Stability Enhancement for Parallel Grid-Connected Inverters by Improved Notch Filter

As parallel inverters connected to the weak grid, the interactions between the inverters and the grid are the potential threat to the system stability. The traditional grid-side inductance current feedback control method with notch filter can suppress the high-frequency oscillation. However, it will lead to stability reduction and even instability. Therefore, a stability enhancement method by the improved notch filter is proposed for parallel grid-connected inverters. This method can effectively restrain parallel inverters' harmonic current into the grid, and accordingly avoid the high-frequency oscillation of impedance network. Furthermore, it improves the phase margin of the system, and thus ensures the sufficient stability of the system in the weak grid. Considering the notch depth and dynamic performance of improved notch filter, the appropriate control parameters are selected. Finally, experimental results verify the validity of the proposed control method.