CN114266213A

CN114266213A - Design method for magnetic integrated structure of EMI filter

Info

Publication number: CN114266213A
Application number: CN202111611037.4A
Authority: CN
Inventors: 林苏斌; 余兴旺; 陈为; 张丽萍
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2021-12-27
Filing date: 2021-12-27
Publication date: 2022-04-01

Abstract

The invention relates to a design method of a magnetic integrated structure of an EMI filter, wherein differential mode inductors are respectively arranged in front of and behind a rectifier bridge of the EMI filterL _dm1AndL _dm2said differential mode inductorL _dm1AndL _dm2integrated on a fully decoupled magnetic core. The method is beneficial to further reducing the size of the filter on the premise of ensuring the noise suppression effect.

Description

Design method for magnetic integrated structure of EMI filter

Technical Field

The invention belongs to the field of filters, and particularly relates to a design method of a magnetic integrated structure of an EMI filter.

Background

In recent years, wide bandgap power electronic devices represented by silicon carbide and gallium nitride have been developed and widely used, so that the entire power electronics subject is in a new period of high-speed development. However, the power electronic devices often cause large electromagnetic interference noise in the high-speed on and off processes, which not only affects the normal operation of the electrical equipment, but also pollutes the power grid, so that it is of great significance to research how to suppress the electromagnetic interference.

The EMI passive filter has the advantages of simple structure, convenient design, low cost and the like, and is widely used for inhibiting electromagnetic interference. The EMI filter can effectively inhibit conducted electromagnetic interference noise of the power converter, and the inhibition mechanism is mainly that filtering inductors are connected in series on an L line and an N line to increase impedance on a noise transmission path and filter capacitors are connected in parallel to bypass the electromagnetic interference noise, so that a power supply product can meet related electromagnetic compatibility standards.

Power converters are currently moving towards high frequency, high power density, high efficiency and low electromagnetic interference, which present significant challenges to the design of EMI filters. With the increase of electromagnetic interference, it is common practice in engineering to increase the inductance and capacitance of the filter, or increase the order of the filter to meet the requirement of electromagnetic compatibility, but this will inevitably increase the weight and volume of the filter, which runs counter to the direction of high power density.

The existing major filter structures include: 1) the filter is placed on the ac side. The filter, L, as shown in FIG. 1_cm1And L_cm2Is a common mode choke, L_dmIs a differential mode filter inductor. Wherein L is_cm1The filter is responsible for suppressing the noise of a high frequency band, and the common mode inductance is generally smaller, so that the differential mode inductance serving as the leakage inductance of the filter is smaller and can be ignored in the analysis of a differential mode filter; and L is_cm2Then the common mode inductance is generally large, which is responsible for suppressing the noise in the low frequency band, thereby obtaining a large leakage inductance (L)_k) To and L_dm、C_x1、C_x2And C_BAnd a second-order differential mode filter is formed, so that a better differential mode noise suppression effect is obtained. 2) The filters discharge an AC side and a DC side. FIG. 2 shows an improvement over the filter topology shown in FIG. 1, C on the AC side of FIG. 1_X2And L_dmIs arranged behind the rectifier bridge and connected with a rectifier filter capacitor C_BConstituting a pi-type filter. Compared with the ac-side safety capacitor, the dc-side capacitor can use a smaller thin-film capacitor, so that this topology is widely adopted. L in the above two filter topologies_cm2The common-mode inductance is generally very large, which is to obtain a larger leakage inductanceTo suppress differential mode noise. In the noise transmission path, the common mode inductor in the EMI filter and the primary and secondary common mode distributed capacitors C of the transformer_QThe common-mode noise suppression circuit is equivalent in series connection in circuit structure, common-mode noise can be suppressed by adjusting inductance of common-mode inductor of EMI filter in common-mode noise suppression, and similarly, transformer C can also be adjusted_QTo suppress common mode noise. With the study of EMI characteristics of planar transformers, there are many methods for obtaining smaller transformers C_Q. Therefore, the inductance of the common mode inductor can be made very small, and the common mode choke L with large volume and inductance is adopted to obtain larger leakage inductance_cm2Is not very cost effective.

Disclosure of Invention

The invention aims to provide a design method of an EMI filter magnetic integrated structure, which is beneficial to further reducing the size of the filter on the premise of ensuring the noise suppression effect.

In order to achieve the purpose, the invention adopts the technical scheme that: a design method for magnetic integrated structure of EMI filter comprises respectively arranging differential mode inductors L in front of and behind a rectifier bridge of the EMI filter_dm1And L_dm2Said differential mode inductance L_dm1And L_dm2Integrated on a fully decoupled magnetic core.

Further, the total decoupling magnetic core comprises a center pillar and two side pillars arranged on two sides of the center pillar, and the differential mode inductance L_dm1、L_dm2The magnetic powder transformer is respectively wound on two side columns, the middle column is made of manganese zinc ferrite material with high magnetic conductivity, and the side columns are made of magnetic powder core material with low magnetic conductivity and strong saturation capacity.

