CN115078837A - Noise source impedance extraction method based on insertion of passive two-port network - Google Patents
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Abstract
The invention relates to a noise source impedance extraction method based on a plug-in passive two-port network, in particular to a noise source impedance extraction method of a power electronic power converter, which is characterized in that 3 random different passive two-port networks are inserted between tested equipment and an LISN (Power electronic Power converter), a relation formula of a real part and an imaginary part of the noise source impedance and a binary quadratic equation set capable of being measured is established, automatic solution is realized through programming, effective frequency points in a range of a conducted EMI test frequency band (9 kHz-30 MHz) are screened out, and the impedance amplitude and the phase of the noise source can be accurately calculated. The invention provides an accurate theoretical basis for predicting the noise current of the LISN end inserted into the EMI filter and designing the high-performance EMI filter; the invention has the advantages that: low cost, simple operation, strong practicability and universal applicability.
Description
Technical Field
The invention relates to the technical field of circuits, in particular to a noise source impedance extraction method based on a plug-in passive two-port network.
Background
The power electronic power converter has the advantages of high efficiency, small volume and the like, and is widely applied to many fields. With the application of wide bandgap SiC and GaN switching devices with higher switching frequency and switching speed, the power density of the converter is further improved, and the EMI problem is to be solved more urgently. In order to achieve the desired noise suppression effect, it is necessary to design an EMI filter with superior performance. The performance of an EMI filter is characterized by insertion loss, where the impact of the noise source impedance on the insertion loss is non-negligible.
The amplitude and phase of the noise source impedance are functions of frequency, and are affected by circuit topology, parasitic parameters of components, routing layout of a PCB, power, placement of discrete components and the like. At present, noise source impedance extraction methods mainly include a resonance method, a double current probe method, a single current probe method, a scattering parameter method, and an insertion loss method.
The "resonance method" resonates with the noise source impedance of the converter by adding a resonant inductor or capacitor, and then derives the noise source impedance magnitude from the resonant frequency and quality factors. However, the method is narrow in applicable frequency band and poor in practicability. The double-current probe method injects interference into a circuit through a coupling capacitor by using one injection current probe, then measures the injected interference current by using the other measurement current probe, and calculates the impedance amplitude of a noise source by measuring the current change before and after the interference is injected by using a frequency spectrograph. The single current probe method only uses one measuring current probe as a detection signal, and injects an interference signal into a circuit by using a signal source or a spectrum analyzer. The scattering parameter method is similar to the double-current probe method, signal generating and receiving equipment of the method are vector network analyzers, and transmission parameters and reflection parameters of signal injection and signal detection ports in each test state can be measured and obtained by using the vector network analyzers. The amplitude and the phase of the impedance of the noise source can be obtained simultaneously through theoretical calculation. However, the requirements of the double-current probe method, the single-current probe method and the scattering parameter method on test equipment are high, the measurement process is complex, and the measurement accuracy is reduced due to the non-ideal transmission characteristic of the current probe. The voltage insertion loss method calculates the amplitude range of the impedance of a noise source by serially connecting a common mode inductor and a parallel differential mode capacitor between a tested device and a linear impedance stabilizing network and measuring noise attenuation values before and after inserting the impedance.
Disclosure of Invention
The noise source impedance extraction method based on the plug-in passive two-port network is high in practicability, simple to operate and low in requirement on test equipment, and can accurately extract the impedance amplitude and the phase of a noise source.
The invention adopts the following technical scheme.
