Transformer, converter and leakage inductance adjusting method

Abstract

The invention discloses a transformer, a converter and a leakage inductance adjusting method, the transformer comprises a winding and a magnetic core, the magnetic core is provided with an air gap used for generating a leakage magnetic field, and the winding is close to or partially covers the air gap, so that leakage magnetic flux in the leakage magnetic field generated by the air gap partially enters the winding. According to the transformer, a thin magnetic sheet used for generating leakage inductance in a traditional method is abandoned, so that the mechanical strength of the transformer is enhanced, and meanwhile accurate control over the leakage inductance is achieved through the ratio of the number of turns of high and low coupling windings to the total number of turns; the air gap position of the transformer is reasonably arranged to ensure that the temperature of the winding is not too high while a leakage magnetic field is shielded.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a transformer, a converter and a leakage inductance adjustment method. Background Art

[0002] For existing soft-switching converters, their topological structure requires that an inductor be connected in series at one end of the transformer to implement modulation strategies such as phase shifting and frequency conversion of the primary and secondary circuits of the transformer.

[0003] At present, the inductor mainly adopts an independent inductor connected in series on one side of the transformer, that is, the transformer and the inductor are two independent electrical devices, and only rely on wires to connect the two. At present, the independent inductor is mainly composed of a magnetic core and a winding. In the case of high power, in order to ensure that the gain meets the requirements, the inductance value is relatively small, usually in the range of a few μH to tens of μH. However, due to the large current flowing through and the thick winding wire diameter, the volume of the independent inductor cannot be ignored.

[0004] In recent years, there have been literatures that replace independent inductors with transformer leakage inductance to reduce the size of power supply devices, which is usually called: magnetic integrated transformer. The leakage inductance of the transformer usually needs to be controlled by the transformer air gap, and the magnetic field strength at the air gap is relatively large; if the winding is arranged at the air gap, the winding can shield the leakage magnetic field at the air gap, significantly reducing the leakage magnetic field in the space outside the air gap, but it will cause serious eddy current loss and significant heating of the winding at this location; if the air gap is placed at the non-wound magnetic core, the winding temperature can be significantly controlled, but the leakage magnetic field at the air gap will seriously affect the safe and stable operation of nearby circuits.

[0005] Although the air gap can control the transformer leakage inductance, it also affects the transformer excitation inductance. Therefore, the air gap is not completely used to adjust the leakage inductance. It is more necessary to accurately control the coupling degree between the primary and secondary windings. However, in the existing literature, a third magnetic column is generally added between the primary and secondary winding magnetic columns to change the coupling degree of the primary and secondary windings. However, if the required leakage inductance is small, the magnetic column added by this method is thin, the mechanical strength is insufficient, and it is easy to break.

[0006] Therefore, how to control the leakage inductance in the transformer without adding additional magnetic columns and make the leakage inductance not affect nearby circuits is an urgent problem to be solved. Summary of the invention

[0007] The present invention provides a transformer, a converter and a leakage inductance adjustment method, which can control the leakage inductance in the transformer without adding an additional magnetic column and make the leakage inductance not seriously affect the nearby circuits.

[0008] The technical solution adopted by the present invention is to design a transformer, wherein an air gap for generating a leakage magnetic field is provided on the magnetic core, and the winding is adjacent to or partially covers the air gap, so that the leakage magnetic flux in the leakage magnetic field generated by the air gap partially enters the winding.

[0009] In some embodiments, the number of the magnetic cores is at least two, and the air gap is disposed at the junction of different magnetic cores.

[0010] In certain embodiments, an end of at least one of the magnetic cores is adjacent to a side wall of another of the magnetic cores, and a gap between an end of the winding magnetic core and a side wall of another of the connecting magnetic cores is the air gap.

