Electromagnetic interference filter capacitance optimal distribution method and system

Abstract

The invention belongs to the technical field of filter capacitance distribution, and discloses an electromagnetic interference filter capacitance optimal distribution method and system, and the method comprises the steps: obtaining a noise source impedance value and a load impedance value of an electromagnetic interference filter under a first impedance condition, and obtaining a first impedance value of the electromagnetic interference filter based on a filter insertion loss minimum principle; determining an optimal capacitance distribution coefficient under the first impedance condition; dividing the type of noise source impedance based on the noise frequency band, and determining an optimal capacitance distribution coefficient meeting a single standard exceeding frequency point under a second impedance condition according to the type of the noise source impedance and a pre-configured slope section of insertion loss; and when the optimal capacitance distribution coefficients corresponding to the plurality of frequency points exceeding the standard are different, determining the optimal capacitance distribution coefficients suitable for all the frequency points exceeding the standard according to the principle that the number of turns of the magnetic core is minimum. From the perspective of realizing optimal insertion loss, the invention discloses an optimal distribution method of electromagnetic interference filter capacitance under different impedance conditions.

Description

Technical Field

[0001] The invention relates to filter capacitance modal distribution, and in particular to an electromagnetic interference filter capacitance optimal distribution method and system. Background Art

[0002] In order to reduce the pollution of power electronic equipment to the power grid and prevent mutual interference and coupling between electrical equipment, various industries have formulated corresponding standards to limit the conducted interference of products. Although frequency jitter technology, PCB layout optimization, soft switching technology, offset technology and other technologies can effectively suppress conducted noise, according to existing research results, few products can reduce the conducted interference to below the specified limit without the use of electromagnetic interference (EMI) filters. In other words, in order for electrical equipment to meet electromagnetic compatibility requirements, electromagnetic interference (EMI) filters are essential components of electrical equipment. With the increase in power density and switching frequency of power electronic converters, it is crucial to design EMI filters that meet EMC (Electromagnetic Compatibility) indicators and are small in size.

[0003] EMI filters have become a bottleneck restricting the development of power density. In recent years, research on EMI filter technology can be mainly divided into three aspects: one is the use of integration technology to reduce volume and weight; the second is the parameter precision design method considering the noise source impedance and component frequency characteristics; the third is active EMI filter technology.

[0004] For example, the prior art includes:

[0005] Single-stage and multi-stage integrated EMI filters are proposed based on EE and EIE type magnetic cores (EE and EIE cores are both magnetic components used in power electronic equipment). Compared with homemade traditional filters, the volume of the single-stage integrated filter is reduced by 40%, but the magnetic core of this structure has an air gap and cannot use nanocrystalline materials with high magnetic permeability.

[0006] A fully integrated design scheme for EMI filters based on UU-type magnetic cores (UU-type magnetic cores are magnetic components used in power electronic equipment) and flexible multilayer metal foils. Three integrated structures are designed, which not only reduces the volume and weight of the filter, but also can independently design CM (Common Mode) and DM (Differential Mode) filter elements. However, the relative dielectric constant of the flexible dielectric material is not high (generally between 2 and 4), and the integrated capacitance cannot be greatly improved. In addition, the low reliability of the flexible multilayer metal foil may lead to insufficient filter capacitance, short circuit or open circuit of the filter circuit.

[0007] A low permeability differential mode inductor is placed in the window of the common mode inductor. The two inductors share the same winding structure, which greatly reduces the volume of the inductor and increases the differential mode inductance value. However, it will increase the winding capacitance and deteriorate the high frequency performance.

[0008] By extracting the amplitude and phase of the noise source impedance, a design method considering the noise source impedance and component frequency characteristics is proposed. However, the mismatch of the noise source impedance, load impedance and filter components is not considered. The noise source impedance of the actual converter is different in different frequency bands and exhibits different impedance characteristics. Impedance mismatch is difficult to meet in the entire frequency band. Therefore, how to optimize the topology and design parameters needs to be studied urgently.

[0009] CL, LC and CLC are all common topologies used in the design of electromagnetic interference (EMI) filters in power electronic converters. The traditional topology selection method is based on the qualitative impedance mismatch principle and relies on the designer's experience. The parameters of the CLC topology are designed based on equal capacitance values ​​on both sides (capacitance divided in half) and approximate formulas. However, the noise source impedance characteristics of power electronic converters are diverse and vary greatly with frequency. It is difficult for traditional design methods to achieve optimal design in both topology selection and parameter design methods.

[0010] Therefore, how to provide an optimal capacitor allocation method and system for an electromagnetic interference filter is a problem that needs to be solved urgently. Summary of the invention

[0011] The embodiments of the present invention provide an electromagnetic interference filter capacitor optimal allocation method and system to solve the problem that the prior art is difficult to achieve optimal design in both topology selection and parameter design methods.

[0012] 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.

[0013] According to a first aspect of an embodiment of the present invention, a method for optimally allocating capacitance of an electromagnetic interference filter is provided.

[0014] In one embodiment, an electromagnetic interference filter capacitance optimal allocation method includes:

[0015] Obtain the noise source impedance value and the load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitance distribution coefficient under the first impedance condition based on the principle of minimum filter insertion loss;

[0016] The noise source impedance is classified into types based on the noise frequency band, and the optimal capacitance allocation coefficient under the second impedance condition and satisfying a single over-standard frequency point is determined for the noise source impedance type and the pre-configured slope segment of the insertion loss;

[0017] When the optimal capacitance allocation coefficients corresponding to multiple out-of-standard frequency points are different, the optimal capacitance allocation coefficient applicable to all out-of-standard frequency points is determined according to the principle of minimum number of core turns.