A noise source impedance extraction method based on a plug-in passive two-port network is used for extracting the noise source impedance of a power converter and comprises the following steps;
step S1, the EMI noise source of the device under test EUT is represented by a Davinin equivalent circuit, namely, as the impedance Z of the noise source s Sum noise voltage source V s In a serial form;
step S2, using the ideal resistor R for the linear impedance stabilization network LISN LISN Expressing that the ideal resistors with different resistance values are respectively used for representing the equivalent load impedance R of the LISN end when measuring the common mode noise source impedance and the differential mode noise source impedance LISN ；
Step S3, inserting three arbitrary different passive two-port networks N between EUT and LISN i Taking i as 1, 2 and 3; n is a radical of i The accurate impedance characteristic curve of the passive device is measured by an impedance analyzer; z i Indicating insertion into a passive two-port network N i Input impedance when viewed from the EUT side; i is i Indicating insertion into a passive two-port network N i Port noise current from the EUT side;
step S4, setting the impedance Z of the noise source s Respectively real part and imaginary part of s_Re And Z s_Im The real part and imaginary part of the input impedance Zi are Z i_Re And Z i_Im (ii) a When inserted into a passive two-port network N i Time, noise current I i Is expressed in modulus as
Step S5, by inserting 3 different passive two-port networks N i Then, the real part Z of the impedance of the noise source is established through a formula I s_Re And an imaginary part Z s_Im And a system of two-dimensional quadratic equations between which can be measured is
Wherein the noise current I i The real part of the input impedance Z i_Re And an imaginary part Z i_Im Are all values obtained by measurement, the real part of the impedance Z of the noise source s_Re And an imaginary part Z s_Im Is an unknown quantity;
step S6, solving a binary quadratic equation set corresponding to each test frequency point in the range of the conducted EMI test frequency band through software programming circulation to obtain the impedance Z of the noise source s Real part Z of s_Re And imaginary part Z s_Im ；
And S7, screening effective frequency points in the range of the conducted EMI test frequency band, and calculating the impedance amplitude and the phase of the noise source.
In step S2, when measuring the common mode noise source impedance, R LISN ＝R loadCM 25 Ω, when measuring the differential mode noise source impedance, R LISN ＝R loadDM ＝100Ω。
Step S6, when solving the noise source impedance, judging whether the binary quadratic equation set expressed by the formula II has solution or not according to the following method to screen the effective frequency point set f m ，
Impedance Z of noise source s Real part Z of s_Re And an imaginary part Z s_Im The system of binary quadratic equations is expressed as the real part Z of the impedance of the noise source as independent variable and dependent variable respectively s_Re Function Z of s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) Is expressed as
In which the transition variables are each
a＝(I 1 2 Z 1_Im -I 2 2 Z 2_Im )/(I 1 2 -I 2 2 )
b＝[I 1 2 (Z s_Re +Z 1_Re ) 2 -I 2 2 (Z s_Re +Z 2_Re ) 2 ]/(I 1 2 -I 2 2 )
c＝(I 2 2 Z 2_Im -I 3 2 Z 3_Im )/(I 2 2 -I 3 2 )
d＝[I 2 2 (Z s_Re +Z 2_Re ) 2 -I 3 2 (Z s_Re +Z 3_Re ) 2 ]/(I 2 2 -I 3 2 )
Wherein the function Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) When the two circular tracks have an intersection point, the noise source impedance corresponding to the frequency point has a solution; note Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) The radius of the corresponding circle is R 1 And R 2 The distance between the centers of the two circles is D, and the expression is as follows:
in which the transition variables are each
f＝(Z 1_Re I 1 2 -Z 2_Re I 2 2 )/(I 2 2 -I 1 2 )
g＝(Z 1_Im I 1 2 -Z 2_Im I 2 2 )/(I 2 2 -I 1 2 )
h＝(Z 2_Re 2 I 2 2 -Z 1_Re 2 I 1 2 )/(I 2 2 -I 1 2 )
k＝(Z 2_Im 2 I 2 2 -Z 1_Im 2 I 1 2 )/(I 2 2 -I 1 2 )
l＝(Z 2_Re I 1 2 -Z 3_Re I 3 2 )/(I 3 2 -I 2 2 )
m＝(Z 2_Im I 1 2 -Z 3_Im I 3 2 )/(I 3 2 -I 2 2 )
n＝(Z 3_Re 2 I 3 2 -Z 2_Re 2 I 2 2 )/(I 3 2 -I 2 2 )
p＝(Z 3_Im 2 I 3 2 -Z 2_Im 2 I 2 2 )/(I 3 2 -I 2 2 )
Based on the geometric theory, when two circular tracks have intersection points, the binary quadratic equation set expressed by the formula II has solutions, and the sufficient condition is expressed by the formula
R 1 +R 2 ≥D∧|R 1 -R 2 The formula is less than or equal to seven;
obtaining effective frequency points in the range of the conducted EMI test frequency band and the corresponding real part Z of the impedance of the noise source through programming according to a formula II, a formula IV, a formula V, a formula VI and a formula VII s_Re And an imaginary part Z s_Im Further obtain the amplitude | Z of the noise source impedance s I andphase theta (Z) s ) (ii) a Is given by the formula
The inserted passive two-port network is any passive two-port network;
after the noise current of the LISN end is obtained through measurement, the noise current I is deduced according to the series-parallel connection relation of the impedance i Then, the amplitude | Z of the impedance of the common mode noise source in the conduction frequency band range is obtained by solving according to a formula II, a formula IV, a formula V, a formula VI and a formula VII sCM I and phase θ (Z) sCM ) The amplitude value | Z of the differential mode noise source impedance can be obtained in the same way sDM I and phase θ (Z) sDM )。
In step S7, the range of the EMI test frequency band is 9kHz to 30 MHz.
