Power converter noise source impedance extraction method and device

Abstract

The invention provides a power converter noise source impedance extraction method and device, and relates to the technical field of power electronics. The power converter noise source impedance extraction method comprises the following steps: inserting different passive elements with known impedance into a noise source side of a circuit to be detected at least twice, and acquiring a first reflection coefficient and a first transmission coefficient corresponding to the noise source side of the circuit to be detected when the passive elements are inserted into the noise source side of the circuit to be detected every time; a standard resistor with known impedance is adopted to replace a passive element in the circuit to be tested, the power converter to be tested and a load of the power converter to be tested, and a second reflection coefficient and a second transmission coefficient corresponding to the passive element in the circuit to be tested, the power converter to be tested and the load of the power converter to be tested are replaced with the standard resistor are obtained. According to the impedance of the passive element and the corresponding first reflection coefficient and first transmission coefficient, and the impedance of the standard resistor and the corresponding second reflection coefficient and second transmission coefficient, the noise source impedance of the to-be-measured power converter is accurately obtained.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a method and device for extracting noise source impedance of a power converter. Background Art

[0002] In the field of power electronics, with the development of power converters (such as switching power supplies and inverters), high efficiency, high density and high frequency have become the trend. However, these high-frequency switching operations will generate serious EMI (Electromagnetic Interference), especially conducted interference, which will affect the normal operation of electronic equipment. In order to reduce EMI, it is very important to design high-performance filters, and the design of filters depends on the accurate extraction of the noise source impedance of the power converter. Summary of the invention

[0003] The purpose of the present application is to provide a method and device for extracting the noise source impedance of a power converter, so as to accurately extract the noise source impedance of the power converter.

[0004] In order to achieve the above purpose, the technical solution adopted in this application is as follows:

[0005] In a first aspect, the present application provides a power converter noise source impedance extraction method, which is applied to a power converter noise source impedance extraction system, the system comprising: a dual current probe, a vector network analyzer VNA, and a circuit to be tested including a power converter to be tested, the dual current probe is connected to the VNA, and the dual current probe is embedded in the circuit to be tested, the method comprising:

[0006] Inserting different passive elements with known impedance at least twice on the noise source side of the circuit under test, and obtaining, through the VNA, a first reflection coefficient and a first transmission coefficient corresponding to each time the passive element is inserted on the noise source side of the circuit under test;

[0007] Replacing the passive components, the power converter and the load of the circuit under test with a standard resistor with known impedance, and obtaining, through the VNA, a second reflection coefficient and a second transmission coefficient corresponding to when the passive components, the power converter and the load of the circuit under test are replaced with the standard resistor;

[0008] The noise source impedance of the power converter to be tested is determined according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

[0009] Further, the dual current probe includes a current injection probe and a current receiving probe, and the step of determining the noise source impedance of the power converter to be tested according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient comprises:

[0010] Obtaining a first voltage ratio according to the first reflection coefficient and the first transmission coefficient; wherein the first voltage ratio refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when a passive component is inserted into the noise source side of the circuit under test;

[0011] Obtain a second voltage ratio according to the second reflection coefficient and the second transmission coefficient; wherein the second voltage refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when the passive components of the circuit under test, the power converter under test and its load are replaced by the standard resistor;

[0012] The noise source impedance of the power converter to be tested is determined according to the impedance of the passive element and the first voltage ratio corresponding thereto, the impedance of the standard resistor and the second voltage ratio corresponding thereto.

[0013] Further, the passive component is a common-mode inductor, and the noise source impedance of the power converter to be tested is a common-mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises:

[0014] When different common-mode inductors with known impedances are inserted twice into the noise source side of the circuit to be tested, the common-mode noise source impedance of the power converter to be tested is determined by using Cramer's law to solve a preset common-mode noise source impedance equation based on the impedance of the first common-mode inductor and its corresponding first voltage ratio, the impedance of the second common-mode inductor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio.

[0015] Further, when different common-mode inductors with known impedances are inserted twice into the noise source side of the circuit to be tested, the step of determining the common-mode noise source impedance of the power converter to be tested is performed by solving a preset common-mode noise source impedance equation using Cramer's law according to the impedance of the first common-mode inductor and its corresponding first voltage ratio, the impedance of the second common-mode inductor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio, and comprising:

[0016] The common mode noise source impedance Z of the power converter to be tested S,CM Satisfies the following formula:

[0017]

[0018] Among them, Z L,CM1 is the impedance of the first common mode inductor, is the first voltage ratio corresponding to the first common mode inductance, Z L,CM2 is the impedance of the second common mode inductor, is the first voltage ratio corresponding to the second common mode inductor, Z STD is the impedance of the standard resistor, is the second voltage ratio corresponding to the standard resistance.

[0019] Further, the passive component is a common-mode inductor, and the noise source impedance of the power converter to be tested is a common-mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises:

[0020] When different common-mode inductors with known impedances are inserted into the noise source side of the circuit to be tested for at least three times, the common-mode noise source impedance of the power converter to be tested is determined by solving a preset common-mode noise source impedance equation using the least squares method based on the impedances of the common-mode inductors and their corresponding multiple first voltage ratios, the impedance of the standard resistor and its corresponding second voltage ratio.

