Design of higher order LCL filters that are used in grid-connected inverter applications involves multiple constraints. The filter requirements are driven by tight filtering tolerances of standards such as IEEE 519-1992 and IEEE P1547.2- 2003. Higher order LCL filters are essential to achieve these regulatory standard requirements at compact size and weight. This paper discusses the design procedure for these higher order LCL filters. The design procedure is analysed in per-unit basis so results can be generalized for different applications and power levels. This paper also gives guidelines for actual construction of the inductor based on a proposed fringing flux model. Experimental results of filtering characteristics show a good match with analysis in the frequency range of interconnected inverter applications.
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