PhD student Anuj Maheshwari, MS student Soumil Chaubal, IEEE members Elie Libbos & Debranjan Mukherjee, MS student Debojyoti Mazumdar, and PhD student Parag Bajaj with Advisor A. Banerjee

High-phase count machines are well known to have reduced dc bus utilization compared to conventional three-phase drives.  High-phase count machines for fault tolerance and variable-pole induction machine drives are two examples.  Variable-pole machines need more than three phases to support electronic pole changing.  Two complementary approaches to improve variable pole induction machine base speed and high-speed torque capability are proposed.  Base speed improvement is achieved with a modulation technique that increases dc bus utilization by 11.5% for the highest operating pole count.  An optimization framework for loss minimization is developed considering the simultaneous operation of multiple poles and cases, including no synchronization between operating poles, stator flux synchronization, and stator voltage synchronization.  The framework shows that voltage synchronization improves torque by 49.5% at maximum operating speed.  The benefits of the approach compared to a conventional Variable pole operation are shown in Figure 12.  A proposed control architecture Figure 13 enables one pole configuration to operate under vector control and others under scalar control, thereby eliminating parameter dependence for stator voltage synchronization.  Experimental results on a toroidally wound 36-slot machine validate the proposed modulation strategy, control architecture, and high-speed torque improvement from synchronized stator voltage injection.

Figure 12. Torque-speed envelope of a variable-pole induction machine improves at base speed (point A) by zero sequence injection and at maximum speed (point B) by harmonic injection.  The base speed increases by 11.5% and torque at maximum speed increases by 49.5%.

Figure 13. Control architecture using two parallel closed-loop controllers at low and intermediate speeds.  At high speeds, one pole excitation uses closed-loop control, and the other controls voltage magnitude to ensure voltage synchronization.