Power electronics unit

Abstract

The invention relates to a power electronics unit (1) with at least two electronic power modules (2), with a holder (6) which holds the power modules (2) in a position in which they are arranged next to one another to form an intermediate space (9) and lie opposite one another with their main side surfaces (3) to be cooled, and with a cooling device (10) arranged in the intermediate space (9) which is designed in such a way that it cools the power modules (2) via their main side surfaces (3) by means of a cooling liquid.According to the invention, the cooling device (10) has at least one cooling element (11) through which the cooling liquid flows, wherein the cooling element (11) has a fluid-tight cooling liquid shell (15) which surrounds a cooling liquid space (16) through which the cooling liquid flows and contains two opposing flexible surfaces (19) which, when pressurized by the cooling liquid flowing through the cooling element (11), lie flat against the two main side surfaces (3) of the power modules (2) to be cooled in heat-dissipating contact.

Description

The invention relates to a power electronics unit, in particular an inverter or a power inverter, especially for an electric drive system of a motor vehicle, having at least two electronic power modules, having a holder which holds the power modules in a position in which they are arranged next to one another forming a space and are opposite one another with their main side faces to be cooled, and having a cooling device for cooling the power modules.A power electronics unit of the generic type is known from DE 10 2017 214 482 A1, in which at least two power modules are held in a housing in such a way that an intermediate space is formed between them. A first housing part and a second housing part are arranged in the interspace, which housing part bear flat against a main side surface of the first power module or against a main side surface of the second power module, on the one hand, and form a passage for a cooling medium between them, on the other hand. Heat generated by the power modules is dissipated from their main side surfaces to be cooled to the cooling medium via the two housing parts. A flexible cooling structure is arranged in the passage, with which improved heat transfer is to be achieved by flow guidance or turbulence generation in the cooling medium. During the assembly of the power electronics unit, the housing parts holding the power modules are joined together. The cooling structure is designed to be flexible in such a way that the two housing parts which approach one another during the joining together can compress the cooling structure. This ensures that the cooling structure bears against the two heat-transferring housing parts with a certain prestressing force.The object of the invention is to provide a power electronics unit mentioned at the beginning which is improved with regard to the cooling device.The object is achieved in the power electronics unit mentioned at the beginning in that the cooling device has at least one cooling element through which a cooling liquid flows, which cooling element is arranged in the interspace between the two power modules and is designed in such a way that the cooling liquid cools the power modules via their main side faces. The cooling element has a fluid-tight cooling liquid jacket which surrounds a cooling liquid space through which the cooling liquid flows and contains two flexible surfaces lying opposite one another which, when the cooling liquid flowing through the cooling element is pressurized, bear flat against the two main side surfaces of the power modules to be cooled in heat-dissipating contact.In this case, the heat-dissipating planar bearing of the flexible surfaces of the cooling liquid casing of the cooling element against the two main side surfaces of the power modules to be cooled is effected by a (reversibly) flexible deformation of these surfaces under the action of the pressure by the cooling liquid flowing through the cooling element and by a corresponding adaptation of the outer contour or the outer shape of the cooling liquid casing and thus of the cooling element to the outer structure or the outer shape of the adjacent main side surfaces of the power modules to be cooled.Advantageous embodiments of the invention are specified in the dependent claims.Such a power electronics unit according to the invention is provided for use, for example, in battery-electric vehicles, the drive trains of which use high-voltage batteries of, for example, 400 V or 800 V, which also have to supply additional units of 48 V and 12 V. The power electronics unit is designed as a converter for DC / DC conversion. Furthermore, such a power electronics unit can be designed to carry out the AC / DC conversion in an inverter when charging the high-voltage battery of the vehicle.The power electronics unit has two or more power modules. Such a power module has semiconductors which heat up strongly during operation. The power module is suitably partially or substantially completely embedded in molding compound of non-conductive material such as plastic. The heat