Transient stability is one of the main issues in the field of power systems. On the other hand, using FACTS devices has been proposed for the purpose of maximizing the lines conductivity given the restrictions involved, including the issue of stability. This study seeks to take steps towards the improvement of a multi-machine power system stability in faulty conditions, using two FACTS devices including TCSC and SVC. The control system for the FACTS devices is constructed here based on the so called energy function method. Meanwhile, in order to achieve a prescribed optimal performance, the coefficients of the designed controller are tuned by PSO algorithm. Possessing the theoretical analysis, the simulation results are also demonstrated to show the performance of the proposed control algorithm.