JP7591466B2 - Power conversion unit and power conversion device - Google Patents

Description

The present invention relates to a power conversion unit and a power conversion device.

In recent years, various efforts have been made to reduce the use of fossil fuels in order to reduce _CO2 emissions from the perspective of preventing global warming. For example, the power source of automobiles has been electrified, and hybrid automobiles and electric automobiles equipped with motors are becoming more popular. By electrifying engines that used fossil fuels, _CO2 emissions are reduced, and it is expected that this will contribute to the prevention of global warming.

Power conversion devices are widely used to control the rotational speed of motors. Power conversion devices are essential for improving the operating efficiency of motors in hybrid and electric vehicles, as well as other products. In general, power conversion devices are installed as auxiliary equipment to main equipment such as motors that use electricity and storage batteries that store electricity.

Currently, with the widespread use of motors, storage batteries, and other power sources, there is a demand for smaller and lighter power systems. In addition, motors, storage batteries, and other important components of power systems are required to have higher voltages and larger capacities. There is also a demand for smaller and lighter power conversion devices from the perspective of improving output density and reducing installation constraints. There is also a demand for performance that can handle high voltages and large capacities.

As motors, storage batteries, etc. become more widespread, these devices will inevitably be used in a variety of environments. As motors, storage batteries, etc. become more widespread, it is expected that the environments in which these devices, including auxiliary equipment, are used will also expand. For this reason, power conversion devices are required to be not only compact, lightweight, and capable of handling high voltages and large capacity, but also capable of handling a variety of usage environments.

For example, for every 100 m increase in altitude, the temperature drops by approximately 0.6°C. Condensation is more likely to occur at low temperatures, so when a power conversion device is used at high altitude, it is more likely to cause short circuits, deterioration or damage to circuit elements, and deterioration or alteration of materials. Furthermore, at high altitudes, not only the temperature but also the air pressure is lower, so power conversion devices are required to have different performance than when used at low altitudes. It is known that in low-pressure environments, aerial discharges are more likely to occur according to Paschen's law.

As main engines become higher voltage and larger capacity, there is a demand for highly reliable power conversion devices designed to maintain the desired operation for long periods of time, even in environments prone to low-temperature degradation, thermal degradation, mechanical destruction due to thermal stress, short circuits, and insulation breakdown. If the device is designed to be resistant to temperatures and air pressures that deviate from normal temperature and pressure, as well as temperature and air pressure changes, it will be possible to use devices with the same specifications in a variety of environments, which is expected to improve the mass production and cost efficiency of the devices.

Patent Document 1 describes technology related to miniaturizing power conversion devices. It also describes typical resin materials used for the housings and printed circuit boards of power conversion devices.

JP 2020-178406 A

Currently, power conversion devices are required to be compact, lightweight, and capable of handling high voltages and large capacity. They are also required to have high resistance to temperatures and pressures that deviate from normal temperature and pressure, as well as temperature and pressure changes. It is important to maintain electrical insulation for a long period of time even in operating environments where air pressure drops and condensation are likely to occur, and high insulation reliability is required.

In general, a power conversion device incorporates within its housing a circuit board on which circuit elements are mounted, a heat dissipation mechanism that dissipates heat from the circuit elements to the outside, and other components. The heat dissipation mechanism includes a heat dissipation member made of a material with high thermal conductivity, and a heat exchange mechanism that circulates a refrigerant, which form a heat transfer path from the inside of the housing to the outside. The space inside the housing is filled with an electrically insulating sealing resin (molding resin) to electrically insulate the circuit elements, circuit board, heat dissipation mechanism, and other components.

If the sealing resin contains low molecular weight components such as air and moisture, these components will expand and evaporate when the power conversion device is placed in a low-pressure environment, causing voids in the sealing resin and expanding the gaps between the sealing resin and other components. In addition, if the power conversion device is placed in a low-temperature environment, moisture is likely to condense, making it easy for the moisture to concentrate locally in the space inside the housing.

If voids occur in the sealing resin or if the sealing resin peels off from the circuit board or the like to create gaps, when a large voltage is applied, an electric field will concentrate in the voids or gaps, making it easier for discharges to occur in the gaps, resulting in a problem of reduced electrical insulation provided by the sealing resin. In particular, when a power conversion device is used in a low-pressure environment, air discharges are more likely to occur in accordance with Paschen's law, and there is a risk of a significant decrease in electrical insulation.

As a sealing resin, a thermosetting resin potting material that shows fluidity in an uncured state is widely used. Normally, a material that shows low viscosity in an uncured state is selected as the potting material to suppress voids and gaps. In addition, when filling the space inside the housing, degassed potting material is filled under reduced pressure conditions to prevent the formation of voids and gaps.

However, even when such a filling method is used, it is difficult to completely remove low molecular weight components such as air and moisture contained in the sealing resin. Furthermore, resin materials are sometimes used for housings and circuit boards because they are lightweight and easy to process. The resin material may contain low molecular weight components such as air and moisture. When the power conversion device is used in a low pressure environment, the low molecular weight components contained in the resin material may migrate to the sealing resin side due to the pressure difference.

The technology described in Patent Document 1 improves the heat dissipation structure in order to cool the heat-generating components built into the device. However, although the device described in Patent Document 1 improves heat dissipation from the inside to the outside, it does not take measures to ensure insulation reliability when used in a low-pressure environment.

The present invention aims to provide a power conversion unit that has high operational reliability even at temperatures and pressures that deviate from normal temperature and pressure, suppresses voids in the sealing resin and gaps on the surface of the sealing resin, and maintains high electrical insulation performance, and a power conversion device equipped with the same.

To solve the above problems, the power conversion unit of the present invention comprises a housing, a heat sink disposed in the space inside the housing, a circuit board thermally connected to the heat sink, a switching element provided on the circuit board, and a sealing resin filled in the space inside the housing, and has a gas barrier material between the circuit board and the sealing resin.

The power conversion device according to the present invention also includes the power conversion unit and a frame that is connected to the power conversion unit and is electrically grounded.

