Power conversion device

Abstract

Provided is a power conversion device equipped with a transformer 1, the power conversion device having a low loss and wide designable range of leakage inductance and enabling a reduction in size. The power conversion device comprises a transformer 1 having: an iron core 10 to which a magnetic leg 11 is provided; and a plurality of coils 20 wound around the magnetic leg 11 at mutually different positions. The transformer 1 has a magnetic flux guiding member 30 composed of a magnetic material having a shape that covers the portions of the plurality of coils 20 that are exposed at the outer side of the iron core 10. The magnetic flux guiding member 30 includes: a coil outer periphery covering section 30A that is arranged at the outer peripheral sections of the plurality of coils 20; an inter-coil covering section 30B that protrudes from the coil outer periphery covering section 30A and stretches between the plurality of coils 20; and a pair of coil end face covering sections 30C that are connected to the coil outer periphery covering section 30A and cover the sides of the plurality of coils 20 that are on the opposite sides thereof from the portions covered by the inter-coil covering section 30B.

Description

Power Conversion Device

[0001] The present invention relates to a power conversion device.

[0002] For example, power conversion devices used in electric vehicles have a DCDC conversion function that converts DC power into DC power of a different voltage. In such power conversion devices, input DC power is converted into AC power by an input inverter circuit having a switching element, the converted AC power is converted into AC power of a different voltage via a transformer, and the converted AC power of a different voltage is converted into DC power by an output converter circuit and output.

[0003] FIG. 7 is a cross-sectional view of a conventional transformer.

[0004] As shown in Fig. 7, a conventional transformer 1 has an iron core 10 provided with magnetic legs 11 and two coils 20 wound around magnetic legs 11 at different positions. The two coils 20 are, for example, a first coil 20A that functions as a low-voltage coil and a second coil 20B that functions as a high-voltage coil. The coils 20 are sealed with an insulating material 25. A portion of the iron core 10 is connected to a housing 50 of the power conversion device via a heat transfer member 40.

[0005] Documents that disclose a structure similar to that of the conventional transformer 1 shown in FIG. 7 include, for example, Patent Document 1.

[0006] Japanese Patent Application Laid-Open No. 2004-39847

[0007] Here, in the structure of the conventional transformer 1 in Patent Document 1 and in Fig. 7, as shown in Fig. 7, there is a problem in that the coil 20 has a portion exposed outside the iron core 10, and leakage magnetic flux 31 generated by the coil 20 is likely to spread in the portion exposed outside the iron core 10. Therefore, electronic components such as switching elements and capacitors of the power conversion device must be located away from the transformer 1, which is an obstacle to miniaturizing the power conversion device.

[0008] Furthermore, there are problems such as in-plane eddy current loss occurring when the leakage flux 31 interlinks the coil 20, and stray load loss occurring in surrounding components due to the leakage flux 31 leaking outside the transformer 1.

[0009] Furthermore, in a power conversion device, when adjusting the voltage ratio by phase, leakage inductance is required, and it is necessary to accurately adjust in advance the magnitude of the leakage inductance of the transformer 1. However, in the configuration of the conventional transformer 1, the only means for adjusting the magnitude of the leakage inductance is to adjust the degree of coupling between the two coils 20 by changing the size of the gap between the first coil 20A and the second coil 20B (the distance between the coils), which means that there is a limit to the range in which the magnitude of the leakage inductance can be adjusted, and there is also the problem that the designable range of the leakage inductance is narrow.

[0010] Furthermore, when SiC devices are used as switching elements in power conversion equipment, the switching frequency is limited to approximately 100 kHz. However, when GaN devices are used, which are expected to become widely used in the 2030s, the switching frequency will rise to the MHz range, requiring a wider designable range for leakage inductance.

[0011] The problem to be solved by the present invention is to provide a power conversion device including a transformer that allows a wide design range for leakage inductance, has low loss, and is miniaturized.

[0012] In order to solve the above-mentioned problems, the power conversion device of the present invention is a power conversion device equipped with a transformer having an iron core with magnetic legs and a plurality of coils wound at different positions on the magnetic legs, wherein the transformer has a magnetic flux induction member made of a magnetic material shaped to cover the portions of the plurality of coils that are exposed on the outside of the iron core, and the magnetic flux induction member has a coil outer covering portion arranged on the outer periphery of the plurality of coils, an inter-coil covering portion that protrudes from the coil outer covering portion between the plurality of coils, and a pair of coil end surface covering portions that are connected to the coil outer covering portion and cover the portions of the plurality of coils opposite to those covered by the inter-coil covering portion.