[0018] In one embodiment, based on the principle of minimum filter insertion loss, determining the optimal capacitance allocation coefficient under the first impedance condition includes:

[0019] When Z L =s L Calculate the insertion loss of the EMI filter and analyze the value of the angular frequency (rad / s), where: Z L represents the filter inductor impedance, s represents the scattering parameter, which is a network parameter based on the relationship between the incident microwave and the reflected microwave, and L represents the filter inductor value (H);

[0020] When the angular frequency is less than the frequency point for determining whether the electromagnetic interference filter is the optimal topology (i.e., the frequency point for determining whether CL / LC is the optimal topology in a 50Ω-50Ω system), and the insertion loss of the electromagnetic interference filter is the lowest, the ratio of the square of the load voltage modulus when the filter is not connected to the load voltage modulus when the filter is connected is obtained;

[0021] When the ratio of the load voltage when the filter is not connected to the square of the load voltage modulus when the filter is connected is the smallest, the optimal capacitance allocation coefficient is obtained under the condition that the angular frequency is less than the frequency point for determining whether the electromagnetic interference filter is the optimal topology;

[0022] When the angular frequency is greater than the frequency point for determining whether the electromagnetic interference filter is the optimal topology, based on the monotonicity analysis of the ratio of the load voltage when the filter is not connected to the square of the modulus of the load voltage when the filter is connected, several real number solutions are obtained as the optimal capacitance allocation coefficients under the condition that the angular frequency is greater than the frequency point for determining whether the electromagnetic interference filter is the optimal topology;

[0023] Based on the situation that the frequency point at which the optimal solution is determined to be 0.5 is lower than the target frequency point, the optimal capacitance allocation coefficient under the first impedance condition is determined from the optimal capacitance allocation coefficient under the condition that the angular frequency is lower than the frequency point at which the electromagnetic interference filter is determined to be the optimal topology and the optimal capacitance allocation coefficient under the condition that the angular frequency is higher than the frequency point at which the electromagnetic interference filter is determined to be the optimal topology.

[0024] In one embodiment, the optimal capacitance allocation coefficient includes: the optimal capacitance allocation coefficient is equal to 0, the optimal capacitance allocation coefficient is equal to 1, and the optimal capacitance allocation coefficient is equal to 0.5.

[0025] In one embodiment, classifying the types of noise source impedance based on the noise frequency band includes:

[0026] The impedance of the noise source with a frequency band lower than the preset frequency band threshold is taken as the capacitive impedance; the impedance of the noise source with a frequency band higher than the preset frequency band threshold is taken as the inductive impedance.

[0027] In one embodiment, for the noise source impedance type and the pre-configured insertion loss slope segment, determining the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point includes:

[0028] According to the slope of the actual insertion loss, the analysis process of the optimal capacitance distribution coefficient is divided into several sections;

[0029] According to the insertion loss of the electromagnetic interference filter, the optimal capacitance distribution coefficient of each segment is determined, and the optimal capacitance distribution coefficient selection formula is constructed;

[0030] Substitute the actual noise frequency point obtained into the optimal capacitance allocation coefficient selection formula, and use the calculation result of the minimum required inductance value as the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point;

[0031] The optimal capacitance allocation coefficient selection formula includes an optimal capacitance allocation coefficient selection formula when the noise source impedance is capacitive impedance and an optimal capacitance allocation coefficient selection formula when the noise source impedance is inductive impedance.

[0032] In one embodiment, the selection items in the optimal capacitance distribution coefficient selection formula when the noise source impedance is a capacitive impedance include: 0, 1, 0.5, n1, n2 and

[0033] Among them, n1 and n2 represent the two optimal solutions under the capacitive noise source impedance;

[0034] R s and C s They represent the resistance and capacitance of the capacitive noise source impedance respectively, and C represents the total required filter capacitance value (F);

[0035] α is expressed as a proportionality coefficient, which is 0.5 for capacitive noise source impedance and 2 for inductive noise source impedance.

[0036] In one embodiment, the selection items in the optimal capacitance distribution coefficient selection formula when the noise source impedance is an inductive impedance include: 0, 1, 0.5, n3, n4 and

[0037] Among them, n3 and n4 represent the two optimal solutions under the inductive noise source impedance;

[0038] R s and L s They represent the resistance and capacitance of the inductive noise source impedance respectively, and C represents the total required filter capacitance value;

[0039] α is represented as a proportionality coefficient.

[0040] In one embodiment, when the optimal capacitance allocation coefficients corresponding to multiple over-standard frequency points are different, determining the optimal capacitance allocation coefficient applicable to all over-standard frequency points according to the principle of minimum number of magnetic core turns includes:

[0041] Obtain the optimal allocation coefficient for each over-standard frequency point; calculate the inductance value and number of turns that meet all over-standard frequency points, and select the number of turns representative of the corresponding over-standard frequency point from the number of turns calculated at any over-standard frequency point;

[0042] According to the principle of minimum core turns and in combination with the selected representative turns of the out-of-spec frequency points, the optimal capacitance distribution coefficient applicable to all out-of-spec frequency points is determined.

[0043] In one embodiment, the number of turns corresponding to any over-standard frequency point is selected from the number of turns calculated at any over-standard frequency point to represent the number of turns that corresponds to the over-standard frequency point, including:

[0044] From the turns calculated at any exceeding frequency point, select the turns with the largest value as the representative turns.

[0045] According to a second aspect of an embodiment of the present invention, a system for optimally allocating capacitance of an electromagnetic interference filter is provided.

