An EMI filter optimization method and system based on noise source impedance

Abstract

The application belongs to the technical field of filter optimization, and discloses an EMI filter optimization method and system based on noise source impedance, which comprises the following steps: measuring noise source impedance corresponding to common mode and differential mode of a transformer and original noise, judging insertion loss demand based on the original noise, and determining a frequency point of interest by using the insertion loss demand; determining a capacitance value of a safety capacitor based on a capacitance value determination rule, analyzing an inductance value required by the frequency point of interest under a topology cluster by using an impedance characteristic value of the safety capacitor after the impedance characteristic value of the safety capacitor is determined according to the capacitance value, and determining a common mode optimal topology; selecting a magnetic core based on a magnetic core selection rule, determining a total differential mode capacitance and a number of turns required by an inductance corresponding to the frequency point of interest according to the magnetic core information, and selecting a differential mode optimal topology by using the total differential mode capacitance; and determining a filter optimization scheme according to the common mode optimal topology, the differential mode optimal topology and the impedance characteristic value. The application realizes the functions of quantitative and accurate optimal topology and parameter optimization design of the filter.

Description

TECHNICAL FIELD

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

[0002] EMI filters are divided into passive and active, wherein the passive filter is composed of inductors and capacitors, has low cost, relatively mature technology and stable performance, and has been widely applied; the active EMI filter has an operational amplifier inside, which can amplify the sampled noise (current or voltage) and compensate for a phase-reversed noise current or voltage, and due to the system bandwidth limitation, the active EMI filter has certain advantages below 10 MHz, and a passive filter is still needed to solve the problem in the high frequency band.

[0003] With the increase of the switching frequency of the power converter, the electromagnetic interference problem caused by high voltage rate is more and more serious, and the current means for suppressing conducted EMI include frequency jittering technology, PCB layout optimization, soft switching technology, cancellation technology and filter technology, wherein the first four technologies reduce the noise source amplitude through different methods, but according to the existing research results, few products can completely solve the problem of excessive conducted EMI without adding an EMI filter, so the EMI filter is an essential component of electrical equipment.

[0004] The EMI filter related scheme in the prior art is designed according to the insertion loss relationship formula under the ideal noise source impedance condition, but the noise source impedance of the actual circuit varies greatly with frequency and cannot meet the assumed condition in the full frequency band, and at the same time, the actual filter inductors and capacitors also have frequency characteristics, and the noise source impedance and the load impedance are mismatched to play the performance of the filter.

[0005] Therefore, how to provide an EMI filter optimization method and system based on noise source impedance is a problem to be solved at present. SUMMARY

[0006] The EMI filter optimization method and system based on noise source impedance provided by the embodiments of the present application solve the problem that the noise source impedance of the actual circuit varies greatly with frequency and cannot meet the assumed condition in the full frequency band in the prior art.

[0007] To have a basic understanding of some aspects of the disclosed embodiments, a brief overview is given below. This part is not a general review, nor is it intended to determine the key / important elements or delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a prelude to the detailed description that follows.

[0008] According to a first aspect of an embodiment of the present application, a noise source impedance-based EMI filter optimization method is provided.

[0009] In one embodiment, the noise source impedance-based EMI filter optimization method comprises:

[0010] Measuring noise source impedance corresponding to the common mode and differential mode of the transformer and original noise, determining the insertion loss requirement based on the original noise, and determining the frequency point of interest based on the insertion loss requirement;

[0011] Determining the capacitance value of the safety capacitor based on the capacitance value determination rule, determining the impedance characteristic value of the safety capacitor according to the capacitance value, analyzing the inductance value required by the frequency point of interest under the topology cluster using the impedance characteristic value, and determining the common mode optimal topology;

[0012] Selecting a magnetic core based on the magnetic core selection rule, determining the number of turns and total differential mode capacity required by the inductor corresponding to the frequency point of interest according to the magnetic core information, and selecting the differential mode optimal topology using the total differential mode capacity;

[0013] Determining the filter optimization scheme according to the common mode, differential mode optimal topology and impedance characteristic value, and adjusting the filter optimization scheme based on the judgment result.

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

[0015] Measuring noise source impedance corresponding to the common mode and differential mode of the transformer based on the noise path analysis method, and setting the input frequency according to the preset test requirement to determine the original noise of the common mode and differential mode of the transformer;

[0016] Obtaining the difference between the original noise and the noise limit value, and adding the difference result to the threshold value to determine the insertion loss requirement corresponding to the common mode and differential mode of the transformer, and determining the required insertion loss spectrum based on the insertion loss requirement;

[0017] Based on the preset frequency curve range, selecting a slope to approach the required insertion loss spectrum in the defined order direction to perform frequency response analysis, and selecting the tangent frequency point according to the analysis result;

[0018] Arranging the tangent frequency points in the order of reaching the tangent state, and selecting the tangent frequency points of a preset group number as the frequency points of interest based on the arrangement result.

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

[0020] In one embodiment, the capacitance value of the safety capacitor is determined based on a capacitance value determination rule, after determining the impedance characteristic value of the safety capacitor according to the capacitance value, the inductance value required for the concerned frequency point under the topology cluster is analyzed using the impedance characteristic value, and the common mode optimal topology is determined, including:

[0021] The safety capacitor is selected based on the preset electromagnetic compatibility rule, and the capacitance value corresponding to the safety capacitor is determined according to the selection result, and the resonance frequency of the safety capacitor is determined using the capacitance value result;

[0022] The impedance characteristic value of the safety capacitor is determined based on the resonance frequency and the impedance analysis technology, and the complete insertion loss under the topology cluster is analyzed 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 for the common mode concerned frequency point under the topology cluster to meet the insertion loss demand, 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 CL filter insertion loss calculation function, LC filter insertion loss calculation function, CLC filter insertion loss calculation function and LCL filter insertion loss calculation function;

[0025] 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 represents the noise source impedance, Z LCM represents the common mode inductance, Z Cy represents the impedance of the safety capacitor.

