Stepless Speed Regulation Study of a Wound Pole-Fixed Bearingless Induction Motor With Three Windings

Aiming at the high cost of the frequency transformers in the traditional bearingless induction motor with two windings (BIM2W), this article studies a new type of BIM with three windings (BIM3W) which can realize the variable-voltage and variable-load speed regulation. Based on analyzing the magnetic field distribution with odd pole pairs and dipole pairs, the pole-fixed wound rotor is designed, and a novel wound BIM3W is proposed by embedding with an extra speed regulation winding ( W_S-R ) in the stator. Then, the winding distribution is studied and optimized, the equivalent impedance in the stator side of the wound rotor is deduced, and the motor speed expression is fitted into a nonlinear equation by the least square method. Further, the speed regulation strategy is proposed by changing the voltage of the W_S-R and the torque winding ( W_T ) in low and high speed area, and adjusting the applied load in middle speed area. Besides, the inductance matrix of the three windings is discussed and the vector control method based on rotor flux-oriented is adopted to realize simultaneous control of the electromagnetic torque and suspension force. Finally, the experimental platform is established to further verify the feasibility. Simulation and experimental results show that the designed BIM3W not only achieves the stepless speed regulation in whole range, but also has a well suspension performance.