Voltage-balancing strategies for diode-clamped multilevel converters

This paper explores space-vector modulation strategies for diode-clamped multilevel converters. The analysis is focused on the voltage-balancing issue, since this is a very difficult task in high-order multilevel converters. Two strategies for selecting redundant vectors in the space-vector diagram are explained; both of them are based on minimizing a quadratic parameter related with voltage imbalance in the capacitors. Simulation results show similar behavior of the four-level converter for both modulation strategies. As expected, voltage balance cannot be achieved for some operating conditions that involve deep modulation indices and the existence of active currents. The limits in which the four-level converter cannot achieve charge balance by nearest-three-vector modulation are verified.