Patent Publication Number: US-2023164963-A1

Title: Liquid-cooled power electronics unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to German Patent Application No. DE 10 2021 130 926.3, filed on Nov. 25, 2021, which is hereby incorporated by reference herein. 
     FIELD 
     The invention relates to a liquid-cooled power electronics unit. The invention also relates to a power electronics unit of a motor vehicle with an electric traction drive. 
     BACKGROUND 
     Power electronics units are subject to high demands regarding the cooling and the galvanic separation of the high-voltage power semiconductors and a low-voltage circuit for controlling the power semiconductors. Liquid cooling of high-voltage power semiconductors is known from DE 10 2007 050 417 A1. However, in such an arrangement, the low-voltage circuit would have to be provided as a separate unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following: 
         FIG.  1    illustrates a liquid-cooled power electronics unit according to an embodiment of the invention. 
       SUMMARY 
       In an embodiment, the present invention provides a liquid-cooled power electronics unit, comprising a planar circuit board body having conductor tracks, a wet side with a wet space for carrying a dielectric cooling liquid, and a fluidically separated dry side, wherein at least two high-voltage power semiconductors are arranged on the circuit board body on the wet side within the wet space, the high-voltage power semiconductors being cooled by the cooling liquid, and an electronic low-voltage circuit is arranged on the dry side of the circuit board body. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the invention relates to a liquid-cooled power electronics unit with a plurality of high-voltage power semiconductors and with an electronic low-voltage circuit for actuating the high-voltage power semiconductors. An aspect relates to a power electronics unit of a motor vehicle with an electric traction drive, for example to a power electronics unit of a converter for the charging process of the traction battery or for the operation of the engine. 
     In an embodiment, the present invention provides a compact liquid-cooled power electronics unit with an integrated electronic low-voltage circuit which is galvanically separated from the power semiconductors. 
     The liquid-cooled power electronics unit according to an embodiment of the invention has a planar circuit board body having conductor tracks, wherein a wet side, on which a dielectric cooling liquid flows, and a dry side are fluidically separated from each other. The power electronics unit forms, on the wet side, a wet space through which the dielectric cooling liquid flows, wherein all the high-voltage power semiconductors or the entire high-voltage circuit are/is arranged on the wet side of the circuit board body or in the wet space. The high-voltage power semiconductors are electrically connected to each other by conductor tracks mounted on the circuit board body. All the high-voltage power semiconductors are preferably arranged in a single wet space. In contrast, the electronic low-voltage circuit is arranged on the dry side of the circuit board body and is therefore in this way fluidically isolated and separated from the wet side or from the high-voltage power section. 
     A low-voltage circuit in the present case is understood to mean a circuit which has voltages of at most 60 V. The high-voltage circuit operates with voltages of more than 60 V, in particular with voltages of several 100 V up to over 1000 V. The low-voltage circuit and the high-voltage circuit are therefore preferably galvanically separated from each other, wherein this separation is identical to the fluidic separation. Since the lm-voltage circuit controls the high-voltage power semiconductors, at least one potential-separating signal link for transmitting the control signals from the low-voltage circuit to the high-voltage power semiconductors is present between the low-voltage circuit and the high-voltage power semiconductors. The potential-separating signal link can be optical, capacitive and/or inductive. 
     In principle, the high-voltage power semiconductors and the high-voltage power section on the one hand and the low-voltage circuit on the other hand can be arranged next to each other on the same side of the planar circuit board body, wherein the fluidic separation between the high-voltage power section and the low-voltage circuit is formed by a separating wall placed fluid-tight on the circuit board body. 
     Particularly preferably, however, the planar circuit board body itself separates the wet space from the dry space such that the high-voltage power section with the high-voltage power semiconductors is arranged on one base surface of the circuit board body and the low-voltage circuit is arranged on the opposite base surface of the circuit board body. A very compact design of the whole power electronics unit can be realized in this way. 
     Preferably, a heat sink is mounted on the distal side of a high-voltage power semiconductor or of a plurality of high-voltage power semiconductors in each case, said heat sink improving the heat spreading and accordingly increasing the size of the effective heat-exchange surface area. The heat sink can be a metal heat sink but can also consist of a plastic potting material which encloses the power semiconductor in question. The heat sink can have fins or needles for increasing the size of its surface area. 
