Research On Insulation Resistance Monitoring Method Of Electric Vehicle

Due to the deteriorating global environment and the increasingly severe energy crisis,the electric vehicle is playing a more and more important role in the automotive industry.Unlike the traditional car,the power source of electric car is high-voltage battery pack,which makes electric cars require higher insulation performance.If the electric vehicle’s insulation breaks down during in operation,it will have serious consequences.In order to ensure the safe and reliable operation of electric vehicle,it is necessary to monitor the insulation status of electric vehicles in real time.Therefore,it is urgent to design a set of products that can monitor the insulation performance of electric vehicles in real time and accurately.The main work of this paper is as follows:(1)This paper studies the structure and composition of high voltage electrical subsystem of electric vehicle,the definition of insulation resistance of electric vehicle,the status of insulation monitoring of electric vehicle and the usual monitoring methods,and analyzes the principles,advantages and disadvantages of various methods.On this basis,the method which divides voltage by the series resistor to monitor insulation resistance is proposed in this paper.(2)The hardware circuit of the insulation resistance monitoring system is designed in this article which includes SCM core control circuit,power supply circuit,analog to digital conversion circuit,communication circuit and isolation circuit and so on.The working process of the monitoring system is that the PWM detecting signal with certain frequency and amplitude which outputted by the SCM that is injected into the electric vehicle’s high-voltage electrical subsystem.Then,the amplitude of the detection signal that is injected into high voltage system is sampled and the insulation resistance of the electric vehicle is calculated by the dividing voltage resistor.(3)This paper designs the software program of insulation monitoring system,includes detection signal generation and injection program,AD sampling program,SPI communication program and CAN communication program,and so on.The software program development environment is CodeWarrior programming platform and programmed by the C language.(4)When the design of monitoring system’s hardware circuit and software program are completed,the hardware circuit and program are combined for functional verification in this paper.The comprehensive debugging of the system is carried outthrough the experimental platform,which solves the problems existing in the monitoring system and further improves the performance of the monitoring system.At the same time,the improvement measures are put forward in this paper to overcome the shortcomings of insulation monitoring system.