Analysis and Design of the Feedforward Strategy for Inverters in the Weak Grid with Sequence Impedance Model

The weak grid has gradually become the conventional working environment for the existing distributed energy sources, and the instability caused by the interaction between the grid and the inverter has drawn much attention. For the actual grid- connected system, there are two significant control methods. One is the resonant controller, used to reduce the harmonics for the quality of grid current. The other is the grid voltage feedforward strategy, which is quite important for system stability and no inrush start-up. However, the system might become unstable if these two strategies are used together, since the grid voltage feedforward will cause the loss of phase margin at the resonant frequency of resonant controller. Therefore, a band-stop feedforward strategy is proposed to solve this contradiction while balancing the advantages of these two important strategies, which is carefully designed based on the sequence impedance model. An experimental platform is built to verify the effectiveness of the proposed method.