The invention provides an accurate theoretical basis for predicting the noise current of the LISN end inserted into the EMI filter and designing the high-performance EMI filter, and has the advantages that: low cost, simple operation, strong practicability and universal applicability.
Compared with the prior art, the invention has the following advantages:
(1) the cost is low: compared with a current probe method and a scattering parameter method, the invention has low requirements on used equipment, and only needs one EMI receiver, one linear impedance stabilizing network and one current clamp;
(2) the principle is simple, the practicality is strong: the amplitude and phase information of the noise source impedance can be obtained only by inserting 3 random different passive two-port networks and solving the corresponding equation set.
(3) The manual calculation amount is small: and software programming is adopted for systematic solution, so that the manual workload and the accuracy of noise source impedance calculation are reduced.
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The invention is described in further detail below with reference to the following figures and detailed description:
FIG. 1 is a schematic diagram of a noise source impedance extraction method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an equivalent circuit for a noise source impedance extraction method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a noise source impedance solution trace according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a passive two-port network selected in a common-mode noise source impedance extraction experiment according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a passive two-port network selected in a differential mode noise source impedance extraction experiment according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of the calculation result of the common mode noise source impedance amplitude according to the embodiment of the present invention;
FIG. 7 is a schematic diagram illustrating the phase calculation result of the impedance of the common mode noise source according to the embodiment of the present invention;
FIG. 8 is a diagram illustrating a calculation result of the impedance amplitude of the differential mode noise source according to an embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating a phase calculation result of a differential mode noise source impedance according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of the impedance characteristic of the common mode inductor according to the embodiment of the present invention;
FIG. 11 is a schematic diagram of a differential mode capacitance-impedance characteristic of an embodiment of the present invention;
FIG. 12 is a schematic diagram of a common mode noise source impedance verification experiment according to an embodiment of the present invention;
fig. 13 is a schematic diagram of a differential mode noise source impedance verification experiment according to an embodiment of the present invention.
