Electric power conversion device

Abstract

An electric power conversion device according to the present invention is provided with a smoothing capacitor C comprising a capacitor element 11, a metal capacitor case 14 that houses the capacitor element 11, a plastic film, and a resin 15. A sheet metal for shaping the capacitor case 14 is a metal-resin composite sheet metal in which a plastic film is bonded to the inner surface side of the capacitor case 14. The inside of the capacitor case 14 is filled with the resin 15. This configuration improves the cooling efficiency of the capacitor in the electric power conversion device.

Description

Power Conversion Device

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

[0002] FIG. 1 shows the circuit configuration of an inverter unit as an example of a general power conversion device, and FIG. 2 shows the configuration of a conventional inverter unit.

[0003] In the inverter unit 10, the capacitor C, which serves to smooth the DC link voltage, is a heat-generating component because a current always flows through it. Therefore, the capacitor C needs to be cooled.

[0004] 2 shows an example of a structure for cooling the power semiconductor (IGBT package) 1 and capacitor C in the inverter unit 10 by water cooling. There are also other structures for cooling heat-generating components by attaching them to self-cooling fins or air-cooling fins. Patent Document 1 discloses prior art for these structures.

[0005] In the existing configuration, as shown in FIG. 2, cooling is achieved by placing the capacitor C in contact with the housing 4 of the inverter unit 10 via a thermally conductive sheet 3 placed on the bottom surface (or sometimes on the top surface) of the capacitor C.

[0006] Meanwhile, Patent Document 2 discloses a prior art in which an aluminum resin composite panel is used for a weight sensor capacitor. However, Patent Document 2 does not mention that a current of a predetermined amount or more flows through the weight sensor capacitor, generating heat, or that the configuration of Patent Document 2 has a cooling effect.

[0007] JP 2021-197838 A JP 2011-22120 A

[0008] However, the actual heat generating part of the capacitor C is inside the molded capacitor C (the capacitor element and internal conductors). The heat generated inside the capacitor C is dissipated via the resin mold → the case of the capacitor C → the thermally conductive sheet 3 → the housing 4 of the inverter unit 10 → the flow path 5, so sufficient cooling performance cannot be obtained.

[0009] Downsizing and heat generation of individual items are issues in achieving a compact inverter unit 10 (high output density). Because the capacitor C is a large component within the inverter unit 10 (often the largest component in volume among the electrical components shown in the electrical circuit of FIG. 1), the heat generated by this capacitor C has been a bottleneck.

[0010] For the reasons described above, improving the cooling efficiency of the capacitor in the power conversion device is an issue to be addressed.

[0011] The present invention was devised in view of the above-mentioned problems in the conventional art, and one aspect of the present invention is a power conversion device equipped with a smoothing capacitor, wherein the capacitor comprises a capacitor element, a metal capacitor case that houses the capacitor element, and a resin that is filled inside the capacitor case, and the metal sheet that forms the capacitor case is a metal-resin composite metal sheet with a plastic film attached to the inner surface of the capacitor case.

[0012] In one aspect, the capacitor is fixed to the housing of the power conversion device or to a heat sink attached to the housing of the power conversion device with a thermally conductive adhesive.

[0013] In one aspect, the power converter is characterized in that a flow path through which a coolant flows is formed in the housing of the power converter or the heat sink.

[0014] In one embodiment, the capacitor case is made of aluminum.

[0015] According to the present invention, it is possible to improve the cooling efficiency of the capacitor in the power conversion device.

[0016] The present invention relates to a power converter and a capacitor, and is a circuit diagram of the power converter and a capacitor according to the present invention.

[0017] Hereinafter, an embodiment of the power conversion device according to the present invention will be described in detail with reference to FIGS.

