A Wideband Impedance Measurement Method for Common-Mode Inductors Based on Three-Port Network Calibration Technology

Abstract

A broadband impedance measurement method for common-mode inductors based on three-port network calibration technology relates to impedance characterization methods for passive electromagnetic interference filter components. A customized measurement fixture is designed based on the number, size, and distribution of the pins of the common-mode inductor under test, as well as the required impedance type. The influence of parasitic parameters is reduced by separating the excitation carrier and voltage sensing loops. A calibration component with known impedance is used to simulate the common-mode inductor. Relationship coefficients related to the impedance analyzer and measurement fixture are defined through a three-port network equivalent circuit and solved using Cramer's law. The common-mode inductor is directly measured, and parameter compensation is performed on the measurement results using the relationship coefficients, achieving broadband and high-precision impedance measurement of common-mode inductors.

Description

Technical Field

[0001] This invention relates to impedance characterization methods for passive electromagnetic interference filter components, particularly a broadband impedance measurement method for common-mode inductors based on three-port network calibration technology, which belongs to the field of electromagnetic interference research technology. Background Technology

[0002] Electromagnetic interference (EMI) poses potential hazards to both power electronic systems and the environment. For example, in aerospace and transportation, EMI can affect navigation and control systems, leading to misdirection, loss of control, and accidents. In medical equipment, EMI can interfere with the normal operation of critical detection and treatment devices, posing risks to patient safety and treatment outcomes. Therefore, various industries have established strict regulations and standards to ensure the electromagnetic compatibility (EMC) of equipment. To enable power electronic products to meet corresponding EMC standards, passive common-mode inductors are commonly used to provide high impedance to attenuate high-frequency EMI noise. However, due to the complex structure of common-mode inductors, accurate characterization and acquisition of their wideband impedance are difficult. Therefore, in industrial design, the selection of common-mode inductors often requires multiple trials and experiments, significantly increasing product cycle time and cost. Furthermore, for aerospace and electric vehicle applications, selecting the optimal common-mode inductor to minimize filter size and mass while addressing EMC issues is paramount. Therefore, accurate wideband impedance characterization of common-mode inductors is crucial for subsequent component selection and filter design.

[0003] Currently, there are three main methods for characterizing the broadband impedance of common-mode inductors: analytical calculation, numerical simulation, and measurement. While these methods differ in principle and characteristics, they all achieve basic common-mode inductor impedance measurement. However, the first two methods involve disassembling or building a three-dimensional physical model of the common-mode inductor and calculating its impedance frequency response using physical formulas or electromagnetic simulation software. Therefore, detailed physical geometry and material information of the component are indispensable, but this information is often difficult for third parties to access. Furthermore, these two methods require many assumptions and premises, such as assuming uniform distribution of the copper wire windings, which leads to deviations between analytical calculations or simulation estimates and actual values. These deviations increase with frequency and component structural complexity. The third method directly measures the component using impedance measuring instruments, such as impedance analyzers and vector network analyzers, along with their corresponding fixtures. However, because common-mode inductors lack standardized design specifications and packaging, their structures and pin distributions vary widely, resulting in a lack of suitable fixtures on the market. Some custom-designed fixtures are used to connect the non-standard pin ports of common-mode inductors to the coaxial ports of measuring instruments; however, these fixtures also introduce parasitic parameters that affect the accuracy of the final measurement.

[0004] Currently, traditional methods can only ensure accurate impedance characterization of common-mode inductors within 10 MHz, which is insufficient to meet the electromagnetic compatibility standard frequency range (up to 30 MHz) for commercial electronic equipment and the standard frequency range (up to 108 MHz and above) for electric vehicles and aerospace. Therefore, there is an urgent need for a wide-bandwidth, high-precision common-mode inductor impedance measurement method, which is of great significance for solving electromagnetic interference problems. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a broadband impedance measurement method for common-mode inductors based on three-port network calibration technology. It features a customized measurement fixture design that separates the excitation current-carrying and voltage sensing circuits to reduce the influence of parasitic parameters. Based on the three-port network calibration technology, the relationship coefficients of the measurement fixture are derived to calibrate and compensate for parasitic parameters and calibrate the measurement device, thereby achieving broadband and high-precision impedance measurement.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a common-mode inductor broadband impedance measurement method based on three-port network calibration technology, comprising the following steps:

