Study On Direct Drive Permanent Magnet Motor For Traction Wheel Of Bullet Train

At present,asynchronous motor with reducer are used together in our country’s bullet train,The drive shaft is driven by the speed reducer,and the axle drives the wheel to realize the traction transmission.Permanent magnet synchronous motor direct drive wheel of this new type of traction drive system compared with traditional traction drive system have wider high efficiency operating range,simple structure,high transmission efficiency,less maintenance,energy saving,small volume,low noise and a series of advantages.Bullet train requires at low speed the motor output large torque to improve vehicle acceleration to reduce the acceleration time,and the motor can be long time efficient operation in the high-speed stage,and not because of permanent magnet motor with high-speed rotation make its back EMF too high,resulting in restarting difficult problems.In order to meet the special requirements of the permanent magnet motor,the following work has been carried out in this paper on a permanent magnet synchronous motor which can be switched from series to parallel:First of all,this paper analyzes the running characteristics of the bullet train and the superiority and the realization method of the direct drive of the permanent magnet motor.The permanent magnet motor which can be switched from series to parallel is used to meet the special requirements of permanent magnet motor.At low speed,the windings are connected in series to improve the torque output;When the speed exceeds the turning speed,the winding is switched to a parallel state,so as to reduce the back EMF,and avoid the problem of the difficulty of re throwing because the back EMF is higher than the voltage of the inverter.The mathematical model of permanent magnet synchronous motor is constructed,and the steady state analysis is carried out.A direct drive permanent magnet motor is designed,which can be switched from series to parallel.Secondly,the cause of cogging torque of the direct drive permanent magnet motor is analyzed and deduced.The cogging torque suppression method is established,and the motor is optimized.The effects of the number of poles and slots on the cogging torque are studied.The number of poles and the number of slots are selected.In order to ensure the safe operation of the motor at the highest speed and reduce the leakage of the rotor as far as possible,the mechanical strength of the rotor is analyzed.The influence of the magnetic isolation bridge on the mechanical strength of the rotor under different width was studied.The finite element model of electrical,magnetic and mechanical coupling field is established to verify the validity of the design method.Finally,the wide range speed regulation method of the direct drive permanent magnet motor of the traction wheel is studied.Comparative analysis of the traditional weak magnetic control wide speed regulation method and the wide speed regulation method of the series parallel connection,It is concluded that the wide speed regulation method of the winding from series to parallel is more suitable for the working condition of the bullet train.The control flow and the switching method of the series connection and parallel connection of the winding are established.