| The term electromagnetic pulse(EMP)comes from the lightning of nature,where a transient electromagnetic field appears.Lightning occurs about 100 times per second worldwide,and every instantaneous electromagnetic field increases the current by ten thousand amperes per us.These instantaneous large current from the power line and the signal line go into the electronic equipment through the conduction coupling,and then generate induced voltage and current in the equipment components,If these induced voltage and the current exceeds the damage threshold of components,ranging from little interference into permanent damage.UWB-EMP is a fast rising edge(≤ 5ns)of impulses in the time domain,wide spectral coverage,from very low frequency to several GHz(most of the energy concentrated in low frequency).A large number of shortwave,ultra-short wave communication equipment and high-speed ultra-large scale integrated circuits work in these bands.When the ultra-wideband electromagnetic pulse coupled with the energy interacts with these devices,it may cause some devices be disturbed,degraded or even damaged.The ultra-wideband electromagnetic pulse of different electronic equipment is different.To analyze the ultra-wideband electromagnetic pulse effect threshold,it is necessary to clarify the two key points: how does the ultra-wideband electromagnetic pulse enter the interior of the electronic device;how much the energy coupling coefficient and the characteristic parameters of sensitive device port sensing ultra-wideband electromagnetic pulse is.In addition,In addition,it is necessary to know the effect of sensitive electronic devices.In this paper,discussed the characteristics of several common conduction disturbances of ultra-wideband electromagnetic pulse from the perspective of conduction interference protection.Then,according to the characteristics of the jamming signal and the working characteristics of the existing magnetic materials,the appropriate filter circuit is selected.In Chapter 1,introduced the sources of ultra-wideband electromagnetic pulses and the current status of domestic and international research;In Chapter 2,the damaging effects of ultra-wideband electromagnetic pulse on the power system is studied,in order to find out the most effective means of protection,it is necessary to be definitely to understand the mechanism of ultra-wideband electromagnetic pulse;In Chapter 2,designed an EMI filter for the protection against conducted interference of ultra-wideband electromagnetic pulses.Here,the EMI filter is placed between the power supply line and the power converter input,it is mainly used to suppress common mode(CM)and differential-mode(DM)noise,in the frequency band from 100 KHz to 3GHz,the insertion loss can rearch 60 dB.In order to achieve the design index,the paper selects the typical Chebyshev low-pass LC filter to achieve this function after comparing with the attenuation characteristics of various functional filters.Then,the frequency characteristics of the existing magnetic materials are analyzed.According to the magnetic permeability distribution of the magnetic materials,the guard frequency band is divided into low,medium and high frequency band.Selected the iron nanocrystalline core with high magnetic permeability in the low frequency band,the manganese zinc ferrite and nickel-zinc ferrite in the middle and high frequency band and the special high frequency band use the hollow inductance and feed through capacitor which is fixed on the partition by bolts.Considering the LC device working in such a wide frequency band,the resonant point generated by parasitic parameters of itself will affect the insertion loss at high frequency band.To solve this problem,analyzed the frequency model of the LC device and optimized the filter circuit in the case of the parasitic capacitance exists.Finally,tested the main indicators of the EMI filter insertion loss,it can basically meet the design requirements.Then according to related test requirements of the existing electromagnetic pulse conduction interference,build a test platform and inject electromagnetic pulse current waveform between the filter line to line and line to ground.The ultra-wideband test system selects Swiss Montena here: which includes a high-voltage pulse generator,a semi-parabolic antenna,an oscilloscope and son on.The high-voltage pulse generator transmits the high-voltage pulse to a semi-parabolic antenna(HIRA,radiating for coupling filter),and then measure the electric-field pulses of radiation by using a probe.If the filter in strong interference environments,in order to ensure the normal transmission of measured signals,a fiber optic launcher is added to the measurement link system,so that the required signals transmitted over the fiber link.The oscilloscope is used in the test system to collect and display the signal measured by the probe.Finally,these signals are stored and formed a test report in the computer.Compared the ultra-wideband EMI filter in the paper with the common EMI filter,there is additional electromagnetic pulse protection part in the front input,and the structure of the ultra-wideband EMI filter including low-frequency pulse relief protection unit and the high-frequency protection unit.The low-frequency protection unit includes arrester,delay inductance and varistor.Arrester and varistor used to absorb the low frequency energy of electromagnetic pulse.The delay inductance is used to prolong the rising edge time of electromagnetic pulse.The high frequency protection unit includes typical LC filter circuit and feed Pass filter(feed through capacitor),LC resonant circuit be used to absorb electromagnetic pulse IF energy,filter inductance absorb of electromagnetic pulse high frequency energy,the feed through capacitor used to absorb electromagnetic pulse high frequency energy.Delay,absorption,bypass resonance,RF shielding,etc.be used to cut down the power line coupled ultra-wideband electromagnetic pulse energy in this paper,so that the normal working range of power equipment is insured. |
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