CN110211799B - Method for designing turns of shielding winding of flyback power transformer - Google Patents

Method for designing turns of shielding winding of flyback power transformer Download PDF

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CN110211799B
CN110211799B CN201910491642.9A CN201910491642A CN110211799B CN 110211799 B CN110211799 B CN 110211799B CN 201910491642 A CN201910491642 A CN 201910491642A CN 110211799 B CN110211799 B CN 110211799B
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winding
shielding
secondary winding
turns
transformer
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CN110211799A (en
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陈恒林
赵聪聪
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Zhejiang University ZJU
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Zhejiang University ZJU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/28—Coils; Windings; Conductive connections
    • H01F27/288—Shielding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/33—Arrangements for noise damping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only

Abstract

The invention discloses a design method of the turns of a shielding winding of a flyback power transformer, which comprises the following steps: (1) selecting a transformer, and measuring the structural size of the transformer; (2) solving the distributed capacitance and the number of turns N of the shielding winding between the primary winding and the secondary winding of the transformer and between the shielding winding and the secondary windingshThe relational expression of (1); (3) calculating the turns N of different shielding windingsshCommon mode current i of lower transformerCMTo obtain a common mode current iCMNumber of turns N of shielding windingshThe functional relationship of (a); (4) according to the relation equation g (N) of the number of turns of the shielding winding and the equivalent coefficient of the common-mode currentsh) Solving equation | g (N)sh) And (4) taking the root of the integer | as 0 and obtaining the optimal number of turns of the shielding winding for inhibiting the common-mode current of the transformer. Compared with the prior common mode rejection technology, the method has the advantages of high design flexibility, simple implementation method, low manufacturing cost, no need of additionally increasing the volume of the device and obvious rejection effect.

Description

Method for designing turns of shielding winding of flyback power transformer
Technical Field
The invention belongs to the technical field of transformer design, and particularly relates to a method for designing the number of turns of a shield winding of a flyback power transformer.
Background
The flyback power supply has a simple structure and a small volume, and is widely applied to communication and service systems and low-power electronic equipment; power semiconductor devices in the flyback power supply generate Electromagnetic interference (EMI) noise during switching operations, and therefore certain EMI suppression measures are often used in product design to meet related EMC standards. With the trend of high frequency and miniaturization of switching power supplies, the high switching frequency of the switching devices leads to more serious EMI problems, which make it difficult for the switching power supply products to meet the relevant EMC standards, and on the other hand, even if the relevant EMC standards can be met, the EMI can form common mode noise on the more sensitive load side, causing serious interference to the electronic load.
The common-mode interference can be effectively reduced by adopting the filter to suppress the common-mode interference, but due to the strict requirement of leakage current, the common-mode filter is usually composed of elements such as a small capacitor, a large inductor and the like, which often increases the product volume and the cost; the method can effectively reduce the volume of the filter and achieve good suppression effect, but the flexibility is not high in the design and manufacture of the actual transformer, and the manufacture precision cannot be guaranteed due to more variables related to the selection of the shielding structure.
And the winding shielding is adopted to suppress the common mode noise, so that the method is convenient for actual production and manufacture, reduces the production cost and can effectively suppress the common mode interference. Fig. 1 shows a transmission path of a common mode current when a winding shield is added, an EMI interference source of a flyback power supply includes a primary MOSFET and a secondary diode, and the directions of the common mode currents generated by the primary MOSFET and the secondary diode are opposite; when a shielding measure is not adopted, because the common-mode currents generated by the primary side MOSFET and the secondary side diode are not equal, the common-mode currents in the transformer cannot be offset, and the common-mode noise transmitted to the load side is large.
In order to realize the best common mode noise suppression effect, the number of turns of the shielding winding needs to be reasonably designed; the design method at the present stage is usually calculated according to experience, experimental test or repeated simulation, and a large amount of test and simulation resources are needed, so that a forward quantitative design method for the number of turns of the shielding winding is urgently needed.
Disclosure of Invention
In view of the above, the invention provides a method for designing the number of turns of a shielding winding of a flyback power transformer, which solves the optimal number of turns of the shielding winding when the best suppression effect is achieved by researching the relationship between the magnitude of the common-mode current and the number of turns of the shielding winding, does not need repeated experimental tests and simulation calculation, does not increase the burden of filter design, and has the advantages of simple design and low cost.
