Research On Flux-weakening Speed Expansion Of Permanent Magnet Synchronous Motor With Pole-changing

Permanent magnet synchronous motor has the advantages of small volume,high torque density,high efficiency and good variable frequency speed regulation performance.It is widely used in new energy vehicles,aerospace,rail transit and other industrial fields.Since the rotor magnetic field of the permanent magnet synchronous motor is excited by the permanent magnet and cannot be adjusted,and the back potential of the motor is proportional to the speed,it is necessary to increase the direct axis demagnetization current for weak magnetic control when the motor runs above the turning speed,so as to meet the limit of the inverter voltage.In order to improve the weak magnetic capacity of PMSM,the direct axis inductance can be increased first,but the increase of the direct axis inductance will reduce the power factor of the motor.On the other hand,compared with the electrically excited synchronous motor,the direct axis inductance of the permanent magnet synchronous motor is much smaller under the same electrical load,so its direct axis inductance cannot be large.Secondly,the weak magnetic energy of the permanent magnet synchronous motor can be improved by reducing the permanent magnet flux,but the torque density of the motor decreases.In order to meet the needs of torque density and weak magnetic speed expansion of permanent magnet synchronous motor at the same time,the pole-changing idea,permanent magnet synchronous motor and weak magnetic speed regulation are cleverly combined in this paper,and a permanent magnet synchronous motor with weak magnetic speed regulation through pole-changing is proposed.The main research contents are as follows:(1)Starting with the connection mode of stator windings and the superposition structure of permanent magnets with different number of poles in the rotor,the pole-changing weak magnetism principle of permanent magnet synchronous motor is proposed.Four different pole-changing combinations are proposed,and the winding coefficients of different pole-changing combinations are derived.In order to determine the reasonable variable stage structure,the harmonic components of the magnetic field of each variable pole combination armature were analyzed by finite element method.The stacking method of embedded permanent magnet is proposed and the characteristics of the stacking structure are analyzed.(2)By optimizing the shape of rotor core and injecting specific harmonics into the air gap magnetic field,the air gap magnetic field was optimized for the 12-slot,8-pole,4-pole and 2-pitch pole-changing motor,and the influence of stator auxiliary slot structure on the torque ripple of each pole and the cogging torque of the motor was studied.(3)The principle of weak magnetic speed expansion of the pole-changing motor is studied,the quadrature-axis inductance and direct-axis inductance and permanent magnet flux of the motor are calculated under different pole numbers.Finally,the operation characteristics of the motor before and after pole change are analyzed theoretically,and the switching points of magnetic field with different pole numbers are determined.