[0007] Step 1: Design a customized measurement fixture based on the number, size, and distribution of the pins of the common-mode inductor under test, as well as the required impedance type;

[0008] Step 2: Use a calibration piece with known impedance to simulate common-mode inductance, define the relationship coefficients between the impedance analyzer and the measurement fixture through the three-port network equivalent circuit, and solve the relationship coefficients according to Cramer's rule;

[0009] Step 3: Directly measure the common-mode inductance, and use the relationship coefficient to compensate for the parameters of the measurement results to realize the measurement of common-mode inductance impedance.

[0010] Furthermore, step one is detailed as follows:

[0011] Step 11: Obtain the number, radius, and distribution information of the pins of the common-mode inductor under test;

[0012] Steps 1 and 2: Select the type of impedance required;

[0013] Step 13: Design a measuring fixture based on the results determined in Step 11 and Step 12. The measuring fixture is based on a double-sided printed circuit board. Its design includes three considerations: separating the current-carrying and voltage-sensing circuits, keeping the circuit board traces straight or at an obtuse angle, and setting the corresponding pads according to the common-mode inductor pin information.

[0014] Furthermore, step two is detailed as follows:

[0015] Step 21: Insert three sets of calibration pieces into the measuring fixture to obtain the corresponding uncalibrated measurement values. and In the formula, and These represent the induced voltages of the three sets of calibration components in the impedance analyzer. and These represent the excitation currents of the three sets of calibration components in the impedance analyzer;

[0016] Step 22: Establish the impedance matrix Γ to characterize the influence of parasitic parameters of the measurement fixture;

[0017] A measurement device is established, comprising an impedance analyzer, a measuring fixture, and calibration components. The impedance analyzer consists of an excitation current-carrying module and an induced voltage module. The voltage and current corresponding to the excitation current-carrying module are represented as V1 and I1, respectively, and the voltage and current corresponding to the induced voltage module are represented as V2 and I2, respectively. The voltage and current corresponding to the measured object are represented as V3 and I3, respectively. The parasitic impedance of the measuring fixture is characterized by the impedance matrix Γ.

[0018]

[0019] In the formula, Z ij (i, j = 1, 2, 3) represent the coefficients of the impedance matrix Γ in the three-port network of the measuring device. Therefore, the following relationship exists:

[0020]

[0021] At the same time, according to Ohm's law and the measurement principle of impedance analyzers, the following exists:

[0022]

[0023] In the formula, Z M Z represents the uncalibrated measurement value of the analyte. V Z represents the internal resistance of the inductive voltage module. x This represents the actual impedance of the measured object. Expanding the above relationship, we can obtain:

[0024]

[0025]

[0026]

[0027] The final expression is:

[0028]

[0029] In the formula:

[0030]

[0031]

[0032]

[0033] Where A, B, and C are the relationship coefficients;

[0034] Steps 2 and 3: Pre-obtain the actual impedance frequency response of the three sets of calibration components. and

[0035] Step Two Four: Calculate the relationship coefficients A, B, and C;

[0036] Since three sets of uncalibrated measurement values ​​of the calibration pieces have been obtained in the measuring device... and and actual impedance frequency response and Connecting the relationships in step two, we can obtain:

[0037]

[0038]

[0039]

[0040] Therefore, the correlation matrix for the relationship coefficients is as follows:

[0041]

[0042] The relation coefficients A, B, and C can be solved using Cramer's rule.

