Regenerative Cascaded Cell Inverter with Active Filter

Abstract

In the medium voltage application it is very beneficial to use cascaded inverters. Traditionally, this type of inverter is based on diode front end and bulky phase shifting transformer. Due to the demand of 4 quadrant drives and more severe grid requirement, the cascaded inverters with active front end have been started to emerge in the market. This article introduces regenerative cascade inverter topologies. After a short summary about the topologies, single-phase cell solution with NPC is analyzed in detail. Since one of the most challenging problems is the elimination of low order grid harmonic at low motor speed, the article demonstrates the origin of this harmonics. After the clarification of the harmonic generation phenomenon, a novel harmonic elimination method is introduced. Apart from the description of the new elimination concept, the proper controller structure is described as well. Finally, the performance of the novel method is verified by Matlab simulation.