Resonance propagation of ac filters in a large-scale microgrid

Research into microgrids has become more promising during recent years. It has the potential of leading to a more resilient electric power delivery system in the face of system disturbances. Low pass ac filters are frequently adopted in microgrid power electronic interfaces that convert dc power to ac power because most of today´s distribution grids have ac voltages. Compared to a simple L filter, higher order filters, such as LC or LCL filters, are preferred due to their more effective reduction of switching-frequency harmonics and smaller sizes. However, the resonance problems caused by paralleling multiple converters with LCL filters, especially those converters having large power ratings (e.g., in the MVA range), must be accounted for when designing the entire microgrid. The analyses and designs should consider not only the resonant stability of a single converter but also the resonance propagation between multiple converters. A microgrid resonance propagation circuit model is built and investigated in this paper. Experimental waveforms validate the proposed analyses.