A design method for magnetic integrated structure of EMI filter

Abstract

The present invention relates to a method for designing a magnetic integrated structure of an EMI filter, in which differential mode inductors are respectively arranged before and after the rectifier bridge of the EMI filter. L dm1 and L dm2 , the differential mode inductance L dm1 and L dm2 Integrated on a fully decoupled magnetic core. This method is conducive to further reducing the size of the filter while ensuring the noise suppression effect.

Description

Technical Field

[0001] The invention belongs to the field of filters, and in particular relates to a magnetic integrated structure design method for an EMI filter. Background Art

[0002] In recent years, wide bandgap power electronic devices represented by silicon carbide and gallium nitride have been introduced and used more and more widely, which has brought the entire power electronics discipline into a new era of rapid development. However, power electronic devices often cause large electromagnetic interference noise during the high-speed opening and closing process, which not only affects the normal operation of electrical equipment, but also pollutes the power grid. Therefore, it is of great significance to study how to suppress electromagnetic interference.

[0003] EMI passive filters are widely used to suppress electromagnetic interference due to their simple structure, convenient design and low cost. EMI filters can effectively suppress the conducted electromagnetic interference noise of power converters. The suppression mechanism is mainly to increase the impedance on the noise transmission path by connecting filter inductors in series with the L line and the N line and to bypass the electromagnetic interference noise by connecting filter capacitors in parallel, so that the power supply products can meet the relevant electromagnetic compatibility standards.

[0004] At present, power converters are developing towards high frequency, high power density, high efficiency and low electromagnetic interference, which brings great challenges to the design of EMI filters. With the increase of electromagnetic interference, the common practice in engineering is to increase the filter inductance and capacitance, or increase the order of the filter to meet the electromagnetic compatibility requirements, but this will inevitably increase the weight and volume of the filter, which runs counter to the direction of high power density.

[0005] The existing main filter structures include: 1) The filter is placed on the AC side. Figure 1 The filter shown, L cm1 With L cm2 is a common mode choke, L dm is the differential mode filter inductor. cm1 Responsible for suppressing high-frequency noise, the common-mode inductance is generally small, so the differential-mode inductance as its leakage inductance is even smaller and can be ignored in the differential-mode filter analysis; while L cm2 It is responsible for suppressing low-frequency noise. The common-mode inductance is generally large, thus obtaining a large leakage inductance (L k ) to L dm , C x1 , C x2 and C B A second-order differential mode filter is formed to obtain a better differential mode noise suppression effect. 2) The filter is placed on the AC side and the DC side. Figure 2 Shown is Figure 1 The improvement made on the filter topology shown in the figure will Figure 1 C on the AC sideX2 With L dm Place it after the rectifier bridge and the rectifier filter capacitor C B Compared with the AC side safety capacitor, the DC side can use a smaller film capacitor, so this topology is widely used. cm2 The common mode inductance is generally large in order to obtain a larger leakage inductance to suppress differential mode noise. In the noise transmission path, the common mode inductance in the EMI filter and the common mode distributed capacitance C of the primary and secondary sides of the transformer Q The circuit structure is equivalent to series connection. In common-mode noise suppression, the common-mode noise can be suppressed by adjusting the inductance of the common-mode inductor of the EMI filter. Similarly, the common-mode noise can be suppressed by adjusting the transformer C Q To suppress common mode noise. With the in-depth study of the EMI characteristics of planar transformers, there are many methods to obtain smaller transformer C Q Therefore, the inductance of the common mode inductor can be very small. In order to obtain a larger leakage inductance, a common mode choke L with a large volume and inductance is used. cm2 It is not cost-effective. Summary of the invention

[0006] The object of the present invention is to provide a method for designing a magnetic integrated structure of an EMI filter, which is conducive to further reducing the volume of the filter while ensuring the noise suppression effect.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is: a method for designing a magnetic integrated structure of an EMI filter, in which a differential mode inductor L is respectively arranged before and after the rectifier bridge of the EMI filter. dm1 and L dm2 , the differential mode inductance L dm1 and L dm2 Integrated on a fully decoupled magnetic core.

[0008] Furthermore, the fully decoupled magnetic core includes a middle column and two side columns arranged on both sides of the middle column, and the differential mode inductor L dm1 , L dm2 They are respectively wound on two side columns, the middle column is made of manganese-zinc ferrite material with high magnetic permeability, and the side columns are made of magnetic powder core material with low magnetic permeability and strong saturation ability.

[0009] Furthermore, the fully decoupled magnetic core includes a middle column and two side columns arranged on both sides of the middle column, and the differential mode inductor L dm1 , L dm2 They are respectively wound on two side columns. The middle column and the side columns are both made of manganese-zinc ferrite material with high magnetic permeability, but air gaps are opened on the side columns.

