Research On On-line Monitoring Technology Of Permanent Magnet Temperature For Hign Density Permanent Magnet Motor

Permanent magnet motors are widely used in rail transportation,electric vehicles,aerospace and other fields due to their small size,high efficiency and high power density.Permanent magnet motor is the core component of electric traction.Due to its harsh working environment,the internal temperature rise of the motor is serious.Under the influence of strong magnetic field and temperature,the permanent magnet of the motor has the risk of irreversible demagnetization,which seriously affects the motor performance.In the design phase of the permanent magnet motor,although the risk of permanent magnet loss is considered,the actual operating conditions of the motor cannot be accurately simulated,and the complicated online operating conditions will cause the permanent magnet to exceed the safe use range,causing serious consequences.Therefore,the temperature monitoring technology of high-density permanent magnet motor rotor permanent magnets has become one of the key technologies to be solved in high-density permanent magnet motor systems.At the same time,for the torque closed-loop control system,the ability to predict the temperature of the permanent magnet in real time is of great significance to improve the control accuracy of the system.The research contents of this article are as follows:(1)Study the temperature rise mechanism and source of temperature rise of permanent magnet motors for traction,analyze the effects of eddy current loss and harmonic loss inside the motor on temperature rise of permanent magnets,and analyze the effect of different heat dissipation methods on temperature rise of permanent magnets.Solve the heat balance equation of the permanent magnet under the influence of the loss and heat dissipation factors,and obtain the change law of the temperature rise of the permanent magnet when the motor is actually running.(2)Based on the change law of the temperature rise of the permanent magnet when the motor is running,in order to solve the problem that the permanent magnet rotation is not easy to measure in real time,an online estimation method based on the centralized parameter thermal network(LPTN)is proposed.First,a four-node deep gray-scale thermal network model and a loss model based on operating parameters and temperature are established,and its initial thermal capacity parameters and thermal resistance parameters are derived based on the theory.In order to achieve online estimation and improve estimation accuracy,an extended Kalman filter algorithm with a fading factor is used to dynamically update the thermal resistance parameters to achieve the online estimation of the permanent magnet temperature in the thermal network.(3)Aiming at the proposed method for on-line estimation of permanent magnet temperature,design and manufacture a permanent magnet temperature and magnetic field distribution measurement system for experimental verification.This system fixes the FPC board with multiple temperature and magnetic field sensors in the slot and contacts the permanent magnet by slotting the rotor core axially at the rotor core connected to the permanent magnet.The shaft end instrument rotates coaxially with the shaft,The sensor data is transmitted to the upper computer through WIFI to collect.Through laboratory tests,the experimental results are compared and analyzed with the results of simulation analysis to verify the effectiveness of the proposed online temperature estimation method for permanent magnets,and to reach an accuracy of less than 3°C for the estimation of permanent magnets.Thermal analysis provides a reference.