Design and analysis of observer-based active damping for LCL filter resonance in grid-connected converter

Due to its superiority over L and LC filters, LCL filters are widely used to connect PWM converters to the grid. However, the resonance problem produced by these filters requires more effort in the design process to damp it. Active damping techniques which use the sensed capacitor current are widely used in this regard; however this requires an additional current sensor which increases the overall cost. In this paper, an observer is employed in the control system to estimate the capacitor current without the need for additional sensors. A systematic design and analysis for the observer-based active damping system is introduced in this paper. The simulation results and the experimental verification are presented as well.