The Line Flow Control of Multiple UPFCs for Enhancing Power System Security

Abstract

This article presents a method to determine operating points of Unified Power Flow Controllers (UPFC), the line flow control of which can enhance system security level. The decoupledmodel has been employed as a mathematical model of UPFC for power flow analysis so as to analyze the effect of these devices on the power system. The security index that indicates the congestion level of transmission line has been proposed and minimized by iterative method. The sensitivity of objective function for control variables of an UPFC has been derived, and it represents the change in the security index for a given set of changes in real power outputs of UPFC. The proposedalgorithmwithsensitivity analysis gives the optimalset of operatingpoints of multiple UPFCs that reduces the index or increases the security margin, and Marquart method has been adoptedas an optimization methodbecause of stable convergence. The algorithm is verified by the 10-unit, 39-bus New England system that includes multiple UPFCs. The simulation results show that the power flow congestion can be relieved in the normal state and the security margin can be guaranteed even in a fault condition by the cooperative operation of multiple UPFCs.

Keywords:

• Unified Power Flow Controllers (UPFC)
• Decoupled Model
• Security Margin
• Power Flow Congestion
• Security Index