Wide Speed Range PMSM Sensorless Direct Torque Control

As a kind of high efficiency motor made of permanent magnet material,permanent magnet synchronous motor(PMSM)has the advantages of high power density,good dynamic performance and strong reliability.PMSM is widely used in industry,transportation and civil fields,which has positive significance for promoting the construction of ecological civilization and achieving the grand goal of carbon neutral.As a high performance control strategy,direct torque control(DTC)has the advantages of fast dynamic response and good robustness.However,the traditional DTC also has the disadvantage of large torque ripple,which limits the application of this method.This thesis introduces an improved method of DTC based on torque angle.To realize this method,position sensor is needed to provide position information which increases the system cost and reduces the system reliability.To solve this problem,this thesis studies the sensorless control technology of PMSM DTC.First,the development status of DTC technology of PMSM is introduced in this thesis,during which the sensorless control was put emphasis on.Secondly,the mathematical model of PMSM is established,and the principle of traditional DTC is analyzed.Traditional DTC is not sensitive to rotor position information,so it has great advantages to use sensorless control.However,due to the disadvantages of flux linkage,large torque ripple and unstable switching frequency,the application of the traditional DTC is limited.In view of these shortcomings,this thesis introduces an improved DTC based on torque angle.The simulation results show that the improved method has excellent dynamic performance and steady-state performance.Then,the wide speed range sensorless control of PMSM DTC is studied.Based on the salient-pole model,in view of the tedious calculation problem caused by the traditional high-frequency rotating voltage injection method when the motor is running at low speed,this thesis analyzes an estimation method to obtain the rotor position and stator flux by using the phase inductance.The position and stator flux are obtained by using the phase inductance which can be obtained by injecting high-frequency voltage.When the motor is running at medium and high speed,the stator flux sliding mode observer is constructed by using the active flux based on the fundamental wave model.According to the active flux,the stator flux,rotor position and speed information of the motor can be easily calculated.Furthermore,in order to achieve the wide speed operation requirements,two methods requiring a shifting strategy to transfer from low speed to high speed are combined.Finally,the experimental platform is built,and the hardware circuit and software are designed.The wide speed range sensorless control of PMSM DTC is carried out on the platform and the results show that the proposed scheme is feasible and effective.