Design Aspects and Performance Evaluation of Pole-Phase Changing Induction Machines

Pole-phase changing induction machines (IMs) offer the capability to extend the torque-speed envelope compared to their fixed pole-phase counterparts. Dynamic pole-changing can achieve higher torque levels at lower speeds, utilizing higher pole numbers, and extended flux-weakening range with lower pole-number operations. This paper investigates the design impact on the optimum pole-phase changing behavior and respective split of the operating region to different pole-phase operations. Additionally, the improvement in terms of the overall torque per ampere capability and efficiency is illustrated. For the purposes of the analysis, two different IMs with wound independently-controlled stator coils (WICSC) and different original pole numbers are evaluated in an effort to quantify the extent of the benefits of pole-phase changing. These geometries correspond to machines that were originally designed with 2- and 6 magnetic poles, respectively. It is shown that, in the case of the original 2-pole WICSC machine, shifting to a higher pole number is notably beneficial in terms of efficiency in a significant part of the operating region, whereas in the original 6-pole, both higher and lower pole numbers significantly enhance the overall torque capability and efficiency. The results highlight the notable benefits of pole-phase changing IMs and offer deep insight towards the derivation of standard design guidelines for these machines.