CN103823127A - Conductive common-mode/differential-mode noise separation method - Google Patents

Abstract

The invention discloses a conductive common-mode/differential-mode noise separation method, belonging to the technical field of conductive electromagnetic compatibility noise measurement. Radiofrequency current probe measurement and software separation calculation are combined, and the method is suitable for conductive interference measurement on a single phase line. The method comprises the following measuring steps: I, directly measuring a phase line, center line and common-mode conducted interference spectrum by using a radiofrequency current probe, connecting the output end of the current probe to a spectrometer through a coaxial line, and driving the spectrometer to work in a peak detection mode; II, calibrating interference spectrum data obtained in the step I, and measuring the transmission admittance of the current probe and the coaxial line used in the step I by using a vector network analyzer; III, putting the corrected data IL, IN and ICM into a formula to obtain a differential-mode current spectrum IDM so as to obtain the interference voltage in a differential mode and a common mode. By adopting a test method, the conducted interference spectrum on each line can be measured rapidly, and separation of common-mode and differential-mode interference is realized. The method is mainly applied to online measurement of electromagnetic compatibility noise.

Description

A kind of conduction common mode/differential mode noise separation method

Technical field

The invention belongs to conductive electromagnetic compatibility noise measurement technical field.

Technical background

Being widely used of power electronics, brings increasingly serious electromagnetic interference problem.Conduction electromagnetic interference noise is divided into common-mode noise and two kinds of mode of differential mode noise.In monophase system, differential mode noise is present between phase line and center line, and common-mode noise refers to phase line or center line interference voltage over the ground.Before product export, need the interference producing while measuring its work, according to criteria limit and interfering data, effective inhibition means reasonable in design.For the different qualities of common-mode noise and differential mode noise, deviser need to propose different inhibition methods.The measurement of conduction electromagnetic interference (EMI) and the separation of common mode/differential mode thereof are very important research contents of electromagnetic compatibility fields of measurement.

Chinese scholars has been done large quantity research to CM/DM separation method, has proposed different separation methods.U.S. Paul(Paul C R, Hardin K B.Diagnosis and reduction of conducted noise emission[J] .IEEE Transaction on EMC, 1988,30 (4): 553-560) adopt a pair of radio-frequency transformer (RFT) that is 1:1 with center tap, no-load voltage ratio as core, disclose a kind of separated network of selecting the mode output of CM/DM with mechanical switch.Due to the mechanical type feature of switch itself, can cause noise, thereby affect the high frequency recognition performance of separated network.After this, See(See K Y.Network for conducted EMI diagnosis[J]. Electronic Letters, 1999,35 (17): 1446-1447) utilize two broadband radio-frequency transformer (RFT)s, make the noise in " phase line " and " center line " realize vector " addition ", " subtracting each other " function, isolate common and different mode signal, improved the adverse effect of bringing due to mechanical switch.The Guo(Ting Guo of the U.S., Chen D Y, Lee F C.Separation of the common

mode and differential

mode conducted EMI noise[J] .IEEE Transaction on Power Electronics, 1996,11 (3): 480-488) one is disclosed based on 0 °/180 ° power combiners, can well obtain the output of differential mode and common mode, greatly improve the performance of separated network.But because cost is too high, be difficult to extensively promote the use of.

Shuo Wang, Fred.C.Lee and Willem Gerhardus Odendaal. has announced " a kind of common mode differential mode noise separation method of single-phase Conduction Interference " (Characterization, evaluation, and design of noise separator for conducted EMI noise diagnosis[J], IEEE transactions on power electronics, 2005,20 (4): 974-982), designed a separation vessel being formed by the line transformer of two 1:1.When work, the T1 of two transformers in separation vessel and T2 are respectively as differential mode choke coil and common mode choke, and the voltage drop in the impedance of 50 Ω is respectively common and different mode signal.When the test of this separation method, separation vessel need be connected in to two output terminals of linear impedance stabilization network, the interference that Devices to test produces, by difference output common mode and the difference mode signal at two input ends by choking coil.Use this separation vessel can effectively isolate common and different mode signal, but must guarantee that the impedance of the input end of V1 and the input end of V2 is 50 Ω, and resistance value is along with the frequency change of noise source, this just requires the characteristic impedance of choking coil in strict conformity with design needs.The characteristic impedance of choking coil is not only relevant with the loss of coil, also with the leakage inductance of two inductance and between distributed capacitance relevant, this brings difficulty with regard to the making of giving choking coil.

