Analysis of the unipolar PWM techniques

The unipolar pulsewidth modulation (PWM) techniques with sinusoidal sampling are analysed for single- and three-phase inverters from the point of view of the load voltage spectra, the voltage and the flux (current) distortion factors. It is shown that for single-phase application the unipolar modulation ensures excellent-close to optimised pulse distribution-results, but in case of three-phase three-level inverters with one carrier wave the results are far from the ones produced by the optimised PWM. With three symmetrically shifted carrier waves, better voltage shapes and lower distortion factors can be obtained. Theoretical investigations were confirmed by the digital simulations