Research On The Key Technology Of EMI Test System For New Energy Vehicle Under Dynamic Conditions

As a promising role in the automotive industry,new energy vehicles have the characteristics of zero pollution,high energy efficiency and low noise,which will make them go further than traditional internal combustion engine vehicles.EMI test is one of the key tests for new energy vehicles.Thus,this dissertation focuses on the study of"Research on the key technology of EMI test system"to study the indirect measurement method of braking force of new energy vehicles under dynamic conditions based on AVL drum system,EMI test method for new energy vehicle under dynamic conditions based on fast Fourier transform?FFT?and dot frequency scanning?DFS?,real-time EMI test system integration technology for new energy vehicle under dynamic conditions based on finite state machine?FSM?,and other key technical issues.Important academic value and practical significance are shown for promoting the emerging industries and improving EMI test technology and equipment.The research was supported by the Guangzhou Science and Technology Plan Project?201504010037?.This dissertation reviews the research progress at home and abroad from the aspects of new energy vehicle EMI test standard,vehicle EMI test technology,vehicle parameter in-situ detection technology under dynamic condition.The main research content includes:?Based on the EMI test platform under steady conditions of the standard SAE J551-5:2012,this dissertation analyzes the technical requirements of EMI test for new energy vehicle under dynamic conditions,and focuses on the overall integrated design and key technology analysis of EMI test system.It is pointed out that the EMI test platform under steady condition based on SAE J551-5:2012 using a single spectrum analyzer.Superheterodyne can meet the requirements of amplitude accuracy,frequency test range and resolution of EMI test under dynamic conditions,but the real-time performance of EMI test is not enough.AVL chassis dynamometer can only meet the EMI test requirements under idling and cruise conditions of SAE J551-5:2012.But it can not measure the braking force under braking condition.EMI test subsystem and drum subsystem are independent and hard to work cooperatively.The original EMI test platform under steady condition of SAE J551-5:2012 has been unable to meet the EMI test requirements under dynamic conditions of new energy vehicle.This dissertation carry out the overall integration scheme design of EMI test system for new energy vehicle under dynamic conditions,and point out that it is necessary to solve the key technologies such as indirect measurement of braking force under dynamic condition,real-time EMI acquisition under dynamic conditions,and integration of EMI test system,so as to meet the requirements of frequency test range,frequency resolution,real-time performance and amplitude accuracy of EMI test for new energy vehicle dynamic conditions.The key technologies and breakthrough of indirect measurement technology of braking force under dynamic conditions,real-time EMI acquisition technology under dynamic conditions and integration technology of test system are analyzed,which lays a foundation for subsequent research.?The indirect measurement method of braking force of new energy vehicles under dynamic conditions based on AVL drum system is systematically studied.The principle diagram of in place detection parameters and flow chart of in place detection module under dynamic conditions based on AVL chassis dynamometer are clarified.The indirect measurement method of braking force for new energy vehicle under dynamic conditions based on AVL drum system is proposed.The standard size sealing bolts?for oil change and exhaust?only needs to be replaced temporarily with hydraulic sensors.It can indirectly measure the braking force,which is convenient and practical.Based on the thrust formula of the hydraulic cylinder,the force transmission of the brake wheel cylinder and the relative motion of the wheel and the drum,the mechanical model of the wheel and the axis is established.The relationship between the braking force and the linear speed of the wheel is deduced.The braking force model of the vehicle at low speed,idling speed and high speed is analyzed,and the corresponding indirect measurement formula of the braking force is derived.The parameter calibration method of indirect measurement mathematical model and measurement processes are studied.Based on the fact that every brake wheel cylinder has an exhaust bolt?for the first oil change and exhaust?,it is easy to disassemble.The exhaust bolt can be quickly installed with a hydraulic sensor to measure the oil pressure of the brake wheel cylinder,and the vehicle braking force can be obtained.Combined with the linear speed of the drum,it can calibrate and identify the parameters with good accuracy and practical application value.This dissertation studies a simple and fast parameter calibration processes,so that the shortest way of steps can be completed to obtain the drum linear acceleration in different states.The experimental results show that the maximum relative error between the calculated value and the actual measured value of the braking force is less than 1%.The maximum nonlinear error between the linear equation of the indirect measurement formula of braking force and the linear equation based on the measured value of the braking force is less than 0.009.The indirect measurement method of the braking force has high accuracy and practicability.?The EMI test method based on FFT and DFS for new energy vehicles under dynamic conditions is systematically studied.This dissertation proposes an EMI test method based on FFT and DFS for new energy vehicles under dynamic conditions,which makes full use of FFT's rapidity and DFS's accuracy to effectively expand their applications,making EMI test under dynamic conditions possible.Based on the features of accelerating,sliding and braking conditions,the identification method for accelerating,sliding and braking conditions was proposed.Different dynamic conditions can be identified from any group of speed and acceleration curves,realizing the automation of dynamic condition identification during vehicle measurement process.The comprehensive EMI key evaluation indexes system of new energy vehicles was built,including characteristic point with maximum amplitude points.U_max is an index for extreme value evaluation.?is a comprehensive index for overall region evaluation.And?is an index for local region evaluation.The calculation formula of each index is deduced,while the physical significance of each index is expounded.EMI test method based on FFT and DFS for new energy vehicle under dynamic conditions was applied to GA5 PHEV produced by Guangzhou Automobile Group Co.,Ltd.,and the electric test vehicles of Zotye Auto Co.,Ltd.and BYD Co.,Ltd.The results indicate that EMI of new energy vehicles can be tested under dynamic conditions with high accuracy,and the evaluation indexes are operable.With the same instruments,by reducing f_span from 29.85 MHz to 0.9 MHz,k Hz.DFS is used to EMI test with±0.36 d B amplitude accuracy.?The integration and experimental research of the real-time EMI test system of new energy vehicles based on the finite state machine are studied.On the basis of the existing hardware,the multi-channel time stamp compensation formula and the estimation formula of the multi-channel synchronous acquisition value are derived.The performance improvement method for serial acquisition card based on time stamp compensation is proposed,which effectively improves the authenticity and real-time performance of the serial acquisition card measurement data.It has the characteristics of simple implementation and good universality without replacing the acquisition card.The acquisition experiment of actual vehicle data shows that the performance improvement method for serial acquisition card can effectively overcome the time stamp inconsistency of different multi-channel data,which are speed and torque obtained by PCI 8602 serial acquisition card.The real-time EMI test system model for new energy vehicle based on the finite state machine is established.Model accessibility analysis and optimization are carried out.The real-time EMI test system for new energy vehicle based on finite state machine is developed,including the platform selection,software architecture,sub module workflow,as well as key modules,function realization and debugging.The EMI test for new energy vehicles under dynamic conditions is applied on several test vehicles.The results show that the EMI test method based on FFT and DFS for new energy vehicles under dynamic conditions make full use of FFT's rapidity and DFS's accuracy.It can test EMI for new energy vehicles under dynamic conditions with high accuracy.The index for extreme value evaluation,the index for overall region evaluation,the index for local region evaluation are scientific and operable.In addition,the EMI test method under dynamic conditions is used to test the influence by the variation of acceleration,resistance,power,driving mode and other on the test vehicle EMI,which lays the foundation for the future EMI test,improvement and standard formulation of relevant vehicle models.