[0021] Further, the passive component is a differential mode capacitor, and the noise source impedance of the power converter to be tested is a differential mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises:

[0022] When different differential mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested three times, the differential mode noise source impedance of the power converter to be tested is determined by solving a preset differential mode noise source impedance equation using Cramer's law based on the impedance of the first differential mode capacitor and its corresponding first voltage ratio, the impedance of the second differential mode capacitor and its corresponding first voltage ratio, the impedance of the third differential mode capacitor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio.

[0023] Further, when different differential mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested three times, the step of determining the differential mode noise source impedance of the power converter to be tested is performed by using Cramer's law to solve a preset differential mode noise source impedance equation according to the impedance of the first differential mode capacitor and its corresponding first voltage ratio, the impedance of the second differential mode capacitor and its corresponding first voltage ratio, the impedance of the third differential mode capacitor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio, and comprising:

[0024] The differential mode noise source impedance Z of the power converter to be tested S,DM Satisfies the following formula:

[0025]

[0026] Among them, Z C,DM1 is the impedance of the first differential mode capacitor, is the first voltage ratio corresponding to the first differential mode capacitance, Z C,DM2 is the impedance of the second differential mode capacitor, is the first voltage ratio corresponding to the second differential mode capacitance, Z C,DM3 is the impedance of the third differential mode capacitor, is the first voltage ratio corresponding to the third differential mode capacitance, Z STD is the standard resistor, is the second voltage ratio corresponding to the standard resistance.

[0027] Further, the passive component is a differential mode capacitor, and the noise source impedance of the power converter to be tested is a differential mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises:

[0028] When different differential-mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested at least four times, the differential-mode noise source impedance of the power converter to be tested is determined by solving a preset differential-mode noise source impedance equation using the least squares method based on the impedances of the multiple differential-mode capacitors and their corresponding multiple first voltage ratios, the impedance of the standard resistor and its corresponding second voltage ratio.

[0029] In a second aspect, the present application provides a power converter noise source impedance extraction device, which is applied to a power converter noise source impedance extraction system, the system comprising: a dual current probe, a vector network analyzer VNA, and a circuit to be tested including a power converter to be tested, the dual current probe is connected to the VNA, and the dual current probe is embedded in the circuit to be tested, the device comprising:

[0030] A first acquisition module is used to insert different passive elements with known impedance at least twice on the noise source side of the circuit under test, and obtain, through the VNA, a first reflection coefficient and a first transmission coefficient corresponding to each time the passive element is inserted on the noise source side of the circuit under test;

[0031] A second acquisition module is used to replace the passive components in the circuit under test, the power converter under test and its load with a standard resistor with known impedance, and obtain, through the VNA, a second reflection coefficient and a second transmission coefficient corresponding to when the passive components in the circuit under test, the power converter under test and its load are replaced with the standard resistor;

[0032] The determination module is used to determine the noise source impedance of the power converter to be tested according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

[0033] Compared with the prior art, this application has the following beneficial effects:

[0034] The power converter noise source impedance extraction method provided by the present application inserts different passive elements with known impedance at least twice on the noise source side of the circuit to be tested, and obtains the first reflection coefficient and the first transmission coefficient corresponding to each time the noise source side of the circuit to be tested is inserted with the passive element through VNA. The passive elements in the circuit to be tested, the power converter to be tested and its load are replaced by standard resistors with known impedance, and the second reflection coefficient and the second transmission coefficient corresponding to the passive elements in the circuit to be tested, the power converter to be tested and its load are replaced by standard resistors through VNA. According to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient, the noise source impedance of the power converter to be tested is accurately obtained.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians of the art without making creative work are within the scope of protection of the present application.

[0037] Figure 1 It is one of the principle diagrams of the dual current probe method in the prior art;

[0038] Figure 2 This is the second schematic diagram of the dual current probe method in the prior art;

[0039] Figure 3 A flowchart of a method for extracting noise source impedance of a power converter provided in an embodiment of the present application;

[0040] Figure 4 This is a schematic diagram of the steps of step 300 in the embodiment of the present application;

[0041] Figure 5 A circuit to be tested into which a common-mode inductor is inserted is provided in an embodiment of the present application;

[0042] Figure 6 An equivalent circuit after a common-mode inductor is inserted into a circuit to be tested provided in an embodiment of the present application;

[0043] Figure 7 A circuit to be tested into which a differential mode capacitor is inserted is provided in an embodiment of the present application;

[0044] Figure 8 An equivalent circuit after a differential mode capacitor is inserted into a circuit to be tested provided in an embodiment of the present application;

[0045] Fig. 9 An equivalent circuit of a circuit to be tested provided in an embodiment of the present application before and after a common-mode inductor is inserted;

[0046] Fig.10 An equivalent circuit of a circuit to be tested provided in an embodiment of the present application before and after a differential mode capacitor is inserted;

[0047] Fig.11 A functional module of a power converter noise source impedance extraction device provided in an embodiment of the present application.

[0048] Icons: 10 - power converter noise source impedance extraction device; 11 - first acquisition module; 12 - second acquisition module; 13 - determination module. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0050] In the description of this application, it should be noted that relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The term "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium.

[0051] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0052] As mentioned in the background technology, with the increase of power converter switching frequency, the high dv / dt and di / dt generated by high-frequency switching form serious EMI through parasitic inductance and capacitance in the circuit loop. An important measure to reduce EMI is to design a filter with matching and excellent performance. Since the determination of the topology structure of the high-voltage EMI filter needs to follow the "impedance mismatch" theory, and the design of the filter's component parameters is also affected by the noise source, it is necessary to accurately extract the power converter noise source impedance before designing the EMI filter.

