A method and apparatus for determining the insertion loss of an EMI filter

Abstract

The present application relates to the technical field of power electronics, and particularly relates to a method and device for determining the insertion loss of an EMI filter. The method comprises: obtaining a noise source impedance and a load impedance corresponding to each frequency point in a preset frequency range when the filter is not connected; obtaining an equivalent impedance of the filter when connected in series between the noise source and the load based on the characteristic of the forward transmission coefficient of the filter under a standard characteristic impedance varying with frequency; determining a first load voltage and a second load voltage based on the source impedance, the load impedance and the equivalent impedance, wherein the first load voltage is the load voltage corresponding to each frequency point before the filter is connected, and the second load voltage is the load voltage corresponding to each frequency point after the filter is connected; and obtaining the insertion loss of the filter corresponding to each frequency point in the preset frequency range based on the first load voltage and the second load voltage. The above technical solution can improve the measurement accuracy and calculation efficiency of the insertion loss.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method and apparatus for determining the insertion loss of an EMI filter. Background Technology

[0002] In power electronic equipment and systems, the high-frequency switching action of power devices will generate serious electromagnetic interference conducted emissions. EMI filters are usually installed to suppress noise. Accurately predicting the insertion loss of EMI filters under actual operating conditions is the key to ensuring the effectiveness of filter design.

[0003] In existing technologies, insertion loss is typically predicted using derivation methods based on T-parameters and measurement methods based on S-parameters. However, T-parameter-based methods rely on ideal open-circuit and short-circuit boundary conditions, which are disrupted by parasitic parameters under high-frequency operating conditions, leading to significant measurement difficulties and insufficient accuracy. S-parameter-based methods are strictly dependent on the 50Ω standard characteristic impedance, making them unsuitable for adapting to variations in noise source and load impedances in real-world engineering scenarios. Furthermore, using generalized scattering parameters for modeling involves solving complex high-order equations, resulting in computational redundancy and inefficiency.

[0004] Therefore, there is an urgent need to provide a new technical solution to address the aforementioned technical problems. Summary of the Invention

[0005] This invention provides a method and apparatus for determining the insertion loss of an EMI filter, which can improve the measurement accuracy and calculation efficiency of insertion loss.

[0006] In a first aspect, embodiments of the present invention provide a method for determining the insertion loss of an EMI filter, comprising: Obtain the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range when no filter is connected; Based on the characteristic of the filter's forward transmission coefficient changing with frequency under standard characteristic impedance, the equivalent impedance of the filter when connected in series between the noise source and the load is obtained. Based on the source impedance, load impedance, and equivalent impedance, the first load voltage and the second load voltage are determined respectively. The first load voltage is the load voltage at each frequency point corresponding to the two ends of the load before the filter is connected, and the second load voltage is the load voltage at each frequency point corresponding to the two ends of the load after the filter is connected. Based on the first load voltage and the second load voltage, the insertion loss of the filter at each frequency point within the preset frequency range is obtained.

[0007] Secondly, embodiments of the present invention also provide an insertion loss determination apparatus for an EMI filter, comprising: The source impedance determination module obtains the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range when no filter is connected. The equivalent impedance determination module, connected to the source impedance determination module, obtains the equivalent impedance of the filter when it is connected in series between the noise source and the load based on the characteristic that the forward transmission coefficient of the filter changes with frequency under the standard characteristic impedance. The load voltage determination module is connected to the equivalent impedance determination module. Based on the source impedance, load impedance and equivalent impedance, it determines the first load voltage and the second load voltage, respectively. The first load voltage is the load voltage at each frequency point before the filter is connected, and the second load voltage is the load voltage at each frequency point after the filter is connected. The insertion loss determination module is connected to the load voltage determination module. Based on the first load voltage and the second load voltage, it obtains the insertion loss of the filter at each frequency point within a preset frequency range.

[0008] Thirdly, embodiments of the present invention also provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it implements the method described in any embodiment of the present invention.

[0009] Fourthly, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the methods described in any embodiment of the present invention.

