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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. A proportional–integral (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 mainly depends on the sampling frequency. Such a problem can be overcome by adding an active damping (AD) 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 AD. In addition, an antiwindup compensator arises naturally into the controller when considering the limits on the control input. An important feature of the proposed PI current controller is its ability to retain the nominal transient response achieved with state-feedback control even in the presence of model uncertainty and external disturbances. 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. [ABSTRACT FROM AUTHOR]

In this paper, a robust nonlinear generalised predictive control (GPC) method is proposed by combining an integral sliding mode approach. The composite controller can guarantee zero steady-state error for a class of uncertain nonlinear systems in the presence of both matched and unmatched disturbances. Indeed, it is well known that the traditional GPC based on Taylor series expansion cannot completely reject unknown disturbance and achieve offset-free tracking performance. To deal with this problem, the existing approaches are enhanced by avoiding the use of the disturbance observer and modifying the gain function of the nonlinear integral sliding surface. This modified strategy appears to be more capable of achieving both the disturbance rejection and the nominal prescribed specifications for matched disturbance. Simulation results demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

A nonlinear predictive control (NPC) scheme in a cascaded structure for a permanent magnet synchronous motor drive is proposed. Taylor series expansion is used to predict the system response over a finite horizon. As NPC cannot remove completely the steady-state error in the presence of mismatched parameters and external perturbation, a disturbance observer is used to estimate the offset caused by parametric uncertainties and the load torque variation. In addition, input constraints (restrictions on the magnitude) are considered in the synthesis of the disturbance observer, resulting in an equivalent cascaded proportional integral action with an antiwindup compensator. The validity of the proposed controller was tested via simulation and experiment. Excellent results were obtained with respect to the speed trajectory tracking, stability, and disturbance rejection. [ABSTRACT FROM PUBLISHER]

A robust nonlinear predictive controller for permanent-magnet synchronous motors is proposed. The nonlinear predictive control law is formulated by optimizing a novel cost function. A key feature of the proposed control is that it does not require the knowledge of the external perturbation and parameter uncertainties to enhance the robustness. A zero steady-state error is guaranteed by an integral action of the controller. The stability of the closed-loop system is ensured by convergence of the output-tracking error to the origin. The proposed control strategy is verified via simulation and experiment. High performance with respect to speed tracking and current control of the motor has been demonstrated. [ABSTRACT FROM PUBLISHER]