[0053] Since the vector network analyzer (VNA) cannot directly extract the online noise source impedance of the power converter under high-voltage working conditions, the dual current probe method is currently mostly used to obtain the noise source impedance of the power converter. The dual current probe method was first used to inject interference current into the circuit through a coupling capacitor by combining a signal generator with an injection current probe, and then use another current probe to measure the injected interference current. The spectrum analyzer is used to measure the changes before and after the interference current to obtain the noise source impedance amplitude. Later, the improvement measures were to directly embed the current probe into the circuit without using isolation capacitors and inductors, and use VNA instead of signal generation and test equipment to obtain the phase information of the noise source impedance.

[0054] The principle of the dual current probe method in the prior art is first explained below.

[0055] See also Figure 1 , Figure 1The figure shows the basic setup of online impedance measurement using dual current probes. The current injection probe (IIP) and the current receiving probe (RIP) are connected to the CH1 port and CH2 port of the VNA respectively. The system under test (SUT) in the online test is powered by a DC or AC power supply through wiring. S and Z S are the equivalent online voltage source and impedance respectively. The online impedance of the SUT load is represented by Z SUT Indicates that Z W is the equivalent impedance of the wiring connection, so the comprehensive impedance of the circuit is Z X =Z S +Z W +Z SUT .

[0056] Based on the cascaded two-port A matrix parameters are as follows Figure 2 The equivalent circuit shown in Figure 1. Among them, V sig is the signal source of the VNA, Z CH1 and Z CH2 are the output impedances of CH1 and CH2 of the VNA, respectively. IIP together with the clamped wire can be modeled as a two-port network M IIP , where one port represents the input port of the IIP and the other port represents the two ends of the clamped wire. Similarly, the RIP and the clamped wire can also be modeled as a two-port network M RIP . M X is the transfer parameter network of the impedance being measured. sig The frequency is much higher than the system online operating frequency (DC, 50, 60Hz), so at f sig The frequency of V S Treated as a short circuit.

[0057] According to the definition and properties of the cascaded two-port, the voltage and current input and output and the transfer parameter A matrix of the three two-port networks have the following relationship:

[0058]

[0059] Where V1 and I1 are the test signal voltage and current at the IIP input port, respectively; V2 and I2 are the test signal voltage and current at the RIP output port, respectively. The following can be solved:

[0060]

[0061] The ratio of V1 to V2 can be directly measured using a VNA. According to the definition of S parameters, V1 = (S11 +1)V sig and V2 = S 21 V sig ,then:

[0062]

[0063] Among them, S 11 is the reflection coefficient, S 21 is the transmission coefficient. In order to simplify the expression of formula (2), we have:

[0064]

[0065] Where k and b are coefficients that are only related to frequency:

[0066]

[0067] The traditional dual current probe method uses a short circuit and 50Ω load calibration method to obtain the above coefficients k and b, and then solves the overall impedance of the circuit when connected to the actual working circuit. X Use short circuit and 50Ω load to replace them respectively, and record the voltage ratio at this time as and Then we have:

[0068]

[0069] The unknown coefficients k and b can be derived by two calibrations:

[0070]

[0071] Substituting formula (7) into formula (4), after the SUT is connected, the voltage ratio is Then the overall impedance Z of the measured circuit can be obtained X for:

[0072]

[0073] The disadvantage of the existing dual current probe method is that it does not take into account the irrational characteristics of the calibration components at high frequencies due to parasitic parameters, which leads to inaccurate extraction of high-frequency noise source impedance. In actual measurement applications, when the EMI noise is stronger than the injected current signal, the signal-to-noise ratio of the impedance information extracted by this method is very low, and there is even a risk of damaging the VNA under high noise. In actual high-voltage (such as 350V switching power supply or inverter) circuit application test scenarios, this method is difficult to apply when using short-circuit load calibration due to safety issues.

[0074] Based on the deficiencies of the prior art, an embodiment of the present application provides a method for extracting noise source impedance of a power converter, which is applied to a system for extracting noise source impedance of a power converter, the system comprising: a dual current probe, a vector network analyzer VNA, and a circuit to be tested including a power converter to be tested. The dual current probe is connected to the VNA, and the dual current probe is embedded in the circuit to be tested.

[0075] See also Figure 3 A method for extracting noise source impedance of a power converter provided in an embodiment of the present application includes steps S100 to S300.

[0076] S100: inserting different passive components with known impedance at least twice on the noise source side of the circuit under test, and obtaining, through a VNA, a first reflection coefficient and a first transmission coefficient corresponding to each time the passive component is inserted on the noise source side of the circuit under test.

[0077] S200: Use standard resistors with known impedance to replace passive components in the circuit under test, the power converter under test and its load, and obtain through VNA the second reflection coefficient and the second transmission coefficient corresponding to when the passive components in the circuit under test, the power converter under test and its load are replaced by the standard resistors.

[0078] It can be understood that since the VNA is connected to the dual current probe, and the dual current probe is embedded in the circuit to be tested, each time a passive component is inserted into the noise source side of the circuit to be tested, the corresponding first reflection coefficient and first transmission coefficient can be collected by the VNA. In other words, the first reflection coefficient and the first transmission coefficient can be collected once by the VNA each time a passive component is inserted. Similarly, when the passive components of the circuit to be tested, the power converter to be tested, and its load are replaced with standard resistors, the second reflection coefficient and the second transmission coefficient can be collected by the VNA.

