Research On Detection Of Asymmetry In Permanent Magnet Synchronous Motor Using Stator Current

Permanent magnet synchronous motor(PMSM)has the advantages of simple structure,reliable operation,small size,and high efficiency,and is widely used in CNC machine tools,robots,and other fields.With the passage of time,the permanent magnet synchronous motor will undergo demagnetization,inverter performance degradation,stator resistance inter-turn short circuit,which resulting in distortion of the amplitude of the three-phase stator current output by the motor and the phase difference of the three-phase current,that is called the three-phase asymmetry phenomenon,resulting in the torque and speed fluctuation of the motor,the vibration is intensified,the heat loss is increased,the efficiency is reduced,and the working performance of the equipment is directly affected.At present,there is a lack of quantitative indicators for the detection of three-phase asymmetric state by stator current,and there is no unified criterion for determining the three-phase asymmetric state.In this paper,by studying the correlation between stator current signal characteristic change and three-phase asymmetric state,a quantitative index of three-phase asymmetry is established,the criterion of three-phase asymmetric fault is determined,and a three-phase asymmetric state detection method for permanent magnet synchronous motor based on stator current is proposed.The main research contents and conclusions are as follows:(1)The current research status of permanent magnet synchronous motor condition detection at home and abroad is reviewed,and the current research problems of three-phase asymmetric state detection are summarized.The research content and ideas of this paper are proposed.(2)Combined with the working principle of permanent magnet synchronous motor,the mathematical model in the three-phase asymmetric state is derived.Based on Matlab/Simulink software platform,a three-phase asymmetric state simulation analysis model was established.Aiming at the three-phase asymmetry problem caused by the short circuit between turns of stator resistance,the accuracy of the simulation model is verified by comparing the simulation with the measured sub-current waveform,and the simulation of stator current signal in the three-phase asymmetric state is realized.(3)Through the statistical analysis of the time-domain characteristics of the simulated stator current,the time-domain characteristic indexes of the current such as peak,peak factor and margin factor were screened.The fusion calculation of the characteristic indicators and the extraction of fusion indicators were carried out by the Copula function,and the linear correlation coefficient and contour peak index were determined as the fusion indicators to characterize the change of three-phase asymmetric state,and the quantification of the three-phase asymmetric state of PMSM was realized.(4)In order to establish the three-phase asymmetric fault evaluation criterion,the influence of inter-turn short circuit,demagnetization,inverter aging,inductance reduction and other phenomena on the characteristic indicators is determined through simulation experiments.Based on the relationship between the three-phase asymmetry of stator current and the torque fluctuation coefficient,a method for obtaining the three-phase asymmetric fault criterion of permanent magnet synchronous motor is proposed.The stator current data of the motor with three-phase asymmetric fault under constant speed,variable speed working conditions and vibration conditions were measured by fault injection test technology,and the effectiveness of the three-phase asymmetric state detection method according to the stator current was verified.It provides a technical means to realize the detection of three-phase asymmetric state of permanent magnet synchronous motor.