generated is dissipated via a cooling device. The power module is designed in such a way that it has two mutually opposite outer sides, which are referred to as main side faces and via which the cooling takes place by means of the cooling elements. The fluid-tight cooling liquid jacket is arranged in the intermediate space between two adjacent power modules which are opposite one another with their main side surfaces. The cooling liquid jacket is bulgeed out by the pressure of the cooling liquid flowing through it and is placed or pressed against the heated main side surfaces of the two power modules which are to be cooled. Depending on the pressure applied by the cooling liquid to the cooling liquid jacket, the proportion or the size of the flexible surface with which the cooling liquid jacket abuts or is pressed against the main side surfaces varies. The cooling element is expediently formed in such a way that the cooling liquid jacket makes contact with substantially the entire surface of the main side surface of each of the two power modules in planar heat-transferring contact at a correspondingly high pressure of the cooling liquid. Expediently, the size of the cooling liquid jacket accordingly corresponds approximately to the size of the power module.Expediently, a control or regulating device having at least one temperature sensor is provided for adjusting the liquid pressure of the cooling liquid in the cooling liquid jacket of the cooling element. With such a control or regulating device, the cooling capacity can be adapted as required via the respective pressure with which the cooling liquid jacket is pressed against the power module. This allows active cooling of the power modules that can be regulated as a function of temperature. For example, at low temperature, such as during a cold start of the electric drive motor of a vehicle, the cooling power can be reduced or completely switched off by reducing the pressure of the cooling liquid. In principle, a targeted regulation of the cooling power is possible by increasing or by reducing the contact pressure pressing the cooling liquid jacket against the power module. Data of an integrated temperature measurement of the power module can be used here to control a throughflow limiter, which is formed, for example, as a piezomechanical valve and which controllably limits the throughflow of the cooling liquid through the cooling elements.Due to its flexibility, the cooling liquid jacket adapts itself to irregularities or to changes in shape of the power modules on their main side surfaces. As a result, intimate contact between the cooling liquid jacket and the main side surface of the power module is maintained even in the case of changes in shape of the power modules due to temperature fluctuations or high temperature differences and also due to aging processes of the power modules. Furthermore, changes in shape in the arrangement of the power modules relative to the cooling elements or to the cooling liquid jacket, in particular due to temperature fluctuations or high temperature differences, as well as air gaps that may be present during operation, are also compensated. The requirements for the quality and the dimensional accuracy of the power modules on their main side surfaces can thus be reduced.The cooling liquid jacket is basically designed in such a way that it can bulge flexibly in its arrangement in the interspace in a planar manner in the two opposite directions toward the power modules. The cooling liquid jacket can be made of any flexible fluid-tight material, such as a particularly coated fabric.According to a preferred embodiment, it is provided that the cooling liquid jacket or at least its flexible surfaces is formed by a flexible film. Such a flexible film is, for example, a metal foil or a plastic film or else a multilayer film. The cooling liquid jacket is formed in particular by welding or adhesive bonding of a film or of a plurality of such film pieces. Furthermore, the cooling liquid jacket can be formed in the manner of a closed bag or film pouch.According to a further preferred embodiment, it is provided that the cooling element has a frame carrying the cooling liquid jacket. The frame is preferably rectangular and has a size such that it holds the cooling liquid jacket in the interspace approximately congruently with the main side surfaces of the two power modules in a stable position. The frame is preferably made of a plastic such as polyamide. The two films forming the cooling liquid jacket are attached to the frame in a fluid-tight manner, for example by lamination or adhesive bonding. Expediently, the cooling liquid jacket is formed with a solid or reinforced circumferential edge, by means of which the cooling liquid jacket is fastened to the frame. The fastening is effected, for example, by clamping, riveting or welding. Expediently, the edge of the cooling liquid jacket contains a plurality of fastening openings for the passage of screws, which can be fixed at assigned screw-on points or screw-on openings of the frame and hold the edge or the cooling liquid jacket detachably on the frame.According to a further preferred