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

[0029] The vacuum permeability and effective cross-sectional area corresponding to the alternative magnetic core are obtained, and the inductance factor of the alternative magnetic core is obtained by combining the vacuum permeability, effective cross-sectional area and effective length of the magnetic circuit;

[0030] The alternative magnetic core with the highest inductance factor and the highest saturation magnetic density is selected as the target magnetic core based on the inductance factor and the preset rule, and the turns required for the magnetic core of the differential mode inductance under the condition of the differential mode concerned frequency point are calculated according to the common mode inductance value and the inductance factor;

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

[0032] The common mode leakage inductance is taken as the differential mode inductance, and the total differential mode capacity required for the topology cluster to meet the insertion loss demand under the condition of the differential mode noise source impedance at the differential mode attention frequency point is calculated, and the topology with the minimum total differential mode capacity is selected as the differential mode optimal 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 represents the vacuum permeability, A 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 represents the relative permeability of the magnetic core.

[0036] In one embodiment, the filter optimization scheme is determined according to the common mode, differential mode optimal topology and impedance characteristic value, and the application effect of the filter is judged by using the optimization scheme to build a test machine, and the filter optimization scheme is adjusted based on the judgment result, including:

[0037] The filter optimization scheme is defined according to the common mode optimal topology and the differential mode optimal topology and the corresponding impedance characteristic value, and the filter test machine is built by using the optimization scheme, and the volume difference between the filter test machine and the historical filter is compared based on the built result;

[0038] The filter test machine is added to the simulation machine based on the simulation simulation technology, and the common mode noise and the differential mode noise corresponding to the filter test machine are obtained;

[0039] The noise difference between the common mode noise, the differential mode noise and the 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 the second aspect of the embodiment of the application, an EMI filter optimization system based on noise source impedance is provided.

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

[0042] The attention frequency point determination unit is configured to measure the noise source impedance corresponding to the common mode and the differential mode of the converter and the original noise, judge the insertion loss demand based on the original noise, and determine the attention frequency point by using the insertion loss demand.

[0043] The common mode topology structure determination unit determines the capacitance value of the safety capacitor based on a capacitance value determination rule, determines the impedance characteristic value of the safety capacitor according to the capacitance value, analyzes the inductance value required by the frequency point of interest under the topology cluster by using the impedance characteristic value, and determines the common mode optimal topology.

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

[0045] The filter building judgment unit is configured to determine a filter optimization scheme according to the common mode and differential mode optimal topologies and the impedance characteristic value, build a test prototype by using the optimization scheme to judge the application effect of the filter, and adjust the filter optimization scheme based on the judgment result.

[0046] In one embodiment, the frequency point of interest determination unit comprises:

[0047] The noise source impedance acquisition module is configured to measure the noise source impedance corresponding to the common mode and the differential mode of the transformer based on a noise path analysis method, and determine the original noise of the common mode and the differential mode of the transformer by setting an input frequency according to a preset test requirement.

[0048] The insertion loss frequency spectrum acquisition module is configured to acquire a difference value between the original noise and a noise limit value, add the difference value result to a threshold value to determine the insertion loss requirement corresponding to the common mode and the differential mode of the transformer, and determine the required insertion loss frequency spectrum based on the insertion loss requirement.

[0049] The tangent frequency point selection module is configured to select a tangent frequency point by selecting a tangent line to perform frequency response analysis in a defined order direction close to the required insertion loss frequency spectrum based on a preset frequency curve range, and select the tangent frequency point according to the analysis result.

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

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

[0052] In one embodiment, the computer device comprises 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 an embodiment of the present application, a computer readable storage medium is provided.

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

[0055] The technical scheme provided by the embodiment of the present application can include the following beneficial effects:

[0056] 1. The present application considers the improved optimization method of the impedance of the noise source of the transformer, the frequency characteristics and the mismatch of the filter inductance and capacitance, and increases the topology optimization link, avoids the problem of repeated adjustment and dependence on engineering experience in the traditional method, and realizes the topology optimization, efficient parameter optimization design and optimization of the volume of the EMI filter.

[0057] 2. Based on the complete insertion loss expression of each topology under the topology cluster condition, the required inductance value under each topology is obtained according to the required insertion loss of the multiple noise exceeding frequency points of interest, and the topology with the minimum inductance value, i.e. the optimal topology, is selected, so as to realize the quantitative and accurate optimization of the topology and the parameter optimization design.

[0058] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0059] The drawings incorporated into the specification and forming a part of the specification, show embodiments consistent with the present application, and together with the specification, serve to explain the principles of the present application.

[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 CL type filter equivalent circuit schematic diagram according to an exemplary embodiment;

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

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

[0066] Figure 7 is an inductance impedance frequency characteristic comparison schematic diagram according to an exemplary embodiment;

[0067] Figure 8is a plot of a capacitive impedance frequency characteristic according to an example embodiment;

[0068] Figure 9 is a plot of a CL filter IL according to an example embodiment;

[0069] Figure 10 is a plot of a Z s , Z L , Z LCM , and Z Cy impedance according to an example embodiment;

[0070] Figure 11 is a plot of an IL whether the impedance is mismatched according to an example embodiment;

[0071] Figure 12 is a plot of a CM noise source impedance magnitude / phase according to an example embodiment;

[0072] Figure 13 is a plot of a DM noise source impedance magnitude / phase according to an example embodiment;

[0073] Figure 14 is a plot of a raw CM noise according to an example embodiment;

[0074] Figure 15 is a plot of a raw DM noise according to an example embodiment;

[0075] Figure 16 is a plot of a CM required common mode insertion loss according to an example embodiment;

[0076] Figure 17 is a plot of a DM required differential mode insertion loss according to an example embodiment;

[0077] Figure 18 is a plot of a 0.1 uF safety Y capacitor impedance characteristic according to an example embodiment;