[0046] In one embodiment, the electromagnetic interference filter capacitance optimal allocation system includes:

[0047] A first capacitance optimal allocation module, used to obtain the noise source impedance value and the load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitance allocation coefficient under the first impedance condition based on the principle of minimum filter insertion loss;

[0048] A second capacitance optimal allocation module is used to classify the types of noise source impedance based on the noise frequency band, and determine the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point according to the noise source impedance type and the pre-configured slope segment of the insertion loss;

[0049] The multi-exceeding-frequency-point capacitance optimal allocation module is used to determine the optimal capacitance allocation coefficient applicable to all the exceeding-frequency points according to the principle of minimum number of magnetic core turns when the optimal capacitance allocation coefficients corresponding to the multiple exceeding-frequency points are different.

[0050] According to a third aspect of an embodiment of the present invention, a computer device is provided.

[0051] In some embodiments, 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.

[0052] According to a fourth aspect of embodiments of the present invention, a computer-readable storage medium is provided.

[0053] 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.

[0054] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0055] The present invention provides an optimal allocation method and system for electromagnetic interference filter capacitors, which unifies the three topologies of CL, LC and CLC into a CLC topology, and establishes a unified expression for the insertion loss of CL, LC and CLC electromagnetic interference filters. From the perspective of achieving optimal insertion loss, the optimal allocation method for CLC filter capacitors under 50Ω noise source impedance and actual noise source impedance is studied, and the difference in insertion loss between traditional allocation and optimal allocation is explained. Based on the optimal allocation method and system for electromagnetic interference filter capacitors provided by the present invention, an actual converter is optimized for electromagnetic interference, and simulation and experiment verify the effectiveness of the proposed method.

[0056] 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

[0057] 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.

[0058] Figure 1 is a flow chart showing a method for optimally allocating capacitance of an electromagnetic interference filter according to an exemplary embodiment;

[0059] Figure 2 is a principle block diagram of an electromagnetic interference filter capacitance optimal allocation system according to an exemplary embodiment;

[0060] Figure 3 is a structural schematic diagram of a computer device according to an exemplary embodiment;

[0061] Figure 4 It is the equivalent circuit diagram of CL type filter;

[0062] Figure 5 It is the equivalent circuit diagram of LC filter;

[0063] Figure 6 It is the equivalent circuit diagram of CLC type electromagnetic interference filter;

[0064] Figure 7 This is a comparison chart of the insertion loss of CL / CLC filters with the same parameters;

[0065] Figure 8 It is the noise source impedance frequency curve;

[0066] Fig. 9 This is the insertion loss diagram of the CLC filter under certain ideal parameters;

[0067] Fig.10 This is a schematic diagram of the relationship between insertion loss and optimal capacitance distribution coefficient at 40kHz;

[0068] Fig.11 This is a graph of insertion loss and optimal capacitance distribution coefficient at 400kHz;

[0069] Fig.12 It is the flow chart of solving the optimal distribution coefficient;

[0070] Fig.13 is the CM noise source impedance magnitude / phase plot;

[0071] Fig.14 is the original CM noise map;

[0072] Fig.15 is the required common-mode insertion loss plot;

[0073] Fig.16 This is the impedance characteristic diagram of 10nF safety capacitor;

[0074] Fig.17 This is the common mode impedance diagram of the 7-turn W380 magnetic ring;

[0075] Fig.18 is the filter insertion loss plot for each allocation coefficient;

[0076] Fig.19 The noise spectrum after adding filters with different coefficients is shown in the figure. DETAILED DESCRIPTION

[0077] 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.

[0078] 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.

[0079] As used herein, the term "plurality" means two or more than two, unless otherwise specified.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0085] Figure 1 An embodiment of the electromagnetic interference filter capacitance optimal allocation method of the present invention is shown.

[0086] In this optional embodiment, the electromagnetic interference filter capacitance optimal allocation method includes:

[0087] Step S101, obtaining a noise source impedance value and a load impedance value of an electromagnetic interference filter under a first impedance condition, and determining an optimal capacitance allocation coefficient under the first impedance condition based on a principle of minimum filter insertion loss;

[0088] Step S103, classifying the types of noise source impedance based on the noise frequency band, and determining the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point according to the noise source impedance type and the pre-configured slope segment of the insertion loss;

[0089] Step S105 , when the optimal capacitance allocation coefficients corresponding to the multiple out-of-standard frequency points are different, the optimal capacitance allocation coefficient applicable to all the out-of-standard frequency points is determined according to the principle of minimum number of magnetic core turns.

[0090] Figure 2 An embodiment of an electromagnetic interference filter capacitance optimal allocation system of the present invention is shown.

[0091] In this optional embodiment, the electromagnetic interference filter capacitance optimal allocation system includes:

[0092] The first capacitance optimal allocation module 201 is used to obtain the noise source impedance value and the load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitance allocation coefficient under the first impedance condition based on the principle of minimum filter insertion loss;

[0093] The second capacitance optimal allocation module 203 is used to classify the types of noise source impedance based on the noise frequency band, and determine the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point according to the noise source impedance type and the pre-configured slope segment of the insertion loss;

[0094] The multi-exceeding-frequency-point capacitance optimal allocation module 205 is used to determine the optimal capacitance allocation coefficient applicable to all the exceeding-frequency points according to the principle of minimum number of magnetic core turns when the optimal capacitance allocation coefficients corresponding to the multiple exceeding-frequency points are different.

[0095] In order to facilitate understanding of the above technical solutions of the present invention, the above technical solutions of the present invention are further described below from the perspective of architecture and principle, as follows:

[0096] 1. Analysis of the optimal capacitance distribution coefficient of CLC type EMI filter

[0097] like Figure 4-Figure 6 As shown in the figure, there are three EMI filter topology equivalent circuit diagrams: CL, LC, and CLC. s is the noise source voltage, Z s is the noise source impedance, Z r is the noise equivalent load impedance, Z L is the filter inductor impedance, Z C , Z C2 , Z C1 For different filter capacitor impedances.

