Design of PI controller together with active damping for grid-tied LCL filter systems using Disturbance Observer-Based Control approach

The main advantage of the LCL filter in grid-tied converters is its ability to achieve a better harmonic mitigation in comparison with L filter. PI regulator can be considered as a good candidate for controlling the LCL filter system, as it is more convenient for real-time implementation. However, PI controller is not capable of stabilizing the grid-tied LCL filter system when the resonance frequency of the LCL network is below a certain value that is mainly depending on the sampling frequency. Such a problem can be overcome by adding an active damping to the PI controller. This paper presents the design, implementation, and performance testing of a stable PI current controller for a grid-tied inverter using LCL filter. The design process is based on combining Feedback Linearization (FBL) technique with a Disturbance Observer-Based Control (DOBC). It turns out that the composite controller, consisting of FBL and DOBC, reduces to a PI current controller associated with a linear state-feedback control that plays the role of an active damping. In addition, an anti-windup compensator arises naturally into the controller when considering the limits on the control input. The proposed controller was verified through simulation and experimental tests. The results demonstrated the ability of the controller to provide good transient and steady-state performances.