Controlling Rotor Vibrations of a Two-Pole Induction Machine With Unipolar Actuator

A three-phase two-pole induction machine has been fitted with coils wound around the machine shaft inside the end shields of the machine. The coils induce unipolar flux in to the machine when supplied with a controllable voltage supply. These windings act as a unipolar actuator that can be used to produce radial force on the rotor. The machine does have a short-circuited extra four-pole stator-winding to reduce unbalanced magnetic pull (UMP) due to the interaction of the two- and four-pole flux components. In two-pole machines, unipolar flux and slot harmonics cause the whirling orbit of an eccentric rotor to pulsate with double slip frequency. The unipolar actuator will mitigate this pulsation when voltage is supplied to the unipolar coils at slip frequency and at correct phase. Current needed to remove pulsation is higher than what is needed to counter the measured unipolar flux. Effects of zero frequency unipolar flux are studied. Theory and measurements are presented.