Robust control strategy for single-stage inverters under severe grid disturbances
The proliferation of Inverter-Based Resources (IBRs) necessitates the enhancement of control systems to ensure dependable operation, particularly in suboptimal grid conditions. Conventional control methods, such as Phase-Locked Loop (PLL)-based Grid-Following (GFL) and droop-based Grid-Forming (GFM) strategies, often exhibit suboptimal performance under substantial grid disturbances. This paper introduces a novel Model Predictive Universal Control (MPUC) scheme for a single-stage three-phase inverter that effectively integrates both Grid-Forming (GFM) and Grid-Following (GFL) characteristics. The MPUC is designed with a cascaded predictive architecture, wherein the outer loop uses Finite-Control-Set Model Predictive Control (FCS-MPC) for power and voltage regulation, while the inner loop uses Continuous-Control-Set Model Predictive Control (CCS-MPC) for current tracking. The methodology includes a delay-compensation mechanism and a dynamic virtual impedance loop, aimed at improving the feasibility of digital implementation and stabilizing Grid-Forming (GFM) systems. The proposed MPUC is thoroughly assessed, compared with conventional dual-loop PI and droop control methodologies, in MATLAB/Simulink across a range of challenging conditions, including balanced and unbalanced voltage sags and frequency fluctuations. The simulation results indicate a 60% reduction in settling time, a decrease in Total Harmonic Distortion (THD) of the grid current from 4.8% to 2.0% under non-linear loads, as well as a consistent fault ride-through capability. The MPUC provides a cohesive and efficient strategy for enhancing the resilience of next-generation power systems primarily governed by power electronic converters.