Research And Development Of Insulation Monitoring Device For Electric Vehicles

The global shortage of non-renewable energy and the deterioration of the climate environment have brought severe challenges to the development of modern society.Electric vehicles using clean energy have been highly valued by governments.The development of electric vehicles can not only reduce environmental pollution,but also revitalize the domestic automobile industry and occupy the commanding heights of new technologies.The safety performance of electric vehicles is the basis for the operation of electric vehicles.The high-voltage insulation performance of electric vehicles is the core content of vehicle electrical safety technology,which is of great significance to passenger safety and safe operation of vehicles.In this thesis,based on the research and analysis of IMD(Insulation Monitoring Device)background for electric vehicles,in view of the influence of vehicle voltage fluctuation and system Y capacitance on the existing measurement technology,the improvement scheme is proposed,and an insulation monitoring device with more perfect performance is developed.Firstly,this thesis builds an insulation monitoring circuit model based on the electric vehicle electrical system using low frequency injection method.Considering the fluctuation of the vehicle voltage,the calculation formula of insulation resistance under different conditions is derived.Next,the influence of system Y capacitor on vehicle insulation performance and insulation resistance measurement is analyzed.Based on the transient analysis of the circuit model,IFM(Interval Fitting Method)and PIM(Parameter Identification Method)are proposed to identify the system Y capacitance by the sampled data.Then,the hardware and software of insulation monitoring device are designed and implemented.The hardware system uses NXP 9S12XEQ512 microcontroller,including the minimum system module,power circuit,injection signal generator,sampling circuit,filter circuit and CAN(Control Area Network)module.Under the complex conditions of automobile electronic operation,type selection of components,schematic circuit drawing and PCB(Printed Circuit Board)are carried out.The software system includes three layers:driver,interface and application.The software design of each layer is closely related to the hardware circuit.Finally,the experimental environment and test platform were built to verify the interval fitting method and parameter identification method,as well as the insulation resistance measurement model under different states.The experimental results show that the proposed measurement method can effectively eliminate the influence of vehicle voltage fluctuation and system Y capacitance on the measurement device,and the relative error of insulation resistance can be limited within 5%,which improves the reliability and accuracy of the insulation resistance measurement system.