Per unit model of UPFC and its optimal control

The unified power flow controller (UPFC) is considered as the most effective FACTS controller, however, the realization of its functions depends mainly on its control strategy and parameter setting. Based on a set of properly selected base values, a per unit model and an equivalent circuit for the UPFC are developed in this paper. Further, a power oscillation damping (POD) controller for UPFCs is designed, which has a similar structure to the power system stabilizer (PSS). The per unit model and the POD controller for UPFCs are tested in a typical system using NETOMAC and the parameters of the POD optimized through minimizing the objective function. It is shown that the per unit model for the UPFC developed in the paper has clear physical meaning and is easily realized in a program like NETOMAC. The simulation results show the control strategy proposed in the paper can effectively enhance the stability of the system and damp the oscillations of the system.