EMI filter optimization method and system based on noise source impedance

Abstract

The invention belongs to the technical field of filter optimization, and discloses an EMI filter optimization method and system based on noise source impedance, and the method comprises the steps: measuring the noise source impedance and original noise corresponding to a common mode and a differential mode of a converter, judging an insertion loss demand based on the original noise, and determining a concerned frequency point through the insertion loss demand; the capacitance value of the safety capacitor is determined based on a capacitance value judgment rule, after the impedance characteristic value of the safety capacitor is determined according to the capacitance value, the impedance characteristic value is used for analyzing the inductance value needed by the concerned frequency point under the topological cluster, and a common-mode topological structure is determined; selecting a magnetic core based on a magnetic core selection rule, determining the number of turns required by the inductor corresponding to the concerned frequency point and the total differential mode capacity according to the magnetic core information, and selecting a differential mode optimal topology by using the total differential mode capacity; and determining a filter optimization scheme according to the common-mode and differential-mode optimal topology and the impedance characteristic value. According to the method, quantitative accurate optimization topology and parameter optimization design functions of the filter are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of filter optimization, and in particular to an EMI filter optimization method and system based on noise source impedance. Background Art

[0002] EMI filters are divided into passive and active types. Passive filters are composed of passive devices such as inductors and capacitors. They have low cost, relatively mature technology, and stable performance and have been widely used. Active EMI filters contain active device operational amplifiers, which can amplify the sampled noise (current or voltage) through operational amplifiers to compensate for a noise current or voltage with an opposite phase. Due to system bandwidth limitations, compared with passive EMI filters, active EMI filters have certain advantages in frequency bands below 10MHz, and passive filters are still needed to solve high frequency bands.

[0003] As the switching frequency of power converters increases, electromagnetic interference problems caused by high voltage change rates become more serious. The current means of suppressing conducted EMI include: frequency jitter technology, PCB layout optimization, soft switching technology, offset technology, filter technology, etc. The first four technologies reduce the amplitude of the noise source through different methods. However, from the existing research results, few products can completely solve the problem of excessive conducted EMI without installing EMI filters. Therefore, EMI filters are indispensable components of electrical equipment.

[0004] The EMI filter scheme in the prior art is designed based on the insertion loss relationship derived under the condition of ideal noise source impedance. However, the noise source impedance of the actual circuit varies greatly with frequency and it is impossible to meet the assumed conditions in the entire frequency band. At the same time, the actual filtering inductance and capacitance also have frequency characteristics, and the performance of the filter can only be brought into play when they are mismatched with the noise source impedance and load impedance.

[0005] Therefore, how to provide an EMI filter optimization method and system based on noise source impedance is a problem that needs to be solved urgently. Summary of the invention

[0006] The embodiment of the present invention provides an EMI filter optimization method and system based on noise source impedance to solve the problem in the prior art that the noise source impedance of the actual circuit varies greatly with frequency and cannot meet the assumed conditions in the entire frequency band.

[0007] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0008] According to a first aspect of an embodiment of the present invention, a method for optimizing an EMI filter based on noise source impedance is provided.

[0009] In one embodiment, a method for optimizing an EMI filter based on noise source impedance includes:

[0010] Measure the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determine the insertion loss requirement based on the original noise, and use the insertion loss requirement to determine the frequency of interest;

[0011] Determine the capacitance of the safety capacitor based on the capacitance determination rule. After determining the impedance characteristic value of the safety capacitor based on the capacitance, use the impedance characteristic value to analyze the inductance value required for the frequency point of interest under the topology cluster and determine the common mode topology structure.

[0012] Select the core based on the core selection rules, determine the required number of inductor turns and total differential mode capacitance corresponding to the frequency of interest based on the core information, and use the total differential mode capacitance to select the optimal differential mode topology;

[0013] The filter optimization scheme is determined based on the optimal topology and impedance characteristic values ​​of common mode and differential mode, and a test prototype is built using the optimization scheme to determine the application effect of the filter. The filter optimization scheme is adjusted based on the judgment results.

[0014] In one embodiment, measuring the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determining the insertion loss requirement based on the original noise, and determining the frequency point of interest using the insertion loss requirement includes:

[0015] The noise source impedance corresponding to the common mode and differential mode of the converter is measured based on the noise path analysis method, and the input frequency is set according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter;

[0016] Obtain the difference between the original noise and the noise limit, and add the difference result to the threshold to determine the insertion loss requirements corresponding to the common mode and differential mode of the converter, and determine the required insertion loss spectrum based on the insertion loss requirements;

[0017] Based on the preset frequency curve range, select the oblique line to approach the required insertion loss spectrum in the defined order to perform frequency response analysis, and select the tangent frequency point according to the analysis results;

[0018] The tangent frequency points are arranged in the order of reaching the tangent state, and a preset number of groups of tangent frequency points are selected as focus frequencies based on the arrangement result.

[0019] In one embodiment, the preset frequency curve range is 20 dB / dec-60 dB / dec, and the order direction is defined from left to right.

[0020] In one embodiment, the capacitance of the safety capacitor is determined based on the capacitance determination rule, and after the impedance characteristic value of the safety capacitor is determined according to the capacitance, the impedance characteristic value is used to analyze the inductance value required for the frequency point of interest under the topology cluster, and the common mode topology structure is determined, including:

[0021] Select a safety capacitor based on a preset electromagnetic compatibility rule, determine the capacitance corresponding to the safety capacitor according to the selection result, and determine the resonant frequency of the safety capacitor using the capacitance result;

[0022] Determine the impedance characteristic value of the safety capacitor based on the resonant frequency and impedance analysis technology, and analyze the complete insertion loss under the topological cluster according to the loss calculation function set;

[0023] The impedance characteristic value, interactive analysis technology, complete insertion loss and common-mode noise source impedance are combined to calculate the common-mode inductance value required to meet the insertion loss requirement at the common-mode focus frequency under the topology cluster, and the topology corresponding to the minimum inductance value is selected as the common-mode optimal topology.

[0024] In one embodiment, the loss calculation function set includes a CL filter insertion loss calculation function, an LC filter insertion loss calculation function, a CLC filter insertion loss calculation function, and an LCL filter insertion loss calculation function;

[0025] Among them, the expression of the CL filter insertion loss calculation function is:

[0026]

[0027] In the formula, IL CL Represents the complete insertion loss value of the CL filter, Z L represents the equivalent load impedance, Z s is the noise source impedance, Z LCM represents the common mode inductance, Z Cy Indicates the safety capacitor impedance.

