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This paper presents a hybrid particle swarm optimization algorithm (HPSO) as a modern optimization tool to solve the discrete optimal power flow (OPF) problem that has both discrete and continuous optimization variables. The problem is classified as constrained mixed integer nonlinear programming with multimodal characteristics. The objective functions considered are the system real power losses, fuel cost, and the gaseous emissions of the generating units. Two different types of fuel cost functions are considered in this study, namely the conventional quadratic function and the augmented quadratic function to introduce more accurate modeling that incorporates the valve loading effects. The latter model presents nondifferentiable and nonconvex regions that challenge most gradient-based optimization algorithms. The proposed algorithm makes use of the PSO, known for its global searching capabilities, to allocate the optimal control settings while Newton-Raphson algorithm minimizes the mismatch of the power flow equations. A hybrid inequality constraint handling mechanism that preserves only feasible solutions without the need to augment the original objective function is incorporated in the proposed approach. To demonstrate its robustness, the proposed algorithm was tested on the IEEE 30-bus system with six generating units. Several cases were investigated to test and validate the consistency of detecting optimal or near optimal solution for each objective. Results are compared to solutions obtained of MATPOWER software outcomes that employs sequential quadratic programming algorithm to solve the OPF. The impact of the proposed inequality constraint handling method in improving the HPSO performance is illustrated. Furthermore, a study of HPSO parameters tuning with regard to the OPF problem is presented and analyzed.