General design rules for space harmonic cancellation in multiphase machines with multiple converters and star-polygonal windings

This paper presents a general rule for the design of m-phase machines supplied by n-converters that employ a hybrid star-polygonal winding in each m-phase set. This rule shows that for any m-phase machine supplied by n-converters, there exists a set of feasible slot-pole numbers in conjunction with the star-polygonal connection that allows for optimum winding MMF harmonic performance. This also allows for tables of feasible solutions to be generated, including coil pitch and calculated winding factors. From this, the star of slots method is used to obtain the winding layout of any feasible machine for comparison of its winding MMF harmonic performance. An example 3-phase machine is investigated and a number of trends for all m-phase n-converter machines can be identified. In machines with a coil pitch of 1, excellent harmonic elimination is observed for all non-torque producing harmonics and machine performance is all-round enhanced. A prototype machine has been manufactured and EMF and static torque measurements validate the predictions.