Research On Wrapped Modular PMSM For Ball Mill Direct Drive

Wrapped modular permanent magnet synchronous motor for direct drive is proposed to solve the problems,such as long drive chain,large space,low efficiency and frequent maintenance,caused by the transmission torque of the existing ball mill drive system through gears.Taking the grinding cylinder of ball mill as the rotor support,the transmission gear between the motor and the grinding cylinder can be cancelled,which will improve the transmission efficiency and stability of the system.Modular stators are utilized to improve the production and processing of the motor.What's more,each module stator can be supplied power independently,greatly reducing the converter capacity and voltage level.However,the use of direct drive system will also bring some problems: the size of the grinding cylinder is large,and the traditional assembling method of the stator and rotor can not meet the demand;the magnetic circuit structure is complex,and it is necessary to analyze the magnetic circuit,determine the magnetic flux leakage coefficient accurately and quickly to shorten the research period;last but not least,block rules of modular stators.In view of these problems,this paper has done the following work.Design of permanent magnet motor for ball mill.For the modular motor for ball mill,the appropriate stator slot type,winding shape and poles and slots combination are selected.Compared with the utilization ratio of the surface mounted radial rotor structure and the tangential built-in rotor structure,the rotor structure suitable for the ball mill is selected.In addition,for the permanent magnet direct drive system of ball mill,a new type of stator and rotor assembly structure is proposed.The small wheels distributed along the circumference between the stator and rotor replace the traditional bearings for assembly,bearing and limit,which can greatly reduce the occurrence of rotor eccentricity,excessive air gap and other problems caused by processing,assembly and other reasons,and reduce the consumption of permanent magnet and other materials.The leakage coefficient of the spoke type permanent magnet synchronous motor with half closed slot is studied.According to the different flux paths,the whole flux is mainly divided into air gap flux,permanent magnet air gap end leakage flux and permanent magnet shaft end leakage flux.The equivalent magnetic circuit diagram is given and the magnetic flux of each part is calculated.According to the ratio of the main flux to the tooth-tip leakage flux as the ratio of the path area they pass through in the air gap,the air gap flux is divided into the main flux and the tooth tip leakage flux,and the leakage coefficient of the motor can be attained.On this basis,the change of leakage coefficient and the selection of the thickness of non-magnetic bushing under different air gap length are analyzed and calculated.The block rule of modular stators is studied.The influence of different block positions on the no-load back EMF and cogging torque of the motor are analyzed.Based on the method of winding splitting,a rule of modular stator block is put forward,and the method is applied to block a 150 pole 180 slot permanent magnet motor.The result of analysis is very close to that of the finite element method.