An LADRC-based dual-loop control strategy for grid-connected grid-forming inverters

Abstract

The robustness degradation of grid-forming inverters operating under strong-grid environments with high short-circuit ratios remains a critical challenge when conventional dual-loop PI-based voltage-current control is employed. This study aims to improve the stability and robustness of grid-forming inverters under strong-grid conditions while maintaining the basic dual-loop control structure for practical implementation. To overcome the limitation of conventional dual-PI control, a dual-loop control framework integrating linear active disturbance rejection control (LADRC) is developed, in which LADRC is applied to the outer voltage loop while the inner current loop retains a PI controller. A comprehensive mathematical representation of the grid-forming inverter is formulated, and a complete control architecture is subsequently established, based on which the detailed design of the LADRC-based outer voltage loop is systematically elaborated. The effects of key LADRC parameters on control performance are thoroughly analyzed, and corresponding guidelines for parameter tuning are derived. The analysis shows that the proposed LADRC-based voltage loop can enhance voltage regulation capability, improve disturbance rejection performance, and reduce the sensitivity of the inverter to strong-grid operating conditions. Hardware-in-the-loop experimental validation is conducted, and the results confirm that compared with conventional dual-PI control, the proposed LADRC-PI strategy effectively suppresses oscillatory behavior and significantly enhances the robustness of grid-forming inverters under strong-grid conditions.