WO2015059552A1

WO2015059552A1 - Power converter

Info

Publication number: WO2015059552A1
Application number: PCT/IB2014/002196
Authority: WO
Inventors: Kentaro Hirose
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-10-24
Filing date: 2014-10-22
Publication date: 2015-04-30
Also published as: JP2015082951A

Abstract

A power converter includes a semiconductor element, a cooler, a capacitor element, and a metallic case. The cooler cools the semiconductor element. The capacitor element is connected with the semiconductor element. The metallic case houses the semiconductor element, the cooler, and the capacitor element. The metallic case has a partition wall that separates a cooler housing space, which houses the semiconductor element and the cooler, and a capacitor housing space, which houses the capacitor element, from each other. The capacitor element is fixed to a wall surface through an insulating spacer, the wall surface being other than the partition wall among wall surfaces that define the capacitor housing space. A space between the wall surfaces that define the capacitor housing space, and the capacitor element is filled with a resin.

Description

POWER CONVERTER

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a power converter such as a voltage converter and an inverter.

2. Description of Related Art

[0002] Power converters are used in various places. Hybrid vehicles have become popular in recent years, and hybrid vehicles (and electric vehicles including fuel cell electric vehicles) carry power converters that convert direct-current power of a battery into alternating current for driving a traction motor. A typical power converter converts electric power by switching of a semiconductor element called a power transistor. A power converter is often provided with a capacitor element in order to suppress pulsation of current due to switching of a semiconductor element, or as one of parts of a voltage conversion circuit. As power to be handled becomes larger, amounts of heat generation in a semiconductor element and a capacitor element are increased. Therefore, a power converter that handles a large amount of power includes a cooler that cools a semiconductor element and so on. A typical power converter that handles a large amount of power is an in-vehicle inverter that supplies electric power to a traction motor of a hybrid vehicle or an electric vehicle.

[0003] An example of such an in-vehicle power converter is disclosed in Japanese Patent Application Publication No. 2012-217322 (JP 2012-217322 A). In the power converter described in JP 2012-217322 A, a housing space of a case for the power converter is divided into a cooler housing space that houses a semiconductor element and a cooler, and a capacitor housing space that houses a capacitor element. The capacitor element is housed in a case exclusively for a capacitor (a capacitor case), and the capacitor case is housed in the capacitor housing space. In short, the capacitor element is housed in two cases.

[0004] According to the technology described in JP 2012-217322 A, the capacitor element is sealed within the capacitor case by a sealing member. Sealing of the capacitor element is achieved by filling a space between an inner surface of the case and the capacitor element with a resin as disclosed in Japanese Patent Application Publication No. 2012-151378 (JP 2012-151378 A).

SUMMARY OF THE INVENTION

[0005] When a capacitor element is housed in two cases as described in JP 2012-217322 A, it is difficult to radiate heat of the capacitor element. The invention relates to a power converter including a semiconductor element, a cooler, and a capacitor element, and provides a technology to enhance heat dissipation efficiency of the capacitor element.

[0006] A power converter according to an aspect of the invention includes a semiconductor element, a cooler, a capacitor element, and a metallic case. The cooler cools the semiconductor element. The capacitor element is connected with the semiconductor element. The metallic case houses the semiconductor element, the cooler, and the capacitor element. The metallic case has a partition wall that separates a cooler housing space, which houses the semiconductor element and the cooler, and a capacitor housing space, which houses the capacitor element, from each other. The capacitor element is fixed to a wall surface through an insulating spacer, the wall surface being other than the partition wall among wall surfaces that define the capacitor housing space. A space between the wall surfaces that define the capacitor housing space, and the capacitor element is filled with a resin. The resin may be of a type that originally has fluidity but is then solidified after being filled. This means that the resin around the capacitor element may be obtained by potting as stated above. "The wall surfaces that define the capacitor housing space" include a wall surface serving as a bottom portion of the capacitor housing space.

[0007] In the power converter, the capacitor element is directly housed in one case (the case for the power converter), and the space between an inner wall surface of the case and the capacitor element is filled with resin. Therefore, heat dissipation from the capacitor element to the case is excellent. Since the capacitor element is housed in the metallic case, insulation countermeasures are necessary. In the above-mentioned power converter, the capacitor element is fixed to the case through the insulating spacer, and the resin is not filled in a state where the capacitor element is in direct contact with the metallic case. Typically, the insulating spacer is made of a resin. The insulating spacer may be provided with a depression to be fitted to the capacitor element, or a rib that positions the capacitor element.

