Research On The Pre-assessments Of Electromagnetic Compatibility In Automobile

The pre-assessment of Electromagnetic Compatibility (EMC) in automobile is an emerging subject. Because of its own complexity, the difference between the theoretical simulation and the actual test is extremely big. Thus, the actual test and the statistic method to analyze the massive data are still the best two ways to check the EMC of an electric device till now. However, the automobile electric engineers often empirically solve the EMC problems in automobile, not systematically.The overseas famous automobile manufacturers seriously appreciated the research of the EMC problem in automobile, and have built their own research center and laboratories, or established research and test center cooperated with university.Due to the automotive industry in our country is laggard, the understanding of the importance of automotive EMC is insufficient and the corresponding laws are not perfect, so the automotive electric engineers major focus on functional design, few consideration given to the problems of EMC. Under this background, the Specialized Research Fund for the Doctoral Program of Higher Education supported the work names the EMC analysis and simulation in automobile (No. 20050183019), which aims to enhance the efficiency of solution, reduce the cost and apply the digital simulation and mathematics modeling to the research. The author prime tasks are as follows:(1) Establishment of pre-assessment models based on the actual EMC test standards in automobile.On the base of necessary research on automotive unique electromagnetic environments and the major interference, the automotive EMC systematic method, which was composed of pre-assessments, digital simulation and actual test, was proposed. To improve the pertinence of the models and accuracy of choosing parameters, the author analyzed the EMC test standards and its principles. According to the principle of actual test, the conductive and radiative anti-interference models were established. The pre-assessment model that the radiative interference effected the lines as an AC voltage source through coupling was established based on the actual test principle. The equivalent source effected the inside device which was connected with the lines. The time domain waveforms of automotive conducted interference were summed up, and the corresponding spectrum was equivalent to the frequency conversion voltage source. The disturbance of the specific electric component inside the device was obtained through circuit topology analysis method.(2)To obtain the uncertain parameters in EMC analysis, a fuzzed method was proposed.Because of the randomness of lines arrangements in automobile, the distance between lines in pre-assessment of crosstalk was replaced by"scope", which was a fuzzy mathematics conception, the author have deduced the corresponding formulas also.As for the simple estimation of crosstalk in harness, the distance between lines was difficult to determine. The distance was replaced by"scope"in the analysis. Fuzzy inference was a technique of ascertaining massive early or the same product data with the mathematical methods. The model could be revised itself with the accumulation of the data, and the accuracy of calculation was artificial. The calculation error was determined by the actual test data and the fuzzy interval division. character,the fuzzy relation set was ascertained from the merging of the fuzzy implication relations. In this paper, on the basis of measurement method, the major work of improving the algorithm efficiency and accuracy was analyzed.(3) An error back propagation adding momentum factors artificial neural network was used for calculating the coupling parameters in the pre-assessment of crosstalk between lines.The best way to get the coupling parameters is through actual measurement, which is impracticable in pre-assessments. To address this contradiction, the author proposed using theoretical values as the input parameters of the neural network, and the corresponding actual measurement values as the error correction of the output. To achieve further efficiency of assessment, the momentum factors were added to the network on the basis of self-adjusting. After training and contrasting the absolute error of the output, the author gave the principle of establishing factors.Due to its good capability in auto-adapted learning, a method between traditional theoretical calculation and actual test was obtained. This method was simple, efficient, and versatile compared with the traditional theoretical method. In view of the actual coupling parameters measurement, the author adopted changing source frequency and measurement position, through two attenuation constants and phase shift parameters to determine the values of coupling parameters. The method of crosstalk assessment in this paper could provide basis of classification baled in the automotive wiring harness.(4) According to automobile its own characters of radiative interference, a variable grid FDTD method according to excitation source partition coefficients was proposed and the author have deduced the corresponding calculation formulas.As the radiative interference in automobile belong to wide band frequency, unintentional emission source, the acquisition data and the corresponding spectrum did not have homosexual enough to represent the characteristics of the interference source. But the sweeping of band-pass method could get the features of frequency and peak of the interference. The feature spectrum of the collected data was obtained by the wavelet packet decomposition based on the actual test of radiation source in automobile. The source was simulated by a double modulation time-harmonic excitation source, which could separate the frequency in the time domain.Because of single grid FDTD cost long computing time, the mutative grid of FDTD corresponding to the division coefficient of the feature spectum, local subgridding format, the interface of two medium processing and the boundary condition were analyzed. The essence of this approach was changing the grid with the source frequency coefficient, which greatly reduced the amount of computation, improved the efficiency of assessments.(5) Aiming at all the models suggested in this paper, the author have programmed the corresponding calculation procedures.The author used Visual C++ and Matlab mixed programming, combined the Matlab powerful computing, data processing capabilities with VC excellent programming capabilities together. The application software package aiming at pre-assessment of EMC in automobile was developed. Howerve, because of the limited time, the author did not modify the parameters in the software, which is the main content of the next work also.Main creations in the paper:(1) The application of fuzzy inference algorithm to estimate the distance between lines in the automotive wire harness. The fuzzy relation set was ascertained from the merging of the fuzzy implication relations. And the membership functions as the correction factors of the prediction scope were constructed. (2) An error back propagation adding momentum factors artificial neural network of calculating the coupling parameters in the pre-assessment of crosstalk was proposed. According to the theoretical calculation values and the actual test, the weight coefficients and the thresholds could be determined through training. A method between traditional theoretical calculation and actual test was obtained. According to the absolute error of network output and actual test value, the the momentum factor can determined.(3) The radiative interference source was simulated by a double modulation time-harmonic excitation source. On the research of the distribution of early test data, the feature spectrum of the collected data was obtained by the WPD based on the energy of the sub-band frequency.(4)Combined with Maxwell partial differential equation, a variable grid FDTD method according to excitation source partition coefficients was proposed. It greatly reduced the amount of calculation and the memory when deal with the high-frequency and large size space interference problems. Local subgridding format, the interface of two medium processing and the boundary condition were analyzed.Based on the above research findings, the problems that need to further study are as follows:(1) In order to solve the EMC problems at the source, it is necessary to investigate the mechanism of the automobile itself conducted and radiative interference.(2) The parameters in the models should be modified through lots of actual tests, the purpose is to reduce the margin and increase the approximate degree.(3) The external automotive EMI source needed to be further studied.