An Improved Cascaded H-bridge Multilevel Inverter Controlled by an Unbalanced Voltage Level Sigma-Delta Modulator

Jingsheng Liao
Mehdi Ferdowsi, Missouri University of Science and Technology

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Multilevel inverters have been proven to be viable solutions for high-power automotive motor drive applications due to their high volt-ampere ratings. Cascaded H-bridge inverters are a promising breed of multilevel inverters which generally require several independent dc sources. Replacement of all but one of the dc sources with capacitors in cascaded H-bridge multilevel inverters, which leads to single-dc-source per-phase cascaded inverters, has recently gained popularity. However, very few efforts have been made to address the challenging problem of voltage regulation in the replacing capacitors. In this paper, applicability of a real-time voltage control technique named unbalanced voltage level sigma-delta modulation technique to provide voltage regulation across the replacing capacitors is examined. In addition, a new voltage ratio for the H-bridge cells is introduced, which simplifies the control tasks. Analytical and simulation results prove the effectiveness of the proposed scheme.