[0079] In addition, in the embodiment of the present application, the standard resistor and the impedance of each passive component are known, and the standard resistor and the impedance of each passive component can be extracted in advance using an impedance analyzer.

[0080] S300: Determine the noise source impedance of the power converter to be tested according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

[0081] In an alternative embodiment, see Figure 4 The implementation process of step 300 may include sub-steps S310 to S330.

[0082] S310: Obtain a first voltage ratio according to a first reflection coefficient and a first transmission coefficient.

[0083] S320: Obtain a second voltage ratio according to the second reflection coefficient and the second transmission coefficient.

[0084] In the embodiment of the present application, the dual current probe includes a current injection probe (i.e., IIP) and a current receiving probe (i.e., RIP), wherein both the current injection probe and the current receiving probe are connected to the VNA, and both the current injection probe and the current receiving probe are embedded in the circuit to be tested.

[0085] According to the formula (3) mentioned above, as long as the reflection coefficient S is obtained by VNA, 11 and the transmission coefficient is S 21 , the ratio of the voltage at the current injection probe to the voltage at the current receiving probe can be calculated

[0086] It can be understood that the first voltage ratio can be calculated based on the first reflection coefficient and the first transmission coefficient. The first voltage ratio refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when a passive component is inserted into the noise source side of the circuit under test.

[0087] Similarly, the second voltage ratio can be calculated based on the second reflection coefficient and the second transmission coefficient. The second voltage refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when the passive components of the circuit under test, the power converter under test and its load are replaced with standard resistors.

[0088] S330: Determine the noise source impedance of the power converter to be tested according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio.

[0089] In the embodiment of the present application, the passive element may be a common-mode inductor or a differential-mode capacitor.

[0090] When the passive component is a common-mode inductor, the noise source impedance of the power converter to be tested is the common-mode noise source impedance. At this time, the impedance of each common-mode inductor and its corresponding first voltage ratio, as well as the impedance of the standard resistor and its corresponding second voltage ratio, can be used to solve the preset common-mode noise source impedance equation, thereby obtaining the common-mode noise source impedance of the power converter to be tested.

[0091] It should be noted that when testing the common-mode noise source impedance of the power converter under test, different common-mode inductors need to be inserted at least twice on the noise source side of the circuit under test.

[0092] Optionally, when different common-mode inductors are inserted into the noise source side of the circuit under test twice, the Cramer's law can be used to solve the preset common-mode noise source impedance equation. When different common-mode inductors are inserted into the noise source side of the circuit under test at least three times, the least squares method can be used to solve the preset common-mode noise source impedance equation.

[0093] The following uses an example in which different common-mode inductors are inserted twice into the noise source side of the circuit to be tested as an example to illustrate the derivation process and solution method of the preset common-mode noise source impedance equation.

[0094] like Figure 5 As shown in the figure, a common-mode inductor is inserted into the noise source side of the circuit under test. Since the insertion of the common-mode inductor only affects the common-mode impedance of the loop, it is equivalent to directly connecting the inductor impedance in series in the loop. Its equivalent circuit can be shown as follows: Figure 6 shown.

[0095] Place the experimental equipment and the circuit to be tested according to the requirements and test standards for common-mode EMI noise source impedance extraction. IIP (current injection probe) and RIP (current receiving probe) are connected to the CH1 port and CH2 port of the VNA respectively. When embedding IIP and RIP in the circuit to be tested, the loop area formed by the cables should be as small as possible to prevent common-mode radiation problems. In addition, the distance d between IIP and RIP should be kept within a certain range to avoid direct mutual coupling due to the close placement of the dual current probes. Subsequent tests must be based on the condition that the dual current probes are weakly coupled.

[0096] The power converter under test in the online test is powered by a noise voltage source through a cable. S is the noise voltage source, Z S,CM is the common-mode noise source impedance of the power converter under test, Z W1 is the cable impedance, Z LISN,CM is the common mode impedance of the artificial power network LISN. The impedance information of LISN and cables can be extracted in advance by the impedance analyzer (i.e., Z LISN,CM , Z W1 is known).

[0097] Insert different common-mode inductors L at the noise source of the circuit under test. CMi (i=1,2), whose impedance can be extracted in advance by an impedance analyzer and is denoted as Z L,CMi .

[0098] Each time a new common-mode inductor is inserted, the total common-mode impedance of the circuit under test changes, which is recorded as Z xi,CM , then:

[0099] Z xi,CM =Z LISN,CM +Z W1 +ZL,CMi +Z S,CM #(9)

[0100] The expression for the comprehensive common-mode impedance of the circuit under test is as follows:

[0101]

[0102] Written in the form of a matrix equation:

[0103]

[0104] in, It means that the noise source side of the circuit under test is inserted with impedance Z L,CM1 The first voltage ratio corresponding to the first common-mode inductance is, It means that the noise source side of the circuit under test is inserted with impedance Z L,CM2 The first voltage ratio corresponding to the second common-mode inductance, k CM 、b CM and Z S,CM Is an unknown quantity.