[0008] An electrode of the capacitor element may face the insulating spacer. The capacitor element could swing in areas other than the area where the capacitor element faces the insulating spacer, but the surface facing the insulating spacer, to which the capacitor element is fixed, does not come into contact with the case. By arranging the electrode of the capacitor on the surface facing the insulating spacer, insulation between the capacitor element and the case is ensured without fail.

[0009] A depression may be provided in the wall surfaces that define the capacitor housing space. Further, the filling resin may enter the depression. Thus, due to an anchor effect, the filling resin is prevented from rising from the capacitor housing space. The same effect is obtained by providing a rib instead of the depression. However, in order to provide a rib, it is necessary to increase the capacitor housing space to secure a space between a distal end of the projection and the capacitor element, which is not space efficient. By employing the depression, the capacitor housing space is used efficiently.

[0010] In order to enhance an effect of cooling the capacitor element further, a bas bar that connects the semiconductor element with the capacitor element may be routed along the partition wall. The bus bar is a conductive member for reducing internal resistance, and is typically an elongate plate-shaped (or bar-shaped) metallic member. Copper is often used for the bus bar, and copper has high thermal conductivity. By routing such a bus bar along the partition wall, heat of the capacitor element is transferred to the bus bar, then to the partition wall in the vicinity of the bas bar, and dispersed to the entire case. In short, by routing the bus bar as stated above, heat dissipation performance of the capacitor element is enhanced. The bas bar of the capacitor element may also be arranged in parallel to the partition wall of the metallic case. A part of a magnetic field generated from current flowing the bus bar is absorbed by the partition wall that is in parallel to the bus bar, thereby reducing inductance. As a result, a loss is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a block diagram of an electric power system for a hybrid vehicle including a power converter according to an example;

FIG. 2 is a top view of the power converter;

FIG. 3 is a sectional view taken along the line III - III in FIG. 2; and

FIG. 4 is a perspective view of an insulating spacer.

DETAILED DESCRIPTION OF EMBODIMENTS

[0012] A power converter according to an example is explained with reference to the drawings. The power converter according to the example is a device that is mounted on a hybrid vehicle, converts direct-current power of a battery into alternating current, and supplies the alternating current to a traction motor. First of all, an electric power system of the hybrid vehicle including the power converter is explained.

[0013] FIG. 1 shows a block diagram of an electric power system of a hybrid vehicle 30. A main battery 31 is connected with a power converter 2 through a system main relay 32. The power converter 2 has a structure in which a booster circuit 33, which boosts electric power of the main battery 31, and an inverter circuit 35, which converts direct-current power into alternating-current power, are connected with each other in series. Output of the inverter circuit 35 corresponds to an output of the power converter 2 and is supplied to a motor 37. Output torque of the motor 37 and output torque of an engine 36 are combined or distributed at a power split device 38 and transmitted to a wheel shaft 39.

[0014] General description of a circuit structure of the power converter 2 is provided. The booster circuit 33 is structured of a series-connected circuit of two power transistors 21a, 22a, a reactor 16, and a filter capacitor 5a connected in parallel with an input port of the booster circuit 33. One end of the reactor 16 is connected with a midpoint of the series-connected circuit, and the other end of the reactor 16 is connected with the input port of the booster circuit 33. A diode is connected with each of the power transistors in inverse parallel. In the inverter circuit 35, three sets of series-connected circuits made of two power transistors 21b, 22b are connected with each other in parallel. In FIG. 1, reference numerals of some, of the power transistors are omitted. Alternating current is outputted from a midpoint of the three sets of series-connected circuits. A diode is connected with each of the power transistors 21a, 21b, 22a, 22b in inverse parallel. The power transistors included in the booster circuit 33 and the power transistors included in the inverter circuit operate on receiving a PWM signal from a controller 34. Detailed explanation of structures of the booster circuit 33 and the inverter circuit 35 are well known, and thus omitted.

[0015] Since large current to be supplied to the traction motor 37 flows in each of the elements of the booster circuit 33 and the inverter circuit 35, a large amount of heat is generated. Typical examples of elements with a large amount of heat generation are the power transistors 21a, 21b, 22a, 22b, the filter capacitor 5a, a smoothing capacitor 5b, and the reactor 16 shown in FIG. 1. Both of the booster circuit 33 and the inverter circuit 35 include the series-connected circuit made of the two power transistors. The inverter circuit 35 has three sets of the series-connected circuits. The power transistors 21a, 21b on a high potential side of the series-connected circuits are called upper arm transistors, and the power transistors 22a, 22b on a low potential side are called lower arm transistors. Hereinbelow, the upper arm transistors are generally denoted by a reference numeral 21, and the lower arm transistors are generally denoted by a reference numeral 22.