The present invention provides a power conversion unit that has high operational reliability even at temperatures and pressures that deviate from normal temperature and pressure, suppresses voids in the sealing resin and gaps on the surface of the sealing resin, and maintains high electrical insulation performance, and a power conversion device equipped with the same.

1 is a perspective view of a power conversion unit according to a first embodiment of the present invention; 1 is a cross-sectional view of a power conversion unit according to a first embodiment of the present invention. 1A and 1B are diagrams illustrating a structure of a heat transfer path for dissipating heat from a switching element. FIG. 6 is a cross-sectional view of a power conversion unit according to a second embodiment of the present invention. FIG. 11 is a cross-sectional view showing a state in which a power conversion unit according to a second embodiment of the present invention is divided. FIG. 11 is a cross-sectional view of a power conversion unit according to a third embodiment of the present invention. FIG. 11 is a cross-sectional view of a power conversion unit according to a fourth embodiment of the present invention. FIG. 11 is a cross-sectional view of a power conversion unit according to a fifth embodiment of the present invention. 13 shows an example of a circuit of a power conversion unit according to a sixth embodiment of the present invention. FIG. 13 is a perspective view of a power conversion unit according to a seventh embodiment of the present invention. FIG. 13 is a cross-sectional view of a power conversion unit according to a seventh embodiment of the present invention.

The following describes a power conversion unit according to one embodiment of the present invention, and a power conversion device including the same, with reference to the drawings. Note that in the following drawings, common configurations are given the same reference numerals and duplicated descriptions are omitted.

<<Embodiment 1>>
Fig. 1A is a perspective view of a power conversion unit according to a first embodiment of the present invention. Fig. 1B is a cross-sectional view of the power conversion unit according to the first embodiment of the present invention. Fig. 1B corresponds to a cross-sectional view taken along line II in Fig. 1A.
As shown in Figures 1A and 1B, the power conversion unit U of this embodiment is composed of an input side unit (input side power conversion section) 14 on the input side and an output side unit (output side power conversion section) 15 on the output side.

The power conversion unit U includes a switching element 1 (see FIG. 1B), a circuit board 2, a resonant capacitor 3 (see FIG. 8), a smoothing capacitor 4 (see FIG. 8), housings 5a and 5b, housing lids 6a and 6b, an upper electrode plate 7, a lower electrode plate 8, a sealing resin 9, an O-ring 10, a cooling path 11, a heat sink 12, etc.

The power conversion unit U is provided with gas barrier materials (materials with gas barrier properties) 20a, 20b between the sealing resin 9 and other components to prevent voids in the sealing resin 9 caused by low molecular weight components such as air and moisture, and gaps on the surface of the sealing resin 9 caused by peeling of the sealing resin 9 due to these components.

As shown in Figures 1A and 1B, the input side unit 14 includes an input side housing 5a and an input side housing cover 6a that closes the housing 5a. The output side unit 15 includes an output side housing 5b and an input side housing cover 6b that closes the housing 5b. The input side housing 5a and the output side housing 5b each have an opening on one side. The input side and output side housing covers 6a, 6b are screwed in place so as to cover the openings and can be opened and closed freely.

The input side housing 5a and housing cover 6a, and the output side housing 5b and housing cover 6b form the outer shell of the power conversion unit U. The power conversion unit U is provided in a mating structure of the input side unit 14 and the output side unit 15, with the housing covers 6a, 6b butted together on both outsides and joined together with bolts n1.

As shown in FIG. 1B, a circuit board 2 is housed inside the input side housing 5a and the output side housing 5b. Circuit elements such as a plurality of switching elements 1, a resonant capacitor 3 (see FIG. 8), and a smoothing capacitor 4 (see FIG. 8) are mounted on the circuit board 2. The input side unit 14 and the output side unit 15 are composed of similar circuit components, components related to heat dissipation of the circuit, etc.

Circuit elements such as the switching element 1 become heat-generating components that generate Joule heat due to their own resistance while the unit is in operation. Heat generation in the circuit causes thermal degradation and thermal stress in the circuit elements and materials, leading to malfunctions and deterioration over time. Therefore, the heat generated by the heat-generating components is dissipated to the cooling path 11 provided between the input unit 14 and the output unit 15.

The switching element 1 is electrically connected to the circuit board 2 via bonding wires and leads. The switching element 1 is disposed inside the circuit board 2 inside the housings 5a and 5b. The surface of the switching element 1 opposite the circuit board 2 is in contact with the upper electrode plate 7. The terminal of the switching element 1 is electrically connected to the upper electrode plate 7.

The upper electrode plate 7 forms a circuit together with the switching element 1. The surface of the upper electrode plate 7 opposite the switching element 1 is in contact with the heat sink 12. The surface of the heat sink 12 opposite the upper electrode plate 7 is in contact with the lower electrode plate 8. The upper electrode plate 7 and the lower electrode plate 8 are formed of an electrically conductive material with high thermal conductivity. The heat sink 12 is formed of an electrically insulating material with high thermal conductivity. The lower electrode plate 8 can be at ground potential.

The upper electrode plate 7 and the heat sink 12 are provided for each of the multiple switching elements 1. The upper electrode plate 7 and the heat sink 12 are arranged so as to penetrate the surface of the housings 5a and 5b opposite the housing lids 6a and 6b. The lower electrode plate 8 is arranged in a recess provided on the surface of the housings 5a and 5b opposite the housing lids 6a and 6b. The lower electrode plate 8 is in contact with the heat sink 12 provided for each switching element 1.

The switching element 1 and the upper electrode plate 7 are stacked on top of each other and thermally connected. The upper electrode plate 7 and the heat sink 12 are stacked on top of each other and thermally connected. The heat sink 12 and the lower electrode plate 8 are stacked on top of each other and thermally connected. These components form a heat transfer path that dissipates heat from the heat-generating component toward the cooling path 11.

The heat sink 12 is molded integrally with the housings 5a and 5b. Integral molding makes it easier to manufacture the heat sink 12 and the housings 5a and 5b, and shortens the manufacturing process of the power conversion unit U. However, the heat sink 12 may be provided separately from the housings 5a and 5b.