[0028] In one embodiment, a magnetic core is selected based on a magnetic core selection rule, the required number of turns of the inductor corresponding to the frequency point of interest and the total differential mode capacitance are determined according to the magnetic core information, and the optimal differential mode topology is selected using the total differential mode capacitance, including:

[0029] Obtain vacuum magnetic permeability and effective cross-sectional area corresponding to the candidate magnetic core, and combine the vacuum magnetic permeability, effective cross-sectional area and effective length of the magnetic circuit to obtain the inductance factor of the candidate magnetic core;

[0030] Based on the inductance factor and preset rules, the candidate magnetic core with the highest inductance factor and the highest saturation magnetic density is selected as the target magnetic core, and the required number of turns of the magnetic core of the differential mode inductor under the differential mode focus frequency condition is calculated according to the common mode inductance value and the inductance factor;

[0031] Select the number of turns required for the highest core of the differential mode inductor, and perform the common mode winding test according to the number of turns result, and use the test results to obtain the differential mode inductor impedance characteristics and the leakage inductance of the common mode inductor;

[0032] The common-mode leakage inductance is used as the differential-mode inductance, and combined with the differential-mode noise source impedance to calculate the total differential-mode capacitance required for the topology cluster to meet the insertion loss requirements under the differential-mode focus frequency conditions. The topology with the smallest total differential-mode capacitance is selected as the optimal differential-mode topology.

[0033] In one embodiment, the calculation formula of the inductance factor is:

[0034]

[0035] In the formula, A L (f) represents the inductance factor, μ o A represents the vacuum permeability, e represents the effective cross-sectional area of ​​the magnetic core, l represents the effective length of the magnetic circuit, f represents the frequency, μ r Indicates the relative magnetic permeability of the core.

[0036] In one embodiment, a filter optimization scheme is determined according to the common mode and differential mode optimal topology and impedance characteristic values, and a test prototype is built using the optimization scheme to determine the application effect of the filter. Adjusting the filter optimization scheme based on the determination result includes:

[0037] Define the filter optimization scheme according to the common-mode optimal topology, the differential-mode optimal topology and the corresponding impedance characteristic values, and use the optimization scheme to build a filter test machine. Compare the volume difference between the filter test machine and the historical filter based on the construction results;

[0038] Based on the simulation technology, the filter test machine is installed on the simulation prototype to obtain the common mode noise and differential mode noise corresponding to the filter test machine;

[0039] The noise difference between the common mode noise, differential mode noise and historical noise value is obtained, and the application effect of the filter under the optimization scheme design is judged based on the noise difference and the volume difference, and the filter optimization scheme is adjusted based on the judgment result.

[0040] According to a second aspect of an embodiment of the present invention, an EMI filter optimization system based on noise source impedance is provided.

[0041] In one embodiment, an EMI filter optimization system based on noise source impedance includes:

[0042] A focus frequency determination unit is used to measure the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determine the insertion loss requirement based on the original noise, and determine the focus frequency using the insertion loss requirement;

[0043] The common-mode topology structure determination unit determines the capacitance of the safety capacitor based on the capacitance determination rule, and after determining the impedance characteristic value of the safety capacitor according to the capacitance, uses the impedance characteristic value to analyze the inductance value required for the concerned frequency point under the topology cluster, and determines the common-mode topology structure;

[0044] A differential mode topology determination unit is used to select a magnetic core based on a magnetic core selection rule, determine the required number of inductor turns and total differential mode capacitance corresponding to a frequency point of interest according to the magnetic core information, and select the optimal differential mode topology using the total differential mode capacitance;

[0045] The filter construction judgment unit is used to determine the filter optimization scheme according to the common-mode and differential-mode optimal topologies and impedance characteristic values, and use the optimization scheme to build a test prototype to judge the application effect of the filter, and adjust the filter optimization scheme based on the judgment results.

[0046] In one embodiment, the focus frequency point determination unit includes:

[0047] A noise source impedance acquisition module is used to measure the noise source impedance corresponding to the common mode and differential mode of the converter based on the noise path analysis method, and to set the input frequency according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter;

[0048] Insertion loss spectrum acquisition module, used to obtain the difference between the original noise and the noise limit, and add the difference result to the threshold to determine the insertion loss requirements corresponding to the common mode and differential mode of the converter, and determine the required insertion loss spectrum based on the insertion loss requirements;

[0049] The tangent frequency point selection module is used to select a slash line close to the required insertion loss spectrum in a defined order based on a preset frequency curve range to perform frequency response analysis, and select a tangent frequency point according to the analysis results;

[0050] The focus frequency selection module is used to arrange the tangent frequency points in the order of reaching the tangent state, and select a preset number of tangent frequency points as focus frequencies based on the arrangement result.

[0051] According to a third aspect of an embodiment of the present invention, a computer device is provided.

[0052] In one embodiment, the computer device includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0053] According to a fourth aspect of embodiments of the present invention, a computer-readable storage medium is provided.

[0054] In one embodiment, the computer-readable storage medium stores a computer program, and the computer program implements the steps of the above method when executed by a processor.

[0055] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0056] 1. The present invention takes into account the converter noise source impedance, filter inductance, capacitor frequency characteristics and mismatch, and adds a topology optimization link, avoiding the problem that the traditional method needs repeated adjustments and relies on engineering experience, and realizes the topology optimization of EMI filters, efficient parameter optimization design and volume optimization.

[0057] 2. The present invention is based on the complete insertion loss expression of each topology under the condition of topological clustering. According to the insertion loss required for multiple noise exceeding frequency points of concern, the required inductance value under each topology is obtained, and the topology with the smallest inductance value, the optimal topology of Owei, is selected, realizing quantitative and accurate topology optimization and parameter optimization design.

[0058] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0060] Figure 1 is a flow chart of an EMI filter optimization method based on noise source impedance according to an exemplary embodiment;

[0061] Figure 2 is a design flow chart of an EMI filter optimization method based on noise source impedance according to an exemplary embodiment;

[0062] Figure 3 is a principle block diagram of an EMI filter optimization system based on noise source impedance according to an exemplary embodiment;

[0063] Figure 4 is a schematic diagram of an equivalent circuit of a CL filter according to an exemplary embodiment;

[0064] Figure 5 is a schematic diagram showing IL comparison when Zs is different according to an exemplary embodiment;

[0065] Figure 6 is a schematic diagram showing a comparison of Zs, ZL, ZLCM, and ZCY impedances according to an exemplary embodiment;

[0066] Figure 7 is a schematic diagram showing a comparison of inductor impedance frequency characteristics according to an exemplary embodiment;

[0067] Figure 8is a schematic diagram showing a comparison of capacitance-impedance frequency characteristics according to an exemplary embodiment;