[0078] Figure 19 is a plot of a permeability and inductance factor frequency variation curve according to an example embodiment;

[0079] Figure 20 is a plot of a 7 turn W515 magnetic ring common mode impedance according to an example embodiment;

[0080] Figure 21 is a plot of a CLC filter insertion loss simulation results compared to a required common mode insertion loss according to an example embodiment;

[0081] Figure 22is a schematic diagram of 1.55uF safety Y capacitance impedance characteristics according to an example embodiment;

[0082] Figure 23 is a schematic diagram of an LCDM filter simulation insertion loss versus required differential mode insertion loss according to an example embodiment;

[0083] Figure 24 is a schematic diagram of common mode noise according to an example embodiment;

[0084] Figure 25 is a schematic diagram of differential mode noise according to an example embodiment;

[0085] Figure 26 is a schematic diagram of improved / legacy core volume comparison according to an example embodiment;

[0086] Figure 27 is a schematic diagram of improved / legacy filter volume comparison according to an example embodiment;

[0087] Figure 28 is a schematic diagram of common mode noise with and without filter according to an example embodiment;

[0088] Figure 29 is a schematic diagram of differential mode noise with and without filter according to an example embodiment;

[0089] Figure 30 is a schematic diagram of a computer device according to an example embodiment. DETAILED DESCRIPTION

[0090] The following description and drawings are illustrative of specific embodiments thereof and are not intended to limit the scope of the embodiments. Parts and features of some embodiments can be included or substituted in or for parts and features of other embodiments. The scope of the embodiments encompassed herein includes the whole scope of the claims together with all available equivalents of the claims. In this document, the terms "first", "second", etc. are used merely to distinguish one element from another, and do not require or imply any actual relationship or order between the elements. In fact, the first element can be referred to as the second element, and vice versa. Also, the terms "comprises", "comprising", or any other variations thereof are intended to cover a non-exclusive inclusion, such that a structure, device, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such structure, device, or apparatus. Without further limitation, an element defined by an "includes a" statement does not exclude the presence of additional identical elements in the structure, device, or apparatus that includes the element. Various embodiments are described in progressive stages, each of which focuses on the differences from other embodiments, and the same or similar parts between various embodiments can be referred to each other.

[0091] The terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, as used herein, indicate relative positions or orientation relationships based on the positions or orientation relationships shown in the drawings, and are only used for the convenience of description herein and simplification of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In the description herein, unless otherwise specified and limited, the terms "mount", "connect", "connection" should be understood broadly, for example, it can be a mechanical connection or an electrical connection, it can be a communication between two elements inside, it can be a direct connection, or an indirect connection through an intermediate medium, and the specific meaning of the above terms can be understood by those skilled in the art according to the specific circumstances.

[0092] In this document, the term "multiple" means two or more, unless otherwise specified.

[0093] In this document, the character " / " represents an "or" relationship between the objects before and after it. For example, A / B means: A or B.

[0094] In this document, the term "and / or" is a description of the relationship between the objects, which means that there can be three relationships. For example, A and / or B means: A or B, or, A and B, the three relationships.

[0095] It should be understood that although the steps in the flowchart are shown in a sequential order following the arrows, the steps are not necessarily executed in the order shown by the arrows. Unless otherwise explicitly stated herein, the execution of the steps is not necessarily limited to the order shown in the figure, and the steps can be executed in other orders. Moreover, at least some of the steps in the figure can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of the sub-steps or stages is not necessarily sequential, but can be round-robin or alternating with at least some of the other steps or sub-steps or stages of the other steps.

[0096] Each module in the device or system of the present application can be implemented wholly or partially by software, hardware, and a combination thereof. The above modules can be embedded in or independent of the processor in the computer device in hardware form, or stored in the memory in the computer device in software form, so as to be called and executed by the processor to perform the operations corresponding to the above modules.

[0097] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0098] Figure 1 With Figure 2 An embodiment of the noise source impedance-based EMI filter optimization method of the present application is shown.

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

[0100] Step S101, measure the noise source impedance corresponding to the common mode and differential mode of the transformer and the original noise, determine the insertion loss requirement based on the original noise, and determine the frequency point of interest using the insertion loss requirement;

[0101] Step S103, determine the capacitance value 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 value, analyze the inductance value required by the frequency point of interest under the topology cluster using the impedance characteristic value, and determine the common mode optimal topology;

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

[0103] Step S107, determine the filter optimization scheme according to the common mode, differential mode optimal topology, and impedance characteristic value, 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.

[0104] In the optional embodiment, when the noise source impedance corresponding to the common mode and differential mode of the transformer is measured based on the noise path analysis method, the original noise of the common mode and differential mode of the transformer is determined according to the preset test requirement by setting the input frequency, the difference between the original noise and the noise limit value is obtained, the threshold value is added to the difference result to determine the insertion loss requirement corresponding to the common mode and differential mode of the transformer, the required insertion loss spectrum is determined based on the insertion loss requirement, the frequency response analysis is performed according to the defined order direction close to the required insertion loss spectrum by selecting the oblique line based on the preset frequency curve range, and the tangent frequency points are selected according to the analysis result; the tangent frequency points are arranged according to the order of reaching the tangent state, and the tangent frequency points of the preset group number are selected as the concerned frequency points based on the arrangement result.

[0105] In the optional embodiment, when the capacitance value of the safety capacitor is determined based on the capacitance determination rule, the impedance characteristic value of the safety capacitor is determined according to the capacitance value, the inductance value required by the concerned frequency point under the topology cluster is analyzed by using the impedance characteristic value, and the common mode optimal topology is determined, the safety capacitor can be selected based on the preset electromagnetic compatibility rule, the capacitance value corresponding to the safety capacitor is determined according to the selection result, and the resonance frequency of the safety capacitor is determined by using the capacitance value result; the impedance characteristic value of the safety capacitor is determined based on the resonance frequency and the impedance analysis technology, the complete insertion loss under the topology cluster is analyzed according to the loss calculation function set, the common mode inductance value required for the common mode concerned frequency point to meet the insertion loss requirement under the topology cluster is calculated by combining the impedance characteristic value, the interactive analysis technology, the complete insertion loss and the common mode noise source impedance, and the topology corresponding to the minimum inductance value is selected as the common mode optimal topology.