[0105] Only the common mode inductor, the power converter and its load in the circuit to be tested are removed, and then a standard resistor is connected. The impedance of the standard resistor can be extracted in advance by the impedance analyzer and recorded as Z STD . So we have:

[0106]

[0107] in, It means that the common mode inductor of the circuit to be tested, the power converter to be tested and its load are replaced as a whole with an impedance of Z STD The standard resistance is the ratio of the voltage at IIP to the voltage at RIP, that is, the second voltage ratio.

[0108] Substituting formula (12) into formula (11) and eliminating b CM After that, we can get a binary equation system (k CM , Z S,CM is the unknown quantity), and is organized into the form of a non-homogeneous linear equation system Ax=b as follows:

[0109]

[0110] Among them, the determinant of the coefficient of matrix A is According to Cramer's law, as long as the inserted common-mode inductors are different (Z L,CM1 ≠Z L,CM2 ), then |A|≠0, and the linear equation system has a unique solution:

[0111]

[0112] Among them, Z L,CM1 is the impedance of the first common mode inductor, is the first voltage ratio corresponding to the first common mode inductance, Z L,CM2 is the impedance of the second common mode inductor, is the first voltage ratio corresponding to the second common mode inductor, Z STD is the impedance of the standard resistor, is the second voltage ratio corresponding to the standard resistance.

[0113] Based on the above steps, it can be seen that when different common-mode inductors are inserted twice on the noise source side of the circuit under test, the A matrix in formula (13) (i.e., the preset common-mode noise source impedance equation) is a 2*2 square matrix. Formula (15) can be obtained by solving the preset common-mode noise source impedance equation using Cramer's rule. Substitute into formula (15), and finally use computer software programming to calculate the common-mode noise source impedance Z of the power converter to be tested S,CM .

[0114] When different common-mode inductors are inserted at least three times on the noise source side of the circuit under test, the preset common-mode noise source impedance equation is an overdetermined system of equations, that is, the number of equations is greater than the unknown quantity (i.e., k CM , Z S,CM ) number. At this time, the least square method can be used to solve the preset common-mode noise source impedance equation to obtain the common-mode noise source impedance Z of the power converter to be tested. S,CM .

[0115] When the passive component is a differential mode capacitor, the noise source impedance of the power converter to be tested is the differential mode noise source impedance. At this time, the impedance of each differential mode capacitor and its corresponding first voltage ratio, as well as the impedance of the standard resistor and its corresponding second voltage ratio, can be used to solve the preset differential mode noise source impedance equation, thereby obtaining the differential mode noise source impedance of the power converter to be tested.

[0116] It should be noted that when testing the differential-mode noise source impedance of the power converter under test, different differential-mode capacitors need to be inserted at least three times on the noise source side of the circuit under test.

[0117] Optionally, when different differential mode capacitors are inserted into the noise source side of the circuit to be tested three times, the preset differential mode noise source impedance equation can be solved by Cramer's law. When different differential mode capacitors are inserted into the noise source side of the circuit to be tested at least four times, the preset differential mode noise source impedance equation can be solved by the least square method.

[0118] The following takes the case where different differential mode capacitors are inserted three times into the noise source side of the circuit to be tested as an example to illustrate the derivation process and solution method of the preset differential mode noise source impedance equation.

[0119] like Figure 7 As shown in the figure, a differential mode capacitor is inserted into the circuit to be tested. Since the insertion of the differential mode capacitor only affects the differential mode impedance of the loop, it is equivalent to directly connecting the capacitor impedance in parallel with the loop. Its equivalent circuit can be shown as follows Figure 8 shown.

[0120] Arrange the experimental equipment and the circuit to be tested according to the requirements and test standards for differential mode EMI noise source impedance extraction. According to the requirements for current probe clamps for differential mode current testing, bend the cable and pass it through IIP and RIP. The cable impedance is Z W2 . It is important to minimize the loop area formed by the cables to prevent differential mode radiation problems. In addition, the distance d between IIP and RIP should be kept within a certain range to avoid direct mutual coupling caused by placing the dual current probes too close together. Subsequent tests must be based on the condition that the dual current probes are weakly coupled.

[0121] Insert different differential mode capacitors C at the noise source of the circuit to be tested. DMi (i=1,2,3), whose impedance can be extracted in advance by an impedance analyzer and is recorded as Z C,DMi .

[0122] Each time a new differential mode capacitor is inserted, the total differential mode impedance of the circuit under test changes, which is recorded as Z xi,DM , then:

[0123] Z xi,DM =Z LISN,DM +Z W2 +Z C,DMi ||Z S,DM #(16)

[0124] Among them, Z LISN,DM is the differential impedance of LISN, Z W2 is the cable impedance, Z S,DM is the differential mode noise source impedance of the power converter under test, Z C,DMi ||Z S,DM Represents Z C,DMi With Z S,DM The impedance after parallel connection is

[0125] The expression for the comprehensive differential mode impedance of the circuit to be measured is as follows:

[0126]

[0127] Written in the form of a matrix equation:

[0128]

[0129] in, It means that the noise source side of the circuit under test is inserted with impedance ZC,DM1 The first voltage ratio corresponding to the first differential mode capacitance is, It means that the noise source side of the circuit under test is inserted with impedance Z C,DM2 The first voltage ratio corresponding to the second differential mode capacitance is, It means that the noise source side of the circuit under test is inserted with impedance Z C,DM3 The first voltage ratio corresponding to the third differential mode capacitance, k DM 、b DM and Z S,DM Is an unknown quantity.

