I. Introduction
The electrical power energy demands are grown every year forcing the power transmission systems to work nearby its loadability and stability limits. There are two solutions in order to overcome this problem. The first solution is to install new transmission lines but it will be complicated and difficult process to solve the problem by this solution due to environmental, economic and political issues and the long time required for designing and construction. The second solution, which is widely used, is to utilize Flexible AC Transmission Systems (FACTS) devices [1]. These devices depend on solid-state converters and they can control several parameters in electrical transmission network such as voltage magnitude, line reactance and phase angle difference. They have the ability to reduce the heavily loaded lines flows, adjust the bus voltages at the required levels, enhance the efficiency of the power transfer capability and enhance the stability of the power system network [2], [3]. The advantages of using FACTS devices are low installations and operations cost, operating with no pollution and its fast and effective control manner [4].