| As power system is more and more complex, Low frequency oscillations in big electric network becomes more and more serious. Unified power flow controller is the most valuable and universal device in the Flexible AC Transmission Systems, which can improve system stability and damp Low frequency oscillations by adjusting properly.The main content is as follows: Low frequency oscillations is analyzed and researched. The theory to analyze to the simple machine infinite system of unit of joining UPFC that is set up is studied, which expounds how to inhibit Low-Frequency oscillations by introducing Lyapunov method. PID of UPFC and fuzzy PID controller are designed. The simulation of low frequency oscillations taking place in the simple machine infinite system of the unit , shows that the systematic stability of improvement by UPFC is very obvious The fuzzy control strategy based on the revision factor is adopted. The corresponding controller is designed. The comparison with PID and fuzzy PID, shows that it can enhance control quality better. Using the fuzzy controller based on the revision factor to carry on the simulation to the multi-computer system between the region and inside the region, which indicates UPFC could damp system low frequency oscillations effectively and improve the system stability.
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