An optimal capacitor allocation method and system for electromagnetic interference filters

Abstract

This invention belongs to the field of filter capacitor allocation technology, and discloses an optimal capacitor allocation method and system for electromagnetic interference (EMI) filters. The method includes: obtaining the noise source impedance and load impedance values ​​of the EMI filter under a first impedance condition; determining the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss; classifying the noise source impedance type based on the noise frequency band; determining the optimal capacitor allocation coefficient under a second impedance condition that satisfies a single out-of-range frequency point, based on the noise source impedance type and a pre-configured slope segment of insertion loss; when the optimal capacitor allocation coefficients corresponding to multiple out-of-range frequency points are different, determining the optimal capacitor allocation coefficient applicable to all out-of-range frequency points based on the principle of minimizing the number of magnetic core turns. This invention, from the perspective of achieving optimal insertion loss, discloses an optimal capacitor allocation method for EMI filters under different impedance conditions.

Description

Technical Field

[0001] This invention relates to filter capacitor mode distribution, and particularly to an optimal capacitor allocation method and system for electromagnetic interference filters. Background Technology

[0002] To reduce the pollution of the power grid by power electronic devices and prevent mutual interference coupling between devices, various industries have established corresponding standards to limit conducted interference. Although technologies such as frequency dithering, PCB layout optimization, soft switching, and cancellation techniques can effectively suppress conducted noise, current research shows that few products can achieve conducted interference below the specified limits without using electromagnetic interference (EMI) filters. Therefore, EMI filters are essential components for electrical equipment to meet electromagnetic compatibility (EMC) requirements. With the increasing power density and switching frequency of power electronic converters, designing EMI filters that meet EMC standards and are compact in size is crucial.

[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: first, using integration technology to reduce size and weight; second, parameter-precision design methods that consider noise source impedance and component frequency characteristics; and third, active EMI filter technology.

[0004] For example, the prior art includes:

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

[0006] An integrated design scheme for an EMI filter based on a UU-shaped magnetic core (a magnetic component used in power electronic equipment) and flexible multilayer metal foil is proposed. Three integrated structures are designed, which not only reduces the size and weight of the filter, but also allows for the independent design of CM (Common Mode) and DM (Differential Mode) filter elements. However, the flexible dielectric material has a relatively low permittivity (generally between 2 and 4), which cannot significantly increase the integrated capacitance. Furthermore, the low reliability of the flexible multilayer metal foil may lead to insufficient filter capacitance, short circuit or open circuit in the filter circuit.

[0007] A low-permeability differential-mode inductor is placed within the window of a common-mode inductor. The two inductors share the same winding structure, which greatly reduces the inductor volume while increasing the differential-mode inductance value. However, this leads to an increase in winding capacitance and a deterioration in high-frequency performance.

[0008] By extracting the amplitude and phase of the noise source impedance, a design method considering the noise source impedance and the frequency characteristics of the components is proposed. However, the problem of noise source impedance, load impedance and filter component mismatch 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 across the entire frequency range. Therefore, how to optimize the topology and design parameters urgently needs to be studied.

[0009] CL, LC, and CLC are common topologies used in electromagnetic interference (EMI) filter design for power electronic converters. Traditional topology selection methods are based on qualitative impedance mismatch principles and rely on designer experience. The parameters of CLC topologies are designed based on equal capacitance values ​​on both sides (capacitance is halved) and approximate formulas. However, the impedance characteristics of noise sources in power electronic converters are diverse and vary greatly with frequency, making it difficult to achieve optimal design in both topology selection and parameter design using traditional methods.

[0010] Therefore, how to provide an optimal capacitor allocation method and system for electromagnetic interference filters is an urgent problem to be solved. Summary of the Invention

[0011] This invention provides a method and system for optimal capacitor allocation in electromagnetic interference filters, which solves the problem that existing technologies struggle to achieve optimal design in both topology selection and parameter design.

[0012] To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or to describe the scope of protection of these embodiments. Its sole purpose is to present some concepts in a simple form as a prelude to the detailed description that follows.

[0013] According to a first aspect of the present invention, an optimal capacitor allocation method for an electromagnetic interference filter is provided.

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

[0015] Obtain the noise source impedance and load impedance values ​​of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss.

[0016] Based on the noise frequency band, the types of noise source impedances are classified. For the noise source impedance type and the slope segment of the pre-configured insertion loss, the optimal capacitance allocation coefficient is determined under the second impedance condition and satisfying the single out-of-range frequency point.

[0017] When the optimal capacitance allocation coefficients for multiple out-of-standard frequency points are different, the optimal capacitance allocation coefficient applicable to all out-of-standard frequency points is determined based on the principle of minimizing the number of magnetic core turns.