[0106] In the optional embodiment, when the magnetic core is selected based on the magnetic core selection rule, the turns number and the total differential mode capacitance required by the inductance corresponding to the concerned frequency point are determined according to the magnetic core information, and the differential mode optimal topology is selected by using the total differential mode capacitance, the vacuum permeability and the effective cross-sectional area corresponding to the candidate magnetic core can be obtained, the inductance factor of the candidate magnetic core is obtained by combining the vacuum permeability, the effective cross-sectional area and the effective length of the magnetic circuit, the candidate magnetic core with the highest inductance factor and the highest saturation magnetic density is selected as the target magnetic core based on the inductance factor and the preset rule, the turns number required by the magnetic core of the differential mode inductance under the condition of the differential mode concerned frequency point is calculated according to the common mode inductance value and the inductance factor, the turns number required by the highest magnetic core of the differential mode inductance is selected, the common mode winding test is performed according to the turns number result, the differential mode inductance impedance characteristic and the leakage inductance of the common mode inductance are obtained by using the test result, the common mode leakage inductance is taken as the differential mode inductance, and the total differential mode capacitance required for the topology cluster to meet the insertion loss requirement under the condition of the differential mode concerned frequency point is calculated by combining the differential mode noise source impedance, and the topology with the smallest total differential mode capacitance is selected as the differential mode optimal topology.

[0107] In the optional embodiment, when the filter optimization scheme is determined according to the common mode and differential mode optimal topologies and impedance characteristic values, the test prototype is built by using the optimization scheme to determine the application effect of the filter, and the filter optimization scheme is adjusted based on the determination result, the filter optimization scheme can be adjusted based on the determination 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 building the filter test machine by using the optimization scheme, and comparing the volume difference between the filter test machine and the historical filter based on the building result; the filter test machine is added to the simulation machine based on the simulation simulation technology, the common mode noise and the differential mode noise corresponding to the filter test machine are obtained; the noise difference between the common mode noise, the differential mode noise and the historical noise value is obtained, and the application effect of the filter under the optimization scheme design is determined based on the noise difference and the volume difference, and the filter optimization scheme is adjusted based on the determination result.

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

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

[0110] The attention frequency point determination unit 201 is used for measuring the noise source impedance corresponding to the common mode and differential mode of the transformer and the original noise, determining the attention frequency point based on the original noise, and determining the attention frequency point based on the insertion loss requirement.

[0111] The common mode topology structure determination unit 203 is used for determining the capacitance value of the safety capacitor based on the capacitance determination rule, and determining the common mode optimal topology by analyzing the inductance value required by the attention frequency point under the topology cluster based on the impedance characteristic value of the safety capacitor.

[0112] The differential mode topology structure determination unit 205 is used for selecting the magnetic core based on the magnetic core selection rule, determining the total differential mode capacity and the number of turns required by the inductance corresponding to the attention frequency point based on the magnetic core information, and selecting the differential mode optimal topology by using the total differential mode capacity.

[0113] The filter building determination unit 207 is used for determining the filter optimization scheme according to the common mode and differential mode optimal topologies and the impedance characteristic values, building the test prototype by using the optimization scheme to determine the application effect of the filter, and adjusting the filter optimization scheme based on the determination result.

[0114] In the optional embodiment, the attention frequency point 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 point selection module (not shown in the figure), and an attention frequency point selection module (not shown in the figure), wherein:

[0115] The noise source impedance obtaining module is configured to measure noise source impedances corresponding to the common mode and the differential mode of the transformer based on a noise path analysis method, and determine original noises of the common mode and the differential mode of the transformer according to input frequencies set according to preset test requirements; the insertion loss frequency spectrum obtaining module is configured to obtain a difference between the original noises and a noise limit value, add the difference to a threshold value to determine insertion loss requirements corresponding to the common mode and the differential mode of the transformer, and determine a required insertion loss frequency spectrum based on the insertion loss requirements; the tangent frequency point selecting module is configured to select tangent frequency points by selecting tangent lines according to a preset frequency curve range, performing frequency response analysis on the tangent lines in a defined sequence direction, and selecting the tangent frequency points as the concerned frequency points according to an analysis result.

[0116] In the traditional design method of the EMI filter, the frequency characteristics of the inductor and the capacitor are not considered, and the insertion loss relationship is derived under the ideal noise source impedance condition for design. However, the noise source impedance of the actual circuit varies greatly with frequency and cannot meet the assumed condition in the full frequency band, and the actual filter inductor and capacitor also have frequency characteristics, and the noise source impedance and the load impedance are mismatched to achieve the performance of the filter.

[0117] The embodiment takes a CL type common mode filter as an example to analyze the influence of the noise source impedance, the frequency characteristics of the filter device and the mismatch on the insertion loss, and the research frequency band in the embodiment is 10 kHz-10 MHz, and the EMC regulation complied with by the EMI is GJB151B-2013, as shown in an equivalent circuit. Figure 4 s s Cy LCM L

[0118] Figure 4 As shown in an equivalent circuit, the complete insertion loss expression of the CL filter can be derived as:

[0119]

[0120] Suppose that 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 corner frequency, IL changes at a fixed slope of +40dB / dec. However, for power electronic converters, the noise source impedance generally varies widely with frequency. The above three assumptions are difficult to meet across the entire frequency range, which can easily lead to deviations between the actual and designed IL (insertion loss at a specific 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 radiator and the primary-secondary coupling capacitance of the isolation transformer. Its impedance decreases with increasing frequency, such as Figure 5 The insertion loss shown in the figure below is for different noise source impedances when the filter inductor is 2mH and the filter capacitor is 0.2uF (line ① is IL when 10kΩ, and line ② is IL when 3nF). The noise source impedance of the upper curve is the 3nF capacitor impedance. The upper curve almost coincides with the complete insertion loss result of the CL filter, whose noise source impedance is a fixed high impedance of 10kΩ (satisfying the assumed conditions).

