A unified approach to analysis and design of random pulsewidth modulation in voltage-source inverters

Analysis of spectral effects of random pulsewidth modulation (RPWM) in voltage-source inverters is presented. The randomized parameter is the width of individual switching intervals, and it is shown that the optimal solution consists in random selection of only two width values whose ratio is not an integer. For the optimal randomization scheme, powers in the dc and fundamental components of the switching function are determined, while the whole remaining power appears as noise. A closed-form expression for the noise spectral density is given. The developed theory provides better understanding of effects of random-width modulation on the power spectrum of inverter output voltage, and allows explicit design of RPWM strategies satisfying specified criteria of spectral optimization. Theoretical considerations are illustrated by computational examples.