Magnet-thermal Coupling Analysis And Parameter Identification Of Squirrel Cage Induction Motor

As the power source core of new energy vehicles,vehicle induction motors are different from ordinary industrial induction motors.Vehicle induction motors have many problems,such as unstable magnetic field,high loss and serious temperature rise due to abundant harmonics of voltage and current and compact structure.Moreover,the control accuracy is susceptible to parameter fluctuations.In order to understand the influence of structural parameters of induction motors for new energy vehicles on loss and distribution of magnetic field and temperature.In this paper,a 180 KW,4000r/min squirrel cage induction motor is designed.Based on numerical method,finite element method and equivalent thermal circuit method,the primary and secondary factors of the coupling effect between the structural parameters of induction motor and the distribution law of magnetic field and temperature field are studied.Aiming at the problem that the key parameters of induction motor are susceptible to fluctuation caused by the change of working conditions,which leads to the reduction of motor performance.A new reference adaptive method(MRAS)based on power-free model is proposed to realize speed identification of induction motors.This paper mainly studies the following four aspects in detail.1)Firstly,aiming at the serious loss of induction motors caused by the large number of stator and rotor parameters and strong coupling,this paper proposes a feature model group of induction motors based on orthogonal experimental optimization method.Combining with the finite element method,the motor loss values and loss curves are calculated.The main and minor factors affecting the loss types of induction motors are studied by the extremum method.The relationship between structural parameters and various losses is revealed and the rationality of the relationship is verified.It lays a theoretical foundation for further loss reduction measures.2)Secondly,aiming at the complex magnetic field caused by the end effect of the motor and its great influence on the loss calculation,a time-stepping 2D finite element motor model is established.The distribution law of flux density and magnetic density line under no-load condition is analyzed.Torque and other numerical values are calculated.According to the electromagnetic scheme of the motor,the distribution of the internal magnetic field and the time-varying current,the loss curves of the components of the motor are studied.3)Thirdly,aiming at the problem of ambiguous temperature law and uneven heat dissipation of the whole machine,Based on the theory of heat transfer,the temperature field of the whole machine is analyzed by using the equivalent thermal circuit method of magnetic-thermal bidirectional coupling.The temperature of each part of the motor is calculated.The heat flux vector diagram inside the motor is analyzed.The direction of heat flow is studied.The cooling system was optimized.4)Fourthy,aiming at the low speed identification accuracy of induction motor in its vector control,a new speed identification method based on reactive power MRAS model is proposed.The method uses back EMF MRAS model to observe the fluctuation of stator resistance in real time.The value of the flux observer is applied to the rotor flux observer.Finally,the observed rotor flux is applied to the adjustable model of reactive power MRAS model.The problem of low speed identification accuracy of induction motor without speed sensor as feedback is solved.The system speed dynamic identification ability is improved.