Multiphase optimal injection PWM with dual carrier frequency to reduce current THD

Multiphase voltage source inverter drives have recently applied to various industrial applications for variable speed motor drives. Both space-vector pulse-width modulation (SVPWM) and discontinuous PWM (DPWM) are commonly used modulators. Under the three-phase setting, it is well known that SVPWM is preferred for small modulation indices, whereas DPWM is better for large modulation indices. However, little detailed discussions on multiphase setting are reported. Further, for phase number higher than 5, no explicit instructions on how to select between SVPWM and DPWM to reduce current total harmonics distortion (THD). This study developed a generalised method to select either SVPWM or DPWM under different reference amplitudes and angles. The method can be easily extended to general N-phase settings. Firstly, a generalised expression of PWM harmonic flux which is proportional to current distortion is derived. Second, by selecting the modulator that corresponds to minimum rms harmonic flux for every carrier period, optimal injection pulse-width modulation (OIPWM) is constructed. The theoretical analyses indicate that the harmonics distortion of OIPWM is greatly improved comparing with conventional SVPWM. A five-phase inverter drive built for experiments verifies the correctness and effectiveness of the proposed OIPWM.