A design method for the number of turns of a shielding winding of a flyback power transformer comprises the following steps:
(1) selecting a transformer for a flyback power supply, and measuring structural parameters of the transformer;
(2) solving the distributed capacitance between the primary winding and the secondary winding of the transformer and the distributed capacitance between the shielding winding and the secondary winding of the transformer;
(3) deducing a system common-mode current i according to the distributed capacitance and the common-mode current propagation pathCMNumber of turns N of shielding windingshAnd calculating the common mode current i by using the relation functionCM；
Figure BDA0002087231960000021
Wherein: i.e. ipjIs the common-mode current between adjacent parts of the j-th section of the primary winding and the secondary winding in the transformer, n is the number of sections of the adjacent parts of the primary winding and the secondary winding in the transformer, ishkCommon-mode current between a k-th shielding winding and the adjacent part of the secondary winding in the transformer is obtained, and m is the number of sections of the shielding winding and the adjacent part of the secondary winding; the above relation function includes gp(Nsh) And gsh(Nsh) Two parts, namely the common-mode current between the adjacent parts of any one section of primary winding and secondary winding in the transformer
Figure BDA0002087231960000022
gp(Nsh) For common mode current ipNumber of turns N of shielding windingshThe relationship function of (1); common mode current between any one section of shielding winding and adjacent part of secondary winding in transformer
Figure BDA0002087231960000023
gsh(Nsh) For common mode current ishNumber of turns N of shielding windingshV is the voltage increment on each turn of winding, t represents time;
(4) make the system common mode current iCMAnd solving the formula as 0, and rounding the root obtained by the solution to obtain the optimal number of turns of the shielding winding.
Further, the structural parameters of the flyback power transformer in the step (1) include the width of the primary winding, the width of the secondary winding, the perimeter and thickness of the medium between the adjacent portions of the primary winding and the secondary winding, the perimeter and thickness of the medium between the adjacent portions of the shielding winding and the secondary winding, the number of turns of the primary winding, the number of turns of the secondary winding, the width of each turn of the primary winding, the width of each turn of the secondary winding, the width of each turn of the shielding winding, and the position of the shielding winding.
Preferably, the position of the shielding winding is the minimum vertical distance between the bottom end of the shielding winding and the bottom end of the primary winding for convenient operation.
Further, in the step (2), a capacitor C is distributed between any one section of the primary winding and the secondary windingps0The calculation expression of (a) is as follows:
Figure BDA0002087231960000031
wherein: epsilonpsIs the dielectric constant of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, lavpsIs the perimeter of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, dpsIs the thickness h of the medium between the adjacent parts of the primary winding and the secondary winding of the corresponding sectionp1And hp2The distance between two ends of the part of the primary winding adjacent to the secondary winding and the low-voltage end of the primary winding is hp2>hp1。
Further, in the step (2), the capacitor C is distributed between any one section of the shielding winding and the secondary windingshs0The calculation expression of (a) is as follows:
Figure BDA0002087231960000032
wherein: epsilonshsFor the dielectric constant of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, /)avshsFor the perimeter of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, dshsFor the thickness of the medium between the corresponding section of the shield winding and the adjacent part of the secondary winding, hsh1And hsh2Shielding the winding from the secondary side for the corresponding sectionThe distance between two ends of the adjacent part of the winding and the low-voltage end of the shielding winding is hsh2>hsh1。
Further, the relation function gp(Nsh) The expression of (a) is as follows:
Figure BDA0002087231960000033
wherein: epsilonpsIs the dielectric constant of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, lavpsIs the perimeter of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, dpsIs the thickness h of the medium between the adjacent parts of the primary winding and the secondary winding of the corresponding sectionp1And hp2The distance between two ends of the part of the primary winding adjacent to the secondary winding and the low-voltage end of the primary winding is hp2>hp1，hs1And hs2The distance between two ends of the part of the secondary winding adjacent to the corresponding section of the primary winding and the low-voltage end of the secondary winding is hs2>hs1，N0Is a multiple of the difference between the voltage change rate of the low-voltage end of the primary winding and the voltage change rate of the low-voltage end of the secondary winding relative to dv/dt, NpAnd NsNumber of turns of primary winding and secondary winding, HpIs the total width of the primary winding, HsThe total width of the secondary winding.
