Analysis of Harmonic Resonances Among Parallel Grid-Connected Inverters

The resonances in parallel grid-connected PV inverters were studied. Considering the effect from the step-up transformers and grid impedance, the transfer functions of different inputs to the output were derived; furthermore, the deficiencies of conventional inverters were pointed out, and a novel method was proposed, which can effectively suppress the harmonic current output, thus avoiding the resonance phenomenon, without any changes of the topology. Then compared Block Diagrams before and after applying the proposed method, theoretically proved the correctness of the virtual conductance method; Finally, simulation models were built to restore resonance phenomenon and to verify the feasibility of the method.