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

[0019] When Z L =s L At that time, the insertion loss of the electromagnetic interference filter was calculated, and the value of the angular frequency (rad / s) was analyzed. Z L denoted by , where s represents the filtering inductor impedance, scattering parameter is a network parameter based on the relationship between incident and reflected microwaves, and L represents the filtering inductance 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, obtain the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter connected.

[0021] When the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter is the smallest, the optimal capacitor allocation coefficient is obtained under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology.

[0022] When the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology, based on the monotonicity analysis of the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter, several real solutions are obtained as the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology.

[0023] Based on the condition that the frequency point of determining the optimal solution is less than the target frequency point, the optimal capacitor allocation coefficient under the first impedance condition is determined from the optimal capacitor allocation coefficient under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology and the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the determination frequency point of whether the electromagnetic interference filter is the optimal topology.

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

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

[0026] The impedance of noise sources with frequencies below a preset threshold is used as capacitive impedance; the impedance of noise sources with frequencies above a preset threshold is used as inductive impedance.

[0027] In one embodiment, determining the optimal capacitance allocation factor that satisfies the single out-of-range frequency point under the second impedance condition, for the noise source impedance type and a pre-configured insertion loss slope segment, includes:

[0028] Based on the slope of the actual insertion loss, the analysis process of the optimal capacitance allocation coefficient is divided into several segments.

[0029] Based on the insertion loss of the electromagnetic interference filter, the optimal capacitor allocation coefficient for each segment is determined, and a formula for selecting the optimal capacitor allocation coefficient is constructed.

[0030] Substitute the actual noise frequency points into the optimal capacitor allocation coefficient selection formula, and take the calculation result with the minimum required inductance value as the optimal capacitor allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point.

[0031] Among them, the optimal capacitor allocation coefficient selection formula includes the optimal capacitor allocation coefficient selection formula when the noise source impedance is capacitive impedance and the optimal capacitor allocation coefficient selection formula when the noise source impedance is inductive impedance.

[0032] In one embodiment, the selection options in the formula for the optimal capacitance allocation factor when the noise source impedance is capacitive include: 0, 1, 0.5, n1, n2, and...

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

[0034] R s and C s The resistor and capacitor are represented by their respective impedances to the capacitive noise source, and C represents the total required filter capacitance value (F).

[0035] α represents the proportionality coefficient, which is 0.5 for capacitive noise source impedance and 2 for inductive noise source impedance.

[0036] In one embodiment, the selection options in the formula for the optimal capacitance allocation factor when the noise source impedance is inductive include: 0, 1, 0.5, n3, n4, and...

[0037] Where n3 and n4 represent the two optimal solutions under the impedance of the inductive noise source;

[0038] R s and L s Here, the resistor and capacitor represent the impedance of the inductive noise source, respectively, and C represents the total required filter capacitance value.

[0039] α represents the proportionality coefficient.

[0040] In one embodiment, when the optimal capacitance allocation coefficients for multiple out-of-range frequency points are different, the optimal capacitance allocation coefficients applicable to all out-of-range frequency points are determined according to the principle of minimizing the number of magnetic core turns, including:

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

[0042] Based on the principle of minimizing the number of core turns, and in conjunction with the selected representative number of turns for the out-of-standard frequency points, the optimal capacitance allocation coefficient applicable to all out-of-standard frequency points is determined.

[0043] In one embodiment, selecting the number of turns corresponding to the out-of-standard frequency point from the number of turns calculated for any out-of-standard frequency point includes:

[0044] Select the number of turns with the largest value from the number of turns calculated at any out-of-standard frequency point as the representative number of turns.

[0045] According to a second aspect of the present invention, an optimal capacitor allocation system for an electromagnetic interference filter is provided.

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

[0047] The first capacitor optimal allocation module is used to obtain the noise source impedance value and load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss.

[0048] The second capacitor optimal allocation module is used to classify the type of noise source impedance based on the noise frequency band, and determine the optimal capacitor allocation coefficient under the second impedance condition and satisfying the single out-of-range frequency point, based on the noise source impedance type and the pre-configured slope segment of the insertion loss.

[0049] The multi-out-of-standard-point capacitor optimal allocation module is used to determine the optimal capacitor allocation coefficient applicable to all out-of-standard-points based on the principle of minimizing the number of magnetic core turns when the optimal capacitor allocation coefficients corresponding to multiple out-of-standard-points are different.

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

[0051] In some embodiments, the computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the method described above.

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

[0053] In one embodiment, a computer program is stored on the computer-readable storage medium, which, when executed by a processor, implements the steps of the above method.