Detailed Description
As shown in the figure, the noise source impedance extraction method based on the insertion of the passive two-port network is used for extracting the noise source impedance of the power converter and comprises the following steps;
step S1, the EMI noise source of the device under test EUT is represented by a Davinin equivalent circuit, namely, as the impedance Z of the noise source s Sum noise voltage source V s In a serial form;
step S2, using the ideal resistor R for the linear impedance stabilization network LISN LISN The method is characterized in that when the impedance of a common-mode noise source is measured and the impedance of a differential-mode noise source is measured, ideal resistors with different resistance values are respectively used for representing equivalent load impedance R of the LISN terminal LISN ；
Step S3, inserting three arbitrary different passive two-port networks N between EUT and LISN i Taking i as 1, 2 and 3; n is a radical of i The accurate impedance characteristic curve of the passive device is measured by an impedance analyzer; z is a linear or branched member i Indicating insertion into a passive two-port network N i Input impedance seen from the EUT side; i is i Indicating insertion into a passive two-port network N i Port noise current from the EUT side;
step S4, setting the impedance Z of the noise source s Respectively real part and imaginary part of s_Re And Z s_Im The real part and imaginary part of the input impedance Zi are Z i_Re And Z i_Im (ii) a When inserted into a passive two-port network N i Time, noise current I i Is expressed in modulus as
Step S5, by inserting 3 different passive two-port networks N i Then, the real part Z of the impedance of the noise source is established through a formula I s_Re And an imaginary part Z s_Im And can be measured as a system of two-dimensional quadratic equations
Wherein the noise current I i The real part of the input impedance Z i_Re And an imaginary part Z i_Im Are all values obtained by measurement, the real part of the impedance Z of the noise source s_Re And an imaginary part Z s_Im Is an unknown quantity;
step S6, solving a binary quadratic equation set corresponding to each test frequency point in the range of the conducted EMI test frequency band through software programming circulation to obtain the noise source resistanceanti-Z s Real part Z of s_Re And an imaginary part Z s_Im ；
And S7, screening effective frequency points in the range of the conducted EMI test frequency band, and calculating the impedance amplitude and the phase of the noise source.
In step S2, when measuring the common mode noise source impedance, R LISN ＝R loadCM 25 Ω, when measuring the differential mode noise source impedance, R LISN ＝R loadDM ＝100Ω。
Step S6, when solving the noise source impedance, judging whether the binary quadratic equation set expressed by the formula II has solution or not according to the following method to screen the effective frequency point set f m ，
Impedance Z of noise source s Real part Z of s_Re And an imaginary part Z s_Im The system of binary quadratic equations is expressed as the real part Z of the impedance of the noise source as independent variable and dependent variable respectively s_Re Function Z of s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) Is expressed as
In which the transition variables are each
a＝(I 1 2 Z 1_Im -I 2 2 Z 2_Im )/(I 1 2 -I 2 2 )
b＝[I 1 2 (Z s_Re +Z 1_Re ) 2 -I 2 2 (Z s_Re +Z 2_Re ) 2 ]/(I 1 2 -I 2 2 )
c＝(I 2 2 Z 2_Im -I 3 2 Z 3_Im )/(I 2 2 -I 3 2 )
d＝[I 2 2 (Z s_Re +Z 2_Re ) 2 -I 3 2 (Z s_Re +Z 3_Re ) 2 ]/(I 2 2 -I 3 2 )
Wherein the function Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) When the two circular tracks have an intersection point, the noise source impedance corresponding to the frequency point has a solution; note Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) The radius of the corresponding circle is R 1 And R 2 The distance between the centers of the two circles is D, and the expression is as follows:
in which the transition variables are each
f＝(Z 1_Re I 1 2 -Z 2_Re I 2 2 )/(I 2 2 -I 1 2 )
g＝(Z 1_Im I 1 2 -Z 2_Im I 2 2 )/(I 2 2 -I 1 2 )
h＝(Z 2_Re 2 I 2 2 -Z 1_Re 2 I 1 2 )/(I 2 2 -I 1 2 )
k＝(Z 2_Im 2 I 2 2 -Z 1_Im 2 I 1 2 )/(I 2 2 -I 1 2 )
l＝(Z 2_Re I 1 2 -Z 3_Re I 3 2 )/(I 3 2 -I 2 2 )
m＝(Z 2_Im I 1 2 -Z 3_Im I 3 2 )/(I 3 2 -I 2 2 )
n＝(Z 3_Re 2 I 3 2 -Z 2_Re 2 I 2 2 )/(I 3 2 -I 2 2 )
p＝(Z 3_Im 2 I 3 2 -Z 2_Im 2 I 2 2 )/(I 3 2 -I 2 2 )
Based on the geometric theory, when two circular tracks have intersection points, the binary quadratic equation set expressed by the formula II has solutions, and the sufficient condition is expressed by the formula
R 1 +R 2 ≥D∧|R 1 -R 2 The formula is less than or equal to seven;
obtaining effective frequency points in the range of the conducted EMI test frequency band and the corresponding real part Z of the impedance of the noise source through programming according to a formula II, a formula IV, a formula V, a formula VI and a formula VII s_Re And an imaginary part Z s_Im Further obtain the amplitude | Z of the noise source impedance s I and phase θ (Z) s ) (ii) a Is given by the formula
The inserted passive two-port network is any passive two-port network;
after the noise current of the LISN end is obtained through measurement, the noise current I is deduced according to the series-parallel connection relation of the impedance i Then solving according to a formula II, a formula IV, a formula V, a formula VI and a formula VII to obtain the amplitude value | Z of the impedance of the common mode noise source in the conduction frequency band range sCM I and phase θ (Z) sCM ) The amplitude value | Z of the differential mode noise source impedance can be obtained in the same way sDM I and phase θ (Z) sDM )。
In step S7, the range of the EMI test frequency band is 9kHz to 30 MHz.
