Power conversion device

Abstract

A power conversion device (50) comprises: a rectangular parallelepiped housing (100) made of a heat transfer material; a power conversion circuit (20) disposed in the housing; and a capacitor (10) having at least one flat surface and connected to the power conversion circuit while the flat surface is disposed so as to be in contact with the inner surface of the housing. Thus, heat emitted from the capacitor when the power conversion device operates is efficiently conducted to the housing and dissipated from the surface of the housing to the outside, so that the capacitor can be efficiently cooled.

Description

Power converter

[0001] The present disclosure relates to a power converter for an electric vehicle.

[0002] When a power converter such as an inverter or a converter operates, a large amount of ripple current flows through the smoothing capacitor provided in the DC power supply unit. When ripple current flows through the smoothing capacitor, the capacitor generates heat due to the equivalent series resistance component of the capacitor.

[0003] In a power converter mounted on an electric vehicle, the capacitor is housed in a casing together with other heat sources such as a circuit board including a switching element and a bus bar, so the amount of heat generated inside the casing inevitably increases. As a result, the temperature rise inside the casing becomes significant. Exposing the capacitor to high-temperature conditions accelerates its deterioration and leads to a reduction in service life, so it is necessary to efficiently dissipate heat from the capacitor.

[0004] For example, some power converters including a semiconductor module and a smoothing capacitor in a casing have a heat conduction portion that conducts heat generated by the smoothing capacitor to the casing. (Patent Document 1)

[0005] Japanese Patent Laid-Open No. 2019-115237

[0006] In the power converter disclosed in Patent Document 1, the lower surface of the smoothing capacitor is screw-fixed to the bottom surface inside the casing via a heat conduction portion such as a heat conductive sheet. Heat generated by the capacitor is configured to be transmitted from the lower surface of the capacitor to the casing through the heat conduction portion and discharged from the surface of the casing. However, in a power converter mounted on a vehicle, it is necessary to densely incorporate heat-generating components such as a semiconductor module and a capacitor in a casing of limited volume. In this case, particularly in a configuration where cooling of the capacitor depends on the thermal conductivity of the heat conduction portion interposed between the capacitor and the casing, there is a risk that cooling will be insufficient.

[0007] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a power converter in which the smoothing capacitor of a DC power supply unit can efficiently dissipate heat.

[0008] To solve the above problems, the power conversion device according to this disclosure comprises a rectangular parallelepiped housing made of a heat transfer material, a power conversion circuit disposed within the housing, and a capacitor having at least one plane, which is positioned so as to abut the inner surface of the housing and connected to the power conversion circuit.

[0009] The power conversion device described herein has the effect of efficiently cooling the smoothing capacitor.

[0010] Circuit diagram showing the configuration of the power converter according to Embodiments 1 and 2. Figure 2 showing the arrangement inside the housing of the power converter according to Embodiment 1. Cross-sectional view A-A in Figure 2 showing the arrangement inside the housing of the power converter according to Embodiment 2. Cross-sectional view A-A in Figure 4 showing the arrangement inside the housing of the power converter according to Embodiment 2.

[0011] A power conversion device according to an embodiment of the present disclosure will be described in detail below with reference to the drawings. In the following description, multiple components of the same type will be indicated by subscripts, but the subscripts may be omitted as appropriate when describing them without distinguishing between them.

[0012] Embodiment 1. Figure 1 is an example of a circuit diagram of a power conversion device mounted on a vehicle according to Embodiment 1, and shows a typical circuit configuration of a three-phase two-level inverter.

[0013] The power converter 50 comprises a power conversion circuit 20 and a capacitor 10, and is connected in parallel to the DC power supply 80 to form a three-phase two-level inverter. A load (not shown) is connected to the output terminal 51 of the power converter 50.

[0014] The DC power source 80 is, for example, a DC voltage from an overhead line via a current collector, a DC voltage obtained by converting an AC voltage from an overhead line with a converter (not shown), or a DC voltage supplied from a battery. The power converter 50 converts the DC power input from the DC power source 80 into AC power and supplies it to the load.

[0015] Capacitor 10 is connected to a DC power supply 80 and is charged by the power supplied from the DC power supply 80. Capacitor 10 removes power supply noise from the DC power supply 80 and switching noise when the switching elements described later are operating. Capacitor 10 has terminals 10a and 10b, and multiple capacitor elements are connected in series and parallel between terminals 10a and 10b via wiring material inside the housing of capacitor 10.

