Research On Health State Evaluation Method Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)has been widely used in CNC machine tools because of its high power to mass ratio,energy utilization ratio and good servo performance.At present,the lack of mature numerical control machine tool key systems and components of fault prediction methods and techniques,maintenance policy is still the later maintenance and preventive maintenance planning,unable to fully take into account the actual running state,hard to avoid cause sudden shutdown accident due to lack of maintenance and production safety accidents,and the waste of resources caused by excessive maintenance and economic losses.In this paper,the working principle of permanent magnet synchronous motor is analyzed firstly,the traditional formula of torque is deduced and the relationship between torque and phase current is expounded.While explaining the mechanism of typical faults such as demagnetization,bearing wear and interturn short circuit,the harmonic formula,bearing damage evaluation index and eccentric damage evaluation index were derived respectively,and the validity of the formula was verified with the samples of fault modes already appearing.Secondly,through analysis,it is known that the performance degradation of PMSM caused by demagnetization,bearing wear and inter-turn short circuit will cause the corresponding stator current order harmonics and rotor magnetic field order harmonics.Different order harmonics will lead to the increase of output torque fluctuations and aggravate the vibration and noise of the motor.The influence of different harmonic order on the torque fluctuation of PMSM is considered and the traditional mathematical model of torque fluctuation is optimized.Then,on the basis of defining the influencing stresses,the validity of the proposed method is verified by comparing the calculated torque fluctuation coefficient with the results directly measured by the sensor.By obtaining the current waveform of permanent magnet synchronous motor,Fourier decomposition of the signal is carried out,the main order of the waveform and the corresponding amplitude are calculated,and the results are obtained by putting it into the torque model.Finally,in order to torque ripple coefficient,eccentric index and the characteristics of demagnetization index as input,establish characteristic matrix,based on the ideal solution to find out the positive and negative ideal solution,then based on the markov distance to find out the test sample with the best solutions or worst differ degree,to quantify the health state of permanent magnet synchronous motor,can get a specific measure of the health status of each product in the real value of the current state of the health standard for evaluating motor.It lays the technical foundation for making the optimal maintenance decision for the machine tool.