Control of Modular Multilevel Converters Using an Overlapping Multihexagon Space Vector Modulation Scheme

This paper introduces a novel space vector modulation scheme that can be applied for the control of modular multilevel cascaded converters (MMCCs) with any number of levels. This is achieved by using basic two-level or three-level hexagons to determine the switch states and the duty cycles separately within one tier of the converter which is a cascade of three-level H-bridge, five-level flying capacitor, or neutral point-clamped inverters. Many such hexagons can be overlapped, with phase shift relative to each other, for the control of a complete MMCC, instead of extending a single hexagon to regions corresponding to the number of levels. This approach simplifies the modulation algorithm and brings flexibility in shaping the output voltage waveforms. Also, this proposed method achieves good waveform quality at low switching frequency, hence resulting in low switching losses. Simulation and experimental results are presented to verify the advantageous features of the method.