[0098] For the CLC topology, let C = C1 + C2, C1 = nC, C2 = (1-n)C. When Where s represents the s-domain parameter, C is the required total filter capacitance value (F), and n = 0 and 1 correspond to LC and CL topologies respectively. Therefore, the three topologies can be unified into the CLC topology. The unified expression of CLC insertion loss can be derived as:

[0099]

[0100] Among them, n∈[0,1], when n=0, IL CLC =IL LC ; When n = 1, IL CLC =IL CL .

[0101] 1.1 Z sThe optimal distribution of CLC capacitors at 50Ω

[0102] First, the noise source impedance Z s , load impedance Z r The capacitance allocation method is analyzed under the condition of 50Ω and ideal passive components. For a 50Ω-50Ω system, the insertion loss of the LC (n=0) and CL (n=1) topologies is the same.

[0103] When Z L =sL, the insertion loss of the CLC filter in formula (1) can be expressed as:

[0104]

[0105] in: s represents the s-domain parameter, C represents the required total filter capacitance value (F), L represents the required filter inductance value (H), f(n) represents the ratio of the load voltage when no filter is connected to the square of the load voltage when the filter is connected, and ω is the angular frequency (rad / s).

[0106] Taking the derivative of f(n) with respect to n, we get:

[0107]

[0108] Where: h(n)=2500L 2 ω 6 C 2 n 2 -2500L 2 C 2 ω 6 n+2500LCω 4 +L 2 ω 4 is a partial equation in f′(n).

[0109] Analyzing the h(n) expression, we can see that:

[0110] When ω<ω0, h(n)>0, then Knowable When , f(n) is the smallest, that is, the CLC filter has the lowest insertion loss. ω0 represents the frequency point for determining whether CL / LC is the optimal topology in a 50Ω-50Ω system.

[0111] When ω>ω0, h(n)=0 has two different real solutions:

[0112]

[0113] Table 1 Monotonicity analysis of f(n)

[0114]

[0115]

[0116] As can be seen from Table 1, the maximum value of f(n) can only occur at n = 0, 0.5, and 1. The following analyzes the conditions under which the insertion loss of n = 0.5 is greater than that of n = 0 (or n = 1).

[0117] Based on formula 2, we can get:

[0118]

[0119] The solution is: f>f s ,in: The frequency point (Hz) for determining whether the optimal solution is 0.5.

[0120] Figure 7 IL simulation when n=0.5 (thin dashed line) and n=0,1 (thick solid line) with an inductance of 2mH and a total capacitance of 20nF.

[0121] Depend on Figure 7 The simulation results show that under the same filter parameters, the IL after 455.75kHz CLC(n＝0.5) >IL CL , and the 455.75kHz in the simulation result is consistent with the theoretical f s =455.75kHz is consistent.

[0122] In summary, in a 50Ω-50Ω system, the optimal capacitance distribution coefficient of the CLC filter is n=0(1) or 0.5. When f<f s When n=0(1) is the optimal solution; when f>f s When n=0.5, it is the optimal solution. s It is generally much smaller than the frequency of interest, so it can be considered that CLC (n=0.5) is optimal in the 50Ω-50Ω system.

[0123] 1.2 Z s Optimal Allocation of CLC Capacitors for Non-50Ω Conditions

[0124] The noise source impedance of actual power electronic converters generally changes with frequency, and its amplitude varies over a wide range, and even the impedance characteristics of the entire frequency range may change. Figure 8 The figure shows the differential mode noise source impedance of a converter, which has capacitive impedance characteristics in the low frequency band and inductive characteristics in the high frequency band. Therefore, when designing an EMI filter, it must be designed according to the noise source impedance characteristics at the over-standard frequency point. The following analyzes the optimal capacitor allocation method of the CLC filter when the noise source impedance in the frequency band of interest is capacitive and inductive (resistive is included, so it is not analyzed separately here).

[0125] Order Z s =x+yj, where x is the real part of the noise source impedance, y is the imaginary part of the noise source impedance, and Z r =50α, α is the proportionality coefficient, in CM, α=0.5; in DM, α=2, the CLC insertion loss formula can be deduced as follows:

[0126]

[0127] After rearranging, we can get formula (5):

[0128]

[0129] Finally, the inductance expression required to satisfy IL can be obtained:

[0130]

[0131] Where, e, d, and k are partial equations in equation (5):

[0132]

[0133] e=2(x+50α-ωC50αy)[ω 3 C 2 (1-n)50αny-(1-n)50αω 2 C-ω 2 Cnx]+

[0134] 2(y+ωC50αx)[ω-ω 3 C 2 (1-n)50αnx-ω 2 CNY]

[0135]

[0136] Solution for n:

[0137] Method 1:

[0138] Since n∈[0,1], the simulation step size can be set to 0.01 based on the simulation software (e.g., Matlab). Using the iterative algorithm, when the noise frequency and C are known, the n values ​​are substituted one by one, and the IL required to meet the frequency is calculated by equation (6). CLC The inductance value of the minimum inductance value is the optimal capacitance distribution coefficient n at this frequency point. This method has many iterations and a relatively large amount of calculation.

[0139] The following analytical expressions for several possible optimal allocation coefficients are derived through analysis of the maximum insertion loss conditions under capacitive and inductive noise source impedances. This can reduce the amount of calculation and also help understand the relationship between the parameters.

[0140] Method 2: Derivation of the analytical expression of the optimal distribution coefficient

[0141] 1) When Z s When it is capacitive (Zs=Rs+1 / sCs), the CLC insertion loss formula can be derived as follows:

[0142]

[0143] Where B1(n) is:

[0144]

[0145] Since the A1 term in equation (7) is a constant at the noise-exceeding frequency and has nothing to do with n, the optimal capacitor allocation method is analyzed here mainly based on the B1 term.

