On comparing the symmetrical and non-symmetrical selective harmonic elimination pulse-width modulation technique for two-level three-phase voltage source converters

Selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It is shown recently that symmetry requirements can be relaxed as a constraint. This changes the way the problem is formulated and different solutions can be found. This study presents different formulations of the problem, namely quarter-, half-wave symmetry and non-symmetrical waveform. A critical evaluation and comparison between the three schemes are reported here based on various aspects, such as number of eliminated harmonics, harmonic spectrum profile, harmonic phasing, converter performance, computational time and solution space limitations. Selected simulation and experimentally validated results are presented to confirm the theoretical work of this study. This manuscript is a revised and extended version of earlier paper that was presented at the IEEE PESC 2008, Rhodes, Greece, 15-19 June 2008, and has not been submitted to any other journal for consideration and possible publication.