[0010] This invention provides a method and apparatus for determining the insertion loss of an EMI filter. It can obtain the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range under actual operating conditions. Utilizing the characteristic that the forward transmission coefficient of the filter changes with frequency under standard characteristic impedance, the filter is equivalent to the impedance connected in series between the noise source and the load. The insertion loss is then obtained by calculating and comparing the load voltage before and after the filter is connected. Without knowing the filter's internal topology and component parameters, the equivalent impedance corresponding to each frequency point within the preset frequency range can be extracted solely based on the externally measurable forward transmission coefficient. This effectively avoids the problems of the T-parameter method at high frequencies, where parasitic effects cause the ideal open / short circuit boundary conditions to fail, and the measurement difficulties and insufficient accuracy of its calculation results, which are easily affected by load fluctuations. It improves computational efficiency and engineering practicality while ensuring prediction accuracy. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a flowchart of the method for determining the insertion loss of an EMI filter provided in an embodiment of the present invention; Figure 2 This is a hardware architecture diagram of the electronic device provided in an embodiment of the present invention; Figure 3 This is a structural diagram of the insertion loss determination device for an EMI filter provided in an embodiment of the present invention; Figure 4 This is an equivalent circuit diagram provided by an embodiment of the present invention for extracting common-mode source impedance using a single inductor method; Figure 5 This is an equivalent circuit diagram provided by an embodiment of the present invention for extracting differential-mode source impedance using a single capacitor method; Figure 6 This is a schematic diagram illustrating the definition of an S-parameter provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of an S-parameter standard circuit provided in an embodiment of the present invention; Figure 8 This is an equivalent circuit diagram provided by an embodiment of the present invention when no filter is connected; Figure 9 This is an equivalent circuit diagram of a filter provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of measured common-mode noise without a filter provided in an embodiment of the present invention; Figure 11 This is a measured common-mode noise with added filter provided in an embodiment of the present invention; Figure 12 This is an embodiment of the present invention providing a common-mode noise source impedance amplitude curve under actual operating conditions; Figure 13 This is a schematic diagram of an ideal S-parameter curve of a filter provided in an embodiment of the present invention; Figure 14 This is a schematic diagram comparing an insertion loss curve with a measured insertion loss curve provided in an embodiment of the present invention; Figure 15 This is a data table provided in an embodiment of the present invention for a filter, such as a loss prediction process. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but 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.

[0014] Please refer to Figure 1 This invention provides a method for determining the insertion loss of an EMI filter, the method comprising: Step 100: Obtain the noise source impedance and load impedance corresponding to each frequency point within the preset frequency range when no filter is connected; Step 102: Based on the characteristics of the filter's forward transmission coefficient changing with frequency under standard characteristic impedance, obtain the equivalent impedance of the filter when connected in series between the noise source and the load. Step 104: Determine the first load voltage and the second load voltage based on the source impedance, load impedance, and equivalent impedance, respectively; Wherein, the first load voltage is the load voltage at each frequency point corresponding to the two ends of the load before the filter is connected, and the second load voltage is the load voltage at each frequency point corresponding to the two ends of the load after the filter is connected; Step 106: Based on the first load voltage and the second load voltage, obtain the insertion loss of the filter at each frequency point within the preset frequency range.

[0015] In this embodiment, in practical applications, the noise source impedance and load impedance are usually not constant resistance values, but complex impedances exhibiting complex phase-change characteristics as the frequency changes. Therefore, the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range are extracted. The forward transmission coefficient is obtained based on the filter's scattering parameters, thereby deriving the filter's equivalent impedance. After obtaining the noise source impedance, load impedance, and equivalent impedance, the first load voltage before the filter and the second load voltage after the filter are calculated using formulas, and the filter's insertion loss is calculated based on the first and second load voltages.

[0016] It should be noted that the scattering coefficient of a filter is a general standard parameter used to characterize the high-frequency characteristics of a two-port network. When the standard S-parameters are directly applied to actual circuits where the source impedance or load impedance deviates from 50Ω, the S-parameters cannot directly reflect the signal transmission behavior in the actual circuit due to the port reflection effect. In this embodiment, by converting the scattering parameter into an equivalent impedance, a mapping from the normalized parameter in the RF domain to the physical impedance in the low-frequency circuit domain can be achieved. This conversion allows the EMI filter to be abstracted as an impedance element with a definite ohmic value, thereby eliminating the impedance reference difference between the standard test environment and the actual application environment.