[0011] In some embodiments, the number of the magnetic cores is four, and the four magnetic cores are adjacent to form a rectangular frame, wherein two opposite magnetic cores are winding cores, and the other two magnetic cores are connecting cores, the ends of the winding cores are adjacent to the side walls of the connecting cores, and the winding is wound around both of the winding cores.

[0012] In certain embodiments, a spacer is provided in the air gap to space the magnetic cores on both sides, and the spacer is connected to the skeleton of the transformer.

[0013] In some embodiments, the winding includes a high-coupling winding and a low-coupling winding, the high-coupling winding is the laminated portion of the primary winding and the secondary winding of the transformer; the low-coupling winding is the laminated portion of the primary winding or the secondary winding and itself.

[0014] In some embodiments, at least two magnetic cores are arranged opposite to each other, an air gap is arranged between the two magnetic cores, the high-coupling winding and the low-coupling winding are wound on both the two magnetic cores, the low-coupling winding on one of the magnetic cores is the primary winding, and the low-coupling winding on the other magnetic core is the secondary winding.

[0015] In some embodiments, at least two magnetic cores are arranged opposite to each other, and the air gap is arranged between the two magnetic cores. The primary winding and the secondary winding are both wound on one of the magnetic cores. The winding package on the magnetic core includes a high-coupling winding in the middle and a low-coupling winding at both ends. The low-coupling windings at both ends are the primary winding and the secondary winding respectively.

[0016] A converter comprises the transformer.

[0017] A transformer leakage inductance adjustment method is used for the transformer. First, the leakage inductance is adjusted initially by adjusting the size of the air gap. Then, the leakage inductance is adjusted accurately by adjusting the ratio of the number of turns of the high-coupling winding to the low-coupling winding.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The transformer of the present invention uses leakage inductance to replace independent inductance, so that the structure of the transformer is compact, and the winding around the air gap is used to absorb part of the air gap leakage magnetic flux, so that the leakage magnetic flux in the space outside the air gap is small, and the leakage magnetic flux is prevented from seriously affecting the operation of the surrounding circuits. The heat dissipation surface of the winding at the air gap is large, which is convenient for using heat dissipation devices such as heat dissipation glue to dissipate heat at the air gap, thereby avoiding the winding at the air gap from being affected by the leakage magnetic flux and causing excessive temperature. The size of the air gap can be conveniently adjusted by the spacing of the magnetic cores, and then the size of the excitation inductance and the leakage magnetic flux can be conveniently adjusted.

[0020] The present invention divides the winding into a high-coupling winding and a low-coupling winding for winding, and the coupling degree of the primary and secondary windings can be adjusted without adding magnetic columns, which has lower costs; by allocating the number of turns of the high-coupling winding and the low-coupling winding, the coupling degree of the primary and secondary windings can be accurately controlled, and the leakage inductance can be accurately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is described in detail below in conjunction with specific embodiments and drawings. In order to show details and facilitate understanding of its principles, it is not necessarily drawn to scale, and similar reference numerals may describe similar components in different views. The drawings generally illustrate the embodiments discussed herein by way of example and not limitation. Among them:

[0022] Figure 1 is a schematic diagram of a transformer according to an embodiment.

[0023] Figure 2 This is a schematic diagram of the transformer with the frame removed.

[0024] Figure 3 yes Figure 2 Schematic diagram from another angle.

[0025] Figure 4 is a schematic diagram of another embodiment of a transformer.

[0026] Figure 5 yes Figure 4 Schematic diagram of the magnetic core of the transformer.

[0027] Figure 6 It is a schematic diagram of the stacked winding of the primary and secondary windings.

[0028] Figure 7 It is a schematic diagram of the primary and secondary sides being wound with their respective winding stacks.

[0029] Figure 8 It is a schematic diagram of the simulation results of the transformer leakage magnetic field.

