An Add-On Self-Tuning Control System for a UPFC Application

This paper presents an add-on self-tuning (ST) control scheme for a Unified Power Flow Controller (UPFC) to assist its conventional PI control system in damping power oscillations. The ST control algorithm is based on a Pole Shift (PS) technique that has previously been successfully applied in Adaptive Power System Stabilizers (APSSs). For a wide range of operating conditions, the conventional PI-UPFC unless returned suffers from insufficient/nonoptimal damping performance. To overcome this problem, the authors propose supplementing the PI controllers with an ST feedback loop comprised of an identifier and a PS control algorithm. With a CRLS identifier tracking the system conditions online, this scheme eliminates the need for PI parameter retuning. Further, to correctly identify system parameters during large disturbances, a constrained recursive least squares (CRLS) identification procedure is adopted here. An improved damping performance with the proposed add-on scheme assisting the nonoptimal PI-UPFC is demonstrated for a two-area power system.