[0010] Furthermore, the magnetic resistance R mThe calculation formula is as follows:

[0011]

[0012] Wherein, A and L are the cross-sectional area and length of the magnetic circuit, respectively, and μ represents the magnetic permeability of the material; when the cross-sectional area and length of the magnetic circuit are constant, the magnetic resistance is inversely proportional to the magnetic permeability; in the fully decoupled magnetic core, through structural design and material selection, the magnetic resistance of the middle column is much smaller than that of the side column, so that the side column L dm1 Most of the magnetic flux generated by the winding flows through the center column, and only a very small part of the magnetic flux passes through L dm2 winding, thereby reducing the differential mode inductance L dm1 With L dm2 Mutual inductance makes the coupling coefficient K of the fully decoupled magnetic core less than 5%.

[0013] Furthermore, the differential mode inductor L dm1 and L dm2 The sense is equal.

[0014] Furthermore, the differential mode inductor L dm1 , L dm2 The size is:

[0015]

[0016] Among them, L dm is the differential mode filter inductor, L k For leakage inductance.

[0017] Compared with the prior art, the present invention has the following beneficial effects: it provides a method for designing a magnetic integrated structure of an EMI filter. The EMI filter designed by this method can further reduce the volume of the filter while ensuring that the noise suppression effect remains unchanged, thereby improving the power density of the whole machine, which is of great significance for the design of miniaturized filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the AC side filter topology structure in the prior art;

[0019] Figure 2 It is an AC side plus DC side filter topology structure in the prior art;

[0020] Figure 3 It is the topological structure of the magnetic integrated structure of the filter in the embodiment of the present invention;

[0021] Figure 4 It is a topological simplified structure of the magnetic integrated structure of the filter in the embodiment of the present invention;

[0022] Figure 5 It is a topological decoupling structure of the magnetic integrated structure of the filter in the embodiment of the present invention;

[0023] Figure 6 is a schematic structural diagram of a fully decoupled magnetic core in an embodiment of the present invention;

[0024] Figure 7 is an insertion loss curve under different coupling coefficients K in an embodiment of the present invention;

[0025] Figure 8 3 is a comparison diagram of noise spectra before and after integration in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] In the transmission path of common mode noise, the common mode distributed capacitance C of the primary and secondary sides of the transformer Q The common mode inductor in the EMI filter is equivalent to the common mode inductor in series in the circuit structure, so the transformer C can be used in the transformer design. Q Designed to be small enough, due to the low frequency capacitor C Q The capacitance of the transformer is often much larger than the inductance of the common-mode inductor, so the suppression effect of the common-mode inductor on the common-mode noise will be greatly weakened. Q , can greatly reduce the common mode inductance L cm2 The sensitivity and volume can even be eliminated without L cm2 As for the suppression of differential mode interference, consider the differential mode inductor L dm1 and L dm2 Integrated on a magnetic core to achieve differential mode suppression. dm1 and L dm2 Simple integration on a magnetic core will inevitably produce a strong mutual inductance M, which will be generated at C after decoupling. B1 The capacitor branch generates a large coupling inductance M, which increases the high-frequency impedance of the capacitor, thereby deteriorating C B1The bypass effect of the branch on the differential mode noise current affects the filtering performance of the entire filter.

[0030] Therefore, this embodiment provides a method for designing an EMI filter magnetic integrated structure. Figure 3-5 As shown, differential mode inductors L are set before and after the rectifier bridge of the EMI filter. dm1 and L dm2 , the differential mode inductance L dm1 and L dm2 Integrated on a fully decoupled magnetic core.

[0031] On this basis, this embodiment designs a fully decoupled magnetic core structure, such as Figure 6 As shown, the fully decoupled magnetic core includes a middle column 1 and two side columns 2 arranged on both sides of the middle column, and the differential mode inductor L dm1 , L dm2 They are respectively wound on the two side columns 2, the middle column 1 is made of manganese-zinc ferrite material with high magnetic permeability, and the side columns 2 are made of magnetic powder core material with low magnetic permeability and strong saturation ability. In this embodiment, the fully decoupled magnetic core does not need to have an air gap.

[0032] In other embodiments of the present invention, the middle column and the side columns may both be made of manganese-zinc ferrite material with high magnetic permeability, but air gaps are required on the side columns of the fully decoupled magnetic core.

[0033] Magnetic resistance R m The calculation formula is as follows:

[0034]

[0035] Wherein, A and L are the cross-sectional area and length of the magnetic circuit, respectively, and μ represents the magnetic permeability of the material; when the cross-sectional area and length of the magnetic circuit are constant, the magnetic resistance is inversely proportional to the magnetic permeability; in the fully decoupled magnetic core, through structural design and material selection, the magnetic resistance of the middle column is much smaller than that of the side column, so that the side column L dm1 Most of the magnetic flux generated by the winding flows through the center column, and only a very small part of the magnetic flux passes through L dm2 winding, thereby reducing the differential mode inductance L dm1 With L dm2 Mutual inductance makes the coupling coefficient K of the fully decoupled magnetic core less than 5%. In this embodiment, the relative magnetic permeability of the magnetic powder core used is 60. The higher the magnetic permeability of the manganese-zinc ferrite material, the smaller the coupling coefficient will be. In this embodiment, the relative magnetic permeability of the manganese-zinc ferrite material used is 3300, so the coupling coefficient is as low as 1.8%. Theoretically, the lower the coupling coefficient, the better the effect. In fact, a coupling coefficient lower than 5% is acceptable.

