Research On EMI Generated By Parasitic Parameters In EV Drive System

In recent years, electric vehicle(EV) developed fast because of the deterioration of environment, the demand for cars and the increasing contradiction between the supply and the demand of oil. With the deepening research of EV, researchers paid more attention to its electromagnetic compatibility. DC/AC inverter is one of the most important electronic components of EV drive system, which will cause voltage or current jump on working process.Electromagnetic interference will be produced because of this jump and then affect the normal operation of electronic equipment and vehicle, which is a hidden danger of EV.This paper analyzed main interference sources, coupling paths and electromagnetic interference generated in EV drive system and paid attention to the initiation of electromagnetic interference, the formation of a loop and sensitive equipment of control circuit.It can be concluded that the operation of high frequency switching may generate di/dt in parasitic inductance, which then produced pulsating current and differential mode interference.In addition, dv/di in parasitic capacitance of the inverter’s bridge produced the charge-discharge current and common mode interference.During the experiment, the author analyzed the results of simulation and precision impedance analyzer measurement and calculated the parasitic parameters of the DC side support capacitor, discharge resistance, the heat sink that connected to the inverter switch and power cable, and then established their equivalent circuit model.On the basis of these parameters, the ideal model and model considering various parasitic parameters of elements were established in the environment of Saber simulation software. By taking the DC/AC inverter system as the research object, the amplitude of the electromagnetic interference signals was measured and the importance of parasitic parameters for running state of driving system was analyzed.It is incided that with the increase of frequency, the perceptual characteristics of filter capacitor increased while the filtering effect decreased. Although the parasitic parameters of unshielded cable were small, but considering the coupled electromagnetic interference among cables, shielded cables worked obviously safely than unshielded cables, confirming that the differential mode interference was mainly related with the inductance and capacitance among the phase loop, but common mode interference was largely depended on the fin parasitic capacitors to the ground.