An integrated design approach of LCL filters based on nonlinear inductors for grid-connected inverter applications

•A design approach of LCL filters for grid-connected inverters is presented.•Feedback control is employed to damp the filter resonance.•Improved robustness and dynamic performance of the control system are achieved. This work presents a modified design procedure for an LCL filter topology that takes into account the optimization of the current control loop in terms of both robustness and dynamic performances. The proposed approach considers some issues that are usually neglected by the most common design methodologies, e.g., the nonlinear variation of the inductances as a function of the frequency and instantaneous currents. Based on the analysis of the equations that describe the behavior of the filter, a novel methodology that integrates the design of the filter inductances, a feedforward controller, and an active damping method is developed. As a result, the complexity of the feedback control system can be reduced and a simple proportional-integral (PI) controller is employed in the current control loop, with low steady-state error and simple tuning. Experimental results are discussed to validate the theoretical assumptions.