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.