[0054] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0055] This invention provides an optimal capacitor allocation method and system for electromagnetic interference (EMI) filters. It unifies CL, LC, and CLC topologies into a single CLC topology, derives a unified expression for the insertion loss of CL, LC, and CLC EMI filters, and studies the optimal capacitor allocation methods for CLC filters under 50Ω noise source impedance and actual noise source impedance, focusing on achieving optimal insertion loss. The differences in insertion loss between traditional and optimal allocation methods are also explained. Based on this invention, EMI optimization design was performed on a practical converter, and simulations and experiments verified the effectiveness of the proposed method.

[0056] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0057] The accompanying drawings, which are incorporated in and form 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 This is a flowchart illustrating an optimal capacitor allocation method for an electromagnetic interference filter according to an exemplary embodiment;

[0059] Figure 2 This is a block diagram illustrating the principle of an optimal capacitor allocation system for an electromagnetic interference filter according to an exemplary embodiment;

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

[0061] Figure 4 This is the equivalent circuit diagram of a CL-type filter;

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

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

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

[0065] Figure 8 This is a noise source impedance-frequency curve.

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

[0067] Figure 10 This is a schematic diagram showing the relationship between insertion loss and optimal capacitance allocation factor at 40kHz.

[0068] Figure 11 This is a graph showing the relationship between insertion loss and optimal capacitance allocation factor at 400kHz.

[0069] Figure 12 This is a flowchart for solving the optimal allocation coefficients;

[0070] Figure 13 This is a diagram showing the impedance amplitude / phase of a CM noise source.

[0071] Figure 14 This is the original CM noise image;

[0072] Figure 15 This is the required common-mode insertion loss diagram;

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

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

[0075] Figure 18 This is a filter insertion loss diagram for each allocation coefficient;

[0076] Figure 19 The noise spectrum after adding filters with different coefficients is shown in the figure. Detailed Implementation

[0077] The following description and accompanying drawings fully illustrate specific embodiments described herein to enable those skilled in the art to practice them. Some embodiments may include or substitute parts and features of other embodiments. The scope of the embodiments herein encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, the terms “first,” “second,” etc., are used only to distinguish one element from another without requiring or implying any actual relationship or order between the elements. Indeed, a first element can also be referred to as a second element, and vice versa. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure, apparatus, or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a structure, apparatus, or device. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the structure, apparatus, or device that includes said element. The various embodiments described herein are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0078] The terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" used in this document to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings. They are used solely for the convenience of describing the document and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description herein, unless otherwise specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two elements; they can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0079] In this document, unless otherwise stated, the term "multiple" means two or more.

[0080] In this article, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0081] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0082] It should be understood that although the steps in the flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order constraint on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0083] The modules in the apparatus or system of this application can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0084] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

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

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

[0087] Step S101: Obtain the noise source impedance value and load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss.

[0088] Step S103: Based on the noise frequency band, classify the types of noise source impedances, and determine the optimal capacitance allocation coefficient under the second impedance condition and satisfying the single out-of-range frequency point for 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 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 minimizing the number of magnetic core turns.

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

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

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

[0093] The second capacitor optimal allocation module 203 is used to classify the type of noise source impedance based on the noise frequency band, and determine the optimal capacitor 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 slope segment of the insertion loss.

[0094] The multi-out-of-standard-point capacitor optimal allocation module 205 is used to determine the optimal capacitor allocation coefficient applicable to all out-of-standard-points based on the principle of minimizing the number of magnetic core turns when the optimal capacitor allocation coefficients corresponding to multiple out-of-standard-points are different.

[0095] To facilitate understanding of the above technical solutions of the present invention, the following further describes the above technical solutions of the present invention from the perspectives of architecture and principle, as follows:

[0096] I. Analysis of Optimal Capacitor Allocation Coefficients for CLC Type EMI Filters

[0097] like Figures 4-6 The figures shown are equivalent circuit diagrams for three EMI filter topologies: CL, LC, and CLC, where V s Z is the noise source voltage. s Z is the impedance of the noise source. r Z is the noise equivalent load impedance. L For the filter inductor impedance, Z C Z C2 Z C1 For different filter capacitor impedances.

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

[0099]

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

[0101] 1.1, Z sOptimal allocation of CLC capacitors at 50Ω

[0102] First, consider the noise source impedance Z. s Load impedance Z r The capacitance distribution method is analyzed under the conditions of 50Ω and ideal passive devices. For 50Ω-50Ω systems, the insertion loss of LC(n=0) and CL(n=1) topologies is the same.

[0103] When Z L When = sL, the insertion loss of the CLC type filter in equation (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 without filter to the square of the load voltage with filter, and ω is the angular frequency (rad / s).

[0106] Differentiating 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 This is a partial equation in f′(n).

