Experimental Comparison of Current Source and Voltage Source Active Filters with and without the Series-Connected Capacitor

摘要

Active filters are an effective way to decrease harmonics caused by nonlinear loads. Nevertheless, the price, the size and the power losses have often been drawbacks with the active harmonic filters. Power losses of the active filter can be decreased using series-connected capacitors between the supply and the inverter bridge. These structures are usually called transformerless active harmonic filters. In the paper, five active filter topologies are compared, two of which are conventional and three of which are connected with series-connected capacitors. First, the main circuits and the digital control systems are presented. The filtering performances of the systems with two different kinds of 20 kVA nonlinear load are examined and finally the power losses and efficiencies of the active filters are studied. The comparison is based on experimental tests with the prototypes constructed. The results clearly show the properties of the active filters examined. In addition, the results prove that active filters with series-connected capacitors offer a considerable choice for harmonic filtering when high efficiency is desired and capacitive reactive power is needed.