Electromagnetic Interference And Suppression In Power Inverter System Of Electric Vehicles

The electromagnetic interference(EMI) and suppression method of power inverter system in electric vehicles were studied in this paper. The research was divided into five parts: EMI source and propagation path analysis, EMI modeling and simulation, EMI experiment, EMI suppression and EMI analysis after installed.Firstly, the EMI source and propagation path were analyzed according to results of the experiment. The rapidly switching devices and crystal oscillators are the main EMI source in the system, so the frequency characteristics of IGBTs in main power circuit, MOSFETs in DC-DC converter and crystal oscillators of PCB in controller were studied. Equivalent circuits were established according to the propagation paths of both high-and-low frequency differential-mode(DM) interference and CM interference. Both the effect of different motor speed, different motor toque and different installation on EMI and the effect of dc circuit and ac circuit on dc common-mode(CM) current and ac CM current were in agreement with the experimental results theoretically.Secondly, the effect of different motor speed, different motor toque and different installation on EMI was analyzed and the components responsible for the EMI were confirmed by establishing the high frequency circuit model of the EMI in the system. Positive conducted EMI was simulated according to the PSPICE model. The power inverter system PSPICE model was established based on measurement as a two-port network system to confirm the components responsible for the EMI resonances according to the transfer characteristic of the system and the effect from the parasitic parameter of components on EMI was analyzed.Thirdly, conducted EMI experiment and radiated EMI experiment on power inverter system were performed. The difference of the EMI generated from the system was analyzed under both load and idle conditions. Both the effect of different motor speed, different motor toque and different installation on EMI and the effect of dc circuit and ac circuit on dc common-mode(CM) current and ac CM current were studied.Fourthly, both suppression inside the system and outside the system were analyzed and verified. CM choke and RC filter were added inside the system according to the impedance characteristic of the components and the magnitude at the resonances was decreased. Different suppression methods were analyzed according to the CM propagation path and virified by experiment.The calculation of a filter was highlighted as a example to suppress the EMI exceeding the standard.Finally, EMI generated after the power inverter system installed was studied. Radiated EMI test model and radiated EMI model after installation were constructed to analyze the the difference between the EMI charateristics before and after system installed in the vehicle. Filters were calculated to reduce the EMI below the standard limit.