Example (b):
FIG. 1 is a schematic diagram of the extraction of the impedance of a noise source based on the insertion of a passive two-port network, where Z is s Representing the impedance of the noise source, V s Is a noise voltage source; n is a radical of i The inserted ith passive two-port network is represented, i is 1, 2 and 3, and the accurate impedance characteristic curve of the passive device can be measured by an impedance analyzer; i is i Indicating insertion into a passive two-port network N i The current of time; r LISN Is the equivalent impedance of LISN, the equivalent impedance value depends on the type of noise source impedance experiment. When testing common mode noise, R LISN ＝R loadCM 25 Ω; when testing differential mode noise, R LISN ＝R loadDM ＝100Ω；Z i Indicating insertion into a passive two-port network N i The input impedance of the ports 1-1' can be obtained by the series-parallel connection equivalent of the internal impedance of the ports. V 1 And V 2 Representing the port voltages at ports 1-1 'and ports 2-2', respectively.
When the port 1-1' is inputted with impedance Z in the left part of the circuit in FIG. 1 i After the equivalent substitution, the noise source impedance test circuit can be equivalent to fig. 2.
In order to obtain the noise source impedance Z s Amplitude of (c) | Z s I and phase θ (Z) s ) Z is a symbol s Respectively real part and imaginary part of s_Re And Z s_Im Then the input impedance Z of the port 1-1 i Respectively real part and imaginary part of i_Re And Z i_Im . When inserted into a passive two-port network N i Time, noise current I i Can be expressed in a modulus of
In order to establish the real part Z of the impedance of the noise source s_Re And an imaginary part Z s_Im And can be measured by inserting 3 different passive two-port networks N i Then, with respect to noise, the following equation (1) can be establishedReal part of the impedance of the sound source Z s_Re And an imaginary part Z s_Im The system of binary quadratic equations of (1):
in the formula of noise current I i The real part of the input impedance Z i_Re And imaginary part Z i_Im All can be obtained by experimental measurement, and only has the real part Z of the impedance of the noise source s_Re And an imaginary part Z s_Im Is an unknown quantity. Within the range of conducted EMI test frequency band, an EMI receiver is adopted to measure and obtain noise current data of each frequency point, and a program is compiled through a mathematical software platform to automatically and circularly solve a binary quadratic equation set corresponding to each frequency point, so that the noise source impedance Z is easily obtained s Real part Z of s_Re And an imaginary part Z s_Im 。
However, in the process of solving the noise source impedance, the solution of the noise source impedance data at a plurality of frequency points cannot be converged due to the influence of uncertain factors such as measurement errors, test environments, high-frequency line parasitic parameters and the like. Therefore, it is necessary to determine whether the binary quadratic equation (5) has a solution to screen the effective frequency point set f m . If the noise source impedance Z s Real part Z of s_Re And an imaginary part Z s_Im When the independent variable and the dependent variable are respectively taken, the equation (5) of the binary quadratic equation set can be expressed as Z relative to the real part of the impedance of the noise source s_Re Function Z of s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re )。
In which the transition variables are respectively
a＝(I 1 2 Z 1_Im -I 2 2 Z 2_Im )/(I 1 2 -I 2 2 )
b＝[I 1 2 (Z s_Re +Z 1_Re ) 2 -I 2 2 (Z s_Re +Z 2_Re ) 2 ]/(I 1 2 -I 2 2 )
c＝(I 2 2 Z 2_Im -I 3 2 Z 3_Im )/(I 2 2 -I 3 2 )
d＝[I 2 2 (Z s_Re +Z 2_Re ) 2 -I 3 2 (Z s_Re +Z 3_Re ) 2 ]/(I 2 2 -I 3 2 )
As shown in fig. 3, function Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) When the two circular tracks have an intersection point, the noise source impedance corresponding to the frequency point has a solution. Note Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) The radius of the corresponding circle is R 1 And R 2 The distance between the centers of the two circles is D.
