Leakage transformer

Abstract

To provide a leakage transformer capable of suppressing a change in a leakage inductance value.SOLUTION: A leakage transformer 1 used in a converter includes: an assembly which includes a cylindrical central leg portion and a pair of side leg portions each having an inner surface where a side facing the central leg portion is recessed in an arc shape; a first primary winding 40a and a second winding 40b formed by winding an insulated wire on a bobbin; and a pair of magnetic members 20a, 20b each having a cylindrical shape, each magnetic member being disposed such that the inside thereof faces the central leg portion. The first winding, the second winding and the pair of magnetic members are disposed between the central leg portion and the pair of side leg portions, and the pair of magnetic members is disposed between the first winding and the second winding. The central leg portion and the side leg portions are Mn-based ferrite. The relation of the distance G1 between an inner arc surface of the magnetic member and an outer peripheral surface of the central leg portion and the distance G2 between an outer arc surface of the magnetic member and an inner surface of each side leg portion satisfies G1≥G2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a leakage transformer used in, for example, a resonant converter. [Background technology]

[0002] Electric vehicles such as EVs (Electric Vehicles) and PHEVs (Plug-in Hybrid Electric Vehicles), which have become increasingly popular in recent years, are equipped with devices such as electric motors and chargers, and the power supplies used in these vehicles require inductance components such as transformers and choke coils that can withstand high voltages and currents, as well as electronic components that use these components.

[0003] One example of a power supply device is a bidirectional isolated converter. The converter shown in the circuit diagram of Figure 7 is known as a DAB (Dual Active Bridge) type converter. DC / AC conversion unit 221 is configured with a bridge section consisting of a smoothing capacitor and four switches S1 to S4, such as IGBTs (Insulated Gate Bipolar Transistors). AC / DC conversion unit 261 is configured with a bridge section consisting of four switches S5 to S8 and a smoothing capacitor. Inductors 230 and 231 and a transformer 251 are disposed between DC / AC conversion unit 221 and the bridge section of AC / DC conversion unit 261. Note that inductors 230 and 231 can be replaced by the leakage inductance of a high-frequency transformer. A leakage transformer configured to reduce the degree of coupling between the input and output windings of the transformer to increase the leakage inductance and obtain the required inductance value for the converter may be used. Inductor 230 serves as the leakage inductance on the primary side of the leakage transformer, and inductor 231 serves as the leakage inductance on the secondary side of the leakage transformer.

[0004] FIG. 8 is a cross-sectional view of the transformer described in Patent Document 1, showing an example of the configuration of a leakage transformer. This transformer is configured by combining a pair of E-shaped ferrite cores 114, each including a center leg 114a and two outer legs 114b, so that the tips of the center legs 114a and the outer legs 114b abut against each other. A primary coil 110 and a secondary coil 112 are disposed facing the center leg 114a with a gap between them. A magnetic plate 115 made of ferrite is interposed between the opposing surfaces of bobbins 111 and 113, on which the primary coil 110 and the secondary coil 112 are disposed. The magnetic plate 115 is housed in recesses formed in the bobbins 111 and 113, so that gaps are formed between the outer periphery of the center leg 14a of the ferrite core 114 and between the outer legs 14b and the outer periphery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-172135 Summary of the Invention [Problem to be solved by the invention]

[0006] Until now, no particular attention has been paid to variations in the position of the magnetic plate 115, but the inventors have discovered that in a transformer having the configuration described below, the leakage inductance value can vary significantly depending on the position of the magnetic plate.

[0007] Transformers made up of multiple components are usually configured to create clearances between the components to facilitate assembly, which results in variations in the position of magnetic plate 115, which is placed between center leg 114a and outer leg 114b of ferrite core 114. This can result in different leakage inductance values ​​for each transformer.

[0008] In the DAB converter, a current I LSince the inductance is controlled, if the inductance value becomes smaller, the current increases, causing copper loss, and furthermore, soft switching may not be possible, resulting in increased losses during switching. Also, if the inductance value becomes larger, the current may become smaller, raising concerns that transmitted power may decrease. In other words, if the leakage inductance of a transformer is used instead of inductors 230 and 231, the leakage inductance value of the transformer may affect converter operation.

