An Asynchronously Excited Brushless Wound Field Synchronous Machine

This paper proposes a novel brushless wound field synchronous machine with only one set of stator windings. Employing the principles of pole phase modulation, two independent spatial harmonics are created: one rotates synchronously and the other rotates asynchronously to induce current on an extra set of rotor windings called the induction winding. This current is rectified and supplied to the rotor field winding. The stator current excitations are defined to provide independent control over the speed and magnitude of the two spatial flux harmonics. Furthermore, this approach allows for self-starting from zero speed. The impacts of varying the speed and magnitude of the harmonics on the motor performance for traction application is studied with FEA. This topology eliminates the need of brushes in wound field synchronous machines; however, the induction torque can be offset by the increased saturation in the machine due to the presence of the asynchronous harmonic.