The Optimization Research Of High Performance In Field Weakening For The Asynchronous Machine Controller Of Electric Vehicle

With the globalization of energy and environmental problems becoming increasingly serious,electric vehicle has become more and more popular with the advantages of efficient,clean and pollution-free.Because of its simple structure,low cost,easy maintenance,wide speed range,Asynchronous motor is widely used in the field of electric vehicle.In this paper,several key problems of induction motor for electric vehicle in field-weakening are studied:voltage pulse width modulation strategy,current regulator,current distribution strategy.In this paper,the dynamic and static performance of induction motor based on rotor field oriented vector control system is analyzed theoretically under the base speed,and it is simulated by Matlab/Simulink platform,and the field-weakening control System block diagram is presented at last.Then the voltage pulse over-modulation strategy(SVPWM)and current regulator are introduced.As the motor speed increases gradually,the back EMF is close to the maximum output voltage of the inverter,which will cause the dynamic tracking effect of the current to deteriorate and can not respond to the change of speed or load rapidly.Therefore,the over-modulation algorithm of the field-weakening research is of great significance.In this paper,the over-modulation algorithm is analyzed in-depth and puts forward a more simple and convenient calculation method.The over-modulation algorithm makes the calculation of hold angle and the correction angle linearization,the change of voltage amplitude smaller.The algorithm makes the output voltage fundamental wave move smoothly from the linear modulation region to the six-step step wave mode,increasing the voltage output range,making the system in the field-weakening area to achieve maximum torque output.Current regulator of the motor control system,the core control unit,its performance is great important.In this paper,a model predictive control current regulator based on Laguerre function is proposed to predict the state quantities of the system based on the past and present information,and to take into account the expected value of the control object and the change of the control volume.The optimal control law is obtained through the optimal control.Finally,based on the previous control strategy,the current distribution strategy of the high speed and weak magnetic field above the base speed is discussed considering the limitation of the maximum output voltage and the maximum current of the inverter.Firstly,the conventional field-weakening control method,the improved field-weakening control algorithm and the method based on the voltage close loop of field-weakening are analyzed,the advantages and disadvantages of each method are analyzed.At last,a new field weakening control method based on the switch active time of closed-loop voltage vector switching is presented.The proposed control method has better dynamic response than the former.The simulation model of the system is established by using Matlab/Simulink.The over-modulation strategy,the model predictive control regulator based on Laguerre function and the new method of field-weakening control are respectively validated.The experimental platform is built and the experiment is verified.