Sensitivity-based coordination to controllable ranges of UPFCs to avoid active power loop flows

Abstract

With its power setting decided by power system conditions, the unified power flow controller (UPFC) changes the direction of the power flow of the transmission branches, possibly yielding or intensifying the active power loop flows (APLFs). This paper studies the controllable range of the active power setting of the UPFC to avoid the APLF. The sensitivity between the active power setting of the UPFC and the active power flow of the critical branch is proposed, and iteratively solved to find the marginal power setting yielding zero active power flow of the critical branch. The controllable range of the active power setting to avoid the APLFs is decided by the max/min marginal power settings. The coordinated model between the series and shunt converters is newly proposed to determine corresponding controllable ranges with the change of the voltage setting, and the coordinated model of multiple UPFCs is proposed to decide active power settings of multiple UPFCs. The Floyd-Warshall algorithm is improved to satisfy the rule of rectangular algorithm, thus to find the APLFs and the critical branches. The numerical results on the New England 39-bus system show the feasibility and effectiveness of the proposed models.