embodiment, it is provided that the holder has a circuit carrier which is formed, for example, by a printed circuit board or a printed circuit board (PCB) or a ceramic substrate, such as a DCB or AMB substrate. Connectors for the power modules and frame holders for the frames of the cooling elements are arranged on the carrier in alternating sequence. Advantageously, the electrical and / or electronic contacting of the power modules is also carried out via the plug connectors, which are inserted into the plug connectors, for example, by means of a contact strip and are held by these. Thus, electrical or electronic functions such as, for example, current transmission and signal transmission or else driver and control functions can be transmitted via the carrier.Expediently, the cooling liquid shells of the cooling elements contain inlet connections and outlet connections for the cooling liquid. The inlet connections and outlet connections are arranged on the cooling elements in such positions that the cooling elements or the cooling liquid shells are connected to one another fluidically in series connection or alternatively in parallel connection via the inlet and outlet connections. Expediently, the cooling device with the cooling elements is connected to a main cooling circuit of an electric drive unit of a vehicle having the power electronics unit.According to a further preferred embodiment, it is provided that, with regard to EMC shielding of the power modules, the foil is electrically conductive and has an electrically insulating surface layer. One side of the film is thus electrically conductive and the other side of the film is electrically insulated. A film having an electrically insulating surface layer is, for example, a multilayer film or composite film in which at least the surface layer is electrically insulating. Current generated during EMC shielding is dissipated via the conductive side of the foil which is connected to a ground potential (GND or ground). The power modules contacting the foil at its electrically insulated surface layer may therefore have exposed metallic areas at their major side surfaces facing and contacting the insulated side of the foil in this embodiment. Insulation of the power module on its main side surface is not required.In an alternative configuration, the film is likewise formed in an electrically conductive manner with regard to an EMC shield or it has an electrically conductive surface layer. An electrically conductive foil is, for example, a metal foil made of an electrically conductive metal. A film having an electrically conductive surface layer is, for example, a multilayer film or composite film in which at least the surface layer is electrically conductive. In this embodiment, the power modules are formed in an electrically insulated manner on their main side face facing the conductive foil or the conductive side of the foil, e.g. from electrically insulating material, such as, for example, by plastic foam encapsulation or plastic injection molding or by a mold compound of non-conductive material or plastic embedding the electrical and / or electronic components of the power module. Current generated during EMC shielding is dissipated via the foil connected to ground potential (GND or ground).The above-described designs therefore avoid contact, which is impermissible with regard to EMC shielding, between conductive metal or the electrically conductive foil and conductive metal of the power module on its heat-transferring main side surface.With regard to EMC shielding, it is provided according to a further preferred embodiment that at least one electrically conductive shielding layer for EMC shielding is arranged on the frame. This additional shielding layer, for example a copper sheet or a conductive shielding foil, increases the EMC shielding of the power modules of the power electronics unit. Preferably, the electrically conductive shielding layer is arranged in the cooling liquid space of the cooling element or in the cooling liquid casing. The current generated by EMC radiation is discharged via the cooling liquid or via a cable connected to the shielding layer and connected to a ground potential. However, the additional shielding layer can also be provided outside the cooling liquid jacket and adjoining it in a planar manner.The flexible cooling liquid jacket thus replaces a rigid cooling element made of metal known from the prior art, which cooling element is attached to the power module, for example, by means of an adhesive bond or by means of a heat-conducting paste, and is thermally coupled to the power module. Due to different coefficients of expansion of the different materials of the cooling element and of the power module embedded, for example, in a plastic mold compound, detachment of the cooling element can occur, whereby the heat transfer during the cooling of the power module is reduced or even largely prevented. This disadvantageous effect is avoided by the flexible cooling liquid jacket of the power electronics unit according to the invention.A power electronics unit according to the invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing. It