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

Multi-resonances phenomena occurs 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 variation of grid impedance. To this end, this paper proposes a hybrid multi-resonances suppression method based on the improved Dual-Division-Summation (D-D-Σ) method and virtual admittance strategy. Multi-resonances are divided into dynamic resonance and static resonance, which dynamic resonance frequency shifts with 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 multi-resonance suppression method can adapt to parameter changes and simplify 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 paper.