Because the length issue of current probe size or line exists, coiling clamp is measured differential mode noise and is become difficulty.Add extra difference mode/common mode separated network, this can increase undoubtedly measures cost and test period.

Summary of the invention

The object of this invention is to provide a kind of conduction common mode/differential mode noise separation method, it can solve effectively, and noise on monophase system power lead extracts and the separation problem of common mode/differential mode noise.

The object of the invention is to be achieved through the following technical solutions: a kind of conduction common mode/differential mode noise separation method, implementation step is as follows:

Step 1: prepare access test environment, connecting test equipment;

Step 2: measure Switching Power Supply phase line, center line and common mode interference current spectrum, use current probe and frequency spectrograph to measure the interference spectrum within the scope of selected survey frequency, comprise Conduction Interference and common mode Conduction Interference on Conduction Interference in phase line, center line;

Step 3: the frequency spectrum data in calibration steps two, the transmission admittance Y that adopts vector network analyzer method calibration current to pop one's head in _t, substitution following formula, obtains phase line interference current frequency spectrum

center line interference current frequency spectrum with common mode interference frequency spectrum

I=V+Y _t

Step 4, software separate differential mode interference current spectrum, the frequency spectrum data that second step is obtained

with

substitution following formula, calculates differential mode interference current spectrum:

$\left|{\stackrel{\→}{I}}_{\mathrm{DM}}\right|=\frac{1}{2}\sqrt{{\left|{\stackrel{\→}{I}}_L\right|}^2+{\left|{\stackrel{\→}{I}}_N\right|}^2-2{\left|{\stackrel{\→}{I}}_{\mathrm{CM}}\right|}^2}$

Step 5, the interference voltage of surveying are the voltage drop of electric current in 50 Ω loads, and therefore interference voltage can obtain by following formula: U=50 × I.

It is the frequency spectrum by program reading current probe data measured and background noise data and vector network analyzer that described software separates; The unit that electric current is recorded to probe data and background noise data is converted into uV by dBuV; Electric current is recorded to probe data subtracting background noise data, obtain L line, N line and common mode voltage; And read vector network analyzer S parameter S ₂₁measuring frequency band data; Revise transmission admittance Y; Obtain L line, N line and common mode current | I _l|, | I _n| and | I _cM|, calculate and separate differential-mode current output.

Measure and software separable programming by current probe, consider the impact of common-mode noise and differential mode noise phase place, realized that noise on monophase system power lead extracts and the separating of common mode/differential mode noise.

Use current probe to measure phase line interference, center line interference and the layout of both common mode interference noises and different measurement clamp modes.Use the interference of the isolated outer net of linear impedance stabilization network, current probe connects frequency spectrograph and measures the interference spectrum that Devices to test produces.Wherein L and N are respectively power input live wire and center line;

with be respectively phase line input end electric current, center line input end electric current, common mode current and differential-mode current; | I _l|, | I _n| and | I _cM| be respectively phase line noise current frequency spectrum, center line noise current frequency spectrum and both common mode noise current frequency spectrums that frequency spectrograph detects.Phase line, current in middle wire and common mode between the two, differential-mode current relation can be expressed as:

${\stackrel{\→}{I}}_L={\stackrel{\→}{I}}_{\mathrm{CM}}+{\stackrel{\→}{I}}_{\mathrm{DM}}---\left(1\right)$

${\stackrel{\→}{I}}_N={\stackrel{\→}{I}}_{\mathrm{CM}}-{\stackrel{\→}{I}}_{\mathrm{DM}}---\left(2\right)$

Can find out, common mode current exists phase line and center line electric current over the ground, and differential-mode current is present between the two.In the time that current probe pincers are clamped phase line (center line), the data that frequency spectrograph receives are the noise spectrum of phase line (center line); When current probe clamps while clamping phase line and center line simultaneously, the data that frequency spectrograph receives are common-mode noise frequency spectrum between the two.

The data that directly receive by frequency spectrograph are voltage unit, and current probe measurement is interference current on line.Therefore, need to calibrate current probe.