[0130] Only the differential mode capacitors, the power converter and its load in the circuit to be tested are removed, and then a standard resistor is connected. The impedance of the standard resistor can be extracted in advance by the impedance analyzer and recorded as Z STD . So we have:

[0131]

[0132] in, It means that the differential mode capacitor of the circuit to be tested, the power converter to be tested and its load are replaced as a whole with an impedance of Z STD The standard resistance is the ratio of the voltage at IIP to the voltage at RIP, that is, the second voltage ratio.

[0133] Substitute formula (19) into formula (18) and eliminate b DM After that, we can get a three-variable equation system (k DM , Z S,DM , k DM Z S,DM is the unknown quantity), and is organized into the form of a non-homogeneous linear equation system Ax=b as follows:

[0134]

[0135] Among them, the determinant of the A matrix coefficient is:

[0136]

[0137] According to Cramer's law, as long as the inserted differential mode capacitors are different Then |A|≠0, the linear equation system has a unique solution:

[0138]

[0139] Among them, Z C,DM1 is the impedance of the first differential mode capacitor, is the first voltage ratio corresponding to the first differential mode capacitance, Z C,DM2 is the impedance of the second differential mode capacitor, is the first voltage ratio corresponding to the second differential mode capacitance, Z C,DM3 is the impedance of the third differential mode capacitor, is the first voltage ratio corresponding to the third differential mode capacitance, Z STD is the standard resistor, is the second voltage ratio corresponding to the standard resistance.

[0140] Based on the above steps, it can be seen that when different differential mode capacitors are inserted three times on the noise source side of the circuit under test, the A matrix in formula (20) (i.e., the preset differential mode noise source impedance equation) is a 3*3 square matrix. The preset differential mode noise source impedance equation can be solved by Cramer's rule to obtain formula (22). Substitute into formula (22), and finally use computer software programming to calculate the differential mode noise source impedance Z of the power converter to be tested S,DM .

[0141] When different differential mode capacitors are inserted at least four times on the noise source side of the circuit under test, the preset differential mode noise source impedance equation is an overdetermined set of equations, that is, the number of equations is greater than the unknown quantity (i.e., k DM , Z S,DM , k DM Z S,DM ) number. At this time, the least square method can be used to solve the preset differential mode noise source impedance equation to obtain the differential mode noise source impedance Z of the power converter to be tested. S,DM .

[0142] Furthermore, the embodiment of the present application also provides a method for verifying the common-mode noise source impedance Z of the power converter to be tested based on the insertion loss method. S,CM and differential mode noise source impedance Z S,DM The correctness of the method is divided into the common mode noise source impedance Z S,CM Verify and differential mode noise source impedance Z S,DM verify.

[0143] Before using the power converter noise source impedance extraction method provided in the present application to extract the noise source impedance of the power converter to be tested, the original common mode noise voltage V on the LISN is obtained by using the EMI conducted high voltage voltage method and the differential common mode separator and the EMI receiver. CM and differential mode noise voltage V DM .

[0144] Next, we first calculate the common mode noise source impedance Z S,CM The verification method is introduced.

[0145] The equivalent circuit of the circuit under test before and after the common mode inductor is inserted is as follows: Fig. 9 As shown in the figure, V SIt is the sum of the working bias voltage and the noise source voltage. At the test frequency, the working bias voltage can be regarded as a short circuit at the test frequency of interest. After inserting the common-mode inductor, connect the two outputs of the LISN to the two input ports of the differential common-mode separator, and then connect its common-mode output port to the EMI receiver to obtain a new common-mode noise voltage V″. CMi .

[0146] According to the insertion loss IL CMi (unit dB) is calculated as follows:

[0147]

[0148] So we have:

[0149]

[0150] Among them, the common mode impedance of LISN is Z LISM,CM , cable impedance Z W1 , the inserted common mode inductor impedance Z L,CMi can be pre-extracted by the impedance analyzer, the common-mode noise source impedance Z S,CM The noise source impedance of a power converter is extracted using the power converter noise source impedance extraction method provided in the embodiment of the present application.

[0151] Each time the common-mode inductor is replaced, |V C ′ M ′ i | and the common-mode noise voltage value calculated above |V′ CMi |For comparison, if they are similar, the correctness of the amplitude of the common-mode noise source impedance obtained by the power converter noise source impedance extraction method provided in the embodiment of the present application can be verified.

[0152] For differential mode noise source impedance Z S,DM The verification method is as follows:

[0153] The equivalent circuit of the circuit under test before and after the differential mode capacitor is inserted is as follows: Fig.10 As shown, similarly, V S It is the sum of the working bias voltage and the noise source voltage. At the test frequency, the working bias voltage can be regarded as a short circuit at the test frequency of interest. After inserting the differential mode capacitor, connect the two outputs of the LISN to the two input ports of the differential common mode separator, and then connect its common mode output port to the EMI receiver to obtain the new differential mode noise voltage value V′. DMi .

[0154] According to the insertion loss IL DMi The definition of (unit dB) is:

[0155]

[0156] So we have:

[0157]

[0158] Among them, the differential mode impedance of LISN is Z LISN,DM , cable impedance Z W2 , the inserted differential mode capacitor impedance Z C,DMi can be pre-extracted by the impedance analyzer, the differential mode noise source impedance Z S,DM The noise source impedance of a power converter is extracted using the power converter noise source impedance extraction method provided in the embodiment of the present application.

