Effects of Power Oscillations Damping Controllers by UPFC Using Different Fault Conditions

Weakly damped power swings are one of the main problems endangering secure operation of power systems. This paper presents two methods , based on the use of nonlinear system model , to improve damping of power swings using UPFC. A statevariable control strategy has been derived using local available signals of real and reactive power. The results of simulation tests of two control methods, undertaken using a small multi-machine system model, have been presented. The simulations show that the methods make good results in different fault places and clearing time. The results present that controlling series part of UPFC can damp power oscillation by state-variable control method, but simultaneous control of shunt and series part of UPFC can damp voltage oscillations by direct Lyapunov method. Key-Words: Transient stability, Local measurement, Flexible ac transmission systems (FACTS) , UPFC , Power oscillations damping.