shows in schematic representations: FIG. 1 shows a sectional view of a power electronics unit with electronic power modules and cooling elements; FIG. 2 is a sectional view of one of the cooling elements of the power electronics unit shown in FIG. 1 ; and FIG. 3 shows a side view of the power electronics unit.A power electronic unit 1 has a plurality of electronic power modules 2. Such a power electronics unit 1 is provided for use, for example, in battery-electric vehicles, the drive trains of which use high-voltage batteries of, for example, 400 V or 800 V, which must also supply additional units of 48 V and 12 V. The power electronic unit 1 is designed as a converter for DC / DC conversion. Furthermore, such a power electronics unit 1 can be designed to carry out the AC / DC conversion in an inverter when charging the high-voltage battery of the vehicle. The power modules 2 have semiconductor components which heat up during operation and which have to be cooled.The power electronics unit 1 illustrated in FIG. 1 has three power modules 2. The power modules 2 are of the same or similar construction and have in principle an approximately rectangular shape with two mutually opposite outer sides which form main side faces 3 of the power module 2. Each power module 2 has a contact unit 5, for example a contact strip, on its lower edge 4, which projects downward on the power module 2. The power electronics unit 1 furthermore has a holder 6, on which the power modules 1 are held. The holder 6 contains a circuit carrier 7 such as a printed circuit board (PCB). The holder 6 has plug connectors 8 for the power modules 2. The power modules 2 are inserted into the plug connectors 8 by means of their contact strip and are held by them. The plug connectors 8 also contain electrical contacts for electrical contacting of the power module 2.The plug connectors 8 are arranged on the carrier 7 next to one another and spaced apart from one another in such a way that the power modules 2 are arranged in a position upright relative to the carrier 7 and parallel to one another. In each case two adjacent power modules 2 are arranged at a distance from one another forming a defined intermediate space 9. The two power modules 2 delimiting the intermediate space 9 are situated with their respective main side faces 3 opposite one another. The distances between two power modules 2 are expediently of the same size.A cooling device 10 for removing heat generated in the power modules 2 has a plurality of identically constructed cooling elements 11. In each case, a cooling element 11 is arranged in the two intermediate spaces 9 between two adjacent power modules 2 (FIG. 1 ). A further cooling element 11 is arranged on the outside of each of the two outer power modules 2 in front of their respective outer main side surfaces 3. These two further cooling elements 11 located on the outside with respect to the group of power modules 2 adjoin, on their side 12 facing away from the respectively adjoining power module 2, a supporting structure 13 which provides an external support of the cooling element 11. The distance of the supporting structure 13 from the outer main side surface 3 of the outer power module 2 expediently corresponds to the distance between two power modules 2. the supporting structure 13 is fastened, for example, to the carrier 7 or and / or to a housing (not shown) of the power electronics unit 1 or a part of the housing.Each cooling element 11 contains a preferably rectangular frame 14, to which a cooling liquid jacket 15 is fastened, which surrounds a cooling liquid space 16 through which a cooling liquid flows. The cooling liquid jacket 15 is made of a flexible film 17. Two pieces of flexible film 17 are of such a size and shape that they are secured to the frame 14 with their edges 18 spaced apart from one another in a fluid-tight manner and form the cooling liquid space 16 between them. The frame 14 is made, for example, from a plastic, such as polyamide, to which the two films 17 are attached in a fluid-tight manner, for example by lamination. The two flexibly deformable foils 17 form surfaces 19 of the cooling liquid jacket 15 which are provided for bearing against the main side surfaces 3 of the power modules 2 to be cooled.The holder 6 of the power electronic unit 1 includes a frame holder having frame holding parts 20 fixed to the carrier 7 so as to also alternate with the connectors 8 in the direction of the series arrangement of the alternating power modules 2 and the cooling members 11. The frame holder of a frame 14 has, for example, two frame holding parts 20 spaced apart from one another in the longitudinal direction of the frame 14, which holding parts are formed, for example, in the form of clamps and into which the frame 14 is inserted with a lower frame part 21 and held in an upright position. The frame holder can additionally have a fixing of the frames 14, for example on their upper frame parts 22. The fixing (not shown) can be supported in particular on the housing.Each cooling element 11 has an inlet connection 23 and an outlet connection 24 for the cooling liquid flowing through the cooling element 11. The