[0013] According to the present invention, in a power conversion device equipped with a transformer, the designable range of leakage inductance can be widened, loss can be reduced, and miniaturization can be achieved.

[0014] A cross-sectional view of a transformer according to a first embodiment. A cross-sectional view of the AA' cross-sectional view of Figure 1. A circuit diagram of a power conversion device according to a first embodiment. A top view of a power conversion device according to a first embodiment. A cross-sectional view of a transformer according to a second embodiment. A circuit diagram of a power conversion device according to a second embodiment. A cross-sectional view of a conventional transformer.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing and each embodiment, the same or similar components are designated by the same reference numerals, and redundant explanations will be omitted.

[0016] Fig. 1 is a cross-sectional view of a transformer according to Example 1. Fig. 2 is a cross-sectional view taken along line AA' in Fig. 1.

[0017] The transformer 1 of this embodiment has an iron core 10 provided with magnetic legs 11 and a plurality of coils 20 wound around the magnetic legs 11 at different positions.

[0018] 2, the iron core 10 has a frame-shaped portion and magnetic legs 11 provided inside the frame-shaped portion. Note that the shape of the iron core 10 shown in this embodiment is an example and is not limited to this.

[0019] In this embodiment, the multiple coils 20 are configured, for example, by a first coil 20A that functions as a low-voltage coil and a second coil 20B that functions as a high-voltage coil. Here, an example is shown in which the copper wire that configures each coil 20 is sealed with an insulating material 25, but this is not limiting.

[0020] The coils 20 have portions disposed inside the iron core 10 as shown in FIG. 2 and portions exposed to the outside of the iron core 10 as shown in FIG.

[0021] 1 , the transformer 1 of this embodiment is configured to include a magnetic flux guide member 30 made of a magnetic material and shaped to cover the exposed portions of the plurality of coils 20 on the outside of the iron core 10. The magnetic flux guide member 30 includes a coil outer covering portion 30A arranged on the outer periphery of the plurality of coils 20, an inter-coil covering portion 30B protruding from the coil outer covering portion 30A between the plurality of coils 20, and a pair of coil end covering portions 30C connected to the coil outer covering portion 30A and covering the sides of the plurality of coils 20 opposite the portions covered by the inter-coil covering portion 30B. The pair of coil end covering portions 30C includes a first coil end covering portion 30C1 arranged on the upper side of FIG. 1 and a second coil end covering portion 30C2 arranged on the lower side of FIG. 1 .

[0022] Because the relative permeability of the magnetic material constituting the magnetic flux guide member 30 is much greater than that of air, leakage magnetic flux 31 generated by the multiple coils 20 is guided to flow inside the magnetic flux guide member 30. As a result, it is possible to prevent leakage magnetic flux 31 from spreading further outside from the magnetic flux guide member 30. This makes it possible to arrange electronic components such as switching elements 60 and capacitors 61 of a power conversion device 100 including a transformer 1 in close proximity to the transformer 1, as shown in FIG. 4 , which will be described later, and thus makes it possible to reduce the size of the power conversion device 100.

[0023] Furthermore, the magnetic flux guide member 30 can reduce the leakage magnetic flux 31 that links with the coil 20, thereby reducing in-plane eddy current loss that occurs when the leakage magnetic flux 31 links with the coil 20. Furthermore, the leakage magnetic flux 31 can be prevented from spreading further to the outside from the magnetic flux guide member 30, thereby reducing stray load loss that occurs in components around the transformer 1. Reducing these losses can reduce overall loss by, for example, about 20%.

[0024] Furthermore, the parameters for adjusting the magnitude of leakage inductance include not only the size of the gap between the first coil 20A and the second coil 20B (the distance between the coils), but also the relative permeability of the magnetic flux guide member 30, the dimensions of the magnetic flux guide member 30, and the shape of the magnetic flux guide member 30. This widens the designable range of leakage inductance compared to a case where only air is used without the magnetic flux guide member 30. In particular, the magnetic flux guide member 30 can widen the lower limit of the magnitude of leakage inductance. This makes it possible to adjust the voltage ratio by phase in the power conversion device 100. Note that while the inter-coil cover portion 30B contributes most significantly to the effect of widening the designable range of leakage inductance, the pair of coil end surface cover portions 30C also contribute to widening the designable range of leakage inductance.

