Evaluation of control strategies for LCL grid-tied distributed generation systems

The LCL filter is one of the most used filters in grid connected distributed generation. It is mainly due to its efficiency and reduced physical size when compared to a typical L filter. However, the LCL filter has an inherent resonance frequency that can lead the system to instability or power quality degradation. The converter or the grid current can be used as controlled variable in the current controller. Based in this context, this paper analyzes the stability and studies the control issues brought by the dynamics of the LCL filter. A comparative analysis of the results provided by the use of different controlled variable in the current controller is presented. An evaluation of PI and PD control is done to verify which one is the better option to be used in the current control. A theoretical analysis is carried out based in the pole-zero map of the system, Bode diagrams and numerical simulation.