[0017] In one embodiment of the present invention, the equivalent impedance of the filter is calculated using the following formula: in, For equivalent impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

[0018] In this embodiment, as Figure 6 and Figure 7 As shown, in a standard S-parameter test environment, both the source impedance and the load impedance are equal to the standard characteristic impedance Z0 (usually 50Ω). Figure 13 The ideal S-parameter curves of the EMI filter in this implementation are shown. For most EMI filters, the topology in the low-frequency band or after common-mode / differential-mode decoupling can be equivalent to a series impedance model. Based on the conversion relationship between the ABCD parameters and S-parameters of a two-port network, under impedance matching conditions, the forward transmission coefficient S... 21 With series impedance Z EMI A definite functional correspondence exists. By simplifying and solving the transmission equation, the above formula for calculating the equivalent impedance can be obtained. In this formula, the external characteristics of the filter (i.e., the transmission attenuation of the signal as it passes through the filter) are transformed into an equivalent impedance value connected in series between the noise source and the load. Without knowing the internal component parameters and topology of the filter, the equivalent impedance can be calculated solely from the externally measurable forward transmission coefficient. This allows for the subsequent mapping of data from standard S-parameter testing environments to actual circuits to calculate the insertion loss under real-world operating conditions.

[0019] It should be noted that the embodiments of the present invention are illustrated using a series model as an example. In actual use, if the filter exhibits parallel or other composite topology characteristics, the appropriate equivalent impedance expression can also be derived based on the corresponding ABCD parameter transformation relationship.

[0020] In one embodiment of the present invention, the insertion loss is calculated using the following formula: in, For insertion loss, For the noise source impedance, For load impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

[0021] In this embodiment, the insertion loss is calculated by comparing the load voltage before and after the EMI filter is added. Insertion loss is the ratio of the voltage received on the load before and after the filter is connected. Since the common unit of voltage is amplitude and the common unit of insertion loss is decibel (dB), it is necessary to take the logarithm of the voltage ratio.

[0022] Will Substituting into the above equation and rearranging, we get: because It is generally expressed in logarithmic form, and the above expression can be further transformed as follows: In the above formula, the impedance unit is Ω, and the S-parameter is a dimensionless complex number, which can be represented by dB. For example... Figure 14 The figure shows a comparison between the insertion loss curve calculated by the method of the present invention and the actual test results. Figure 15 This is a data table for intermediate parameters in each step.

[0023] As can be seen, given the actual operating impedance and the standard S-parameters of the filter, the predicted insertion loss can be obtained directly through a single algebraic operation, without the need to construct high-order equations and perform tedious iterative solutions as required by the generalized scattering parameter method. This reduces algorithm complexity, improves prediction efficiency, and is suitable for rapid parameter scanning and optimization during the engineering design phase.

[0024] In one embodiment of the present invention, the noise source impedance includes common-mode source impedance and differential-mode source impedance; The common-mode source impedance is calculated using the following formula: in, For common-mode equivalent load resistance, For common-mode source impedance, The amplitude of the common-mode inductance, This is the measured common-mode attenuation value; The differential-mode source impedance is calculated using the following formula: in, This is the measured differential mode attenuation value. For differential mode source impedance, This represents the amplitude of the differential-mode capacitor.

[0025] In this embodiment, as Figure 4 As shown, when extracting the common-mode source impedance using the single-inductor method, a common-mode inductor with a known amplitude is connected in series in the common-mode noise loop. The specific process for determining the common-mode source impedance based on attenuation data and the impedance values ​​of known impedance components includes: determining the impedance locus circle of the common-mode source impedance based on the amplitude of the common-mode inductor, the measured common-mode attenuation value, and the common-mode equivalent load resistance; determining the maximum and minimum possible values ​​of the common-mode source impedance based on the impedance locus circle; and using the average of the maximum and minimum possible values ​​as the common-mode source impedance. Figure 5 As shown, when extracting the differential-mode source impedance using the single-capacitor method, a differential-mode capacitor with a known amplitude is connected across the differential-mode noise circuit. The specific process for determining the differential-mode source impedance based on attenuation data and the impedance values ​​of known impedance components includes: under the condition that the differential-mode source impedance is much smaller than the differential-mode equivalent load resistance, determining the differential-mode source impedance based on the measured differential-mode attenuation value and the amplitude of the differential-mode capacitor. Figure 10 and Figure 11 The measured common-mode noise in this embodiment is shown with and without a filter. Figure 12 The common-mode noise source impedance amplitude curve under actual operating conditions extracted in this implementation case is shown.

[0026] In one embodiment of the present invention, the first load voltage is calculated using the following formula: in, The first load voltage, For noise source voltage, For the noise source impedance, This is the load impedance.

