Fundamental Modulation: Multi-pattern Scheme with an Entire Range of Modulation Indices for Multilevel Cascaded Converters

The paper presents a new modulation strategy—Fundamental Modulation, which features low switching losses due to the fact that all the switches operate at the fundamental frequency, in addition, with which the converter can operate with an entire range of modulation indices (i.e. from 0 to more than 1) based on selective harmonic elimination. To realize it, a multi-pattern method is presented to compute the switching angles in a multilevel converter so as to produce the required fundamental voltage while at the same time not generate the selective harmonics. Including the staircase scheme, previous work has shown that it is possible to produce solutions only for higher ranges of the modulation index with selective harmonic elimination (SHE). Here multi-pattern are shown to extend the lower range of modulation indices for which such switching angles still exist. In particular, it is shown that all patterns require solving the same set of equations where each pattern is distinguished by the location of the roots of SHE equations. The experimental result verify the precise, practicality and feasibility of Fundamental modulation with multi-pattern method.