Common-mode voltage reduction PWM algorithm for AC drives

Abstract

The impact of common-mode voltage generated by PWM AC drives on motor bearings is well known. Several algorithms for common-mode voltage reduction have been proposed in the literature. While a few algorithms assume ideal switching and fall apart when non-idealities like inverter dead time are considered, some others are effective only in a limited operating range of the drive. In this paper, a previously proposed algorithm that is best suited for practical implementation is modified to include compensation for dead time and reflected wave motor over-voltage stress, while still producing output voltage waveforms with reduced common-mode content. Experimental results are provided to show the reduction in common-mode voltage over the entire operating range, with other performance attributes such as reflected wave motor over-voltage identical to conventional space-vector PWM. The advantages of applying the algorithm to a fully regenerative AC drive are also demonstrated.