[0016] The power conversion circuit 20 is connected to the DC power supply 80 and the capacitor 10, and converts the power supplied from the DC power supply 80. The power conversion circuit 20 has two switching elements connected in series, corresponding to the U-phase, V-phase, and W-phase. The switching elements are controlled by a switching control unit (not shown) and are switched on and off. By switching the switching elements on and off, the power conversion circuit 20 converts the supplied DC power into three-phase AC power.

[0017] Figures 2 and 3 schematically show the arrangement of components such as capacitors according to Embodiment 1 when housed in a roughly rectangular parallelepiped housing 100.

[0018] The capacitor 10 is housed in the enclosure 100 along with the power conversion circuit 20, busbars, other wiring materials, and a switching control unit. Terminals 10a and 10b of the capacitor 10 are electrically connected to the power conversion circuit 20, which is located nearby to reduce wiring inductance, by wiring materials such as busbars.

[0019] In this embodiment, the capacitor 10 has a rectangular parallelepiped shape, with one side in contact with the inner surface 101b of the bottom surface of the housing 100, and the other side in contact with the inner surface 101s of the side surface. Here, "contact" means direct contact without any intervening material.

[0020] The capacitor 10 may have mounting portions on surfaces that are in contact with the inner surface 101s of the side or the inner surface 101b of the bottom. By engaging the mounting portions with fastening members such as bolts through through holes provided in the housing 100, the capacitor 10 can be securely fixed in close contact with the inner surface of the housing 100.

[0021] The housing 100 is made of a heat-conducting material with high thermal conductivity, such as metal. The housing 100 is installed under the vehicle or on the roof, etc., so as to be in contact with the outside air, with the positive direction of the Z-axis in Figure 2 being upward.

[0022] When the power converter 50 is operating, a ripple current containing voltage fluctuations flows through the capacitor 10 from the DC power supply 80. When a ripple current flows through the capacitor 10, heat is generated due to the equivalent series resistance (ESR) component, and the casing of the capacitor 10 becomes hot.

[0023] The heat from the capacitor 10 is quickly transferred to the inner surface 101b of the bottom of the housing 100 and the inner surface 101s of the side of the housing 100, which it is in contact with, and further conducted to the parts of the housing 100 that the capacitor 10 is not in contact with, and then released to the surroundings from the entire outer surface of the housing 100.

[0024] As explained above, by having the capacitor 10 in contact with the inner surface of the housing 100, the heat generated by the capacitor 10 can be directly conducted to the housing 100, enabling efficient cooling. Furthermore, since it becomes unnecessary to provide a large space around the capacitor for cooling or to make the capacitor itself larger, the housing 100 can be made smaller.

[0025] Embodiment 2. As described in Embodiment 1, the capacitor 10 comes into contact with the inner surface of the housing 100, which is made of a heat-transferring material, so that the heat from the capacitor 10 is directly conducted to the housing 100 and released to the outside air. In light of the fact that capacitors 10 used in vehicles tend to have a large mass, when the capacitor 10 is secured to the housing 100, a frame member 40 that reinforces the housing 100 may be added.

[0026] Figure 4 shows a case where a frame member 40 is provided on the outside of the surface of the housing 100 that the capacitor 10 contacts, having a U-shaped cross-section perpendicular to the longitudinal direction and a flat contact surface with the housing 100.

[0027] The frame member 40 is made of a heat-conducting material with high thermal conductivity, such as metal. The frame member 40 has holes so that it can be locked to the mounting portion 11 of the housing 100 and the capacitor 10 by fastening members 41 such as bolts. The capacitor 10, the housing 100, and the frame member 40 are fastened together and fixed by the fastening members 41. This prevents the position of the capacitor 10 from shifting and impairing the contact state with the inner surface of the housing 100.

[0028] The frame member 40 is not limited to a U-shape; it may also be L-shaped, for example, as long as it has a surface that contacts the outside air in addition to the surface that contacts the housing 100. The frame member 40 having a surface that contacts the outside air but does not contact the housing 100 contributes to the efficient release of heat conducted from the housing 100. In other words, by being fixed to the outer surface of the housing 100, the frame member 40 effectively functions as a heat sink for the housing 100.

[0029] The direction in which the frame member 40 is fixed to the outer surface of the housing 100 is arbitrary, but if the longitudinal direction is perpendicular to the direction of travel of the vehicle on which the housing 100 is installed, the contact area with the airflow along the direction of travel of the vehicle increases, and the cooling effect is further enhanced. For this reason, if the direction of travel of the vehicle to which the housing 100 is attached is the Y-axis direction, the cooling effect is enhanced if the frame member 40 extends in the Z-axis direction on the inner surface 101s of the side surface of the housing 100 that is parallel to the YZ plane, as shown in Figure 4.

