Nonlinear power system damping control strategies for the unified power flow controller (UPFC)

In this paper, a nonlinear UPFC damping control strategy based on a combination of PI and fuzzy controllers is proposed to damp low frequency electromechanical power oscillations. The proposed control scheme coordinates the unique power flow control features in different control modes of a UPFC to allow the best damping effects to be achieved. The detailed system structure and design procedure of fuzzy controllers are addressed and discussed in full. Comprehensive computer simulations on a modified IEEE 9-bus test system have been carried out to verify the proposed control scheme. Simulation results reconfirm that the proposed control algorithm is practically implementable and the UPFC is the most powerful FACTS device which is able to provide flexible control functions required for the real-time power flow regulation and fast transient control of power systems.