Input Current Harmonics in a Regenerative Multicell Inverter With Single-Phase PWM 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 by a three-phase multicell cascade inverter, with single-phase pulsewidth modulation rectifiers at the input side of each cell; thus, the entire topology is able to regenerate power to the net. This paper identifies accurately the harmonic generation process in the dc-link voltage, the input current of each cell, and, therefore, at the input side of the inverter. Moreover, this paper proposes a method to reduce and, in some cases, eliminate the input current harmonics, reaching a very high input power factor for any operation condition. Simulation and experimental results are provided to validate the theoretical analysis.