[0030] In the figure, 1. air gap; 2. winding core; 3. connecting core; 5. high coupling winding; 6. low coupling winding; 7. primary winding; 8. secondary winding; 9. spacer. DETAILED DESCRIPTION

[0031] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments, and the following embodiments do not limit the invention involved in the claims. In addition, all combinations of the features described in the embodiments are not necessarily required for the solutions of the invention.

[0032] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0033] Example

[0034] like Figure 1 , 2 As shown in Figure 3, a transformer includes a winding and a magnetic core, wherein the magnetic core is provided with an air gap 1 for generating a leakage magnetic field, and the winding is adjacent to or partially covers the air gap 1, so that part of the leakage magnetic field of the air gap 1 enters the winding.

[0035] The winding being adjacent to the air gap means that the winding is close to the air gap, and the winding is flush with the air gap or relatively close to the air gap.

[0036] The winding partially covers the air gap, which means that the air gap is covered by the winding but not completely.

[0037] There are at least two magnetic cores, and the air gap 1 is arranged at the junction of different magnetic cores. The end of at least one magnetic core is adjacent to the side wall of another magnetic core, and the gap between the end of the winding magnetic core 2 and the side wall of another connecting magnetic core 3 is the air gap 1.

[0038] The number of the magnetic cores in this embodiment is four, and the four magnetic cores are adjacent to form a rectangular frame, wherein two opposite magnetic cores are winding cores 2, and the other two magnetic cores are connecting cores 3, the ends of the winding cores 2 are adjacent to the side walls of the connecting cores 3, the windings are wound around the two winding cores 2, the magnetic cores are fixed on the supporting frame of the transformer, and a spacer 9 is provided in the air gap 1 to separate the magnetic cores on both sides, and the spacer 9 is connected to the frame of the transformer.

[0039] It also includes a heat dissipation device, which is used to dissipate heat from the winding and the magnetic core. For example, the heat dissipation device can be a heat dissipation glue in contact with the winding and the magnetic core.

[0040] First, for magnetic integrated transformers, adding an air gap in the transformer can simultaneously adjust the transformer's excitation inductance Lm and leakage inductance L k , the specific calculation formula of the air gap is:

[0041] Assume that the maximum transformer winding voltage amplitude is V max , the transformer winding voltage frequency is at least f smin , then the number of transformer turns is:

[0042]

[0043] In the formula, B max is the maximum magnetic induction intensity, which is determined by the type of core material; Ae is the core cross-sectional area.

[0044] The total reluctance is:

[0045]

[0046] Where, L m is the transformer excitation inductance, which is derived from the operating characteristics of the topology.

[0047] Since the magnetic permeability of ferrite magnetic material is much greater than the magnetic permeability of air, the magnetic resistance of ferrite is ignored, and the magnetic resistance is mainly provided by the air gap. The required air gap width gap is:

[0048] gap=Rm·μ 0 ·Ae (3)

[0049] In the formula, μ 0 is the magnetic permeability of air.

[0050] From equations (2) and (3), it can be seen that the excitation inductance can be determined by the width of the air gap and the cross-sectional area of ​​the core, and the expression is:

[0051]

[0052] The formula for calculating leakage inductance is:

[0053] L k =(1-coef 2 )L m ·Lm (5)

[0054] Where coef is the coupling coefficient between the primary and secondary windings.

[0055] From equations (4) and (5), it can be seen that leakage inductance is related to magnetizing inductance and coupling coefficient. When the magnetizing inductance is constant, the larger the air gap, the lower the coupling coefficient of the primary and secondary windings, the larger the leakage magnetic field, and the larger the leakage inductance; when the coupling coefficient is constant, the larger the air gap, the lower the magnetizing inductance, and the smaller the leakage inductance.

[0056] Since the magnetic permeability of the magnetic material used in the magnetic column is relatively high, much greater than the magnetic permeability of air, the magnetic resistance of the magnetic column is much smaller than the magnetic resistance of air. Most of the magnetic lines of force are confined inside the magnetic column, and there are few magnetic lines distributed outside the magnetic column.

