Hybrid modulation for asymmetrical cascaded multilevel converters under fault conditions

This paper proposes a simple hybrid modulation strategy for asymmetrical cascaded multilevel converters (ACMCs) with fault conditions. The algorithm is described by means of an example, considering a converter with one 1pu cell and one 2pu cell per phase. The modulation integrates the benefits of both the geometrical and space vector approaches. The last one is used to define the voltages to be synthesized by the high-voltage-low-frequency (HVLF) cells, avoiding the overmodulation of the low-voltage-high-frequency LVHF cells. The carrier-based geometrical approach is used for the LVHF cells to simplify the implementation of the algorithm. As a result, this new modulation is considerably simplified when compared to the space vector. Finally, experimental results are shown to validate the proposed modulation strategy.