Turk J Elec Eng & Comp Sci (2015) 23: 2278 – 2288 c ⃝ T ¨ UB ˙ ITAK doi:10.3906/elk-1305-258 Turkish Journal of Electrical Engineering & Computer Sciences http://journals.tubitak.gov.tr/elektrik/ Research Article Opposition-based gravitational search algorithm applied to economic power dispatch problems consisting of thermal units with emission constraints Serdar ¨ OZY ¨ ON 1, * , Celal YAS ¸AR 1 , Burhanettin DURMUS ¸ 1 , Hasan TEMURTAS ¸ 2 1 Department of Electrical and Electronics Engineering, Dumlupınar University, K¨ utahya, Turkey 2 Department of Computer Engineering, Dumlupınar University, K¨ utahya, Turkey Received: 30.05.2013 • Accepted/Published Online: 18.09.2013 • Printed: 31.12.2015 Abstract: In this study, a multiobjective environmental economic power dispatch problem has been converted into a single-objective optimization problem using the weighted sum method. For the solution of the converted problem, the gravitational search algorithm (GSA), which is one of the latest algorithms, has been used. In order to increase the performance of the GSA, opposite positioning quality has been added to the structure of the algorithm (OGSA). The obtained results show that the proposed algorithm has obtained better results and has provided a faster convergence. The 30-bus 6-generator test system has been selected for application of the OGSA. The transmission line losses have been added to the problem by using a B loss matrix. Optimum solutions of the problem have been obtained for different weights and the results have been verified. Key words: Environmental economic, power dispatch, gravitational search algorithm, opposition-based learning, weighted sum method 1. Introduction The economic power dispatch problem is defined as the setting of active power outputs of generation units, for the system load to be satisfied by the units under system constraints and at minimum cost [1]. In general, power generation units use coal, petroleum, and natural gas as fossil fuels. These fossil fuels cause atmospheric waste emission, composed of particles and gases. These emitted waste gases include CO 2 , SO 2 , and NO x . These gases are harmful for all living beings and cause global warming. Among these, SO 2 emission only depends on fuel depletion and therefore it is easier to perform mathematical modeling. However, NO x emission depends on several factors like steam boiler temperature and air mixture. Therefore, it is extremely hard to perform modeling of NO x gas emission. NO x emission is also more hazardous than other contaminants [2]. In addition to the minimization of fuel costs, emitted hazardous gases should also be considered in economic dispatch problems. These multiobjective power dispatch problems considering environmental pollution as well are referred to as environmental economic power dispatch problems [1,2]. The problem converts to a multiobjective optimization problem when one would like to minimize both fuel cost function and emission amount. These problems are solved in the literature with different two methods. The first is direct and the second one is to modify and then apply methods that solve these problems. One of the methods used for a modified approach is the weighted sum method (WSM) [1]. * Correspondence: serdar.ozyon@dpu.edu.tr 2278