The housings 5a, 5b and the housing lids 6a, 6b can be made of an appropriate material. Examples of materials that can be used for the housings 5a, 5b and the housing lids 6a, 6b include glass fiber reinforced polyphenylene sulfide (PPS), ABS resin, polyamide, epoxy resin, unsaturated polyester resin, etc.

The linear expansion coefficient of the materials of the housings 5a, 5b and the housing lids 6a, 6b is preferably close to that of the upper electrode plate 7, the lower electrode plate 8, and the heat sink 12 in order to prevent peeling or cracking from adjacent components.

The heat sink 12 can be made of any suitable material as long as it is electrically insulating and has high thermal conductivity. Materials that can be used for the heat sink 12 include inorganic substances such as aluminum oxide, aluminum nitride, and silicon nitride, and resin materials with high thermal conductivity. Examples of resin materials with high thermal conductivity include epoxy resins to which fillers with high thermal conductivity such as aluminum oxide and aluminum nitride have been added.

In the power conversion unit U, the power conversion section with power conversion function is divided into an input side unit 14 and an output side unit 15. The input side unit 14 and the output side unit 15 are arranged opposite each other with the cooling path 11 in between. This structure makes it easier to ensure electrical insulation between the input side unit 14 and the output side unit 15, and heat dissipation from each unit to the cooling path 11.

The lower electrode plate 8 of the input unit 14 and the lower electrode plate 8 of the output unit 15 each form the wall of the cooling path 11. A cooling medium is passed through the cooling path 11 to remove heat from the heat-generating components.

The cooling path 11 is formed between the input side unit 14 and the output side unit 15, and is composed of the input side cooling path 11a and the output side cooling path 11b. The input side cooling path 11a is provided so as to contact the surface of the input side housing 5a opposite the housing lid 6a. The output side cooling path 11b is provided so as to contact the surface of the output side housing 5b opposite the housing lid 6b.

An O-ring 10 is attached to the joint surface between the input unit 14 and the output unit 15. The provision of the O-ring 10 helps prevent leakage of the cooling medium from the cooling path 11.

In FIG. 1B and other figures, the lower electrode plate 8 is in contact with the cooling path 11, but it may be provided so as to be in close proximity to the cooling path 11 without contacting it. For example, instead of the lower electrode plate 8, another material with high thermal conductivity can be used as a material forming the wall of the cooling path 11. Such a material can be disposed between the lower electrode plate 8 and the cooling path 11 to form a heat transfer path.

Fig. 2 is a diagram showing the structure of a heat transfer path for dissipating heat from a switching element, and corresponds to a view taken along line II in Fig. 1B.
2 , the upper electrode plate 7 is provided to be wider than the switching element 1. The switching element 1 is disposed toward the center of the upper electrode plate 7. In addition, the heat sink 12 is provided to be wider than the upper electrode plate 7. The upper electrode plate 7 is disposed toward the center of the heat sink 12. In addition, the lower electrode plate 8 is provided to be wider than the heat sink 12.

When configured in this manner, heat from the switching element 1 is transferred to successively larger components. The heat transfer area expands from the switching element 1 toward the lower electrode plate 8, improving heat dissipation from the switching element 1. In addition, the creepage distance between the upper electrode plate 7 and the lower electrode plate 8 is increased, ensuring electrical insulation between the electrodes. The heat sink 12, which is wider than the upper electrode plate 7, allows for both insulation between the upper electrode plate 7 and the lower electrode plate 8 and heat dissipation.

As shown in FIG. 1B, a space p is provided inside the housing 5a of the input unit 14 and inside the housing 5b of the output unit 15. The space p inside the housings 5a and 5b accommodates components of the circuit, components related to heat dissipation of the circuit, etc. The other areas of the space p are filled with sealing resin 9.

The sealing resin 9 acts to ensure electrical insulation and protect the circuit elements, etc. The sealing resin 9 electrically insulates between the circuit board 2 and the housings 5a and 5b, between the circuit board 2 and the housing covers 6a and 6b, between the conductors of the circuit board 2, and around the circuit elements. It also protects the circuit elements, wiring, etc. from external forces applied from outside the housings 5a and 5b, and from moisture, dust, etc. that can cause insulation breakdown due to tracking and material deterioration.

As the sealing resin 9, a silicone-based resin that has fluidity in an uncured state and does not have fluidity after curing is preferred in terms of electrical stability, flexibility, heat resistance, moisture resistance, moldability, etc. Examples of silicone-based resins include organopolysiloxane. As the sealing resin 9, for example, a silicone gel or a silicone elastomer can be used.

Circuit elements such as the switching element 1 and bonding wires that electrically connect the circuit elements may be sealed with a sealing material different from the sealing resin 9. For example, it is preferable to seal the bonding wires with epoxy resin or the like. In a structure in which the bonding wires are exposed, using a sealing material with a low elastic modulus and high flexibility can prevent the wires from being damaged.

When the circuit elements are electrically connected using leads that are stronger than bonding wires, it is preferable to use a silicone elastomer with a higher elastic modulus than silicone gel as the sealing resin 9, since there is no need to consider damage due to stress. By using a silicone elastomer with high adhesiveness, voids due to gas expansion are less likely to occur even in low-pressure or low-temperature environments, and peeling is also less likely to occur, making partial discharge less likely to occur.

On the other hand, silicone gel is prone to voids due to gas expansion in low pressure environments. It is also prone to condensation accumulation in low temperature environments. However, in the power conversion unit U, silicone gel can also be used because the gas barrier materials 20a, 20b block oxygen and water vapor. When silicone gel is used as the sealing resin 9, a low elastic modulus can be obtained, which can greatly reduce the stress applied to circuit elements such as the switching element 1, the circuit board 2, the bonding wires themselves, and their joints. Furthermore, when silicone gel is used, a sealing resin 9 with high flexibility and adhesion can be obtained.

