Development of Optimal Control for Distribution Line Active Filter with LC Power Filter

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Control techniques for LC filter, active filter and active filter with LC filter were developed and verified by the experiment. The inductance of the ferrite core was used in the LC filter. By using only LC filter, it was confirmed to have to adjust LC accurately according to the system impedance.The optimal servo and PI controller were used for an active filter. In this system, digital IIR Butterworth HPF was used to obtain the compensation current. The compensation characteristic corresponding to this cut-off frequency was examined. Total harmonic distortion factor was minimized at the cut-off frequency about 20Hz and THD was small without HPF.LC filter and an active filter were connected in parallel. Capacitors of the filter were changed and THD was measured. THD minimum point became flat compared with the case of only LC filter. It was confirmed that the compensation characteristic was maintained even if the L and C were changed. From the current waveform of an active filter, the inverter output was decreased.Therefore, the control method of the active filter system with LC filter was obtained.