Power electronics unit

Abstract

The invention relates to a power electronics unit (1) having: at least two electronic power modules (2); a holder (6) which holds the power modules (2) in a position in which they are arranged next to one another so as to form an intermediate space (9) and lie opposite one another with their main side surfaces (3), which are to be cooled; and a cooling device (10) which is arranged in the intermediate space (9) and 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 casing (15) which surrounds a cooling liquid chamber (16) through which the cooling liquid flows, and contains two flexible surfaces (19) which lie opposite one another and, when pressure is applied by the cooling liquid flowing through the cooling element (11), bear flat against the two main side surfaces (3), which are to be cooled, of the power modules (2) in heat-dissipating contact.

Description

[0001] Description

[0002] Power electronics unit

[0003] 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, with at least two electronic power modules, with a holder that holds the power modules in a position in which they are arranged next to one another, forming an intermediate space, and lie opposite one another with their main side surfaces to be cooled, and with a cooling device for cooling the power modules.

[0004] DE 10 2017 214 482 A1 discloses a generic power electronics unit in which at least two power modules are held in a housing such that a gap is formed between them. A first housing part and a second housing part are arranged in the gap, which, on the one hand, lie flat against a main side surface of the first power module and, on the other hand, against a main side surface of the second power module, respectively, and, on the other hand, form a passage for a cooling medium between them. Heat generated by the power modules is dissipated from their main side surfaces to be cooled via the two housing parts to the cooling medium. A flexible cooling structure is arranged in the passage, with which improved heat transfer is achieved by directing the flow or generating turbulence in the cooling medium. During assembly of the power electronics unit, the housing parts holding the power modules are joined together.The cooling structure is designed to be flexible enough that the two housing parts can compress the cooling structure as they approach each other during assembly. This ensures that the cooling structure adheres to the two heat-transferring housing parts with a certain preload.

[0005] The invention is based on the object of providing a power electronics unit as mentioned above which is improved with regard to the cooling device.

[0006] The object is achieved in the power electronics unit mentioned above in that the cooling device has at least one cooling element through which a coolant flows, which element is arranged in the space between the two power modules and is designed to cool the power modules via their main side surfaces by means of the coolant. The cooling element has a fluid-tight coolant shell that surrounds a coolant chamber through which the coolant flows and contains two opposing flexible surfaces that, when pressurized by the coolant flowing through the cooling element, bear flatly against the two main side surfaces of the power modules to be cooled, in heat-dissipating contact.

[0007] The heat-dissipating surface contact of the flexible surfaces of the cooling liquid shell of the cooling element on the two main side surfaces of the power modules to be cooled is achieved by a (reversible) flexible deformation of these surfaces under the influence of the pressure from 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 shell 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.

[0008] Advantageous embodiments of the invention are specified in the dependent claims.

[0009] Such a power electronics unit according to the invention is intended for use, for example, in battery-electric vehicles whose drive trains

[0010] High-voltage batteries with, for example, 400 V or 800 V are used, which must also supply auxiliary units with 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 perform AC / DC conversion in an inverter when charging the vehicle's high-voltage battery.

[0011] The power electronics unit has two or more power modules. Such a power module has semiconductors that heat up considerably during operation. The power module is expediently partially or substantially completely embedded in molding compound made of a non-conductive material such as plastic. The generated heat is dissipated via a cooling device. The power module is designed such that it has two opposing outer sides, referred to as main side surfaces, via which cooling is achieved by means of the cooling elements. The fluid-tight coolant sleeve is arranged in the space between two adjacent power modules whose main side surfaces are opposite one another. The coolant sleeve is bulged by the pressure of the coolant flowing through it and is applied or pressed against the heated main side surfaces of the two power modules that are to be cooled.Depending on the pressure exerted by the cooling liquid on the cooling liquid sleeve, the proportion or size of the flexible surface with which the cooling liquid sleeve rests or is pressed against the main side surfaces varies. The cooling element is expediently designed such that, at a sufficiently high cooling liquid pressure, the cooling liquid sleeve makes surface-to-surface heat-transfer contact with essentially the entire surface of the main side surface of each of the two power modules. The size of the cooling liquid sleeve therefore expediently corresponds approximately to the size of the power module.