As shown in FIG. 1B, gas barrier materials (materials with gas barrier properties) 20a and 20b are provided around the sealing resin 9. The gas barrier materials 20a and 20b are provided as films, thin films, etc., using resin materials with low gas permeability to oxygen, water vapor, etc. In FIG. 1B, the input side unit 14 is provided with an input side gas barrier material 20a. The output side unit 15 is provided with an output side gas barrier material 20b.

The gas barrier materials 20a, 20b can be interposed between the circuit board 2 and the sealing resin 9, between the housings 5a, 5b and the sealing resin 9, or between the housing lids 6a, 6b and the sealing resin 9. In other words, they can be arranged in close contact with each other so as to be located at the interface between the circuit board 2 and the sealing resin 9, the interface between the housings 5a, 5b and the sealing resin 9, or the interface between the housing lids 6a, 6b and the sealing resin 9.

The sealing resin 9 may contain low molecular weight components such as air and moisture. Low molecular weight components expand and evaporate in a low pressure environment. Therefore, if these components are contained in the sealing resin 9, voids may occur in the sealing resin 9 when the unit is placed in a low pressure environment. In addition, the gap between the sealing resin and other components may be enlarged, causing the sealing resin 9 to peel off from the surfaces of the other components. When the sealing resin peels off, a large gap occurs between the sealing resin 9 and the other components.

Furthermore, if the unit is placed in a low-temperature environment, moisture condenses and tends to concentrate locally in the space inside the housings 5a and 5b. If the moisture migrates to the periphery of the circuit board 2 or to circuit elements such as the switching element 1, insulation breakdown due to tracking becomes more likely to occur. Furthermore, if the concentrated moisture evaporates, voids and gaps are more likely to occur if the unit is placed in a low-pressure environment.

If voids or gaps occur in the sealing resin 9, when a large voltage is applied, an electric field will concentrate in the voids or gaps, making it easier for discharges to occur within these gaps. In particular, if the unit is placed in a low-pressure environment, air discharges are more likely to occur in accordance with Paschen's law, making it easier for insulation breakdown to occur inside and around the sealing resin 9. This reduces the electrical insulation provided by the sealing resin 9, which creates the problem of compromising the insulation reliability required over the long term.

It is possible to remove low molecular weight components such as air and moisture from the sealing resin 9 beforehand by degassing it while it is uncured. The sealing resin 9 can also be filled into the interior of the housings 5a and 5b under reduced pressure conditions to prevent the intrusion of air, moisture, and the like. However, even if the sealing resin 9 is degassed or filled under reduced pressure conditions, it is not easy to completely remove the low molecular weight components contained in the sealing resin 9. These components may concentrate locally in the space inside the housings 5a and 5b and cause problems.

In addition, when a resin material is used for the housings 5a, 5b or the circuit board 2, the resin material may contain low molecular weight components such as air and moisture. If these components are contained in the sealing resin 9, they may diffuse due to the pressure difference and migrate into the sealing resin 9 when the unit is placed in a low pressure environment. The low molecular weight components such as air and moisture that migrate into the sealing resin 9 create voids and gaps in the sealing resin 9, reducing the electrical insulation provided by the sealing resin 9.

In contrast, if gas barrier materials 20a, 20b are provided between the circuit board 2 and the sealing resin 9, between the housings 5a, 5b and the sealing resin 9, or between the housing lids 6a, 6b and the sealing resin 9, it is possible to prevent gases such as oxygen and water vapor contained in the housings 5a, 5b and the circuit board 2 from migrating to the sealing resin 9 side. In addition, regardless of the degassing of the sealing resin 9 or the filling conditions of the sealing resin 9, it is possible to prevent condensation of moisture contained in the sealing resin 9 or moisture that has infiltrated from the outside of the housings 5a, 5b into the inside. It is possible to prevent condensation from concentrating locally in the space inside the housings 5a, 5b.

Therefore, when the unit is placed in a low-pressure or low-temperature environment, the formation of voids or gaps in the sealing resin 9 can be suppressed. Voids in the sealing resin 9 and peeling of the sealing resin 9 are suppressed, making it difficult for dielectric breakdown to occur inside or around the sealing resin 9. Since the high electrical insulation performance of the sealing resin 9 is maintained for a long period of time, a unit with high insulation reliability is obtained. Furthermore, even at temperatures and pressures that deviate from normal temperature and pressure, failure due to dielectric breakdown is unlikely to occur, and a unit with high operational reliability is obtained.

The gas barrier materials 20a, 20b can be placed on the surface of the circuit board 2, the inner surfaces of the housings 5a, 5b, or the inner surfaces of the housing lids 6a, 6b by adhering, pressing, or the like, before filling the inside of the housings 5a, 5b with the sealing resin 9.

The gas barrier materials 20a and 20b may be a film or thin film with a single layer structure, or a film or thin film with a laminated structure. As the gas barrier materials 20a and 20b, any of materials having both oxygen barrier properties and water vapor barrier properties, and a combination of a material having oxygen barrier properties and a material having water vapor barrier properties can be used.

Examples of materials that have both oxygen barrier properties and water vapor barrier properties include materials that have an oxygen gas permeability coefficient of 0.001× ^{10-10 cm3} (STP)cm/( ^cm2 ·s·cmHg) or less and a water vapor gas permeability coefficient of 300× ^{10-10 cm3} (STP)cm/( ^cm2 ·s·cmHg) or less at 25° C. When such materials are used, the material itself has high oxygen barrier properties and water vapor barrier properties, so that the diffusion of gases such as oxygen and water vapor can be efficiently suppressed with a thin layer.

Specific examples of such materials include ethylene-vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylidene chloride (PVDC), MXD nylon, and modified products thereof. MXD nylon is a polyamide obtained by condensing meta-xylylenediamine (MXD), and examples of such materials include polyamide MXD-6, which is a condensate with adipic acid, and condensates and modified products with other aliphatic polycarboxylic acids, aromatic polycarboxylic acids, and the like.

