Research And Implementation Of Flux Weakening Control Strategy For PMSM

Nowadays,with the increasing environmental pollution,the state proposed to promote the development of new energy industry in an all-round way in the two sessions of 2018.Electric vehicles,as new energy vehicles,have the advantages of energy saving and environmental protection.With the government continuing to increase subsidies and preferential policies for new energy vehicles,new energy vehicles have good development prospects and are an important part of the realization of "Made in China 2025".The AC drive system composed of permanent magnet synchronous motor(PMSM)has many outstanding performances,such as high resolution,accurate positioning,wide speed range,stable operation at low speed and small torque ripple,which make it widely used in electric vehicle drive system.Due to the complex operating conditions of the vehicle,the drive system has a wide speed range,strong torque output capability and good stable running capacity.Therefore,this paper mainly studies the anti-disturbance ability of PMSM speed control system and the stable operation performance of high-speed magnetic flux-weakening speed expansion.Firstly,the vector control of permanent magnet synchronous motor is analyzed,and the mathematical model of permanent magnet synchronous motor is established.The principle of coordinate transformation and the principle of SVPWM implementation in vector control are deduced.In the vector control,in order to improve the output torque capability and reduce the switching tube loss,the maximum torque current ratio control strategy is adopted at the base speed.In view of the shortcomings of traditional PI control that can not meet the high performance operation of PMSM,the sliding mode speed control which is insensitive to disturbance and parameter changes and fast response speed is adopted,and the sliding mode control is improved accordingly,which effectively weakens the inherent chattering problem of sliding mode control and improves the anti-disturbance performance of the system.Secondly,the principle of flux-weakening control of permanent magnet synchronous motor is expounded,the operation area and restriction conditions in the process of flux-weakening control are analyzed,and the current-leading angle flux-weakening control strategy is proposed.Through the analysis of current-leading angle flux-weakening control principle,the traditional current-leading angle flux-weakening control strategy has serious stator current oscillation in the process of high-speed flux-weakening,which leads to large torque ripple.The research finds that there are two main reasons for the current oscillation caused by high-speed field weakening: one is that the PMSM cross-axis current is not completely decoupled;the other is that the traditional leading-angle flux weakening control uses the maximum voltage deviation between the stator voltage and the output voltage of the inverter as the leading-angle of the output,because the maximum output voltage of the inverter is given in advance,the voltage deviation is not kept to be the smallest and there is hysteresis.The output leading angle changes unsteadily during the modulation process,which leads to the dq current oscillation and the DC bus voltage not being fully utilized during the magnetic weakening process.In this paper,the leading angle is obtained by minimizing the voltage vector deviation before and after SVPWM modulation by gradient descent principle.The internal model control theory is used to decouple the PMSM cross-axis current,which effectively solves the current oscillation problem in the process of high-speed magnetic weakening and improves the torque output ability in the process of magnetic weakening to a certain extent.Finally,on the motor drive platform based on rapid control prototype,a fast control prototype model of PMSM flux-weakening control strategy is built according to off-line simulation model.The code generated automatically by system compilation is downloaded to the controller of hardware-in-the-loop simulation system to control the speed control system of PMSM,which verifies that the improved scheme of advanced angle flux-weakening system is more robust and effective.It weakens the current oscillation in the process of magnetic weakening and improves the system’s torque output capability.