[0159] Each time the differential mode capacitor is replaced, |V D ′ M ′ i | and the differential mode noise voltage value calculated above |V D ′ Mi |For comparison, if they are similar, the correctness of the amplitude of the differential mode noise source impedance obtained by the power converter noise source impedance extraction method provided in the embodiment of the present application can be verified.

[0160] In order to execute the corresponding steps in the above embodiments and various possible methods, an implementation method of a power converter noise source impedance extraction device is provided below.

[0161] For further information, see Fig.11 , Fig.11 This is a functional module diagram of a power converter noise source impedance extraction device 10 provided in an embodiment of the present application. It should be noted that the basic principle and technical effect of the power converter noise source impedance extraction device 10 provided in this embodiment are the same as those of the above-mentioned embodiments. For the sake of brief description, for parts not mentioned in this embodiment, reference can be made to the corresponding contents in the above-mentioned embodiments. The device is applied to a power converter noise source impedance extraction system, which includes: a dual current probe, a vector network analyzer VNA, and a circuit to be tested including a power converter to be tested, the dual current probe is connected to the VNA, and the dual current probe is embedded in the circuit to be tested. The power converter noise source impedance extraction device 10 includes:

[0162] The first acquisition module 11 is used to insert different passive components with known impedance at least twice on the noise source side of the circuit under test, and obtain the first reflection coefficient and the first transmission coefficient corresponding to each time the passive component is inserted on the noise source side of the circuit under test through the VNA.

[0163] The second acquisition module 12 is used to replace the passive components in the circuit under test, the power converter under test and its load with a standard resistor with known impedance, and obtain through the VNA the second reflection coefficient and the second transmission coefficient corresponding to when the passive components in the circuit under test, the power converter under test and its load are replaced with the standard resistor.

[0164] The determination module 13 is used to determine the noise source impedance of the power converter to be tested according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

[0165] In summary, the power converter noise source impedance extraction method provided by the embodiment of the present application is to insert different common-mode inductors or differential-mode capacitors with known impedances on the noise source side of the circuit to be tested multiple times, and calculate the first voltage ratio corresponding to each common-mode inductor or differential-mode capacitor and the second voltage ratio corresponding to the standard resistor through dual current probes and VNA, and select Cramer's law or least squares method to solve the preset common-mode noise source impedance equation or the preset differential-mode noise source impedance equation according to the number of insertions, so as to extract the common-mode noise source impedance and differential-mode noise source impedance of the power converter to be tested online. During the measurement process, since the insertion of common-mode inductors or differential-mode capacitors has a suppressive effect on the common / differential-mode noise of the circuit to be tested, the influence of noise on VNA is reduced, making the signal-to-noise ratio higher. In addition, the power converter noise source impedance extraction method provided by the embodiment of the present application is to obtain the power converter noise source impedance by inserting common-mode inductors or differential-mode capacitors. Compared with the existing dual current probe method using short-circuit load calibration, the present application considers the irrational characteristics of high-frequency components during the calibration process to make the extracted noise source impedance data more accurate.

[0166] In addition, the embodiment of the present application also provides a method for verifying the correctness of the noise source impedance, which can ensure the correctness of the noise source impedance obtained by the power converter noise source impedance extraction method provided by the embodiment of the present application, and provides an important basis for guiding the design of corresponding common-mode and differential-mode EMI filters.

[0167] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0168] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential features of the present application. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present application. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for extracting noise source impedance of a power converter, characterized in that: The invention is applied to a power converter noise source impedance extraction system, the system comprising: a dual current probe, a vector network analyzer (VNA), and a circuit to be tested including a power converter to be tested, the dual current probe being connected to the VNA, and the dual current probe being embedded in the circuit to be tested, and the method comprising: Inserting different passive elements with known impedance at least twice on the noise source side of the circuit under test, and obtaining, through the VNA, a first reflection coefficient and a first transmission coefficient corresponding to each time the passive element is inserted on the noise source side of the circuit under test; Replacing the passive components, the power converter and the load of the circuit under test with a standard resistor with known impedance, and obtaining, through the VNA, a second reflection coefficient and a second transmission coefficient corresponding to when the passive components, the power converter and the load of the circuit under test are replaced with the standard resistor; The noise source impedance of the power converter to be tested is determined according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

2. The method for extracting noise source impedance of a power converter according to claim 1, characterized in that: The dual current probe comprises a current injection probe and a current receiving probe. According to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient, the step of determining the noise source impedance of the power converter to be tested comprises: Obtaining a first voltage ratio according to the first reflection coefficient and the first transmission coefficient; wherein the first voltage ratio refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when a passive component is inserted into the noise source side of the circuit under test; Obtain a second voltage ratio according to the second reflection coefficient and the second transmission coefficient; wherein the second voltage refers to the ratio of the voltage at the current injection probe to the voltage at the current receiving probe when the passive components of the circuit under test, the power converter under test and its load are replaced by the standard resistor; The noise source impedance of the power converter to be tested is determined according to the impedance of the passive element and the first voltage ratio corresponding thereto, the impedance of the standard resistor and the second voltage ratio corresponding thereto.