[0012] A control or regulating device comprising at least one temperature sensor is expediently provided for adjusting the fluid pressure of the coolant in the coolant sleeve of the cooling element. With such a control or regulating device, the cooling performance can be adjusted as needed via the respective pressure with which the coolant sleeve is pressed against the power module. This enables temperature-dependent, controllable active cooling of the power modules. For example, at low temperatures, such as during a cold start of a vehicle's electric drive motor, the cooling performance can be reduced or completely switched off by reducing the coolant pressure. In principle, targeted control of the cooling performance is possible by increasing or decreasing the contact pressure pressing the coolant sleeve against the power module.Data from an integrated temperature measurement of the power module can be used to control a flow limiter, which is designed, for example, as a piezomechanical valve and controllably limits the flow of the coolant through the cooling elements.

[0013] Due to its flexibility, the cooling liquid jacket adapts to unevenness or changes in the shape of the power modules on their main side surfaces. This maintains close contact between the cooling liquid jacket and the main side surface of the power module, even when the power modules change shape due to temperature fluctuations or significant temperature differences, as well as due to aging processes of the power modules. Furthermore, changes in the shape of the power modules relative to the cooling elements or the cooling liquid jacket, particularly due to temperature fluctuations or significant temperature differences, as well as any air gaps that may occur during operation, are compensated for. The requirements for the quality and dimensional accuracy of the power modules on their main side surfaces can thus be reduced.

[0014] The coolant sleeve is generally designed in such a way that it can flexibly expand in the two opposite directions toward the power modules. The coolant sleeve can be made of any flexible, fluid-tight material, such as a coated fabric.

[0015] According to a preferred embodiment, the coolant sleeve, or at least its flexible surfaces, is / are formed from a flexible film. Such a flexible film is, for example, a metal foil or a plastic film, or even a multilayer film. The coolant sleeve is formed, in particular, by welding or gluing one or more such film pieces together. Furthermore, the coolant sleeve can be formed in the form of a closed bag or film pouch.

[0016] According to a further preferred embodiment, the cooling element comprises a frame supporting the coolant sleeve. The frame is preferably rectangular and sized to hold the coolant sleeve in a stable position in the intermediate space, approximately congruent with the main side surfaces of the two power modules. The frame is preferably made of a plastic such as polyamide. The two films forming the coolant sleeve are attached to the frame in a fluid-tight manner, e.g., by lamination or gluing. The coolant sleeve is expediently formed with a rigid or reinforced peripheral edge, with which the coolant sleeve is attached to the frame. The attachment is achieved, e.g., by clamping, riveting, or welding.Conveniently, the edge of the coolant sleeve contains several fastening openings for the passage of screws, which can be fixed to associated screwing points or screwing openings of the frame and detachably hold the edge or the coolant sleeve to the frame.

[0017] According to a further preferred embodiment, the holder has a circuit carrier, which is formed, for example, by a circuit board or a printed circuit board or PCB (printed circuit board) or a ceramic substrate, such as a DCB or AM B substrate. Connectors for the power modules and frame holders for the frames of the cooling elements are arranged in alternating sequence on the carrier. Expediently, the electrical and / or electronic contacting of the power modules, which are plugged into the connectors, for example by means of a contact strip and are held by them, also takes place via the connectors. Electrical or electronic functions such as power transmission and signal transmission or even driver and control functions can thus be transmitted via the carrier.

[0018] The cooling fluid jackets of the cooling elements expediently contain inlet and outlet connections for the cooling fluid. The inlet and outlet connections are arranged on the cooling elements in such positions that the cooling elements or the cooling fluid jackets are fluidically connected to one another via the inlet and outlet connections in series or, alternatively, in parallel.

[0019] The cooling device with the cooling elements is expediently connected to a main cooling circuit of an electric drive unit of a vehicle having the power electronics unit.

