The Limits of Pole Changing Operation of a Nine-phase Induction Motor

Through the use of the pole-phase modulation technique, it is possible to electronically change the number of poles of a nine-phase, four pole induction motor, so that it operates in a twelve-pole condition. This technique avoids the need for modification of the machine’s winding connections and the use of extra components. The developed torque in an induction machine is proportional to the number of poles, so in this second configuration, the machine becomes capable of producing higher torque values. However, an increase in the number of poles of the machine reduces its magnetizing inductance by a factor of the square of the number of poles, leading to an increase in its magnetizing current by the same factor. Consequently, this causes a higher temperature rise of the machine, which can damage its windings and decrease its lifespan. This work conducts a study on the temperature rise of the machine, which involves a experimental test to obtain its thermal model, and simulations along with its electromagnetic model, in order to establish time limits for the machine operation under high-torque conditions, without exceeding the temperature limit dictated by its insulation temperature rating. Experimental results will also be shown regarding the impacts of pole-changing at the electric drive performance metrics, such as DC bus voltage oscillation and its output current.