Calibrating principle: I is interference current on line, and V1 and V2 represent that respectively impedance is the voltage drop of linear impedance stabilization network and the frequency spectrograph of 50 Ω, are dB value, by the transmission admittance dBs of Y(unit of current probe and coaxial cable) can be expressed as:

Y=V ₁-V ₂-34 （3）

Vector network analyzer one port is connected to the input end of calibrating installation, and two ports connect the output terminal of current probe, and the output terminal of calibrating installation connects 50 Ω broadband loads.Measure scattering parameter S ₂₁, transmitting so admittance formula (3) can become:

Y=-S ₂₁-34 （4）

The transmission admittance Y correcting current probe test data obtaining with formula (4), obtains phase line, center line and common mode interference current spectrum.

Adopt software separable programming, obtain differential mode interference electric current.Can not directly add formula (2) with formula (1), because formula (1), (2) are vectors, directly be added the impact of having ignored phase place.The phase differential of supposing common mode current and differential-mode current is θ, so formula (1), formula (2) the right and left is carried out square, meets:

|I _L| ²=|I _CM| ²+|I _DM| ²+2I _CM·I _DMcosθ （5）

|I _N| ²=|I _CM| ²+|I _DM| ²-2I _CM·I _DMcosθ （6）

Above-mentioned formula (5) and formula (6) equal sign the right and left are added, and the impact of cancellation phase place, obtains differential mode interference current spectrum amplitude:

$I_{\mathrm{DM}}=\frac{1}{2}\sqrt{{\left|I_L\right|}^2+{\left|I_N\right|}^2-2{\left|I_{\mathrm{CM}}\right|}^2}---\left(7\right)$

By formula (7), can obtain at each frequency the amplitude of differential mode interference electric current.

Interference voltage is the voltage drop of interference current in 50 Ω impedances.Interference current and interference voltage meet following relationship:

U _L=50×I _L （8）

U _N=50×I _N （9）

U _CM=50×I _CM （10）

U _DM=50×I _DM （11）

Above-mentioned U _l, U _n, U _cMand U _dMbe the phase line, center line, differential mode and the common mode disturbance voltage that adopt the present invention to obtain.

The present invention's advantage and effect is compared with prior art:

Technical scheme of the present invention is by different clamp modes, can Quick Measurement line on total Conduction Interference noise and common mode/differential mode noise.According to interference noise relation on common mode/differential mode noise and each line, can fast and effeciently calculate differential mode interference noise by software separable programming, and then obtain the interference noise on each line, and realize the separation of common mode/differential mode noise.

Accompanying drawing explanation:

Fig. 1 is process flow diagram of the present invention

Fig. 2 is the process flow diagram of software separable programming of the present invention

Fig. 3 is that current probe of the present invention is measured layout and interference current distribution plan

Fig. 4 is Calibration of Current Probe schematic diagram of the present invention

Fig. 5 is that the present invention uses vector network analyzer Calibration of Current Probe connection layout

Fig. 6 is the commercial Switching Power Supply phase line of the present invention and the center line interference voltage test result at 150kHz～1MHz frequency band

Fig. 7 is the commercial Switching Power Supply phase line of the present invention and the center line interference voltage test result at 1MHz～30MHz frequency band

Fig. 8 is the commercial Switching Power Supply common mode of the present invention and the differential mode interference voltage test result at 150kHz～1MHz frequency band

Fig. 9 is the commercial Switching Power Supply common mode of the present invention and the differential mode interference voltage test result at 1MHz～30MHz frequency band

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described: measuring process of the present invention is as follows:

One, prepare access measurement environment, connect measuring equipment:

The device that the present embodiment is prepared comprises: 3 one of commercial Switching Power Supplies, current probe 5(Beijing great Ze company produces, model ZN23101) one, Calibration of Current Probe device 6(Beijing great Ze company produces, model ZN23302) one, linear impedance stabilization network 1(Beijing great Ze company produces, model ZN3770A) one, Agilent company of the frequency spectrograph 4(U.S. produces, model N9000A) one, Agilent company of the vector network analyzer 2(U.S. produces, model E5071C) one, standard calibration part (Agilent company of the U.S., model 85032E) a set of, characteristic impedance 50 Ω coaxial cables are some, one, computing machine.

Use the interference of linear impedance stabilization network 1 isolated outer net, current probe 5 connects frequency spectrograph 4 and measures the interference spectrum that Devices to test 3 produces.

Two, measure Switching Power Supply phase line, center line and common mode interference current spectrum: by commercial Switching Power Supply 3, access measurement environment.The measurement frequency band of frequency spectrograph 4 is made as respectively 150kHz～1MHz and 1MHz～30MHz, and test point is 1001.Here arrange two and measure frequency bands, reduce the survey frequency lower limit of frequency spectrograph 4 and the impact of sampling point quantity, choose like this impact of measuring frequency band and can avoid zero point, be beneficial to data observation.

