Study On Control Strategy For Electric Vehicle

Automobile industry is one of the largest and the most important industry all the world, and it is also the main support industry in almost every developed country. Because motor is the core of the electric vehicle power system, naturally the motor's control technology is the core technology in the field of electric vehicle. According to the traits of electric vehicle in this paper, on the basis of a practical project of Tianjin EV Co., we developed an electric vehicle controller ACEVC72-6 for a nine kilowatts asynchronous machine. In terms of high efficiency some works about dynamic torque and field weakening were done by simulations, and there are some emphases on quick torque respond, economizing on energy and maximum torque in the field weakening.According to the application traits of electric vehicle drive control strategy and regenerative brake strategy were studied in the range of whole speed. On the basis of analyzing sorts of asynchronous machine's control strategy, the basic control strategy made is torque closed-loop control. Mathematic model on optimizing control strategy in medium speed was put forward on the basis of loss model, and this strategy was completed by controlling excitation. On account of electric vehicle's own traits and running characteristics, combining with variable structure control (VSC) theory and variable frequency vector control theory, a novel VSC model with three independent control algorithms was put forward further. Variable frequency vector control strategy of constant flux guarantees the quickly dynamic torque in low speed. The efficiency optimization vector control strategy of variable flux increases the running distance of electric vehicle in medium speed. Maximum torque control strategy of variable flux effectively promotes the acceleration traits in high speed.Based on the comprehensively deep research on the AC induction machine mathematic model, a novel speed and current regulator, the active disturbance rejection controller (ADRC), is proposed to achieve high performance AC induction machine drive, which has great ability of adaptation and better performance against disturbance. What's more, speed estimate was completed from the current regulator as above. The active disturbance rejection strategy is independence of plant models.ADRC is composed of three parts, tracking differentiator, extended state observer and nonlinear state error feedback control law. By using the extended state observer, the AC system has stronger robustness, which can overcome nonlinearity and coupling of the parameters of AC induction machine. Also, it can surmount parameters excursion caused by temperature change.Due to the model of DC-DC chopper in two quadrants, some researches of regenerative brake were done in this paper, and the microcosmic course of PWM circuit was analyzed. On this basis, a novel regenerative brake control strategy adaptable to electric vehicle was put forward-constant feedback current control. The mathematical model of constant feedback current control and control equations of overcoming regenerative brake's dead zone were calculated. The relations of feedback efficiency of brake power, back electromotive force of motor and feedback current was studied.Finally, sorts of control strategies and regenerative brake strategy were simulated by MATLAB and got some good conclusions. At the same time simulation and experimental results were compared and studied, the control stratigies above was proved feasible further.