Study On The Conducted Electromagnetic Interference Modeling And Restraint Of Electric Vehicle Motor Drive System

With the shortage of non-renewable energy and automobile exhaust emissions are polluting the air, the electrical vehicle development rapidly which has the advantage of energy-efficient and environmentally friendly. However, the increase of electronic equipment and improvement of electrical integration degree in automobile,which make the electromagnetic compatibility problems of electrical vehicle become more serious. As one of the main interferences in vehicle, the motor drive system is causing electromagnetic disturbance while working, especially the common-mode interference.Not only it affects the regular work of its own system, but also disturb the operation of any other units. The conducted electromagnetic interference of motor drive system in electrical vehicle is studied, the main contents are as follows:1 、 The SVPWM operating principle of motor drive system is studied, the mechanism of producing of electromagnetic interference in DC/AC inverter is researched, and the conducted EMI propagation paths are discussed.2、A modeling method of motor equivalent circuit is proposed. By regarding the three-phase ac electromotor as a three-port network with a common end, the pi-type equivalent circuit is established. The impedance parameters of motor ports are measured and converted to admittance parameters, then rational functions of admittance components are obtained by using vector fitting method. The rational functions can be realized with RLC lumped-element, so the equivalent circuit of motor is established in conducted interference spectrum.3、By combining with dynamometer, the experimental platform is built, aimed to obtain the EMI data while the motor drive system works in different states. The interference source is established, as same the inverter parasitic parameters model and the motor model with impedance data. Based on the multi-conductor transmission line(MTL) theory, the equivalent circuit of cable is proposed, the impedance parameters are calculated with analytical method, while the capacitance and inductance parameters are simulated in Maxwell 2D finite element software. The prediction and simulation model of motor drive system is built in Simulink software, and verified by comparing with the measurement data.4、Common-mode EMI of motor drive system is studied, and the characteristics are researched with Fourier analysis. Several restraining methods of common-mode EMI are introduced in this paper. A modified second order RLC low-pass filter circuit is adopted to restrain the electromagnetic disturbance at the output of inverter. The filter parameters are obtained through numerical calculation, and inhibitory effect of filter which aim at common-mode voltage and current is simulated.