PWM techniques for an open-end winding seven-phase drive with a single DC source supply

In an open-end winding drive topology two voltage source inverters (VSIs) are connected to the two separate sets of terminals of the stator winding. The most frequently investigated topology uses two two-level VSIs that require two isolated dc-bus supplies. The other alternative is to use a single dc-bus voltage source, which then requires elimination of the common-mode voltage to avoid the zero-sequence current flow. This paper investigates a seven-phase open-end winding topology, with the two two-level VSIs fed from a single dc supply. Hence, in addition to zeroing on average voltages in all non-flux/torque producing planes, it is necessary to restrict the zero-sequence current flow, which would be caused by the common-mode part of the phase voltages. The switching states providing zero common-mode voltage (CMV) are indentified and the corresponding space vectors determined. A correlation between these space vectors and the space vectors that are used in standard seven-phase two-level VSI modulation is investigated and a simple carrier-based PWM is proposed, based on this correlation. The method is implemented in simulations and experiments and the results are presented to verify the concept.