A 3-PHASE PWM STRATEGY USING A STEPPED REFERENCE WAVE-FORM

The theoretical derivation of a carrier-based three-phase PWM technique using a stepped reference waveform is presented. The reference waveform is divided into 30-degrees intervals, with each interval being controlled individually to control the magnitude of the fundamental harmonic. This process contrasts with the commonly used approach of amplitude modulating the entire reference waveform to control the fundamental harmonic. The resultant PWM technique is shown to be similar to a square-wave strategy but with a lower current distortion being obtained at high fundamental magnitudes and high carrier frequencies. The practical realization of the PWM technique is described using performance criteria such as minimum pulse widths, peak carrier frequencies, and the current distortion.