Calculation of current total harmonic distortion for a three-phase two-level inverter with LCL-filter

This paper addresses calculation of current Total Harmonic Distortion (THD) for a three-phase two-level PWM inverter with an LCL-filter. Analytical approach introduced in late 1980s for a two-level inverter with inductance dominated load is generalized accounting for the smoothing effect of an LCL-filter. Though the obtained closed-form analytical solutions initially assume (infinitely) large ratio of switching and fundamental frequencies, they are practically accurate for the ratios of (apparent) switching and fundamental frequencies larger than 25-30. The formulas reveal a three-phase two-level PWM inverter current THD dependence on LCL-filter parameters and modulation index and can be easily modified to cover a grid-connected inverter case.