Selecting stepped reference waveforms for PWM inverter drives to minimize the current distortion

Four modulation techniques that use three steps per 90 degrees of the fundamental cycle are analyzed. The functional relationships between each of the steps, determined by a current distortion minimization procedure, are shown to change with the carrier frequency and the magnitude of the fundamental. The lowest current distortion characteristics are obtained by selecting modulating techniques to cover specified ranges of the fundamental magnitude. Stepped waveforms are shown to be competitive with sinewave regular sampling techniques, and near-optimal performance can be obtained at low carrier frequencies. Operation at very high fundamental magnitudes is possible with minimal current distortion and well-defined switching periods. Theoretical developments are discussed which form the basis for specifying three-phase stepped PWM techniques that exhibit low current distortion levels.<>