A Novel Control Scheme for a Unified Power Flow Controller

In this paper real, reactive power and voltage balance of the UPFC system is analyzed. Two important results related to UPFC control has been obtained. First, it is indicated that the shunt converter provides all the required reactive power during the power flow changes if the UPFC bus voltage is constant. Second, the UPFC bus voltage can be controlled both from the sending side and from the receiving side. Based on the analysis a novel coordination controller is proposed here for a UPFC. The basic control strategy is such that the shunt converter of the UPFC controls the transmission line reactive power flow and the DC link capacitor voltage. The series converter controls the transmission line real power flow and the UPFC bus voltage. The real/reactive power coordination controllers in the UPFC control system can get good performance both during transient and stable conditions. Experimental works have been conducted to verify the effectiveness of the proposed control strategy