Modern power systems are highly complex. Power electronic based systems and other static equipment that provide controllability of power flow and voltage are named Alternative Current Transmission System (FACTS) Controllers. FACTS is one of the most popular electrical grid technologies, the aim of which is that the electrical network from a passive device for transporting electricity transforms into an instrument that actively participates in controlling the operating regimes of electrical networks. Exists four main types of FACTS controllers are series devices, shunt devices, combined series – shunt devices, combined series – series devices. The optimal allocation of Thyristor Controlled Series Compensations (TCSC) and STATCOM can improve the transmission capacity. The controllability also ensures improvement of security of power systems under contingency conditions where power system stability is threatened. Power system voltage stability is one of the main areas of focus when there is a mismatch between generation and demand. A major function of a FACTS Controller is power oscillation damping involving flow frequency oscillations that threaten system security under peak power flow conditions. It is proposed to improve the damping of low-frequency oscillations by placing a unified power flow controller in the power system. The effectiveness of the application is demonstrated on a test example of a network with a voltage of 220, 330 and 500 kV.