Research On Control System Of Asynchronous Motor For Electric Vehicle Based On Prediction Of Rotor Position Angle

With the emergence of global primary energy shortages and atmospheric environmental pollution,electric vehicles with advantages such as less pollution and high efficiency and energy saving have become the development focus of the automotive industry in the past two decades.Motor drive technology is one of the key technologies of electric vehicles,and its level directly affects the performance of electric vehicles.Asynchronous motors have the advantages of low cost and high,and have been widely used in the field of electric vehicles for several years.Therefore,it is of great significance to study the drive control system of low voltage and high current asynchronous motors applied to electric vehicles.This paper first establishes the mathematical model of the asynchronous motor,and derives its motor model under the three-phase stationary coordinate system,twophase stationary coordinate system,and two-phase rotating coordinate system in combination with the vector control theory,and then analyzes the asynchronous motor control scheme based on the rotor field orientation.On this basis,space vector pulse width modulation,the key technology of vector control of asynchronous motor drive system,is derived and analyzed.In order to improve the asynchronous motor control scheme based on indirect rotor magnetic field orientation,this paper studies the identification method of the motor parameters required for control and the stator current distribution scheme for a given torque.A method for parameter identification of stationary motors is designed.The method does not require the motor to reach the no-load and stalled states.The threephase voltage pulse width modulation is used to realize offline identification of the motor parameters,and the error voltage caused by the inverter and the dead zone is compensated.It is easy to operate and has good identification accuracy.At the same time,a stator current distribution scheme based on the maximum torque per current is designed based on the control characteristics and energy-saving requirements of the electric vehicle.An asynchronous motor model considering iron loss is established in Simulink,and the energy-saving efficiency of the scheme was verified.Finally,the problem of insufficient accuracy of position detection and speed calculation when the low-line-number photoelectric encoder is applied to the electric vehicle motor drive system is analyzed,and the impact of this problem on the acceleration performance of the electric vehicle is analyzed.Based on the traditional asynchronous motor control scheme,a rotor flux angle observation module based on position rather than speed is designed,thereby avoiding interference of speed calculation errors caused by low-line-number photoelectric encoders.At the same time,a rotor position angle prediction algorithm based on on-line acceleration identification is proposed,combined with online inertia identification and load observer to realize real-time observation of rotor acceleration,so as to predict the rotor position angle at the next moment.The position update point of photoelectric encoder corrects the predicted value to improve the position accuracy.This solution can effectively improve the decoupling accuracy of the asynchronous motor control system using a low-linenumber photoelectric encoder,thereby improving acceleration performance.