Hasan Siahkali - Electrical Engineering Department, South Tehran Branch, Islamic Azad University, Tehran, Iran.

This paper presents a new approach to unit commitment (UC) problems using a particle swarm optimization (PSO) technique. The mid term UC problem has a cost function with equality and inequality constraints that make the problem of finding the global optimum difficult by using any mathematical approach. In this paper, a modified PSO (MPSO) mechanism is suggested to deal with the equality and inequality constraints in the UC problems. The proposed MPSO is applied to a 10-unit test system and the results of the MPSO are compared with the results of conventional numerical methods such as mixed integer nonlinear programming (MINLP).