[0016] The smoothing capacitor 5b is connected between the booster circuit 33 and the inverter circuit 35 in parallel. The smoothing capacitor 5b suppresses pulsation of current inputted into the inverter circuit 35. As shown well in FIG. 1, the power converter 2 has the plurality of series-connected circuits of the upper arm transistors 21 and the lower arm transistors 22. However, any of the series-connected circuit is connected with the filter capacitor 5a and the smoothing capacitor 5b in parallel.

[0017] A hardware layout within a case of the power converter 2 is explained. FIG. 2 is a top view of the power converter 2 (a cover is not shown). FIG. 3 is a sectional view taken along the line III - III in FIG. 2.

[0018] Inside of a case 3 for the power converter 2 is divided into three spaces (a capacitor housing space Spl, a cooler housing space Sp2, and a substrate housing space Sp3). Refer to FIG. 3 for the substrate housing space Sp3. The case 3 is made of aluminum.

[0019] A laminated unit 10 and the reactor 16 are housed in the cooler housing space Sp2. The laminated unit 10 is a device in which a plurality of flat plate-shaped coolers 12 and a plurality of flat plate-shaped semiconductor modules 20 are laminated alternately. One end of the laminated unit 10 in the lamination direction abuts on an inner surface of a side wall of the case 3, and the other end is pressed by a leaf spring 15. The reactor 16 is arranged on the opposite side of the laminated unit 10 through the leaf spring 15. [0020] The semiconductor modules 20 are explained. Two power transistors are sealed in each of the semiconductor modules 20 (see FIG. 3). The two power transistors are sealed by a resin package 23. The two power transistors are the upper arm transistor 21 and the lower arm transistor 22, which are connected with each other in series within the resin package 23. Although not shown, a diode, which is connected with each of the power transistors in inverse parallel, is also sealed in the semiconductor module 20. The diodes are located on the back sides of the power transistors 21, 22 in FIG. 3. In short, one of the semiconductor modules 20 corresponds to one of the series-connected circuits.

[0021] As shown in FIG. 3, three terminals 20a, 20b, and 20c extend from an upper end of the resin package 23. The terminal 20a corresponds to a high potential side terminal of the series-connected circuit of the power transistor, and the terminal 20b corresponds to a low potential side terminal of the series-connected circuit of the power transistor. The terminal 20c corresponds to a midpoint of the series-connected circuit. A bus bar is connected with each of the terminals 20a, 20b, and 20c. However, the bus bars are not shown in FIG. 2. In FIG. 3, bus bars 8a, 8b for connecting the terminals 20a, 20b with the filter capacitor 5a are shown. The bus bars will be explained later. The circuit diagram in FIG. 1 also shows that the series-connected circuit of the upper arm transistor 21 and the lower arm transistor 22, the filter capacitor 5a, and the smoothing capacitor 5b are connected with each other in parallel.

[0022] Gate terminals 21d, 22d, which lead to a gate of each of the power transistors 21, 22, extend from a lower end of the resin package 23. The gate terminals 21d, 22d extend from the cooler housing space Sp2 to the substrate housing space Sp3, and are connected with the controller 34 (see FIG. 1; the controller 34 is not shown in FIG. 2 and FIG. 3) housed in the substrate housing space Sp3.

[0023] A coolant supply pipe 13 and a coolant discharge pipe 14 pass through the plurality of coolers 12 that structure the laminated unit 10, and the coolant supply pipe 13 and the coolant discharge pipe 14 extend outside the case 3. Inside of each of the coolers 12 is a hollow space. A coolant supplied from outside through the coolant supply pipe 13 passes inside the coolers 12 and is discharged outside through the coolant discharge pipe 14. The cooler 12 on one end of the laminated unit 10 is in contact with the case 3. Each of the coolers 12 cools the power transistors 21, 22 within the semiconductor modules that are in contact with both sides of the cooler 12, and also cools the reactor 16, the filter capacitor 5 a, and the smoothing capacitor 5 b through the metallic case 3.

