Insulation Monitoring Device Based On Small Signal Injection Method

In recent years,electric vehicles have developed rapidly.More and more cars are loaded with energy-supplied battery packs.The use of electrical energy to power cars is an environmentally friendly solution and a trend in the future of automobiles.However,there are many problems that need to be solved in the comprehensive promotion of electric vehicles,and the insulation problem of power devices is one of them.In order to monitor the insulation status of the battery pack in real time,electric vehicle insulation monitoring device is studied and designed in this thesis.On the basis of analysis and calculation of working principle of the electric vehicle insulation monitoring device,the functional modules of the hardware circuit are designed.Considering the equivalent capacitance of the battery pack,the influence of it on the measurement is analyzed in detail,and an effective solution is proposed.Then the software program of the monitoring device is designed to realize the main functions of the electric vehicle insulation monitoring device.The details are as follows:Firstly,according to the working conditions of electric vehicles,compared with the existing insulation monitoring methods,the small signal injection method suitable for electric vehicles is selected.Combined with the working principle of insulation monitoring device in electric vehicles,the general circuit topology is summarized.The method is analyzed and calculated.Secondly,the functional circuits for implementing insulation monitoring based on this method are designed,including power supply circuit,voltage regulator circuit,signal generation circuit,signal control circuit,filter circuit and voltage measurement circuit,etc.Some important circuits are verified by simulation software.Then,according to the circuit design scheme and referring to the PCB design rules,the PCB is designed and manufactured.After that,the influence of the equivalent capacitance of the battery pack on the measurement is analyzed.The solution is proposed and the theoretical calculation is carried out.The main program frame of the monitoring device and each functional module are designed to complete the overall design of the electric vehicle insulation monitoring device.In the end,the sample is manufactured and tested,and the test results and the waveforms of the main measurement points are analyzed to verify the correctness of the design.It has been verified that the sample can achieve insulation monitoring function with good stability and meet the design requirements.In addition,according to the test results,the improvement direction of the design is proposed.