CN101629980A - Method for testing performance of EMI filter based on scattering parameter - Google Patents

Abstract

The invention discloses a method for testing the performance of an EMI filter based on a scattering parameter. The invention carries out scattering parameter modeling on the filter, a load and circuits forming the filter and the load, and the characteristic parameters of the circuits can be obtained through transformation by measuring the scattering parameter. In the actual measurement, the invention only needs to use a network vector analyzer and a component to be measured and does not need to use other hardware, which effectively avoids an extra hardware error. Secondly, for the filter and the load, the invention not only establishes the circuit models of the filter and the load but also establishes the modality models of the filter and the load, and fully considers a condition that a noise signal can generate a modality change in the circuits. Simultaneously, the invention measures the amplitude-frequency characteristic and the phase-frequency characteristic of the filter so as to be convenient for evaluating the effects of filtering the noise signal in the filter from two aspects of the amplitude value and the phase. The invention has simple and easy realization method, reduces the hardware error and puts forward an effective solution for accurately measuring the characteristics of the filter.

Description

Electromagnetic interface filter performance test methods based on scattering parameter

Technical field

What the present invention relates to is to utilize scattering parameter to test and improve for conduction Electromagnetic interference filter performance, for the design of conduction Electromagnetic interference filter of research power electronic equipment is provided fundamental basis, for the inhibition of conduction electromagnetic interference noise is that the performance test of electromagnetic interface filter provides method, this invention belongs to the technical field of electromagnetic compatibility device design and Design of Filter.

Background technology

The effective ways that suppress the EMI noise are that the design electromagnetic interface filter suppresses for noise.At present the loss of insertion method arranged for what the design of electromagnetic interface filter was mainly adopted, promptly insert the attenuation degree of noise behind the electromagnetic interface filter, the general ratio of voltage magnitude that adopts calculates expression insertion loss, and its value is big more, and the ability that the expression wave filter suppresses noise is strong more.But in the electromagnetic interface filter design process, can what must consider be effectively suppress noise signal and can predict because the asymmetry of filter configuration or because the mode conduction resistance in the electric network and the MODAL TRANSFORMATION OF A that causes in wave filter.These performances of wave filter are directly connected to the quality that suppresses effect for noise signal.

Summary of the invention

Scattering parameter is a kind of parameter matrix of describing network internal character by incident wave on the port and reflection wave, is also referred to as wave parameter usually.Adopt scattering parameter to test following advantage for performance of filter:

1 can calculate accurately at the attenuation of real circuits median filter for the common mode noise signal.

2 can predict because filter configuration is asymmetric or the MODAL TRANSFORMATION OF A that causes owing to the mode conduction resistance in the electric network.

3 adopt the scattering parameter designing filter can save loaded down with trivial details wave filter selection course, and the process of its selection can select to reach the process of reduction fast by software.

The present invention utilizes the scattering parameter method to test for filter characteristic, and test circuit is made of linear impedance stabilization network (LISN), vector network analyzer, network analyzer and load (EUT).Overcome the technological deficiency that prior art exists.Characteristics of the present invention are: 1, utilize vector network analyzer to measure the scattering parameter of circuit noise.2, measure wave filter scattering parameter characteristic, and combine for performance of filter with the scattering parameter of circuit noise and to analyze.3, utilize the power circuit of isolating electric network noise via linear impedance stabilization network, it is input in the middle of Switching Power Supply and the load by wave filter, constitute complete electric power loop, carry out the extraction of noise through linear impedance stabilization network (LISN), and set up corresponding circuit model and mode model, thereby improve for the performance of wave filter.

The electromagnetic interface filter performance test methods based on scattering parameter that the present invention proposes, its measuring principle as shown in Figure 1.For the mensuration of performance of filter, can set up its circuit model and mode model by scattering parameter, and combine with the load module of phase factor and to test.

According to the difference of travel path, the conduction electromagnetic interference (EMI) can be divided into differential mode (DM) interference and common mode (CM) is disturbed.Differential mode interference is meant the undesired signal in the loop that phase line of power and center line constituted, and common mode interference is meant by phase line of power or center line and ground wire and is constituted interference in the loop.

According to the character of scattering parameter, can be one or four port networks with the wave filter equivalence, when adopting scattering parameter to test, need four equations to characterize eight relations between the ripple variable, in these four equations, have 16 S parameters, wherein S _NnBe reflection coefficient, S _MnBe transmission coefficient (m ≠ n).

