Input current harmonics in a regenerative multi-cell inverter with single-phase active rectifiers

Harmonics are a very important issue in the design and operation of medium voltage inverter drives due to restrictions imposed by regulations. This paper studies the harmonics generated in a three-phase cascaded multi-cell inverter with single-phase active front end (AFE) at the input side of each cell. This study identifies accurately the origin of the harmonics present in the DC link voltage and in the input currents and discusses methods to reduce and, in some cases, eliminate them. It has been established that the low-frequency harmonics in the primary input current can be cancelled by an appropriate interconnection of the cells and of the input transformer.