[0146] B1(n) -1 、s 0 、s 1 、s 2 、s 3 The corresponding slopes are -20dB / dec, 0dB / dec, 20dB / dec, 40dB / dec, and 60dB / dec. Since the slope of the actual insertion loss is Fig. 9 As shown, it is the joint action of polynomials, and the ideal parameters are (Zs / Zr: 50Ω, L=2mH, C=10nF). Each noise exceeding frequency point will be located in different slope segments from -20dB / dec to 60dB / dec, and the optimal capacitance allocation coefficient corresponding to different slope segments may also be different. Therefore, each optimal allocation coefficient n is analyzed in sections, and then the required minimum inductance value is found. Figure 7-Figure 9 In the figure, IL is the insertion loss, f(Hz) is the frequency, mag is the amplitude, Phase is the phase, Zs is the noise source impedance, and measured is the actual measurement.

[0147] Since s in item B1 -1 and 0 It has nothing to do with n, so it is not analyzed here.

[0148] When 1 When the term plays a major role, the CLC insertion loss can be approximated as:

[0149]

[0150] R s and C s The resistance and capacitance represent the capacitive noise source impedance respectively.

[0151] At this time, n=1 and IL is maximum.

[0152] When1 -s 2 When the two factors play a dominant role, the CLC insertion loss can be expressed as:

[0153]

[0154] Since this is s 1 -s 2 The polynomial of plays a major role, while s 1 and 2 The coefficients are all fixed. When the frequency increases by multiples, R S Generally not large, so s50αCR s The influence of can be ignored, so formula (10) can be approximated as formula (11):

[0155]

[0156] Where P(n) is the partial equation in equation (11):

[0157]

[0158] Taking the derivative of P(n) we get:

[0159]

[0160] Let P'(n) = 0, and its root n1 can be solved into the following three cases:

[0161]

[0162] Where n1 is the capacitive noise source impedance s 1 -s 2 The optimal solution of n when it plays a major role, u1, v1, q1, p1, a1, b1, c1, d1 are the partial equations after P(n) is derived:

[0163]

[0164]

[0165] When 2 When it plays a dominant role, the CLC insertion loss can be expressed as:

[0166]

[0167] at this time IL max.

[0168] s 2 -s 3 When the two factors play a dominant role, the CLC insertion loss can be expressed as:

[0169]

[0170] Where Q(n) is the partial equation in equation (14):

[0171]

[0172] After taking its derivative, the optimal solution distribution coefficient is:

[0173]

[0174] Where n2 is the capacitive noise source impedance s 2 -s 3 The optimal solution for n when it plays a major role, u2, v2, q2, p2, a2, b2, c2 are the partial equations after the derivative of Q(n).

[0175] When 3 When the CLC insertion loss is dominant, it can be expressed as, where Z C1 , Z C2 The impedances of capacitors C1 and C2 are:

[0176]

[0177] At this time, when , IL is maximum.

[0178] Therefore, when the noise source impedance is capacitive, the optimal distribution coefficient can only be:

[0179] Finally, based on the actual noise frequency, substitute the distribution coefficients in turn. The coefficient with the smallest required inductance value is the optimal one.

[0180] 2) When the noise source impedance is inductive

[0181] Similarly, it can be deduced that when Z s =R s +sL s The optimal distribution coefficient when it is inductive is:

[0182]

[0183] in:

[0184]

[0185] a3=4ω 2 (50αCR s ) 2 ;

[0186] b3=-6ω 2 50αCL s Rs -6ω 2 (50αCR s ) 2 ;

[0187] c3=2(R s -50α) 2 +2ω 2 (L s ) 2 +200ω 2 αCL s R s +2ω 2 (50αCR s ) 2 ;

[0188] d3=100α(R s -50α)

[0189] Among them, n3 is an optimal solution for n in the inductive noise source impedance, and u3, v3, q3, p3, a3, b3, and c3 are partial equations after the CLC insertion loss is derived.

[0190]

[0191] a4=10000(Cα) 2 (R s +ωL s ) 2 ,b4=15000(Cα) 2 (R s +ωL s ) 2 -300CL s R s α

[0192]

[0193] Among them, n4 is an optimal solution for n in the inductive noise source impedance, and u4, v4, q4, p4, a4, b4, and c4 are partial equations after the CLC insertion loss is derived.

[0194] The above gives the possible optimal distribution coefficient expressions when the noise source impedance is capacitive and inductive respectively. The required L value at a certain over-standard frequency point can be calculated using formula (6), and finally the n with the smallest L is taken as the optimal distribution coefficient. Compared with method 1, the calculation workload can be greatly reduced.

[0195] 3) The processing method when the optimal n is different at different over-standard frequency points

[0196] Since the optimal solution n is obtained at a single frequency point, and there are multiple over-standard points in the actual spectrum, there may be a problem that the optimal n at different over-standard frequency points is different. s =5Ω, L s =10nH).

[0197] like Figure 10-11 As shown in the figure, the optimal n for the over-standard frequencies of 40kHz and 400kHz are 0 and 0.458 respectively. IL is the insertion loss, ILmax is the maximum insertion loss, and n is the distribution coefficient.