[0127] like Figure 6 (① is Z s 3nF wire, 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 The comparison results of several impedance characteristics show that as the frequency increases, the capacitive noise source impedance gradually decreases. After 1MHz, Assumption 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 as the frequency increases, the difference in IL (insertion loss at a certain frequency point) becomes larger whether the noise source impedance frequency characteristics are considered. At the same time, similarly, in reality, there are cases where Assumption 1 and Assumption 3 are not met, which will also lead to differences in IL (insertion loss at a certain frequency point).

[0128] and the conventional design is to design the L, C parameters with a 40dB / dec slope tangent to the required IL at the corner frequency, and the inductance and capacitance values are considered constant, i.e. the complete insertion loss of the CL filter, but in fact the filter elements are not ideal, Figure 7 and Figure 8 The comparison of the ideal / measured impedance characteristics of the inductance (2mH) and capacitance (0.2uF) respectively (the line ① is ideal, and the line ② is actual) shows that the resonance frequency of the capacitance is 1.3MHz, and if the frequency exceeds the resonance frequency, it becomes inductive, and the impedance increases with the frequency, such as Figure 9 When the source impedance and the load impedance are both 50Ω, it can be seen that Figure 9 The IL difference in (① ideal, ② actual) before 1.3MHz is caused by the inductance frequency characteristics, and the difference after 1.3MHz is caused by the inductance and capacitance frequency characteristics, so if the frequency characteristics of the filter elements are not considered in the design, the insertion loss difference will be large with the increase of the frequency.

[0129] As shown in Figure 10 (① Z Cy measured-0.2uF line, ② Z Cy measured-0.2uF line, ③ Z L measured-0.2u1 line, ④ Z s measured-0.2uF line, ⑤ Z LCM measured-0.2uF line), the common mode impedance Z LCM and Z L , Z Cy has been in a mismatch state in the research frequency band, but the measured impedance Z Cy (measured-0.2uF) has frequency characteristics, which is different from the ideal state Z Cy (ideal-0.2uF) at 400kHz, causing the change in the mismatch state of Z s impedance, such as Figure 11 (① IL CL C Y -measured-0.2uF line, ② IL LC C Y -measured-0.2uF line, ③

[0130] IL CLC C Y -measured-0.1uF line, ④ IL CL C Y -ideal-0.2uF line) shows that IL CL (measured-0.2uF) and IL CL(ideal-0.2uF) produces difference at 400kHz, the capacitor C y (measured-0.2uF) reaches self-resonant frequency, its IL CL (Measured-0.2uF) gradually decreases, and at 6MHz, due to Z Cy (measured-0.2uF) at this time is higher than the noise source impedance value, at this time the filter capacitor loses its effect, leaving only the inductor to continue filtering, so the effect is greatly discounted, in addition, if the common mode noise source impedance is often greater than the load impedance according to the traditional design concept, then the CL topology will be selected, then it will be found that IL CL (measured-0.2uF) is not as good as LC filter, and CLC filter (two capacitors are 0.1uF) IL is higher than CL / LC filter at 100kHz, so the design method considering only the mismatch of noise source impedance and load impedance is not perfect enough, in order to meet the IL requirement, a larger size problem will occur, so when designing the filter, the problem of topology optimization should be considered, as can be seen from the above, due to the influence of the traditional design method not considering the noise source impedance, component frequency characteristics, and topology optimization, the actual insertion loss is very different from the theory, often cannot meet the requirements, resulting in the actual design will increase the inductance / capacitance value to improve IL, resulting in a larger size of the filter, low design efficiency and other problems.

[0131] In view of the above shortcomings, the embodiment proposes an improved design method considering noise source impedance, component frequency characteristics and topology optimization, and the design flow chart is as shown in Figure 1 and Figure 2 .

[0132] Compared with the traditional design method, in the case of known noise source impedance frequency characteristics, total filter capacitance C and model selection, the improved method uses the complete insertion loss expression of CL, LC, CLC and LCL topologies, and obtains the required inductance value under each topology according to the required insertion loss of multiple attention noise exceeding frequency points. The topology with the smallest required inductance value is considered as the optimal topology, which realizes quantitative and accurate topology optimization and parameter optimization design. At the same time, the frequency characteristics of the magnetic permeability of the magnetic core are considered in the design of the inductance magnetic component in the whole frequency range. The noise source impedance characteristics, as well as the frequency characteristics of the capacitor and the inductor, are considered in the design process. Finally, the optimal design scheme meeting the requirements of the whole frequency band is obtained.

[0133] Since the insertion loss slope of the four topologies is between 20-60dB / dec, the selection principle of the attention exceeding frequency points is: using the slope of 20-60dB / dec to approach the required insertion loss frequency spectrum from left to right (i.e. from low to high frequency), and the first several frequency points that are tangent are the main attention frequency points. Considering the frequency characteristics of the capacitor and the inductor, the second tangent frequency points can also be listed as the attention frequency points.

[0134] The complete insertion loss expressions for LC, CLC, and LCL topologies are:

[0135]

[0136] This embodiment takes the design of EMI filter for a 3kW, 270VDC / 28VDC prototype as an example to specifically illustrate the improved design process:

[0137] Step 1: Measure the noise source impedance characteristics;

[0138] There are many methods for measuring noise source impedance, such as noise path analysis, insertion loss method, dual current probe method, etc. This embodiment uses the noise path analysis method to measure and obtain the following Figure 12 and Figure 13 The noise source impedance and phase ( Figure 12 The middle line ① is the CM common mode noise source impedance amplitude, ② is the phase, Figure 13 The middle line ① is the DM differential mode noise source impedance amplitude, and ② is the phase).

