Disturbance Observer-Based Control for Three-Phase Grid-Tied Inverter with LCL Filter

This article presents the design and performance evaluation of disturbance observer-based control for grid-tied inverter with LCL filter. The proposed controller consists of a combination of a state feedback control with disturbance observer. Specifically, the composite controller is developed to regulate the current injected to the grid despite the variation in system parameters. Such variations are compensated for by the disturbance observer, while the state feedback control takes on the responsibility to ensure the stability of the closed-loop system. The developed controller is designed in the \alpha \beta stationary frame to cope with both balanced and unbalanced grid voltages. This mandates using a disturbance observer that has a resonant action property to compensate for sinusoidal disturbances with a view to ensure asymptotic tracking of sinusoidal current reference. However, under control saturation, the resonator buildup can cause the transient response to deteriorate by exhibiting a large overshoot. This problem is tackled by considering control saturation in the design process. As a result, an antiwindup compensator arises naturally in the composite controller. Experimental tests were conducted to evaluate the performance of the controller under different operating conditions. The obtained results show that the proposed controller is capable of achieving a perfect tracking of sinusoidal reference with a good transient response during both balanced and unbalanced grid voltages. Moreover, it was demonstrated that, without the antiwindup scheme, the percentage overshoot under the composite controller can reach 95% during control saturation, while the proposed anti-windup scheme improved the transient response by eliminating the overshoot.