Generalised overmodulation approach applied to symmetrical and asymmetrical cascaded multilevel converters with faults on the converter power cells

摘要

In this work, a generalised hybrid overmodulation strategy for symmetrical and asymmetrical cascaded multilevel converters with faulty cells is proposed. This approach allows the converter to operate with a wider range of modulation indexes even with faults on the power cells, compared with the case where just operation on the linear region is considered. As a result, the operating range of the converter can be expanded. The proposed algorithm simplifies the modulation, as it does not need to calculate and store offline multiple trajectories for the voltage reference, as usually is the case with overmodulation strategies; this task is performed online. Due to the nature of cascaded multilevel converters, two kinds of overmodulation can happen during faults on the converter power cells, which are discussed in this paper. Then, solutions are presented in order to deal with all of these operating conditions. Experimental results with a hardware-in-the-loop platform are given to verify and validate the theoretical analysis.