[0139] The specific steps of the noise path analysis method are as follows: 1. Using the Norton / Thevenin theorem, the switch tube is equivalent 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 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 capacitors are regarded as short-circuited, and the transformer is regarded as open-circuited when measuring differential-mode impedance; 2. Using the superposition theorem, the noise conduction path of each power supply when acting alone is analyzed one by one, and simplified into the final circuit. Then, the components related to the noise source impedance are obtained, and the impedance of the related components is measured to obtain the noise source impedance.

[0140] Step 2: Measure the original noise of the converter to determine the required insertion loss and the frequency of interest;

[0141] (1) Measure the raw noise of the converter:

[0142] According to the test requirements of GJB151B-2013, the measured Figure 14 and Figure 15 The original CM and DM noise shown ( Figure 14 The middle ① line is the original CM common mode noise, ② is the limit line, Figure 15 The line ① in the center represents the original DM differential mode noise, and the line ② represents the limit line. The limit line curve represents the noise limit specified in the standard at an input voltage of 270V. The design requirement is to ensure that the conducted noise meets the standard in the 10k-10MHz frequency band.

[0143] (2) Determine the required insertion loss:

[0144] The required insertion loss is obtained by subtracting the noise limit and adding 6dB:

[0145] IL req (dB)=Noise CM / DM -Limit+6;

[0146] The required insertion loss of common mode and differential mode (DM) is shown in Figs. 2 and 3, respectively. Figure 16 and Figure 17 .

[0147] (3) Determine the frequency points of interest:

[0148] Draw a 20-60dB / dec slope from left to right (i.e. from low to high frequency) to approach the required insertion loss spectrum, and the first tangent and sub-tangent frequency points are the frequency points of interest. According to this method, the frequency points of interest of common mode are 427kHz, 1.28MHz and 1.7MHz, and the frequency points of interest of differential mode are 199kHz, 427kHz, 854kHz and 1.28MHz.

[0149] Step three, determine the total capacitance value and type of Y capacitor;

[0150] According to the EMC regulation GJB151B-2013 corresponding to the product: the capacitance of each polarity line to ground is not more than 75nF / kW, so the allowed capacitance of a single line is 0.2uF, and the total capacitance can be selected as 0.4uF. In order to ensure that the capacitance can play a role at the frequency points of interest, the self-resonant frequency of the capacitor should be greater than 1.7MHz. In theory, the smaller the capacitance, the better the high-frequency performance, but too many capacitors in parallel will occupy a large volume. In this embodiment, MKP material is selected as the safety capacitor with a single capacitance of 0.1uF, and its resonant frequency is 2MHz. The impedance characteristics of the capacitor are measured by using an impedance analyzer E5061B as shown in Fig. 4. Figure 18

[0151] Step four, CM topology and common mode inductance optimization;

[0152] With the help of Matlab software, according to the complete insertion loss expression of CL, LC, CLC and LCL different topologies, the CM inductance values required by each frequency point of interest to meet the required insertion loss are calculated under the known Y capacitor impedance and CM noise source impedance frequency characteristics, as shown in Table 1, and the topology with the smallest inductance value is selected as the optimal topology.

[0153] Table 1 CM inductance of each topology to meet the required IL at the frequency points of interest

[0154]

[0155] ​As shown in Table 1, the CLC filter requires the least inductance at all frequencies of interest, so the CLC topology is ultimately selected. If the optimal topology differs at different frequencies of interest, continue designing the magnetic components under several optimal topologies. After selecting the magnetic core, calculate the number of turns required for each topology to meet all IL requirements. The topology with the fewest turns is the optimal one.

[0156] Step 5: Design the inductor core and number of turns, and test the impedance and leakage inductance.

[0157] Generally, the magnetic cores suitable for common-mode inductors are: ferrite and nanocrystalline. 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 value change rate is also low with increasing frequency, and is suitable for medium and high noise. Amorphous material has ultra-high magnetic permeability, low inductance value change rate, no hysteresis and stretching phenomenon, and the influence of parasitic capacitance is not obvious within 10kHz-10MHz, so it is inductive in the entire frequency band. In this embodiment, a W515 magnetic core with a size of 19x11x8mm is selected.

[0158] The actual number of turns N required for the common-mode inductor is:

[0159]

[0160] Inductance factor:

[0161]

[0162] Where, l represents 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 core. At the same time, the frequency characteristics of magnetic permeability and inductance factor are measured. Figure 19 As shown in the figure (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:

[0163] Table 2 The number of turns required for the W515 magnetic ring under the common mode inductance required at the three frequency points

[0164] f (Hz) L cm (uH)]]> 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

[0165] In order to meet the required inductance value at each frequency point of interest, the number of turns is finally selected as 7 turns. Figure 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.

[0166] Step 6: Simulate and verify the CM filter IL;

[0167] The 7-turn designed / wound W515 magnetic core inductance impedance characteristics, 2 parallel 0.1uF capacitor impedance, noise source impedance are introduced into the CLC complete insertion loss expression to calculate the filter insertion loss or simulate the filter insertion loss by using ADS (Advanced Design System) software, as shown in Figure 21 (① is ILCLC, ② is CM required IL), it can be seen that the design requirements are met.

[0168] Similar to the CM filter design method, the optimal topology and parameters of the differential mode filter can be designed: in this embodiment, the leakage inductance of the CM inductor is used as the differential mode inductance, and the actual measured inductance value changes little with frequency, so the minimum value 1.42uH is taken, and the DM noise source impedance is combined to calculate the total differential mode capacitance of each topology that meets the required DM IL at the DM concerned frequency point, as shown in Table 3. The topology with the smallest total differential mode capacitance is selected as the optimal topology.