[0027] In this embodiment, as Figure 8 As shown, without an EMI filter, the noise source directly supplies power to the load, and the source impedance and load impedance are connected in series to divide the voltage. According to Kirchhoff's voltage law, the voltage across the load in this case is the first load voltage, which is calculated as the ratio of the load impedance to the sum of the source impedance and the load impedance, multiplied by the noise source voltage. The first load voltage provides a reference value for subsequent calculations of insertion loss.

[0028] In one embodiment of the present invention, the second load voltage is calculated using the following formula: in, This is the second load voltage. For noise source voltage, For the noise source impedance, For load impedance, This is the equivalent impedance.

[0029] In this embodiment, as Figure 9 As shown, after connecting the EMI filter, the filter is connected in series between the noise source and the load in the form of its equivalent impedance. At this time, the noise source, the filter's equivalent impedance, and the load impedance are connected in series, resulting in a voltage divider. The voltage across the load is the second load voltage, which is calculated as follows: first, the voltage divider across the filter is determined by the ratio of the filter's equivalent impedance to the sum of the source impedance and the filter's equivalent impedance; then, the voltage divider across the load is determined by the ratio of the load impedance to the sum of the filter's equivalent impedance and the load impedance; multiplying these two values ​​and then multiplying by the noise source voltage gives the second load voltage. By comparing the first and second load voltages, the change in load voltage before and after connecting the filter can be determined.

[0030] In one embodiment of the present invention, the forward transmission coefficient is obtained as follows: With the filter connected to the working circuit and the working circuit in normal operation, the first noise signal at the filter input terminal and the second noise signal at the output terminal are collected. The first noise signal is the broadband noise signal generated by the switching of the power devices in the working circuit. The first spectral amplitude of the first noise signal at each frequency point within a preset frequency range and the second spectral amplitude of the second noise signal at each frequency point within a preset frequency range are obtained respectively. The forward transmission coefficient of the filter at each frequency point is obtained based on the ratio of the second spectral amplitude to the first spectral amplitude at each frequency point.

[0031] In this embodiment, as Figure 4 As shown, the EMI filter is connected to the operating circuit, and the operating circuit is in normal operation. Power devices in the operating circuit (such as IGBTs and MOSFETs) generate broadband high-frequency noise during normal switching. The spectrum of this noise signal covers the operating frequency band of the EMI filter (e.g., 150kHz-30MHz). In this embodiment, this naturally occurring switching noise is used as a test signal, allowing for online extraction of the forward transmission coefficient without the need for any additional external signals, while the filter is operating normally.

[0032] Specifically, current or voltage probes are installed at the input and output ends of the filter to simultaneously acquire the first noise signal at the input and the second noise signal at the output. To ensure phase consistency of the two signals during frequency domain analysis, the input and output probes use the same trigger signal or clock source for synchronous sampling, ensuring precise alignment of the two signals on the time axis. The acquired time-domain signals are converted into frequency-domain signals via Fourier transform to obtain the first spectral amplitude of the input noise signal at each frequency point within a preset frequency range, and the second spectral amplitude of the output noise signal at each frequency point within the same preset frequency range. The forward transmission coefficient can be obtained under normal filter operation without shutdown, circuit disconnection, filter disassembly, or external signal source injection. When this method is combined with the aforementioned insertion loss determination method, real-time online monitoring of the filter's insertion loss during actual operation can be achieved. If the insertion loss in a certain frequency band decreases significantly, it indicates filter performance degradation, triggering a maintenance alarm in a timely manner, thereby achieving online diagnosis and early warning of the filter's health status.

[0033] It should be noted that the amplitude difference between the input and output signals originates from the attenuation effect of the filter on the noise signal. Therefore, for each frequency point within the preset frequency range, comparing the second spectral amplitude with the first spectral amplitude yields the amplitude of the forward transmission coefficient corresponding to that frequency point. By calculating all frequency points in this manner, the forward transmission coefficient of the filter at each frequency point within the preset frequency range can be obtained.

[0034] like Figure 2 , Figure 3 As shown, this embodiment of the invention provides a device for determining the insertion loss of an EMI filter. The device embodiment can be implemented in software, hardware, or a combination of both. From a hardware perspective, as... Figure 2 The diagram shown is a hardware architecture diagram of an electronic device for determining the insertion loss of an EMI filter, as provided in an embodiment of the present invention. (Except for...) Figure 2 In addition to the processor, memory, network interface, and non-volatile memory shown, the electronic device in the embodiment may also include other hardware, such as a forwarding chip responsible for processing packets. Taking software implementation as an example, such as... Figure 3 As shown, a device in a logical sense is formed by the CPU of the electronic device in which it is located reading the corresponding computer program from the non-volatile memory into the memory for execution.

