Optimal inductance ratio of LCL filter for grid connected inverters considering with low order harmonics

Grid injecting ac current from grid connected inverters contains harmonic components which can be effectively attenuated by LCL type filters with comparably low filter cost. Recent researches tell that the current harmonics stem not only from high order PWM switching itself but also from low order dead time control for the PWM switching. However, low order current harmonics from the dead time control are not fully investigated yet. This paper shows that the ratio of filter inductances in LCL filters is one of important factors relating with the filter performance. This paper analyses frequency responses of LCL filters to get optimal inductance ratio in grid connected inverters. Simulation results verify proposed optimal inductance ratio for LCL filters to attenuate both high order switching harmonics and low order dead time control harmonics.