[0068] Fig. 9 is a schematic diagram showing a comparison of a CL type filter IL according to an exemplary embodiment;

[0069] Fig.10 is a diagram showing Z according to an exemplary embodiment. s , Z L , Z LCM and Z Cy Impedance comparison diagram;

[0070] Fig.11 is a schematic diagram of IL comparison showing whether impedance is mismatched according to an exemplary embodiment;

[0071] Fig.12 is a schematic diagram of CM noise source impedance magnitude / phase according to an exemplary embodiment;

[0072] Fig.13 is a schematic diagram of DM noise source impedance amplitude / phase according to an exemplary embodiment;

[0073] Fig.14 is a schematic diagram of original CM noise according to an exemplary embodiment;

[0074] Fig.15 is the original DM noise shown according to an exemplary embodiment;

[0075] Fig.16 is a schematic diagram of common-mode insertion loss required by CM according to an exemplary embodiment;

[0076] Fig.17 is a schematic diagram of differential mode insertion loss required by DM according to an exemplary embodiment;

[0077] Fig.18 is a schematic diagram of impedance characteristics of a 0.1uF safety-standard Y capacitor according to an exemplary embodiment;

[0078] Fig.19 is a schematic diagram of a frequency variation curve of magnetic permeability and inductance factor according to an exemplary embodiment;

[0079] Fig. 20 is a schematic diagram of common mode impedance of a 7-turn W515 magnetic ring according to an exemplary embodiment;

[0080] Fig.21 is a schematic diagram showing a comparison between a CLC filter insertion loss simulation result and a required common mode insertion loss according to an exemplary embodiment;

[0081] Fig. 22is a schematic diagram of impedance characteristics of a 1.55uF safety-standard Y capacitor according to an exemplary embodiment;

[0082] Fig.23 is a schematic diagram showing a comparison between a simulated insertion loss of an LCDM filter and a required differential mode insertion loss according to an exemplary embodiment;

[0083] Fig.24 is a schematic diagram of common mode noise according to an exemplary embodiment;

[0084] Fig.25 is a schematic diagram of differential mode noise according to an exemplary embodiment;

[0085] Fig.26 is a schematic diagram showing a volume comparison of an improved / conventional magnetic core according to an exemplary embodiment;

[0086] Fig. 27 is a schematic diagram showing a volume comparison of an improved filter and a traditional filter according to an exemplary embodiment;

[0087] Fig.28 is a schematic diagram of common mode noise before and after adding a filter according to an exemplary embodiment;

[0088] Fig.29 is a schematic diagram of differential mode noise before and after adding a filter according to an exemplary embodiment;

[0089] Fig.30 The figure is a schematic diagram showing the structure of a computer device according to an exemplary embodiment. DETAILED DESCRIPTION

[0090] The following description and accompanying drawings fully illustrate the specific embodiments of this article so that those skilled in the art can practice them. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of this article includes the entire scope of the claims, as well as all available equivalents of the claims. Herein, the terms "first", "second", etc. are only used to distinguish one element from another, without requiring or implying any actual relationship or order between these elements. In fact, the first element can also be called the second element, and vice versa. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the structure, device or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such structure, device or equipment. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the structure, device or equipment including the elements. Each embodiment is described in a progressive manner herein, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0091] The terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. in this document indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing this document and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of this document, unless otherwise specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, it can also be the internal communication of two elements, it can be a direct connection, or it can be an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0092] As used herein, the term "plurality" means two or more than two, unless otherwise specified.

[0093] In this document, the character " / " indicates that the preceding and following objects are in an "or" relationship. For example, A / B means: A or B.

[0094] In this article, the term "and / or" is a description of the association relationship between objects, indicating that three relationships may exist. For example, A and / or B means: A or B, or, A and B.

[0095] It should be understood that, although the various steps in the flow chart are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear description in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the figure may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0096] Each module in the device or system of the present application can be implemented in whole or in part by software, hardware, or a combination thereof. The above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above modules.

[0097] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0098] Figure 1 and Figure 2 An embodiment of the EMI filter optimization method based on noise source impedance of the present invention is shown.

[0099] In this optional embodiment, the EMI filter optimization method based on noise source impedance includes:

[0100] Step S101, measuring the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, judging the insertion loss requirement based on the original noise, and determining the focus frequency point using the insertion loss requirement;

[0101] Step S103, determining the capacitance of the safety capacitor based on the capacitance determination rule, and after determining the impedance characteristic value of the safety capacitor according to the capacitance, analyzing the inductance value required for the concerned frequency point under the topology cluster by using the impedance characteristic value, and determining the common mode topology structure;

[0102] Step S105, selecting a magnetic core based on a magnetic core selection rule, determining the required number of turns of the inductor corresponding to the frequency point of interest and the total differential mode capacitance according to the magnetic core information, and selecting the optimal differential mode topology using the total differential mode capacitance;

[0103] Step S107, determining a filter optimization scheme according to the common-mode and differential-mode optimal topologies and impedance characteristic values, and using the optimization scheme to build a test prototype to determine the application effect of the filter, and adjusting the filter optimization scheme based on the determination result.

[0104] In this optional embodiment, when measuring the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, judging the insertion loss requirement based on the original noise, and determining the frequency of interest using the insertion loss requirement, the noise source impedance corresponding to the common mode and differential mode of the converter can be measured based on the noise path analysis method, and the input frequency can be set according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter; the difference between the original noise and the noise limit is obtained, and the difference result is added to the threshold to determine the insertion loss requirement corresponding to the common mode and differential mode of the converter, and the required insertion loss spectrum is determined based on the insertion loss requirement; based on the preset frequency curve range, a diagonal line is selected to perform frequency response analysis in a defined order direction close to the required insertion loss spectrum, and tangent frequencies are selected according to the analysis results; the tangent frequencies are arranged in the order of reaching the tangent state, and a preset number of tangent frequencies are selected as frequency of interest based on the arrangement results.

[0105] In this optional embodiment, after determining the capacitance of the safety capacitor based on the capacitance determination rule and determining the impedance characteristic value of the safety capacitor based on the capacitance, the impedance characteristic value is used to analyze the inductance value required for the frequency point of interest under the topological cluster and determine the common-mode topological structure, the safety capacitor can be selected based on the preset electromagnetic compatibility rule, and the capacitance corresponding to the safety capacitor is determined according to the selection result, and the resonant frequency of the safety capacitor is determined using the capacitance result; the impedance characteristic value of the safety capacitor is determined based on the resonant frequency and impedance analysis technology, and the complete insertion loss under the topological cluster is analyzed according to the loss calculation function set; the impedance characteristic value, interactive analysis technology, complete insertion loss and common-mode noise source impedance are combined to calculate the common-mode inductance value required to meet the insertion loss requirement at the common-mode frequency point of interest under the topological cluster, and the topology corresponding to the minimum inductance value is selected as the common-mode optimal topology.