Measure under frequency band at these two, change the clamp mode of current probe 5, obtain different noise spectrums.In the time that current probe 5 pincers are clamped phase line (center line), the data that frequency spectrograph 4 receives are the noise spectrum of phase line (center line); When current probe 5 clamps while clamping phase line and center line simultaneously, the data that frequency spectrograph 4 receives are common-mode noise frequency spectrum between the two.

Three, calibration current probe: the frequency sweep frequency band of vector network analyzer 2 is set to 150kHz～1MHz and two kinds of situations of 1MHz～30MHz equally, and sampling point is chosen and is 1001 points.Under these two frequency bands, calibration current probe 5.First use standard calibration part, a port of calibration vector network analyzer 2 and two ports.Current probe 5 is put into calibrating installation 6, and a port, two ports of vector network analyzer 2 are connected with the input end of calibrating installation 6, the output terminal of current probe 5 respectively, the output termination 50 Ω matched loads 7 of calibrating installation 6.In vector network analyzer 2, obtain S ₂₁family curve.By S ₂₁family curve data substitution formula (4), obtain the transmission admittance of current probe, i.e. substitution Y=-S ₂₁-34.

Correcting current probe measurement data: the transmission admittance Y correcting current probe test data that above-mentioned steps two obtains, obtains phase line center line and common mode interference current spectrum,

with

Four, software is isolated differential mode interference electric current

the interference current substitution formula (7) that above-mentioned steps three obtains, obtains differential mode interference electric current it is substitution $I_{\mathrm{DM}}=\frac{1}{2}\sqrt{{\left|I_L\right|}^2+{\left|I_N\right|}^2-2{\left|I_{\mathrm{CM}}\right|}^2}.$

Five, obtain each line interference voltage and common mode, differential mode disturbance volt: the interference current that above-mentioned steps (3) and step (4) obtain

with

substitution formula (8), (9), (10) and (11), obtain interference voltage frequency spectrum U respectively _l, U _n, U _cMand U _dM.

Through measuring and software separating treatment, obtain phase line interference voltage and center line interference voltage, common mode disturbance voltage and the differential mode disturbance volt frequency spectrum in 150kHz～1MHz and two frequency bands of 1MHz～30MHz of commercial Switching Power Supply.

Claims (2)

1. a conduction common mode/differential mode noise separation method, implementation step is as follows:

Step 1: prepare access test environment, connecting test equipment;

Step 2: measure Devices to test phase line, center line and common mode interference current spectrum, use current probe and frequency spectrograph to measure the interference spectrum within the scope of selected survey frequency, comprise Conduction Interference and common mode Conduction Interference on Conduction Interference in phase line, center line;

Step 3: the frequency spectrum data in calibration steps two, the transmission admittance Y that adopts vector network analyzer method calibration current to pop one's head in _t, substitution following formula, obtains phase line interference current frequency spectrum

center line interference current frequency spectrum

with common mode interference frequency spectrum

I=V+Y _t

Step 4, software separate differential mode interference current spectrum, the frequency spectrum data that second step is obtained

with

substitution following formula, calculates differential mode interference current spectrum:

$\left|{\stackrel{\→}{I}}_{\mathrm{DM}}\right|=\frac{1}{2}\sqrt{{\left|{\stackrel{\→}{I}}_L\right|}^2+{\left|{\stackrel{\→}{I}}_N\right|}^2-2{\left|{\stackrel{\→}{I}}_{\mathrm{CM}}\right|}^2}$

Step 5, the interference voltage of surveying are the voltage drop of electric current in 50 Ω loads, and therefore interference voltage can obtain by following formula: U=50 × I.

2. a kind of conduction common mode/differential mode noise separation method according to claim 1, is characterized in that: it is the frequency spectrum by program reading current probe data measured and background noise data and vector network analyzer that described software separates; The unit that electric current is recorded to probe data and background noise data is converted into uV by dBuV; Electric current is recorded to probe data subtracting background noise data, obtain L line, N line and common mode voltage; And read vector network analyzer S parameter S ₂₁measuring frequency band data; Revise transmission admittance Y; Obtain L line, N line and common mode current | I _l|, | I _n| and | I _cM|.Calculate and separate differential-mode current output.

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