Transient stability improvement of power system with UPFC control by using transient energy function and sliding mode observer based on locally measurable information

•This paper proposes a non-linear method to improve the transient stability of power systems.•The Network-preserving model (NPM) is intended for the power system model.•The proposed control law is obtained using four UPFC control variables.•The time-derivative signals of the controller are estimated based on a 2-order SMO. This paper proposes a non-linear technique to improve the transient stability of power systems with a unified power flow controller (UPFC) based on locally measurable information. The proposed method is developed by applying the direct Lyapunov function. The whole control system contains both elementary control approach and an additional control scheme. In the elementary control, the TEF method is investigated for modeling the damping control of the power system with UPFC. In the additional control, the time-derivative signals of the controller are estimated with a 2nd order SMO. The significance of the study is in the use of a complete UPFC model. The other main feature of the proposed method is its robustness properties against changes in the system topology. The simulation results in the case of a single machine connected to an infinite bus, the IEEE 14-bus, and the IEEE 9-bus power system illustrate the efficiency of the proposed control technique under severe disturbances. The results reveal that the proposed control technique for UPFC reduces the first swing of oscillations acceptably and increases stability margins significantly.