[0035] This embodiment provides an insertion loss determination device for an EMI filter, comprising: The source impedance determination module 300 acquires the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range when no filter is connected. The equivalent impedance determination module 302 is connected to the source impedance determination module. Based on the characteristic that the forward transmission coefficient of the filter changes with frequency under the standard characteristic impedance, it obtains the equivalent impedance of the filter when it is connected in series between the noise source and the load. The load voltage determination module 304 is connected to the equivalent impedance determination module. Based on the source impedance, load impedance and equivalent impedance, it determines the first load voltage and the second load voltage, respectively. The first load voltage is the load voltage at each frequency point corresponding to the two ends of the load before the filter is connected, and the second load voltage is the load voltage at each frequency point corresponding to the two ends of the load after the filter is connected. The insertion loss determination module 306 is connected to the load voltage determination module. Based on the first load voltage and the second load voltage, it obtains the insertion loss of the filter corresponding to each frequency point within a preset frequency range.

[0036] In this embodiment of the invention, the source impedance determination module 300 can be used to execute step 100 in the above method embodiment, the equivalent impedance determination module 302 can be used to execute step 102 in the above method embodiment, the load voltage determination module 304 can be used to execute step 104 in the above method embodiment, and the insertion loss determination module 304 can be used to execute step 104 in the above method embodiment.

[0037] In one embodiment of the present invention, the equivalent impedance of the filter is calculated using the following formula: in, For equivalent impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

[0038] In one embodiment of the present invention, the insertion loss is calculated using the following formula: in, For insertion loss, For the noise source impedance, For load impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

[0039] In one embodiment of the present invention, the noise source impedance includes common-mode source impedance and differential-mode source impedance; The common-mode source impedance is calculated using the following formula: in, For common-mode equivalent load resistance, For common-mode source impedance, The amplitude of the common-mode inductance, This is the measured common-mode attenuation value; The differential-mode source impedance is calculated using the following formula: in, This is the measured differential mode attenuation value. For differential mode source impedance, This represents the amplitude of the differential-mode capacitor.

[0040] In one embodiment of the present invention, the first load voltage is calculated using the following formula: in, The first load voltage, For noise source voltage, For the noise source impedance, This is the load impedance.

[0041] In one embodiment of the present invention, the second load voltage is calculated using the following formula: in, This is the second load voltage. For noise source voltage, For the noise source impedance, For load impedance, This is the equivalent impedance.

[0042] In one embodiment of the present invention, the forward transmission coefficient is obtained in the following manner: With the filter connected to the working circuit and the working circuit in normal operation, the first noise signal at the input terminal and the second noise signal at the output terminal of the filter are collected. The first noise signal is a broadband noise signal generated by the switching of power devices in the working circuit. The first spectral amplitude of the first noise signal at each frequency point within a preset frequency range and the second spectral amplitude of the second noise signal at each frequency point within the preset frequency range are respectively obtained. The forward transmission coefficient of the filter at each frequency point is obtained based on the ratio of the second spectral amplitude to the first spectral amplitude at each frequency point.

[0043] It is understood that the structures illustrated in the embodiments of the present invention do not constitute a specific limitation on an insertion loss determination device for an EMI filter. In other embodiments of the present invention, an insertion loss determination device for an EMI filter may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0044] The information interaction and execution process between the modules in the above-mentioned device are based on the same concept as the method embodiment of the present invention, and the specific details can be found in the description of the method embodiment of the present invention, and will not be repeated here.

[0045] This invention also provides an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements a method for determining the insertion loss of an EMI filter according to any embodiment of this invention.

[0046] This invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform an insertion loss determination method for an EMI filter according to any embodiment of this invention.

[0047] Specifically, a system or apparatus equipped with a storage medium may be provided, on which software program code implementing the functions of any of the embodiments described above is stored, and the computer (or CPU or MPU) of the system or apparatus may read and execute the program code stored in the storage medium.

[0048] In this case, the program code read from the storage medium can itself implement the function of any of the above embodiments, and therefore the program code and the storage medium storing the program code constitute part of the present invention.

