Fuzzy logic based UPFC controller for damping low frequency oscillations of power systems

Low frequency oscillations (LFO) in power system occur usually because of lack of damping torque to overcome disturbances in power system such as changes in mechanical power. Traditionally, power system stabilizers (PSS) are being used to damp these oscillations. Unified power flow controller (UPFC) is a well-known FACTS device that can control power flow in transmission lines. It can also replace PSS to damp low frequency oscillations effectively through direct control of voltage and power. In this paper a linearized Heffron-Philips model of a (single machine-infinite bus) power system with a unified power flow controller is developed. The designed fuzzy-based UPFC controller adjusts four UPFC inputs by appropriately processing of the input error signal, and provides an efficient damping. The results of the simulation show that the UPFC with fuzzy-based controllers is more effective in damping LFO compared to UPFC with PID controllers.