Active damping for grid-connected LCL filter based on optimum controller design using injected grid current feedback only

LCL filters are widely used for grid-connected converters because its superiority over L and LC filters, however the resonance problem produced by these filters requires a more effort in the design process to damp it. Active damping techniques which use the sensed capacitor current are widely used in this regard to solve this problem; however this requires an increase in the number of sensors. Based on the optimum design for PI controller, this paper introduces an active damping method based on the capacitor estimated current without increase in the number of sensors. This is achieved by using an additional observer loop as a feedback in the controller loop to estimate the capacitor current. The simulation results for the proposed control algorithm are introduced in this work.