Temperature Field Analysis Of PMSM Based On Thermo-fluid-Magnetic Coupling

Permanent magnet synchronous motors(PMSM)are widely used in the industrial field due to their advantages of large power density,small size,and high speed.The rotor excitation is provided by permanent magnet(PMs)materials instead of excitation windings.This compact structure will cause the difficulty in heat dissipation of the motor.Excessive temperature will cause irreversible demagnetization of the PMs,causing problems such as a decrease in the output torque of the motor.Therefore,accurate calculation of the motor temperature distribution is particularly important for its safe and stable operation.The simulation analysis is widely used as a simple and convenient calculation method,and accurate loss values in thermal simulation analysis are one of the main factors that affect the calculation results.However,most of the motor losses are electromagnetic losses,and the temperature change will have a certain impact on the electromagnetic losses,so considering the coupling relationship between multiple physical fields can improve the calculation accuracy.With the rapid development of computer technology and computing methods and the integration of a variety of commercial simulation software,the gap between multiple physics fields is gradually broken,and the coupling analysis of multiple physics fields is becoming more and more common.In this paper,a coupled temperature rise model of the three physical fields of thermo-fluid-magnetic is established by using the finite element software,and the influence of temperature rise and air gap air flow is considered to improve the accuracy of temperature field calculation.The specific work content is as follows:(1)Establishment of finite element model,First.Firstly,the electromagnetic field model,the flow field model and the temperature field model are established by using Maxwell and fluent software respectively,and the relevant boundary conditions are set up,etc.,and then the calculation model is simplified from the point of view of the physical field.Finally,based on the reason that the permanent magnet motor is driven by the inverter,a space vector pulse width modulation inverter model is established to improve the accuracy of the electromagnetic loss calculation result.(2)Theoretical analysis of motor losses and loss reduction measures.Firstly,the mechanism of loss generation is explained by theoretical analysis and finite element simulation results,and then propose a method to reduce its loss based on its generation mechanism,and verify the effectiveness of the proposed method through electromagnetic calculation results.Finally,the principle of the loss separation method of the permanent magnet motor is given,and the various losses of the permanent magnet motor are separated through three different experiments.(3)The establishment of a three-physics coupling model.Firstly,the physical parameters that influence the calculation of electromagnetic loss are analyzed in detail from loss producing components,and establish a two-way coupling relationship between Maxwell and Fluent.Then,the electromagnetic loss changes and the final temperature rise distribution before and after the iteration between electromagnetic field and temperature field are compared.Finally,based on the reason that the temperature of the permanent magnet of the permanent magnet motor is not easy to measure,a permanent magnet temperature estimation model is established,and the permanent magnet temperature is estimated in the final experiment.(4)Motor temperature measurement and temperature estimation experiment.The winding temperature is directly measured by four identical thermal resistances,while the temperature of PMs is estimated by the established estimation model.The temperature without iterative calculation is higher than the measured value through the experimental verification,but as the number of iterations increases,the final temperature value of the motor decreases and gradually approaches the measured value,which shows that the coupling model can provide better calculation accuracy than the single temperature field model.