Further, the relation function gsh(Nsh) The expression of (a) is as follows:
Figure BDA0002087231960000041
wherein: epsilonshsFor the dielectric constant of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, /)avshsFor the perimeter of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, dshsFor the thickness of the medium between the corresponding section of the shield winding and the adjacent part of the secondary winding, hsh1And hsh2For the shield winding of the corresponding section, the two ends of the part adjacent to the secondary winding are respectively connected with the shieldDistance h between low voltage ends of the shaded windingssh2>hsh1，hs3And hs4The distance between the two ends of the part of the secondary winding adjacent to the corresponding shielding winding and the low-voltage end of the secondary winding is hs4>hs3，N1The difference between the low-voltage terminal voltage change rate of the shielding winding and the low-voltage terminal voltage change rate of the secondary winding is a multiple of dv/dt, NshAnd NsNumber of turns, k, of shield winding and secondary winding, respectivelyshFor the width of the shield winding per turn, HsThe total width of the secondary winding.
Further, the distance hp1、hp2、hs1、hs2、hsh1、hsh2、hs3、hs4All through the structural parameters of the winding and the number N of turns of the shielding windingshIs expressed in functional form.
Compared with the prior art, the invention has the following beneficial technical effects:
1. the actual manufacturing process is simple, and the production cost is low; the shielding winding is generally made of copper wires made of the same materials as the primary and secondary windings, winding modes are completely the same, production efficiency is high, the bottom end of the shielding winding is set to be close to the bottom ends of the primary winding and the secondary winding to the maximum extent, variables needing to be considered in the winding process are reduced, and accuracy and reliability of actual manufacturing are guaranteed.
2. The common mode rejection effect is obvious, and the design task of the filter can be reduced; by adopting the method of the invention to reasonably design the turns of the shielding winding, a relatively ideal common mode noise suppression effect can be achieved, thereby effectively reducing the volume of the filter or eliminating the design task of the filter; the whole volume and weight of the device can be reduced because the shielding winding is added in the transformer without additionally increasing the volume of the device.
3. The design process is simple and convenient, and the time cost is saved; by adopting the method, the optimal turn number of the shielding winding can be directly obtained through derivation calculation without repeated experiments and numerical simulation, the design period is shortened, and the time cost is saved.
Drawings
Fig. 1 is a schematic diagram of a common-mode current propagation path of a flyback power supply with a shielding winding.
Fig. 2(a) is a schematic diagram of the distributed capacitance between the primary winding and the secondary winding.
Fig. 2(b) is a schematic diagram of the distributed capacitance between the secondary winding and the shield winding.
Fig. 3 is a schematic diagram of a transformer.
FIG. 4(a) is 0. ltoreq.NshAnd (5) a structural section view of the transformer at the temperature of ≦ 21.
FIG. 4(b) shows that 22. ltoreq. NshAnd the structural section of the transformer is less than or equal to 26.
In FIG. 4(c), N is 27. ltoreq. NshThe structure of the transformer is less than or equal to 52 in cross section.
FIG. 5(a) shows the number of turns N of the shield windingshThe common mode noise spectrum diagram of the load side of the flyback power supply is 11.
FIG. 5(b) shows the number of turns N of the shield windingshThe common mode noise spectrum diagram of the load side of the flyback power supply is 26.
FIG. 5(c) shows the number of turns N of the shield windingshThe common mode noise spectrum diagram of the load side of the flyback power supply is 40 hours.
FIG. 5(d) shows the number of turns N of the shield windingshAnd (6) a common mode noise spectrum diagram of the load side of the flyback power supply at 48 hours.
FIG. 5(e) shows the number of turns N of the shield windingshThe common mode noise spectrum diagram at 52 hours on the load side of the flyback power supply.
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
The invention relates to a design method of turns of a shielding winding of a flyback power supply transformer, which is characterized in that the common-mode current i is found by analyzing a common-mode interference path in a switching power supply and expressing the distributed capacitance between two pairs of adjacent windings (a primary winding and a secondary winding, and a secondary winding and the shielding winding) by using directly measurable structural parameters and the turns of the shielding windingCMNumber of turns N of shielding windingshFunctional relationship i betweenCM＝g(Nsh) X dv/dt, and then by solving the equation | g (N)sh) Root of | ═ 0, resulting in a shielded windingThe optimal number of turns specifically comprises the following steps:
(1) and selecting a transformer for the flyback power supply, and measuring structural parameters of the transformer.
