The increasing need for energy requires using existing energy sources more efficiently. Because it is the active power that supplies useful power for industrial facilities, reactive power must be minimized, and supplied by another source instead of electrical grid. Therefore, reactive power supplied by the grid can be reduced via by correcting power factor of the grid. In electrical power systems, power factor correction is called reactive power compensation. Generating reactive power during excessive excitation, synchronous motors are used as dynamic compensators in power systems. Synchronous motors are more cost-effective for industrial facilities when they are used to generate mechanic power and compensate reactive power, which increases the efficiency of industrial facilities. There are various studies focusing on the efficiency, capacity and stability of the power system via reactive power compensation in the literature. In today's world, there are numerous optimization techniques inspired by biological systems. One of these techniques is Particle Swarm Optimization (PSO) inspired by the movements of swarms of birds. This study focuses on the reactive power compensation of a power system by controlling the excitation current of a synchronous motor via PSO based PID and Ziegler Nichols (Z-N) based PID controllers.