R 1 And R 2 The expression that the distance between the centers of two circles is D is as follows:
in which the transition variables are each
f＝(Z 1_Re I 1 2 -Z 2_Re I 2 2 )/(I 2 2 -I 1 2 )
g＝(Z 1_Im I 1 2 -Z 2_Im I 2 2 )/(I 2 2 -I 1 2 )
h＝(Z 2_Re 2 I 2 2 -Z 1_Re 2 I 1 2 )/(I 2 2 -I 1 2 )
k＝(Z 2_Im 2 I 2 2 -Z 1_Im 2 I 1 2 )/(I 2 2 -I 1 2 )
l＝(Z 2_Re I 1 2 -Z 3_Re I 3 2 )/(I 3 2 -I 2 2 )
m＝(Z 2_Im I 1 2 -Z 3_Im I 3 2 )/(I 3 2 -I 2 2 )
n＝(Z 3_Re 2 I 3 2 -Z 2_Re 2 I 2 2 )/(I 3 2 -I 2 2 )
p＝(Z 3_Im 2 I 3 2 -Z 2_Im 2 I 2 2 )/(I 3 2 -I 2 2 )
According to the geometric theory knowledge, the sufficient condition that two circular tracks have intersection points or a binary quadratic equation set formula (5) has solution is
R 1 +R 2 ≥D∧|R 1 -R 2 |≤D (7)
By combining the formulas (2), (4) and (7), the effective frequency point in the range of the conducted EMI test frequency band and the corresponding real part Z of the impedance of the noise source can be easily and automatically obtained by programming s_Re And an imaginary part Z s_Im Further, the amplitude | Z of the noise source impedance can be obtained s I and phase θ (Z) s )。
When the provided noise source impedance extraction method is used for calculating the common mode noise source impedance and the differential mode noise source impedance, 3 different passive two-port networks are required to be selected. In the experiment, 3 passive two-port networks as shown in fig. 4 were constructed using 3 common mode inductors with different inductance values, and the impedances thereof were respectively Z in table 1 cm1 、Z cm2 And Z cm3 (wherein Z cm3 Representing a short circuit inductance impedance, i.e., the inductance is zero); 3 passive two-port networks as shown in fig. 5 are constructed by adopting 3 differential mode capacitors with different capacitance values, and the impedances of the two passive two-port networks are respectively Z in table 1 dm1 、Z dm2 And Z dm3 (wherein Z dm3 Representing an open capacitance impedance, i.e., zero capacitance).
The two-port network of FIG. 4 is selected for the common-mode noise source impedance extraction experiment, and the corresponding ports 1-1' input impedance Z i The equivalence is as follows: z i ＝25+Z cmi (ii) a Differential mode noise source impedance extraction experiment selects the two-port network of FIG. 5, and its corresponding port 1-1' input impedance Z i Can be equivalent to: z i ＝100//Z dmi 。
TABLE 1 high frequency parameters of impedance in passive two-port networks
After the KH23101 current clamp is adopted to measure the noise current of the LISN end, the noise current I can be deduced according to the series-parallel connection relation of the impedances i According to the formulas (2), (4) and (7), the amplitude | Z of the impedance of the common-mode noise source in the conduction frequency band range can be obtained by solving sCM I and phase θ (Z) sCM ) As shown in fig. 6 and 7. Similarly, the amplitude | Z of the differential mode noise source impedance sDM I and phase θ (Z) sDM ) As shown in fig. 8 and 9.