[0106] In this optional embodiment, when selecting a magnetic core based on a magnetic core selection rule, determining the required number of turns of inductance and the total differential mode capacitance corresponding to the frequency of interest based on the magnetic core information, and selecting the optimal differential mode topology using the total differential mode capacitance, the vacuum permeability and effective cross-sectional area corresponding to the candidate magnetic core can be obtained, and the vacuum permeability, effective cross-sectional area and effective length of the magnetic circuit can be combined to obtain the inductance factor of the candidate magnetic core; based on the inductance factor and the preset rule, the candidate magnetic core with the highest inductance factor and the highest saturation magnetic density is selected as the target magnetic core, and the required number of turns of the magnetic core of the differential mode inductor under the differential mode frequency of interest is calculated based on the common-mode inductance value and the inductance factor; the required number of turns of the magnetic core with the highest differential mode inductance is selected, and a common-mode winding test is performed according to the number of turns result, and the differential mode inductor impedance characteristics and leakage inductance of the common-mode inductor are obtained using the test results; the common-mode leakage inductance is used as the differential mode inductance, and the total differential mode capacitance required for the topology cluster to meet the insertion loss requirement under the differential mode frequency of interest is calculated in combination with the differential mode noise source impedance, and the topology with the smallest total differential mode capacitance is selected as the optimal differential mode topology.

[0107] In this optional embodiment, when determining the filter optimization scheme according to the common-mode and differential-mode optimal topologies and impedance characteristic values, and using the optimization scheme to build a test prototype to determine the application effect of the filter, and adjusting the filter optimization scheme based on the judgment result, the filter optimization scheme can be adjusted based on the judgment result, including: defining the filter optimization scheme according to the common-mode optimal topology and the differential-mode optimal topology and the corresponding impedance characteristic values, and using the optimization scheme to build a filter test machine, and comparing the volume difference between the filter test machine and the historical filter based on the construction result; adding the filter test machine to the simulation prototype based on simulation technology to obtain the common-mode noise and differential-mode noise corresponding to the filter test machine; obtaining the noise difference between the common-mode noise, the differential-mode noise and the historical noise values, and judging the application effect of the filter under the optimization scheme design based on the noise difference and the volume difference, and adjusting the filter optimization scheme based on the judgment result.

[0108] Figure 3 An embodiment of an EMI filter optimization system based on noise source impedance of the present invention is shown.

[0109] In this optional embodiment, the EMI filter optimization system based on noise source impedance includes:

[0110] The concerned frequency determination unit 201 is used to measure the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determine the insertion loss requirement based on the original noise, and determine the concerned frequency using the insertion loss requirement;

[0111] The common mode topology structure determination unit 203 determines the capacitance of the safety capacitor based on the capacitance determination rule, and after determining the impedance characteristic value of the safety capacitor according to the capacitance, uses the impedance characteristic value to analyze the inductance value required for the concerned frequency point under the topology cluster, and determines the common mode topology structure;

[0112] The differential mode topology determination unit 205 is used to select a magnetic core based on the magnetic core selection rule, determine the required number of turns of the inductor corresponding to the frequency point of interest and the total differential mode capacitance according to the magnetic core information, and select the optimal differential mode topology using the total differential mode capacitance;

[0113] The filter construction judgment unit 207 is used to determine the filter optimization scheme according to the common mode and differential mode optimal topologies and impedance characteristic values, and use the optimization scheme to build a test prototype to judge the application effect of the filter, and adjust the filter optimization scheme based on the judgment result.

[0114] In this optional embodiment, the attention frequency determination unit 201 includes: a noise source impedance acquisition module (not shown in the figure), an insertion loss spectrum acquisition module (not shown in the figure), a tangent frequency selection module (not shown in the figure) and an attention frequency selection module (not shown in the figure), wherein:

[0115] A noise source impedance acquisition module is used to measure the noise source impedance corresponding to the common mode and differential mode of the converter based on the noise path analysis method, and set the input frequency according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter; an insertion loss spectrum acquisition module is used to obtain the difference between the original noise and the noise limit, and add the difference result to the threshold to determine the insertion loss requirement corresponding to the common mode and differential mode of the converter, and determine the required insertion loss spectrum based on the insertion loss requirement; a tangent frequency point selection module is used to select an oblique line in a defined order direction to approach the required insertion loss spectrum based on a preset frequency curve range to perform frequency response analysis, and select tangent frequencies according to the analysis results; a focus frequency point selection module is used to arrange the tangent frequencies in the order of reaching the tangent state, and select a preset number of tangent frequencies as focus frequencies based on the arrangement results.

[0116] In the traditional design method of EMI filter, the frequency characteristics of inductance and capacitance are not taken into consideration, and the design is based on the insertion loss relationship derived under the condition of ideal noise source impedance. However, the noise source impedance of the actual circuit varies greatly with frequency and it is impossible to meet the assumed conditions in the entire frequency band. At the same time, the actual filtering inductance and capacitance also have frequency characteristics, and the performance of the filter can only be brought into play when they are mismatched with the noise source impedance and load impedance.

[0117] This embodiment takes the CL type common mode filter as an example to analyze the influence of noise source impedance, filter component frequency characteristics and mismatch on insertion loss. In this embodiment, the research frequency band is 10kHz-10MHz, and the EMC regulations that EMI complies with are GJB151B-2013, such as Figure 4 The equivalent circuit shown in the figure, where V s is the noise source voltage, Z s is the noise source impedance, Z Cy is the impedance of Y capacitor (safety capacitor), Z LCM is the common mode inductance, Z L is the equivalent load impedance.

[0118] Figure 4 The equivalent circuit shown in Figure 1 derives the complete insertion loss expression of the CL filter as:

[0119]

[0120] Assume Z s >>Z Cy (Condition 1), Z s >>Z L (Condition 2), Z LCM >>Z L (Condition 3), and L (inductor) and C (capacitor) are ideal devices, that is, Z LCM =sL,Z Cy=sC / 1, the complete insertion loss expression of the CL filter can be simplified to:

[0121] IL CL ≈20lg[|1+s 2 LC|];

[0122] Wherein, s=jω, j represents an imaginary unit, and ω represents an angular frequency (rad / s).

[0123] The IL used in the traditional design method of CL filter is CL The expression, its turning frequency is:

[0124]

[0125] After the turning frequency, IL changes at a fixed slope of +40dB / dec. However, for power electronic converters, the noise source impedance generally changes over a wide range with frequency. The above three assumptions are difficult to meet over the entire frequency range, which can easily cause deviations between the actual and designed IL (insertion loss at a certain frequency point).