Further, the total decoupling magnetic core comprises a center pillar and two side pillars arranged on two sides of the center pillar, and the differential mode inductance L_dm1、L_dm2The middle column and the side columns are made of manganese zinc ferrite materials with high magnetic conductivity, and air gaps are formed in the side columns.

Further, the reluctance R_mThe calculation formula of (a) is as follows:

wherein A and L are respectively the cross-sectional area and length of the magnetic circuit, and mu represents the magnetic permeability of the material; when the cross-sectional area and the length of the magnetic circuit are fixed, the magnetic resistance is inversely proportional to the magnetic conductivity; in the fully decoupled magnetic core, through structural design and material selection, the magnetic resistance of the middle column is far smaller than that of the side columns, and the side columns L_dm1The majority of the flux generated by the winding flows through the center leg, while only a very small portion of the flux is linked through L_dm2Winding to reduce differential mode inductance L_dm1And L_dm2And mutual inductance is realized, so that the coupling coefficient K of the fully decoupled magnetic core is less than 5%.

Further, the differential mode inductance L_dm1And L_dm2Equal in sensitivity.

Further, the differential mode inductance L_dm1、L_dm2The size of (A) is as follows:

wherein L is_dmIs a differential mode filter inductor, L_kThe leakage inductance is obtained.

Compared with the prior art, the invention has the following beneficial effects: the EMI filter designed by the method can further reduce the size of the filter on the premise of ensuring that the noise suppression effect is not changed, so that the power density of the whole machine is improved, and the design method has important significance for the miniaturization of the filter.

Drawings

FIG. 1 is a prior art AC side filter topology;

FIG. 2 is a prior art AC side plus DC side filter topology;

FIG. 3 is a topology of a filter magnetic integration structure in an embodiment of the invention;

FIG. 4 is a topologically simplified structure of a filter magnetic integrated structure in an embodiment of the present invention;

FIG. 5 is a topological decoupling structure of the magnetic integrated structure of the filter in the embodiment of the present invention;

FIG. 6 is a schematic structural diagram of a fully decoupled magnetic core in an embodiment of the invention;

FIG. 7 is an insertion loss curve for different coupling coefficients K in an embodiment of the present invention;

FIG. 8 is a comparison graph of integrated pre-and post-noise spectra in an embodiment of the invention.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The common mode distributed capacitance C of the primary side and the secondary side of the transformer is in the transmission path of the common mode noise_QIs equivalently connected in series with the common-mode inductor in the EMI filter in circuit structure, so that the transformer C can be designed in the design of the transformer_QDesigned to be small enough due to the low band capacitance C_QThe capacitance value of the common mode inductor is usually much larger than the inductance value of the common mode inductor, so that the common mode noise suppression effect of the common mode inductor is greatly reduced. Common mode distributed capacitance C of transformer is rationally designed_QCan greatly reduce the common mode inductance L_cm2Can even be dispensed with L_cm2. Regarding the suppression of the differential mode interference, the differential mode inductance L is considered_dm1And L_dm2And the two magnetic cores are integrated on one magnetic core to achieve the effect of differential mode suppression. But ifOnly mixing L_dm1And L_dm2The simple integration on a magnetic core inevitably generates strong mutual inductance M which is separated and then is separated on C_B1The capacitive branch generates a large coupling inductance M, which increases the capacitive high-frequency impedance and thus degrades C_B1The bypass effect of the branch on the differential mode noise current influences the filtering performance of the whole filter.

Therefore, this embodiment provides a design method for a magnetic integrated structure of an EMI filter, as shown in fig. 3 to 5, differential mode inductors L are respectively disposed before and after a rectifier bridge of the EMI filter_dm1And L_dm2Said differential mode inductance L_dm1And L_dm2Integrated on a fully decoupled magnetic core.

On this basis, the present embodiment designs a full decoupling magnetic core structure, as shown in fig. 6, the full decoupling magnetic core includes a center pillar 1 and two side pillars 2 disposed at two sides of the center pillar, and the differential mode inductance L is_dm1、L_dm2The magnetic powder magnetic core is respectively wound on two side columns 2, the middle column 1 is made of manganese zinc ferrite material with high magnetic conductivity, and the side columns 2 are made of magnetic powder core material with low magnetic conductivity and strong saturation capacity. In this embodiment, the fully decoupled magnetic core does not require an open air gap.

In other embodiments of the present invention, the central pillar and the side pillars may both be made of high permeability manganese-zinc-ferrite material, but an air gap is required on the side pillars of the fully decoupled magnetic core.

Magnetic resistance R_mThe calculation formula of (a) is as follows:

wherein A and L are respectively the cross-sectional area and length of the magnetic circuit, and mu represents the magnetic permeability of the material; when the cross-sectional area and the length of the magnetic circuit are fixed, the magnetic resistance is inversely proportional to the magnetic conductivity; in the fully decoupled magnetic core, through structural design and material selection, the magnetic resistance of the middle column is far smaller than that of the side columns, and the side columns L_dm1The majority of the flux generated by the winding flows through the center leg, while only a very small portion of the flux is linked through L_dm2Winding to reduce differential mode inductance L_dm1And L_dm2And mutual inductance is realized, so that the coupling coefficient K of the fully decoupled magnetic core is less than 5%. In this example, a magnetic powder core having a relative magnetic permeability of 60 was used. The higher the permeability of the manganese-zinc ferrite material, the smaller the coupling coefficient will be. In this embodiment, the manganese-zinc ferrite material used has a relative magnetic permeability of 3300, so that the coupling coefficient is as low as 1.8%. Theoretically, the lower the coupling coefficient, the better the effect, and in practice, coupling coefficients below 5% are acceptable.

