Impact of DC-link voltage ripples on the machine-side performance in NPC H-bridge topology

In this paper, the impact of dc-link voltage ripples on the machine-side spectrum is investigated. The analysis is targeted for a high-power converter using NPC H-bridge topology. Due to the high amplitude of 2^nd harmonic and additional f₀/2 sub-harmonic that is introduced by a special modulation scheme, their impacts on the machine are at question. In this work, these questions are addressed via mathematical modeling followed by simulations and experimental validations. The conclusions are that the 2^nd harmonic in the dc-link leads to a small amount of amplitude distortion of the command voltage, while the f₀/2 sub-harmonic generates small amount of 2^nd and 4^th even-order harmonics. These voltage ripples do not harm the machine and will not reduce the output voltage capability of the converter.