SVPWM Voltage Balancing Boundary Analysis and Extension of Single-Phase Cascaded Multilevel Rectifier

To ensure the voltage-balancing capability of the cascaded H-bridge multilevel rectifier (CHMR), the voltage-balancing space vector pulsewidth modulation (VB-SVPWM) is constructed by combining the minimum energy characteristic. However, the existing voltage balancing modulation strategy could fail under extreme conditions of unbalanced cell loading or when some cells are unloaded due to failure. The power transfer limitations of the sub-cell terminals determine the voltage balancing boundary (VBB) for the VB-SVPWM under several load scenarios. Extension methods are also considered for situations out of this VBB. Following the theoretical derivation and the relationship between the number of no-load cells, the load unbalance index, the number of cascaded cells, the modulation index, and the power factor, a wider VBB can be reconstructed by modifying these above variables. Simulations and experiments are conducted with a three-level, three-cell cascaded rectifier to validate the VBB of the proposed VB-SVPWM and its expansion.