According to the noise source impedance Z s The calculation result of (a) can predict the noise current of the LISN terminal after any EMI filter is inserted. Therefore, the actually measured noise current and the predicted noise current can be carried out when the LED driving power supply experimental prototype worksAnd comparing, and further verifying the accuracy of the method.
The specific verification method comprises the following steps: a common-mode inductor L with a random value of 470 mu H is connected in series between the tested device and the LISN CM (ii) a Incorporation of a differential-mode capacitance C with a random value of 68nF between the device under test and the LISN x 。
L can be measured by adopting an impedance analyzer WK6500B CM And C x Including amplitude and phase. Because the impedance analyzer does not correspond to the frequency point data derived from the EMI receiver, the original common mode (differential mode) noise current and the frequency point of the noise source impedance which are adopted when the noise current is predicted by the background calculation correspond to the frequency point derived from the EMI receiver. Therefore, it is necessary to apply to L CM And C x The measured impedance values are fitted to find the impedance values at the same measurement frequency points as the EMI receiver, as shown in fig. 10 and 11.
The noise current predicted by the noise source impedance extraction method is compared with the actually measured noise current, and the correctness of the method is verified, as shown in fig. 12 and 13.
Although the illustrative embodiments of the present invention have been described in order to facilitate those skilled in the art to understand the present invention, it is to be understood that the present invention is not limited to the scope of the embodiments, and that various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined in the appended claims, and all matters of the invention using the inventive concepts are protected.
Claims (5)
1. A noise source impedance extraction method based on a plug-in passive two-port network is used for extracting the noise source impedance of a power converter, and is characterized in that: comprises the following steps;
step S1, the EMI noise source of the device under test EUT is represented by a Davinin equivalent circuit, namely, as the impedance Z of the noise source s Sum noise voltage source V s In a serial form;
step S2, using the ideal resistor R for the linear impedance stabilization network LISN LISN Show, measure togetherRespectively representing equivalent load impedance R of the LISN end by using ideal resistors with different resistance values when the mode noise source impedance and the differential mode noise source impedance are measured LISN ；
Step S3, inserting three arbitrary different passive two-port networks N between EUT and LISN i Taking i as 1, 2 and 3; n is a radical of i The accurate impedance characteristic curve of the passive device is measured by an impedance analyzer; z i Indicating insertion into a passive two-port network N i Input impedance seen from the EUT side; i is i Indicating insertion into a passive two-port network N i Port noise current from the EUT side;
step S4, setting the impedance Z of the noise source s Respectively real part and imaginary part of s_Re And Z s_Im The real part and imaginary part of the input impedance Zi are Z i_Re And Z i_Im (ii) a When inserted into a passive two-port network N i Time, noise current I i Is expressed in modulus as
Step S5, by inserting 3 different passive two-port networks N i Then, the real part Z of the impedance of the noise source is established through a formula I s_Re And an imaginary part Z s_Im And can be measured as a system of two-dimensional quadratic equations
Wherein the noise current I i The real part of the input impedance Z i_Re And an imaginary part Z i_Im Are all values obtained by measurement, the real part of the impedance Z of the noise source s_Re And an imaginary part Z s_Im Is an unknown quantity;
step S6, solving a binary quadratic equation set corresponding to each test frequency point in the range of the conducted EMI test frequency band through software programming circulation to obtain the impedance Z of the noise source s Real part Z of s_Re And an imaginary part Z s_Im ；
And S7, screening effective frequency points in the range of the conducted EMI test frequency band, and calculating the impedance amplitude and the phase of the noise source.
