CN1996030A - Device for detecting internal impedance of conductive electromagnetic interference noise source - Google Patents

Abstract

The measuring conductivity electromagnetic interference noise source inner resistance device comprises electric power, LISN, known resistance feature filtering element, equipment to be measured, with electric line from the electric source directly entering into the LISN, passing known resistance feature filtering element, finally to the equipment to be tested to form a complete circuit. It has higher precision, and simple operation. It can make judgment for the inner resistance feature, provide premise for the EMI filter design, matching the resistance of the filter in design.

Description

Measure the device of conductive electromagnetic interference noise source internal impedance

Technical field

What the present invention relates to is the device that the internal impedance of conduction electromagnetic interference (EMI) noise source is measured, and for conduction EMI Noise Suppression is that the design of electromagnetic interface filter provides the prerequisite basis, belongs to electromagnetic compatibility device design and technical field of measuring.

Background technology

Electromagnetic interface filter is the effective measures that suppress electromagnetic interference (EMI), the main difficulty of design electromagnetic interface filter is: it needs comparatively accurately to know the size of noise source impedance and loaded impedance, and electromagnetic interface filter manufacturer designs at specific noise source impedance and loaded impedance, may there be effect fully when being used for power electronic equipment, because the internal impedance of each noise source is also inequality, and the matching relationship between interference source impedance and the filter impedance directly has influence on the filter effect of wave filter, therefore, accurately estimating noise source internal driving has significance for effective inhibition of electromagnetic interference (EMI).

Summary of the invention

The objective of the invention is resistance matching problem at electromagnetic interface filter in the above-mentioned electromagnetic compatibility, a kind of device based on improved insertion loss method and Hilbert transform mensuration conductive electromagnetic interference noise source internal impedance is provided, it can provide perfect and economical and practical noise source test solution for enterprise and product design slip-stick artist, the present invention both can satisfy the general requirement of noise source modeling, the reality test is compared with notional result, can provide the good premise condition for the design of next step electromagnetic interface filter, effective inhibition of EMI noise again simultaneously.

The present invention measures the device of conductive electromagnetic interference noise source internal impedance, by filter element, the equipment under test formation of power supply, line impedence stabilizing network (LISN), known impedance characteristic; The power lead of coming from power supply is directly inputted to the line impedence stabilizing network (LISN), by the filter element of known impedance characteristic, then is input in the equipment under test, constitutes a whole piece electric power loop.

Line impedence stabilizing network (LISN) structure (as shown in Figure 1) of adopting international standards is connected on respectively on L and the N line by the inductance of 2 50uH; The electric capacity of 2 1uF is positioned at inductance input end (left side), is connected in parallel on respectively between L-E and the N-E; The resistance of the electric capacity of 2 0.1uF and 2 1K Ω, 2 50 Ω is positioned at inductance output end (right side), after 1K Ω and the 50 Ω parallel connections with the capacitances in series of 0.1uF, then be connected across between L-E and the N-E respectively, the effect of LISN is to provide power supply for equipment under test, the noise of insulating power supply side enters test loop simultaneously, also the noise of isolating switch power generation prevents to pollute electrical network, and the stable impedance of one 50 Ω is provided for test loop.

The filter element of above-mentioned known impedance characteristic when measuring common code impedance, is a common mode choking coil, is connected between LISN and the equipment under test; Adopt series connection to insert the method estimating noise source common mode model of loss, the filter element of the known impedance characteristic of connecting between online resistance stabilizing network and the transducer, record the variation relation of LISN port interference voltage and electric current by wave filter, calculate the impedance and the noise source frequency spectrum in common-mode noise source.

The filter element of above-mentioned known impedance characteristic when measuring the differential mode impedance, is realized by resistance and capacitances in series, and an electric capacity is connected as an integral body with resistance, is connected in parallel between LISN and the equipment under test.Adopt the method estimating noise source differential mode model that inserts loss in parallel, the filter element of known impedance characteristic in parallel between online resistance stabilizing network and the transducer, record the variation relation of LISN port interference voltage and electric current by wave filter, calculate the impedance and the noise source frequency spectrum in differential mode noise source.

