Practical Online Modulation Method for Current Ripple and Switching Losses Reduction in the Three-Phase Voltage Source Inverters

Abstract

Convectional optimal pulsewidth modulation (PWM) current ripple reduction methods divide the vector space sectors into subsectors, where the reference vector is synthesized with a theoretically optimal sequence. However, extra CPLD/FPGA is needed for the lookup table and the PWM signal generation for alternative sequences. Moreover, when swapping in between sequences, extra switching and losses are introduced, which is particularly significant for low sample ratio operations. This article starts with an intuitive perspective on the sequence for current ripple reduction. Then, an online method is proposed to dynamically compute and select the sequence with the lower current ripples throughout the vector space. The proposed stationary frame current ripple vector locus peak computation and comparison methods can be efficiently implemented in DSPs. The proposed online method is equally effective in ripple reduction as the CPLD/FPGA based offline-optimized methods. Moreover, with low sample ratio commonly used in practice, the proposed method has even less switching losses, as it avoids extra switching during the sequences swapping. Elaborate lab setup makes it possible to obtain the switching losses of the previous methods over wide ranges of motor drive operation. Thereby, the switching losses advantages of the proposed method are validated.