Hybridized SVPWM Algorithm for Multilevel CHB Inverter With DC-Link Voltage Control Capability

The deployment of a space vector pulsewidth modulation (SVPWM) scheme in controlling cascaded H-bridge multilevel inverter (CHB MLI) is quite challenging; especially, when a substantial number of output voltage levels are involved and the dc-link voltages are out of balance. In this article, a simple SVPWM algorithm for CHB MLI is proposed. In the proposed algorithm, all the H-bridges in an inverter phase are treated as a single H-bridge. Consequently, the CHB MLI can be treated as a three-level cascaded H-bridge (CHB) inverter, regardless of the number of series-connected H-bridges. This approach simplifies the construction of the space vector diagram even in dc-link voltage imbalance scenarios. The proposed voltage balancing strategy is based on two approaches: interphase balancing and energy exchange between H-bridges in a phase of the CHB MLI. The former is realized by the appropriate selection of active vectors for an equivalent three-level CHB inverter. The latter is realized through the appropriate distribution of duty factors, determined in the first step of the algorithm; their unity or zero values operate the H-bridges in actively connected or bypassed modes in view of commutation losses reduction. Simulation and experimental results are presented for the authentication of the proposed algorithm on a seven-level CHB MLI.