[0020] According to a further preferred embodiment, with regard to EMC shielding of the power modules, the film 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 with 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 discharged via the conductive side of the film connected to a ground potential (GND). The power modules contacting the film at their electrically insulated surface layer can therefore, in this embodiment, have exposed metallic regions on their main side surfaces, which face the insulated side of the film and contact it.Insulation of the power module on its main side surface is not required.

[0021] In an alternative design, also with a view to EMC shielding, the film is electrically conductive or it has an electrically conductive surface layer. An electrically conductive film is, for example, a metal foil made of an electrically conductive metal. A film with 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 electrically insulated on their main side surface facing the conductive film or the conductive side of the film, e.g. from electrically insulating material such as a plastic foam or plastic overmolding or from a molding compound made of non-conductive material or plastic that embeds the electrical and / or electronic components of the power module.Current generated during EMC shielding is discharged via the foil connected to the ground potential (GND).

[0022] The designs described above therefore avoid contact between conductive metal or the electrically conductive foil and conductive metal of the power module on its heat-transferring main side surface, which is inadmissible with regard to EMC shielding.

[0023] With regard to EMC shielding, according to a further preferred embodiment, 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. The electrically conductive shielding layer is preferably arranged in the coolant chamber of the cooling element or in the coolant casing. The current generated by EMC radiation is dissipated via the coolant 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 coolant casing and flatly adjacent to it.

[0024] The flexible coolant sleeve thus replaces a rigid metal cooling element known from the prior art, which is attached to the power module, for example, by means of an adhesive or thermal paste, and thermally coupled to it. Different expansion coefficients between the different materials of the cooling element and the power module, which is embedded, for example, in a plastic mold compound, can lead to detachment of the cooling element, which reduces or even largely eliminates heat transfer during cooling of the power module. The flexible coolant sleeve of the power electronics unit according to the invention avoids this disadvantageous effect.

[0025] A power electronics unit according to the invention is explained in more detail below using exemplary embodiments with reference to the drawing. It shows schematic representations:

[0026] Fig. 1 shows a sectional view of a power electronics unit with electronic power modules and cooling elements;

[0027] Fig. 2 in a sectional view of one of the cooling elements of the power electronics unit shown in Fig. 1; and

[0028] Fig. 3 shows a side view of the power electronics unit.

[0029] A power electronics unit 1 comprises several electronic power modules 2. Such a power electronics unit 1 is intended for use, for example, in battery-electric vehicles whose drivetrains use high-voltage batteries with, for example, 400 V or 800 V, which must also supply auxiliary units with 48 V and 12 V. The power electronics unit 1 is designed as a converter for DC / DC conversion. Furthermore, such a power electronics unit 1 can be designed to perform AC / DC conversion in an inverter when charging the vehicle's high-voltage battery. The power modules 2 comprise semiconductor components that heat up during operation and require cooling.

[0030] The power electronics unit 1 shown in Fig. 1 has three power modules 2. The power modules 2 are of the same or similar construction and generally have an approximately rectangular shape with two opposing outer sides that form the main side surfaces 3 of the power module 2. Each power module 2 has a contact unit 5 on its lower edge 4, e.g. a contact strip that projects downwards on the power module 2. The power electronics unit 1 further has a holder 6 on which the power modules 1 are held. The holder 6 contains a circuit carrier 7 such as a circuit board or a printed circuit board or a PCB (printed circuit board). The holder 6 has connectors 8 for the power modules 2. The power modules 2 are plugged into the connectors 8 by means of their contact strips and are held by them.The connectors 8 also contain electrical contacts for electrical contacting of the power module 2.

[0031] The 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. Two adjacent power modules 2 are arranged at a distance from one another forming a defined gap 9. The two power modules 2 defining the gap 9 face each other with their respective main side surfaces 3. The distances between any two power modules 2 are expediently equal.