[0169] Table 3 X capacitance value required by each topology when meeting the required insertion loss at the DM concerned frequency point and the optimal topology

[0170]

[0171] From Table 3, it can be seen that at each concerned frequency point, the LC required capacitance is the smallest, so this topology is selected here. Since the frequency of the maximum peak value is 1.2M, an X capacitor with MKP material, a self-resonant frequency of 1MHz and a capacitance of 1.55uF is selected. The actual measured 1.55uF X capacitor impedance characteristics are as shown in Figure 22 .

[0172] After obtaining the leakage inductance value, DM noise source impedance and X capacitor frequency characteristics, it can be simulated to verify whether the DM filter IL meets the required IL, and the result is as shown in Figure 23 (upper is ILLC, lower is required IL), it can be seen from Figure 23 (① is ILCLC, ② is DM required IL) that the designed DM filter meets the required IL, and the above is an improved design method considering noise source impedance and element frequency characteristics.

[0173] Step seven, experimental verification;

[0174] (1) Traditional design results: According to the traditional design method, it is considered 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 type topology is selected for common mode, and the LC type topology is selected for differential mode. The CM turning frequency (16.9893 kHz), the DM turning frequency (51.602 kHz) and the Y capacitance value are calculated. The required common mode inductance is 220uH. Since the W515 magnetic core is not suitable, the amorphous magnetic ring T60006-L2025-W380-05 is selected, whose size is 25x16x10mm. According to the magnetic core data manual, the inductance factor is 50uH≤A L ≤95uH at 10kHz, A L =50uH, the inductance is 220uH, and the number of turns is as follows:

[0175]

[0176] 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 traditional method does not consider the frequency characteristics of the filter elements. The measured common mode / differential mode noise is as shown in Figure 24 and Figure 25 , respectively. Figure 24 (① is original, and ② is after installation) and Figure 25 (① is original, and ② is after installation) can be seen that the common mode EMI noise is still seriously out of standard, that is, there is a large difference between the theoretical design and the actual effect. The DM filter also fails to meet the requirements. Finally, after debugging, the inductance needs to be wound 7 turns with a value of 1.8mH to meet the noise index.

[0177] (2) Optimized design results:

[0178] According to the noise source impedance characteristics, element impedance characteristics, and optimized design results of topology selection, a filter test machine is built. In the case of the same height, due to the addition of the step of topology optimization in the design scheme, the topology changes, the common mode inductance volume is reduced, the filter size is reduced from 133mm*30.5mm to 123mm*26.5mm, the volume is reduced by 24.4%, and the volume of the magnetic core / filter of the two methods is compared as shown in Figure 26 and Figure 27 . At the same time, the noise measured after the filter designed by the optimization method is installed in the sample machine is as shown in Figure 28 and Figure 29 . From Figure 28 (① is original, and ② is after installation) and Figure 29 (① is original, and ② is after installation) can be seen that the new method can achieve one-time compliance, realize precise optimization design, and the CM filter volume is significantly reduced, which can prove the effectiveness of the design method.

[0179] Due to the wide range of variation of the impedance of the noise source of the power electronic converter with frequency, the traditional EMI filter design method has the problems of topology optimization difficulty, large difference between actual noise suppression effect and theory, and the need for multiple trial and error. The improved design method proposed in the present application considers the influence of the noise source impedance, the filter inductance and the frequency characteristics of the capacitor on the IL of the filter. Based on the complete insertion loss expression under each topology, the required parameter values at multiple concerned frequency points are calculated by using MATLAB simulation software or a self-programmed program, thereby realizing optimal topology selection and EMI filter parameter optimization design. The design process is clear, rigorous and reliable, and has strong operability. The performance of the EMI filter designed by the optimization method proposed in the present embodiment can meet the standard at one time, and the volume of the EMI filter is smaller than that of the traditional design.

[0180] In one embodiment, a computer device, which can be a server, has an internal structure diagram as shown in Figure 30 The computer device includes a processor, a memory and a network interface connected by a system bus. The processor of the computer device is configured 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 running the operating system and the computer program in the non-volatile storage medium. The database of the computer device is configured to store static information and dynamic information data. The network interface of the computer device is configured to communicate with an external terminal through a network connection. The computer program is executed by the processor to implement the steps in the above method embodiments.

[0181] Those skilled in the art can understand that Figure 30 The structure shown in the above

[0182] In addition, the present application also provides a computer device including a memory and a processor, the memory stores a computer program, and the processor implements the steps in the above method embodiments when executing the computer program.

[0183] In addition, the present application also provides a computer readable storage medium, which stores a computer program, and the computer program implements the steps in the above method embodiments when executed by a processor.

[0184] 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 relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when executed, can include the processes of the above-mentioned embodiments. Any reference to memory, storage, database or other medium used in each embodiment of the present application 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 but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0185] The present application is not limited to the structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present application is only limited by the appended claims.

Claims

1. A method for EMI filter optimization based on noise source impedance, comprising: The EMI filter optimization method comprises: Measuring the noise source impedance and the original noise corresponding to the common mode and the differential mode of the transformer, judging the insertion loss requirement based on the original noise, and determining the frequency points of interest using the insertion loss requirement; Selecting the safety capacitor based on the preset electromagnetic compatibility rule, determining the capacitance value corresponding to the safety capacitor according to the selection result, and determining the resonance frequency of the safety capacitor using the capacitance value result; Determining the impedance characteristic value of the safety capacitor based on the resonance frequency and the impedance analysis technology, and analyzing the complete insertion loss under the topology cluster according to the loss calculation function set; Combining the impedance characteristic value, the interactive analysis technology, the complete insertion loss and the common mode noise source impedance, calculating the common mode inductance value required for the common mode frequency point to meet the insertion loss requirement under the topology cluster, and selecting the topology corresponding to the minimum inductance value as the common mode optimal topology; Obtaining the vacuum permeability and the effective cross-sectional area corresponding to the alternative magnetic core, and combining the vacuum permeability, the effective cross-sectional area and the effective length of the magnetic circuit to obtain the inductance factor of the alternative magnetic core; Selecting the alternative magnetic core with the highest inductance factor and the highest saturation magnetic density as the target magnetic core based on the inductance factor and the preset rule, and calculating the number of turns required for the magnetic core of the differential mode inductance under the differential mode frequency point condition according to the common mode inductance value and the inductance factor; Selecting the number of turns required for the highest magnetic core of the differential mode inductance, and performing common mode winding test according to the number of turns result, and obtaining the differential mode inductance impedance characteristic and the leakage inductance of the common mode inductance using the test result; Taking the common mode leakage inductance as the differential mode inductance, and combining the differential mode noise source impedance to calculate the total differential mode capacitance required for the topology cluster to meet the insertion loss requirement under the differential mode frequency point condition, and selecting the topology with the smallest total differential mode capacitance as the differential mode optimal topology; Determining the filter optimization scheme according to the common mode, the differential mode optimal topology and the impedance characteristic value, and using the optimization scheme to build a test prototype to judge the application effect of the filter, and adjusting the filter optimization scheme based on the judgment result.

