Current control of grid connected inverter with LCL filter utilizing two degree-of-freedom control

The LCL-filtered current controlled voltage source inverter (VSI) is commonly applied for integrating distributed generation into the utility grid. Due to the topology of the LCL filter, multi-loop control strategies using different feedback control variables have been developed to fulfill the goal of generating the desired active and reactive power by controlling the output current of the VSI. According to the analysis of the closed-loop transfer function of the control system, the output current of the inverter is a function of commanded reference current input and disturbance input which indicates the imperfect control performances of the VSI especially at the presence of nonlinearities and unpredictable behaviors of the loads. In order to achieve a good compensation of the disturbance, in this work a two degree-of-freedom (DOF) controller, based on an inverse dynamic model is applied to the LCL filter. In particular, two control schemes for design of the DOF controller are proposed and compared in this paper. The two control schemes are compared both from an analytical point of view and in simulation. A real time testing approach finally completes the analysis.