[0198] Therefore, the optimal allocation coefficient can be determined according to the actual situation. The specific method is as follows: Assuming that the optimal coefficients corresponding to the over-standard frequency points f1, f2, and f3 are n1, n2, and n3 respectively, in the case of the allocation coefficient n1, the inductance value (L) that satisfies the over-standard point (f1, f2, f3) IL is calculated. 11 , L 12 , L 13 ) and number of turns (N 11 、N 12 、N 13 ), and similarly calculate the distribution coefficients n2 and n3 under the same core, and the inductance value (L) that meets the exceeding point (f1, f2, f3) IL 21 , L 22 , L 23 , L 31 , L 32 , L 33 ) and number of turns (N 21 、N 22 、N 23 、N 31 、N 32 , L 33 ), where N1=Max{N 11 , N 12 , N 13},N2=Max{N 21 , N 22 , N 23}, N3=Max{N 31 , N 32 , N 33}, the coefficient corresponding to the least number of turns among N1, N2, and N3 is the final optimal allocation coefficient. An example is shown in Table 2, and the flow chart is shown in Fig.12 As shown, Fig.12 Included:

[0199] Determine the noise frequency point, total capacity and noise source impedance at the frequency point to be suppressed; when Z s =R s +1 / sC s When Z s=R s +sL s , substitute different n values ​​in turn to calculate the required inductance value for each frequency point, and find the minimum inductance value and the corresponding optimal coefficient n, determine the optimal allocation coefficient n at a single frequency point, select the magnetic core to measure its magnetic permeability, and based on the optimal n at each frequency point, calculate the inductance value and number of turns N that meet all the exceeded frequency points, where the n value corresponding to the least number of turns is the final allocation coefficient. Fig.12 In , n1-n6 represent several possible optimal solutions.

[0200] Table 2 Example of final optimal distribution coefficient

[0201]

[0202]

[0203] 4) Difference in insertion loss between traditional distribution and optimal distribution

[0204] The traditional CLC filter is based on the simplified insertion loss formula IL CLC ≈20lg(|1+n(1-n)s 3 LC 2 |) The optimal distribution coefficient n is 0.5. s When it is capacitive, the maximum modulus value of |B1(n)| in equation (8) is |B max (n)|For the following situation:

[0205]

[0206] When hour, for:

[0207]

[0208] Assumption B 12 (n) is a polynomial:

[0209] It's obvious

[0210] Also available:

[0211]

[0212] That is, the IL of the optimal solution n CLC (including CL / LC) The maximum difference of IL better than n = 0.5 is 6dB, but it is also necessary to pay attention to the resonant frequency in item B1(n), such as s 1 Term and -1 Term At the resonance point, s in B1(n) -1 and 1 The terms will cancel out to 0, but There will be no missing items, resulting in The ratio becomes larger, and the specific difference needs to be determined according to the actual situation. Similarly, when the noise source impedance is inductive, it is easy to get the same conclusion that the difference at the resonant frequency cannot be judged, and the maximum difference outside the resonant frequency is 6dB.

[0213] 2. Simulation and Experimental Verification

[0214] Here, taking the 3kW 270VDC / 28VDC prototype as the object, a common-mode EMI filter was designed according to the proposed design method, and simulation and experimental verification were carried out.

[0215] First, the common mode noise source impedance is measured. The present invention uses the noise path analysis method to measure and obtain the following Fig.13 The noise source impedance magnitude (bold line) and phase (thin line) are shown. It can be seen that the CM noise source impedance is basically capacitive within the 10MHz range. Fig.13 In the figure, mag is the amplitude, Phase is the phase, Zscm is the common-mode noise source impedance, f(Hz) is the frequency, and measured is the actual measurement.

[0216] Then test the common mode noise as Fig.14 (bold line), the noise minus the EMC regulatory limit and then add 6dB to get Fig.15 The insertion loss ILreq required for the common-mode filter is shown in Figure 1. The peak points of the switching frequency and its multiples need to be paid attention to: 0.42MHz, 1.26MHz, 2.1MHz, 2.94MHz, 3.78MHz, 4.62MHz, and 5.46MHz. Fig.14 and Fig.15 In the equation, IL is the insertion loss, f(Hz) is the frequency, and CM-IL is req is the required insertion loss for common mode, Mag is the amplitude, Limit line is the limit line, and Original CMnoise is the original common mode noise.

[0217] According to the EMC regulations corresponding to the product: the capacitance of each polar 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 is less than 0.4uF. In order to facilitate the verification of the IL difference under each distribution coefficient, the total capacitance is set to 200nF. The basic unit is a capacitor with a self-resonant frequency of 6MHz and a capacitance of 10nF. There are 10 capacitors for each polar line. The impedance characteristics of a single capacitor are as follows: Fig.16 shown. Fig.16 In the equation, mag is the amplitude, Phase is the phase, and Z C is the impedance of the required capacitor and f(Hz) is the frequency.

[0218] Then, according to the concerned frequency points and noise source impedance, the optimal distribution coefficient and the corresponding required inductance value are calculated by method 1 and method 2. The specific results are shown in Table 3.

[0219] Table 3 CM focuses on the optimal allocation coefficient n of CLC topology under the noise frequency

[0220]

[0221]

[0222] The magnetic permeability of the core made of microcrystalline (iron-based) material is very high in the frequency range of 10k-10MHz. Therefore, the W380 (a product model) core is selected and the required number of turns is calculated based on its actual inductance factor at each frequency point. The results are shown in Table 4.

[0223] Table 4 CM focuses on the number of turns required for the W380 core at the noise frequency

[0224] F(MHz) Required inductance uH Inductance factor AL Required number of turns N 0.42 253 5.69 7 1.26 50.6 2.48 5 2.10 34 1.67 5 2.94 25 1.27 5 3.78 19.2 1.05 5 4.62 15.8 0.89 5 5.46 13 0.79 4

[0225] According to the results in Table 4, 7 turns are required to meet the required inductance values ​​at all frequency points.

