Modulation Strategies for Direct-Link Drive for Open-End Winding AC Machines

Switching common-mode voltages generated by conventional pulse-width modulated inverters are known to cause bearing currents in ac machines. These undesirable currents may result in bearing damage. A direct-link drive for open-end winding ac machines has recently been proposed. Some advantages of the drive include: 1) common-mode voltage suppression, 2) no storage elements, and 3) ability to achieve up to 1.5 times the peak input phase voltage across the machine phase windings. In this paper, pulsewidth modulation strategies for the drive are proposed. Two strategies are based on space vector modulation and suppress common-mode voltage at the machine terminals. One carrier-based strategy achieves 1.5 times the peak input phase voltage across the machine phase windings but causes switching common-mode voltage at the machine terminals. Simulation and experimental results are presented to verify the operation of the drive.