[0043] Furthermore, step three is detailed below:

[0044] Step 31: Insert the common-mode inductor under test into the measuring fixture to obtain the uncalibrated measurement value Z of the common-mode inductance. n ;

[0045] Step 32: Use relationship coefficients A, B, and C for calibration compensation;

[0046] Step 33: Obtain the frequency response of the common-mode inductor impedance under test

[0047]

[0048] in, The frequency band range is related to the actual impedance frequency response of the calibration piece and the frequency range of the impedance analyzer.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] 1. This invention is based on the principle of an automatic balanced bridge impedance analyzer and features a customized measurement fixture design. It is suitable for common-mode inductors commonly used in power electronics. By designing separate excitation current-carrying and voltage sensing circuits, the influence of parasitic parameters is reduced from the source, thereby increasing measurement accuracy.

[0051] 2. Based on three-port network calibration technology, the relationship coefficients representing the parasitic parameters of the measuring fixture are obtained by using three sets of calibration components with known impedances, and the equivalent circuit that can accurately characterize the measuring device is obtained. Through parameter compensation, high-precision impedance extraction of common mode inductance within 120 MHz can be achieved.

[0052] 3. Commonly used broadband common-mode inductor impedance characterization methods are often based on analytical calculations or numerical simulations, which require a large amount of accurate prior information on component geometry and materials to establish a three-dimensional physical model. The deviation of the information will lead to the distortion of the prediction results, so it is not suitable for third parties to use. At the same time, the process of analytical calculation and numerical simulation is cumbersome and time-consuming, so it is not suitable for large-scale use. In contrast, the method of this invention can be directly measured using measuring instruments and corresponding fixtures, which is more accurate, simpler to operate, and less time-consuming.

[0053] 4. This invention is simple to operate, has a wide frequency range, consumes little time, and has high reliability. It can achieve accurate common-mode inductance impedance characterization, which can promote the selection and optimization design of subsequent electromagnetic interference filter components. It is of great significance for solving electromagnetic interference problems in traditional industries and electric vehicle fields. Attached Figure Description

[0054] Figure 1 This is a flowchart of the common-mode inductor broadband impedance measurement method of the present invention;

[0055] Figure 2 This is a schematic diagram of the structure of a typical common-mode inductor in this invention;

[0056] Figure 3 This is the equivalent circuit diagram for measuring different types of impedance of a typical common-mode inductor in this invention;

[0057] Figure 4 This is the equivalent circuit diagram of the three-port network of the measuring device in this invention;

[0058] Figure 5 These are the magnitudes of the relationship coefficients A, B, and C in the embodiment;

[0059] Figure 6 These are the phases of the relationship coefficients A, B, and C in the embodiment;

[0060] Figure 7 This is a comparison diagram of the amplitude of the three-phase common-mode inductance before and after the relationship coefficient calibration in the embodiment;

[0061] Figure 8 This is a phase comparison diagram of the three-phase common-mode inductors before and after the relationship coefficient calibration in the embodiment;

[0062] Figure 9 This is a measurement accuracy verification diagram from the embodiment. Detailed Implementation

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0064] This invention first obtains the pin information of the common-mode inductor, including the number, radius, and distribution of the pins, to design a customized printed circuit board-type measurement fixture. Simultaneously, based on the characteristics of four-port sensing technology, it separates the test circuits for excitation current carrying and voltage sensing to minimize the influence of introduced parasitic parameters on the measurement. Then, three sets of calibration components with known impedance are inserted into the measurement fixture, and an impedance analyzer is connected to obtain the uncalibrated measurement values ​​corresponding to the three sets of calibration components. A three-port equivalent circuit network of the measurement device, including the impedance analyzer, measurement fixture, and calibration components, is established. The parasitic influence of the measurement fixture is characterized by a 3×3 impedance matrix. Therefore, three relational coefficients can be used to represent the actual impedance of the three sets of calibration components and the uncalibrated measurement values. By using the actual impedance of the three sets of calibration components and the uncalibrated measurement values, the specific values ​​of the three relational coefficients can be determined. Finally, the common-mode inductor is inserted into the measurement fixture to obtain its measurement value before parasitic parameter compensation, and calibration compensation is performed using the known three relational coefficients. Thus, the parasitic parameter influence of the measurement fixture is compensated, resulting in a wide-bandwidth, high-precision impedance frequency response.

