Repetitive control strategy for grid-connected converters in stationary frame

In the synchronous rotating frame, coupling exists in the mathematical model of the grid-connected inverters adopting LCL filters. And serious distortion occurs in the inverter output current under unbalanced grid voltage or with low order harmonics in the grid voltage. Considering problems mentioned above, this paper presents a current repetitive control strategy in the stationary frame. The proposed method does not require the Park transformation or the decoupling process. It is able to effectively reduce the total harmonic distortion of the injected grid current. The specific design method of the repetitive controller is provided, considering the hardware parameters of the LCL filter and the influence of the system delay. Simulation and experimental results are presented in the end, which verifies the validity of the theoretical analysis and the effectiveness of the proposed method.