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 neutral-point-clamped (NPC) H-bridge topology. Due to the high amplitude of second harmonic and additional f0/2 subharmonic 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 second harmonic in the dc-link leads to a small amount of amplitude distortion of the command voltage, while the f0/2 subharmonic generates small amount of second and fourth even-order harmonics. These voltage ripples do not harm the machine and will not reduce the output voltage capability of the converter.