Flexible Hexagon, an Approach to Utilize Distributed Module Voltages to Reduce Voltage-Time Area Errors of Multilevel Converters

In this paper, a new approach to utilize varying module voltages in multilevel converters (MC) is presented. By actively distributing the module voltages within a defined range, additional intermediate switching levels become available. Using these enables output voltages with lower voltage-time area
errors (VTAE) and therefore output currents with reduced ripple without requiring a higher switching frequency or larger filter components. Since the proposed modulation method adds module voltage dependent and thus, flexible, additional sub-triangles in the αβ-plane, it is referred to as Flexible-Hexagon Modulation. Calculation results demonstrate that improved module voltage distributions can reduce the mean VTAE compared to an MC with equal module voltages across a wide operating range by about 50%.