2. The noise source impedance based EMI filter optimization method of claim 1, wherein, The measurement of the noise source impedance and the original noise corresponding to the common mode and the differential mode of the transformer, the judgment of the insertion loss requirement based on the original noise, and the determination of the frequency points of interest using the insertion loss requirement comprise: Measuring the noise source impedance corresponding to the common mode and the differential mode of the transformer based on the noise path analysis method, and determining the original noise of the common mode and the differential mode according to the preset test requirement and the input frequency; Obtaining the difference between the original noise and the noise limit value, and adding the difference result to the threshold value to determine the insertion loss requirement corresponding to the common mode and the differential mode of the transformer, and determining the required insertion loss spectrum based on the insertion loss requirement; Based on the preset frequency curve range, selecting a straight line to perform frequency response analysis in the defined order direction close to the required insertion loss spectrum, and selecting the tangent frequency point according to the analysis result; Arranging the tangent frequency points in the order of reaching the tangent state, and selecting the tangent frequency points of a preset group number as the frequency points of interest based on the arrangement result.

3. The noise source impedance based EMI filter optimization method of claim 2, wherein, The preset frequency curve range is 20dB / dec-60dB / dec, and the defined order direction is from left to right.

4. The noise source impedance based EMI filter optimization method of claim 3, wherein, The loss calculation function set comprises CL filter insertion loss calculation function, LC filter insertion loss calculation function, CLC filter insertion loss calculation function and LCL filter insertion loss calculation function; The expression of the CL filter insertion loss calculation function is: where IL CL represents the complete insertion loss value of the CL filter, Z L represents the equivalent load impedance, Z s represents the noise source impedance, Z LCM represents the common mode inductance, Z Cy represents the safety capacitor impedance.

5. The noise source impedance based EMI filter optimization method of claim 4, wherein, The formula for calculating the inductance factor is: wherein A L (f) represents the inductance factor, μ o represents the vacuum permeability, A e represents the effective cross-sectional area of the core, l represents the effective length of the magnetic path, f represents the frequency, μ r represents the relative permeability of the core.

6. The noise source impedance based EMI filter optimization method of claim 1, wherein, The filter optimization scheme is determined according to the common-mode optimal topology and the impedance characteristic value, and the application effect of the filter is judged by building a test prototype based on the optimization scheme, and the filter optimization scheme is adjusted based on the judgment result, which comprises: The filter optimization scheme is defined according to the common-mode optimal topology and the differential-mode optimal topology and the corresponding impedance characteristic value, and the filter test machine is built using the optimization scheme, and the volume difference between the filter test machine and the historical filter is compared based on the building result; The filter test machine is installed on the simulation machine based on the simulation technology, and the common-mode noise and the differential-mode noise corresponding to the filter test machine are obtained; The noise difference between the common-mode noise, the differential-mode noise and the 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.

7. A noise source impedance based EMI filter optimization system, comprising: The EMI filter optimization system comprises: The attention frequency point determination unit is used for measuring the noise source impedance corresponding to the common-mode and differential-mode of the converter and the original noise, judging the insertion loss requirement based on the original noise, and determining the attention frequency point using the insertion loss requirement; The common-mode topology structure determination unit determines the capacitance value of the safety capacitor based on the capacitance determination rule, and determines the impedance characteristic value of the safety capacitor according to the capacitance value, and analyzes the inductance value required by the attention frequency point under the topology cluster using the impedance characteristic value, and determines the common-mode optimal topology; The differential-mode topology structure determination unit is used for selecting the magnetic core based on the magnetic core selection rule, determining the number of turns and the total differential-mode capacitance required by the inductance corresponding to the attention frequency point according to the magnetic core information, and selecting the differential-mode optimal topology using the total differential-mode capacitance; The filter building judgment unit is used for determining the filter optimization scheme according to the common-mode optimal topology and the impedance characteristic value, and building a test prototype to judge the application effect of the filter using the optimization scheme, and adjusting the filter optimization scheme based on the judgment result.

8. The noise source impedance based EMI filter optimization system of claim 7, wherein, The attention frequency point determination unit comprises: The noise source impedance acquisition module is used for measuring the noise source impedance corresponding to the common-mode and differential-mode of the converter based on the noise path analysis method, and determining the original noise of the converter according to the input frequency set according to the preset test requirement; The insertion loss frequency spectrum acquisition module is used for obtaining the difference between the original noise and the noise limit value, and adding the difference result and the threshold value to determine the insertion loss requirement corresponding to the common-mode and differential-mode of the converter, and determining the required insertion loss frequency spectrum based on the insertion loss requirement; The tangent frequency point selection module is used for selecting a tangent according to the definition order direction close to the required insertion loss frequency spectrum based on the preset frequency curve range, performing frequency response analysis, and selecting the tangent frequency point according to the analysis result; The attention frequency point selection module is used for arranging the tangent frequency points in the order of reaching the tangent state, and selecting the tangent frequency points of a preset group number as the attention frequency points based on the arrangement result.

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