The demand for electrical motors in electric and hybrid electric vehicles is increasing dramatically. Using Permanent Magnet (PM) motors as one of the brushless motor options is challenging because of the manufacturing process and extremely volatile cost. This invention involves an electric machine without or reduced rare-earth materials, containing a multiphase stator winding that can operate without brushes and slip-rings and reduces the overall cost and required maintenance. The invention discloses a novel self-excited machine that uses harmonic excitation to eliminate slip-rings and brushes. The rotor has two sets of winding, the field winding for the synchronous torque generation and the auxiliary winding for exciting the field winding. A multiphase winding is proposed to produce additional independent harmonic magnetomotive force (MMF) to induce current on the auxiliary rotor winding. A converter is employed to convert the induced ac currents on the auxiliary winding to ac or dc current for the field windings, so that the rotor flux interacts with the stator fundamental MMF to produce electromagnetic torque. Since the harmonic MMF is controlled with harmonic portion of stator current, then the frequency of induced voltage can be compensated independently from the fundamental MMF frequency. The concept can be added to the conventional PM motors to reduce rare-earth materials and the cost, alongside increasing the efficiency and reliability in the field weakening region.
Name: Sheikh Ismail