efficient and robust than the LR approach