In this paper, voltage stability assessment of a real power system subjected to a large disturbance is introduced by a combination of static and dynamic approaches. In the first part of the study, the system is analyzed for both normal operation and contingencies by using static analysis tool in which continuation power flow method (CPF) is performed. In order to improve static and dynamic voltage stability, a shunt flexible AC transmission system (FACTS) device, static synchronous compensator (STATCOM) is employed to the system as an additional voltage support device. However, action of the STATCOM is directly influenced by proper functioning of the controller. Poorly tuned STATCOM controller results in voltage oscillations. Main purpose of the paper is optimal parameter tuning of the STATCOM in order to improve the dynamic voltage control capability in the case of occurence of a severe disturbance in the power system. Therefore, in the second part of the study, the tuning problem of the STATCOM is converted to an optimization problem which minimizes the voltage deviations. Particle swarm optimization (PSO) technique is applied to the problem in search of the optimal control parameters of the STATCOM.