[0065] Reference Figure 1 As shown, the common-mode inductor broadband impedance measurement method based on three-port network calibration technology includes the following steps:

[0066] Step 1: Design a customized measurement fixture based on the number, size, and distribution of the pins of the common-mode inductor under test, as well as the required impedance type, as detailed below:

[0067] Step 11: Obtain the number, radius, and distribution information of the pins of the common-mode inductor under test;

[0068] Common-mode inductors are typically single-phase and three-phase common-mode inductors, with structures referencing... Figure 2 As shown, both contain a high-permeability magnetic core. The single-phase common-mode inductor has two sets of copper wire windings and four lead terminals a, a′, b, b′, while the three-phase common-mode inductor has three sets of copper wire windings and six lead terminals a, a′, b, b′, c, c′. The radius and distribution of these lead terminals vary depending on the specific product.

[0069] Steps 1 and 2: Select the type of impedance required;

[0070] Among them, the impedance type of common-mode inductors is generally divided into two types: common-mode information and differential-mode information. The equivalent circuit for measuring the corresponding impedance is referenced. Figure 3 As shown;

[0071] Step 13: Design the measuring fixture based on the results determined in Step 11 and Step 12;

[0072] The measuring fixture is based on a double-sided printed circuit board and is used to adapt to the automatic balancing bridge of the impedance analyzer to provide an electrical circuit between the impedance analyzer and the common-mode inductor under test. Its design includes three considerations: separating the excitation current-carrying and voltage sensing circuits, keeping the circuit board traces straight or obtuse, and setting the corresponding pads according to the pin information of the common-mode inductor.

[0073] Step 2: Use a calibration device with known impedance to simulate the common-mode inductance. Define the relationship coefficients between the impedance analyzer and the measurement fixture through the equivalent circuit of a three-port network, and solve for them according to Cramer's rule, as follows:

[0074] Step 21: Insert three sets of calibration pieces into the measuring fixture to obtain the corresponding uncalibrated measurement values. and In the formula, and These represent the induced voltages of the three sets of calibration components in the impedance analyzer. and These represent the excitation currents of the three sets of calibration components in the impedance analyzer;

[0075] Step 22: Establish the impedance matrix Γ to characterize the influence of parasitic parameters of the measurement fixture;

[0076] Establish a measurement device including an impedance analyzer, measuring fixtures, and calibration components. The equivalent circuit of the three-port network of the measurement device is referenced. Figure 4 As shown, the impedance analyzer is divided into an excitation current-carrying module and an induced voltage module. The voltage and current corresponding to the excitation current-carrying module are represented by C1 and I1, respectively, and the voltage and current corresponding to the induced voltage module are represented by V2 and I2, respectively. The voltage and current corresponding to the measured object are represented by V3 and I3, respectively. For a system where the instrument and fixture are fixed, the parasitic impedance of the measuring fixture can be characterized by the impedance matrix Γ.

[0077]

[0078] In the formula, Z ij (i, j = 1, 2, 3) represent the coefficients of the impedance matrix Γ in the three-port network of the measuring device. Therefore, the following relationship exists:

[0079]

[0080] At the same time, according to Ohm's law and the measurement principle of impedance analyzers, the following exists:

[0081]

[0082] In the formula, Z M Z represents the uncalibrated measurement value of the analyte. VZ represents the internal resistance of the inductive voltage module. x This represents the actual impedance of the measured object. Expanding the above relationship, we can obtain:

[0083]

[0084]

[0085]

[0086] The final expression is:

[0087]

[0088] In the formula:

[0089]

[0090]

[0091]

[0092] Where A, B, and C are the relationship coefficients;

[0093] Steps 2 and 3: Pre-acquire the actual impedance frequency response of the three sets of calibration components. and

[0094] Step Two Four: Calculate the relationship coefficients A, B, and C;

[0095] Since three sets of uncalibrated measurement values ​​of the calibration pieces were obtained in steps 21 and 23, and and actual impedance frequency response and Connecting the relationships in step two, we can obtain:

[0096]

[0097]

[0098]

[0099] Therefore, the correlation matrix for the relationship coefficients is as follows:

[0100]

[0101] The relation coefficients A, B, and C can be solved using Cramer's rule.