Differential mode and common mode interference concentrate circuit model can be reduced to one port network as shown in Figure 2.In following analysis: Z _NWhen differential mode Z _SDM, be Z during common mode _SCM, V _SWhen differential mode V _SDM, be V when common mode _SCM, V is V when differential mode _DM, be V during common mode _CM

In order to determine the impedance Z of equipment under test _SWith source V _S, the filter element of introducing known impedance characteristic (series connection or in parallel) calculates Z by examination at the variation relation of LISN port interference voltage and electric current between LISN and equipment under test _SAnd V _SNumerical value.Utilize Hilbert transform to measure the phase information of noise source impedance again.

Apparatus of the present invention both can be carried out general internal impedance test at all kinds of noise sources, and precision is higher, and simple to operate, only just can calculate the frequency spectrum in noise source impedance curve to be measured and source thereof by impedance instrument and wave filter.By this method of testing, not only can determine the internal impedance value of noise source, can also be by amplitude and the phase information that calculates internal impedance, thereby can judge the character of internal impedance, that draw internal impedance and be capacitive or perception, further the design for electromagnetic interface filter provides prerequisite, promptly satisfies the impedance matching property of wave filter when Design of Filter, thereby effectively electromagnetic interference (EMI) is suppressed, make it to satisfy the EMC standard.

Description of drawings

The internal impedance assay device structures block diagram of Fig. 1 equipment under test of the present invention

Fig. 2 differential mode and common mode interference are concentrated circuit model

Fig. 3 utilizes the method for inserting impedance in parallel to estimate the differential mode model

The method that Fig. 4 utilizes series connection to insert impedance is determined the common mode model

Fig. 5 linear time invariant one-port network

The amplitude curve of Fig. 6 network

The phase place that the phase place of Fig. 7 reality and Hilbert transform are derived

Fig. 8 semibridge system DC-DC transducer and Conduction Interference test setting

Fig. 9 differential mode noise source impedance curve

Figure 10 differential mode noise source frequency spectrum

Figure 11 common-mode noise source impedance curve

Figure 12 common-mode noise source frequency spectrum

Embodiment

Below in conjunction with specific embodiments and the drawings, the present invention is described in further detail.

Embodiment 1, utilize the differential mode noise source and the internal impedance thereof of the determinator test of conductive electromagnetic interference noise source internal impedance DC-DC transducer shown in Figure 8.

Measure the device of conductive electromagnetic interference noise source internal impedance, by filter element, the equipment under test formation of power supply, line impedence stabilizing network (LISN), known impedance characteristic; The power lead of coming from power supply is directly inputted to the line impedence stabilizing network (LISN), by the filter element of known impedance characteristic, then is input in the equipment under test, constitutes a whole piece electric power loop.The filter element of above-mentioned known impedance characteristic is realized by resistance and capacitances in series, and an electric capacity is connected as an integral body with resistance, is connected in parallel between LISN and the equipment under test as shown in Figure 1 and Figure 4.

At first the floating ground of transducer can be eliminated the influence of common mode interference,, behind impedance Z shunt in the parallel connection, become Z in the load of LISN side equivalent noise by shown in Figure 3 _D=Zshunt//Z _NThe differential mode noise voltage table is shown

$V_{\mathrm{DM}}=Z_D{\mathrm{gI}}_{\mathrm{DM}}=\frac{Z_D{\mathrm{gV}}_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}+Z_D}---\left(1\right)$

Choose an impedance Z shunt1, satisfy relational expression | Z _Shunt1|? | Z _N|, can get

Z _D1＝Z _shunt1//Z _N≈Z _N?(2)

Then

$V_{\mathrm{<figure-callout\; id="1"\; label="DM"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">DM</figure-callout>}1}={\mathrm{<figure-callout\; id="1"\; label="Z\; D"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_D{\mathrm{<figure-callout\; id="1"\; label="gl\; DM"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">gl</figure-callout>}}_{\mathrm{DM}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="Z\; D"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_D{\mathrm{gV}}_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}+{\mathrm{<figure-callout\; id="1"\; label="Z\; D"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_D}\&ap;\frac{Z_N{\mathrm{gV}}_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}+Z_N}\&ap;V_{\mathrm{SDM}}---\left(3\right)$

Choose another one impedance Z shunt2, satisfy relational expression | Z _Shunt2|=| Z _SDM|, can get so

Z _D2＝Z _shunt2//Z _N?≈?Z _shunt2?(4)

