Optimum Power Oscillation Damping Improvement Using an Add-on Self Tuning Control System for Upfc Application

This project presents a new addon self tuning control scheme to supplement its conventional PI control system in damping low frequency inter area power oscillations. Low frequency (0.1 to 0.8 Hz) inter-area oscillations are often observed when power systems interconnected through weak tie lines are subjected to disturbances such as faults, line outages and sudden load changes. Power System stabilizers(PSS) that are invented are suitable for damping local area(intra-area) oscillations. UPFC is a versatile FACTS device that can be effectively used for damping such inter area power oscillations. For a wide range of operating conditions, the conventional PI controlled UPFC unless retuned suffers from insufficient or non optimal damping performance. In addition tuning of PI controllers is a complex task in a large power system network. Artificial Neural networks and fuzzy logics require either offline training or inference rules which are ineffective for damping oscillations in a dynamic power system. To overcome these problems it is proposed to supplement the PI controller with an (Self Tuning) ST feedback loop comprised of an identifier and a Pole Shifting (PS) control algorithm. The ST control algorithm which is based on a Pole Shift technique has previously been successfully applied in Adaptive Power System Stabilizers (APSSs). A constrained recursive least squares (CRLS) identification procedure is adopted here to correctly identify system and smooth out parameter variations efficiently during large disturbances (i.e., large power swings) following a fault condition. With a CRLS identifier tracking the system conditions online, this scheme eliminates the need for PI parameter retuning. The identifier works on an estimated plant model of a power system; an auto-regressive moving average (ARMA) model which is simple and involves only a minor calculation step. A two area power system is considered with different abnormal conditions(faults) as case studies where the damping performance is considerably improved in an optimum manner with the proposed add-on scheme and the comparative results are presented.