[0018] [Embodiment] First, a typical power conversion device (e.g., an inverter unit, hereinafter referred to as the inverter unit) will be described based on the electrical circuit diagram in Fig. 1. As shown in Fig. 1, a capacitor (e.g., a film capacitor) C is connected between a P terminal and an N terminal. Furthermore, switching elements Su, Sx, switching elements Sv, Sy, and switching elements Sw, Sz are connected in series between the P terminal and the N terminal. The switching elements are, for example, IGBTs, and the switching elements Su to Sz constitute a power semiconductor (IGBT package) 1.

[0019] A motor M is connected to the AC side of the power semiconductor 1 (the connection point of the switching elements Su and Sx, the connection point of the switching elements Sv and Sy, and the connection point of the switching elements Sw and Sz). A current sensor 2 is provided between the power semiconductor 1 and the motor M.

[0020] The capacitor C serves to smooth the DC link voltage. A discharge resistor R is connected in parallel to the capacitor C. The discharge resistor R is provided to discharge the charge in the capacitor C when the input power of the inverter unit 10 is turned off, thereby preventing electric shock accidents.

[0021] The capacitor C of this embodiment is shown in Fig. 3. The left side of Fig. 3 is an exploded perspective view of the capacitor C, and the right side of Fig. 3 is a perspective view of the capacitor C after assembly.

[0022] The capacitor C includes a capacitor element 11, a P-side conductor 12, an N-side conductor 13, and a capacitor case 14. The capacitor element 11 is housed in the capacitor case 14 with the P-side conductor 12 and the N-side conductor 13 connected to each other. The capacitor case 14 is then filled with resin 15.

[0023] The capacitor case 14 is generally made of a resin material such as PPS (Polyphenylene sulfide), but aluminum or other metals with high thermal conductivity may also be used to improve cooling performance.

[0024] However, since the potting (filling) resin 15 and the metal of the capacitor case 14 are incompatible, there is a high possibility that the resin 15 will peel off from the capacitor case 14 due to expansion and contraction.

[0025] Therefore, a metal-resin composite sheet metal is used, in which a plastic film (not shown) is attached to the sheet metal used to form capacitor case 14, and the capacitor case is manufactured so that the plastic film faces the inner surface of capacitor case 14. Because there is good compatibility between metal capacitor case 14 and the plastic film, and between filled resin 15 and the plastic film, the risk of resin 5 peeling off from capacitor case 14 is reduced.

[0026] 4 is a perspective view showing the capacitor C and the housing 4 of the inverter unit 10 in this embodiment. In this embodiment, the housing 4 of the inverter unit 10 is formed with a flow path through which a refrigerant (for example, water) flows.

[0027] Conventionally, a heat conductive sheet was attached to the bottom surface of the capacitor case 14, and the capacitor C was installed so that it was in contact with the housing 4 of the inverter unit 10 via the heat conductive sheet, so that heat was dissipated only from the bottom surface of the capacitor case 14 to the housing 4 of the inverter unit 10.

[0028] In this embodiment, the capacitor case 14 is fixed to the housing 4 of the inverter unit 10 with a thermally conductive adhesive. The capacitor case 14 is in contact with the housing 4 of the inverter unit 10 not only on its bottom surface but also on its sides. The portion of the housing 4 of the inverter unit 10 from the bottom to the dotted line is in contact with the side of the capacitor case 14. The thermally conductive adhesive is applied to the bottom and side surfaces of the capacitor case 14 to fix it to the housing 4 of the inverter unit 10. As a result, it is possible to dissipate heat to the housing 4 of the inverter unit 10 not only from the bottom surface of the capacitor case 14 but also from the side surfaces.

[0029] [Explanation of Function and Operation] Aluminum or other metals are used as the material for the capacitor case 14. By using a metal with high thermal conductivity for the capacitor case 14, it is expected that the heat dissipation performance from the capacitor C to the housing 4 of the inverter unit 10 will be improved.

[0030] Furthermore, since the metal of the capacitor case 14 and the resin 15 filled therein are incompatible, there is a possibility that the resin 15 will peel off from the capacitor case 14. Therefore, a metal-resin composite sheet metal is used, in which a plastic film is attached to the metal sheet of the capacitor case 14, so that the inner surface of the capacitor case faces the plastic film. Because the metal capacitor case 14 and the plastic film, and the resin 15 and the plastic film, are compatible with each other, it is possible to prevent the resin 15 from peeling off from the capacitor case 14.

