Control of a continuously operated pole-changing induction machine

Pole-phase modulation is a method of adjusting the pole-phase ratio of an electrical machine. Based on this method, an induction machine has been developed to operate in either a 12-pole-3-phase or a 4-pole-9-phase configuration. For applications requiring high torque, the 12-pole-3-phase configuration is used, whereas, 4-pole-9-phase configuration is used for applications requiring high speeds. Currently, switching between configurations requires the machine to be de-energized. For applications such as electric vehicle drives, induction machines are required to have both high starting torque and an extended speed range. There, unlike in a starter/alternator, continuous torque production is necessary. Continuous pole-phase modulation allows an induction machine to change configurations without the need to de-energize its windings. The result is an equivalent induction machine with extended speed-torque capability. A smooth transition (minimum torque ripple) and optimal torque production are desired during pole-changing. A method is presented to accomplish both in a 12/4 pole induction machine. The induction machine is modelled as two independent machines acting on the same load. The two machines operate simultaneously and produce independent torques. Pole changing is accomplished by increasing the torque output of one machine while decreasing the torque output of the other machine.