This work presents a new method for simultaneous adjustment of automatic voltage regulator (AVR) and power system stabilizer (PSS) parameters to control voltage oscillations and damping in a synchronous generator using the particle swarm optimization algorithm (PSO) with two stages. The increment of a new stage aims to improve the efficiency of the PSO method, providing a better performance of the system. The algorithm was developed in Matlab software and used for the linearized 3-order model of a synchronous generator connected to an infinite bus. To analyze the performance of the controllers an objective function was used based on the system time response to a change in the reference voltage. The results were compared with the values found by the classical design method of the conventional tuning technique.