The positions of the primary winding and the secondary winding of the transformer, the distributed capacitance between the secondary winding and the shielding winding and the position of the shielding winding are shown in fig. 2(a) and 2(b), the winding mode of the winding, the air gap, the widths of the primary winding and the secondary winding and the like are all related, so that the structural parameters of the transformer, including the width H of the primary winding, need to be measured in advancepWidth H of secondary windingsPerimeter l of the medium between adjacent portions of the primary winding and the secondary windingpsAnd thickness dpsThe perimeter l of the medium between the adjacent portions of the shield winding and the secondary windingshsAnd thickness dshsPrimary winding turn number NpSecondary winding turn number NsWidth k of each turn of shield windingshAnd shield winding position H0Shielding winding position H0The vertical distance between the bottom end of the shield winding and the bottom end of the primary winding.
(2) Solving the distribution capacitance between the primary winding and the secondary winding and the number N of turns of the shielding windingshAnd the distributed capacitance between the shield winding and the secondary winding and the number of turns N of the shield windingshThe functional relationship of (a).
As shown in fig. 2(a) and 2(b), the distributed capacitances between the primary winding and the secondary winding of the transformer and between the secondary winding and the shielding winding can be expressed as functions of parameters such as the width of adjacent portions of the windings, the thickness of the medium between the windings, the perimeter, the dielectric constant and the like, and the parameters are related to the number of turns of the primary winding of the transformer, the number of turns of the secondary winding, the winding mode and the material of the transformer and the like. Therefore, after the structure and the material of the transformer are determined, the structure capacitance is only equal to the number N of turns of the shielding windingshThen, the distributed capacitance between the adjacent parts of the primary winding and the secondary winding and the number N of turns of the shielding winding are obtainedshAs well as the distributed capacitance between the shield winding and the adjacent portion of the secondary winding and the number of turns N of the shield windingshThe functional relationship of (a).
The distributed capacitance between each section of adjacent parts of the primary winding and the secondary winding is as follows:
Figure BDA0002087231960000061
the distributed capacitance between the adjacent parts of each segment of the shielding winding and the secondary winding is as follows:
Figure BDA0002087231960000062
(3) deducing different numbers of turns N of shielding windingshCommon mode current i of lower transformerCMObtaining a relation function i between the common mode current and the number of turns of the shielding windingCM＝g(Nsh)×dv/dt。
For any section of the adjacent parts of the primary winding and the secondary winding of the transformer, the common-mode current i between the adjacent partspThe calculation method of (2) is as follows:
Figure BDA0002087231960000063
Figure BDA0002087231960000064
wherein: epsilonpsIs the dielectric constant of the medium between adjacent portions of the primary winding and the secondary winding, /)avpsIs the perimeter of the medium between adjacent portions of the primary winding and the secondary winding, dpsIs the thickness h of the medium between the adjacent parts of the primary winding and the secondary windingp1And hp2The distance (h) between the two ends of the part of the primary winding adjacent to the secondary winding and the low-voltage end of the primary windingp2>hp1)，hs1And hs2Respectively the distance (h) between the two ends of the part of the secondary winding adjacent to the primary winding and the low-voltage end of the secondary windings2>hs1)，N0The voltage change rate of the low-voltage end of the primary winding and the voltage change rate of the low-voltage end of the secondary winding are multiples of the difference of the voltage change rates of the low-voltage ends of the primary winding and the secondary winding relative to dv/dt, and when the low-voltage ends of the primary winding and the secondary winding are static potential points, N is0The value is 0; n is a radical ofpAnd NsNumber of turns of primary winding and secondary winding, HpIs the total width of the primary winding, HsThe total width of the secondary winding.
For any section of shielding winding of the transformer and the adjacent part of the secondary winding, the common mode current i between the adjacent partsshThe calculation method of (2) is as follows:
Figure BDA0002087231960000071
Figure BDA0002087231960000072
wherein: epsilonshsIn order to shield the dielectric constant of the medium between the winding and the adjacent part of the secondary winding, /)avshsFor shielding the perimeter of the medium between the winding and the adjacent part of the secondary winding, dshsIn order to shield the thickness of the medium between the winding and the adjacent part of the secondary winding, hsh1And hsh2The distance (h) between the two ends of the part of the shielding winding adjacent to the secondary winding and the low-voltage end of the shielding windingsh2>hsh1)，hs3And hs4The distance (h) between the two ends of the part of the secondary winding adjacent to the shielding winding and the low-voltage end of the secondary windings4>hs3)，N1When the low-voltage end of the shielding winding and the low-voltage end of the secondary winding are static potential points, N is a multiple of the difference of the low-voltage end voltage change rate of the shielding winding and the low-voltage end voltage change rate of the secondary winding relative to dv/dt1The value is 0; n is a radical ofshAnd NsNumber of turns, k, of shield winding and secondary winding, respectivelyshFor the width of the shield winding per turn, HsThe total width of the secondary winding.
