Optimized use of selective harmonic elimination techniques for three-phase AC/DC converters for high power applications

The use of optimized firing patterns for selective harmonic elimination presents several advantages over other modulating techniques. Particularly, in terms of number of eliminated harmonics and commutation frequency. However, the high amplitude for the first group of characteristic harmonics is considered a disadvantage. This paper presents an improvement in the use of selective harmonic elimination techniques for high power rectifiers when two or more three-phase AC/DC cells are simultaneously operated. Indeed, the relative displacement and modulation indexes of the modulating techniques are optimized in order to minimize the amplitude of the first group of characteristic harmonics. Thus minimizing the THD of the AC line currents. The paper includes a systematic formulation of the equations and procedure for the displacement and modulation index computation. Preliminary simulated results confirm the validity of theoretical considerations.