
Filtering Techniques for Power Quality Improvement 38-51
controller to better compensate the low-frequency harmonics. e low-frequency analysis of supply
current is shown in Figure 38.64a and b. e THD of this supply current is decreased from 28.83%
to 4.9% with the direct current control technique implemented with the U-PWM controller and
from 28.83% to 2.2% with the indirect current control technique implemented with the U-PWM
controller.
In order to evaluate the impact of U-PWM controller, one has to perform a spectrum analysis of the
same steady-state waveforms at the switching frequency. e results of the analysis are shown in Figu