hp1、hp2、hs1、hs2、hsh1、hsh2、hs3、hs4All through the structural parameters of the winding and the number N of turns of the shielding windingshIs expressed in functional form. Referring to FIGS. 2(a), hp1＝H0+ksh×NshIn which H is0For shielding the bottom end of the winding from the formerThe vertical distance between the bottom ends of the side windings; h isp2＝kp×Np2Wherein k ispFor the width of the primary winding per turn, Np2Is the primary winding hp2The number of turns of the winding between the vertex of the corresponding section and the low-voltage end of the primary winding; h iss1＝H0+ksh×Nsh，hs2＝ks×Ns2Wherein k issFor the width of the secondary winding per turn, Ns2Is the secondary winding hs2The number of turns of the winding between the vertex of the corresponding section and the low-voltage end of the secondary winding. Referring to FIGS. 2(b), hsh1＝0；hsh2＝ksh×Nsh；hs3＝ks×Ns3In which N iss3Is the secondary winding hs3The number of turns of the winding between the vertex of the corresponding section and the low-voltage end of the secondary winding; h iss4＝hs3+ksh×Nsh。
According to the practical structure of the transformer, the common-mode current i between the adjacent parts of each segment of the primary winding and the secondary winding is adjustedpAnd a common mode current i between adjacent portions of each of the shield winding and the secondary windingshAnd accumulating and summing to further obtain the relation between the total common-mode current of the transformer and the number of turns of the shielding winding:
Figure BDA0002087231960000081
wherein: i.e. ipjIs the common-mode current between adjacent parts of the j-th section of the primary winding and the secondary winding in the transformer, n is the number of sections of the adjacent parts of the primary winding and the secondary winding in the transformer, ishkCommon-mode current between adjacent parts of a kth shielding winding and a secondary winding in the transformer is used, and m is the number of sections of the adjacent parts of the shielding winding and the secondary winding in the transformer; at a certain frequency point, dv/dt is constant.
(4) According to the g (N) obtainedsh) Solving for | g (N)sh) And (4) taking the root of 0 and rounding to obtain the optimal number of turns of the shielding winding which can minimize the common-mode current.
From the above formula of common mode current, when | g (N)sh) ' MaxHour, common mode current iCMAt a minimum, since the number of turns of the shield winding must be an integer, | g (N) can be solvedsh) And (4) taking the root of 0 and rounding to obtain the optimal number of turns of the shielding winding.
The following describes the embodiments of the present invention in further detail with reference to the design example of the transformer shielding winding of the flyback power supply.
The principle of the transformer circuit adopted in the present embodiment is shown in fig. 3, in which 2-3 are primary windings, 4-5 are auxiliary windings, and 6-7 are secondary windings. The transformer has a structure as shown in FIG. 4(a) -FIG. 4(c), in which PW1、PW2、PW3Is a primary winding, SHW is a shield winding, SW is a secondary winding, APW is an auxiliary winding, Hp1、Hp2、Hp3Are respectively PW1、PW2、PW3Width of (H)p＝Hp1+Hp2+Hp3Is the total width of the primary winding, HsIs the width of the secondary winding, H0For shielding the distance H from the bottom of the winding to the bottom of the primary winding1minThe minimum distance, k, from the top of the shield winding to the top of the primary winding in practical fabricationshThe specific values of these structural parameters for the width of the shield winding per turn are shown in table 1:
TABLE 1
Figure BDA0002087231960000082
Figure BDA0002087231960000091
The distributed capacitance between the adjacent parts of the primary winding and the secondary winding is as follows:
Figure BDA0002087231960000092
the distributed capacitance between the adjacent parts of the shielding winding and the secondary winding is as follows:
Figure BDA0002087231960000093
according to the different widths of the shielding windings, the determination of the distributed capacitance parameters and the composition of the common-mode current can be divided into the following three cases:
① when k is more than or equal to 0sh×Nsh≤Hp3-H0I.e. 0. ltoreq.NshAt ≦ 21, as shown in FIG. 4(a), the common mode current between the primary winding and the secondary winding has ip1、ip2、ip3Three parts, and the shielding winding and the secondary winding only have one section of adjacent part, so that the common mode current between the shielding winding and the secondary winding is only ish1Thus, there are:
iCM＝ip1+ip2+ip3+ish1
