Design of current-controller with PR-regulator for LCL-filter based grid-connected converter

In the application of LCL-filter based converters, the structure and parameters of current-controller is very important for the system stability and output current quality. This paper presents a filter-capacitor current feedback control scheme for grid-connected converter. The controller is consisted of a proportional-resonance regulator and a proportional regulator. Unlike the existing control strategy with unit capacitor current feedback, the proposed method applies the proportional regulator to the feedback path, which can decouple these two regulators, and simplify the tuning process. Controller parameters are tuned with the aid of root-locus of system close-loop transfer function, which can provide better grasp of the influence of individual parameters and make the design process visible and holistic without any simplification and assumption. The validity, reasonability and feasibility of the control strategy and the proposed current controller design method are verified by the simulation results of a 50kVA grid-connected inverter.