Control of a Cascaded H-bridge Multilevel Inverter with Failed Cells for Grid-Connected Application

This paper proposes an advanced approach to control a cascaded H-bridge multilevel photovoltaic (PV) inverter with failed cells for large-scale grid-connected applications. A major challenge of these PV systems come from the uneven power distribution among the PV cells on the same phase due to environmental conditions, which then leads to a power imbalance between the three-phases. The power imbalance issue can also come from the presence of at least one H-bridge cell fully damaged and bypassed. To produce a balanced three-phase voltage and current regardless of the fact that the phase-to-neutral voltages are imbalanced, a neutral-shift method is proposed in this paper. It is based on the modification of the PWM reference phase voltage angles combined to injection of a dynamic homopolar component. A multi-carrier phase-disposition PWM strategy with a switching optimization function has been also suggested.