[0009] Although the variation in the position of the magnetic plate 115 can be reduced by reducing the clearance between the components and minimizing the dimensional variation that occurs during the manufacture of each component, this can make the components difficult to combine, increasing the assembly time, and the increased costs of increasing the precision of each component can be passed on to the price, resulting in a higher price for the transformer.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a leakage transformer that can suppress changes in leakage inductance value. [Means for solving the problem]

[0011] The present invention provides a leakage transformer for use in a converter with a switching frequency of 80 kHz or more and 300 kHz or less, comprising: an assembly having a cylindrical central leg and a pair of side legs each having an inner surface that is recessed in an arc shape on the side facing the central leg; first and second windings formed by winding insulated wire around a bobbin; and a pair of magnetic members that are arc-shaped plate-shaped cores and are arranged so that their inner surfaces face the central leg, wherein the first winding, the second winding, and the pair of magnetic members are arranged between the central leg and the pair of side legs, and the pair of magnetic members are arranged between the first winding and the second winding; the central leg and the side legs are made of Mn-based ferrite; and a relationship between a distance G1 between the inner arc surface of the magnetic member and the outer peripheral surface of the central leg and a distance G2 between the outer arc surface of the magnetic member and the inner surfaces of the side legs satisfies G1 ≧ G2.

[0012] In the leakage transformer of the present invention, the inner arc length Li of the magnetic member is shorter than the outer arc length Lo.

[0013] In the leakage transformer of the present invention, the outer arc length Lo of the magnetic member is equal to or less than the arc length Lm of the inner surface of the side leg portion.

[0014] In the leakage transformer of the present invention, the assembly is made up of a pair of E-shaped cores. In the leakage transformer of the present invention, the bobbin has an arc-shaped recess for determining the position of the magnetic member. The leakage transformer of the present invention also has an arc-shaped recess that determines the position of the magnetic member. Furthermore, in the leakage transformer of the present invention, the initial permeability μi at 25° C. and 100 kHz is 2500 or more. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a leakage transformer that can suppress changes in leakage inductance value. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a perspective view of a leakage transformer according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a leakage transformer according to an embodiment of the present invention. [Figure 3] 1 is a perspective view showing a leakage transformer according to an embodiment of the present invention, exploded into its constituent members; [Figure 4] FIG. 2 is a plan view for explaining the shape of a magnetic member used in the leakage transformer of the embodiment of the present invention. [Figure 5] 1 is a plan view for explaining the shape of a side leg portion of an assembly used in a leakage transformer according to an embodiment of the present invention. FIG. [Figure 6] FIG. 10 is a plan view illustrating the position of a magnetic member disposed between a center leg and a side leg of an assembly in a leakage transformer according to an embodiment of the present invention. [Figure 7] 1 is an equivalent circuit of a DAB converter in which a leakage transformer according to an embodiment of the present invention is used. [Figure 8] FIG. 1 is a cross-sectional view showing an example of a conventional leakage transformer. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of a leakage transformer according to the present invention will be described below, but the present invention is not limited to the following embodiments. Fig. 1 is a perspective view of a leakage transformer according to one embodiment of the present invention, Fig. 2 is a cross-sectional view of the central portion of Fig. 1 taken along the xy plane, and Fig. 3 is a perspective view showing the leakage transformer exploded into its constituent parts. Note that in each figure, the lead wires of the windings provided in the leakage transformer are omitted. Similarly, other components that do not need to be shown are omitted as appropriate.

[0018] The leakage transformers shown in Figures 1 to 3 are used in converters with switching frequencies of 80 kHz to 300 kHz, and are also applicable to converters using the DAB, LLC, and phase-shift full-bridge methods.They can be placed in a plane measuring 45 mm in length and 52 mm in width, excluding the lead wires, and are an example of a suitable configuration for a leakage transformer with a height of 40 mm or less.

[0019] The leakage transformer 1 comprises an assembly having a central leg and side legs, a plurality of windings stacked and passing through the central leg of the assembly, and a magnetic member sandwiched between the windings and located between the central leg and the side leg of the assembly, with the windings wound around a bobbin.

[0020] The illustrated leakage transformer 1 includes a pair of E-shaped cores 10a, 10b that form an assembly, magnetic members 20a, 20b for forming leakage inductance, a first bobbin 30a and a second bobbin 30b (hereinafter, these may be collectively referred to as bobbins) that include cylindrical bodies, and a first winding 40a and a second winding 40b (hereinafter, these may be collectively referred to as windings) that are formed of conductive wire wound around regions 34a, 34b that are sandwiched between the flanges of the bobbins 30a, 30b.

