LCL Filter Parameter Selection Using Graphical Method for a 13.8 kV ac 1.1 MVA 7-level Flying Capacitor Grid-Connected Converter Utilizing Variable Switching Frequency

LCL filter is widely used in dc to ac power converters due to its ability to provide higher attenuation at high frequencies (HF), favorable inductor size trade-off, and enhanced system dynamics response. This is particularly advantageous in renewable energy and grid-connected applications which require compliance with power quality standards (e.g. IEEE Std 519 and IEEE Std 1547). Although the design procedure for LCL filters has been extensively discussed, existing methods often focus their consideration on 2-level or 3-level neutral point clamped converters, constant switching frequency, and passive damping. This paper presents an LCL filter design procedure using a graphical method for a 1.1 MVA 13.8 kV ac 22 kV dc 7-level flying capacitor multilevel (FCML) grid-connected converter based on 10 kV SiC MOSFETs. The method accounts for any number of levels, variable switching frequency, and active damping. This graphical method can help designers gain insight into filter performance and iterate to select the optimal filter parameters.