This article proposes and experimentally validates a new chattering-free fixed-time robust sliding mode controller for the grid-connected three-phase two-level inverter through an RL filter. The proposed method addresses the reference trajectory tracking problem of grid current, enabling precise control of the power injected into the grid. Advanced nonlinear sliding surfaces and control laws are designed with the primary objective of enhancing the robustness of the closed-loop system under the proposed controller. More specifically, this work concentrates on achieving robustness against variations in filter parameters and grid impedance. The control laws are formulated to alleviate chattering in the control signal. The notion of fixed-time stability is incorporated into the controller’s design to ensure fixed-time convergence for both reaching and sliding phases and the ability to adjust the guaranteed settling time regardless of initial conditions. The fixed-time stability of the closed-loop system is proved using Lyapunov theory. The simulation and experimental results validate the effectiveness of the proposed method. It demonstrates precise tracking capability and robust performance, especially when compared with a finite-time sliding mode controller and a conventional asymptotic sliding mode controller.

This paper investigates a fixed‐time convergence issue using the sliding mode observer‐based controller for a class of uncertain nonlinear double integrator systems. This observer‐based controller is designed assuming that only the first state measurement is available and there is no information about external disturbances and modeling uncertainties. A new form of sliding mode observer in combination with a sliding mode controller is designed to estimate unmeasured state and unknown disturbances and uncertainties as well as provide the estimated data in the control law. A novel form of sliding surfaces for the robust observer‐based controller is proposed for which fixed‐time convergence is guaranteed to achieve trajectory tracking. In the proposed fixed‐time scheme, the bound on the settling time is user‐defined using design parameters regardless of the system's initial conditions. The control law and observer law are designed such that the chattering issue is alleviated in the control signal. The stability analysis of the closed‐loop system using the observer‐based controller is established via the Lyapunov theory. The validity of the controller design is tested by applying and simulating an example of a robot manipulator in Simulink/MATLAB. The superiority of the proposed method is demonstrated by comparing it with two other methods from the relevant literature.

Achieving optimal dynamic performance and effective filtering simultaneously presents a significant challenge in three-phase proportional-integral (PI)-phase-locked loop (PLL) systems. To address this challenge, the article introduces a novel approach by replacing the PI controller with a terminal sliding mode (TSM) controller within a synchronous reference frame-based PLL. The quadrature signal generator-based second-order generalized integrator is adopted for three-phase PLL systems to leverage its advanced filtering capabilities. A new advanced sliding surface and a control law are defined, incorporating multiple design parameters and ensuring a smooth control signal. This approach effectively minimizes chattering without compromising the controller’s robustness and fast dynamic response. The stability of the TSM-PLL is proven using Lyapunov’s theory, ensuring finite-time convergence. The proposed TSM-PLL is extensively evaluated under various normal and abnormal grid conditions, including weak grids, unbalanced voltages, harmonic distortion, and phase jumps, and compared against state-of-the-art PLLs. The experimental results reveal notable enhancements in convergence rate, transient response, oscillation reduction, minimum steady-state error of the PLL, and improved quality of the current injected into the grid.