PSO-tuned fixed-time sliding mode voltage and current controllers for grid-forming inverters

This paper focuses on enhancing the performance of capacitor voltage and inverter current controllers for grid-forming inverters (GFMIs) equipped with an LC filter, ensuring seamless transitions from off-grid to grid-tied modes. A novel Particle Swarm Optimization-Tuned Fixed-time Sliding Mode Control (PSO-FSMC) method is introduced and applied within a cascaded voltage and current control framework for GFMIs. This paper presents a new and straightforward approach for designing sliding surfaces and control laws of the FSMC, specifically focusing on balancing chattering reduction, singularity avoidance, and ensuring both rapid response and strong robustness. An innovative application of the PSO algorithm optimizes 24 control parameters of the FSMC, aimed at reducing tracking errors during transitions from off-grid to on-grid modes. The effectiveness of the proposed PSO-FSMC is rigorously tested and compared with well-established PI voltage and current controllers through simulations conducted in MATLAB/SimPowerSystems. The behavior of the closed-loop system using the proposed controller is evaluated during transitions from autonomous to grid-connected modes under both ultra-weak and ultra-strong grid conditions. Results confirm that the proposed method significantly outperforms the PI controller, achieving a 97% reduction in tracking errors in both transient and steady-state responses.