[0036] In the fully decoupled magnetic integrated structure designed in this embodiment, the differential mode inductor L dm1 and L dm2The inductance of L is equal to obtain better differential mode filtering performance. dm1 and L dm2 Located before and after the rectifier bridge, this will cause the current flowing through L dm1 and L dm2 The current directions of the inductors are not equal, so a larger middle column cross-sectional area is required to prevent the middle column magnetic core from saturating. Nevertheless, under the premise of satisfying the unchanged noise suppression effect, the magnetic integrated structure designed by the present invention can still make the filter volume smaller.

[0037] The following is a specific description of a PFC+flyback power supply. Its circuit topology is as follows: Figure 2 As shown. Where L cm1 It is a very small nickel-zinc common mode inductor, which mainly suppresses the interference of the radiation section. It is not designed here. The other relevant parameters of the filter are as follows:

[0038] Table 1 Filter parameters of the original scheme

[0039]

[0040]

[0041] Based on the idea of ​​the present invention, by reasonably designing the effective capacitance of the common-mode port of the transformer, a 0.5mH common-mode inductor can be used to replace the original 18mH common-mode inductor to achieve the same common-mode suppression effect. dm Using L dm1 With L dm2 The integrated structure is replaced by Where L k =60uH. If only L dm Simply split into two inductors, namely L dm1 With L dm2 Winding on the same magnetic ring will cause the two inductors to produce a strong coupling inductance M. The influence of different coupling coefficients on the filtering performance can be analyzed through the filter insertion loss. Figure 4 As shown, R dm is the LISN equivalent differential mode resistance, V s is the noise voltage, and R0 is the internal impedance of the noise source. When no filter is inserted, R dm The voltage drop V1 is:

[0042]

[0043] After inserting the filter, the inductor L dm1 With L dm2 After decoupling, the equivalent structure is as follows Figure 5 As shown, the node voltage method is used to calculate R dm The voltage across the two ends is U n1Solve and write the equation as follows:

[0044]

[0045] Insertion loss is defined as the ratio of the voltage after insertion into a given transmission system to the voltage before insertion. Combining equations (2) and (3), the insertion loss IL of the differential mode filter can be obtained: dm for:

[0046]

[0047] After substituting the specific parameters into the calculation, the insertion loss curve under different coupling coefficients K is obtained, where Depend on Figure 7 It can be seen that when K continues to increase, the insertion loss curve continues to move upward, indicating that the noise suppression effect continues to weaken, so the coupling coefficient needs to be reduced as much as possible.

[0048] Winding Figure 6 After the full decoupling differential mode inductor is shown, the experimentally measured coupling coefficient is only 1.8%. Figure 2 The filter topology shown is improved to Figure 3 As shown, the related parameters of the improved filter are shown in Table 2. Compared with Table 1, it can be found that the total volume of the inductor is reduced by 42% and the total volume of the filter is reduced by 20% by adopting the integrated differential mode inductor filter solution proposed by the present invention.

[0049] Table 2 Parameters of integrated filter

[0050]

[0051] To further verify the feasibility of the present invention, a noise test is performed on a PFC+flyback power supply. Figure 8 As shown, the filter solution using integrated differential mode inductors can not only effectively reduce the filter volume, but also has the same noise suppression effect as the existing solution, thereby proving the feasibility of the present invention.

[0052] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for designing a magnetic integrated structure of an EMI filter, characterized in that: Differential mode inductors are set before and after the rectifier bridge of the EMI filter. L dm1 and L dm2 , the differential mode inductance L dm1 and L dm2 Integrated on a fully decoupled magnetic core; The fully decoupled magnetic core includes a middle column and two side columns arranged on both sides of the middle column, and the differential mode inductor L dm1 , L dm2 They are respectively wound on the two side columns, the middle column is made of manganese-zinc ferrite material with high magnetic permeability, and the side columns are made of magnetic powder core material with low magnetic permeability and strong saturation ability; The fully decoupled magnetic core includes a middle column and two side columns arranged on both sides of the middle column, and the differential mode inductor L dm1 , L dm2 The middle column and the side column are respectively wound on the two side columns, and the middle column and the side column are made of manganese-zinc ferrite material with high magnetic permeability, but an air gap is opened on the side column; Magnetic resistance R m The calculation formula is as follows: ; in, A and L are the cross-sectional area and length of the magnetic circuit, and μ represents the magnetic permeability of the material. When the cross-sectional area and length of the magnetic circuit are constant, the magnetic resistance is inversely proportional to the magnetic permeability. In the fully decoupled magnetic core, the magnetic resistance of the middle column is much smaller than that of the side column through structural design and material selection, so that the side column L dm1 Most of the magnetic flux generated by the winding flows through the center column, and only a very small part of the magnetic flux flows through the L dm2 winding, thereby reducing the differential mode inductance L dm1 and L dm2 Mutual inductance, so that the coupling coefficient K of the fully decoupled magnetic core is less than 5%; The differential mode inductor L dm1 and L dm2 The sense of is equal; The differential mode inductor L dm1 , L dm2 The size is: ; in, L dm is the differential mode filter inductor, L k For leakage inductance.

Images