Patent Publication Number: US-2022225529-A1

Title: Power electronics system with busbars of hollow design for direct capacitor cooling; and electric motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of PCT Appin. No. PCT/DE2020/100259 filed Mar. 30, 2020, which claims priority to DE 102019111111.0 filed Apr. 30, 2019, the entire disclosures of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a power electronics system for an electric motor of a motor vehicle drive, i.e., a drive train of a motor vehicle, such as a car, truck, bus or other utility vehicle, comprising a first busbar, a second busbar electrically insulated relative to the first busbar and at least one capacitor, wherein the at least one capacitor, by way of its first electrode, makes contact with a plate-like receiving region of the first busbar and, by way of its second busbar, makes contact with a plate-like receiving region of the second busbar. The disclosure also relates to an electric motor, which is preferably used as the drive engine of a drive train of a purely electrically or hybrid-powered motor vehicle, comprising this power electronics system. 
     BACKGROUND 
     Generic power electronics systems are already sufficiently known in the prior art. In this respect, DE 10 2016 218 151 A1 discloses an integrated electronics assembly kit comprising at least one busbar, which is fixed to a cooling component via an electrical insulation layer. 
     Further prior art is known from DE 10 2016 219 213 A1. A power electronics system is disclosed herein, wherein a cooling device has at least one heat tube that absorbs part of an amount of waste heat. 
     Thus, in principle, different versions of power electronics systems are known which contribute to cooling the built-in components as efficiently as possible and thus increasing the power density. While in principle it would be possible to increase the number of capacitors or to dimension the capacitors larger in order to transmit greater power, this would in turn involve considerable disadvantages in terms of installation space. 
     Another disadvantage of the designs known from the prior art is that the power electronics systems realized to implement the highest possible power density often have a relatively complex structure. In addition, the feasibility of the power electronics system is often linked to a certain minimum size. 
     SUMMARY 
     Therefore, the object of the present disclosure is to eliminate the disadvantages known from the prior art and, in particular, to implement a power electronics system with a further increased power density, wherein the power electronics system comprises the simplest possible structure and a small number of components. 
     According to the disclosure, this is achieved by the fact that at least one of the two busbars is hollow in design, with the direct formation of a cooling duct. 
     By designing at least one busbar as a waveguide busbar, the busbar that is already present is used directly as part of a cooling device without significantly increasing the total number of components or the installation space requirement. The power density of the corresponding power electronics system can thus be significantly increased once again. 
     Further advantageous embodiments are claimed and explained in more detail below. 
     It is therefore also advantageous if the at least one hollow busbar forms a hollow wall, which is sealed/closed off relative to its surroundings at its lateral end edges. As a result, the busbar is implemented with the largest possible hollow space. 
     In this context, it is additionally advantageous if the first busbar forms a first cooling duct which is connected to an inlet connection of the first busbar that can be connected to a coolant inlet. As a result, a cooling duct of the first busbar can be further connected to a coolant supply in a particularly simple manner during operation. 
     If both busbars, i.e., both the first busbar and the second busbar, are (each) hollow in design with the formation of a cooling duct, the cooling capacity of the cooling device is further improved during operation. 
     It is therefore additionally advantageous if the second busbar has a second cooling duct which is connected to a return connection of the second busbar that can be connected to a coolant return. As a result, a connection on the return side of a coolant supply is also implemented in a particularly simple manner. 
     Furthermore, it is advantageous if the cooling ducts are directly connected to one another. In this context, it has been found to be particularly advantageous if the cooling ducts of the two busbars are hydraulically connected to one another via a connecting element. 
     In this respect, it is also advantageous if the connecting element is designed as a tube. The tube is then connected to the first cooling duct at its first end and connected to the second cooling duct at its second end. This keeps the design particularly simple. The connecting element is preferably implemented as an electrical insulator. 
     With regard to the positioning of the connecting element, in order to generate an effective coolant circuit during operation, it is advantageous if the connecting element is received on an end region of the respective busbar facing away from the return connection and/or the inlet connection. Expressed in other words, this means that the connecting element, viewed in the axial direction of the busbar, is arranged on an axial side of the receiving region facing away from the return connection and the inlet connection. 
     For the connection of the power electronics system, it is advantageous if both busbars form a plurality of mounting regions that are arranged/protruding towards a common side of the at least one capacitor. The mounting regions are preferably implemented as tabs. It is also advantageous in this context if both the (first) mounting regions of the first busbar and the (second) mounting regions of the second busbar lie in a common mounting plane. 
     The disclosure further relates to an electric motor for a motor vehicle, comprising a power electronics system according to the disclosure according to at least one of the previously described embodiments. The power electronics system is used in a typical manner to control the electric motor, i.e., to forward electrical energy supplied to the stator of the electric motor or generated by said stator. 