$\left(\begin{array}{c}{b}_1\\ b_2\\ b_3\\ {\mathrm{<figure-callout\; id="4"\; label="b"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">b</figure-callout>}}_4\end{array}\right)=\left(\begin{array}{cccc}{S}_{11}& S_{12}& S_{13}& S_{14}\\ S_{21}& S_{22}& S_{23}& S_{24}\\ S_{31}& S_{32}& S_{33}& S_{34}\\ S_{41}& S_{42}& S_{43}& S_{44}\end{array}\right)\left(\begin{array}{c}{a}_1\\ a_2\\ a_3\\ a_4\end{array}\right)\&DoubleRightArrow;\left[b\right]=\left[S\right]\left[a\right]---\left(1\right)$

The present invention is based on the electromagnetic interface filter performance test methods of scattering parameter, adopt the scattering parameter designing filter, its step is as follows:

1: at first, set up the circuit model and the mode model of wave filter,, adopt the scattering parameter method, measure the scattering parameter of its circuit, thereby set up the circuit model of wave filter, secondly, adopt matrixing to obtain the mode model of wave filter only for wave filter.

2: circuit model and the mode model of setting up load, at first, the noise circuit equivalent of load is become one by three impedances and two two-port network circuit models that voltage source is formed, and (see figure 2) adopts the scattering parameter of this circuit, just can determine circuit impedance Z ₁, Z ₂And Z ₃Two voltage sources are then by the port voltage of Measurement Network and the circuit impedance Z that tries to achieve ₁, Z ₂And Z ₃Common determine, thereby obtain the circuit model of load.Adopt similar method, also can obtain the mode model of load.Be about to the equivalence of load mode and become one by common code impedance Z _CM, the differential mode impedance Z _DM, conduction resistance Z _TMWith two noise voltage source V _NCM, V _NDMThe two-port network (see figure 3) of forming.And utilize corresponding relation between mode model and the circuit model, try to achieve the mode Model parameter.

3: calculate for the model emulation of setting up good wave filter and load according to Fig. 4, its circuit model of emulation at first adopts the circuit model of wave filter and load.Obtain the port voltage V of circuit by emulation _LAnd V _NAnd the scattering parameter of entire circuit.

4: for entire circuit mode model emulation, adopt the mode model of wave filter and load by Fig. 5, obtain the common mode voltage V of circuit _CMWith differential mode voltage V _DM

5: for the definite model of being set up and the validity of artificial circuit, the needs test is with two kinds of electronic installations of modeling and will predict that when this device is connected with wave filter its inner conduction is disturbed.At first adopt manual testing's device, this device comprises three complicated impedances and two internal source voltages (as Fig. 6).Can test the correctness of the method for setting up mode by the circuit of setting up.The voltage source V of manual testing's device _N1' and V _Nn' adopt a radio frequency generating means that contains two equivalent amplifiers and a phase shifter to realize that its frequency range is from 50kHz to 35MHz.After circuit is set up, by calculating and actual measurement divides other parameter that arrives circuit, and both result compared, find that it has good consistance.

6: after the circuit model of manual circuit device and mode model are all known, can be applied to prediction under varying environment, Conduction Interference is through the value after the filter filtering.Build circuit and see Fig. 7.The port voltage V of circuit _LWith V _NObtain two groups of respective value respectively by calculating and measuring, vector network analyzer can be measured the amplitude and the frequency of noise signal.Through calculating simulation and test simulation as can be seen, it is consistent with the actual measurement gained that circuit calculates modeling.

7: measured circuit noise is compared with current standard.Will decay by the noise behind the wave filter, and can reach the requirement of formulating electromagnetic compatibility standard in the world with the noise of guaranteeing the entire circuit system.

8: in order to detect the adaptability of modeling method for real circuits, the signal that adopts high frequency signal generator to transmit 4MHz is given circuit.At first obtain the circuit model and the mode model of noise source by test; Next tests the scattering parameter of contemplated wave filter, and sets up its mode model; Test out the port voltage V of circuit model and mode model then _L, V _N, V _CM, V _DMAt last the port voltage that records is compared with the port voltage that calculates, see whether consistently, and compare, see to meet the successful property of international standard with the checking Design of Filter with current international standard.

