Sensorless Restarting Process Of Traction Permanent Magnet Synchronous Motor

Permanent Magnet Synchronous Motor(PMSM) has the advantages of large starting torque and high efficiency, which are very suitable for traction motors in railway system. To avoid using mechanical speed and position sensors so as to improve the reliability of traction system, the PMSM sensorless control method and restarting process are researched in this thesis.Firstly, the mathematic model of PMSM and the vector control strategy is analysed. Secondly, the stator flux sensorless control method to estimate the speed and rotor position is researched. The modified integrator with variable limit and cut-off frequency is applied to replace the pure integrator to avoid the DC-bias. The active flux is applied to estimate the rotor position of interior PMSM(IPMSM) exactly using the estimating stator flux.However the traction motor would always work in coasting condition, the restarting process after coasting also needs the exact speed and rotor position information. As there is no current in the motor winding during coasting, the common estimating method is no longer matched and the short circuit current vector method is used. This method would make the motor short out twice to estimate the speed and rotor position based on the short circuit current at the restart moment. Besides, the transition process between stator flux method and short circuit current vector method is also researched. Then, the PMSM sensorless control simulation model is built based on the Matlab/Simulink. And on the PMSM experimental platform based on the Myway control system, the experiments of PMSM sensorless control and restart using stator flux method and short circuit current vector method are completed. Simulation and experimental results of different speed and torque certify that the stator flux method has a high precision on middle-high speed region, and by using the short circuit current vector method the motor could restart smoothly after coasting.