Research On Electrical Fast Transient Source And Its Full-Link Interference Coupling Path

Electrical fast transient(EFT)is a kind of transient sudden change interference signal,which will seriously endanger the normal operation of electronic systems.At present,research methods for EFT are experimental testing and simulation modeling.After analyzing the advantages and disadvantages of these two research methods,this thesis decides to use simulation modeling to study the related issues of EFT.At the same time,in view of the low accuracy of the simulation model faced in the current research on the EFT source generator simulation,and the difficulty in finding potential interference paths in the simulation research,the research goals of this thesis are put forward as follows: A simulation model that can accurately simulate the EFT source generator is established,and a full-link interference simulation model of the device under test is established,and on this basis,the full-link analysis of the EFT interference coupling path is realized.Firstly,this thesis expounds the basic theory of EFT from the aspects of the generation mechanism,interference mechanism and basic characteristics of EFT.According to the circuit schematic diagram of the EFT source generator stipulated by the IEC international standard,a corresponding mathematical model is established.At the same time,the regulations and requirements of IEC international standards for EFT immunity test are introduced as theoretical guidance for the subsequent establishment of EFT test simulation platform.Secondly,by comparing and analyzing the difference between the EFT waveform specified by the IEC standard and the output waveform of the actual EFT generator,it is pointed out that it is necessary to establish an EFT source simulation circuit model that can simulate the output waveform of the actual EFT generator,and based on the established the mathematical model,by introducing the cosine function term,realizes the description of the damped oscillation phenomenon in the actual EFT output waveform,thus obtaining a more accurate simulation model of the EFT source generator.By comparing the simulation waveform results with the actual EFT generator output waveform,the correctness of the improved simulation model is verified.At the same time,in the electromagnetic simulation software CST,the three-dimensional equipment model of the EFT source generator was established,and combined with the obtained simulation waveform results,the simulation of the actual EFT source generator equipment was realized.Thirdly,the rationality of choosing the rectangular pulse signal source as the tested equipment in the EFT immunity simulation test is expounded,and the simulation circuits of the tested equipment with and without EFT interference are established respectively.By comparing the output waveforms of the circuit under two different conditions,it is explained from the circuit level perspective when the EFT interference enters the internal circuit of the tested device,it will cause the device to function abnormally.In order to study the coupling path of EFT interference into the internal circuit,a full-link simulation model of the device from the external device casing to the internal PCB and then to the circuit on the board is established.Finally,combined with multiple established simulation models,an EFT immunity test simulation platform is built.Based on this platform,the full-link simulation analysis of the EFT interference coupling path is carried out for the tested equipment from the aspects of shell surface current,transient current changes of internal circuit components,and magnetic field effects caused by radiation interference.At the same time,combined with the experimental test results,the closed-loop verification of the simulation results shows that the device under test has poor anti-EFT interference performance,so it needs to be redesigned and rectified.According to the characteristics of EFT signal,the corresponding protective device is given,and the effectiveness is verified by simulation comparison.It shows that the addition of the protective device improves the anti-interference performance of the device under test.The EFT source generator simulation model established in this thesis has higher accuracy,can simulate the damped oscillation characteristics and bipolar characteristics of the EFT pulse.It can simulate for the EFT generator output waveform provided by the instrument manufacturer.The model that is applied to the EFT immunity test can obtain more credibility.In addition,the whole-link analysis method used in the thesis can effectively find the potential EFT interference propagation path,which has important guiding significance for further proposing measures to suppress EFT interference.