PhD student Matthew Magill with advisor P. T. Krein
Continuing improvements in cost/performance/complexity trade-offs in power electronics allow increasingly complicated inverter arrangements to be used to increase electric machine system performance without substantial cost requirements. In addition to improved system reliability and decreased component ratings, a large number of electrical inputs allows for the electronic adjustment of an induction machine’s magnetic pole-count, or electronic pole-changing. To understand potential benefits of electronic pole-changing, and how inverter, control, and machine-winding design decisions affect drive system performance, appropriate steady-state and dynamic models for high inverter count induction machines have been developed. Figure 1 provides a comparison of steady-state torque vs. speed estimates using the developed analytical method and finite element analysis. Results obtained for a machine excited with 18 independently controlled inverter inputs display the ability to develop multiple torque vs. speed profiles from a single magnetic structure and winding arrangement.

Figure 1: Comparison of torque vs. speed profiles in dual 2-pole/6-pole operation with 18 inverter inputs

Figure 1: Comparison of torque vs. speed profiles in dual 2-pole/6-pole operation with 18 inverter inputs

An experimental test bed designed and built to validate the developed models is shown in Figure 2. The prototype machine consists of a 36-slot induction machine stator lamination that has been rewound using 36 individual toroidal coils. This unconventional winding design offers utmost machine flexibility and supports 3-, 6-, 9-, 12-, and 18-phase operations with 2, 4, 6, or 12 magnetic poles. This research is supported by the Grainger Center for Electric Machinery and Electromechanics.

 

Figure 2: Toroidally-wound induction machine experi-mental test bed

Figure 2: Toroidally-wound induction machine experi-mental test bed