inlet connections 23 and the outlet connections 24 of the cooling element 11 illustrated in FIG. 1 are arranged and connected to one another in such a way that the cooling elements 11 are arranged in a cooling circuit forming a series connection and the cooling liquid flows through the cooling elements 11 in this series connection. For this purpose, the first left cooling element 11 in the arrangement of FIG. 1 contains the inlet connection 23 in its upper region, preferably on the left film 17 of the cooling liquid jacket 15. The outlet connection 24 is located in the lower region of the cooling element 11, preferably on the opposite right film 17 of the cooling liquid jacket 15. A lower connecting line 25 connects the outlet connection 24 of the first cooling element 11 to the inlet connection 23 of the second cooling element 11. An upper connecting line 25 connects the outlet connection 24 of the second cooling element 11 to the inlet connection 23 of the third cooling element 11, Even if the power electronics unit 1 has more than the four cooling elements 11 shown for more than three power modules 2.As an alternative to the series connection shown, the inlet connections 23 and the outlet connections 24 and their connecting lines 25 are arranged in such a way that the cooling elements 1 are arranged in a cooling circuit forming a parallel connection and the cooling liquid flows through the cooling elements 11 in this parallel connection. For this purpose, each cooling element 11 has, both in its upper region and in its lower region, in each case at least one inlet connection 23 and one outlet connection 24.The power electronics unit 1 has a shielding device with at least one shielding means for EMC shielding. Such a shielding means is the foil 17 in such a preferred first embodiment, in which it is formed of electrically conductive material forming an EMC shielding layer and has an electrically insulating surface layer. Current generated during the EMC shielding is dissipated via the cooling liquid circulating in the cooling circuit and contacting the EMC shielding layer. The cooling liquid is connected to a ground potential (GND or ground), for example to a vehicle frame when the power electronics unit 1 is used in an electric vehicle drive.Such a shielding means further constitutes the foil 17 also in such a preferred second embodiment, in which it is formed from electrically conductive material or has an electrically conductive surface layer and thus provides an EMC shielding. In this embodiment, the power modules are formed in an electrically insulated manner on their main side face facing the film, for example by a plastic foam encapsulation or plastic injection molding or by a mold compound of non-conductive material or plastic embedding the electrical and / or electronic components of the power module. Current generated during EMC shielding is dissipated via the foil 17 connected to ground potential (GND or ground).The foil 17 can furthermore be formed according to a preferred third embodiment from electrically insulating material without an electrically conductive layer providing an EMC shield. For EMC shielding, a further shielding means is provided which is formed by at least one electrically conductive shielding layer 26 which is arranged on the frame 14 of the cooling element 11 and can optionally be used in the first and second embodiments of the film 17 explained above. The shielding layer 26 is formed of, for example, a copper sheet. The shielding layer 26 extends in a planar manner and preferably in a central plane of the frame 14. The current generated during the EMC shielding is discharged via the cooling liquid or via a cable 27 connected to the shielding layer 26 and connected to the ground potential.Furthermore, the shielding layer 26 can also be attached to the frame 14 in such a way that it is arranged outside the cooling liquid jacket 15, covers the frame opening surrounded by the frame 14 and lies flat against the cooling liquid jacket 15. The cooling or heat dissipation from the power module 2 takes place via this shielding layer 26 and the cooling liquid casing 15 to the cooling liquid. The shielding layer 26 is expediently formed to be thin and flexible in such a way that it can adapt to the cooling liquid casing 15.However, the shielding layer 26 can also be formed as a deformation-resistant structure, for example as a copper sheet, which is attached to the frame 14 of the cooling element 11 and covers the frame opening. The cooling liquid jacket 15 attached to the frame 14 abuts the shielding layer 26 under the action of the cooling liquid. This embodiment can be used in particular with the external cooling elements 11, which are each bounded by the associated supporting structure 13. The support structure 13 forms the support surface for the shielding layer 26. The cooling element 11 thus has an outer side formed by the supporting structure 13. The shielding layer 26 is preferably arranged on the outer side of the supporting structure 13 facing away from the cooling liquid casing 15, but can also be arranged on the inner side of the supporting structure 13 facing the cooling liquid