Modeling of Unified Power Flow Controllers Using a Current Injection Method for Transient Stability Analysis

This paper presents a dynamic simulation of the unified power flow controller (UPFC) using a current injection method. Flexible AC transmission system (FACTS) devices give more flexibility of control for security and economic operation of power systems. Difficulties of modeling UPFC in the conventional dynamic simulation programs arise from the fact that the injected voltage by the series inverter is superimposed on the shunt inverter side voltage. A solution can be a current injection method, in which a serial part of UPFC is converted to a parallel equivalent circuit using source transformation, and two current sources affect each other at every time step. To verify efficiency of this method, the proposed model is applied for the transient analysis of an example power system