[0025] Furthermore, when a GaN device is used as the switching element 60, the switching frequency rises to the MHz range, and a wider designable range of leakage inductance is required than before. However, according to this embodiment, it is also possible to accommodate switching frequencies of the MHz range.

[0026] By forming the magnetic flux guide member 30 from the same magnetic material as the iron core 10, it is possible to suppress an increase in the material cost of the transformer 1. Furthermore, by forming the magnetic flux guide member 30 from a magnetic material different from that of the iron core 10, it is possible to give the magnetic flux guide member 30 a relative permeability different from that of the iron core 10, thereby widening the designable range of leakage inductance.

[0027] 1, it is desirable that the magnetic flux guide member 30 faces the iron core 10 with a predetermined gap 32 therebetween. If the magnetic flux guide member 30 and the iron core 10 are in contact with each other, the magnetic flux generated in the iron core 10 flows into the magnetic flux guide member 30, causing a problem of a decrease in efficiency of, for example, about 20% compared to a case in which the magnetic flux guide member 30 is not present. Therefore, providing the gap 32 can prevent this.

[0028] Furthermore, in this embodiment, it is desirable that at least one of the pair of coil end surface covering portions 30C and a portion of the iron core 10 are connected to the housing 50 of the power conversion device 100 via a heat transfer member 40. While FIG. 1 illustrates an example in which the second coil end surface covering portion 30C2 is connected to the housing 50, this is not limiting. Alternatively, the first coil end surface covering portion 30C1 may be connected to the housing 50, or both the first coil end surface covering portion 30C1 and the second coil end surface covering portion 30C2 may be connected to the housing 50. The heat transfer member 40 may be, for example, grease or a heat transfer sheet. The housing 50 may be made of, for example, aluminum. The housing 50 is cooled, for example, by water cooling. With the configuration of this embodiment, heat generated in the coil 20 can be dissipated to the housing 50 via the magnetic flux guide member 30, thereby efficiently dissipating heat from the coil 20. While the transformer 1 can be made smaller as the operating frequency increases, there is a problem of increased heat generation in the coil 20. According to this embodiment, heat can be efficiently released through the magnetic flux guide member 30, making it possible to reduce the size.

[0029] FIG. 3 is a circuit diagram of the power conversion device of the first embodiment.

[0030] The power conversion device 100 of this embodiment is a DAB (Dual Active Bridge) converter having an input inverter circuit 70, an output converter circuit 71, a transformer 1, and a control circuit (not shown). The transformer 1 used here is the transformer 1 of this embodiment described with reference to Figures 1 and 2. Note that while the present invention is applied to a DAB (Dual Active Bridge) converter as an example, it is not limited to this, and can be applied to other types of power conversion devices 100 as long as they are equipped with a transformer 1.

[0031] The input inverter circuit 70 has a plurality of switching elements 60 that form a bridge circuit, and a capacitor 61. The switching elements 60 are controlled by a control circuit (not shown). The input inverter circuit 70 converts input DC power, for example, of 400 V or 800 V, into AC power and outputs it to the second coil 20B of the transformer 1.

[0032] The output converter circuit 71 has a plurality of switching elements 60 that form a bridge circuit, and a capacitor 61. The switching elements 60 are controlled by a control circuit (not shown). The output converter circuit 71 receives AC power transformed by the transformer 1 through the first coil 20A of the transformer 1, converts it into 12V DC power that can be used, for example, for the battery of an electric vehicle, and outputs it.

[0033] According to this embodiment, a GaN device is used as the switching element 60, and it is possible to adjust the voltage ratio by phase using a control circuit.

[0034] FIG. 4 is a top view of the power conversion device of the first embodiment.

[0035] In the power conversion device 100 of this embodiment, the magnetic flux induction member 30 can prevent the leakage magnetic flux 31 from spreading further outward from the magnetic flux induction member 30 of the transformer 1, so that electronic components such as the switching element 60, the capacitor 61, and a control circuit (not shown) can be arranged close to the transformer 1, thereby enabling miniaturization.

[0036] Electronic components such as the switching element 60, capacitor 61, and a control circuit (not shown) are mounted on a substrate (not shown). This substrate has an opening in a portion corresponding to the transformer 1, allowing the transformer 1 to come into contact with the housing 50.

[0037] As described above, according to this embodiment, the power conversion device 100 including the transformer 1 can have a wide design range for leakage inductance, low loss, and compact size by providing the magnetic flux guide member 30. Furthermore, heat from the coil 20 can be efficiently dissipated to the housing 50 via the magnetic flux guide member 30.

