Comparisons of Filter Volume, Loss and Temperature Rise in $3\Phi 3\mathrm{W}$ LCL Converters with Direct Digital Control and Different Filter-Inductance-Drop Rates

Filter inductors constructed with powder cores have soft-saturation characteristics and thus, result in inductance varying with their bias currents significantly. Conventionally, the filter inductances in a three-phase LCL converter are designed to have 10%∼15% drop from its initial value to achieve stable and low-THD output currents, resulting in high volume. With wide filter inductance variation (60%∼75%) in the direct digital controlled converters, the overall filter inductor size can be reduced dramatically. How about their losses and the resulted temperature rises? This paper presents comparisons of filter volume, loss and temperature-rise in two
$3 \Phi 3\mathrm{W}$
LCL converters with direct digital control (DDC) and different filter-inductance drop rates. Simulated and experimental results from 33
$\text{kW} 3 \Phi 3\mathrm{W}$
LCL converters have been used to verify the analyses and discussions.