[0021] Each of the pair of E-shaped cores 10a, 10b has a central leg 12a, 12b and a side leg 15a, 15b, which form the central leg and outer leg of the assembly. The bobbins 30a, 30b have through-holes 35a, 35b inside their cylindrical bodies, through which the central legs 12a, 12b of the pair of E-shaped cores 10a, 10b are inserted and butted together to form an assembly, which is then integrated by wrapping insulating tape around their outer peripheries. A gap may be provided between the central legs 12a, 12b of the pair of E-shaped cores 10a, 10b to adjust inductance. The windings 40a, 40b are separated by the bobbins 30a, 30b and magnetic members 20a, 20b to reduce the degree of coupling between them. The magnitude of leakage inductance varies depending on the degree of coupling between the windings 40a, 40b; it is preferable to configure the coupling coefficient to be between 0.970 and 0.995.

[0022] The magnetic members 20a and 20b form a sub-magnetic path that bypasses the magnetic flux in the closed magnetic path formed by the E-shaped cores 10a and 10b. This reduces the degree of coupling between the windings 40a and 40b, thereby increasing leakage inductance. The magnetic members 20a and 20b are arc-shaped plate-shaped cores with a predetermined thickness, as shown in Figure 3. As shown in the plan view of Figure 4, the inner arc length Li is shorter than the outer arc length Lo, and they are arranged so that the inner arc faces the central legs 12a and 12b of the E-shaped core. The inner and outer arcs preferably have the same center. The width D of the magnetic members 20a and 20b is expressed as the difference between the inner arc radius R3 and the outer arc radius R4. The thickness of the magnetic members 20a and 20b is limited by the configuration of the E-shaped cores 10a and 10b and the space occupied by the windings 40a and 40b, but it can be varied within these limitations, thereby changing the leakage inductance value.

[0023] The central legs 12a and 12b of the E-shaped cores 10a and 10b are cylindrical, and the side legs 15a and 15b have inner surfaces that are recessed in an arc shape on the side facing the central legs 12a and 12b, as shown in Figures 3 and 5. It is preferable that almost the entire inner peripheral surface be arc-shaped.

[0024] As shown in Figure 6, the magnetic members 20a, 20b are arranged with the inner arc-shaped portion facing the central leg of the E-shaped core. The outer arc length Lo is preferably equal to or less than the arc length Lm on the inner surface of the side leg of the E-shaped core. To arrange the magnetic members 20a, 20b, it is preferable to provide recesses 32a, 32b in at least one of the bobbins 30a, 30b to accommodate and position the magnetic members 20a, 20b. The recesses 32a, 32b preferably have an arc-shaped portion that follows the shape of the magnetic members 20a, 20b, and more preferably have a similar shape.

[0025] The inventors' research has revealed that variations in leakage inductance can be suppressed by arranging the magnetic members 20a, 20b of the leakage transformer so that the relationship between the distance G1 between their inner arc-shaped sides and the outer periphery of the center legs 12a, 12b and the distance G2 between their outer arc-shaped sides and the arc-shaped sides of the side legs 15a, 15b satisfies G1 ≥ G2. Based on this finding, even if there is variation in the magnetic members 20a, 20b, variation in the leakage inductance of the leakage transformer can be suppressed, reducing the impact on converter operation and ensuring stable operation. It is more preferable to arrange the magnetic members so that the relationship between the distance G1 and the distance G2 satisfies G1 > G2.

[0026] The center of the arc of the inner peripheral surface of the side legs 15a, 15b of the E-shaped cores 10a, 10b is the same as the center of the central legs 12a, 12b, and it is preferable that the width D of the magnetic members 20a, 20b is 0.4≦D / W≦0.7, where W is the difference between the arc radius R2 and the radius R1 of the central legs 12a, 12b.