[0109] Analysis of the expression h(n) shows that:

[0110] When ω < ω0 If h(n) > 0, then It can be known When ω0 is at its minimum, f(n) is minimized, meaning the CLC filter has the lowest insertion loss at this point. ω0 represents the frequency point at which the CL / LC ratio is determined to be the optimal topology in a 50Ω-50Ω system.

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

[0112]

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

[0114]

[0115]

[0116] As shown in Table 1, the maximum value of f(n) can only occur at n = 0, 0.5, and 1. The following analysis addresses the condition where the insertion loss is greater than that at n = 0.5 (or n = 1).

[0117] Based on Equation 2, we can obtain:

[0118]

[0119] We can solve for: f > f s ,in: To determine whether the optimal solution is at a frequency point (Hz) of 0.5.

[0120] Figure 7 This is an IL simulation for 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 Simulation results show that, under the same filter parameters, after 455.75kHz, IL CLC(n＝0.5) >IL CL Furthermore, the 455.75kHz in the simulation results is consistent with the theoretical f. s =455.75kHz consistent.

[0122] In summary, under a 50Ω-50Ω system, the optimal capacitor allocation coefficient for the CLC filter is n = 0 (1) or 0.5. When f < f s When n = 0 (1), it is the optimal solution; when f > f s When n = 0.5, the optimal solution is found. Because f s The frequency is generally much smaller than the frequency of interest, so CLC (n=0.5) can be considered optimal for a 50Ω-50Ω system.

[0123] 1.2, Z s Optimal allocation of CLC capacitors under non-50Ω conditions

[0124] The noise source impedance of a practical power electronic converter typically varies with frequency, and its amplitude varies over a wide range, even across the entire frequency band. For example... Figure 8 The figure shows the differential-mode noise source impedance of a converter, which exhibits capacitive impedance characteristics in the low-frequency range and inductive characteristics in the high-frequency range. Therefore, when designing an EMI filter, it is necessary to design it according to the noise source impedance characteristics at the out-of-range frequency. The following analyzes the optimal capacitor allocation method of the CLC filter when the noise source impedance in the frequency range of interest is capacitive and inductive (resistive impedance is included, so it will not be analyzed separately here).

[0125] Let 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 is the real part of the noise source impedance. r =50α, where α is the proportionality coefficient. For CM, α = 0.5; for DM, α = 2. The CLC insertion loss formula can be derived as follows:

[0126]

[0127] After simplification, we obtain equation (5):

[0128]

[0129] Finally, we can obtain the expression for the inductance value required to satisfy IL:

[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] Methods for solving n:

[0137] Method 1:

[0138] Since n∈[0,1], the simulation step size can be set to 0.01 using simulation software (e.g., Matlab). Using an iterative algorithm, given the noise frequency and C, the n value can be substituted one by one, and the required IL at that frequency can be calculated using equation (6). CLC The optimal capacitance allocation coefficient n at that frequency point is the value of the inductance that corresponds to the smallest inductance. This method involves a large number of iterations and relatively high computational cost.

[0139] The following analysis derives analytical expressions for several possible optimal allocation coefficients based on the maximum insertion loss conditions under both capacitive and inductive noise source impedances. This reduces the computational burden and helps in understanding the relationships between the parameters.

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

[0141] 1) When Z s When the capacitance 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 term A1 in equation (7) is a constant value at the noise exceeding the standard frequency and is independent of n, the optimal allocation method of capacitor is mainly analyzed based on term B1.

[0146] B1(n) s -1 s 0 s 1 s 2 s 3 The terms have corresponding slopes of -20dB / dec, 0dB / dec, 20dB / dec, 40dB / dec, and 60dB / dec. Since the actual insertion loss slope is as follows... Figure 9 As shown, this is the result of multiple polynomials working together, with ideal parameters (Zs / Zr: 50Ω, L=2mH, C=10nF). The noise exceeding the standard frequency points will lie in different slope segments from -20dB / dec to 60dB / dec, and the optimal capacitor allocation coefficients may also differ for different slope segments. Therefore, we need to analyze each optimal allocation coefficient n segment by segment to find the required minimum inductance value. Figures 7-9 In this context, IL represents insertion loss, f(Hz) represents frequency, mag represents amplitude, Phase represents phase, Zs represents noise source impedance, and measured represents actual measurement.

[0147] Because of s in item B1 -1 and s 0 Since it is independent of n, it will not be analyzed here.

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

[0149]

[0150] R s and C s These represent the resistance and capacitance, respectively, as the impedance of the capacitive noise source.

[0151] At this point, n=1, and IL is at its maximum.

