Splicing Sinusoidal Overmodulation Technique Used in Three-phase NPC Five-level Inverters

In this paper, a splicing sinusoidal overmodulation technique with optimal overmodulation algorithm was developed. The splicing sinusoidal modulation waveform is spliced by two sinusoidal curves that can be adjusted independently. The area enclosed by the modulator waveform expands with the increase of the modulation index until it approaches the square wave. The optimal overmodulation algorithm is a traversal algorithm based on the mathematic analysis of harmonics, which is capable of determining the overmodulation waveform with the optimal performance. Compared to conventional counterparts, the proposed technique used in three-phase neutral point clamped five-level inverters is uncomplicated with lower total harmonic distortion. The experimental results validated the new technique.