Study of Harmonic Spectrums for 2L and 3L Voltage Waveforms at Pre-Programmed PWM

The converted power quality is mainly determined by the PWM algorithm. Analysis of scientific and technical literature has determined the method of pre-programmed PWM (PPWM) as the main one for high power converters. PPWM operates effectively at a low switching frequency of semiconductor modules in multi-pulse circuits for connecting to the grid. PPWM switching is carried out according to pre-programmed sequences selected depending on the required voltage spectrum of the converter, from which the harmonics that have the most negative effect on the current quality are completely excluded or mitigated. In this article, we study the harmonic spectrums for 2L and 3L PPWM voltage waveforms signals. PPWM patterns were calculated with quarter-wave symmetry. The patterns are graphically presented as dependences of switching angles on the modulation index. The spectra and coefficients of total harmonic distortion (THD) up to the 50th harmonic of converter voltages were obtained in the full modulation index range. The obtained scientific results help specialists to select the optimal pattern of PPWM to solve the problems of ensuring electromagnetic compatibility.