A Current Decoupling Method for LCL-type Grid-tied Converters Based on Grid Impedance Estimation

The coupling between grid impedance and the control system not only reduces the stability of energy storage converters but also severely impacts the dynamic performance of the system. To achieve a fast dynamic response for LCL-type grid-tied converters under weak grid conditions, a current decoupling method based on grid impedance estimation is proposed. First, a power variation method is employed to estimate the grid impedance, enabling precise identification of the inductive component with only minimal reactive power adjustments. Subsequently, based on the acquired grid impedance information, three feedforward decoupling channels are designed for the current control model under LCL filtering, and decoupled current control in the dq-axis is achieved using a PI controller. A stability analysis based on the impedance model is then presented, demonstrating the high robustness of the proposed method. Finally, simulation and experimental results validate that the proposed approach enables LCL-type grid-tied converters to achieve high-speed dynamic response with the influence of grid impedance.