Research On Conducted Electromagnetic Interference Of Electric Vehicle Motor Drive System Based On Z-source Inverter

In recent years,with environmental pollution is becoming more and more serious,environmental issues have attracted the attention of all countries in the world.Under the background of the increasing shortage of non-renewable energy sources and the environmental pollution caused by automobile exhaust,electric vehicles with the advantages of high-efficiency,energy-saving and environmental friendliness are rapidly growing in the market.Compared with fuel and gas vehicles,the increasing number of power electronic devices in electric vehicles and the increasing degree of electrical integration have made the EMC(Electromagnetic Compatibility)problem even more prominent.As an important part of EV-MDS(Electric Vehicle Motor Drive System),Z-source inverter has a unique buck-boost characteristic,which can replace the cascade structure of converter and inverter,and it is very suitable for application on electric vehicles,but it has the same disadvantage as the traditional inverter with high output CMV(Common Mode Voltage).EV-MDS as the main electromagnetic interference source,the CM-EMI(Common Mode Electromagnetic Interference)produced by the Z-source inverter in the working process is the most serious,which not only affects the normal operation of its own system,but also causes interference to other systems in the vehicle,and seriously threatens the safety of the electric vehicle.Therefore,this thesis mainly focuses on the issue of conducted EMI caused by the operation of EV-MDS based on Z-source inverter.The main contents are as follows.Firstly,the mechanism of EV-MDS conducted EMI is analyzed.The structural components of EV-MDS are introduced,the Z-source network structure and the working principle of the Z-source inverter are analyzed,the capacitance and inductance are designed and its parameters are calculated in the Z-source network.Based on the traditional inverter,the modulation strategy of the Z-source inverter is analyzed,the CMV and CMC(Common Mode Current)generated by the Z-source inverter is deduced in the MDS,the main sources and the propagation path of conducted EMI in the MDS are analyzed in detail,the CM interference and DM(Differential Mode)interference is separated and extracted on LISN.Secondly,EV-MDS conducted EMI is modeled and simulated.In the conducted EMI frequency range,the high-frequency circuit model of each component of MDS is created,including inverter,motor,cable and LISN(Line Impedance Stabilization Network).The conducted EMI mechanism of MDS is analyzed.the circuit simulation model of the MDS conducted EMI is built under MATLAB/Simulink software,and the conducted EMI on the AC and DC sides is simulated and the EMI results are analyzed respectively.By modifying the size of the parasitic capacitance of the switch tube to the ground,the influence of different parasitic capacitance values on the conducted EMI of the MDS is analyzed.Thirdly,the EV-MDS motor-end shaft voltage and shaft current are studied.The generation mechanism of the motor-end shaft voltage and shaft current of PMSM(Permanent Magnet Synchronous Motor)and the effect of CMV on PMSM are expounded.The distributed capacitance existing inside the PMSM motor-end is analyzed.The CM model of the PMSM motor end is created by combining the generation mechanism and distribution capacitance and the path of the shaft current generated by the motor-end is analyzed in detail.Based on the CM model and the calculated CM parameters,the motor-end shaft voltage and shaft current circuit simulation models are built under MATLAB/Simulink software and the simulation analysis is Performed.Finally,the suppression method of EV-MDS conducted EMI is studied.It is decided to use a passive filter to suppress the transmission of EMI in EV-MDS,a CM choke is added on the DC side.An improved RLC two-order low-pass filter is designed on the AC side.the two filters are simultaneously connected with the original circuit simulation model to simulate in the MATLAB/Simulink,and the simulation results are compared with the previously conducted EMI simulation results without a filter,it is concluded that the combination of CM choke and improved RLC two-order low-pass filter has a good inhibitory effect on EV-MDS conducted EMI.