     Expressed in other words, according to the disclosure, a direct active capacitor cooling with a plurality of waveguide busbars (busbars) is realized. The waveguides (busbars) are used as busbars that make contact with a plurality of capacitors. A non-conductive cooling fluid (liquid) flows through the bus bars to dissipate heat from critical regions. Usually, the majority of losses are caused by a high current density within the busbars. By cooling the busbars, these losses are efficiently avoided and the capacitors can be made smaller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the disclosure is now explained in more detail with reference to figures. 
       In the figures: 
         FIG. 1  shows a longitudinal sectional view of a power electronics system according to the disclosure according to a preferred exemplary embodiment, wherein the formation of two busbars which couple a plurality of capacitors to one another can be clearly seen, 
         FIG. 2  shows a perspective full view of the power electronics system according to  FIG. 1 , and 
         FIG. 3  shows a simplified representation of a possible design of an electric motor comprising the power electronics system according to  FIGS. 1 and 2 . 
     
    
    
     The figures are only schematic in nature and serve only for understanding the disclosure. The same elements are provided with the same reference symbols. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , an embodiment of the power electronics system  1  according to the disclosure can be seen in detail. The power electronics system  1  is illustrated in these representations on the part of a capacitor unit and thus is alternatively also referred to as a capacitor unit. During operation, the power electronics system  1  is used to control an electric motor  20 , as shown schematically in connection with  FIG. 3 . The electric motor  20  comprises, for example, a stator  18  that is fixed to the housing and a rotor  19  that is rotatably arranged relative to the stator  18 . In its preferred area of application, the electric motor  20  is used as a drive engine of a hybrid or purely electrically driven motor vehicle. Thus, when in operation, the electric motor  20  is used in a drive train of the corresponding motor vehicle. The power electronics system  1  is typically electrically coupled to the stator  18  to control the electric motor  20 . As a result, electrical energy can, in principle, be supplied to the stator  18  by the power electronics system  1  or be received by the stator  18 . 
     In  FIGS. 1 and 2 , the essential structure of a power electronics system  1  according to the disclosure can be seen. The power electronics system  1  has two busbars  2  and  3  that are electrically insulated relative to one another. A first busbar  2 , has a first plate-like receiving region  6 , as can be clearly seen in  FIG. 2 . A second busbar  3  has a second plate-like receiving region  8 . The two receiving regions  6 ,  8  are aligned parallel to one another. The two receiving regions  6 ,  8  are essentially rectangular. The two receiving regions  6 ,  8  are also arranged at a distance from one another, so that a receiving space  21  is formed between the two receiving regions  6 ,  8 . A plurality of capacitors  4  are arranged in the receiving space  21 . Alternatively, these capacitors  4  can also each be implemented as a capacitor winding and thus form a common capacitor  4 . 
     The respective capacitor  4  has two electrodes  5 ,  7 . A first electrode  5  of the capacitor  4  makes contact with the first receiving region  6  and thus the first busbar  2 . A second electrode  7  of the capacitor  4  makes contact with the second receiving region  8  and thus the second busbar  3 . The capacitors  4  are firmly fixed between the two busbars  2 ,  3  and attached to the respective busbar  2 ,  3  by their electrodes  5 ,  7 . 
     According to the disclosure, each busbar  2 ,  3  forms a hollow wall  10 , as can be clearly seen in  FIG. 1 . This means that the respective busbar  2 ,  3  is designed to be hollow. An inner hollow space  25  of the respective busbar  2 ,  3  forms a cooling duct  9   a ,  9   b . The first busbar  2  therefore forms a first cooling duct  9   a  of a cooling device  22 . The second busbar  3  therefore forms a second cooling duct  9   b  of the cooling device  22 . In  FIG. 1  it can also be clearly seen that the receiving regions  6 ,  8  of the busbars  2 ,  3  are hollow in design, so that the respective cooling duct  9   a ,  9   b  extends so long that it protrudes beyond all the capacitors  4  of the power electronics system  1  in a longitudinal direction of the busbar  2 ,  3 . The first cooling duct  9   a  protrudes beyond all of the capacitors  4  on the part of their first electrodes  5 ; the second cooling duct  9   b  protrudes beyond all of the capacitors  4  on the part of their second electrodes  7 . 
     As can be seen in connection with  FIG. 2 , each busbar  2 ,  3  is provided with a connection  12 ,  13  via which it is connected to a coolant supply of the cooling device  22  during operation. While the first cooling duct  9   a  is provided with an inlet connection  12  which is formed directly on the first busbar  2  (in the form of a borehole), the second busbar  3  has a return connection  13 , wherein the return connection  13  is connected to the second cooling duct  9   b , which is formed directly on the second busbar  3  (in the form of a borehole). 
