An Optimization Method in the Random Switching Frequency SVPWM for the Sideband Harmonic Dispersion

The space vector pulsewidth modulation (SVPWM) has been widely used in ac motors powered by the two-level three-phase inverters. However, significant switching frequency harmonics are generated in the power spectrum (PS) of the output line voltage. To suppress the sideband harmonics near the switching frequency and its integer multiples, a novel cost function using the variance of all higher order harmonics in the PS is established and an optimization method for the selection of the switching frequency is proposed. According to an optimization case study, the optimal switching frequency distribution for the harmonic diffusion is the beta distribution. Furthermore, this article is concerned with the optimization parameter selection, including the number of the discrete switching frequency and the shape parameters of beta distribution to improve the harmonic dispersion effect in the line voltage spectrum. Simulation and experimental results demonstrate that a significant effect of the sideband harmonic dispersion is achieved when the number of discrete switching frequency is 2 × 101-5 × 103 and the beta distribution shape parameters are set as 0.09-0.21. This provides the theoretical basis for the selection of the switching frequency and hence reduces the harmonics near the switching frequency in motor drive systems.