A Robust Control Strategy for UPFC to Improve Transient Stability Using Fuzzy Bang - Bang Control

Unified power flow controller (UPFC) has been widely used to enhance damping of power swings. The control strategy adopted to mitigate power system oscillations in an effective and robust manner is the key issue. Various control methods used to improve the transient stability based on optimal parameters, state variables and injection model were studied. A scheme based on fuzzy bang-bang control is proposed for UPFC in this paper. Using fuzzy logic control (FLC) based on bang-bang control; the UPFC will contribute to the damping of power swings without deteriorating the effect of the other power oscillation damping (POD) devices. The damping effect is robust with respect to loading condition, fault location and network structure. Furthermore, the control inputs are based on rotor-angle signals that are estimated from voltage and power measurements. The FLC design is based on Lyapunov function analysis and is simulated on a single generator power system model. Numerical simulations show that the performance of controller is effective for both single-phase and three-phase fault. This single generator approach can be extended to multi-generator systems.