An example of a combination of a material with oxygen barrier properties and a material with water vapor barrier properties is a laminate of a material having an oxygen gas permeability coefficient of 0.001×10 ⁻¹⁰ cm ³ (STP) cm/(cm ² s cmHg) or less at 25° C. and a material having a water vapor gas permeability coefficient of 300×10 ⁻¹⁰ cm ³ (STP) cm/(cm ² s cmHg) or less at 25° C. Use of such materials allows greater freedom in the layer structure and thickness of each layer.

Specific examples of materials with an oxygen gas permeability coefficient of 0.001× ^{10-10 cm3} (STP)cm/( ^cm2 ·s·cmHg) or less include ethylene-vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylidene chloride (PVDC), MXD nylon, and modified products containing these monomers.

Specific examples of materials having a water vapor gas permeability coefficient of 300× ^{10-10 cm3} (STP)cm/( ^cm2 ·s·cmHg) or less include materials having the above-mentioned oxygen barrier properties, polyethylenes (PE) such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), polyolefins such as polypropylene (PP), polyesters (PEs) such as polyethylene terephthalate (PET), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), polyamides (PA) such as nylon 6 (PA6) and nylon 66 (PA66), polyvinyl chloride (PVC), and modified products containing these monomers.

The thickness of the gas barrier materials 20a, 20b is not particularly limited, but for materials with oxygen barrier properties or water vapor barrier properties, the thickness can be set to, for example, 300 μm or more and 600 μm or less.

The gas barrier materials 20a and 20b may be multi-layered with a base material, a protective layer exhibiting other functionality such as strength, rigidity, scratch resistance, pinhole resistance, heat resistance, water resistance, moisture resistance, oil resistance, and chemical resistance, a gas barrier layer of a metal or inorganic material, and an adhesive layer for bonding materials together, in addition to a resin material having oxygen barrier properties and water vapor barrier properties. As a method for multi-layering, an appropriate method such as a lamination method, a co-extrusion method, or a physical or chemical film formation method can be used depending on the material.

The layer structure of the gas barrier materials 20a, 20b is not particularly limited, but examples include gas barrier layer (oxygen/water vapor), gas barrier layer (oxygen)/gas barrier layer (water vapor), substrate (protective layer)/gas barrier layer (oxygen/water vapor), substrate (protective layer)/gas barrier layer (oxygen)/gas barrier layer (water vapor), substrate (protective layer)/gas barrier layer (oxygen/water vapor)/substrate (protective layer), substrate (protective layer)/gas barrier layer (oxygen)/gas barrier layer (water vapor)/substrate (protective layer), substrate (protective layer)/adhesive layer/gas barrier layer (oxygen/water vapor)/adhesive layer/substrate (protective layer), etc.

As the substrate, biaxially oriented materials having the water vapor barrier properties described above can be used, for example, polyolefins such as polyethylene (PE), polypropylene (PP), and copolymers of these, polyesters (PEs) such as polyethylene terephthalate (PET), and polyamides (PA) such as nylon 6 (PA6) and nylon 66 (PA66).

In FIG. 1B, the gas barrier materials 20a and 20b are interposed only on the side of the circuit board 2 facing the switching element 1 between the circuit board 2 and the sealing resin 9. This arrangement ensures electrical insulation for the circuit elements to which a large voltage is likely to be applied, and makes it possible to omit the need to interpose the material on the opposite side, which can be insulated only by the sealing resin 9. However, the gas barrier materials 20a and 20b may be interposed on the opposite side of the circuit board 2 facing the switching element 1, in addition to the side of the circuit board 2 facing the switching element 1.

In FIG. 1B, gas barrier materials 20a and 20b are respectively interposed between the circuit board 2 and the sealing resin 9, between the housings 5a and 5b and the sealing resin 9, and between the housing lids 6a and 6b and the sealing resin 9. However, as long as gas barrier materials 20a and 20b are provided at least between the circuit board 2 and the sealing resin 9, they do not have to be provided between the housings 5a and 5b and the sealing resin 9 or between the housing lids 6a and 6b and the sealing resin 9. This is because a large voltage is unlikely to be applied between these spaces, and electrical insulation can easily be ensured by the sealing resin 9 alone.

<<Embodiment 2>>
Fig. 3 is a cross-sectional view of a power conversion unit according to a second embodiment of the present invention. Fig. 3 corresponds to the cross-sectional view taken along line II in Fig. 1A.
As shown in Fig. 3, the space p inside the housings 5a, 5b can be provided with an unfilled portion 13 that is not filled with the sealing resin 9. Fig. 3 shows a power conversion unit U1 in which the unfilled portion 13 is provided in the space p inside the housings 5a, 5b. Other configurations of the power conversion unit U1 are substantially similar to those of the power conversion unit U described above.

Air may be present in the unfilled portion 13, but it is preferable that airtightness is ensured from the outside of the housings 5a and 5b. The unfilled portion 13 is preferably formed on the housing lid 6a, 6b side rather than the circuit board 2. In other words, when forming the unfilled portion 13, it is preferable that the surface of the circuit board 2 facing the housing lid 6a, 6b is covered with the sealing resin 9.

The unfilled portion 13 can be formed by filling the space p inside the housings 5a, 5b with uncured sealing resin 9 up to the middle height. The uncured sealing resin 9 is filled into the space p inside the housings 5a, 5b on the bottom side where the circuit board 2 is located. The uncured sealing resin 9 is filled to a height where the circuit board 2 is buried and a cavity remains on the housing lids 6a, 6b side, and then cured.

By providing the unfilled portion 13, heat generated by heat-generating components such as the switching element 1 is transferred to the sealing resin 9, and even if the sealing resin 9 thermally expands, a portion of the sealing resin 9 can escape to the unfilled portion 13. This can prevent the expanded sealing resin 9 from pressing the inner surfaces of the housings 5a and 5b, the inner surfaces of the housing lids 6a and 6b, and the circuit board 2, thereby preventing deformation, damage, and disconnection of the housings 5a and 5b, the housing lids 6a and 6b, the circuit board 2, etc.