[0038] FIG. 5 is a cross-sectional view of a transformer according to a second embodiment.

[0039] The second embodiment is a modification of the first embodiment, and has three coils 20 .

[0040] The multiple coils 20 of this embodiment include a first coil 20A, a second coil 20B, and a third coil 20C. That is, in addition to the first coil 20A and the second coil 20B similar to those of the first embodiment, a third coil 20C that functions as, for example, another low-voltage coil with a different voltage is added.

[0041] Therefore, the inter-coil covering portion 30B in this embodiment has a first inter-coil covering portion 30B1 arranged between the first coil 20A and the second coil 20B, and a second inter-coil covering portion 30B2 arranged between the second coil 20B and the third coil 20C.

[0042] FIG. 6 is a circuit diagram of a power conversion device according to a second embodiment.

[0043] The power conversion device 100 of this embodiment includes an input inverter circuit 70, a first output converter circuit 71A, a second output converter circuit 71B, a transformer 1, and a control circuit (not shown). The first output converter circuit 71A is the same as the output converter circuit 71 of the first embodiment.

[0044] The second output converter circuit 71B has a plurality of switching elements 60 that form a bridge circuit, and a capacitor 61. The switching elements 60 are controlled by a control circuit (not shown). The second output converter circuit 71B receives AC power transformed by the transformer 1 through the third coil 20C of the transformer 1, converts it into DC power of approximately 100 V, and outputs the DC power to generate 100 V AC power that can be used, for example, in an electric vehicle. The output DC power of approximately 100 V is then converted into 100 V AC power by an inverter (not shown).

[0045] The other configurations are the same as those in the first embodiment, and therefore detailed description thereof will be omitted. In this embodiment, the same effects as those in the first embodiment can be obtained.

[0046] Similarly, the present invention may be applied to a configuration in which there are four or more coils 20. In this case, the number of inter-coil covering portions 30B may be increased in accordance with the number of spaces between the coils.

[0047] Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible within the scope of the technical concept of the present invention. In addition, some or all of the configurations described in each embodiment may be combined and applied.

[0048] 1: transformer, 10: iron core, 11: magnetic legs, 20: coil, 20A: first coil, 20B: second coil, 20C: third coil, 25: insulating material, 30: magnetic flux guide member, 30A: coil outer periphery coating portion, 30B: inter-coil coating portion, 30B1: first inter-coil coating portion, 30B2: second inter-coil coating portion, 30C: coil end surface coating portion, 30C1: first coil end surface coating portion, 30C2: second coil end surface coating portion, 31: leakage magnetic flux, 32: air gap, 40: heat transfer member, 50: housing, 60: switching element, 61: capacitor, 70: input inverter circuit, 71: output converter circuit, 71A: first output converter circuit, 71B: second output converter circuit, 100: power conversion device

Claims

1. A power conversion device equipped with a transformer having an iron core with magnetic legs and a plurality of coils wound around the magnetic legs at different positions, wherein the transformer has a magnetic flux guide member made of a magnetic material shaped to cover the portions of the plurality of coils that are exposed on the outside of the iron core, and the magnetic flux guide member has: a coil outer covering portion arranged on the outer periphery of the plurality of coils; an inter-coil covering portion that protrudes from the coil outer covering portion between the plurality of coils; and a pair of coil end surface covering portions connected to the coil outer covering portion and covering the portions of the plurality of coils opposite to those covered by the inter-coil covering portion.

2. The power conversion device according to claim 1, wherein the magnetic flux guide member faces the iron core with a predetermined gap therebetween.

3. A power conversion device according to claim 1, comprising a housing, wherein at least one of the pair of coil end surface covering portions and a part of the iron core are connected to the housing via a heat transfer member.

4. The power conversion device according to claim 1, wherein the magnetic flux guide member is made of the same magnetic material as the iron core.

5. The power conversion device according to claim 1, wherein the magnetic flux guide member is made of a magnetic material different from that of the iron core.

6. A power conversion device according to claim 1, wherein the plurality of coils include a first coil and a second coil, and the inter-coil covering portion is disposed between the first coil and the second coil.

7. A power conversion device according to claim 1, characterized in that the plurality of coils include a first coil, a second coil, and a third coil, and the inter-coil covering portion includes a first inter-coil covering portion disposed between the first coil and the second coil, and a second inter-coil covering portion disposed between the second coil and the third coil.

8. The power conversion device according to claim 1, comprising: a switching element; a capacitor; and a control circuit.

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