[0049] Storage media embodiments for providing program code include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tapes, non-volatile memory cards, and ROMs. Alternatively, program code can be downloaded from a server computer via a communication network.

[0050] Furthermore, it should be clear that not only can the program code read by the computer be executed, but also the operating system or other components operating on the computer can be instructed based on the program code to perform some or all of the actual operations, thereby realizing the function of any of the embodiments described above.

[0051] Furthermore, it is understood that the program code read from the storage medium is written to the memory set in the expansion board inserted into the computer or to the memory set in the expansion module connected to the computer. Then, based on the instructions of the program code, the CPU or other components installed on the expansion board or expansion module execute some and all of the actual operations, thereby realizing the function of any of the above embodiments.

[0052] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or electronic device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or electronic device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or electronic device that includes said element.

[0053] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various storage media that can store program code, such as ROM, RAM, magnetic disk, or optical disk.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the insertion loss of an EMI filter, characterized in that, include: Obtain the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range when no filter is connected; Based on the characteristic of the filter's forward transmission coefficient changing with frequency under standard characteristic impedance, the equivalent impedance of the filter when connected in series between the noise source and the load is obtained. Based on the source impedance, load impedance, and equivalent impedance, the first load voltage and the second load voltage are determined respectively. The first load voltage is the load voltage at each frequency point corresponding to the two ends of the load before the filter is connected, and the second load voltage is the load voltage at each frequency point corresponding to the two ends of the load after the filter is connected. Based on the first load voltage and the second load voltage, the insertion loss of the filter at each frequency point within the preset frequency range is obtained.

2. The method according to claim 1, characterized in that, The equivalent impedance of the filter is calculated using the following formula: in, For equivalent impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

3. The method according to claim 1, characterized in that, The insertion loss is calculated using the following formula: in, For insertion loss, For the noise source impedance, For load impedance, For standard characteristic impedance, This represents the forward transmission coefficient.

4. The method according to claim 1, characterized in that, The noise source impedance includes common-mode source impedance and differential-mode source impedance; The common-mode source impedance is calculated using the following formula: in, For common-mode equivalent load resistance, For common-mode source impedance, The amplitude of the common-mode inductance, This is the measured common-mode attenuation value; The differential-mode source impedance is calculated using the following formula: in, This is the measured differential mode attenuation value. For differential mode source impedance, This represents the amplitude of the differential-mode capacitor.

5. The method according to claim 1, characterized in that, The first load voltage is calculated using the following formula: in, The first load voltage, For noise source voltage, For the noise source impedance, This is the load impedance.

6. The method according to claim 1, characterized in that, The second load voltage is calculated using the following formula: in, This is the second load voltage. For noise source voltage, For the noise source impedance, For load impedance, This is the equivalent impedance.

7. The method according to claim 1, characterized in that, The forward transmission coefficient is obtained in the following way: With the filter connected to the working circuit and the working circuit in normal operation, the first noise signal at the input terminal and the second noise signal at the output terminal of the filter are collected. The first noise signal is a broadband noise signal generated by the switching of power devices in the working circuit. The first spectral amplitude of the first noise signal at each frequency point within a preset frequency range and the second spectral amplitude of the second noise signal at each frequency point within the preset frequency range are respectively obtained. The forward transmission coefficient of the filter at each frequency point is obtained based on the ratio of the second spectral amplitude to the first spectral amplitude at each frequency point.

8. An apparatus for determining the insertion loss of an EMI filter, characterized in that, include: The source impedance determination module obtains the noise source impedance and load impedance corresponding to each frequency point within a preset frequency range when no filter is connected. The equivalent impedance determination module, connected to the source impedance determination module, obtains the equivalent impedance of the filter when it is connected in series between the noise source and the load based on the characteristic that the forward transmission coefficient of the filter changes with frequency under the standard characteristic impedance. The load voltage determination module is connected to the equivalent impedance determination module. Based on the source impedance, load impedance and equivalent impedance, it determines the first load voltage and the second load voltage, respectively. The first load voltage is the load voltage at each frequency point corresponding to the two ends of the load before the filter is connected, and the second load voltage is the load voltage at each frequency point corresponding to the two ends of the load after the filter is connected. The insertion loss determination module is connected to the load voltage determination module. Based on the first load voltage and the second load voltage, it obtains the insertion loss of the filter at each frequency point within a preset frequency range.

9. An electronic device, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed in a computer, causes the computer to perform the method described in any one of claims 1-7.

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