[0102] Step 3: Directly measure the common-mode inductance. By using a relationship coefficient to compensate for the measurement results, a wide-bandwidth, high-precision impedance measurement of the common-mode inductance can be achieved. Details are as follows:

[0103] Step 31: Insert the common-mode inductor under test into the measuring fixture to obtain the uncalibrated measurement value Z of the common-mode inductance. n ;

[0104] Step 32: Use relationship coefficients A, B, and C for calibration compensation;

[0105] Step 33: Obtain the frequency response of the common-mode inductor impedance under test

[0106]

[0107] in, The frequency band range is related to the actual impedance frequency response of the calibration device and the frequency range of the impedance analyzer, and the upper limit is generally 120 MHz.

[0108] By applying the three-port network calibration technology through the above steps, high-precision, wide-bandwidth impedance measurement of common-mode inductors is achieved. Compared with traditional methods, the measurement results are more accurate, the frequency range is wider, the operation is simpler, and the time cost is less.

[0109] Example

[0110] Step 1: Using a commercially available three-phase common-mode inductor (Wurth Elektronik 744837002460) as a test case, we obtained a pin count of 6 and a pin radius of 1.95 mm. Regarding the pin distribution, three pins a′, b′, and c′ are distributed on a circle with a diameter of 25 mm centered on the magnetic core, with an angle of 120 degrees between them; the other three pins a, b, and c are distributed on a circle with a diameter of 60 mm centered on the magnetic core, also with an angle of 120 degrees between them. This forms a centrally symmetrical structure with angles of 60 degrees between pins a and a′, b and b′, ​​and c and c′. Taking common-mode impedance measurement as an example, the equivalent circuit is as follows: Figure 3 As shown, the designed measurement fixture is based on a single-layer double-sided printed circuit board, separating the excitation current-carrying and voltage sensing circuits, keeping the circuit board traces straight or obtuse angles, and setting the corresponding pad positions according to the known common-mode inductor pin information. In this execution, a commercial impedance analyzer (Keysight E4990A) is used to perform the corresponding measurements.

[0111] Step 2: Use three sets of calibration pieces with known impedance to simulate the copper wire winding of a common-mode inductor. Insert them into the measuring fixture and measure them using an impedance analyzer to obtain the uncalibrated values ​​of the three sets of calibration pieces in the measuring device. and Establish the corresponding impedance matrix Γ and obtain the expression containing the relationship coefficients A, B, and C. The actual impedance-frequency response of the three sets of calibration components. and The low-frequency common-mode impedances were obtained using an impedance analyzer and a corresponding commercial two-port fixture (Keysight 16047E), and were approximately 1 ohm, 110 ohms, and 6000 ohms. The relationship coefficients A, B, and C in this embodiment were obtained through the calculation steps described in step two of the specific implementation method. The magnitudes of the relationship coefficients are referenced... Figure 5 As shown, the phase reference of the relation coefficients Figure 6 As shown;

[0112] Step 3: Directly measure the common-mode inductance. Calibrate and compensate the measurement results using relationship coefficients A, B, and C. The amplitudes of the three-phase common-mode inductance before and after calibration are referenced... Figure 7 As shown, the phase reference of the three-phase common-mode inductor before and after calibration Figure 8 As shown.

[0113] To verify the accuracy of the calibrated results, test pieces with known impedances were used to replace the three-phase common-mode inductors. Their actual impedance frequency responses (reference values) were also obtained using an impedance analyzer and a corresponding commercial two-port fixture (Keysight 16047E). Their corresponding low-frequency common-mode impedances were approximately 10 ohms, 100 ohms, and 1000 ohms. The measured values ​​obtained after using the measurement fixture and applying three-port network calibration technology were compared with the actual values ​​to demonstrate the high accuracy of this method. Figure 9 As shown, the method of the present invention can achieve wide-bandwidth, high-precision impedance measurement of common-mode inductors in a simple and reliable manner.