Then

$I_{\mathrm{<figure-callout\; id="2"\; label="DM"\; filenames="A20061016137200131.png"\; state="\{\{state\}\}">DM</figure-callout>}2}=\frac{V_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}+{\mathrm{<figure-callout\; id="2"\; label="Z\; D"\; filenames="A20061016137200131.png"\; state="\{\{state\}\}">Z</figure-callout>}}_D}\&ap;\frac{V_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}+{\mathrm{<figure-callout\; id="2"\; label="Z\; SDM"\; filenames="A20061016137200131.png"\; state="\{\{state\}\}">Z</figure-callout>}}_{\mathrm{SDM}}}\&ap;\frac{V_{\mathrm{SDM}}}{Z_{\mathrm{SDM}}}---\left(5\right)$

Then have

$Z_{\mathrm{SDM}}=\frac{V_{\mathrm{SDM}}}{I_{\mathrm{DM}2}}---\left(6\right)$

Formula (3) substitution formula (6) is got

$Z_{\mathrm{SDM}}=\frac{V_{\mathrm{DM}1}}{I_{\mathrm{DM}2}}---\left(7\right)$

Here, differential mode noise source V _SDMCan be by the differential mode noise voltage V of direct test _DM1Obtain differential mode internal impedance Z _SDMNumerical value then by V _DM1Divided by I _DM2Obtain.

In this test: Z _D1Realize Z by two 50 Ω resistance series connection of LISN (i.e. 100 Ω) _D2Realize by 1 Ω resistance and 1 μ F capacitances in series.Noise voltage shown in Fig. 3 and electric current are directly tested by Tektronix5054 and are obtained.Fig. 9 has provided the Z that obtains _SDMAnd Z _D1And Z _D2Amplitude frequency curve.Figure 10 has provided the V that obtains _SDMSpectrum curve.

Embodiment 2, utilize the common-mode noise source and the internal impedance thereof of the determinator test of conductive electromagnetic interference noise source internal impedance DC-DC transducer shown in Figure 8.

Measure the device of conductive electromagnetic interference noise source internal impedance, by filter element, the equipment under test formation of power supply, line impedence stabilizing network (LISN), known impedance characteristic; The power lead of coming from power supply is directly inputted to the line impedence stabilizing network (LISN), by the filter element of known impedance characteristic, then is input in the equipment under test, constitutes a whole piece electric power loop.The filter element of above-mentioned known impedance characteristic is a common mode choking coil, is connected between LISN and the equipment under test, as shown in Figure 1 and Figure 4.

Consider circuit shown in Figure 4, after introducing impedance Z series, the load of common mode equivalent noise is Zc=Zseries+Z _N, then can get

$V_{\mathrm{CM}}=Z_N{\mathrm{gI}}_{\mathrm{CM}}=\frac{Z_{N}g{V}_{\mathrm{SCM}}}{Z_{\mathrm{SCM}}+Z_C}---\left(8\right)$

Choose an impedance Z series1, satisfy relational expression | Z _Series1|? | Z _SCM|, then

Z _C1＝Z _series1+Z _N≈Z _series1(9)

Can get by formula (8)

$I_{\mathrm{<figure-callout\; id="1"\; label="CM"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">CM</figure-callout>}1}=\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{SCM}}+{\mathrm{<figure-callout\; id="1"\; label="Z\; C"\; filenames="A20061016137200111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_C}\&ap;\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{SCM}}+Z_{\mathrm{serices}}}\&ap;\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{series}}}---\left(10\right)$

Can get by formula (10)

V _SCM＝Z _seriesgI _CM1?(11)

Choose another impedance Z series2, satisfy relational expression | Z _Series2|=| Z _N|, can get so

Z _C2＝Z _series2+Z _N≈Z _N?(12)

Get by formula (8)

$I_{\mathrm{<figure-callout\; id="2"\; label="CM"\; filenames="A20061016137200131.png"\; state="\{\{state\}\}">CM</figure-callout>}2}=\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{SCM}}+{\mathrm{<figure-callout\; id="2"\; label="Z\; C"\; filenames="A20061016137200131.png"\; state="\{\{state\}\}">Z</figure-callout>}}_C}\&ap;\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{SCM}}+Z_N}\&ap;\frac{V_{\mathrm{SCM}}}{Z_{\mathrm{SCN}}}---\left(13\right)$

Get by formula (13)

$Z_{\mathrm{SCM}}=\frac{V_{\mathrm{SCM}}}{I_{\mathrm{CM}2}}---\left(14\right)$

Formula (11) substitution (14) can be got

$Z_{\mathrm{SCM}}=\frac{I_{\mathrm{CM}1}}{I_{\mathrm{CM}2}}g{Z}_{\mathrm{seriesl}}---\left(15\right)$

Then the information of common-mode noise source and internal impedance can be obtained respectively by formula (11) and (15).