[0030] As explained above, by providing the frame member 40 on the outer surface of the surface of the housing 100 that the capacitor 10 contacts, the mechanical strength of the housing 100 can be improved while the frame member 40 functions as a heat sink, thereby improving cooling efficiency.

[0031] In any embodiment, the capacitor 10 may include a single capacitor element within the housing. Also, the number of terminals on the capacitor 10 is not limited to two, but is arbitrary. The number of capacitors 10 arranged inside the housing 100 is not limited to one, but may be multiple. Each of the multiple capacitors 10 has a plane, and they should be arranged so that these planes abut against the inner surface of the housing 100.

[0032] The capacitor 10 can have any shape as long as it has at least one plane, but it is preferably a roughly rectangular parallelepiped. When the capacitor 10 is a roughly rectangular parallelepiped, the contact area is increased by bringing two or more surfaces into contact with two or more inner surfaces of the housing 100, which promotes heat transfer to the housing 100 and also expands the heat distribution on the outer surface of the housing 100, further improving the heat dissipation efficiency.

[0033] The surfaces of the capacitor 10 that contact the inner surface 101b of the bottom surface and the inner surface 101s of the side surface of the housing 100 are not particularly limited, but preferably, as shown in Figures 2 and 4, they are surfaces close to the surface having terminals, that is, surfaces adjacent to the surface having terminals 10a and terminals 10b of the capacitor 10. When multiple capacitor elements are connected between the terminals of the capacitor 10 within the housing of the capacitor 10, the current path of the capacitor elements close to the terminals of the capacitor 10 has relatively smaller inductance and resistance components and lower impedance compared to capacitor elements far from the terminals, for example, due to differences in wiring length. For this reason, current flows more easily to the capacitor elements close to the terminals of the capacitor 10 compared to capacitor elements far from the terminals, and the amount of heat generated is particularly large. In other words, the part of the housing of the capacitor 10 that is close to the terminals gets the hottest, and the amount of heat generated decreases relatively as you move away from the terminals, so by promoting heat dissipation from the surface close to the surface having terminals of the capacitor 10, the cooling effect of the capacitor 10 can be enhanced.

[0034] The power conversion device 50 is not limited to an inverter that converts DC power to AC power. It may also be a converter that converts AC power to DC power, a DC-DC converter that converts DC power to DC power of a different voltage, or a combination of a converter and an inverter. If the power conversion device 50 is a converter, a capacitor 10 is provided in the DC output section, and if it is a DC-DC converter, a capacitor 10 is provided in both the DC input section and the DC output section.

[0035] When the power conversion device 50 is an inverter, a converter, or a combination thereof, the number of phases in the AC portion is not limited to three phases. It may be single-phase or a multi-phase system other than three phases, and can be appropriately selected according to the application.

[0036] The materials used for the housing 100 and frame members 40 are not particularly limited, but include, for example, heat-transmitting materials such as aluminum or iron. Heat is rapidly transferred from the capacitor 10 to the housing 100 and frame members 40 and diffused, thereby improving heat dissipation efficiency.

[0037] Furthermore, although the description of Embodiment 2 showed an example in which the frame member 40 is fixed to the housing 100 by fastening members 41 such as bolts, the method of fixing the frame member 40 is not limited to this. For example, the frame member 40 may be brazed or welded to the outer surface of the surface of the housing 100 that the capacitor 10 abuts.

[0038] The configurations shown in the above embodiments are merely examples, and can be combined with other known technologies. It is also possible to omit or modify parts of the configuration without departing from the gist of the invention.

[0039] 10 Capacitor 11 Mounting part 20 Power conversion circuit 40 Frame member 41 Fastening member 50 Power conversion device 100 Housing

Claims

1. A power conversion device comprising: a rectangular parallelepiped housing made of a heat transfer material; a power conversion circuit disposed within the housing; and a capacitor having at least one plane, the plane being positioned so as to abut the inner surface of the housing, and connected to the power conversion circuit.

2. The power conversion device according to claim 1, wherein the capacitor has at least two planes, and each of the two planes is in contact with the inner surface of the housing.

3. The power conversion device according to claim 1 or 2, wherein the capacitor is in the shape of a rectangular parallelepiped.

4. The power conversion device according to any one of claims 1 to 3, wherein a frame member is provided on the outer surface of the surface of the housing that the capacitor contacts.

5. The power conversion device according to claim 4, wherein the capacitor is fastened to the frame member and the housing by fastening members.

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