[0024] The capacitor housing space Spl and the cooler housing space Sp2 are separated from each other by a partition wall 4. The partition wall 4 is a part of the case 3. The filter capacitor 5 a and the smoothing capacitor 5b are housed in the capacitor housing space Spl. The filter capacitor 5a and the smoothing capacitor 5b are fixed to an insulating spacer 9 made of a resin, and the insulating spacer 9 is fixed to a bottom surface 3b of the capacitor housing space Spl. In other words, the filter capacitor 5a and the smoothing capacitor 5b are fixed to the bottom surface 3b of the capacitor housing space Spl through the insulating spacer 9. FIG. 4 shows a perspective view of the insulating spacer 9. The insulating spacer 9 has a tray shape, and is provided with a depression 9a to which the filter capacitor 5 a is fitted, and a depression 9b to which the smoothing capacitor 5b is fitted. A rib 9c is provided so as to surround the depressions 9a, 9b. The filter capacitor 5a (the smoothing capacitor 5b) is fitted to the depression 9a (the depression 9b), and fixed by a screw (not shown). When the insulating spacer 9 is installed in the capacitor housing space Spl, the rib 9c is fitted to a periphery of a bottom portion of the capacitor housing space Spl, and the insulating spacer 9 is positioned together with the filter capacitor 5a and the smoothing capacitor 5b. Since it is ensured that the filter capacitor 5a and the smoothing capacitor 5b are positioned as stated above, these capacitors are prevented from coming into coittact with the metallic case 3. The bottom surface 3b of the capacitor housing space Spl corresponds to a wall surface other than the partition wall 4 among wall surfaces that define the capacitor housing space Spl.

[0025] The explanation is resumes at FIG. 2 and FIG. 3. The filter capacitor 5a and the smoothing capacitor 5b are positioned by the insulating spacer 9, and are not in direct contact with the metallic case 3. An inner space of the capacitor housing space Spl, which is a space around the filter capacitor 5 a and the smoothing capacitor 5b, is filled with a potting resin 7. The potting resin 7 is an insulator. Top surfaces of the filter capacitor 5a and the smoothing capacitor 5b (top surfaces in a Z-axis direction in the drawings) are also covered by the potting resin 7, and the filter capacitor 5a and the smoothing capacitor 5b are sealed by the potting resin 7. The potting resin 7 obtained as a resin with fluidity is poured into the above-mentioned space and then solidified. In short, the potting resin 7 is filled by potting. As the filter capacitor 5a and the smoothing capacitor 5b are sealed by the insulating spacer 9 and the potting resin 7, insulation of the capacitors is ensured. Depressions 3a, 4a are provided in the wall surfaces that define the capacitor housing space Spl (an inner surface of the side wall of the case 3, and the side surface of the partition wall 4, which define the capacitor housing space Spl). When potting is performed, the resin with fluidity is also flown into the depressions 3a, 4a. As the resin is solidified in the depressions 3a, 4a, an anchor effect happens, thereby preventing the solidified potting resin 7 from rising from the capacitor housing space Spl.

[0026] The filter capacitor 5a is provided with positive and negative electrodes 6 in a surface facing the insulating spacer 9. The bus bars 8a, 8b connect the electrodes 6 with the terminals 20a, 20b (terminals of the power transistors) of the semiconductor module 20 (see FIG. 3). In FIG. 2, the bus bars are not shown. The bus bars 8a, 8b are conductive members for transmitting large current with low resistance, and are made of an elongate copper plate. Starting from the electrodes 6 facing the insulating spacer 9, the bus bars 8a, 8b pass inside the potting resin 7, extend upwardly along the partition wall 4, and are bent towards the semiconductor module 20 at a location where the bus bars 8a, 8b are led outside the potting resin 7. The bus bars 8a, 8b are routed in parallel to each other along the metallic partition wall 4. Heat generated in the filter capacitor 5a is partially transferred to the bus bars 8a, 8b, then further transferred to the partition wall 4 in the vicinity of the bus bars 8a, 8b, and dispersed to the entire case 3. Although not shown, the electrodes of the smoothing capacitor 5b are provided on the surface facing the insulating spacer 9, and the electrodes are connected with the terminals of the semiconductor module 20 by bus bars. These bus bars are also routed along the partition wall 4 like the bus bars 8a, 8b.

