Finite-Time Robust Controller Using Sliding Mode Approach for Grid-Connected Inverters Under Unbalanced and Weak Grids

This article presents and experimentally validates a new chattering-free, finite-time sliding mode controller for grid-connected three-phase inverters, aimed at enhancing the quality of current injected into the grid. The proposed controller is applied to both the current control loop and the phase-locked loop (PLL). It incorporates the finite-time stability concept, ensuring stability within a specific settling time and offering a faster response compared to conventional asymptotic stability. The design features new nonlinear terms with multiple adjustable design parameters in the sliding surfaces and control laws. Additionally, the control signal is smoothed by computing the time integral of the sign function. This approach provides increased flexibility in design parameter selection, effectively balancing fast response, robustness, and chattering elimination. The Lyapunov stability proof for the closed-loop system is analytically obtained for both the reaching and sliding phases. A comprehensive experimental comparison under abnormal grid conditions, including weak grids and unbalanced voltages, highlights the effectiveness of the proposed approach. The results demonstrate improvements in robustness, convergence rate, and chattering reduction, ultimately enhancing the quality of the current injected into the grid.