Low computational cost algorithm for harmonic elimination in multilevel converters

This paper presents an improved selective harmonic elimination procedure for L-level cascaded H-bridge converters operating at the fundamental switching frequency. The procedure is subject to the constraint that l=2⋅2n+1, where n is an integer. Previously, the unknown switching angles were obtained using an analytical formula and the arccos function. The new method replaces the arccos function with a Maclaurin series truncated at the third term. This modification offers the following advantages: (i) much less computational effort; (ii) the absence of truncation errors; (iii) the ability to eliminate low order n harmonics and their multiples from the output voltage waveform, while keeping the fundamental fixed; (iv) low total harmonic distortion with a wide range of modulation indices. In some cases, the procedure mitigates other low order harmonics, in addition to selected harmonics elimination, to meet standard code requirements. The algorithm was successfully simulated for a three-phase inverter assuming l=5,9, and 17 levels.