[0027] As a magnetic material used for the E-shaped cores 10a, 10b and the arc-shaped plate-shaped cores of the magnetic members 20a, 20b, Mn-based ferrite having an initial permeability μi of 2500 or more at 25°C and 100 kHz is preferred. The larger the saturation magnetic flux density Bs, the more compact the core can be, and a saturation magnetic flux density Bs of 280 mT or more is preferred, and 350 mT or more is even more preferred. Furthermore, the larger the initial permeability μi, the more the number of turns of the winding can be reduced, which is preferable because it allows for the miniaturization of the leakage transformer. Furthermore, Mn-based ferrite has a core loss of 920 kW / m at a frequency of 100 kHz, an excitation magnetic flux density of 250 mT, and a temperature of 23°C to 130°C. 3 It is preferable that the core loss at temperatures between 23°C and 130°C is 920 kW / m or less. 3 By setting the value to the value below, it is possible to prevent the leakage transformer used from experiencing thermal runaway even when the converter is continuously driven under maximum load conditions at an ambient temperature exceeding 100°C.

[0028] Each of the windings 40a, 40b is made of a coated wire with an insulating coating on a conductor made of a conductive material such as copper, aluminum, or an alloy thereof. Generally, enameled wire, which is copper wire coated with polyurethane insulation, is used. However, when insulation requirements such as reinforced insulation are required or when high test voltages must be met, it is preferable to use double-insulated or triple-insulated wire, which is a reinforced insulated wire with multiple layers of insulating coating to improve insulation. Especially when switching at high frequencies, it is preferable to use litz wire, twisted wire, or parallel wire for the windings.

[0029] The bobbins 30a and 30b are formed from an insulating resin, and any resin having insulation properties, mechanical strength, chemical resistance, heat resistance, moisture resistance, and moldability may be used. Preferred examples include phenolic resin, diallyl phthalate resin, PPS (Poly Phenylene Sulfide) resin, liquid crystal polymer, PET (Polyethylene Terephthalate) resin, PBT (Poly Butylene Terephthalate) resin, and ABS (Acrylonitrile butadiene styrene) resin, and these may be molded by known methods such as injection molding. [Example]

[0030] We fabricated the leakage transformer shown in Figures 1 to 3 with the following configuration: This leakage transformer can be placed in a plane 45 mm long and 52 mm wide, is 40 mm or less in height, and is configured so that, with an air gap of 0 mm, the input inductance due to the first winding is 1.3 mH, the output inductance due to the second winding is 0.9 mH, and the leakage inductance Le is 28 μH on the primary side and 19.4 μH on the secondary side, and is intended for use in a DAB type inverter with a switching frequency of 100 kHz and a DC input voltage of 370 to 430 V.

[0031] The ferrite used for the E-shaped cores 10a, 10b and the magnetic members 20a, 20b is a Mn-based ferrite having a saturation magnetic flux density Bs of 410 mT at 100°C and an initial permeability μi of 2900 or more at 25°C and 100 kHz. This Mn-based ferrite also has a core loss of 420 kW / m at a frequency of 100 kHz, an excitation magnetic flux density of 200 mT, and a temperature range of 23°C to 130°C. 3 The following is the result.

[0032] The outer dimensions of the E-shaped cores 10a and 10b are 50 mm in the X direction, 17.5 mm in the Y direction, and 32 mm in the Z direction. The radius R1 of the central legs 12a and 12b is 10 mm, the arc radius R2 of the inner peripheral surfaces of the side legs 15a and 15b is 22 mm, and the difference W between the arc radius R2 and the radius R1 is 12 mm. The effective cross-sectional area Ae of the combined E-shaped cores 10a and 10b is 336.2 mm. 2 and the effective magnetic path length le is 85.46 mm.

[0033] The magnetic members 20a and 20b have an arc radius of 16 mm at their center Rm, and the inner arc radius R3 and outer arc radius R4 are different at the same central position based on the center Rm.The width D is 6.4 mm and the thickness is 3.5 mm, but for characteristic comparison, widths D were set to 4.4 mm and 5.4 mm, and thicknesses were also set to 4.5 mm, 5.5 mm, 6.5 mm, and 7.5 mm.As shown in Figure 4, the arc length of magnetic members 20a and 20b is determined by the central angle θ centered at a position a predetermined distance E from the center position that determines the arc radius, and the dimension E was 16.5 mm and the central angle θ was 50 degrees.

[0034] The first winding 40a was formed by winding 12 turns of triple-insulated wire, each consisting of 1,400 wires with a wire diameter of 0.05 mm, around phenolic resin bobbins 30a and 30b, and the second winding 40b was formed by winding 10 turns of triple-insulated wire, each consisting of 1,400 wires with a diameter of 0.05 mm. The distance between the opposing first winding 40a and second winding 40b was 9.7 mm.

