Patent Publication Number: US-2021168965-A1

Title: Integrated thermal-electrical component for power electronics converters

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and benefit of U.S. Provisional patent application Ser. No. 62/942,990 filed Dec. 3, 2019, which is fully incorporated by reference and made a part hereof. 
    
    
     BACKGROUND 
     Power electronic converters interface between energy sources and loads. In many sizes of power systems, power electronic converters can increase the controllability and flexibility of the system. The share of electricity flowing through power electronics is forecasted to increase from 30% in 2005 to 80% in 2030, increasing the demand for lighter, smaller, and more efficient converters. (1) A typical power converter includes active components, passive components, and a cooling component. The cooling component is sometimes a passive component, such as a heat sink. 
     As noted above, typical power converters include both active and passive components. Both active and passive components cause losses in the system. Advancements in power semiconductor technology have reduced the size, weight and power loss of active components in power converters. Today, in some power converters, passive components are approximately 30%-70% of the total weight of the converter, 30%-70% of the total volume of the converter, and cause 30%-40% of the power lost in the converter. (2)-(5) Examples of passive components include DC-link capacitors, differential mode filters, and common mode filters. 
     In some power converters, the DC-link capacitor is used to decouple the dynamics between the converter and its source. The DC-link capacitor may be a large component, and the failure of the DC-link capacitor can cause converter failure. Prior efforts have focused on replacing the DC-link capacitor with active components, however circuits with additional active components may increase the complexity and power loss of the system. (7)-(9) 
     In some power converters, a differential mode (DM) filter is implemented. The DM filter may be used to filter the high-frequency ripple at the output of the power converter. The DM filter may require customization to the converter design. The DM filter also contributes to the power losses, weight, and volume of the converter. 
     In some power converters, a common mode (CM) filter is implemented. The CM filter may be used to suppress unwanted interference in the CM path. This interference may be described as ground leakage current, bearing current, or CM noise. Control or modulation-based methods can reduce CM interference up to the switching frequency. 
     A passive CM filter may then be required to suppress the noise from the switching frequency to tens of MHz defined by the electromagnetic interference (EMI) standards. There are a variety of methods that can be employed to reduce the CM filter size such as adding an active circuit, creating a balancing circuit, or using high precision control combined with a passive circuit. (16)-(19) Generally a CM filter is required to comply with EMI standards due to the presence of parasitic capacitance. 
     Further, the power electronics cooling system may be responsible for about a third of the total converter weight, and multiple thermal resistances present between the hot spot and the cooling medium often inhibit the thermal performance and demand large heat transfer surface areas for proper heat dissipation. (10) In electronics cooling, thermal interface materials (TIMs) serve as thermal pastes that join the electronic devices to their respective heat sinks. Efforts to reduce the thermal resistance of a TIM may be limited by 1) the low thermal conductivity of electric insulation materials, and 2) contact resistance (air gap) between the baseplate and TIM. Direct cooling methods such as impinging jet and embedded microchannels have been proposed to address the thermal challenges related to TIMs, but these approaches may require intricate cooling infrastructure, high cost, and access to limited cutting-edge manufacturing technology. (20)-(22) 
     Therefore, what is needed are devices and systems implementing an integrated thermal-electrical component to solve above mentioned issues. In particular, devices and systems implementing an integrated thermal-electrical capacitor. 
     SUMMARY 
     In one aspect, the present disclosure relates to a heat sink capacitor. In one embodiment, the heat sink capacitor includes: a positive (P) bus, wherein the P bus is comprised of electrically conductive material; a negative (N) bus, wherein the N bus is comprised of electrically conductive material; a first dielectric material; a second dielectric material; and a heat sink comprising a first side and a second side, the first side of the heat sink attached to the first dielectric material and the second dielectric material, wherein the first dielectric material and the second dielectric material are separated by a portion of the heat sink, wherein the first dielectric material electrically insulates the P bus from the first side of the heat sink and the portion of the heat sink that separates the first dielectric material and the second dielectric material to form a first capacitor, and wherein the second dielectric material electrically insulates the N bus from the first side of the heat sink and the portion of the heat sink that separates the first dielectric material and the second dielectric material to form a second capacitor. 
     In one embodiment, the heat sink capacitor includes a printed circuit board; a circuit component attached to the printed circuit board, wherein the circuit component is electrically connected to at least one of the P bus or the N bus and the printed circuit board is separated from the P bus and the N bus by a non-conductive or a semiconductive material. 