The method of testing that the present invention adopts can be tested at the designed performance of filter of all kinds of power electronic equipment noises.Adopt scattering parameter test filter performance, simple to operate and test accurately.By this method of testing, can test performance of filter, further the design for electromagnetic interface filter provides theoretical foundation.

Description of drawings

Fig. 1 is based on the electromagnetic interface filter performance test methods test philosophy figure of scattering parameter

The circuit model of Fig. 2 load, wherein Z ₁, Z ₂And Z ₃Be circuit middle impedance, V _N1, V _NnBe the medium and small signal source of circuit.

The mode model of Fig. 3 load

Fig. 4 has the circuit simulation of the load system of wave filter

Fig. 5 has the load system mode emulation of wave filter

Fig. 6 manual testing device, wherein Z ' ₁By 18 Ω resistance, 1.5nF electric capacity and 50 Ω genertor impedance Z ' _GlForm; Z ' ₂By 18 Ω resistance, 470nH inductance and 50 Ω genertor impedance Z ' _GnForm; Z ' ₃Form by 18 Ω resistance and 6.8nF electric capacity

Fig. 7 has the circuit test of wave filter

Fig. 8 filter circuit model, wherein, Z ₀Be 50 Ω

The mode model of Fig. 9 wave filter, wherein, Z _OCM=25 Ω, Z _ODM=100 Ω

Figure 10 load module scattering parameter acquisition methods

Embodiment

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

Embodiment

Here be the concrete implementation step that example illustrates this method of testing with Fig. 4,5 the circuit that contains wave filter, Fig. 4 is the circuit simulation of system, and Fig. 5 is the mode emulation of system.The conduction electromagnetic interference measurement, EMI measurement equipment of regulation has linear impedance stabilization network LISN (Line Impedance StabilizationNetwork is called for short LISN) and vector network analyzer in the world at present.

The linear impedance network is called artificial mains network or source impedance stabilizing network again, is important electromagnetic compatibility test equipment.This network can effectively shield from the high frequency interference of external electrical network or stop the high frequency interference of load generation to import external electrical network into by supply socket, the power current (as domestic 50Hz electric current) that is provided under the load operate as normal is not provided again simultaneously, and the impedance of 50 stable Ω is provided to equipment under test (being the load circuit among Fig. 4) in radio-frequency region, then interference voltage is transferred on the vector network analyzer.

Vector network analyzer is a kind of instrument that can the measuring system scattering parameter, and this instrument not only can show measured amplitude, can also show the phase place of measuring gained, more comprehensively the performance of analysis circuit noise filter.

Concrete method of testing directly is linked into line impedence stabilizing network L, N with AC power, through being input in wave filter and the load behind the existing impedance stable network (LISN), constitutes a whole piece electric power loop; Carry out the extraction of noise through existing impedance stable network (LISN), the input vector network analyzer is analyzed for noise, and analysis result is compared with the desired result that is calculated, and whether observe both consistent.

At first set up the filter circuit model, a wave filter can be designed to one four port network, and as shown in Figure 8, wherein, the input of L-G port, output voltage and electric current adopt V respectively _IL, V _OL, I _IL, I _OLRepresent that in like manner, the input of N-G port, output voltage and electric current adopt V respectively _IN, V _ON, I _IN, I _ONRepresent that then the S parameter model of this circuit is:

$\left[\begin{array}{c}{b}_{\mathrm{IL}}\\ b_{\mathrm{IN}}\\ b_{\mathrm{OL}}\\ b_{\mathrm{OL}}\end{array}\right]=\left[S\right]\&CenterDot;\left[\begin{array}{c}{a}_{\mathrm{IL}}\\ a_{\mathrm{IN}}\\ a_{\mathrm{OL}}\\ a_{\mathrm{OL}}\end{array}\right]---\left(2\right)$

Secondly, set up the mode of wave filter, as shown in Figure 9, V wherein _ICM, V _IDM, I _ICM, I _IDMBe the input voltage and the electric current of common mode and differential mode, V _OCM, V _ODM, I _OCM, I _ODMOutput voltage and electric current for common mode and differential mode.

