Non-deterministic AM-PWM strategy for three-phase VSI

An important advantage of random or nondeterministic modulation techniques is nonrepetitive spectral characteristics of the output waveforms without energy concentration at distinct harmonics. This absence of distinct harmonics results mainly in reduction of acoustic noise associated with the respective PWM switching, minimization of torque pulsations, etc. In this paper, an amplitude-modulation pulse-width-modulation strategy for three-phase voltage source inverters is proposed. Significant minimization of inverter switching points, due to the lowest possible ratio of the modulation interval over the inverter output period (1:3), makes the proposed strategy very attractive for medium power applications where, for instance, annoyance due to periodic PWM waveforms is of concern. Simulation results are presented and theoretical considerations are also verified experimentally on a laboratory prototype unit