LVRT capability enhancement of a grid connected three phase PV system by ADRC and DSOGI FLL

摘要

Low voltage ride-through is considered as one of the key technologies for the operation of grid-connected photovoltaic power generation systems. At present, the most used control methods are based mainly on PI controllers, and their robustness results are still unsatisfactory. In contrast, this article introduces a new robust control strategy that uses the compensation effect of "total disturbance" before affecting the system; this control strategy is called Active Disturbance Rejection Control (ADRC) method. In addition, most of the controllers use the standard SRF PLL to achieve the phase lock and grid synchronization. However, when the grid voltage is distorted or other unbalanced, it is necessary to use the positive sequence voltage component of the fundamental wave as a reference, but the component of the negative sequence cannot be effectively filtered because of its narrow bandwidth, and then, accurate phase lock cannot be achieved, which may cause a failure. In this purpose, a Double Second Order Generalized Integrator based Frequency Locked Loop (DSOGI-FLL) is proposed and used to improve the system operating performance and non-off-line capability. In order to confirm the robustness of the proposed control strategies, a multiple simulations tests were done by utilizing the Matlab/Simulink software. The results have demonstrated the superiority of the proposed methods and their robustness to symmetrical and unsymmetrical faults.