The scattering parameter model of this mode network is:

$\left[\begin{array}{c}{b}_{\mathrm{ICM}}\\ b_{\mathrm{IDM}}\\ b_{\mathrm{OCM}}\\ b_{\mathrm{ODM}}\end{array}\right]=\left[S_M\right]\&CenterDot;\left[\begin{array}{c}{a}_{\mathrm{ICM}}\\ a_{\mathrm{IDM}}\\ a_{\mathrm{OCM}}\\ a_{\mathrm{ODM}}\end{array}\right]---\left(3\right)$

(2) (3) two formulas can be changed by matrix equation (4):

[S _M]＝[B]·[S]·[A] ^-1 (4)

Wherein, matrix [A], [B] are:

$\left[A\right]=\left[B\right]=\frac{1}{\sqrt{2}}\left[\begin{array}{cccc}1& 1& 0& 0\\ 1& -1& 0& 0\\ 0& 0& 1& 1\\ 0& 0& 1& -1\end{array}\right]$

The 3rd, after filter circuit and mode model are all set up, set up its circuit and mode model for load.Its circuit model equivalence is the circuit of three resistance and two voltage sources, adopts the scattering parameter of the method for testing acquisition load circuit of Figure 10, tries to achieve circuit model middle impedance Z by scattering parameter ₁, Z ₂And Z ₃Value and circuit in the value of voltage source suc as formula (5) (6):

$Z_1=\frac{Z_0(1+S_{11})(1+S_{22})-Z_0{S}_{12}{S}_{21}}{(1-S_{11})(1+S_{22})+S_{12}{S}_{21}-2S_{21}}---(5-1)$

$Z_2=\frac{Z_0(1+S_{11})(1+S_{22})-Z_0{S}_{12}{S}_{21}}{(1+S_{11})(1-S_{22})+S_{12}{S}_{21}-2S_{21}}---(5-2)$

$Z_3=\frac{Z_0(1+S_{11})(1+S_{22})-Z_0{S}_{12}{\mathrm{<figure-callout\; id="21"\; label="S"\; filenames="A2009100348690015H2.png"\; state="\{\{state\}\}">S</figure-callout>}}_{21}}{2S_{21}}---(5-3)$

$V_{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">n</figure-callout>}1}=V_L-\frac{Z_1({\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_3)I_L+Z_1{Z}_2{I}_{\mathrm{<figure-callout\; id="1"\; label="N\; Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">N</figure-callout>}}}{Z_{}}---(6-1)$

$V_{\mathrm{nn}}=V_N-\frac{Z_2({\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1+Z_3)I_N+Z_1{Z}_2{I}_{\mathrm{<figure-callout\; id="1"\; label="L\; Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">L</figure-callout>}}}{Z_{}}---(6-2)$

Wherein, Z ₀Be the reflected impedance of test macro, get 50 Ω usually.V _L, V _N, I _L, I _NBe respectively hot voltage, zero line voltage, live wire electric current, the neutral line current of port.

The 4th, set up the mode model of load circuit, as Fig. 3, the parameter in this circuit can be tried to achieve suc as formula (7) (8) by existing circuit model parameter:

$Z_{\mathrm{CM}}=\frac{2Z_1{Z}_2}{{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1+3Z_2}---(7-1)$

$Z_{\mathrm{DM}}=\frac{4Z_1{Z}_2{\mathrm{<figure-callout\; id="3"\; label="Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_3}{4Z_1{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+3Z_2{Z}_3-Z_1{Z}_3}---(7-2)$

$Z_{\mathrm{TM}}=\frac{2Z_1{Z}_2}{Z_1-Z_2}---(7-3)$

$V_{\mathrm{nCM}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="V\; n"\; filenames="A2009100348690014H3.png,A2009100348690015H1.png"\; state="\{\{state\}\}">V</figure-callout>}}_n+V_{\mathrm{nn}}}{2}---(8-1)$

V _nDM＝V _n1-V _nn (8-2)

The 5th, for the circuit simulation of wave filter and load,, simulate (see figure 4) for the power line network that has connected, wave filter and loaded impedance according to 1, the 2 liang of wave filter set up of step and the circuit model of load.According to artificial circuit, can set up the circuit model of whole powerline network, thereby simulate for the electromagnetic interference noise in the circuit network, obtain the live wire-ground wire voltage V of circuit _LAnd zero line-ground wire voltage V _N

The 6th, for the mode emulation of wave filter and load, copy step 3, carry out mode emulation (as Fig. 5) for the circuit that connects, the circuit mode model that combines the mode model of wave filter and load can obtain the common mode voltage V of circuit through emulation _CMWith differential mode voltage V _DM, and then carry out qualitative and quantitative Diagnosis for undesired signal, from diagnostic result as can be seen because common-mode signal is when being converted into difference mode signal, for the size of filter effects.

