Analysis and Performance of a High-Efficiency Transformerless Hybrid Active Filter

摘要

Active harmonic filters have been widely studied in recent years. Price, size and power losses have been the main problems with conventional active filters. This paper proposes a 3-phase voltage source active filter with series-connected capacitors and an LCL-type line filter (LCLC-VSAF). The system makes it possible to compensate harmonics with a lower dc-link voltage, higher switching frequency, and smaller filter inductors. Moreover, the active filter can be built using a fairly inexpensive standard frequency converter with a lower power rating. Experimental test results will be presented. Harmonics caused by 20 kW nonlinear loads were compensated in the 690 V power system. An active filter built on a commercial 400 V frequency converter with 20 kHz switching frequency was used. Efficiency up to 99 % was achieved.