[0152] When s1 -s 2 When both factors play a major role, the CLC insertion loss can be expressed as:

[0153]

[0154] Since it is s at this time 1 -s 2 The polynomial plays a major role, while s 1 and s 2 The coefficients are all fixed, and as the frequency increases with harmonics, R... S Generally, it's not very large, therefore s50αCR s The effect can be ignored, so equation (10) can be approximated as equation (11):

[0155]

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

[0157]

[0158] Differentiating P(n) gives:

[0159]

[0160] Let P'(n) = 0, we can solve for the root n1 in the following three cases:

[0161]

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

[0163]

[0164]

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

[0166]

[0167] at this time IL is the largest.

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

[0169]

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

[0171]

[0172] The optimal solution distribution coefficients are obtained by taking its derivative:

[0173]

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

[0175] When s 3 When playing a major role, the insertion loss of CLC can be expressed as, where Z C1 Z C2 The impedances of capacitors C1 and C2 are respectively:

[0176]

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

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

[0179] One of the values ​​is used, and finally, based on the actual noise frequency, the allocation coefficients are substituted one by one. 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 For the possible optimal allocation coefficients when considering intuition:

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

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

[0194] The above provides possible optimal allocation coefficient expressions for noise source impedances of capacitive and inductive, respectively. The required L value at a certain out-of-range frequency can be calculated using equation (6), and finally, the n value with the smallest L is taken as the optimal allocation coefficient. Compared with method one, this significantly reduces the computational workload.

[0195] 3) Handling methods when the optimal n differs at different out-of-range frequencies

[0196] Since the solution obtained is the optimal solution n at a single frequency point, while there are multiple out-of-range points in the actual frequency spectrum, the optimal n may differ for different out-of-range frequencies. For example, if the noise source impedance is inductive (R... s =5Ω, L s =10nH).

[0197] like Figures 10-11 As shown, the optimal n values ​​for the out-of-range frequencies of 40kHz and 400kHz are 0 and 0.458, respectively. IL represents the insertion loss, ILmax represents the maximum insertion loss, and n is the allocation coefficient.

[0198] Therefore, the optimal allocation coefficient can be determined based on the actual situation. The specific method is as follows: assuming the optimal coefficients corresponding to the out-of-range frequencies f1, f2, and f3 are n1, n2, and n3 respectively, and with allocation coefficient n1, calculate the inductance value (L) that satisfies the out-of-range frequency (f1, f2, f3) IL. 11 L 12 L 13 ) and number of turns (N) 11 N 12 N 13 Similarly, the distribution coefficients n2 and n3 are calculated to satisfy the inductance value (L) of the excess points (f1, f2, f3) IL under the same magnetic core. 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 minimum number of turns among N1, N2, and N3 corresponds to the final optimal allocation coefficient, as shown in Table 2. The flowchart is as follows: Figure 12 As shown, Figure 12 Includes:

[0199] Determine the noise frequency to be suppressed, the total capacitance, and the noise source impedance at that frequency; when Z s =R s +1 / sC s And when Z s=R s +sL s When different n values ​​are substituted sequentially, the required inductance value for each frequency point is calculated, and the minimum inductance value and the corresponding optimal coefficient n are found. The optimal allocation coefficient n for a single frequency point is determined, the magnetic core is selected and its permeability is measured, and based on the optimal n for each frequency point, the inductance value and number of turns N that satisfy all out-of-standard frequency points are calculated. The n value corresponding to the minimum number of turns is the final allocation coefficient. Figure 12 In the diagram, n1-n6 represent several possible optimal solutions.

[0200] Table 2 Example of final optimal allocation coefficients

[0201]

[0202]

[0203] 4) Differences in insertion loss between traditional and optimal allocation

[0204] Traditional CLC filters are based on the simplified insertion loss formula IL. CLC ≈20lg(|1+n(1-n)s 3 LC 2 |) The optimal allocation coefficient n is found to be 0.5, when Z s When it is capacitive, the maximum modulus of |B1(n)| in equation (8) is |B max (n)| represents the following case:

[0205]

[0206] And when hour, for:

[0207]

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

[0209] It is obvious

[0210] Simultaneously, the following can be introduced:

[0211]

[0212] That is, the IL of the optimal solution n CLC (Including CL / LC) The IL is better than n=0.5 by a maximum difference of 6dB, but attention should also be paid to the resonant frequency in the B1(n) term, such as s 1 term and s -1 term At the resonance point, s in B1(n) -1 and s 1 The item will cancel out to 0, but There will be no missing items, resulting in The ratio increases, and the specific difference depends on the actual situation. Similarly, when the noise source impedance is inductive, it is easy to reach the same conclusion that the difference at the resonant frequency cannot be judged, and there is a maximum difference of 6dB outside the resonant frequency.

[0213] II. Simulation and Experimental Verification

[0214] This paper takes a 3kW 270VDC / 28VDC prototype as an example, designs a common-mode EMI filter according to the proposed design method, and conducts simulation and experimental verification.

