Harmonic Current Suppression Strategy Based on RRESO for LLCL‐Filtered Power Conversion System Under Distorted Grid Voltage

ABSTRACT This paper studies a harmonic current suppression strategy for LLCL‐filtered power conversion system (PCS) under distorted grid voltage condition in order to improve the power quality performance. First, a mathematical model of PCS with LLCL filter is established in αβ reference frame. Then, a modified repetitive resonant extended state observer (RRESO) is proposed to estimate lumped disturbances including both internal and external elements. Repetitive control is adopted in the calibration loop of the observer as an enhancement for estimation and suppression of periodic disturbances. In addition, a grid voltage sag compensator (GVSC) is implemented to improve the accuracy of reference current generation under abnormal grid voltage conditions. Moreover, disturbance rejection capability is certified through frequency–domain evaluation. Stability analysis was also carried out to further validate the robustness of the proposed control method, ensuring stable system operation under parameter drifting scenarios. Finally, a PCS prototype was built up. The experimental results obtained on the basis of the prototype could verify the feasibility of the proposed control strategy and its outperformance of power quality compared to conventional algorithms in PCS applications.