[0032] A cooling device 10 for dissipating heat generated in the power modules 2 has a plurality of similarly constructed cooling elements 11. One cooling element 11 is arranged in each of 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, which are located on the outside with respect to the group of power modules 2, border on a support structure 13 on their side 12 facing away from the adjacent power module 2, which provides external support for the cooling element 11. The distance of the support 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 support structure 13 is, for example, attached to the carrier 7 and / or to a housing (not shown) of the power electronics unit 1 or is a part of the housing.

[0033] Each cooling element 11 contains a preferably rectangular frame 14, to which a cooling liquid sleeve 15 is attached, which surrounds a cooling liquid chamber 16 through which a cooling liquid flows. The cooling liquid sleeve 15 is made of a flexible film 17. Two pieces of the flexible film 17 are sized and shaped such that they are attached to the frame 14 at a distance from one another in a fluid-tight manner by their edges 18, forming the cooling liquid chamber 16 between them. The frame 14 is made, for example, of 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 films 17 form surfaces 19 of the cooling liquid sleeve 15, which are intended to bear against the main side surfaces 3 of the power modules 2 to be cooled.The holder 6 of the power electronics unit 1 has a frame holder with frame holding parts 20, which are fastened to the carrier 7 in such a way that they also alternate with the connectors 8 in the direction of the series arrangement of the alternating power modules 2 and the cooling elements 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 are formed, for example, in the form of clamps, 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 fixation of the frames 14, for example, at their upper frame parts 22. The fixation (not shown) can be supported in particular on the housing.

[0034] Each cooling element 11 has an inlet connection 23 and an outlet connection 24 for the coolant flowing through the cooling element 11. The inlet connections 23 and the outlet connections 24 of the cooling element 11 shown 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 circuit, and the coolant flows through the cooling elements 11 in this series circuit. For this purpose, the first left-hand 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 coolant casing 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 coolant casing 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 drain connection 24 of the second cooling element 11 to the inlet connection 23 of the third cooling element 11. This series-connected arrangement of the inlet connections 23 and the drain connections 24, as well as their connecting lines 25, continues across all cooling elements 11, even if the power electronics unit 1 has more than the four cooling elements 11 shown for more than three power modules 2.

[0035] As an alternative to the illustrated series connection, the inlet connections 23 and the outlet connections 24, as well as their connecting lines 25, are arranged such that the cooling elements 1 are arranged in a cooling circuit forming a parallel connection, and the cooling fluid flows through the cooling elements 11 in this parallel connection. For this purpose, each cooling element 11 has at least one inlet connection 23 and one outlet connection 24 in both its upper and lower regions.

[0036] The power electronics unit 1 has a shielding device with at least one shielding means for EMC shielding. Such a shielding means is represented by the film 17 in such a preferred first embodiment, in which it is made of electrically conductive material that forms an EMC shielding layer and has an electrically insulating surface layer. Current generated during the EMC shielding is dissipated via the cooling fluid circulating in the cooling circuit and contacting the EMC shielding layer. The cooling fluid is connected to a ground potential (GND), e.g., to a vehicle frame when the power electronics unit 1 is used in an electric vehicle drive.

[0037] The film 17 also represents such a shielding means in a preferred second embodiment in which it is formed from electrically conductive material or has an electrically conductive surface layer and thus provides EMC shielding. In this embodiment, the power modules are electrically insulated on their main side surface facing the film, e.g., by a plastic foam or plastic overmolding or by a molding compound made of non-conductive material or plastic that embeds the electrical and / or electronic components of the power module. Current generated during EMC shielding is discharged via the film 17, which is connected to the ground potential (GND).

[0038] Furthermore, according to a preferred third embodiment, the film 17 can be formed from electrically insulating material without an electrically conductive layer providing EMC shielding. 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 be optionally used in the first and second embodiments of the film 17 explained above. The shielding layer 26 is formed, for example, from a copper sheet. The shielding layer 26 extends flatly and preferably in a central plane of the frame 14. The shielding layer 26 is arranged in the coolant chamber of the cooling element 11 or in the coolant sheath 15.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. The cable 27 is expediently led out through the frame 14.