[0226] 2.1 Simulation Verification

[0227] Here, with the help of design software, such as Advanced Design System (ADS), the measured noise source impedance, filter inductance, and filter capacitor impedance frequency characteristics are imported for simulation verification. At the same time, in order to verify whether the distribution coefficient 0.4 is optimal, additional distribution coefficients are added here: 0, 0.2, 0.5, and 1 to compare the IL. The impedance characteristics and IL of the 7-turn W380 core are shown in the figure below. Figure 17-Figure 18 shown. Fig.17 In the figure, mag is the amplitude, Phase is the phase, ZLcm is the common-mode filter inductor impedance, f(Hz) is the frequency, and W380-N is the 7-core model W380 with 7 turns.

[0228] From the simulation results, that is, Fig.18 From the above, we can see that the distribution coefficient of 0.4 is better than other ILs, which is consistent with the theoretical calculation. Therefore, 0.4 is selected as the final distribution coefficient here. Compared with 0.5, the insertion loss is about 2dB higher. Fig.18 In the figure, ① is the insertion loss required by the common mode filter, ② is the insertion loss IL (n = 0), ③ is the insertion loss IL (n = 1), ④ is the insertion loss IL (n = 0.5), and ⑤ is the insertion loss IL (n = 0.4). IL is the insertion loss, n is the distribution coefficient, and f (Hz) is the frequency.

[0229] 2.2 Experimental Verification

[0230] To further verify the above conclusions, an experimental platform was built. A CLC filter with a distribution coefficient of n = 0.4 was configured. The filters with other distribution coefficients only need to change the number and position of capacitors. The noise spectrum after adding filters with different coefficients is as follows Fig.19 As shown, from Fig.19 It can be seen that except for IL(n=0) which still exceeds the limit at 420kHz, the spectra of the other filters all meet the limit requirements, and the filter with n=0.4 has the best effect. Fig.19 In the figure, Limit line is the limit line, mag is the amplitude, IL is the insertion loss, and n is the distribution coefficient. ② is the insertion loss IL (n = 0), ③ is the insertion loss IL (n = 1), ④ is the insertion loss IL (n = 0.5), and ⑤ is the insertion loss IL (n = 0.4).

[0231] The specific noise values ​​are shown in Table 5.

[0232] Table 5 Noise values ​​of the frequency points of interest after adding filters at different frequency (f) distribution coefficients (n)

[0233]

[0234] From the above experiments, it can be seen that the filter with a distribution coefficient of 0.4 has the best suppression effect, which is consistent with the results of theoretical calculations.

[0235] Conclusion

[0236] Aiming at the problem that the noise source impedance amplitude of power electronic converter products has a large range of change, and the traditional EMI design method cannot achieve the optimal design of EMI filter, this paper studies the optimal capacitor allocation method of CLC type (including LC and CL type) filter, and provides the optimal capacitor allocation coefficient solution method and filter design method under different noise source impedance. The method proposed by this invention is used to optimize the common mode EMI filter design of 3kw converter prototype, and the correctness of the method and results is verified by simulation and experiment. The main conclusions and achievements are as follows:

[0237] When the noise source impedance is 50Ω, the optimal distribution coefficient of the CLC filter capacitor is: when f<f s When n = 0 (1), it is the optimal distribution coefficient; when f>f s When n=0.5 is the optimal allocation coefficient, since the actual fs is generally much smaller than the frequency of interest, it can be considered that CLC (n=0.5) is optimal in the 50Ω-50Ω system.

[0238] When the noise source impedance is not 50Ω and varies with frequency over a wide range, the noise source impedance must be considered. The CLC filter has an optimal distribution solution for capacitance at a certain frequency point of interest. When the noise source impedance is capacitive, the optimal distribution coefficient is one of the equations (16); when the noise source impedance is inductive, the optimal distribution coefficient is one of the equations (17): Substituting these possible optimal distribution coefficients into formula (6) can obtain the required inductance under each n, and select the n with the smallest corresponding inductance value as the optimal distribution coefficient for this frequency point.

[0239] There are multiple over-standard frequency points in the actual spectrum. When the optimal allocation coefficients of several main frequency points of concern are different, a processing method is given: the number of turns that meets the IL requirements of all over-standard points is determined based on the required inductance value of the optimal allocation coefficient of each frequency point and the inductance factor of the selected magnetic core. The allocation coefficient n with the largest number of turns is the optimal.

[0240] An optimization design method for CLC type EMI filter is given. This method has the advantages of considering noise source impedance, component frequency characteristics, quantitatively optimizing CL, LC, and CLC topologies to optimize IL, rigorous and reliable design process, and strong operability.

[0241] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Figure 3 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.

[0242] Those skilled in the art will understand that Figure 3 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.

[0243] 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.

[0244] 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.

[0245] 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).

[0246] 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. A method for optimal allocation of capacitance of an electromagnetic interference filter, characterized in that: include: Obtain the noise source impedance value and the load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitance distribution coefficient under the first impedance condition based on the principle of minimum filter insertion loss; The noise source impedance is classified into types based on the noise frequency band, and the optimal capacitance allocation coefficient under the second impedance condition and satisfying a single over-standard frequency point is determined for the noise source impedance type and the pre-configured slope segment of the insertion loss; When the optimal capacitance allocation coefficients corresponding to multiple out-of-standard frequency points are different, the optimal capacitance allocation coefficient applicable to all out-of-standard frequency points is determined according to the principle of minimum number of core turns.