In FIG. 3, the gas barrier materials 20a and 20b are interposed between the circuit board 2 and the sealing resin 9, and between the housings 5a and 5b and the sealing resin 9. The gas barrier materials 20a and 20b are not interposed in the unfilled portion 13. In the unfilled portion 13, the sealing resin 9 does not peel off, and a large voltage is not easily applied, so the gas barrier materials 20a and 20b can be omitted.

FIG. 4 is a cross-sectional view showing a state in which the power conversion unit according to the second embodiment of the present invention is divided.
As shown in Fig. 4, the input side unit 14 and the output side unit 15 can be provided in a freely separable structure. The input side unit 14 and the output side unit 15 can be freely separated by removing the bolt n1 (see Fig. 1A) even before the power conversion unit U1 is installed or after it is in operation. The power conversion unit U shown in Figs. 1A and 1B can also be provided in a similar structure.

By providing the input side unit 14 and the output side unit 15 with a structure that can be freely separated, it is possible to perform insulation tests on each unit even after the power conversion unit U1 has been assembled, such as after operation has been terminated. Only units that have been confirmed to have poor insulation can be replaced, reducing costs and waste.

<<Embodiment 3>>
Fig. 5 is a cross-sectional view of a power conversion unit according to a third embodiment of the present invention. Fig. 5 corresponds to the cross-sectional view taken along line II in Fig. 1A.
As shown in Fig. 5, a moisture absorbent 16 that absorbs moisture can be placed in the unfilled portion 13 that is not filled with the sealing resin 9. Fig. 5 shows a power conversion unit U2 in which a moisture absorbent 16 is placed in the unfilled portion 13. Other configurations of the power conversion unit U2 are substantially similar to those of the power conversion unit U1 described above.

The moisture absorbent 16 may be silica gel, zeolite, calcium oxide, or the like. The moisture absorbent 16 is stored in a storage section 16b provided in the internal space of the housings 5a and 5b. The storage section 16b is disposed in the unfilled section 13 and is located in the same space as the sealing resin 9. The storage section 16b may be provided as a breathable package, container, or the like to store the moisture absorbent 16 in particulate, powder, or other form.

By disposing the moisture absorbent 16 in the unfilled portion 13, it is possible to absorb and remove moisture from the space filled with the sealing resin 9. This can prevent the moisture in the unfilled portion 13 from migrating into the sealing resin 9, and therefore prevent the sealing resin 9 from creating voids or gaps when the unit is placed in a low-pressure or low-temperature environment. Even without placing gas barrier materials 20a, 20b on the side of the circuit board 2 opposite the switching element 1, the effects of moisture can be greatly reduced.

<<Embodiment 4>>
Fig. 6 is a cross-sectional view of a power conversion unit according to a fourth embodiment of the present invention. Fig. 6 corresponds to the cross-sectional view taken along line II in Fig. 1A.
As shown in Fig. 6, the joint surfaces between the housings 5a, 5b and the housing covers 6a, 6b may be provided with O-rings 17. Fig. 6 shows a power conversion unit U3 equipped with the O-ring 17. Other configurations of the power conversion unit U3 are substantially similar to those of the power conversion unit U2.

By providing the O-ring 17, the airtightness in the gap between the housings 5a, 5b and the housing lids 6a, 6b is improved, so that the intrusion of air, moisture, etc. from the outside to the inside of the housings 5a, 5b can be suppressed. Even if the housing lids 6a, 6b are configured to be freely opened and closed, rapid moisture absorption by the moisture absorbent 16 and sealing resin 9 can be prevented when the housing lids 6a, 6b are closed. Therefore, the occurrence of voids and gaps in the sealing resin 9 can be suppressed for a long period of time.

<<Embodiment 5>>
Fig. 7 is a cross-sectional view of a power conversion unit according to a fifth embodiment of the present invention. Fig. 7 corresponds to the cross-sectional view taken along line II in Fig. 1A.
7, an in-board frame 18 can be disposed outside the power conversion unit U1. The power conversion unit U1 and the in-board frame 18 electrically connected to the power conversion unit U1 constitute a power conversion device S.

The internal frame 18 is disposed outside the input unit 14 and outside the output unit 15. The internal frame 18 is provided as a plate-shaped member or the like, and is electrically grounded. The internal frame 18 is formed from a material with high electrical conductivity, and can be electrically connected to the lower electrode plate 8. Providing the internal frame 18 can prevent electric shock when touching the power conversion unit U1.

In FIG. 7, a single power conversion unit U1 is connected to the in-panel frame 18, but multiple power conversion units U1 may be connected. Multiple in-panel frames 18 can be assembled in a row or grid to connect multiple power conversion units U1. The in-panel frame 18 can be provided in a structure that houses or supports the power conversion units U1.

The power conversion device S can include multiple power conversion units U1 and an in-panel frame 18 that houses and supports the power conversion units U1. The power conversion device S can be configured such that the multiple power conversion units U1 are electrically connected to each other in series or parallel. With such a power conversion device S, when connected to a main device such as a motor or storage battery that has a high voltage or large capacity, it is easy to achieve performance that can handle high voltages and large capacity.

Although FIG. 7 shows a power conversion device S including a power conversion unit U1, a similar power conversion device S can be configured for the power conversion unit U shown in FIG. 1A and FIG. 1B, the power conversion unit U2 shown in FIG. 5, and the power conversion unit U3 shown in FIG. 6. In each unit constituting the power conversion device S, the gas barrier materials 20a, 20b do not have to be provided between the housings 5a, 5b and the sealing resin 9 or between the housing lids 6a, 6b and the sealing resin 9, as long as they are provided at least between the circuit board 2 and the sealing resin 9.

<<Embodiment 6>>
FIG. 8 shows an example of a circuit of a power conversion unit according to a sixth embodiment of the present invention.
8, a power conversion circuit C consisting of an input circuit Ua and an output circuit Cb can be built into the input unit 14 and the output unit 15. The input circuit Ca and the output circuit Cb are electromagnetically coupled via a high-frequency transformer 19.

