SVM of Three-Level NPC Inverter with Unbalanced DC-Link

The performance of a Neutral Point Clamped converter is strongly influenced by the quality of the voltage balancing control across the dc-link capacitors. In the operating conditions with either unbalanced voltages or high voltage ripple, the harmonic content of the output voltages can increase if a proper modulation technique is not taken into account. A novel Space Vector Modulation is proposed in this paper that considers the evolution of dc-link voltages within the modulation period as well. In detail, the real voltages of dc-link capacitors are taken into account for the determination of the switching patterns of each modulation interval in order to minimize the output voltage harmonic distortion. This allows improving the performance with respect to a traditional modulation technique, which disregards the real behavior of the dc-link of NPC inverter.