2. The optimal allocation method for electromagnetic interference filter capacitance according to claim 1, characterized in that: The method of determining the optimal capacitance distribution coefficient under the first impedance condition based on the principle of minimum filter insertion loss includes: When Z L =sL, calculate the insertion loss of the electromagnetic interference filter and analyze the value of the angular frequency, where, Z L represents the filter inductor impedance, s represents the scattering parameter, and L represents the filter inductor value; When the angular frequency is less than the frequency point for determining whether the electromagnetic interference filter is the optimal topology and the insertion loss of the electromagnetic interference filter is the lowest, the ratio of the square of the load voltage modulus when the filter is not connected to the load voltage modulus when the filter is connected is obtained; When the ratio of the load voltage when the filter is not connected to the square of the load voltage modulus when the filter is connected is the smallest, the optimal capacitance allocation coefficient is obtained under the condition that the angular frequency is less than the frequency point for determining whether the electromagnetic interference filter is the optimal topology; When the angular frequency is greater than the frequency point for determining whether the electromagnetic interference filter is the optimal topology, based on the monotonicity analysis of the ratio of the load voltage when the filter is not connected to the square of the modulus of the load voltage when the filter is connected, several real number solutions are obtained as the optimal capacitance allocation coefficients under the condition that the angular frequency is greater than the frequency point for determining whether the electromagnetic interference filter is the optimal topology; Based on the situation that the frequency point at which the optimal solution is determined to be 0.5 is lower than the target frequency point, the optimal capacitance allocation coefficient under the first impedance condition is determined from the optimal capacitance allocation coefficient under the condition that the angular frequency is lower than the frequency point at which the electromagnetic interference filter is determined to be the optimal topology and the optimal capacitance allocation coefficient under the condition that the angular frequency is higher than the frequency point at which the electromagnetic interference filter is determined to be the optimal topology.

3. The optimal allocation method for electromagnetic interference filter capacitance according to claim 2, characterized in that: The optimal capacitance allocation coefficient includes: the optimal capacitance allocation coefficient is equal to 0, the optimal capacitance allocation coefficient is equal to 1, and the optimal capacitance allocation coefficient is equal to 0.

5.

4. The method for optimal allocation of capacitance of an electromagnetic interference filter according to claim 1, characterized in that: The classification of noise source impedance types based on noise frequency bands includes: The impedance of the noise source with a frequency band lower than the preset frequency band threshold is taken as the capacitive impedance; the impedance of the noise source with a frequency band higher than the preset frequency band threshold is taken as the inductive impedance.

5. The method for optimal allocation of capacitance of an electromagnetic interference filter according to claim 4, characterized in that: The method of determining the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point for the noise source impedance type and the pre-configured insertion loss slope segment includes: According to the slope of the actual insertion loss, the analysis process of the optimal capacitance distribution coefficient is divided into several sections; According to the insertion loss of the electromagnetic interference filter, the optimal capacitance distribution coefficient of each segment is determined, and the optimal capacitance distribution coefficient selection formula is constructed; Substitute the actual noise frequency point obtained into the optimal capacitance allocation coefficient selection formula, and use the calculation result of the minimum required inductance value as the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point; The optimal capacitance allocation coefficient selection formula includes an optimal capacitance allocation coefficient selection formula when the noise source impedance is capacitive impedance and an optimal capacitance allocation coefficient selection formula when the noise source impedance is inductive impedance.

6. The method for optimal allocation of capacitance of an electromagnetic interference filter according to claim 5, characterized in that: The options in the optimal capacitance distribution coefficient selection formula when the noise source impedance is a capacitive impedance include: 0, 1, 0.5, n1, n2 and Among them, n1 and n2 represent the two optimal solutions under the capacitive noise source impedance; R s and C s They represent the resistance and capacitance of the capacitive noise source impedance respectively, and C represents the total required filter capacitance value; α is represented as a proportionality coefficient.

7. The method for optimally allocating capacitance of an electromagnetic interference filter according to claim 5, characterized in that: The options in the optimal capacitance distribution coefficient selection formula when the noise source impedance is an inductive impedance include: 0, 1, 0.5, n3, n4 and Among them, n3 and n4 represent the two optimal solutions under the inductive noise source impedance; R s and L s They represent the resistance and capacitance of the inductive noise source impedance respectively, and C represents the total required filter capacitance value; α is represented as a proportionality coefficient.

8. The method for optimal allocation of capacitance of an electromagnetic interference filter according to claim 1, characterized in that: When the optimal capacitance allocation coefficients corresponding to the multiple over-standard frequency points are different, determining the optimal capacitance allocation coefficient applicable to all over-standard frequency points according to the principle of minimum number of magnetic core turns includes: Obtain the optimal allocation coefficient for each over-standard frequency point; calculate the inductance value and number of turns that meet all over-standard frequency points, and select the number of turns representative of the corresponding over-standard frequency point from the number of turns calculated at any over-standard frequency point; According to the principle of minimum core turns and in combination with the selected representative turns of the out-of-spec frequency points, the optimal capacitance distribution coefficient applicable to all out-of-spec frequency points is determined.

9. The method for optimal allocation of capacitance of an electromagnetic interference filter according to claim 8, characterized in that: The number of turns corresponding to the over-standard frequency point selected from the number of turns calculated at any over-standard frequency point comprises: From the turns calculated at any exceeding frequency point, select the turns with the largest value as the representative turns.

10. An electromagnetic interference filter capacitor optimal allocation system, characterized in that: include: A first capacitance optimal allocation module, used to obtain the noise source impedance value and the load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitance allocation coefficient under the first impedance condition based on the principle of minimum filter insertion loss; A second capacitance optimal allocation module is used to classify the types of noise source impedance based on the noise frequency band, and determine the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point according to the noise source impedance type and the pre-configured slope segment of the insertion loss; The multi-exceeding-frequency-point capacitance optimal allocation module is used to determine the optimal capacitance allocation coefficient applicable to all the exceeding-frequency points according to the principle of minimum number of magnetic core turns when the optimal capacitance allocation coefficients corresponding to the multiple exceeding-frequency points are different.

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