Resonance propagation of parallel-operated DC-AC converters with LCL filters

With the higher penetration of renewable energy into modern power system, power electronics converters are most commonly employed as the interfaces to the grid. At the same time, to deal with high frequency harmonic components, LCL filters are usually adopted. Although compared to L-filters, LCL filter has higher power density, its resonance problem should be noticed. In a large renewable energy farm, multiple converters inside are connected in parallel. In this way, the analysis of the resonance problem should be expanded. Compared to a conventional single LCL filter system, additional resonance peaks appear in frequency domain analysis results in parallel system. At the same time, considering the capacitor for local reactive power compensation, additional resonance peak in the low frequency range appears. Greater challenges are brought to the system stability. Meanwhile, the harmonic performance is also influenced. In this paper, the resonance propagation of parallel converter system with a local capacitor for reactive power compensation is analyzed in detail. Simulation and experiment results support the theoretical analyses.