Electromagnetic Interference And Suppression Of Power Circuit In Motor Drive System For Electric Vehicle

The EMI characteristics of motor drive system for electric vehicles is researched in thispaper. It includes three parts: theoretical analysis of EMI characteristics, experiment andsimulation of conducted EMI in different workconditions, as well as radiated emission andresearch on different methods of EMI suppression.First of all, the main EMI noise source and transmission ways are studied based on a20kW motor drive system. The EMI noise of the differential mode (DM) and common mode(CM) conducted for power circuits are analyzed by building the equivalent circuit. And theradiated EMI characteristics of the system are calculated by establishing the equivalent modelof DC and AC cables. After comparing the calculated value of conducted and radiated EMIwith standard GB/T18655-2010, the EMI value of power circuits in the motor drive systemis predicted.Secondly, the EMI experiments of the power circuits in the motor drive system arecompleted, which includes DC conducted voltage, three-phase AC cable conducted voltageand conducted current test, CM current test, near-field scanning, etc. The experime nta lmeasured results are compared with the relevant standards (CISPR25/GB/T186552010).And the frequency band which beyond the standard limits are found.Thirdly, the time-domain equivalent model of power circuits is established in the designstudio of CST software to simulate the DC conducted voltage and CM current of powercircuits in the motor drive system. By comparing with the corresponding standard, thefrequency band beyond conducted limit range could be predicted obviously. And by changingthe different parameters, EMI characteristics with different influence parameters could beanalyzed.The feasibility of the simulation model could be verified through comparing withexperiment results which are included DC conducted voltage and radiated value.Finally, the methods of suppressing EMI noise are analyzed to limit the EMI noisewithin the standard limit line. Three improved solution are proposed to rectify the system,including ferrite beads, CM choke and replacing the shield wire cables. The effectiveness ofthese three suppression methods were verified by experiments.