A Hybrid Multiresonances Suppression Method for Nonsynchronous LCL-Type Grid-Connected Inverter Clusters Under Weak Grid

Multiresonance phenomena occur in inverter clusters under weak grid, with more complex resonance characteristics. Traditional suppression methods are difficult to determine control parameters when considering dynamic resonance under the variation of grid impedance. To this end, this article proposes a hybrid multiresonances suppression method based on the improved dual-division-summation (D-D-Σ) method and virtual admittance strategy. Multiresonances are divided into dynamic resonance and static resonance, in which dynamic resonance frequency shifts with the variation of grid impedance, and static resonance frequency remains fixed. D-D-Σ method with strong adaptive ability and paralleled virtual admittance strategy reshaped the inverter output impedance are used to suppress dynamic resonance and static resonance, respectively. The proposed hybrid multiresonance suppression method can adapt to parameter changes and simplify the center frequency design process of traditional paralleled virtual admittance. The experimental results of a parallel system with three inverters verify the feasibility of the proposed method in this article.