     The inlet connection  12  and the return connection  13  are also attached in a hollow protrusion region  23  of the respective busbars  2 ,  3  which form the cooling duct  9   a ,  9   b . Viewed in the longitudinal direction of the busbars  2 ,  3 , the inlet connection  12  and the return connection  13  are arranged to the side of the capacitors  4  on an axial end of the respective busbars  2 ,  3 . In particular, both the inlet and return connections  12 ,  13  are arranged towards a common first axial end region  15   a  of the busbars  2 ,  3 . 
     The two cooling ducts  9   a ,  9   b  are hydraulically connected to one another at a second end region  15   b  of the busbars  2 ,  3  axially facing away from the first end region  15   a . For this purpose, a connecting element  14  is present which is implemented in an electrically insulating manner. The connecting element  14  is implemented as a tube in this embodiment. The connecting element  14  is connected with its first end  26   a  to the first cooling duct  9   a ; with its second end  26   b , the connecting element  14  is connected to the second cooling duct  9   b . It is thus possible to generate a coolant circuit during operation, wherein the coolant, preferably an electrically non-conductive fluid (preferably liquid), initially enters the first cooling duct  9   a  of the first busbar  2  through the inlet connection  12 , flows axially through the first busbar  2  and flows over the region of the connecting element  14  into the second cooling duct  9   b  of the second busbar  3 . The coolant then flows through the second cooling duct  9   b  of the second busbar  3  to the return connection  13 . 
     As can also be seen in connection with  FIGS. 1 and 2 , the busbars  2 ,  3  each have mounting regions  17   a ,  17   b  by means of which, during operation, they are connected to a housing, which is not shown here for the sake of clarity. The first busbar  2  has a plurality of tab-shaped first mounting regions  17   a  arranged at a distance from one another in the longitudinal direction; the second busbar  3  has a plurality of tab-shaped second mounting regions  17   b  arranged at a distance from one another in the longitudinal direction. It can be seen here that the mounting regions  17   a  and  17   b  are located in a common mounting plane. The mounting regions  17   a  and  17   b  are also arranged on a common side. The mounting regions  17   a ,  17   b  are equipped with mounting holes  24  in the form of through holes for receiving a mounting means. 
     Furthermore, it can be seen that mounting holes  24  are also made in the protrusion regions  23  of the first busbar  2  and the second busbar  3 , by means of which the protrusion region  23  can also be used as a mounting region. A mounting hole  24  of the protrusion region  23  of the first busbar  2  is arranged at a distance from the inlet connection  12  and the first cooling duct  9   a . A mounting hole  24  of the protrusion region  23  of the second busbar  3  is arranged at a distance from the return connection  13  and the second cooling duct  9   b.    
     In other words, with this inventive solution, waveguides are used as busbars  2 ,  3 . A non-conductive cooling liquid flows through this, which transports the heat generated from the critical areas. In  FIG. 1 , the interior of a capacitor (capacitor unit  1 ) can be seen. This consists of two busbars (DC busbar plus (first busbar  2 ); DC busbar minus (second busbar  3 )), as well as the non-conductive coolant transfer (connecting element  14 ). The flat windings (capacitors  4 ) are not discussed in detail. As can be seen in  FIG. 2 , the busbars  2 ,  3  are hollow. A non-conductive cooling liquid flows inside the busbars  2 ,  3 . The coolant flows in via the coolant inlet  12 , flows through the DC busbar plus  2  and then flows through the coolant transfer  14  into the DC busbar minus  3 . The liquid flows back to the cooler through the coolant outlet  13 . The majority of the losses occur in the busbars  2 ,  3  due to the high current density. In this concept, the losses are “cooled off” exactly where they arise. This efficient cooling makes it possible to design the condenser  4  to be smaller. This has an effect on the installation space of the entire power electronics system  1 , since there the capacitor  4  represents the largest component in terms of volume. The efficient cooling therefore enables a higher power density. 
     LIST OF REFERENCE NUMBERS 
       1  Power electronics system 
       2  First busbar 
       3  Second busbar 
       4  Capacitor 
       5  First electrode 
       6  First receiving region 
       7  Second electrode 
       8  Second receiving region 
       9   a  First cooling duct 
       9   b  Second cooling duct 
       10  Hollow wall 
       11  End edge 
       12  Inlet connection 
       13  Return connection 
       14  Connecting element 
       15   a  First end region 
       15   b  Second end region 
       16  Side 
       17   a  First mounting region 
       17   b  Second mounting region 
       18  Stator 
       19  Rotor 
       20  Electric motor 
       21  Receiving space 
       22  Cooling device 
       23  Protrusion region 
       24  Mounting hole 
       25  Hollow space 
       26   a  First end 
       26   b  Second end