The power conversion units U, U1, U2, and U3 can have the function of performing AC/DC conversion. The input circuit Ca, the output circuit Cb, and the high-frequency transformer 19 form an AC-DC converter and a resonant DC-DC converter. The high-frequency transformer 19 can be housed in the space inside the housings 5a and 5b.

The input circuit Ca includes a first bridge circuit section 1a, a second bridge circuit section 1b, a resonant capacitor 3, a smoothing capacitor 4, and a primary coil of a high-frequency transformer 19. The output circuit Cb includes a third bridge circuit section 1c, a smoothing capacitor 4, and a secondary coil of a high-frequency transformer 19.

Each of the bridge circuit sections 1a, 1b, and 1c is formed as a full-bridge type circuit by a switching element 1 and a freewheeling diode connected in anti-parallel. As the switching element 1, a semiconductor element such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), GaN, Si, or SiC can be used.

The first bridge circuit section 1a is electrically connected between the positive and negative terminals on the input side of the input circuit Ca. A smoothing capacitor 4 is connected in parallel to the first bridge circuit section 1a. The second bridge circuit section 1b is connected in parallel to the smoothing capacitor 4 of the input circuit Ca. A resonant circuit is connected in parallel to the midpoint of the second bridge circuit section 1b.

The resonant circuit includes a primary coil of a high-frequency transformer 19 and a resonant capacitor 3. The primary coil of the high-frequency transformer 19 is electrically connected between the positive and negative terminals of the input circuit Ca. The secondary coil of the high-frequency transformer 19 is electrically connected between the positive and negative terminals of the output circuit Cb.

The midpoint of the third bridge circuit section 1c is connected in parallel to the secondary coil of the high-frequency transformer 19. A smoothing capacitor 4 is connected in parallel to the third bridge circuit section 1c. The smoothing capacitor 4 of the output side circuit Cb is electrically connected between the positive and negative terminals on the output side of the output side circuit Cb.

The first bridge circuit section 1a receives AC current from a power source. The input AC current is full-wave rectified and converted to DC current. In the second bridge circuit section 1b, the DC current is converted to AC current such as a square wave. The high-frequency transformer 19 converts the AC current to a high frequency. The resonant capacitor 3 reduces the current and voltage during switching through resonance, thereby reducing switching losses. In the third bridge circuit section 1c, the AC current is converted to DC current.

According to the circuit shown in FIG. 8, the resonant DC-DC converter reduces switching losses, so even when the frequency is high, AC/DC conversion can be performed while suppressing power loss. In addition, because conversion to high frequencies can be performed while suppressing power loss, there is no need to use a large core for the high-frequency transformer 19, making it possible to miniaturize the transformer. This allows the unit to be made smaller and lighter.

<<Embodiment 7>>
Fig. 9 is a perspective view of a power conversion unit according to a seventh embodiment of the present invention. Fig. 10 is a cross-sectional view of the power conversion unit according to the seventh embodiment of the present invention.
As shown in Figures 9 and 10, the housing and housing cover forming the outer shell of the unit can be made of porous resin. Figures 9 and 10 show a power conversion unit U4 having a porous outer shell made of resin. The power conversion unit U4 can form a power conversion device S or can be equipped with the circuit shown in Figure 8.

In the power conversion unit U4, the input side unit 14 includes an input side housing 5c and an input side housing lid 6c that closes the housing 5c. The output side unit 15 includes an output side housing 5d and an input side housing lid 6d that closes the housing 5d. The input side housing 5c and the output side housing 5d each have an opening on one side. The input side and output side housing lids 6c, 6d are attached to cover their openings.

A through hole 21 for the cooling pipe is provided on one side of the housings 6c, 6d. From the through hole 21, the cooling pipe 22 is pulled out from the inside of the housings 6c, 6d to the outside. The cooling pipe 22 is connected to a cooling path forming member 23 inside the housings 6c, 6d. The cooling path 11 is formed inside the cooling path forming member 23. The cooling path forming member 23 is formed of a material with high thermal conductivity.

The cooling path forming member 23 is in contact with the surface of the lower electrode plate 8 opposite the heat sink plate 12. The lower electrode plate 8 and the cooling path forming member 23 are stacked on top of each other and thermally connected. The cooling medium inside the cooling path forming member 23 is circulated through the cooling pipe 22 between the housings 6c and 6d and the outside.

These components form a heat transfer path that dissipates heat generated by heat-generating components such as the switching element 1 to the outside of the housings 6c and 6d. The heat dissipation mechanism using the cooling pipes 22 makes it possible to forcibly dissipate heat to the outside of the housings 6c and 6d.

The housings 6c and 6d are provided with through holes (not shown) for drawing out external terminals from the electrodes, similar to the through holes 21 through which the cooling pipes 22 are inserted. The through holes for the external terminals can be provided, for example, on the surface opposite the through holes 21 for the cooling pipes.

By providing such through holes 21 for the cooling pipes and through holes for the external terminals, the area of the outer shell formed by the housings 5c, 5d and the housing lids 6c, 6d, excluding the through holes 21 for the cooling pipes and the through holes for the external terminals, can be made into a porous structure with high thermal insulation and airtightness.

The housings 5c, 5d and the housing lids 6c, 6d are made of a resin with high electrical resistivity. The housings 5c, 5d and the housing lids 6c, 6d are made porous with the pores in the resin matrix being mainly closed pores (closed bubbles). The internal space of the housings 5c, 5d is made airtight, except for the through-holes 21 for the cooling pipes and the through-holes for the external terminals.

The porous housings 5c, 5d and housing lids 6c, 6d can be formed, for example, as a hard foamed body made by foaming resin, or as a molded body with air pores dispersed in a resin matrix. The housings 5c, 5d and housing lids 6c, 6d mainly have closed pores in order to reduce the effects of temperature and air pressure on the inside, but may also have some open pores.

The porous housings 5c, 5d and housing lids 6c, 6d can be formed by any suitable method, such as generating gas in the raw resin by a gas generation reaction or a thermal decomposition reaction, injecting gas into the raw resin to disperse pores, stirring and shearing the raw resin to disperse pores, dispersing porogens in the raw resin and releasing them from the nearly closed pores after curing, dispersing hollow fillers in the raw resin, and dispersing high bulk density fillers in the raw resin and stirring and shearing them to disperse pores.

