Design of robust UPFC controller for damping power system oscillations using H∞ mixed sensitivity technique

This paper is concerned with the problem of designing damping controller for low frequency oscillations in power systems under dynamic uncertainty. Power systems must typically perform over a wide range of operating conditions. The existence of such dynamic uncertainties requires good robustness of the control systems. H∞ mixed sensitivity technique is applied here to the design of robust damping controllers for Unified Power Flow Controllers (UPFCs) to damp power system oscillations under uncertain conditions. Detailed investigations have been carried out by previous researchers considering four alternative (mse, msh, δse, and δsh) UPFC parameter based damping controllers. In this paper, a Single Machine Infinite Bus (SMIB) system incorporating a UPFC is considered. The objective of the UPFC is to provide damping to the low frequency oscillations in the system. Weighted mixed-sensitivity H∞ design approach has been used to design dual damping controller based on δsh (Phase angle of the shunt inverter) and mse (modulating index of series inverter). The controller design is aimed at providing adequate damping to oscillations over a range of operating conditions. The function of the damping controller is to provide auxiliary stabilizing signals in phase with speed deviation (ωΔ). Effectiveness of the proposed controller has been shown over a wide range of operating conditions for the SMIB system with the help of simulation using MATLAB.