casing 15. In any case, an EMC shield is thus provided on such a side of the cooling element 11 on which no power module 2 is located.In the power electronics unit 1, the cooling liquid casing 15 is therefore acted upon and bulged by the pressure of the cooling liquid flowing through it and is thereby placed or pressed against the heated main side surfaces 3 of the two power modules 2 which are to be cooled. The cooling capacity can be adjusted via the magnitude of the pressure and the resulting size of the surface 19 of the cooling liquid jacket 15 with which the cooling liquid jacket 15 abuts the main side surface 3 of the power module 2. The pressure of the cooling liquid is expediently controlled under temperature control. At least one temperature sensor is expediently arranged on the inlet connection 23 or on the outlet connection 24. The pressure of the cooling liquid is controlled, for example, by means of a flow restrictor which is arranged, for example, as a piezomechanical valve in a cooling liquid line leading to the first cooling element and which controllably limits the flow of the cooling liquid through the cooling elements.List of reference characters1 Power electronics unit 2 Power module 3 Main side surface 4 Lower edge 5 Contact unit 6 Holder 7 Circuit carrier 8 Plug connector 9 Intermediate space 10 Cooling device 11 Cooling element 12 Outer side 13 Supporting structure 14 Frame 15 Cooling liquid jacket 16 Cooling liquid space 17 Film 18 Edge 19 Surface 20 Frame holding part 21 Lower frame part 22 Upper frame part 23 Inflow connection 24 Outflow connection 25 Connecting line 26 Shielding layer 27 CableReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 214 482 A1

[0002]

Claims

Power electronics unit (1) - with at least two electronic power modules (2), - with a holder (6) which holds the power modules (2) in a position in which they are arranged next to one another to form an intermediate space (9) and are opposite one another with their main side faces (3) to be cooled, and - with a cooling device (10) for cooling the power modules (2), characterized - in that the cooling device (10) has at least one cooling element (11) through which a cooling liquid flows, which cooling element is arranged in the intermediate space (9) between the power modules (2) and is designed to cool the power modules (2) via their main side faces (3), - wherein the cooling element (11) has a fluid-tight cooling liquid casing (15) which surrounds a cooling liquid space (16) through which the cooling liquid flows and contains two flexible faces (19) lying opposite one another, the cooling liquid flowing through the cooling element (11) is applied under pressure to lie flat against the two main side surfaces (3) of the power modules (2) to be cooled in heat-dissipating contact.Power electronics unit (1) according to Claim 1, characterized in that the cooling liquid casing (15) or at least its flexible surfaces (19) are formed by a flexible film (17).Power electronics unit (1) according to Claim 1 or 2, characterized in that the cooling element (11) has a frame (14) which carries the cooling liquid casing (15).Power electronics unit (1) according to Claim 3, characterized in that the holder (6) has a circuit carrier (7) on which plug connectors (8) for the power modules (2) and frame holders (20) for the frames (14) are arranged in alternating sequence.Power electronics unit (1) according to one of Claims 1 to 4, characterized in that the cooling liquid shells (15) of the cooling elements (11) have inlet and outlet connections (23, 24) for the cooling liquid, and the cooling elements (11) are connected to one another via the inlet and outlet connections (23, 24) in series connection or in parallel connection.Power electronics unit (1) according to one of Claims 2 to 5, characterized in that the film (17) - is electrically conductive and has an electrically insulating surface layer, or - is electrically conductive or has an electrically conductive surface layer, and the power modules (2) are electrically insulated on their main side surface (3) facing the film (17).Power electronics unit (1) according to one of Claims 3 to 6, characterized in that at least one electrically conductive shielding layer (26) for EMC shielding is arranged on the frame (14).Power electronics unit (1) according to Claim 7, characterized in that the electrically conductive shielding layer (26) is arranged in the cooling liquid space of the cooling element (11) or in the cooling liquid casing (15), and the current generated during the EMC shielding is conducted away via the cooling liquid or via a cable (27) connected to the shielding layer (26).Power electronics unit (1) according to one of Claims 1 to 8, characterized in that a control or regulating device having at least one temperature sensor is provided for setting the liquid pressure of the cooling liquid in the cooling liquid casing (15) of the cooling element (11).Power electronics unit (1) according to one of Claims 1 to 9, characterized in that the holder (6) of the power modules (2) is designed to transmit current and signals.

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