Characterization and Selection of Probability Density Function in a Discrete Random Switching Period SVPWM Strategy

Aiming at suppressing the switching frequency harmonics in the integrated permanent magnet synchronous motor (PMSM) systems, a discrete random switching period (DRSP) space vector pulse width modulation (SVPWM) technique is proposed in the present study. In the proposed DRSP-SVPWM technique, the switching period is randomized according to a predefined frequency sequence. Accordingly, the narrow-band harmonics of the switching frequency are extended to a wider range. Then, a mathematical correlation between the probability density function and the harmonic distribution is established. Moreover, the effects of discrete uniform and beta distributions on the harmonic spreading are studied. Based on the proposed DRSP-SVPWM technique, the mathematical expression of the harmonic power spectrum is derived, demonstrating the intrinsic dependency between the discrete random factor and the harmonic energy distribution. Finally, a series of simulations and experimental results are compared to evaluate the performance of the proposed technique. The present study is expected to provide a theoretical basis for the design and selection of discrete frequency sequences. Meanwhile, it provides a reference to investigate the random SVPWM and improve noise and electromagnetic interference in power converters.