Robust LCL filter design for grid-side current single-loop controlled grid-connected converters under weak power grids

摘要

The point of common coupling (PCC) voltage feedforward is widely employed for LCL-type grid-connected converters to prevent the large inrush current during startup and suppress the disturbance of the grid voltage, etc. However, this feedforward loop is usually ignored in the system modeling and stability analysis for simplicity. Such an assumption may not be valid under weak power grids and can even lead to incorrect LCL filter design and unstable current control. In this paper, the detailed modeling of unit PCC voltage feedforward control is presented, and it shows that this control loop can introduce an additional positive feedback of grid-side current. Based on the established model, a robust design region of LCL filter is proposed for grid-side current single-loop control. Following this design guidance, the system can be always stable under grid impedance variation. Experimental results are finally presented to verify the theoretical analysis and robustness design.