Modeling And Analysis For The Conducted Electromagnetic Interference Of Vehicle High-Voltage Electric Drive Systems

Due to the use of high-voltage and high-current power devices,vehicular high-voltage electric drive systems can generate significant conducted electromagnetic interference.In the electric vehicle with dense electronic equipment,high amplitude and wide bandwidth conducted electromagnetic interference seriously affect the normal operation of sensitive equipment and reduce system reliability.In order to quantitatively assess the electromagnetic interference hazards of vehicular high-voltage electric drive systems,an accurate prediction of the conducted electromagnetic interference intensity in the system is necessary for rational electromagnetic compatibility design prior to the manufacturing of electric vehicles,which in turn improves the electromagnetic safety of the vehicles.However,most of the existing electromagnetic interference prediction models for the vehicular high-voltage electric drive system are empirical models,which have narrow applicable frequency bands and low accuracy,and cannot predict high frequency electromagnetic noise.Therefore,this dissertation focuses on the generation mechanism and prediction method of conducted electromagnetic interference in the vehicular high-voltage electric drive system,combined with the research topic of “Simulation and Analysis for the Influence of the Electric Drive System on the Electromagnetic Environment in Vehicles”.The main research work and innovation results are as follows:(1)Aiming at the problems that the existing motor behavioral model is not suitable for time domain simulation,difficult to parameterize and to capture multiple resonances,as well as existing the phenomenon of neglecting low-impendence antiresonance,the three-phase coupled high-frequency behavioral model and the high-frequency behavioral model of the resonant unit for the motor are established.In the first model,the three-phase coupled model is simplified into differential mode model and common mode model.The differential mode and common mode model are parameterized by the series and parallel resonance in the corresponding impedance to determine the parameters of the three-phase coupled circuit.The second model is to process the measured impedance responses of differential mode and common mode,then indirectly obtain the single-phase impedance response.The resonant element is used to construct the equivalent circuit of the series and parallel resonance in each single-phase impedance,and thus the high-frequency model of the whole motor is established.The comparison between simulation results and experimental data shows the effectiveness of the two models.Comparing the simulation efficiency and accuracy,the three-phase coupled model has more advantages in computational efficiency,while the resonant element model has higher precision.(2)Aiming at the problems of narrow frequency range,complicated parameterization program,difficult parameter acquisition and low calculation accuracy of the existing shielded cable high-frequency model,a high-frequency model of shielded cable based on lumped parameter circuit cascade is established.In this model,the inner conductor and the shielding layer of the shielded cable are regarded as independent conductors,and the electrical parameters per unit length of the model are calculated by the combination of numerical method and analytical method.The impedance matrix and admittance matrix per unit length at the maximum operating frequency are given,and the maximum electrical size of the shielded cable and the number of model lumped circuit cascades are derived.The high-frequency model is verified by numerical simulation and experiment.The results indicate that the model can accurately predict the high-frequency electromagnetic noise along the shielded cable.Based on the high-frequency model of shielded cables,the impacts of the cable length,shield thickness,and the angle,diameter,number and conductivity of the braiding wire on the shield effect of cables in the vehicular high-voltage electric drive systems are discussed in depth.(3)Based on the proposed motor behavioral model,multi-conductor transmission line shielded cable model,and the existing high-frequency models of inverter and power battery,a high frequency model of vehicle high voltage drive system which can quickly and accurately quantify the system level conduction emission is established for the problems of difficulty in numerical prediction for conducted electromagnetic interference,narrow frequency range and low accuracy of existing system-level models,and inability to predict high-frequency electromagnetic noise in vehicular high-voltage electric drive systems.The comparison between simulation results and experimental data shows that the model can effectively predict the system-level conducted electromagnetic interference at high frequencies.Compared with the existing frequency modeling techniques,it is further proved that the established vehicular high-voltage electric drive system model has significant advantages in both prediction accuracy and applicable frequency range.Based on the established system-level conducted electromagnetic interference prediction model,the influence laws of motor parasitic capacitance,three-phase cable length,inverter parasitic capacitance,and battery voltage on the system conducted electromagnetic interference are further explored.