In this test, in order to determine Z _SCMAnd V _SCM, a 8mH common mode choke serves as series impedance Z _C1, Z is served as in two 50 Ω resistance parallel connection (i.e. 25 Ω) _C2Figure 11 has provided the Z that obtains _SCMAnd Z _C1And Z _C2Amplitude frequency curve, Figure 12 has provided the V that obtains _SCMSpectrum curve.

Utilize the Hilbert transform method to measure the phase information of noise source impedance

From as can be known top, Z _sAmplitude can obtain, but can not get its phase information.Use Hilbert transform can survey its phase place.

$\&angle;Z_s\left(\mathrm{\&omega;}\right)=\frac{2\mathrm{\&omega;}}{\mathrm{\&pi;}}{\&Integral;}_0^{\&infin;}\frac{\left|Z_s\left(\mathrm{\&xi;}\right)\right|-\left|Z_s\left(\mathrm{\&omega;}\right)\right|}{(\mathrm{\&xi;}+\mathrm{\&omega;})(\mathrm{\&xi;}-\mathrm{\&omega;})}\mathrm{d\&xi;}$

In quite wide frequency range (0-fmax), know the amplitude function | Z _s(ω) |, then can accurately obtain phase function＜Z _s(ω), up to reaching 1/3 of maximum frequency.

Use linear time invariant one-port network as shown in Figure 5, suppose to know the amplitude of circuit input impedance, only reach 20MHz, as shown in Figure 6, dotted line among the amplitude curve of all the other frequency ranges such as the figure.

The phase place of using the Hilbert transform algorithm can obtain same frequency segment is seen Fig. 7 dotted line.As seen, phase place actual and that obtain is very identical in this example.

After the common mode internal impedance of learning Switching Power Supply, just can carry out corresponding Design of Filter.Write out the transport function of wave filter according to noise source internal impedance, loaded impedance (known) and filter construction, secondly determine wave filter the cutoff frequency point, insert the maximum differential loss that loss, passband allow, calculate the value of each components and parts of wave filter at last.

Because the size of noise source impedance is the important evidence of Design of Filter, has only the impedance matching of working as during design, its filtering characteristic of performance of wave filter ability maximal efficiency.Otherwise, if internal impedance the unknown of noise source when carrying out the electromagnetic interface filter design, will be made as the internal impedance of noise source a general value (for example 50 Ω), and carry out a kind of design of universal filter.Because the type of each noise source is diversified, when adopting general electromagnetic interface filter, the problem of impedance mismatching will inevitably appear, and filter insertion loss is reduced, frequency is drifted about; Heavy then wave filter is amplified noise signal.So, various different types of noise source internal impedance is tested, as corresponding Design of Filter basis, can greatly improve the filtering characteristic of wave filter, save financial cost.

Claims (3)

1, a kind of device of measuring the conductive electromagnetic interference noise source internal impedance is made of power supply, line impedence stabilizing network, the filter element of known impedance characteristic, equipment under test; It is characterized in that: the power lead of coming from power supply is directly inputted to the line impedence stabilizing network, by the filter element of known impedance characteristic, then is input in the equipment under test, constitutes a whole piece electric power loop.

2, the device of mensuration conductive electromagnetic interference noise source internal impedance according to claim 1, it is characterized in that: the filter element of described known impedance characteristic, realize by resistance and capacitances in series, one electric capacity is connected as an integral body with resistance, be connected in parallel between line impedence stabilizing network and the equipment under test.

3, the device of mensuration conductive electromagnetic interference noise source internal impedance according to claim 2 is characterized in that: the filter element of described known impedance characteristic is a common mode choking coil, is connected between line impedence stabilizing network and the equipment under test.

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