[0126] For example, for power electronic converters, the common-mode noise source impedance is often the parasitic capacitance of the switch tube drain to the heat sink and the primary-secondary coupling capacitance of the isolation transformer. Its impedance decreases with increasing frequency, such as Figure 5 As shown in the figure (① line is IL when 10kΩ, ② line is IL when 3nF), the insertion loss under different noise source impedances when the filter inductor is 2mH and the filter capacitor is 0.2uF, the noise source impedance of the upper curve is the 3nF capacitor impedance, and the upper curve almost coincides with the complete insertion loss result of the CL filter, and its noise source impedance is a fixed high impedance of 10kΩ (satisfying the assumed conditions).

[0127] like Figure 6 (① is Z s 3nF line, ② is Z s 10kΩ line, ③ is Z Cy Line, ④ is Z LCM Line, ⑤ is Z L Z shown by the line s , Z L , Z LCM , Z Cy From the comparison results of several impedance characteristics, it can be seen that with the increase of frequency, the impedance of the capacitive noise source gradually decreases. After 1MHz, the assumption condition 2 is no longer met. Therefore, compared with the fixed high noise source impedance of 10kΩ, the IL difference gradually increases after 1MHz. It can be seen that with the increase of frequency, the difference in IL (insertion loss at a certain frequency point) whether the noise source impedance frequency characteristic is considered is gradually increasing. At the same time, similarly, there are situations in reality where the assumption conditions 1 and 3 are not met, which will also lead to differences in IL (insertion loss at a certain frequency point).

[0128] In traditional design, a 40dB / dec oblique line is used to design the L and C parameters at the turning frequency that is tangent to the required IL, and the inductance and capacitance values ​​are assumed to be constant, that is, the complete insertion loss of the CL filter. However, actual filter components cannot be ideal. Figure 7 and Figure 8 Comparison of the ideal / measured impedance characteristics of inductance (2mH) and capacitance (0.2uF) (① line is ideal, ② is actual), it can be seen that the resonant frequency of the capacitor is 1.3MHz. If the frequency exceeds the resonant frequency, it becomes inductive, and the impedance increases with the frequency, such as Fig. 9 When the source impedance and load impedance are both 50Ω, it can be seen that Fig. 9 (① is ideal, ② is actual) The IL difference before 1.3MHz is caused by the inductor frequency characteristics, and the difference after 1.3MHz is caused by the influence of the inductor and capacitor frequency characteristics. Therefore, if the frequency characteristics of the filter element are not considered during design, the insertion loss difference will be large as the frequency increases.

[0129] like Fig.10 As shown (① is Z Cy measured-0.2uF line, ② is Z Cy measured-0.2uF line, ③ is measured-0.2u1 line, ④ is Z L Line, ⑤ is Z s Line, ⑥ is Z LCM Line), common mode impedance Z LCM and Z L , Z Cy In the studied frequency band, the impedance Z Cy (measured-0.2uF) has frequency characteristics and ideal state Z Cy (ideal-0.2uF) at 400kHz, resulting in a difference with Z s The impedance mismatch state changes, such as Fig.11 (① is IL CL C Y -Measured-0.2uF line, ② is IL LC C Y -Measured-0.2uF line, ③ is IL CLC C Y -Measured-0.1uF line, ④ is IL CL C Y -ideal-0.2uF line), resulting in IL CL (measured-0.2uF) and IL CL(ideal-0.2uF) produces a difference at 400kHz, the capacitor C y (measured-0.2uF) After reaching the self-resonant frequency, its IL CL (Measured-0.2uF) gradually decreases, and at 6MHz due to Z Cy (measured-0.2uF) is higher than the noise source impedance value at this time. At this time, the filter capacitor loses its function and only the inductor continues to filter, so the effect is greatly reduced. In addition, if the common-mode noise source impedance is often greater than the load impedance according to the traditional design concept, and the CL topology is selected, it will be found that after 1MHz, IL CL (measured-0.2uF) is not as good as the LC filter, while the CLC filter (two capacitors are 0.1uF respectively) IL is higher than the CL / LC filter at 100kHz. Therefore, the design method that only considers the mismatch of noise source impedance and load impedance is not perfect enough. In order to meet the IL requirements, there will be a problem of large volume. Therefore, the problem of topology optimization should be considered when designing the filter. In summary, it can be seen that the traditional design method does not consider the influence of noise source impedance, component frequency characteristics, and topology optimization, resulting in a large difference between the actual insertion loss and the theory, and often cannot meet the requirements. As a result, the actual design will increase the inductance / capacitance value to increase the IL, resulting in a large filter volume and low design efficiency.

[0130] In view of the above shortcomings, this embodiment proposes an improved design method that takes into account noise source impedance, component frequency characteristics and topology optimization. The design flow chart is as follows: Figure 1 and Figure 2 shown.

[0131] Compared with the traditional design method, the improved method uses the complete insertion loss expressions under the CL, LC, CLC, and LCL topologies when the noise source impedance frequency characteristics are known and the total value and model of the filter capacitor C are selected. The required inductance value under each topology is obtained according to the insertion loss required for multiple noise exceeding frequency points of concern. The topology with the smallest required inductance value is considered to be the optimal topology, which realizes quantitative and accurate topology selection and parameter optimization design. At the same time, the frequency characteristics of the magnetic permeability of the magnetic core are considered in the full frequency range to design the inductor magnetic parts. The noise source impedance characteristics and the frequency characteristics of the capacitor and inductor are also considered in the design process, and finally the optimal design scheme that meets the requirements of the entire frequency band is obtained.

[0132] Since the insertion loss slope of the four topologies is between 20-60dB / dec, the principle for selecting the over-standard frequency points of concern is: use the 20-60dB / dec oblique line from left to right (i.e., the frequency is from low to high) to approach the required insertion loss spectrum, and the first few tangent frequencies are the main focus frequencies. Considering the frequency characteristics of capacitors and inductors, the sub-tangent frequencies can also be listed as focus frequencies.

[0133] The complete insertion loss expressions for LC, CLC, and LCL topologies are:

[0134]

[0135] This embodiment takes the design of EMI filter of 3kW, 270VDC / 28VDC prototype as an example to specifically explain the improved design process:

[0136] Step 1: Measure the noise source impedance characteristics;

[0137] There are many methods for measuring noise source impedance, such as noise path analysis method, insertion loss method, dual current probe method, etc. This embodiment uses the noise path analysis method to measure and obtain the following Fig.12 and Fig.13 The noise source impedance and phase ( Fig.12 The middle line ① is the CM common mode noise source impedance amplitude, ② is the phase, Fig.13 The middle line ① is the DM differential mode noise source impedance amplitude, and ② is the phase).

