Research On Torque Observation Method Of Pmsm In Traction Drive System

With the advantages of simple structure,high power density and good reliability,permanent magnet synchronous motors(PMSMs)have been widely used in traction drive system in recent years.In the high power traction drive system,the temperature variation,magnetic saturation and other factors make the motor parameters change obviously,which affects the accuracy of actual torque output.If the output torque of the motor can be observed accurately and the motor torque can be controled in a closed loop based on the observed torque,the torque control performance of the system can be improved significantly.In this paper,the salient-pole PMSM is taken as the research object,and the electromagnetic torque observation method of traction motor is studied.At the same time,based on the sampling circuit designed in the torque observation scheme,the restarting with unknown speed is studied.The main contents are as follows:Compared with the flux model observation method and the power method,the voltage model flux observation method and the power method which only depend on the stator resistance parameters are selected for torque observation.According to the orthogonal relationship between stator flux and back EMF,aiming at the problems of traditional voltage model,such as integral initial value,zero drift and phase amplitude deviation,a full order stator flux observer is established.The stability of the observer is analyzed,and the reasonable observer pole is selected.The influence of stator resistance parameter on the electromagnetic torque is analyzed qualitatively.The performance of torque observation based on stator flux full order observer is verified by simulation and experiment.The performance of the full order observer is limited by the inaccuracy of the reconstructed voltage and the sinusoidal decrease of the PWM voltage in the high-speed domain,then the torque observation by power method is studied.Aiming at the inaccurate problem of traditional voltage reconstruction,a low cost real-time voltage detection scheme for hardware circuits is proposed.The voltage sensor is used to sample the DC bus voltage,and a simple and low cost sampling circuit is designed to detect the voltage level state of the three-phase winding end,so as to obtain the actual voltage loaded between the motor windings.According to the sampling voltage,sampling current and speed information,the power and torque of the motor are observed.The torque observation performance of this method is verified by simulation and experiment.The sampling circuit based on the above design can also realize the detection of motor rotor position and speed information in power-off state.The expressions of position and speed estimation are derived,and the position and speed can be updated six times in a fundamental cycle,which provides relatively accurate initial rotor position angle and speed for the motor restarting with unknown speed without position sensor,and improves the identification speed of position and speed during the process of restart with unknown speed.The performance of the restarting with unknown speed is verified by simulation and experiment.