ACTIVE Disturbance Rejection Control of LCL Grid-Connected Inverter Based on Resonance Extended State Observer

This paper presents an enhanced control strategy for grid-connected inverter systems using LCL type filters. This strategy integrates a prefilter, full state feedback active damping and a resonance extended state observer, implemented in the $\alpha \beta$ coordinate system. A second-order pre-filter is used to attenuate the grid harmonics and extract the sinusoidal component of the grid voltage. This ensures a stable output of high-quality current, especially in the case of unbalanced three-phase grid voltage and excessive grid voltage harmonics. In order to reduce the impact of disturbances (including filter parameter changes, modeling inaccuracies, non-ideal grid conditions and unknown disturbances) on the grid-connected inverter system, the Resonant Extended State Observer (RESO) is introduced. The observer estimates the actual total disturbance and compensates it in real time in the control feedforward loop, which helps to improve the long-term stability and anti-disturbance capability of the system. This strategy further employs full-state feedback active damping to mitigate the impact of LCL resonance on the system. Validation of the presented control strategy is carried out through comprehensive simulation studies using Matlab/Simulink. Demonstrating the feasibility and effectiveness of the control method presented in this article, the simulation results validate the precision of the theoretical analysis.