[0138] Among them, the specific steps of the noise path analysis method are: 1. Use the Norton / Thevenin theorem to equate the switch tube to a voltage source (when there are multiple switch tubes in the same bridge arm, for the convenience of analysis, one switch tube can be equivalent to a voltage source and the other can be equivalent to a current source), the diode is equivalent to a current source, and the transformer is equivalent to a two-capacitor model when measuring common-mode impedance. The input / output capacitor is regarded as a short circuit, and the transformer is regarded as an open circuit when measuring differential-mode impedance; 2. Use the superposition theorem to analyze the noise conduction path of each power supply when it acts alone, and simplify it into the final circuit, and then obtain the components related to the noise source impedance, and measure the impedance of the related components to obtain the noise source impedance.

[0139] Step 2: Measure the original noise of the converter to determine the required insertion loss and the frequency of interest;

[0140] (1) Measure the raw noise of the converter:

[0141] According to the test requirements specified in GJB151B-2013, the measured Fig.14 and Fig.15 The original CM and DM noise shown ( Fig.14 The middle ① line is the original CM common mode noise, ② is the limit line, Fig.15 The line ① in the middle is the original DM differential mode noise, and the line ② is the limit line). The limit line curve is the noise limit specified in the standard when the input voltage is 270V. The design requirement is to make the conducted noise meet the standard in the 10k-10MHz frequency band.

[0142] (2) Determine the required insertion loss:

[0143] The required insertion loss is obtained by subtracting the limit from the noise and adding 6dB:

[0144] IL req (dB) = Noise CM / DM -Limit+6;

[0145] The insertion losses required for common mode and differential mode (DM) are as follows: Fig.16 and Fig.17 shown.

[0146] (3) Determine the frequency of attention:

[0147] Use a 20-60dB / dec oblique line to approach the required insertion loss spectrum from left to right (i.e., frequency from low to high), and use the first and second tangent frequencies as the focus frequencies. According to this method, the common mode focus frequencies can be determined as: 427kHz, 1.28MHz, 1.7MHz; the differential mode focus frequencies are: 199kHz, 427kHz, 854kHz, 1.28MHz.

[0148] Step 3: Determine the total capacitance and model of the Y capacitor;

[0149] According to the EMC regulations GJB151B-2013 corresponding to the product: the capacitance of each polarity line to ground shall not exceed 75nF / kW, so the capacitance of a single line is allowed to be 0.2uF, and the total capacitance can be selected as 0.4uF. In order to ensure that the capacitor at the concerned frequency can play a role, the self-resonant frequency of the capacitor must be greater than 1.7MHz. In theory, the smaller the capacitance, the better the high-frequency performance, but too many capacitors in parallel will have a large volume. In this embodiment, a safety capacitor with a single capacitance of 0.1uF made of MKP material is selected, and its resonant frequency is 2MHz. The impedance analyzer E5061B is used to measure its impedance characteristics as shown in the following figure Fig.18 shown.

[0150] Step 4: CM topology and common mode inductor optimization;

[0151] With the help of Matlab software, according to the complete insertion loss expressions under different topologies of CL, LC, CLC, and LCL, and under the known Y capacitor impedance and CM noise source impedance frequency characteristics, the CM inductance value required to meet the required insertion loss at each frequency point of interest under different topologies is calculated, as shown in Table 1, and the topology with the smallest inductance value is selected as the optimal topology.

[0152] Table 1CM focuses on the common mode sense of each topology to meet the required IL at the noise frequency point

[0153]

[0154] As can be seen from Table 1, the CLC filter has the smallest inductance at each frequency point of interest, so the CLC topology is finally selected. If the optimal topology is different at different frequencies of interest, continue to design magnetic components under several optimal topologies, select the magnetic core and calculate the number of turns required for each topology to meet all ILs. The topology with the least number of turns is the optimal topology.

[0155] Step 5: Design the inductor core and number of turns, and test the impedance and leakage inductance;

[0156] Generally, the magnetic cores suitable for common-mode inductors are: ferrite and nanocrystal. Among ferrites, manganese-zinc ferrite has high low-frequency magnetic permeability and low high-frequency magnetic permeability, and is suitable for medium and low frequencies; nickel-zinc ferrite has low magnetic permeability, but its inductance change rate is also low with the increase of frequency, and is suitable for medium and high noise. Amorphous materials have ultra-high magnetic permeability, low inductance change rate, no hysteresis and expansion phenomenon, and the influence of parasitic capacitance is not obvious within 10kHz-10MHz, so the whole frequency band is inductive. In this embodiment, a W515 magnetic core with a size of 19x11x8mm is selected.

[0157] The actual number of turns N required for the common-mode inductor is:

[0158]

[0159] Inductance factor:

[0160]

[0161] Where l is the effective length of the magnetic circuit (cm); A e Indicates the effective cross-sectional area of ​​the core (cm 2 ); μ o represents the vacuum permeability, μ o =4π*10 -7 , f represents frequency (Hz), μ r Indicates the relative magnetic permeability of the magnetic core. At the same time, the frequency characteristics of the magnetic permeability and inductance factor are measured. Fig.19 As shown in (① is the magnetic permeability, ② is the inductance factor), the number of turns required for the inductor at each frequency point is obtained from the formula for the number of turns required for the actual common-mode inductor. The results are shown in Table 2:

[0162] Table 2 The number of turns required for the W515 magnetic ring under the common mode inductance required for the three frequency points

[0163] f(Hz) <![CDATA[L cm (uH)]]> <![CDATA[A L ]]> N 426.7k 130 2.60E-06 7 1.28M 8 1.14E-06 3 1.7M 0.8 9.09E-07 1

[0164] In order to meet the required inductance value at each frequency point of interest, the number of turns is finally selected as 7 turns. Fig. 20 The impedance characteristic of the 7-turn winding is measured, and the leakage inductance of the common mode inductor at the frequency of interest can be measured.

[0165] Step 6: Simulate and verify the CM filter IL;

[0166] Import the impedance characteristics of the 7-turn designed / wound W515 core inductor, the impedance of the two parallel 0.1uF capacitors, and the noise source impedance into the complete CLC insertion loss expression to calculate the filter insertion loss or use ADS (Advanced Design System) software to simulate the filter insertion loss, such as Fig.21 (① is ILCLC, ② is the IL required by CM), it can be seen that the design requirements are met.