[0039] Furthermore, the shielding layer 26 can also be attached to the frame 14 such that it is arranged outside the coolant sleeve 15, covers the frame opening surrounded by the frame 14, and lies flat against the coolant sleeve 15. Cooling or heat dissipation from the power module 2 takes place via this shielding layer 26 and the coolant sleeve 15 to the coolant. The shielding layer 26 is expediently thin and flexible enough to adapt to the coolant sleeve 15.

[0040] The shielding layer 26 can also be formed as a deformation-resistant structure, e.g., as a copper sheet, which is attached to the frame 14 of the cooling element 11 and covers the frame opening. The coolant sheath 15 attached to the frame 14 adheres to the shielding layer 26 when pressurized by the coolant. This embodiment is particularly suitable for external cooling elements 11, each of which is delimited by the associated support structure 13. The support structure 13 forms the support surface for the shielding layer 26. According to a modified embodiment, the support structure 13 is firmly connected to the frame 14 and is supported by the frame 14. The cooling element 11 thus has an outer side formed by the support structure 13.The shielding layer 26 is preferably arranged on the outer side of the support structure 13 facing away from the cooling liquid sheath 15, but can also be arranged on the inner side of the support structure 13 facing the cooling liquid sheath 15. In any case, an EMC shield is thus provided on the side of the cooling element 11 on which no power module 2 is located.

[0041] In the power electronics unit 1, the coolant sleeve 15 is thus subjected to the pressure of the coolant flowing through it and bulges out, thereby being applied or pressed against the heated main side surfaces 3 of the two power modules 2 that are to be cooled. The cooling performance can be adjusted via the magnitude of the pressure and the resulting size of the area 19 of the coolant sleeve 15 with which the coolant sleeve 15 rests against the main side surface 3 of the power module 2. The pressure of the coolant is expediently regulated by temperature control. At least one temperature sensor is expediently arranged at the inlet connection 23 or at the outlet connection 24. The pressure of the coolant is regulated, for example, by means of a flow limiter, which, for example,is arranged as a piezomechanical valve in a coolant line leading to the first cooling element and controllably limits the flow of the coolant through the cooling elements.

[0042] List of reference symbols

[0043] 1 power electronics unit

[0044] 2 power module

[0045] 3 Main side area

[0046] 4 Bottom edge

[0047] 5 Contact unit

[0048] 6 Bracket

[0049] 7 circuit carriers

[0050] 8 connectors

[0051] 9 gap

[0052] 10 Cooling device

[0053] 11 Cooling element

[0054] 12 Outside

[0055] 13 Support structure

[0056] 14 frames

[0057] 15 Coolant sleeve

[0058] 16 Coolant chamber

[0059] 17 Slide

[0060] 18 rand

[0061] 19 area

[0062] 20 frame holding part

[0063] 21 lower frame part

[0064] 22 upper frame part

[0065] 23 Inlet connection

[0066] 24 Drain connection

[0067] 25 connecting line

[0068] 26 Shielding layer

[0069] 27 cables

Claims

Patent claims 1 . 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, forming an intermediate space (9), and are opposite one another with their main side surfaces (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 surfaces (3), - wherein the cooling element (11) has a fluid-tight cooling liquid shell (15) which surrounds a cooling liquid chamber (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.

2. Power electronics unit (1) according to claim 1, characterized in that the cooling liquid sheath (15) or at least its flexible surfaces (19) are formed by a flexible film (17).

3. Power electronics unit (1) according to claim 1 or 2, characterized in that the cooling element (11) has a frame (14) supporting the cooling liquid sheath (15).

4. 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 order.

5. Power electronics unit (1) according to one of claims 1 to 4, characterized in that the cooling liquid sheaths (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 in series or in parallel via the inlet and outlet connections (23, 24).

6. 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).

7. 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).

8. 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 sheath (15) and the current generated during the EMC shielding is discharged via the cooling liquid or via a cable (27) connected to the shielding layer (26).

9. 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 adjusting the liquid pressure of the cooling liquid in the cooling liquid casing (15) of the cooling element (11).

10. 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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