Two-phase dipolar and unipolar modulation techniques for three-level three-phase inverters
are suggested and compared with conventional three-phase pulsewidth modulation (PWM)
techniques. Two-phase PWMs with 60 degrees (0 degrees and +/-30 degrees shift) and
120 degrees cycles are investigated from the point of view of harmonic losses, motor
voltage spectra, and torque pulsations. It is shown that two-phase dipolar PWMs have
no advantages in comparison with three-phase PWMs, while two-phase unipolar PWMs-in
contrast with three-phase PWMs-considerably decrease the motor harmonic losses and
torque pulsations in the whole motor voltage region. At the same time, the inverter
neutral point control requires reversing to three-phase PWM technique for the duration
of the control.
