Synchronized Space-Vector PWM for Three-Level VSI With Lower Harmonic Distortion and Switching Frequency

Abstract

A novel synchronized space-vector pulsewidth modulation (SSVPWM) strategy is proposed for three-level inverters, which focuses on improving the output waveforms while reducing the device switching frequency. The modulation index m is segmented in linear modulation region reasonably, and the switching sequences are designed at each segmentation independently. The sequences for two reference vector distribution modes are designed, respectively, which ensure the synchronization and symmetry in output waveforms and the minimization of switching frequency. Then, the optimal sequence at each segmentation is selected from the two sequences (corresponding to the two modes) in terms of the weighted total harmonic distortion (THD) of line voltage. The proposed strategy is verified through simulation and experiment on a constant v/f open-loop induction motor drive, and the results show that both line voltage weighted THD and no-load stator current THD can be significantly reduced compared to conventional SSVPWM (CSSVPWM) and space-vector-based synchronized discontinuous PWM (SDPWM) in linear modulation region. Moreover, at a certain reference vector number, the switching frequency can be reduced by 33.3% compared to CSSVPWM and 13.3% to SDPWM. The proposed strategy can also be implemented in the overmodulation region.