[0167] Similar to the CM filter design method, the optimal topology and parameters of the differential mode filter can be designed: In this implementation, the leakage inductance of the CM inductor is used as the differential mode inductance. In fact, the measured inductance value does not change much with frequency, so the minimum value 1.42uH is taken. Then, combined with the DM noise source impedance, the total differential mode capacitance of each topology that meets the required DM IL at the DM focus frequency is calculated as shown in Table 3. The topology with the smallest total differential mode capacitance is selected as the optimal topology.

[0168] Table 3 X-capacitance values ​​and optimal topology required for each topology to meet the insertion loss required for the DM focus frequency

[0169]

[0170] From Table 3, we can see that at each frequency point of interest, the capacitance required by LC is the smallest, so this topology is selected here. Since the frequency of the maximum peak is 1.2M, the MKP material self-resonant frequency is 1MHz and the capacitance is 1.55uF. The impedance characteristics of 5 parallel-connected 1.55uF X capacitors are as follows: Fig. 22 shown.

[0171] After obtaining the leakage inductance value, DM noise source impedance and X capacitor frequency characteristics, the DM filter IL can be simulated to verify whether it meets the required IL. The results are as follows: Fig.23 (ILLC is shown on the top and IL is required on the bottom) Fig.23 (① is ILCLC, ② is the IL required for DM) It can be seen that the designed DM filter meets the required IL. In summary, it is an improved design method that considers the noise source impedance and component frequency characteristics.

[0172] Step 7: Experimental verification;

[0173] (1) Traditional design results: According to the traditional design method, it is believed that the CM source impedance is much larger than the load impedance and the DM source impedance is much smaller than the load impedance. According to the impedance mismatch principle, the CL topology is selected for the common mode and the LC topology is selected for the differential mode. The CM corner frequency (16.9893kHz), DM corner frequency (51.602kHz) and Y capacitance are used to calculate the required common mode inductance of 220uH. Since the W515 core is not applicable, the amorphous magnetic ring T60006-L2025-W380-05 is selected. Its size is 25x16x10mm. According to the core data sheet, its inductance factor is 50uH≤A at 10kHz. L ≤95uH, select A L =50uH, the inductance is 220uH, the number of turns is as follows:

[0174]

[0175] Take 3 turns, and the wound common mode inductance is 330uH, the leakage inductance is 1.5uH, and the required total differential mode capacitance is 8uF. At the same time, the common mode / differential mode noise measured when the filter is designed by the traditional method without considering the frequency characteristics of the filter element is as follows Fig.24 and Fig.25 As shown by Fig.24 (① is original, ② is after installation) and Fig.25 (① is the original, ② is after installation) It can be seen that the common-mode EMI noise is still seriously exceeded, that is, the theoretical design and the actual effect are quite different, and the DM filter also fails to meet the demand. Finally, after debugging, the inductor needs to be wound with 7 turns to increase the inductance to 1.8mH to meet the noise index.

[0176] (2) Optimization design results:

[0177] According to the optimization design results of noise source impedance characteristics, component impedance characteristics, and topology selection, a filter test prototype was built. Under the same height, the design scheme added a topology optimization step, which changed the topology and reduced the common mode volume. The filter size was reduced from 133mm*30.5mm to 123mm*26.5mm, and the volume was reduced by 24.4%. The volume comparison of the core / filter of the two methods is as follows: Fig.26 and Fig. 27 As shown in Figure 2, the noise measured after the filter designed by the optimization method is installed on the prototype is as follows: Fig.28 Shown with Fig.29 ,from Fig.28 (① is original, ② is after installation) and Fig.29 (① is the original, ② is after installation) It can be seen that the new method can achieve the target in one go, realize accurate optimization design, and significantly reduce the volume of the CM filter, which illustrates the effectiveness of the design method.

[0178] Since the noise source impedance of power electronic converters varies widely with frequency, traditional EMI filter design methods have problems such as difficulty in topology optimization, large difference between actual noise suppression effect and theory, and need for repeated attempts. The improved design method proposed in this paper takes into account the influence of noise source impedance, filter inductance, and capacitor frequency characteristics on the filter IL. Based on the complete insertion loss expression under each topology, the required parameter values ​​under multiple frequency points of interest are calculated with the help of MATLAB simulation software or self-compiled small programs, realizing the optimal topology selection and EMI filter parameter optimization design. The design process is clear, rigorous, reliable, and highly operable. The experimental results show that the EMI filter designed by the optimization method proposed in this embodiment can meet the performance standards at one time, and the volume is smaller than the traditional design filter.

[0179] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Fig.30 As shown. The computer device includes a processor, a memory and a network interface connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store static information and dynamic information data. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, the steps in the above method embodiment are implemented.

[0180] Those skilled in the art will understand that Fig.30 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present invention, and does not constitute a limitation on the computer device to which the solution of the present invention is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0181] In addition, the present invention also provides a computer device, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above method embodiment when executing the computer program.

[0182] In addition, the present invention further provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps in the above method embodiment are implemented.

[0183] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided by the present invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0184] The present invention is not limited to the structures which have been described above and shown in the drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. An EMI filter optimization method based on noise source impedance, characterized in that: The EMI filter optimization method includes: Measure the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determine the insertion loss requirement based on the original noise, and use the insertion loss requirement to determine the frequency of interest; Determine the capacitance of the safety capacitor based on the capacitance determination rule. After determining the impedance characteristic value of the safety capacitor based on the capacitance, use the impedance characteristic value to analyze the inductance value required for the frequency point of interest under the topology cluster and determine the common mode topology structure. Select the core based on the core selection rules, determine the required number of inductor turns and total differential mode capacitance corresponding to the frequency of interest based on the core information, and use the total differential mode capacitance to select the optimal differential mode topology; The filter optimization scheme is determined based on the optimal topology and impedance characteristic values ​​of common mode and differential mode, and a test prototype is built using the optimization scheme to determine the application effect of the filter. The filter optimization scheme is adjusted based on the judgment results.

2. The EMI filter optimization method based on noise source impedance according to claim 1, characterized in that: The measuring of the noise source impedance and the original noise corresponding to the common mode and the differential mode of the converter, judging the insertion loss requirement based on the original noise, and determining the frequency point of interest using the insertion loss requirement includes: The noise source impedance corresponding to the common mode and differential mode of the converter is measured based on the noise path analysis method, and the input frequency is set according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter; Obtain the difference between the original noise and the noise limit, and add the difference result to the threshold to determine the insertion loss requirements corresponding to the common mode and differential mode of the converter, and determine the required insertion loss spectrum based on the insertion loss requirements; Based on the preset frequency curve range, select the oblique line to approach the required insertion loss spectrum in the defined order to perform frequency response analysis, and select the tangent frequency point according to the analysis results; The tangent frequency points are arranged in the order of reaching the tangent state, and a preset number of groups of tangent frequency points are selected as focus frequencies based on the arrangement result.