[0215] First, the common-mode noise source impedance was measured. This invention uses noise path analysis to obtain the following measurement results: Figure 13 The noise source impedance amplitude (thick line) and phase (thin line) shown indicate that the CM noise source impedance is basically capacitive within the 10MHz range. Figure 13 In this context, mag represents the amplitude, Phase represents the phase, Zscm represents the common-mode noise source impedance, f(Hz) represents the frequency, and measured represents the actual measurement.

[0216] Then test the common-mode noise, such as Figure 14 (Thick line) The noise level minus the EMC regulatory limit, plus 6dB, is obtained as follows: Figure 15 The required insertion loss ILreq for the common-mode filter is shown. Attention should be paid to several peak points of the switching frequency and its harmonics: 0.42MHz, 1.26MHz, 2.1MHz, 2.94MHz, 3.78MHz, 4.62MHz, and 5.46MHz. Figure 14 and Figure 15 In this context, IL represents insertion loss, f (Hz) represents frequency, and CM-IL req Here, Mag represents the insertion loss required for common mode, the Limit line represents the limit value, and Original CMnoise represents the original common mode noise.

[0217] According to the product's EMC specifications, the capacitance to ground for each polarity line should not exceed 75nF / kW. Therefore, the allowable capacitance for a single line is 0.2uF, and the total capacitance should be less than 0.4uF. To facilitate verification of the IL differences under various allocation factors, the total capacitance is set to 200nF. Using a 10nF capacitor with a material self-resonant frequency of 6MHz as the basic unit, there are 10 capacitors per polarity line. The impedance characteristics of a single capacitor are as follows... Figure 16 As shown. Figure 16 In this context, mag represents the amplitude, phase represents the phase, and Z represents the phase. C Let f(Hz) be the impedance of the required capacitor, and f(Hz) be the frequency.

[0218] Next, based on the frequencies of interest and the impedance of the noise source, the optimal allocation coefficient and the corresponding required inductance value are calculated using Method 1 and Method 2. The specific results are shown in Table 3.

[0219] Table 3. Optimal CLC topology allocation coefficients n at CM noise focus frequencies.

[0220]

[0221]

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

[0223] Table 4 shows the number of turns required for the W380 magnetic core at the noise frequency of concern.

[0224] F(MHz) Required sensitivity value 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 of inductance are required to meet the inductance values ​​for all frequencies.

[0226] 2.1 Simulation Verification

[0227] Here, design software, such as Advanced Design System (ADS), is used to import the measured impedance of the noise source, filter inductor, and filter capacitor frequency characteristics for simulation verification. To verify whether the allocation factor of 0.4 is optimal, additional allocation factors of 0, 0.2, 0.5, and 1 are added to compare the impedance characteristics and impedance IL of the 7-turn W380 core. The comparisons are as follows: Figures 17-18 As shown. Figure 17 In this context, mag represents the amplitude, Phase represents the phase, ZLcm represents the common-mode filter inductor impedance, f(Hz) represents the frequency, and W380-N indicates that the core model is W380 with 7 turns.

[0228] From the simulation results, i.e. Figure 18 As can be seen, the allocation factor of 0.4 is better than the others in terms of IL, which is consistent with the theoretical calculation. Therefore, 0.4 is selected as the final allocation factor here, which is about 2dB higher than 0.5 in terms of insertion loss. Figure 18 In the diagram, ① represents the insertion loss required for the common-mode filter, ② represents the insertion loss IL (n = 0), ③ represents the insertion loss IL (n = 1), ④ represents the insertion loss IL (n = 0.5), and ⑤ represents the insertion loss IL (n = 0.4). IL is the insertion loss, n is the allocation 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 an allocation coefficient n = 0.4 was configured. For filters with other allocation coefficients, only the number and position of capacitors needed to be changed. The noise spectrum after adding filters with different coefficients is as follows: Figure 19 As shown, from Figure 19 It can be seen that except for IL (n=0) which still exceeds the limit at 420kHz, the spectrum of the other filters meets the limit requirements, and the filter with n=0.4 has the best performance. Figure 19 In the diagram, Limit line is the limit value, mag is the amplitude, IL is the insertion loss, and n is the distribution factor. 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 ​​after adding a filter at different frequency (f) allocation coefficients (n) for the focus frequency points.

[0233]

[0234] The above experiments show that the filter with an allocation coefficient of 0.4 has the best suppression effect, which is consistent with the theoretical calculation results.

