The Study On Fault Tolerant Control Strategy For Pure Electric Vehicle Control System

With the deepening development of pure electric vehicle, pure electric vehicles in all aspects of performance has been continuously improved,and the complexity of the system increased as well, which brings about an increasing possibility of fault in sensors, actuators and control units of electronic control system. Therefore higher safety and reliability of vehicle is required. It has become key issue in the research of pure electric vehicle that how to reduce fault rate, improve the accuracy of fault diagnosis and carry out reliable fault-tolerant strategy timely.This topic comes from cooperative research and development project between Jilin province high tech Electric Vehicle Co., Ltd. and Jilin University. By formulating proper fault-tolerant control strategy, this paper tries to perfect the vehicle driving control strategy and improve the driving safety and reliability. The main contents of this paper are as follows:1. Mechanism analysis on typical fault of pure electric vehicle. This paper analyses potential fault of the vehicle and its causes and effects respectively from the accelerator pedal sensor, battery group and motor driving system of pure electric vehicle. Combined with actual situation, the paper chooses accelerate pedal sensor and Li-battery group as the fault diagnosis object.2. Development of fault diagnosis and fault-tolerant control strategy. Firstly, after extracting the characteristics of acceleration pedal sensor fault signal, this paper presents a fault diagnosis method based on logic threshold value, adding fault recognition module to reduce the misdiagnosis rate. And replacing fault signal value dynamically is proposed to deal with accelerator pedal sensor fault, which will not only achieve a smooth transition when fault signal occurs, but also ensure the flexible of signal. Secondly, after the relationship between the available capacity and ambient temperature and charge /discharge rate is found from experiment data, SOC value that makes difference between two modes is corrected, which will perfect the drivingcontrol strategy. Finally, as to motor overload fault, overload time is managed by limiting motor output torque, as to under voltage, over temperature, and over-current fault, cooling treatment and limited output power of motor is carried out respectively according to measured temperature.3. Model building and off-line simulation. The fault-tolerant control strategy is verified by joint simulation between vehicle model created in CRUISE and fault-tolerant control strategy model created in MATLAB/Simulink. The simulation result shows that the fault-tolerant control strategy is effective and that the reliability of vehicle control system can also be improved.4. Hardware-in-the-loop test. Combined with the previous hardware-in-the-loop test platform for vehicle control strategy, this paper builds a vehicle dynamics model and modifies the interface definition of function test, and compiles fault diagnosis and fault-tolerant control strategy program. The fault-tolerant control strategy is tested and verified. The results show that in the range of allowable error, the proposed method of fault diagnosis can detect fault accurately and timely and that fault-tolerant control strategy can improve the safety and reliability of the vehicle.