     In one embodiment, the circuit component is a switching component. 
     In one embodiment, the switching component is a gallium nitride power transistor. 
     In one embodiment, the switching component is a silicon carbide power transistor. 
     In one embodiment, the P bus and/or the N bus each comprise a bus plate and are configured to maximize the surface area of each of the bus plates. 
     In one embodiment, the bus plates are each configured to include a plurality of fins. 
     In one embodiment, the first side of the heat sink is configured to maximize a surface area of the first side of the heat sink. 
     In one embodiment, the first side of the heat sink includes a plurality of fins. 
     In one embodiment, the first dielectric material and the second dielectric material are selected from the group consisting of BaTiO 3 , barium strontium titanate, SrTiO 3 , and TiO 2 . 
     In one embodiment, the first dielectric material is not the same as the second dielectric material. 
     In one embodiment, one or both of the first dielectric material and the second dielectric material are BaTiO 3 . 
     In one embodiment, the circuit component is a power semiconductor 
     In one embodiment, the second side of the heat sink comprises a pin-fin heat sink whose geometry could be plate-fin, porous, and dendritic. 
     In another aspect, the present disclosure relates to a power electronic converter system. In one embodiment, the system includes: a printed circuit board; a circuit component attached to the printed circuit board; and a heat sink capacitor, wherein the heat sink capacitor comprises: a positive (P) bus plate, wherein the P bus plate is comprised of electrically conductive material; a negative (N) bus plate, wherein the N bus is comprised of electrically conductive material; a first dielectric material; a second dielectric material; and a heat sink comprising a first side and a second side, the first side of the heat sink attached to the first dielectric material and the second dielectric material, wherein the first dielectric material and the second dielectric material are separated by a portion of the heat sink, wherein the first dielectric material electrically insulates the P bus plate from the first side of the heat sink and the portion of the heat sink that separates the first dielectric material and the second dielectric material to form a first capacitor, and wherein the second dielectric material electrically insulates the N bus plate from the first side of the heat sink and the portion of the heat sink that separates the first dielectric material and the second dielectric material to form a second capacitor. 
     In one embodiment, the circuit component of the power electronic converter system is a switching component. 
     In one embodiment, the switching component of the power electronic converter system is switched at a frequency of 1 MHz or greater. 
     In one embodiment, the switching component of the power electronic converter system is a gallium nitride power transistor. 
     In one embodiment, the first dielectric material and/or the second dielectric material of the power electronic converter system is selected from the group consisting of BaTiO 3 , barium strontium titanate, SrTiO 3 , and TiO 2 . 
     In one embodiment, the first dielectric material of the power electronic converter system is not the same as the second dielectric material. 
     In one embodiment, the first dielectric material of the power electronic converter system and/or the second dielectric material is BaTiO 3 . 
     In one embodiment, a capacitance of the heat sink capacitor of the power electronic converter system is sufficient for the heat sink capacitor to act as a DC-link capacitor for the power electronic converter. 
     In one embodiment, the P bus plate of the power electronic converter system is attached to a first switching component, and the N bus plate is attached to a second switching component, and the printed circuit board is separated from the P bus plate and the N bus plate by a non-conductive or a semiconductive material. 
     In one embodiment, the P bus plate of the power electronic converter system and/or the N bus plate are configured to maximize the surface area of each of the bus plates. 
     In one embodiment, each of the bus plates of the power electronic converter system are configured to include a plurality of fins. 
     In one embodiment, the first side of the heat sink of the power electronic converter system is configured to maximize a surface area of the first side of the heat sink. 
     In one embodiment, the first side of the heat sink of the power electronic converter system includes a plurality of fins. 
     In one embodiment, the circuit component of the power electronic converter system is a power semiconductor. 
     In one embodiment, the second side of the heat sink of the power electronic converter system includes a pin-fin heat sink whose geometry could be plate-fin, porous, and dendritic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments and together with the description, serve to explain the principles of the disclosed technology. 
         FIGS. 1A-1F  are illustrations comparing a conventional power converter with a power converter that uses integrated thermal/electrical components, including circuit schematics and equivalent circuits of the respective converters. 
         FIG. 2  is a cross-sectional view of a power converter incorporating a capacitive heat sink (CapSink) structure. 
         FIG. 3  is an illustration of an implementation of the disclosed CapSink structure in an embodiment incorporating a pin fin heat sink. 
         FIG. 4  is block diagram of an integrated thermal/electrical component. 
     