[0035] Magnetic members 20a and 20b were adhesively fixed to bobbins 30a and 30b, and the central legs 12a and 12b of E-cores 10a and 10b were inserted into the cylindrical body portions 35a and 35b of bobbins 30a and 30b and combined so as to abut against each other, and an insulating tape was wound around the outer periphery and integrated. The positions of magnetic members 20a and 20b were set as condition 1 (G1 < G2), condition 2 (G1 = G2), and condition 3 (G1 > G2) in relation to the distance G1 between the inner arc side thereof and the outer periphery of central legs 12a and 12b and the distance G2 between the outer arc side and the arc sides of side legs 15a and 15b, and a leakage transformer 1 was created. Table 1 summarizes the dimensions of each part under each condition.

[0036]

Table 1

[0037] Regarding the obtained leakage transformer 1, an Agilent LCR meter (4285A) was used, and the inductance L and leakage inductance Le of the primary side and the secondary side were measured under the test condition of a voltage of 1V. The results are shown in Tables 2 and 3.

[0038]

Table 2

[0039]

Table 3

[0040] The inductance L of the primary and secondary sides of the obtained leakage transformer 1 hardly changed depending on the positions of the magnetic members 20a and 20b under conditions 1 to 3 or the thickness of the magnetic members. On the other hand, the leakage inductance Le of the primary and secondary sides increased as the thickness of the magnetic members increased. Furthermore, among the positions of the magnetic members 20a and 20b under conditions 1 to 3, the leakage inductance Le increased under condition 1, in which the magnetic members 20a and 20b were close to the central legs 12a and 12b of the E-shaped cores 10a and 10b. The leakage inductance Le was approximately the same under condition 2, in which the magnetic members 20a and 20b were positioned centrally between the central legs 12a and 12b and the side legs 15a and 15b of the E-shaped cores 10a and 10b, and condition 3, in which the magnetic members 20a and 20b were close to the outer legs 15a and 15b of the E-shaped cores. According to these results, if the positions of the magnetic members 20a and 20b are such that the distance G1 between their inner arc-shaped sides and the outer periphery of the central legs 12a and 12b and the distance G2 between their outer arc-shaped sides and the arc-shaped sides of the side legs 15a and 15b satisfy the relationship G1≧G2, a leakage transformer with little change in leakage inductance Le can be obtained, and a leakage transformer in which the leakage inductance Le can be changed by changing the thickness of the magnetic members 20a and 20b can be provided. [Explanation of symbols]

[0041] 1 Leakage transformer 10a, 10b E-type core 20a, 20b magnetic members 40a 1st winding 40b Second winding

Claims

1. In a leakage transformer used in a converter with a switching frequency of 80 kHz or more and 300 kHz or less, an assembly including a cylindrical central leg portion and a pair of side leg portions each having an inner surface that is recessed in an arc shape on the side facing the central leg portion; a first winding and a second winding formed by winding an insulated wire around a bobbin; a pair of magnetic members each of which is an arc-shaped plate-shaped core and is arranged so that its inner surface faces the central leg portion; the first winding, the second winding, and the pair of magnetic members are disposed between the central leg and the pair of side legs, and the pair of magnetic members are disposed between the first winding and the second winding; the central leg portion and the side leg portions are made of Mn-based ferrite, a relationship between a distance G1 between the inner arcuate surface of the magnetic member and the outer peripheral surface of the central leg portion and a distance G2 between the outer arcuate surface of the magnetic member and the inner surfaces of the side legs satisfies G1≧G2; Leakage transformer.

2. 2. The leakage transformer according to claim 1, The inner arc length Li of the magnetic member is shorter than the outer arc length Lo. Leakage transformer.

3. 3. The leakage transformer according to claim 1 or 2, The outer arc length Lo of the magnetic member is equal to or less than the arc length Lm of the inner surface of the side leg portion. Leakage transformer.

4. 4. The leakage transformer according to claim 1, The assembly is composed of a pair of E-shaped cores. Leakage transformer.

5. 5. The leakage transformer according to claim 1, The bobbin has an arc-shaped recess that determines the position of the magnetic member. Leakage transformer.

6. 6. The leakage transformer according to claim 1, The Mn-based ferrite has an initial permeability μi of 2500 or more at 25°C and 100 kHz. Leakage transformer.

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