Three-Phase Phase-Locked Loop Based on Terminal Sliding Mode for Grid-Connected Inverters

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.