Materials that can be used for the housings 5c, 5d and the housing covers 6c, 6d include, for example, epoxy resin, polyurethane (PU), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), ethylene vinyl acetate copolymer (EVA), polycarbonate (PC), modified polyphenylene ether (mPPE), polyamide (PA), polyimide (PI), polyamideimide (PAI), etc.

Examples of fillers with a hollow structure include glass balloons, silica balloons, etc.; inorganic fillers with a hollow structure made of alumina, zirconia, carbon, fly ash, shirasu, perlite, etc.; and organic fillers with a hollow structure made of cross-linked acrylic resin, cross-linked styrene-acrylic resin, etc. Examples of high bulk density fillers include flake-shaped, porous, and fibrous fillers.

By forming such a porous outer shell, the unit can be made lighter than a non-porous outer shell. In addition, because the structure has high insulation and airtightness, it has high resistance to temperature and pressure that deviate from the normal temperature and pressure of the external environment in which the unit is placed, as well as to temperature and pressure changes. Since the internal environment within the housing is less susceptible to the temperature and pressure of the external environment, the internal environment is more likely to be kept normal relative to the external environment in which the device is placed, making it less likely that low-temperature deterioration, heat deterioration, and thermal stress caused by the external environment, as well as short circuits and insulation breakdown due to discharge under low pressure, will occur.

When such a porous outer shell is formed, the gas barrier materials 20a, 20b can be interposed between the circuit board 2 and the sealing resin 9, between the porous housings 5c, 5d and the sealing resin 9, or between the porous housing lids 6c, 6d. The resin material forming the housings 5c, 5d and the housing lids 6c, 6d may contain low molecular weight components such as air and moisture. However, by providing the gas barrier materials 20a, 20b, it is possible to prevent gases such as oxygen and water vapor from migrating to the sealing resin 9. The housings 5c, 5d and the housing lids 6c, 6d have a large volume, so the gas barrier properties are more effective than in the case of a non-porous outer shell.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are included as long as they do not deviate from the technical scope. For example, the above-described embodiments are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of an embodiment with another configuration, or to add another configuration to the configuration of an embodiment. It is also possible to add other configurations to, delete configurations, or replace configurations with respect to part of the configuration of an embodiment.

For example, in the power conversion unit described above, the components of the circuit and the components related to heat dissipation of the circuit are illustrated in each figure. However, the arrangement and configuration of these components are not limited to the forms shown in the figures. These components can be arranged and configured as appropriate as long as the power conversion function, electrical insulation function, heat dissipation function, etc. are not impaired.

In the power conversion unit, the paths for supplying and discharging the cooling medium and the input/output terminals electrically connected to the circuit can be provided in appropriate locations on the housing. Furthermore, although the power conversion unit is configured to perform AC/DC conversion, it may also be a device that performs other conversions such as DC/AC conversion, voltage, current, and frequency conversion. Furthermore, the circuit that performs AC/DC conversion is not limited to the circuit shown in FIG. 8.

REFERENCE SIGNS LIST 1 Switching element 2 Circuit board 3 Resonant capacitor 4 Smoothing capacitor 5a, 5b, 5c, 5d Housing 6a, 6b, 6c, 6d Housing cover 7 Upper electrode plate 8 Lower electrode plate 9 Sealing resin 10 O-ring 11 Cooling path 12 Heat sink 13 Unfilled portion 14 Input side unit (input side power conversion portion)
15 Output side unit (output side power conversion section)
16: Moisture absorbent 16b: Storage section 17: O-ring 18: Inner panel frame 19: High frequency transformer 20a, 20b: Gas barrier material (material having gas barrier properties)
21: Through hole 22: Cooling pipe 23: Cooling path forming member U, U1, U2, U3, U4: Power conversion unit S: Power conversion device

Claims (10)

a housing; a heat sink disposed in a space inside the housing; a circuit board thermally connected to the heat sink; a switching element provided on the circuit board; and a sealing resin filled in the space inside the housing;
The power conversion unit has a gas barrier material between the circuit board and the sealing resin. 2. The power conversion unit according to claim 1,
The power conversion unit has a gas barrier material between the housing and the sealing resin, or between a housing lid that closes the housing and the sealing resin. 3. The power conversion unit according to claim 1,
The gas barrier material has a gas permeability coefficient for oxygen of 0.001×10 ⁻¹⁰ cm ³ (STP) cm/(cm ² ·s ·cmHg) or less and a gas permeability coefficient for water vapor of 300×10 ⁻¹⁰ cm ³ (STP) cm/(cm ² ·s ·cmHg) or less. 2. The power conversion unit according to claim 1,
The gas barrier material comprises an ethylene-vinyl alcohol copolymer, polyacrylonitrile, polyvinyl alcohol, polyvinylidene chloride, or MXD nylon. 2. The power conversion unit according to claim 1,
The gas barrier material is a power conversion unit comprising a laminate of a material having an oxygen gas permeability coefficient of 0.001× ^{10-10 cm3} (STP) cm/( ^cm2 ·s·cmHg) or less and a material having a water vapor gas permeability coefficient of 300× ^{10-10 cm3} (STP) cm/( ^cm2 ·s·cmHg) or less. 2. The power conversion unit according to claim 1,
The power conversion unit, wherein the sealing resin is silicone gel or silicone rubber. 2. The power conversion unit according to claim 1,
A power conversion unit in which an unfilled portion that is not filled with the sealing resin is formed in the space inside the housing. 8. The power conversion unit according to claim 7,
A power conversion unit, wherein a moisture absorbent is disposed in the unfilled portion. 2. The power conversion unit according to claim 1,
The power conversion unit has a housing that is porous and has closed pores. A power conversion device comprising a power conversion unit according to any one of claims 1 to 9 and a frame connected to the power conversion unit and electrically grounded.

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