[0027] Some of the advantages of the power converter 2 according to the example are listed blow. Hereinbelow, the filter capacitor 5a and the smoothing capacitor 5b are generally referred to as capacitors 5. In the power converter 2, the capacitors 5 are in contact with the metallic case 3 of the power converter through the potting resin 7. Heat generated by the capacitors 5 is transferred to the case 3 through the potting resin 7. On the other hand, the cooler 12 of the laminated unit 10 are in contact with the case 3, and heat transferred to the case 3 is dissipated outside by the coolant flowing in the coolers 12. In order to enhance heat transfer efficiency from the capacitors 5 to the case 3, the space between the wall surfaces that define the capacitor housing space Spl and the capacitors 5 is narrowed as much as possible. This can cause contact between the capacitors 5 and the metallic case 3. However, in the power converter 2, the capacitors 5 are accurately positioned by the insulating spacer 9 having the depressions for holding the capacitors 5. Therefore, the capacitors 5 and the case 3 are prevented from coming into contact with each other. The electrodes of the capacitors 5 are provided at positions facing the insulating spacer 9. This also prevents the electrodes of the capacitors 5 from coming into contact with the case 3.

[0028] Heat generated by the capacitors 5 is transferred to the case 3 through the potting resin 7. The bus bars 8a, 8b connected with the electrodes 6 of the capacitors 5 are routed along the partition wall 4, which also contributes to heat dissipation of the capacitors 5. As the bus bars 8a, 8b connected with the capacitors 5 are arranged parallel to the partition wall 4 of the metallic case 3, a part of a magnetic field generated from current flowing in the bus bars 8a, 8b is absorbed by the partition wall 4, thereby reducing inductance. As a result, a loss is reduced.

[0029] The depressions 3a, 4a are provided in the wall surfaces that define the capacitor housing space Spl. As the potting resin 7 enters the depressions, an anchor effect happens, thus preventing the potting resin 7 from rising from the capacitor housing space Spl.

[0030] Below are notes regarding the technology explained in the example. The power transistors 21, 22 correspond to an example of a semiconductor element. The filter capacitor 5a and the smoothing capacitor 5b correspond to an example of a capacitor element.

[0031] Further advantages of enhancing heat dissipation efficiency of the capacitor element are explained. A film-type capacitor element is suitable for use as a capacitor element with a large capacity. In the case of a film-type capacitor element, the size of the capacitor element is able to be smaller for the same capacity by reducing a film thickness. However, a reduction of the film thickness narrows a distance between vapor-deposited films, and breakdown voltage performance is deteriorated. Breakdown voltage performance is deteriorated as temperature increases. Therefore, enhancing heat dissipation efficiency of the capacitor element results in lowering of an upper limit of an environmental temperature range of the capacitor element. As the upper limit of the environmental temperature range is lowered, required high-temperature characteristics are eased. This means that requirements for breakdown voltage performance under high temperature are also eased. Thus, it is possible to reduce a film thickness, and, as a result, it is possible to reduce a size of a capacitor element.

[0032] The specific example of the invention has been explained in detail. However, the example is for illustration only, and does not limit the scope of the claims. The technology described in the scope of the claims includes the foregoing example with various modifications and changes. Each of and various combinations of the technical elements explained in this specification and the drawings achieve technical utility, and the technical elements are not limited to the combination stated in the claims at the time of filing. The technology explained in this specification and the drawings as an example is able to achieve the plurality of objectives simultaneously, and has technical utility by achieving one of the objectives.

Claims

CLAIMS:

1. A power converter comprising:

a semiconductor element;

a cooler that cools the semiconductor element;

a capacitor element connected with the semiconductor element;

a metallic case that houses the semiconductor element, the cooler, and the capacitor element, the metallic case having a partition wall that separates a cooler housing space, which houses the semiconductor element and the cooler, and a capacitor housing space, which houses the capacitor element, from each other,

wherein the capacitor element is fixed to a wall surface through an insulating spacer, the wall surface being other than the partition wall among wall surfaces that define the capacitor housing space, and a space between the wall surfaces that define the capacitor housing space, and the capacitor element is filled with a resin.

2. The power converter according to claim 1 wherein

an electrode of the capacitor element faces the insulating spacer.

3. The power converter according to claim 1 or 2 wherein

a depression, which is fitted to the capacitor element, is provided in the insulating spacer.

4. The power converter according to claim 1 or 2 wherein

a rib that positions the capacitor element is provided in the insulating spacer.

5. The power converter according to any one of claims 1 to 4 wherein

a depression is provided in the wall surfaces that define the capacitor housing space.

6. The power converter according to any one of claims 1 to 5 wherein a bas bar that connects the semiconductor element with the capacitor element is routed along the partition wall.