In the fully-decoupled magnetic integrated structure designed by the embodiment, the differential mode inductor L is enabled_dm1And L_dm2The inductance of the differential mode filter is equal, so that better differential mode filtering performance is obtained. Due to L_dm1And L_dm2Respectively before and after the rectifier bridge, which results in a flow through L_dm1And L_dm2Since the inductors have unequal current directions, a larger center leg sectional area is required to prevent saturation of the center leg core. Nevertheless, on the premise of not changing the noise suppression effect, the filter volume can still be smaller under the magnetic integrated structure designed by the invention.

The following is a detailed description of a PFC + flyback power supply, and the circuit topology structure thereof is shown in fig. 2. Wherein L is_cm1The common mode inductor is a small nickel-zinc common mode inductor, and mainly inhibits the interference of a radiation section, and the common mode inductor is not designed here. The remaining relevant parameters of the filter are as follows:

table-original scheme filter parameters

Based on the idea of the invention, by reasonably designing the effective capacitance of the common-mode port of the transformer, a common-mode inductor of 0.5mH can be used for replacing an original common-mode inductor of 18mH to achieve the same common-mode rejection effect, and a differential-mode inductor L_dmBy using L_dm1And L_dm2Is of a size of

Wherein L is_k60 uH. If only L is to be_dmSimply split into two inductances, i.e. L_dm1And L_dm2And the two inductors generate strong coupling inductors M by winding on the same magnetic ring, and the influence of different coupling coefficients on the filtering performance can be analyzed through the insertion loss of the filter. As shown in FIG. 4, wherein R_dmIs an LISN equivalent differential mode resistance, V_sAs noise voltage, R₀Is the internal impedance of the noise source. When no filter is inserted, R_dmVoltage drop V over₁Comprises the following steps:

after inserting the filter, the inductor L_dm1And L_dm2The equivalent structure obtained after decoupling is shown in FIG. 5, and R is subjected to node voltage method_dmVoltage U across_n1The solution is performed, the following equations are written:

the insertion loss is defined as the ratio of the voltage after insertion into a given transmission system to the voltage before, and the insertion loss IL of the differential mode filter can be obtained by combining the components (2) and (3)_dmComprises the following steps:

substituting into specific parameters to obtain insertion loss curves under different coupling coefficients K, wherein

As can be seen from fig. 7, as K increases, the insertion loss curve moves upward, which means that the noise suppression effect decreases, and therefore, it is necessary to reduce the coupling coefficient as much as possible.

After the fully decoupled differential mode inductor shown in fig. 6 is wound, the coupling coefficient is only 1.8% through experimental measurement, the topological structure of the filter shown in fig. 2 is improved to that shown in fig. 3, the improved filter related parameters are shown in table two, and the comparison with the table shows 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 scheme provided by the invention.

TABLE II INTEGRATED POST-FILTER PARAMETERS

In order to further verify the feasibility of the invention, a noise test is performed on one PFC + flyback power supply, as shown in fig. 8, the filter scheme adopting the integrated differential mode inductor not only can effectively reduce the size of the filter, but also has the substantially same noise suppression effect as the existing scheme, thereby proving the feasibility of the invention.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A design method for magnetic integrated structure of EMI filter is characterized by setting differential mode inductors L in front of and behind rectifier bridge of EMI filter_dm1And L_dm2Said differential mode inductance L_dm1And L_dm2Integrated on a fully decoupled magnetic core.

2. The method of claim 1, wherein the fully decoupled magnetic core comprises a center pillar and two side pillars disposed on two sides of the center pillar, and the differential mode inductance L is_dm1、L_dm2The magnetic powder transformer is respectively wound on two side columns, the middle column is made of manganese zinc ferrite material with high magnetic conductivity, and the side columns are made of magnetic powder core material with low magnetic conductivity and strong saturation capacity.

3. The method of claim 1, wherein the fully decoupled magnetic core comprises a center pillar and two side pillars disposed on two sides of the center pillar, and the differential mode inductance L is_dm1、L_dm2The middle column and the side columns are made of manganese zinc ferrite materials with high magnetic conductivity, and air gaps are formed in the side columns.

4. The design method of magnetic integration structure of EMI filter as claimed in claim 2 or 3, wherein R is magnetic resistance_mThe calculation formula of (a) is as follows:

5. The method of claim 1, wherein the differential mode inductance L is a value of_dm1And L_dm2Equal in sensitivity.

6. The method of claim 5, wherein the differential mode inductance L is a value obtained by designing a magnetic integrated structure of an EMI filter_dm1、L_dm2The size of (A) is as follows: