Analysis and design of a passively damping LCL filter in three-phase converters

In three-phase voltage source converters (VSC), the widely used LCL filter can always achieve an excellent attenuation of high frequency harmonics. However, the resonance peak in its impedance characteristic as well as some extra active and reactive power consumptions of the RC branch is inevitably generated, which will definitely increase the complexity of the filter design and VSC control. The output character of a passively damping LCL filter is determined by only three parameters: total inductance L, damping ratio ζ and natural frequency ω_n. Actually, different combinations of the three parameters can produce the same output character. Thus, an optimization approach is essential to select proper values for each element. In this work, detailed analysis of a passively damping LCL filter is firstly carried out. And then, the optimization process is implemented, taken the lowest active and reactive power consumption of the RC branch as the target. Hereafter, the design principles are derived. Finally, the proposed analysis and design approach are validated by the experiments of different filter parameter combinations.