[0057] In the space around the magnetic column, the magnetic induction intensity is low, and the magnetic lines of force are mainly bound in the magnetic column. Only a very small number of magnetic lines of force are distributed in the air around the magnetic core. In the outer space of air gap 1 in the magnetic core, the magnetic induction intensity is large and the number of magnetic lines of force is large. The reason is: since air gap 1 and the space around air gap 1 are filled with air, the magnetic permeability of the air is low and the magnetic resistance is high. At this time, the magnetic lines of force are divergent, and a large number of magnetic lines of force enter the space around air gap 1 and are then bound by the next magnetic column.

[0058] The magnetic induction intensity in the space around air gap 1 is relatively high. If the winding covers or is close to air gap 1, the metal material of the winding will produce obvious eddy current loss in the magnetic field, and this part of the winding will heat up seriously. However, it is not without advantages. Since the magnetic permeability of metal is greater than that of air but less than that of magnetic material, most of the magnetic lines of force in the space around air gap 1 are confined in the winding and then enter the next magnetic column, and the magnetic induction intensity on the outside of the winding is greatly reduced.

[0059] like Figure 1 As shown, in the transformer of this embodiment, the air gap 1 is placed at the connection of the four magnetic cores 3. In addition, the air gap 1 is covered by the winding, but not completely. Since the part of the space outside the air gap 1 that is not covered by the winding is relatively narrow, only the space near the air gap 1 has a high magnetic induction intensity, and the magnetic induction intensity in the outer space is relatively weak. Most of the magnetic lines of force directly enter the winding from the air gap 1 and then enter the magnetic column. Of course, the eddy current loss of the winding near the air gap 1 is relatively large, but since the winding here can directly contact the external heat dissipation device, such as heat dissipation colloid, the heat accumulation is not serious, so the temperature of the winding at this place is not high. If the conventional transformer completely covers the air gap 1 with the winding, especially in the case of laminated winding, the inner winding with severe heat generation is covered by the outer winding, and the heat dissipation device cannot penetrate into it, making it difficult to dissipate heat.

[0060] Different from the traditional transformer air gap setting method, the air gap is set at the intersection of the four magnetic columns. This air gap setting method has the following advantages:

[0061] 1. The leakage magnetic field of the air gap is absorbed by the winding to a certain extent, and the leakage magnetic field in the space outside the air gap is small;

[0062] 2. The winding at the air gap is affected by the leakage magnetic field and generates obvious heat, but the heat dissipation surface of the winding is large and the heat dissipation colloid can be in direct contact, so the winding temperature does not rise sharply;

[0063] 3. Since the magnetic core is only composed of four rectangular magnetic cores, the excitation inductance and leakage magnetic field can be easily adjusted by adjusting the size of the air gap.

[0064] The windings include a high-coupling winding 5 and a low-coupling winding 6. The high-coupling winding 5 is a laminated winding portion of the transformer's primary winding 7 and secondary winding 8. The low-coupling winding 6 is a laminated winding portion of the primary winding 7 or the secondary winding 8 and itself.

[0065] At least two magnetic cores are arranged opposite to each other, an air gap 1 is arranged between the two magnetic cores, the high coupling winding 5 and the low coupling winding 6 are wound on the two magnetic cores, the low coupling winding 6 on one of the magnetic cores is part of the primary winding 7, and the low coupling winding 6 on the other magnetic core is part of the secondary winding 8. The frame is spaced between the high coupling winding 5 and the low coupling winding 6, that is, a spacer 9 is arranged on the frame to be spaced between the high coupling winding 5 and the low coupling winding 6.

[0066] This embodiment is also applicable to various converters having the transformer, and is universal as long as it has a topology structure with an inductor connected in series on one side of the transformer, such as AC-AC power converters, matrix converters, bidirectional DC converters, etc.