② when Hp3-H0≤ksh×Nsh≤Hp2-H0-H1minI.e. 22. ltoreq.NshAt or below 26, as shown in FIG. 4(b), the common mode current between the primary winding and the secondary winding has ip1、ip2The common-mode current between the shielding winding and the secondary winding has ish1Thus, there are:
iCM＝ip1+ip2+ish1
③ when Hp2-H0-H1min≤ksh×Nsh≤2×(Hp2-H0-H1min) I.e. 27. ltoreq.NshAt 52, as shown in FIG. 4(c), the common mode current between the primary winding and the secondary winding has ip1、ip2The common-mode current between the shielding winding and the secondary winding has ish1、ish2Two parts, thus:
iCM＝ip1+ip2+ish1+ish2
in case ① ish1For example, the calculation method is as follows:
Figure BDA0002087231960000094
Figure BDA0002087231960000095
the specific values of the parameters in the formula are shown in table 2:
TABLE 2
Parameter (Unit) Value of Parameter (Unit) Value of
hsh1(mm) 0 hsh2(mm) ksh×Nsh
lavshs(mm) 38.88 dshs(mm) 0.22
N1 0 H0(mm) 0.47
ksh(mm) 0.23 Hs(mm) 7
hs3(mm) Hs–H0–ksh×Nsh hs4(mm) Hs–H0
In this example, since the material between the primary winding and the secondary winding is the same as the material between the shield winding and the material between the secondary windings, εpsAnd epsilonshsValues are the same, the function can be eliminated when simplifying and root-seeking, the value has no influence on the solving result, and can be simply taken as 1; the above calculation method and the values in table 2 can be used to obtain:
gsh1(Nsh)＝0.0092×Nsh 2-0.0128×Nsh
each of i abovepAnd ishCan be expressed as a function of the number of turns of the shielding winding, and the functional relation between the total common-mode current and the number of turns of the shielding winding in each case can be obtained after superposition, and is simplified as follows:
Figure BDA0002087231960000101
Figure BDA0002087231960000102
solving equation | g (N)sh) The root of 0 and rounding off yields an optimal number of turns of 40 for the shield winding.
To verify the effectiveness of the design method, the number of turns N of the shield winding is measuredshSelecting the number N of turns of a shielding winding for common mode noise of a flyback power supply when the common mode noise is changed from 0 to 52shThe experimental results were characterized for the flyback power supply common mode noise spectrogram at 5 typical values (11,26,40,48, 52). FIG. 5(a) shows the number of turns N of the shield windingshA common mode noise spectrogram of the flyback power supply at 11 hours; FIG. 5(b) shows the number of turns N of the shield windingshA common mode noise spectrum diagram of the flyback power supply at 26 hours; FIG. 5(c) shows the number of turns N of the shield windingshA common mode noise frequency spectrum diagram of the flyback power supply at 40 hours; FIG. 5(d) shows the number of turns N of the shield windingshA common mode noise spectrum diagram of the flyback power supply at 48 hours; FIG. 5(e) shows the number of turns N of the shield windingshThe common mode noise spectrum of the flyback power supply is shown at 52. From the frequency spectrum of the practically measured common mode noise, in the frequency band below 8MHz, when the number of turns N of the shielding winding is NshAt 40 hours, the common mode noise of the flyback power supply is the minimum, the suppression effect of the shielding winding is the best, and the actual effect and the calculated result have better consistency, which proves the effectiveness of the proposed design method.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

Claims (4)

1. A design method for the number of turns of a shielding winding of a flyback power transformer comprises the following steps:
(1) selecting a transformer for a flyback power supply, and measuring structural parameters of the transformer;
(2) solving the distributed capacitance between the primary winding and the secondary winding of the transformer and the distributed capacitance between the shielding winding and the secondary winding of the transformer;
for any section of distributed capacitor C between the primary winding and the secondary windingps0The calculation expression of (a) is as follows:
Figure FDA0002370205290000011
wherein: epsilonpsIs the dielectric constant of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, lavpsIs the perimeter of the medium between the adjacent portions of the corresponding section of the primary winding and the secondary winding, dpsIs the thickness h of the medium between the adjacent parts of the primary winding and the secondary winding of the corresponding sectionp1And hp2The distance between two ends of the part of the primary winding adjacent to the secondary winding and the low-voltage end of the primary winding is hp2>hp1；
For any section of the distributed capacitance C between the shielding winding and the secondary windingshs0The calculation expression of (a) is as follows:
Figure FDA0002370205290000012
wherein: epsilonshsFor the dielectric constant of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, /)avshsFor the perimeter of the medium between the shield winding and the adjacent part of the secondary winding of the corresponding section, dshsFor the thickness of the medium between the corresponding section of the shield winding and the adjacent part of the secondary winding, hsh1And hsh2The distance h between the two ends of the part of the corresponding shielding winding adjacent to the secondary winding and the low-voltage end of the shielding windingsh2>hsh1；
(3) Deducing a system common-mode current i according to the distributed capacitance and the common-mode current propagation pathCMNumber of turns N of shielding windingshAnd calculating the common mode current i by using the relation functionCM；
Figure FDA0002370205290000013
Wherein: i.e. ipjIs the common-mode current between adjacent parts of the j-th section of the primary winding and the secondary winding in the transformer, n is the number of sections of the adjacent parts of the primary winding and the secondary winding in the transformer, ishkCommon-mode current between a k-th shielding winding and the adjacent part of the secondary winding in the transformer is obtained, and m is the number of sections of the shielding winding and the adjacent part of the secondary winding;the above relation function includes gp(Nsh) And gsh(Nsh) Two parts, namely the common-mode current between the adjacent parts of any one section of primary winding and secondary winding in the transformer
Figure FDA0002370205290000021
gp(Nsh) For common mode current ipNumber of turns N of shielding windingshThe relationship function of (1); common mode current between any one section of shielding winding and adjacent part of secondary winding in transformer
Figure FDA0002370205290000022
gsh(Nsh) For common mode current ishNumber of turns N of shielding windingshV is the voltage increment on each turn of winding, t represents time;
the relation function gp(Nsh) The expression of (a) is as follows:
Figure FDA0002370205290000023
wherein: h iss1And hs2The distance between two ends of the part of the secondary winding adjacent to the corresponding section of the primary winding and the low-voltage end of the secondary winding is hs2>hs1，N0Is a multiple of the difference between the voltage change rate of the low-voltage end of the primary winding and the voltage change rate of the low-voltage end of the secondary winding relative to dv/dt, NpAnd NsNumber of turns of primary winding and secondary winding, HpIs the total width of the primary winding, HsThe total width of the secondary winding;
the relation function gsh(Nsh) The expression of (a) is as follows:
Figure FDA0002370205290000024
wherein: h iss3And hs4Two ends of the part of the secondary winding adjacent to the corresponding shielding winding are respectively connected with the low-voltage end of the secondary windingAnd h iss4>hs3，N1The difference between the low-voltage terminal voltage change rate of the shielding winding and the low-voltage terminal voltage change rate of the secondary winding is a multiple of dv/dt, NshTo shield the number of turns of the winding, kshThe width of the shield winding for each turn;
(4) make the system common mode current iCMAnd solving the formula as 0, and rounding the root obtained by the solution to obtain the optimal number of turns of the shielding winding.
2. The flyback power transformer shield winding turn number design method of claim 1, wherein: the structural parameters of the flyback power transformer in the step (1) include the width of the primary winding, the width of the secondary winding, the perimeter and thickness of a medium between the adjacent parts of the primary winding and the secondary winding, the perimeter and thickness of a medium between the adjacent parts of the shielding winding and the secondary winding, the number of turns of the primary winding, the number of turns of the secondary winding, the width of each turn of the primary winding, the width of each turn of the secondary winding, the width of each turn of the shielding winding and the position of the shielding winding.
3. The flyback power transformer shield winding turn number design method of claim 2, wherein: and the position of the shielding winding is the minimum vertical distance between the bottom end of the shielding winding and the bottom end of the primary winding.
4. The flyback power transformer shield winding turn number design method of claim 1, wherein: said distance hp1、hp2、hs1、hs2、hsh1、hsh2、hs3、hs4All through the structural parameters of the winding and the number N of turns of the shielding windingshIs expressed in functional form.
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