Development of adaptive UPFC supplementary fuzzy controller for power system stability enhancement

In this paper, a fuzzy logic supplementary controller with gain-varied characteristic is developed for unified power flow controller (UPFC). The attractive feature of the controller is that the gain factor can be adaptively tuned in the control process according to the damping effect. The fuzzy-logic controller is mainly equipped with two fuzzy-logic units with one to switch the UPFC modulation and the other to adjust the gain factors adaptively. Simulation results validate that the proposed UPFC controller can provide good performance for different operating conditions of power system. By comparison, it can be seen that the proposed gain-variable adaptive UPFC controller is more effective in damping power oscillation than a gain-fixed counterpart and the drawback of fuzzy-logic control schemes with constant gain factor is successfully overcome.