2. The noise source impedance extraction method based on the plug-in passive two-port network of claim 1, characterized in that: in step S2, when measuring the common mode noise source impedance, R LISN ＝R loadCM 25 Ω, when measuring the differential mode noise source impedance, R LISN ＝R loadDM ＝100Ω。
3. The noise source impedance extraction method based on the plug-in passive two-port network according to claim 1, characterized in that: step S6, when solving the noise source impedance, judging whether the binary quadratic equation set expressed by the formula II has solution or not according to the following method to screen the effective frequency point set f m ，
Impedance Z of noise source s Real part Z of s_Re And an imaginary part Z s_Im Separately as independent and dependent variables, the system of binary quadratic equations is expressed in terms of the real part of the noise source impedance Z s_Re Function Z of s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) Is expressed as
In which the transition variables are each
a＝(I 1 2 Z 1_Im -I 2 2 Z 2_Im )/(I 1 2 -I 2 2 )
b＝[I 1 2 (Z s_Re +Z 1_Re ) 2 -I 2 2 (Z s_Re +Z 2_Re ) 2 ]/(I 1 2 -I 2 2 )
c＝(I 2 2 Z 2_Im -I 3 2 Z 3_Im )/(I 2 2 -I 3 2 )
d＝[I 2 2 (Z s_Re +Z 2_Re ) 2 -I 3 2 (Z s_Re +Z 3_Re ) 2 ]/(I 2 2 -I 3 2 )
Wherein the function Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) When the two circular tracks have an intersection point, the noise source impedance corresponding to the frequency point has a solution; note Z s_Im1 (Z s_Re ) And Z s_Im2 (Z s_Re ) The radius of the corresponding circle is R 1 And R 2 The distance between the centers of the two circles is D, and the expression is as follows:
in which the transition variables are each
f＝(Z 1_Re I 1 2 -Z 2_Re I 2 2 )/(I 2 2 -I 1 2 )
g＝(Z 1_Im I 1 2 -Z 2_Im I 2 2 )/(I 2 2 -I 1 2 )
h＝(Z 2_Re 2 I 2 2 -Z 1_Re 2 I 1 2 )/(I 2 2 -I 1 2 )
k＝(Z 2_Im 2 I 2 2 -Z 1_Im 2 I 1 2 )/(I 2 2 -I 1 2 )
l＝(Z 2_Re I 1 2 -Z 3_Re I 3 2 )/(I 3 2 -I 2 2 )
m＝(Z 2_Im I 1 2 -Z 3_Im I 3 2 )/(I 3 2 -I 2 2 )
n＝(Z 3_Re 2 I 3 2 -Z 2_Re 2 I 2 2 )/(I 3 2 -I 2 2 )
p＝(Z 3_Im 2 I 3 2 -Z 2_Im 2 I 2 2 )/(I 3 2 -I 2 2 )
Based on the geometric theory, when two circular tracks have intersection points, the binary quadratic equation set expressed by the formula II has solutions, and the sufficient condition is expressed by the formula
R 1 +R 2 ≥D∧|R 1 -R 2 The formula is less than or equal to seven;
obtaining effective frequency points in the range of the conducted EMI test frequency band and the corresponding real part Z of the impedance of the noise source through programming according to a formula II, a formula IV, a formula V, a formula VI and a formula VII s_Re And imaginary part Z s_Im Further obtain the amplitude | Z of the noise source impedance s I and phase θ (Z) s ) (ii) a Is given by the formula
4. The noise source impedance extraction method based on the plug-in passive two-port network of claim 3, characterized in that: the inserted passive two-port network is any passive two-port network;
after the noise current of the LISN end is obtained through measurement, the noise current I is deduced according to the series-parallel connection relation of the impedance i Then solving according to a formula II, a formula IV, a formula V, a formula VI and a formula VII to obtain the amplitude value | Z of the impedance of the common mode noise source in the conduction frequency band range sCM I and phase θ (Z) sCM ) The amplitude value | Z of the impedance of the differential mode noise source can be obtained in the same way sDM I and phase θ (Z) sDM )。
5. The noise source impedance extraction method based on the plug-in passive two-port network of claim 1, characterized in that: in step S7, the range of the EMI test frequency band is 9kHz to 30 MHz.
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| CN105353226A (en) * | 2015-11-03 | 2016-02-24 | 江苏省计量科学研究院 | EMI noise source impedance equivalent parameter extraction method based on scattering parameter and intelligent algorithm |
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