3. The EMI filter optimization method based on noise source impedance according to claim 2, characterized in that: The preset frequency curve range is 20dB / dec-60dB / dec, and the definition order direction is from left to right.

4. The EMI filter optimization method based on noise source impedance according to claim 1, characterized in that: The method of determining the capacitance of the safety capacitor based on the capacitance determination rule, determining the impedance characteristic value of the safety capacitor according to the capacitance, analyzing the inductance value required for the concerned frequency point under the topology cluster by using the impedance characteristic value, and determining the common mode topology structure includes: Select a safety capacitor based on a preset electromagnetic compatibility rule, determine the capacitance corresponding to the safety capacitor according to the selection result, and determine the resonant frequency of the safety capacitor using the capacitance result; Determine the impedance characteristic value of the safety capacitor based on the resonant frequency and impedance analysis technology, and analyze the complete insertion loss under the topological cluster according to the loss calculation function set; The impedance characteristic value, interactive analysis technology, complete insertion loss and common-mode noise source impedance are combined to calculate the common-mode inductance value required to meet the insertion loss requirement at the common-mode focus frequency under the topology cluster, and the topology corresponding to the minimum inductance value is selected as the common-mode optimal topology.

5. The EMI filter optimization method based on noise source impedance according to claim 4, characterized in that: The loss calculation function set includes a CL filter insertion loss calculation function, an LC filter insertion loss calculation function, a CLC filter insertion loss calculation function and an LCL filter insertion loss calculation function; Wherein, the expression of the CL filter insertion loss calculation function is: In the formula, IL CL Represents the complete insertion loss value of the CL filter, Z L represents the equivalent load impedance, Z s is the noise source impedance, Z LCM represents the common mode inductance, Z Cy Indicates the safety capacitor impedance.

6. The EMI filter optimization method based on noise source impedance according to claim 1, characterized in that: The method of selecting a magnetic core based on a magnetic core selection rule, determining the required number of turns of the inductor and the total differential mode capacitance corresponding to the frequency point of interest according to the magnetic core information, and selecting the optimal differential mode topology using the total differential mode capacitance includes: Obtain vacuum magnetic permeability and effective cross-sectional area corresponding to the candidate magnetic core, and combine the vacuum magnetic permeability, effective cross-sectional area and effective length of the magnetic circuit to obtain the inductance factor of the candidate magnetic core; Based on the inductance factor and preset rules, the candidate magnetic core with the highest inductance factor and the highest saturation magnetic density is selected as the target magnetic core, and the required number of turns of the magnetic core of the differential mode inductor under the differential mode focus frequency condition is calculated according to the common mode inductance value and the inductance factor; Select the number of turns required for the highest core of the differential mode inductor, and perform the common mode winding test according to the number of turns result, and use the test results to obtain the differential mode inductor impedance characteristics and the leakage inductance of the common mode inductor; The common-mode leakage inductance is used as the differential-mode inductance, and combined with the differential-mode noise source impedance to calculate the total differential-mode capacitance required for the topology cluster to meet the insertion loss requirements under the differential-mode focus frequency conditions. The topology with the smallest total differential-mode capacitance is selected as the optimal differential-mode topology.

7. The EMI filter optimization method based on noise source impedance according to claim 6, characterized in that: The calculation formula of the inductance factor is: In the formula, A L (f) represents the inductance factor, μ o A represents the vacuum permeability, e represents the effective cross-sectional area of ​​the magnetic core, l represents the effective length of the magnetic circuit, f represents the frequency, μ r Indicates the relative magnetic permeability of the core.

8. The EMI filter optimization method based on noise source impedance according to claim 7, characterized in that: The filter optimization scheme is determined according to the common mode and differential mode optimal topology and impedance characteristic values, and a test prototype is built using the optimization scheme to determine the application effect of the filter. The filter optimization scheme is adjusted based on the judgment result, including: Define the filter optimization scheme according to the common-mode optimal topology, the differential-mode optimal topology and the corresponding impedance characteristic values, and use the optimization scheme to build a filter test machine. Compare the volume difference between the filter test machine and the historical filter based on the construction results; Based on the simulation technology, the filter test machine is installed on the simulation prototype to obtain the common mode noise and differential mode noise corresponding to the filter test machine; The noise difference between the common mode noise, differential mode noise and historical noise value is obtained, and the application effect of the filter under the optimization scheme design is judged based on the noise difference and the volume difference, and the filter optimization scheme is adjusted based on the judgment result.

9. An EMI filter optimization system based on noise source impedance, characterized in that: The EMI filter optimization system includes: A focus frequency determination unit is used to measure the noise source impedance and original noise corresponding to the common mode and differential mode of the converter, determine the insertion loss requirement based on the original noise, and determine the focus frequency using the insertion loss requirement; The common-mode topology structure determination unit determines the capacitance of the safety capacitor based on the capacitance determination rule, and after determining the impedance characteristic value of the safety capacitor according to the capacitance, uses the impedance characteristic value to analyze the inductance value required for the concerned frequency point under the topology cluster, and determines the common-mode topology structure; A differential mode topology determination unit is used to select a magnetic core based on a magnetic core selection rule, determine the required number of inductor turns and total differential mode capacitance corresponding to a frequency point of interest according to the magnetic core information, and select the optimal differential mode topology using the total differential mode capacitance; The filter construction judgment unit is used to determine the filter optimization scheme according to the common-mode and differential-mode optimal topologies and impedance characteristic values, and use the optimization scheme to build a test prototype to judge the application effect of the filter, and adjust the filter optimization scheme based on the judgment results.

10. The EMI filter optimization system based on noise source impedance according to claim 9, characterized in that: The focus frequency determination unit includes: A noise source impedance acquisition module is used to measure the noise source impedance corresponding to the common mode and differential mode of the converter based on the noise path analysis method, and to set the input frequency according to the preset test requirements to determine the original noise of the common mode and differential mode of the converter; Insertion loss spectrum acquisition module, used to obtain the difference between the original noise and the noise limit, and add the difference result to the threshold to determine the insertion loss requirements corresponding to the common mode and differential mode of the converter, and determine the required insertion loss spectrum based on the insertion loss requirements; The tangent frequency point selection module is used to select a slash line close to the required insertion loss spectrum in a defined order based on a preset frequency curve range to perform frequency response analysis, and select a tangent frequency point according to the analysis results; The focus frequency selection module is used to arrange the tangent frequency points in the order of reaching the tangent state, and select a preset number of tangent frequency points as focus frequencies based on the arrangement result.

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