[0235] III. Conclusion

[0236] To address the issue that traditional EMI design methods cannot achieve optimal EMI filter design due to the large amplitude variation of noise source impedance in power electronic converters, this invention studies the optimal capacitor allocation method for CLC-type (including LC and CL types) filters. It presents a method for solving the optimal capacitor allocation coefficients under different noise source impedances, as well as a filter design method. The proposed method was used to optimize the design of a common-mode EMI filter for a 3kW converter prototype. Simulation and experiments verified the correctness of the method and results. The main conclusions and achievements are as follows:

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

[0238] When the noise source impedance is not 50Ω and varies over a wide range with frequency, the noise source impedance must be considered. The CLC filter has an optimal capacitor allocation solution at a certain frequency of interest. When the noise source impedance is capacitive, the optimal allocation coefficient is one of the values ​​in expression (16); when the noise source impedance is inductive, the optimal allocation coefficient is one of the values ​​in expression (17). Substituting these possible optimal allocation coefficients into formula (6) yields the required inductance for each n. The n with the smallest corresponding inductance value is selected as the optimal allocation coefficient for that frequency.

[0239] The actual spectrum contains multiple out-of-standard frequency points. When the optimal allocation coefficients of several key frequency points are different, a solution is given: determine the number of turns that meet the IL requirements of all out-of-standard points based on the required inductance value of the optimal allocation coefficient for each frequency point and the inductance factor of the selected magnetic core. The allocation coefficient n with the most turns is the optimal one.

[0240] An optimized design method for CLC-type EMI filters is presented. This method has the advantages of considering noise source impedance, component frequency characteristics, quantitatively optimizing CL, LC, and CLC topologies to achieve optimal IL, rigorous and reliable design process, and strong operability.

[0241] In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 3 As shown, the computer device includes a processor, memory, and a network interface connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database stores static and dynamic information data. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements the steps in the above method embodiments.

[0242] Those skilled in the art will understand that Figure 3 The structure shown is merely a block diagram of a portion of the structure related to the present invention and does not constitute a limitation on the computer device to which the present invention is applied. A specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0243] In addition, the present invention also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0244] In addition, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method embodiments.

[0245] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this 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 storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0246] This invention is not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this invention is limited only by the appended claims.

Claims

1. A method for optimal capacitor allocation in an electromagnetic interference filter, characterized in that, include: Obtain the noise source impedance and load impedance values ​​of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss. Based on the noise frequency band, the types of noise source impedances are classified. For the noise source impedance type and the slope segment of the pre-configured insertion loss, the optimal capacitance allocation coefficient is determined under the second impedance condition and satisfying the single out-of-range frequency point. When the optimal capacitance allocation coefficients for 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 minimizing the number of magnetic core turns. The determination of the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss includes: When Z L When Z = 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 used to determine whether the electromagnetic interference filter is the optimal topology, and the insertion loss of the electromagnetic interference filter is the lowest, obtain the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter connected. When the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter is the smallest, the optimal capacitor allocation coefficient is obtained under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology. When the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology, based on the monotonicity analysis of the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter, several real solutions are obtained as the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology. Based on the condition that the frequency point of determining whether the optimal solution is 0.5 is less than the target frequency point, the optimal capacitor allocation coefficient under the first impedance condition is determined from the optimal capacitor allocation coefficient under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology and the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the determination frequency point of whether the electromagnetic interference filter is the optimal topology. Specifically, determining the optimal capacitance allocation coefficient for the second impedance condition and satisfying the single out-of-range frequency point, based on the noise source impedance type and the pre-configured slope segment of the insertion loss, includes: Based on the slope of the actual insertion loss, the analysis process of the optimal capacitance allocation coefficient is divided into several segments. Based on the insertion loss of the electromagnetic interference filter, the optimal capacitor allocation coefficient for each segment is determined, and a formula for selecting the optimal capacitor allocation coefficient is constructed. Substitute the actual noise frequency points into the optimal capacitor allocation coefficient selection formula, and take the calculation result with the minimum required inductance value as the optimal capacitor allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point. Among them, the optimal capacitor allocation coefficient selection formula includes the optimal capacitor allocation coefficient selection formula when the noise source impedance is capacitive impedance and the optimal capacitor allocation coefficient selection formula when the noise source impedance is inductive impedance.

2. The optimal capacitor allocation method for electromagnetic interference filters according to claim 1, characterized in that, The optimal capacitor allocation coefficient includes: an optimal capacitor allocation coefficient equal to 0, an optimal capacitor allocation coefficient equal to 1, and an optimal capacitor allocation coefficient equal to 0.

5.

3. The optimal capacitor allocation method for electromagnetic interference filters according to claim 1, characterized in that, The classification of noise source impedance types based on noise frequency bands includes: The impedance of noise sources with frequencies below a preset threshold is used as capacitive impedance; the impedance of noise sources with frequencies above a preset threshold is used as inductive impedance.