    
    
     DETAILED DESCRIPTION 
     Before the present methods and systems are disclosed and described, it is to be understood that the methods and systems are not limited to specific synthetic methods, specific components, or to particular compositions. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. 
     Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes. 
     Disclosed are components that can be used to perform the disclosed methods and systems. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutation of these may not be explicitly disclosed, each is specifically contemplated and described herein, for all methods and systems. This applies to all aspects of this application including, but not limited to, steps in disclosed methods. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods. 
     Some references, which may include various patents, patent applications, and publications, are cited in a reference list and discussed in the disclosure provided herein. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to any aspects of the present disclosure described herein. In terms of notation, “(n)” corresponds to the n th  reference in the list. For example, (3) refers to the 3 rd  reference in the list, namely H. Akagi, T. Yamagishi, N. M. L. Tan, S. Kinouchi, Y. Miyazaki and M. Koyama, “Power-Loss Breakdown of a 750-V 100-kW 20-kHz Bidirectional Isolated DC-DC Converter Using SiC-MOSFET/SBD Dual Modules,” IEEE Transactions on Industry Applications, vol. 51, no. 1, pp. 420-428, January-February 2015. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. 
     The present methods and systems may be understood more readily by reference to the following detailed description of preferred embodiments and the Examples included therein and to the Figures and their previous and following description. 
       FIGS. 1A-1F  are a comparison of a conventional power converter with a power converter that uses integrated thermal and electrical components, including circuit schematics and equivalent circuits.  FIGS. 1A-1C  depict a conventional power converter. The heat sink of the conventional power converter is electrically insulated from the power semiconductors. To achieve electrical insulation and thermal conductance, a layer of thermal interface material (TIM) is be placed between the heat sink baseplate and power semiconductor. This type of structure may cause a steep temperature gradient across the TIM, and may also induce parasitic capacitance between power semiconductors and ground (because the heat sink is typically grounded). The conventional structure therefore may include a short path for common mode (CM) electromagnetic interference (EMI) noise and result in switching losses. 
     In the embodiment shown in  FIGS. 1D-1F , the integrated thermal and electrical component is a heat sink capacitor (CapSink). With reference to the box labelled “Proposed Power Converter with Integrated Thermal/Electrical Components,” some embodiments of the disclosed device eliminate the common mode and differential mode (DM) filter capacitors. In these embodiments, the DC-link capacitor may be considered to be the CapSink. 
     Further, in some embodiments, no thermal interface material is required to join the exemplary power semiconductor or other circuit component to the heat sink. If no thermal interface material is used, the size of the heat sink may be further reduced. Additionally, without thermal interface material, the parasitic capacitance of the heat sink is eliminated. In a conventional electrical converter, a parasitic capacitance exists due to the configuration of heat sink and thermal interface material. This parasitic capacitance may be characterized as a low-impedance path at operational frequencies. In some embodiments where the thermal interface material has been removed, the grounding impedance and motor impedance can be used to suppress CM noise and eliminate the requirement for a CM filter. 
     Similarly, in some configurations of a power converter using a CapSink, the DM inductance is on the order of μH. The DM inductance therefore may be significantly smaller than the inductance of the load (such as a motor) and the cable connecting the load to the converter. Therefore, the DM filter may also be eliminated from the power converter in some embodiments of a CapSink power converter. 
     With reference to  FIG. 1D , the integrated heat sink/busbar/DC-link capacitor reduces the complexity of the exemplary power converter. In some embodiments, the heat sink baseplate may be divided into three parts as shown in  FIGS. 1D and 1E : P bus, N bus, and Neutral. The P bus, N bus and Neutral are insulated from the heat sink by a dielectric material. Switching components may be attached to the N bus plate and P bus plate. In the embodiment shown in  FIGS. 1D-1F , the dielectric material is Barium Titanate (BaTiO 3 ) base ceramic material. The neutral may comprise the main heat sink structure while the P bus and N bus may be part of heat sink baseplate and DC busbar. A plate-pin shaped aluminum structure between P bus, Neutral, and N bus may function as the electrodes of the two integrated capacitors. The dielectric strength of BaTiO 3  allows a large number of fins to be inserted for an increased overlapping area, and the permittivity of BaTiO 3  yields 100 μF-level capacitance without further increasing the heat sink size. The use of dielectric materials other than BaTiO 3  is contemplated to obtain different thermal and electrical characteristics in other embodiments. The conventional power converter circuit schematic ( FIG. 1B ) uses DC-link capacitors separate from the heat sink, resulting in a more complicated power converter design. 
     In a non-limiting example, the power semiconductors are soldered directly onto the baseplate. Since (1) the temperature rise between the power semiconductor and the baseplate is negligible; (2) the surface area between the baseplate and BaTiO 3  is significantly larger; and (3) BaTiO 3  exhibits relatively high thermal conductivity compared to conventional TIMs, the proposed design can achieve higher heat transfer than TIM-based structures. Further, in some embodiments, the parasitic CM capacitors are eliminated as the power semiconductors are no longer insulated from the heat sink. 
     With reference to the common mode equivalent circuit of both the conventional power converter ( FIG. 1C ) and an embodiment of the disclosed power converter ( FIG. 1F ), the embodiment of the disclosed power converter can be represented by a simpler common mode equivalent circuit. The simpler common mode equivalent circuit representing a power converter implementing a CapSink eliminates some components of the conventional power converter. In some embodiments, the capacitance of the heatsink capacitor is sufficient for the heat sink capacitor to act as a DC-link capacitor for a power electronic converter. 
       FIG. 2  depicts the mechanical structure of a power converter  200  including a CapSink. The structure of a heat sink integrated DC-link capacitor  202  includes an N bus plate  204 , which is connected to a dielectric material  206  that electrically insulates the heat sink  208  from the N bus plate  204 . Similarly, the P bus plate  210  is insulated from the heat sink  208  with dielectric material  207 . The dielectric materials  206   207  may be BaTiO 3  or other dielectric materials including barium strontium titanate, SrTiO 3 , and TiO 2 . Additionally, the dielectric materials  206   207  may be different materials. The dielectric materials  206   207  may be separated by a portion of the heat sink  208 . Electrical traces  212  may electrically connect the power semiconductor  212  to the N bus plate  204  and P bus plate  210 . Other circuit components  214  not joined to the CapSink may be placed on the printed circuit board  216 . The N bus and P bus may include fins and other geometries to alter the electrical and thermal characteristics of the CapSink. The heat sink  208  may be designed to maximize the surface area of the heat sink  208 . The N bus plate and P bus plate may also be designed to maximize the surface areas of the N bus plate and P bus plate. 
       FIG. 3  illustrates the mechanical design of a non-limiting example of a converter system configured to implement a CapSink. The embodiment illustrated in  FIG. 3  is a high power-density propulsion inverter. The bottom surface of the power converter depicted in  FIG. 3  is a heat sink, while the top surface depicts a power converter circuit implementing a CapSink. The heat sink design may be a pin-fin design, plate-fin design, dendritic, porous, or any other geometry. The specifications of the proposed embodiment are detailed in Table 1. The embodiment described in Table 1 and illustrated in  FIG. 3  uses Gallium Nitride (GaN) power transistors with MHz-level switching frequency because GaN transistors have lower turn-off switching loss than turn-on loss. However, different embodiments may use other transistor compositions and technologies, or other switching devices. For example, in some embodiments the switching component is a silicon carbide power transistor. Additionally, the embodiment described in Table 1 is configured to apply variable frequency modulation and ensure zero-current switching (ZCS) at the whole fundamental period. Embodiments implementing ZCS have zero-current turn-on, but increased turn-off current. Therefore, in some embodiments implementing ZCS, the switching loss will be significantly reduced. Furthermore, the embodiment described in Table 1 and illustrated in  FIG. 3  does not require any magnetic components or electrolytic capacitors due to the configuration of the CapSink. Alternative embodiments implementing different switching durations and frequencies are also possible. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Power Rating 
                 30 
                 kW 
                 DC-link cap 
                 47 
                 μF 
               