[0114] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0115] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A common-mode inductance wide-band impedance measurement method based on three-port network calibration technique, characterized in that: Includes the following steps: Step 1: Design a customized measurement fixture based on the number, size, and distribution information of the pins of the common-mode inductor under test and the required impedance type. The measurement fixture is based on a double-sided printed circuit board. Its design includes three considerations: separating the current-carrying and voltage-sensing circuits, keeping the circuit board traces straight or obtuse, and setting the corresponding pads according to the pin information of the common-mode inductor. Step 2: Use a calibration device with known impedance to simulate common-mode inductance. Define the relationship coefficients between the impedance analyzer and the measurement fixture through a three-port network equivalent circuit, and solve for these coefficients using Cramer's rule, as follows: Step two: Inserting the three sets of calibration pieces into the measurement fixture to obtain corresponding uncalibrated measurements 、 and : , , , where, 、 and represent the induced voltage of the three sets of calibration pieces in the impedance analyzer, 、 and represent the excitation current of the three sets of calibration pieces in the impedance analyzer; Step 22: Establish the impedance matrix To characterize the influence of parasitic parameters of the measurement fixture; A measurement device is established, comprising an impedance analyzer, a measuring fixture, and calibration components. The impedance analyzer is divided into an excitation current-carrying module and an induced voltage module. The voltage and current corresponding to the excitation current-carrying module are expressed as follows: and The voltage and current corresponding to the sensing voltage module are expressed as follows: and The corresponding voltage and current of the measured object are expressed as follows: and The parasitic impedance of the measuring fixture is measured using an impedance matrix. Characterization: In the formula, ( () represents the impedance matrix in the three-port network of the measuring device. The coefficients of , therefore, the following relationship exists: At the same time, according to Ohm's law and the measurement principle of impedance analyzers, the following exists: ， ， In the formula, This represents the uncalibrated measurement value of the measured object. This indicates the internal resistance of the sensing voltage module. This represents the actual impedance of the measured object. Expanding the above relationship, we can obtain: The final expression is: In the formula: in, , and The coefficient represents the relationship. Steps 2 and 3: Pre-obtain the actual impedance frequency response of the three sets of calibration components. , and ; Step Two Four: Calculate the Relationship Coefficient , and ; Since three sets of uncalibrated measurement values ​​of the calibration pieces have been obtained in the measuring device... , and and actual impedance frequency response , and Connecting this to the relation in step two, we can obtain: Therefore, the correlation matrix for the relationship coefficients is as follows: The correlation coefficients can be solved using Cramer's rule. , and ; Step 3: Directly measure the common-mode inductance, and use the relationship coefficient to compensate for the parameters of the measurement results to realize the measurement of common-mode inductance impedance.

2. The common-mode inductor broadband impedance measurement method based on three-port network calibration technology according to claim 1, characterized in that: Step one is described in detail as follows: Step 11: Obtain the number, radius, and distribution information of the pins of the common-mode inductor under test; Steps 1 and 2: Select the type of impedance required; Step 13: Design a measuring fixture based on the results determined in Step 11 and Step 12. The measuring fixture is based on a double-sided printed circuit board. Its design includes three considerations: separating the current-carrying and voltage-sensing circuits, keeping the circuit board traces straight or at an obtuse angle, and setting the corresponding pads according to the common-mode inductor pin information.

3. The common-mode inductor broadband impedance measurement method based on three-port network calibration technology according to claim 1, characterized in that: Step three is described in detail below: Step 31: Insert the common-mode inductor under test into the measurement fixture to obtain the uncalibrated measurement value of the common-mode inductance. ; Step 32: Using Relationship Coefficients , and Perform calibration compensation; Step 33: Obtain the frequency response of the common-mode inductor impedance under test : in, The frequency band range is related to the actual impedance frequency response of the calibration piece and the frequency range of the impedance analyzer.

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