Patent Publication Number: US-2023162926-A1

Title: Wound capacitor, pulse-controlled inverter and motor vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to German Patent Application No. DE 10 2021 130 457.1, filed on Nov. 22, 2021, which is hereby incorporated by reference herein. 
     FIELD 
     The present invention relates to a wound capacitor. The present invention further relates to a pulse-controlled inverter having such a wound capacitor and a motor vehicle having such a pulse-controlled inverter. 
     BACKGROUND 
     The drive train of an electric vehicle typically includes a battery, an electric motor and an inverter for converting the DC voltage provided by the battery into the multi-phase AC voltage needed to drive the electric motor. A DC link capacitor is typically assigned to the inverter as an energy buffer. The DC link capacitor is used to decouple the DC voltage source (battery) and the electric drive train. 
     The DC link capacitor is used to smooth the switching operations of the pulse-controlled inverter to the HV vehicle electrical system or the battery. The harmonics created by the switching operations of the inverter are smoothed by the capacitor to stabilize the DC voltage. The feeding DC voltage is thus stabilized with the help of the capacitor. 
     The DC link capacitor used here is a plastic film capacitor (referred to technically as “Folko”,  FIGS.  1  and  2   ), for example, which is wound in an alternating layering of electrically conductive metal layers ( 11 ) and dielectric plastic layers ( 12 ). Together with analogously constructed paper, metal paper, double layer, aluminum and tantalum electrolytic capacitors, such capacitors are collectively referred to as “wound capacitors”. 
     The current flows in the DC link are largely responsible for the losses in the DC link capacitor. The constant fluctuations caused by the switching operations of the power semiconductors produce a ripple current that has to be damped. The ripple current component in the DC link capacitor produces a power loss that is released in the form of heat. Said heat is dissipated to the coolant via plates carrying cooling liquid or other heat sinks, and ultimately to the environment in a coolant radiator. The thus retooled coolant can be returned to the capacitor in a closed circuit. 
     The low thermal conductivity of the film winding allows the surface of the capacitor body to be cooled effectively, but not its interior where, according to the prior art, hot regions (hot spots) sometimes form. 
     Such hot spots limit the performance of the capacitor and therefore also that of the connected pulse-controlled inverter. The overheating of conventional capacitors thus inhibits the performance improvement of drive systems for electric vehicles. 
     DE 10 2013 216 941 A1 and DE 10 2018 215 522 A1 teach the forming of duromer cooling channels for cooling the DC link capacitor of a pulse-controlled inverter in the drive train of an electric vehicle. 
     SUMMARY 
     In an embodiment, the present disclosure provides a wound capacitor, comprising a cooling channel for conducting coolant, wherein the cooling channel comprising an electrically non-conductive and thermally conductive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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    shows the perspective view of a wound capacitor according to the prior art; 
         FIG.  2    shows the structure of the wound capacitor in a schematic longitudinal section: 
         FIG.  3    shows a view of a first variant of an embodiment of the invention corresponding to the view of  FIG.  1   ; 
         FIG.  4    shows a perspective view of a second variant of an embodiment of the invention; 
         FIG.  5    shows a perspective view of a third variant of an embodiment of the invention; and 
         FIG.  6    shows a perspective view of a fourth variant of an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, the present invention provides a wound capacitor, a corresponding pulse-controlled inverter and a corresponding motor vehicle. 
     One advantage of embodiments of the present invention lies in the possibility of optimizing the flow control. In view of the given coolant conducting system, the pressure of the coolant is easily adjustable. 
     In an advantageous embodiment, a configuration of cooling channels using electrically non-conductive, thermally conductive material such as plastic, preferably fiber-reinforced, duromer plastics, which have high temperature resistance and high resistance to the coolants is provided. 
     The use of a water-glycol mixture, which has a high thermal capacity and can therefore better absorb and thus dissipate heat, can furthermore be provided as the coolant. 
       FIGS.  3  and  4    both illustrate a wound capacitor ( 10 ) according to an embodiment of the invention having a cooling channel ( 14 ). The plastic used for the cooling channel ( 14 ) (for example a fiber-reinforced duromer) is thermally conductive, electrically non-conductive and chemically resistant to the coolant, which can be a water-glycol mixture, for example. 
     As looking at  FIGS.  3  and  4    together suggests, the possibilities for arranging such cooling channels ( 14 ) made of plastic are virtually limitless. However, both in terms of production practicality and for optimum cooling, heat dissipation at the central hot spot is recommended. In both variants, therefore, the respective cooling channel ( 14 ) extends coaxially through the wound capacitor ( 10 ). 
     The extensions of the inlet ( 15 ) and the outlet ( 16 ) of the wound capacitor ( 10 ), on the other hand, are different in the shown embodiments: Whereas they are aligned radially to the wound capacitor ( 10 ) in the embodiment according to  FIG.  3   , the inlet ( 15 ) and the outlet ( 16 ) according to  FIG.  4    extend in the axial extension of the wound capacitor ( 10 ) and thus perpendicular to the front-side electrical terminals ( 13 ) thereof. 
     An embodiment can also provide that a plurality of wound capacitors have consecutive radial cooling channels which are interconnected (see  FIG.  5    and  FIG.  6   ). In this case, the capacitors can be connected in parallel or in series via busbars, for example made of copper or aluminum. 
     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.