Frequency-division Impedance Shaping Control Method for Grid-connected Inverters in a Weak Grid

In the grid-inverter system, the low-order grid voltage harmonics have serious influences on grid current by power circuit. The problem is generally solved with grid-voltage feedforward, however an additional positive feedback loop will be brought in due to grid voltage feedforward in the weak grid and that's normally unstable for the system. Focusing on the issue, this paper proposes a novel frequency-division impedance shaping method, which respectively adjusts the output impedance of grid-connected inverter with different coefficients in the low-frequency band, mid-frequency band and high-frequency band. With the proposed scheme, the grid-connected inverter can be equipped with strong robustness to grid impedance and high harmonic-rejection ability. Simulation results confirm the effectiveness of the proposed method.