Research On Permanent Magnetsynchronous Direct-drive Motor For Gearless Ball-mill

Gearless ball-mill drive(GMD)systems are used in mines to grind vast amounts of ore into smaller pieces for further processing.GMD systems eliminate all mechanical components of a conventional mill drive system,such as ring-gear,pinion,gearbox,coupling as well as motor shaft and bearings,thus offering better energy efficiency,superior reliability,increased process availability and longer lifespan.In this paper,the working characteristics of permanent magnet synchronous motor for gearless ball mill are analyzed,and the stator and rotor structure are optimized.Also,the control strategy of permanent magnet synchronous direct-drive motor is studied.The specific contents are as follows:Firstly,the structure of permanent magnet synchronous direct-drive motor for Gearless mill drive has been optimized from the following aspects.Permanent magnet synchronous motor winding has various forms,by analyzing the magnetomotive force of the winding,a fractional slot winding with smaller magnetomotive force harmonic content has been designed.Cogging torque is a part of the electromagnetic torque ripples.In order to reduce the cogging torque,torque characteristics under different pole arcs has been analyzed.Then,Flux2 D finite element simulation software was used to analyze the motor back EMF,air gap flux density and stator yoke flux density and optimized motor parameters are obtained..Secondly,based on mathematical model of PMSM,the control strategies of permanent magnet synchronous direct-drive motor are studied.Direct torque control(DTC)is a control technique with a simple structure,it can be applied regardless the motor type.In order to depress the ripple of torque and stator flux in traditional permanent magnet synchronous motor(PMSM)direct torque control(DTC)system,six active voltage vectors of inverter are decoupled in the d-q coordinates.Space vector sectors are re-divided based on rotor flux and the switch table is readjusted in view of fast torque response.Compared with the traditional switching table,the torque can be controlled directly by the voltage vector,and the stator current can be obtained at the same time.Simulations prove the validity of the proposed method.Finally,a prototype of permanent magnet synchronous direct-drive motor used for GMD has been produced and used in a mine.Then,the validity and practicability of GMD has been verified through the experiment.