4. The optimal capacitor allocation method for electromagnetic interference filters according to claim 1, characterized in that, The selection options in the formula for the optimal capacitance allocation coefficient when the noise source impedance is capacitive include: 0, 1, 0.5, n1, n2, and... Where n1 and n2 represent the two optimal solutions under the capacitive noise source impedance, respectively; R s and C s The resistor and capacitor are represented by their respective impedances to the capacitive noise source, and C represents the total required filter capacitance value. α represents the proportionality coefficient.

5. The optimal capacitor allocation method for an electromagnetic interference filter according to claim 1, characterized in that, The selection options in the formula for the optimal capacitance allocation coefficient when the noise source impedance is inductive include: 0, 1, 0.5, n3, n4, and... Where n3 and n4 represent the two optimal solutions under the impedance of the inductive noise source; R s and L s Here, the resistor and capacitor represent the impedance of the inductive noise source, respectively, and C represents the total required filter capacitance value. α represents the proportionality coefficient.

6. The optimal capacitor allocation method for an electromagnetic interference filter according to claim 1, characterized in that, When the optimal capacitance allocation coefficients for multiple out-of-range frequency points are different, the optimal capacitance allocation coefficients applicable to all out-of-range frequency points are determined according to the principle of minimizing the number of magnetic core turns, including: Obtain the optimal allocation coefficient for each out-of-standard frequency point; calculate the inductance value and number of turns for all out-of-standard frequency points, and select the number of turns for the corresponding out-of-standard frequency point from the number of turns calculated for any out-of-standard frequency point. Based on the principle of minimizing the number of core turns, and in conjunction with the selected representative number of turns for the out-of-standard frequency points, the optimal capacitance allocation coefficient applicable to all out-of-standard frequency points is determined.

7. The optimal capacitor allocation method for an electromagnetic interference filter according to claim 6, characterized in that, The selection of the number of turns corresponding to the frequency exceeding the standard point from the number of turns calculated from any frequency exceeding the standard point includes: Select the number of turns with the largest value from the number of turns calculated at any out-of-standard frequency point as the representative number of turns.

8. An optimal capacitor allocation system for an electromagnetic interference filter, characterized in that, include: The first capacitor optimal allocation module is used to obtain the noise source impedance value and load impedance value of the electromagnetic interference filter under the first impedance condition, and determine the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss. The second capacitor optimal allocation module is used to classify the type of noise source impedance based on the noise frequency band, and determine the optimal capacitor allocation coefficient under the second impedance condition and satisfying the single out-of-range frequency point, based on the noise source impedance type and the pre-configured slope segment of the insertion loss. The multi-out-of-standard-point capacitor optimal allocation module is used to determine the optimal capacitor allocation coefficient applicable to all out-of-standard-points based on the principle of minimizing the number of magnetic core turns when the optimal capacitor allocation coefficients corresponding to multiple out-of-standard-points are different. The determination of the optimal capacitor allocation coefficient under the first impedance condition based on the principle of minimizing filter insertion loss includes: When Z L When Z = 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 used to determine whether the electromagnetic interference filter is the optimal topology, and the insertion loss of the electromagnetic interference filter is the lowest, obtain the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter connected. When the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter is the smallest, the optimal capacitor allocation coefficient is obtained under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology. When the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology, based on the monotonicity analysis of the ratio of the load voltage without the filter to the square of the magnitude of the load voltage with the filter, several real solutions are obtained as the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the frequency point used to determine whether the electromagnetic interference filter is the optimal topology. Based on the condition that the frequency point of determining whether the optimal solution is 0.5 is less than the target frequency point, the optimal capacitor allocation coefficient under the first impedance condition is determined from the optimal capacitor allocation coefficient under the condition that the angular frequency is less than the determination frequency point of whether the electromagnetic interference filter is the optimal topology and the optimal capacitor allocation coefficient under the condition that the angular frequency is greater than the determination frequency point of whether the electromagnetic interference filter is the optimal topology. Specifically, determining the optimal capacitance allocation coefficient for the second impedance condition and satisfying the single out-of-range frequency point, based on the noise source impedance type and the pre-configured slope segment of the insertion loss, includes: Based on the slope of the actual insertion loss, the analysis process of the optimal capacitance allocation coefficient is divided into several segments. Based on the insertion loss of the electromagnetic interference filter, the optimal capacitor allocation coefficient for each segment is determined, and a formula for selecting the optimal capacitor allocation coefficient is constructed. Substitute the actual noise frequency points into the optimal capacitor allocation coefficient selection formula, and take the calculation result with the minimum required inductance value as the optimal capacitor allocation coefficient under the second impedance condition and satisfying the single over-standard frequency point. Among them, the optimal capacitor allocation coefficient selection formula includes the optimal capacitor allocation coefficient selection formula when the noise source impedance is capacitive impedance and the optimal capacitor allocation coefficient selection formula when the noise source impedance is inductive impedance.

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