[0031] Furthermore, conventionally, a thermally conductive sheet is attached to the bottom surface of the capacitor case 14 and the capacitor case is installed in the housing 4 of the inverter unit 10, thereby dissipating heat only from the bottom surface of the capacitor case 14 to the housing 4 of the inverter unit 10. In this embodiment, by using a thermally conductive adhesive on the bottom and side surfaces of the capacitor case 14 instead of a thermally conductive sheet and installing the capacitor case 14 in the housing 4 of the inverter unit 10, it becomes possible to dissipate heat not only from the bottom surface of the capacitor case 14 but also from the side surfaces.

[0032] [Effect] According to this embodiment, the cooling capacity of the capacitor C can be improved by using a metal with high thermal conductivity as the material for the capacitor case 14 and by using a thermally conductive adhesive to dissipate heat from the bottom and sides of the capacitor case 14 to the housing 4 of the inverter unit 10.

[0033] Furthermore, capacitor case 14 is made of a metal-resin composite sheet metal with a plastic film attached to the sheet metal, and is fabricated so that the inner surface of the capacitor case faces the plastic film, thereby preventing the resin 15 from peeling off from capacitor case 14. This reduces defects in capacitors C and improves the reliability of the power conversion device.

[0034] Furthermore, the improved cooling capacity of the capacitor C relaxes the requirements for the ESR (Equivalent Series Resistance) of the capacitor C. In other words, since the ESR of the capacitor C can be increased compared to conventional capacitors, it becomes possible to reduce the thickness of the capacitor film. Furthermore, the improved cooling capacity of the capacitor C makes it possible to increase the allowable current value per capacitance. As a result, it becomes possible to miniaturize the capacitor C.

[0035] Furthermore, while conventionally the housing 4 of the inverter unit 10 and the capacitor case 14 are fixed with bolts or the like, in this embodiment the capacitor case 14 is fixed to the housing 4 of the inverter unit 10 with a thermally conductive adhesive, which makes it possible to reduce the number of bolts and the number of parts.

[0036] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims.

[0037] For example, in the present embodiment, the capacitor C (capacitor case 14) is installed in the housing 4 of the inverter unit 10, but the capacitor C (capacitor case 14) may be installed in a water-cooled heat sink or an air-cooled heat sink that is separately attached to the housing 4 of the inverter unit 10. In the case of a water-cooled heat sink, a flow path through which a refrigerant (water) flows is formed in the heat sink.

[0038] Furthermore, in the embodiment, the inverter unit 10 provided with a smoothing capacitor has been described, but the present invention can also be applied to power conversion devices other than inverter units (for example, converters, choppers, etc.).

[0039] C...capacitor R...discharge resistor Su to Sz...switching element M...motor 1...power semiconductor (IGBT module) 2...current sensor 3...thermal conductive sheet 4...inverter unit housing 5...flow path 10...power conversion device (inverter unit) 11...capacitor element 12...P-side conductor 13...N-side conductor 14...capacitor case 15...resin

Claims

1. A power conversion device equipped with a smoothing capacitor, the capacitor comprising: a capacitor element; a metallic capacitor case that houses the capacitor element; and resin that is filled inside the capacitor case, and the sheet metal that forms the capacitor case is a metal-resin composite sheet metal with a plastic film attached to the inner surface of the capacitor case.

2. The power conversion device according to claim 1, wherein the capacitor is fixed to the housing of the power conversion device or to a heat sink attached to the housing of the power conversion device by a thermally conductive adhesive.

3. The power conversion device according to claim 2, wherein a flow path for circulating a coolant is formed in the housing of the power conversion device or in the heat sink.

4. The power conversion device according to claim 1, wherein the capacitor case is made of aluminum.

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