The 7th, adopt an artificial proving installation (Fig. 6) and high frequency signal generator to detect for the validity of model.Wherein, manual testing's device by impedance Z ' ₁(comprise one 18 Ω resistance, a 1.5nF electric capacity and one 50 Ω genertor impedance Z ' _Gl), Z ' ₂(comprise one 18 Ω resistance, a 470nH inductance and one 50 Ω genertor impedance Z ' _Gn) and Z ' ₃(comprising one 18 Ω resistance, a 6.8nF electric capacity) formed; High frequency signal generator gives the signal of a 4MHz of circuit.With test result with compare by calculating the gained desired result, both results coincide better as can be seen.

By above-mentioned experiment as seen, circuit model and mode model are the principal elements that the present embodiment performance of filter is measured, and the major influence factors of choosing the common-mode noise that is the present embodiment circuit of circuit parameter value in the model.Therefore, in this circuit, can improve wave filter erasure signal anti noise by the parameter of revising in the circuit.For other similar wave filters, can study the quality of its performance with the method for this invention, thereby provide foundation for conducting noise and the Filter Design that reduces circuit.

Claims (1)

1, a kind of electromagnetic interface filter performance test methods based on scattering parameter adopts the scattering parameter designing filter, and its step is as follows:

A, the circuit model of setting up wave filter and mode model

Only, adopt the scattering parameter method, measure the scattering parameter of its circuit, thereby set up the circuit model of wave filter, secondly, adopt matrixing to obtain the mode model of wave filter for wave filter;

B, the circuit model of setting up load and mode model

At first, the noise circuit equivalent of load is become one by three impedances and two two-port network circuit models that voltage source is formed, adopt the scattering parameter of this circuit to determine circuit impedance (Z ₁, Z ₂, Z ₃); Two voltage sources are then by the port voltage of Measurement Network and the circuit impedance (Z that tries to achieve ₁, Z ₂, Z ₃) common determine, thereby obtain the circuit model of load; The equivalence of load mode is become one by common code impedance Z _CM, the differential mode impedance Z _DM, conduction resistance Z _TMWith two noise voltage source (V _NCM, V _NDM) two-port network formed, utilize the corresponding relation between mode model and the circuit model, try to achieve the mode Model parameter;

C, calculate for the model emulation of setting up good wave filter and load, its circuit model of emulation at first adopts the circuit model of wave filter and load; Obtain the port voltage (V of circuit by emulation _L, V _N) and the scattering parameter of entire circuit;

D, for entire circuit mode model emulation, adopt the mode model of wave filter and load, obtain the common mode voltage V of circuit _CMWith differential mode voltage V _DM

E, two kinds of electronic installations of test and modeling and prediction are when this device is connected with wave filter, and its inner conduction is disturbed

At first adopt manual testing's device, this device comprises three complicated impedances and two internal source voltages; Set up the correctness of the method for mode, the voltage source V of manual testing's device by the circuit test of setting up ' _N1And V ' _NnAdopt a radio frequency generating means that contains two equivalent amplifiers and a phase shifter to realize that its frequency range is from 50kHz to 35MHz; After circuit is set up, by calculating and actual measurement divides other parameter that arrives circuit, and both result compared;

F, after the circuit model of manual circuit device and mode model are all known, be applied to predict that Conduction Interference is through the value after the filter filtering under varying environment; Build circuit, the port voltage V of circuit _LWith V _NObtain two groups of respective value respectively by calculating and measuring, vector network analyzer is measured the amplitude and the frequency of noise signal;

G, measured circuit noise is compared with current standard, will decay, can reach the requirement of electromagnetic compatibility standard with the noise of guaranteeing the entire circuit system by the noise behind the wave filter;

H, the signal that adopts high frequency signal generator to transmit 4MHz are given circuit, detect the adaptability of modeling method for real circuits; At first obtain the circuit model and the mode model of noise source by test; Next tests the scattering parameter of contemplated wave filter, and sets up its mode model; Test out the port voltage (V of circuit model and mode model then _L, V _N, V _CM, V _DM); At last the port voltage that records is compared with the port voltage that calculates, whether check is consistent, and compares with current international standard, and can check meet the successful property of international standard with the checking Design of Filter.

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