[0067] As a method for adjusting the leakage inductance of a transformer, first, the leakage inductance is initially adjusted by adjusting the size of the air gap 1; then, the leakage inductance is accurately adjusted by adjusting the ratio of the number of turns of the high-coupling winding 5 and the low-coupling winding 6.

[0068] like Figure 6 As shown, the primary and secondary windings are stacked, that is, the primary and secondary windings are coaxially and radially stacked inside and outside, the outer winding is the upper winding, and the inner winding is the lower winding. The magnetic flux flowing through the upper and lower windings is almost the same, and only a very small number of magnetic lines of force flow only through the primary or secondary winding. Therefore, the coupling degree of this part of the primary and secondary windings is very high, that is, coef≈1, and is generally above 0.99, which is referred to as C below. 高 .

[0069] like Figure 7 As shown in the figure, when the primary and secondary windings are wound in layers with their own windings, a small part of the magnetic lines of force generated by the primary and secondary windings form a closed loop through the air and only flow through the inside of the single-sided winding. This part is called the leakage magnetic field. There is a leakage magnetic field in both the primary and secondary windings, and the coupling coefficient between the two is low. In general, coef is about 0.9, which is referred to as C below. 低 .

[0070] Therefore, in the present invention, after the number of turns of the source and secondary windings is determined, the overall coupling coefficient of the primary and secondary windings can be controlled by allocating the proportion of the high-coupling winding and the low-coupling winding. Regarding the influence of the winding conditions of the primary and secondary windings on the leakage inductance, when the primary and secondary windings are completely overlapped, the coupling coefficient of the two will reach the maximum and the leakage inductance will be the minimum; when the primary and secondary windings are not overlapped at all, the coupling coefficient of the two will reach the minimum and the leakage inductance will be the maximum.

[0071] Usually, the number of turns of the primary and secondary windings is large, which also means that the leakage inductance control method proposed above (controlling the overall coupling coefficient of the primary and secondary windings by allocating the proportion of high-coupling windings and low-coupling windings) has higher accuracy.

[0072] like Figure 8 The figure shows the magnetic field intensity result on the longitudinal section of a winding magnetic column of a transformer. The relationship between magnetic field intensity and magnetic induction intensity is: B = Hμ, μ is the magnetic permeability, μ is a constant value in the same magnetic conductive material (air is also a magnetic conductive material), so the magnetic field intensity can directly reflect the magnitude of the magnetic induction intensity.

[0073] At the air gap, the magnetic field strength is significantly greater than other locations in the transformer, up to 500oe, which is consistent with the strong leakage magnetic field at the air gap. However, due to the close distance to the winding, the magnetic field strength in the air gap peripheral space decays faster and has less impact on the circuit. In addition, the magnetic field strength in the low-coupling winding and the frame peripheral space is also significantly higher than the high-coupling winding peripheral space, which is consistent with the leakage magnetic field in the low-coupling winding peripheral space being greater than the high-coupling winding peripheral space. Therefore, Figure 8 As shown, the simulation results verify the theoretical explanation above.

[0074] like Figure 4 , 5 As shown. It is another embodiment of a transformer, which also applies the above-mentioned air gap setting and high and low coupling winding methods. This embodiment includes at least two magnetic cores arranged opposite to each other, with the air gap 1 arranged between the two magnetic cores, the primary winding 7 and the secondary winding 8 are both wound on one of the magnetic cores, and the winding package on the magnetic core includes a high coupling winding 5 located in the middle and low coupling windings 6 located at both ends, and the low coupling windings 6 at both ends are the primary winding 7 and the secondary winding 8 respectively.

[0075] Although only this embodiment is given, other transformers that only wind the primary and secondary windings on the same side of the magnetic core can be deduced by analogy to obtain a magnetic integrated transformer with better comprehensive effect. Figure 1 By analogy, a magnetic integrated transformer with good comprehensive effect is obtained. In this embodiment, an extremely narrow air gap is arranged in the middle of the magnetic core on the other side where the winding is not wound, so as to prevent the thermal deformation and cracking of the non-wound magnetic core and increase the reliability of the transformer.

