Study Of Field-Weakening Control On Electric Vehicle's AC Induction Motor

Electric car is the most promising vehicle in the 21st century, but it still can't compare with fuel vehicle in power performance. Therefore, nowadays the micro-electric vehicle is the most promising industrialized product undoubtedly.Induction motor based on vector control has been widely applied in electric vehicle field. However, in order to adjust the motor speed in this control system, the stator voltage needs to be regulated along with the frequency. Because when the frequency rises to baseband, stator voltage will be limited by the battery maximum voltage and it cannot be further enhanced which make speed stop rising. Furthermore, for security reasons, the micro-electric vehicle in this paper adopts low-voltage high-current control project, so that the speed increase is even more difficult.To achieve wide speed range of electric vehicle, the paper starts with two aspects: maximizing use of the battery voltage and field-weakening control method. In terms of maximizing use of the battery voltage, SVPWM technique which with a higher voltage utilization ratio has been used as well as the over-modulation technique so as to further improve the modulation ratio; and increasing the output voltage in order to expend the speed range of electric vehicle. In the terms of field-weakening control method, considering the problems of the traditional field-weakening control, after studying the motor running state of the field weakening, effective current distribution and optimal current adjustment is adopted which can fully play the motor's torque output capacity in the weak sector, then accelerate the speed.At first the paper gives a simple introduction of the structure and configuration of motor drive system, and discusses the principle of vector control and SVPWM which provide a theoretical basis for the following. Then from the current perspective, the operation state under voltage and current limit conditions with the mathematical model of AC induction motor as a basis has been analyzed; and based on indirect rotor flux oriented induction motor theory, several key issues of weakening control (such as the current distribution of the field weakening region, the current decoupling control, the maximum voltage follower, SVPWM over-modulation strategy and so on) has been studied aiming at the motor operating characteristics in different regions in order to enhance the torque output and dynamic characteristics in field weakening region and discussing key issues'influences to system performance Then building field oriented control system with the Matlab based on SVPWM inverter, and simulating and verifying the above studies for an effective control algorithm. Next building an experimental platform for real-time monitoring, it can make the debugging personnel's on-line debugging and real-time monitoring work easier. Then the hardware structure of this system and related module design based on TMS320F2808 is described as well as the CAN-based network monitoring systems and network layout. Finally through the real vehicle road test, it is verified that when car switches between low-speed area and high-speed area freely, the effect of weakening increases speed is good.