Optimal tracking control for asymmetrical fault ride through in the back-to-back converters

摘要

Asymmetrical faults in the grid cause oscillations in dc-link capacitor voltage or overcurrent in the converters. In this study, an optimal controller with a fixed structure is introduced based on the command generator tracker (CGT) to restrict the fault currents and increase stability performance under asymmetrical grid faults. For this purpose, first, the integrated dynamical model including grid-connected converters and dc-link voltage are introduced. Then, using the optimal control techniques, a CGT is designed to enhance the fault ride through performances. Next, the proposed controller is applied to the system including converter and dc-link at the source side and the dynamic performances of the closed-loop system under different fault conditions are determined. Finally, the simulation results are compared with the other conventional controllers and the dynamic performances of the proposed controller are evaluated. The results indicate that the proposed controller provides stability for the system and satisfies allowable constraints of converter current for different grid fault types such as voltage sags, asymmetrical and symmetrical faults.