Reduction of torque ripple in a wound-rotor brushless doubly-fed machine by using the tooth notching

The torque ripple is a main source of the noise and vibration which has a considerable effect on the performance of the machine. A design technique, tooth notching, which was extensively used in permanent magnet machines, has been innovatively applied to a wound-rotor brushless doubly-fed machine (BDFM) to reduce the torque ripple. First of all, the winding structure, the winding space harmonics and magnetic fields of the stator and the rotor were studied. Then, general analytical expressions of the electromagnetic torque (EMT) for the BDFM were deduced. Finally, prediction of the results was verified by several models which were calculated by the finite-element analysis method, meanwhile, the influences of different tooth-notching structures and the notch depth on the EMT were investigated. It is shown that the torque ripple can be reduced by the suggested design with small increment of the magnetic field saturation and the currents of the control winding and the rotor winding.