Randomized Pulse Pattern Strategy of Synchronized SVPWM for Low-Frequency-Ratio Applications

Low switching frequency operation is preferred in machine drives of high-power applications for controlling the switching loss of power-electronic devices to a tolerable level. Hence, the modulation frequency ratio is usually low. Synchronized space vector pulsewidth modulation (synchronized SVPWM) is a method designed to reduce current harmonic distortion in low-frequency-ratio occasions. However, the switching frequency apparently varies when the pulse pattern of synchronized SVPWM changes, which makes it impossible to fully use the available switching frequency. In this article, the alternative pulse patterns of synchronized SVPWM are extended by the proposed randomized pulse pattern strategy. The proposed strategy divides pulse patterns in a line cycle of the synchronized SVPWM into six pulse pattern units according to the symmetry conditions, and randomly combines these pulse pattern units according to the probability theory. The pulse pattern units from different pulse patterns are analyzed and modified to concatenate together smoothly. The proposed strategy keeps the advantages of synchronized SVPWM that low-order harmonics are suppressed. Meanwhile, lower harmonic distortion and torque ripples are achieved compared with the conventional strategy. The proposed strategy is verified through simulations and experiments.