[0076] Different from the traditional transformer method of adjusting the coupling degree between the primary and secondary sides, the winding is divided into low-coupling winding and high-coupling winding. High-coupling winding means that the primary and secondary windings are stacked on the same magnetic column, and the coupling degree is high; low-coupling winding refers to the part of the primary winding stacked on the primary winding core and the part of the secondary winding stacked on the secondary winding core, and the coupling degree is low; this winding setting method has the following advantages:

[0077] 1. The coupling degree between the primary and secondary windings can be adjusted without adding magnetic columns, which is lower in cost;

[0078] 2. By allocating the number of turns of high-coupling windings and low-coupling windings, the coupling degree of the primary and secondary windings can be accurately controlled, that is, the leakage inductance can be accurately controlled;

[0079] The optimization based on magnetic integrated transformer is mainly reflected in: the setting of air gap reasonably takes into account the heat dissipation of winding and the shielding of leakage magnetic field at the air gap; the setting of winding can achieve high-precision adjustment of leakage inductance through the distribution of turns of high-coupling winding and low-coupling winding.

[0080] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described, or replace them in similar ways, without departing from the spirit of the present invention or exceeding the scope defined by the appended claims.

Claims

1. A transformer, comprising a winding and a magnetic core, characterized in that: The magnetic core is provided with an air gap for generating a leakage magnetic field, and the winding is adjacent to or partially covers the air gap, so that the leakage magnetic flux in the leakage magnetic field generated by the air gap partially enters the winding.

2. The transformer according to claim 1, characterized in that: The number of the magnetic cores is at least two, and the air gap is arranged at the adjacent positions of different magnetic cores.

3. The transformer according to claim 2, characterized in that: An end of at least one of the magnetic cores is adjacent to a side wall of another of the magnetic cores, and a gap between the end of the magnetic core and the side wall of another of the magnetic cores is the air gap.

4. The transformer according to claim 3, characterized in that: There are four magnetic cores, which are adjacent to each other to form a rectangular frame, wherein two opposite magnetic cores are winding cores, and the other two magnetic cores are connecting cores, the ends of the winding cores are adjacent to the side walls of the connecting cores, and the windings are wound around the two winding cores.

5. The transformer according to claim 2, characterized in that: A spacer is provided in the air gap to space the magnetic cores on both sides, and the spacer is connected to the skeleton of the transformer.

6. The transformer according to claim 1, characterized in that: The winding includes a high-coupling winding and a low-coupling winding. The high-coupling winding is a laminated winding portion of a primary winding and a secondary winding of a transformer; the low-coupling winding is a laminated winding portion of a primary winding or a secondary winding and itself.

7. The transformer according to claim 6, characterized in that: At least two magnetic cores are arranged opposite to each other, and the high-coupling winding and the low-coupling winding are wound on both of the two magnetic cores. The low-coupling winding on one of the magnetic cores is the primary winding, and the low-coupling winding on the other magnetic core is the secondary winding.

8. The transformer according to claim 6, characterized in that: It includes at least two magnetic cores arranged opposite to each other, the primary winding and the secondary winding are both wound on one of the magnetic cores, the windings on the magnetic core include a high-coupling winding located in the middle and a low-coupling winding located at both ends, and the low-coupling windings at the two ends are the primary winding and the secondary winding respectively.

9. A converter, characterized in that: Comprising a transformer as claimed in any one of claims 1 to 8.

10. A transformer leakage inductance adjustment method, used for the transformer according to any one of claims 7 to 8, characterized in that: The leakage inductance is initially adjusted by adjusting the size of the air gap; the leakage inductance is accurately adjusted by adjusting the ratio of the number of turns of the high-coupling winding to the number of turns of the low-coupling winding.

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