Electric Vehicle Drive System Control Strategy Research

Recently, the electric vehicle (EV) industry has entered into a new era of rapid development, especially the electric bus. And the induction motor driving system is most widely used. However, the current control strategy of induction motor is still derived from traditional control of motor, which is unable to solve the problems of the electric vehicles’special working conditions and the switch of different working conditions, frequent disturbance and abrupt changes in load, etc. These problems certainly will affect the smooth running of the electric vehicle and even impact the safety of the electric vehicle.In order to solve the problems of the smooth-switch of working conditions and load disturbance rejection in this paper, the main achievements are listed as follows.1. In order to confirm the motor level, characteristic parameters and control objective of specific electric vehicle models, the method of kinetic parameters’match of EV’s driving system is studied in the paper through the analysis of the EV’s safe running statues in all kinds of limited conditions and EV’s kinetic performance index.2. In this paper, induction motor system is considered as the target and the vector control theory of induction motor is studied. On this basis, considering the features of the induction motor such as high power density and high saturation, an improved vector control algorithm is proposed which is based on voltage closed-loop control. The proposed algorithm improves the voltage utilization ratio and ability of torque output. As well as, a kind of voltage decoupling algorithm is used in this paper to improve the speed of torque response.3. For the problems of voltage and current flicker during the switch of EV’s working conditions, a control strategy, the switch of working conditions is replaced by the change of ASR and AVR’s threshold values, is designed in this paper.4. To restrain the abrupt change in load when the EV is running on the road, with the kinematic equations of motor, a load disturbance observer which is based on inverse system is designed in the paper. And the estimated value of load disturbance gained from the observer is sent back to system’s forward path to counteract the influence of load changes.In the paper, all of the above works are simulated. The results indicate that the ability of motor torque output and the speed of torque response are improved by the designed voltage closed-loop feedback control strategy combined with voltage decoupling algorithm effectively; the designed motor flexible control strategy ensures the stability and flexibility of motor current, torque and speed when EV switches the working conditions; the speed fluctuation when speed is influenced by load disturbance is reduced effectively by the designed load disturbance rejection strategy. Besides, on the basis of all above results, this paper designs a solution of20kw induction motor driving controller and finishes the relative experiments. The results of experiments indicate that the designed induction motor driving system for EV satisfies all requirements for running such as, torque accuracy, control accuracy, overload ability and interference rejection ability, etc.