3. The method for extracting noise source impedance of a power converter according to claim 2, characterized in that: The passive component is a common mode inductor, and the noise source impedance of the power converter to be tested is a common mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises: When different common-mode inductors with known impedances are inserted twice into the noise source side of the circuit to be tested, the common-mode noise source impedance of the power converter to be tested is determined by using Cramer's law to solve a preset common-mode noise source impedance equation based on the impedance of the first common-mode inductor and its corresponding first voltage ratio, the impedance of the second common-mode inductor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio.

4. The method for extracting noise source impedance of a power converter according to claim 3, characterized in that: When different common-mode inductors with known impedances are inserted twice into the noise source side of the circuit to be tested, the steps of solving a preset common-mode noise source impedance equation using Cramer's law according to the impedance of the first common-mode inductor and its corresponding first voltage ratio, the impedance of the second common-mode inductor and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, and determining the common-mode noise source impedance of the power converter to be tested include: The common mode noise source impedance Z of the power converter to be tested S,CM Satisfies the following formula: Among them, Z L,CM1 is the impedance of the first common mode inductor, is the first voltage ratio corresponding to the first common mode inductance, Z L,CM2 is the impedance of the second common mode inductor, is the first voltage ratio corresponding to the second common mode inductor, Z STD is the impedance of the standard resistor, is the second voltage ratio corresponding to the standard resistance.

5. The method for extracting noise source impedance of a power converter according to claim 2, characterized in that: The passive component is a common mode inductor, and the noise source impedance of the power converter to be tested is a common mode noise source impedance; according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio, the step of determining the noise source impedance of the power converter to be tested comprises: When different common-mode inductors with known impedances are inserted into the noise source side of the circuit to be tested for at least three times, the common-mode noise source impedance of the power converter to be tested is determined by solving a preset common-mode noise source impedance equation using the least squares method based on the impedances of the common-mode inductors and their corresponding multiple first voltage ratios, the impedance of the standard resistor and its corresponding second voltage ratio.

6. The method for extracting noise source impedance of a power converter according to claim 2, characterized in that: The passive component is a differential mode capacitor, and the noise source impedance of the power converter to be tested is a differential mode noise source impedance; the step of determining the noise source impedance of the power converter to be tested according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio comprises: When different differential mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested three times, the differential mode noise source impedance of the power converter to be tested is determined by solving a preset differential mode noise source impedance equation using Cramer's law based on the impedance of the first differential mode capacitor and its corresponding first voltage ratio, the impedance of the second differential mode capacitor and its corresponding first voltage ratio, the impedance of the third differential mode capacitor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio.

7. The method for extracting noise source impedance of a power converter according to claim 6, characterized in that: When different differential mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested three times, the step of determining the differential mode noise source impedance of the power converter to be tested is performed by using Cramer's law to solve a preset differential mode noise source impedance equation according to the impedance of the first differential mode capacitor and its corresponding first voltage ratio, the impedance of the second differential mode capacitor and its corresponding first voltage ratio, the impedance of the third differential mode capacitor and its corresponding first voltage ratio, and the impedance of the standard resistor and its corresponding second voltage ratio. The equation includes: The differential mode noise source impedance Z of the power converter to be tested S,DM Satisfies the following formula: Among them, Z C,DM1 is the impedance of the first differential mode capacitor, is the first voltage ratio corresponding to the first differential mode capacitance, Z C,DM2 is the impedance of the second differential mode capacitor, is the first voltage ratio corresponding to the second differential mode capacitance, Z C,DM3 is the impedance of the third differential mode capacitor, is the first voltage ratio corresponding to the third differential mode capacitance, Z STD is the standard resistor, is the second voltage ratio corresponding to the standard resistance.

8. The method for extracting noise source impedance of a power converter according to claim 2, characterized in that: The passive component is a differential mode capacitor, and the noise source impedance of the power converter to be tested is a differential mode noise source impedance; the step of determining the noise source impedance of the power converter to be tested according to the impedance of the passive component and its corresponding first voltage ratio, the impedance of the standard resistor and its corresponding second voltage ratio comprises: When different differential-mode capacitors with known impedances are inserted into the noise source side of the circuit to be tested at least four times, the differential-mode noise source impedance of the power converter to be tested is determined by solving a preset differential-mode noise source impedance equation using the least squares method based on the impedances of the multiple differential-mode capacitors and their corresponding multiple first voltage ratios, the impedance of the standard resistor and its corresponding second voltage ratio.

9. A power converter noise source impedance extraction device, characterized in that: The invention is applied to a noise source impedance extraction system of a power converter, the system comprising: a dual current probe, a vector network analyzer VNA and a circuit to be tested including a power converter to be tested, the dual current probe is connected to the VNA, and the dual current probe is embedded in the circuit to be tested, and the device comprises: A first acquisition module is used to insert different passive elements with known impedance at least twice on the noise source side of the circuit under test, and obtain, through the VNA, a first reflection coefficient and a first transmission coefficient corresponding to each time the passive element is inserted on the noise source side of the circuit under test; A second acquisition module is used to replace the passive components in the circuit under test, the power converter under test and its load with a standard resistor with known impedance, and obtain, through the VNA, a second reflection coefficient and a second transmission coefficient corresponding to when the passive components in the circuit under test, the power converter under test and its load are replaced with the standard resistor; The determination module is used to determine the noise source impedance of the power converter to be tested according to the impedance of the passive element and its corresponding first reflection coefficient and first transmission coefficient, the impedance of the standard resistor and its corresponding second reflection coefficient and second transmission coefficient.

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