     Preferably, a metal plate is integrated into the plastic circuit board body, said metal plate extending over most of the base surface of the circuit board body and parallel to both base surfaces of the circuit board body. The metal plate is molded into the circuit board body in an electrically isolated manner. The metal plate firstly serves for better heat distribution or heat spreading and secondly serves in particular for the mechanical stabilization of the circuit board body, the wet side of which can be subjected to a certain overpressure of the dielectric cooling liquid. Preferably, the metal plate is a thick copper plate. 
     Preferably, a sensor for ascertaining a physical quantity of the dielectric cooling liquid is arranged on the wet side of the circuit board body, said sensor being connected to the low-voltage circuit so as to convey information to it. The sensor determines, for example, the temperature of the cooling liquid, its degree of contamination, its conductivity and/or its flow rate. 
     An exemplary embodiment of the invention is explained in more detail in the following text with reference to the drawing. The FIGURE schematically shows in longitudinal section a liquid-cooled power electronics unit with a planar circuit board body which fluidically and electrically separates the wet side that has a dielectric cooling liquid from the dry side on which an electronic low-voltage circuit is arranged. 
     The FIGURE schematically illustrates a liquid-cooled power electronics unit  10  which, for example, forms a converter in a motor vehicle with an electric traction drive. The power electronics unit  10  has a planar circuit board body  20  which is fitted with a plurality of electronic components on both sides. The circuit board body  20  fluidically and galvanically separates a wet side W and a dry side D from each other. On the wet side W, the power electronics unit  10  forms a fluidically closed wet space  30  in which a dielectric cooling liquid  100  flows between a cooling-liquid inlet  35  and a cooling-liquid outlet  36  of the wet space  30 . 
     On the wet side W of the circuit board body  20 , a plurality of high-voltage power semiconductors  40 ,  40 ′ are arranged on the circuit board body  20  within the wet space  30  and are directly electrically connected to other electronic components via conductor tracks  22  arranged on the wet side W of the circuit board body  20 . The operating voltage of the high-voltage power semiconductors  40 ,  40 ′ is several 100 V, for example 400 V or 800 V. 
     Each power semiconductor  40 ,  40 ′ has a heat sink  80 .  82  which brings about heat spreading and an increase in size of the heat-exchanging surface. One heat sink  80  is in the present case a metal heat sink which is provided with a multiplicity of distally protruding cooling fins and is thermally coupled, for example is adhesively bonded, to the power semiconductor  40  in question. The other heat sink  82  is in the present case formed of a plastic potting body  84  which closes off the power semiconductor  40 ′ in question in a fluid-tight manner since the latter is sensitive to liquids. The potting-body heat sink  82  likewise forms distally protruding cooling fins. 
     An electronic low-voltage circuit  50  is provided on the dry side D which in the present case forms an open dry space  32  which can alternatively also be closed, said low-voltage circuit being operated with an operating voltage of at most 60 V. The low-voltage circuit  50  controls, regulates and monitors the high-voltage circuit  42  formed of the high-voltage power semiconductors  40 ,  40 ′. The high-voltage power semiconductors  40 ,  40 ′ are in particular actuated by the low-voltage circuit  50 . 
     The planar circuit board body  20  is formed of an electrically non-conductive plastic base body  22  in which is embedded, approximately in the center, a copper metal plate  24  which is parallel to both base surfaces, mechanically stabilizes the circuit board body  20 , in particular in regard to normal forces, and furthermore brings about extensive heat spreading of the heat generated in the power semiconductors  40 ,  40 ′. 
     The high-voltage power semiconductors  40 ,  40 ′ are connected to the low-voltage circuit  50  via a potential-separating signal link  60  so as to convey information to said low-voltage circuit. Furthermore, a sensor  70 , on the wet-space side, for ascertaining a plurality of physical quantities of the cooling liquid  100  is also connected to the low-voltage circuit  50  via the mentioned signal link so as to convey information in both directions. The sensor  70  ascertains, inter alia, the temperature, the electrical conductivity and the flow rate of the cooling liquid  100 . 
     The signal link  60  is formed of an inductive transceiver element  62  on the wet side W and a corresponding inductive transceiver element  61  on the dry side D. The circuit board body metal plate  24  has in this region an opening  25  which permits the inductive transmission through the circuit board body  20  in this region. 
     The low-voltage circuit  50  is electrically connected to a controller on board the vehicle via a connector plug  90 . 
     While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.