            
           
           
               
               
               
               
            
               
                 Efficiency 
                 99.3% @50% load 
                 Cooling Method 
                 Air Cooled 
               
               
                 @1 MHz 
                 99.0% @100% load 
               
            
           
           
               
               
               
               
               
            
               
                 Input Voltage 
                 416 Vdc-525 Vdc 
                 Target junction 
                 &lt;90 
                 C. 
               
               
                   
                   
                 temperature 
               
               
                 Output Voltage 
                 270 Vac l-l 
                 Heat sink thermal 
                 0.08 
                 C./W 
               
               
                   
                   
                 resistance 
               
            
           
           
               
               
               
               
               
               
            
               
                 Fundamental 
                 2000 
                 Hz 
                 Heat sink mass 
                 600 
                 g 
               
               
                 frequency 
               
               
                 Switching 
                 ~1 
                 MHz 
                 Total mass 
                 &lt;800 
                 g 
               
               
                 frequency 
               
            
           
           
               
               
               
               
               
            
               
                 Circuit 
                 Interleaved three 
                 Power Density 
                 &gt;60 
                 kW/L 
               
               
                 Topology 
                 phase; Zero current 
                   
                 &gt;37 
                 kW/kg 
               
               
                   
                 turn-on 
               
               
                   
               
            
           
         
       
     
       FIG. 4  depicts a block diagram overview of the basic structure of an integrated thermal and electrical capacitor  402 . A bus  404  is joined to a dielectric material  406 , which in turn is connected to a heat sink  408 . The bus  404  is connected to a circuit component  410 . Both the bus  404  and circuit component  410  are electrically isolated from the heat sink  408  by the dielectric  406 . The heat sink  408 , the bus  404  and the dielectric material  406  may be configured in different geometries to optimize different thermal and electrical properties. These geometries include configurations of fins, pins, and other shapes. 
     While the methods and systems have been described in connection with preferred embodiments and specific examples, it is not intended that the scope be limited to the particular embodiments set forth, as the embodiments herein are intended in all respects to be illustrative rather than restrictive. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification. 
     Throughout this application, various publications may be referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the methods and systems pertain. 
     It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims. 
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