Abstract:
In a power electronics system of a next generation vehicle, a power module is provided including a thermoelectric device which is provided in a thermally conductive path between a power device and a cooling plate such that the thermoelectric device creates useful electric power from the waste heat of the power device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Exemplary aspects of the present invention relate to the use of a thermoelectric device to recover waste heat from a semiconductor device in a power electronic system of a hybrid electric vehicle. 
         [0003]    2. Discussion of the Background 
         [0004]    It is widely known that land vehicles, including automobiles, have a large influence on the global environment. One such environmental impact concerns the production and transport of fuel required for vehicles. A second environmental impact is the resultant emissions that are a byproduct of the combustion of the fuel utilized by vehicles for propulsion. 
         [0005]    Next generation vehicles, including hybrid electric vehicles, are one of several ways of addressing the need to reduce the expenditure of non-renewable fuels. Hybrid Electric Vehicles increase the overall (sometimes called well-to-wheel) efficiency of the vehicle by supplementing the power requirements of the combustion engine with an electric machine. Accordingly, hybrid electric vehicles exhibit twin environmental benefits of using less fuel and emitting fewer pollutants. Though typically more fuel efficient than conventional combustion vehicles, hybrid electric vehicles are also optimized to achieve higher levels of efficiency. 
         [0006]    The propulsion drive of a Hybrid Electric Vehicles typically consists of a combustion engine and one or more electric drive components. These electric drives or electric machines are arranged in either series or parallel with the combustion engine. 
         [0007]    In a series arrangement, the electric machine(s) typically provide all of the motive force for the vehicle and the combustion engine typically provides a means for providing electric energy for the electric machine(s). A single electric machine may be used in conjunction with a power splitting device, such as a differential, to provide the motive force to the vehicle wheels. Alternatively, multiple electric machines may be coupled through gear reductions and shafts to the wheels, or so-called wheel-motors may be integrated into the wheel hubs. 
         [0008]    A fuel cell engine may be substituted for the combustion engine in a series hybrid electric vehicle arrangement. Other means of producing electric energy such as gas turbines, hydraulic motors, or the like may also be substituted. 
         [0009]    Conversely, in a parallel Hybrid Electric Vehicle arrangement the combustion engine and the electric machine(s) each provide motive force for the vehicle. That is, torque from the engine is combined with torque from the electric machine(s) to propel the vehicle. A single electric machine is typically provided along the output shaft of the engine prior to the input shaft of the transmission. Alternatively, wheel motors may provide torque to axle shafts that are propelled by the combustion engine. 
         [0010]    Hybrid Electric Vehicles may also combine series and parallel architectures. Such a system combines the electric machines and the combustion engine such that an electric machine may provide motive force alone or in parallel with the combustion engine. Furthermore, in the series/parallel Hybrid Electric Vehicle system another electric machine may simultaneously generate electricity or also provide motive force. This architecture sometimes called a power-split hybrid electric drive, can seamlessly change between engine-only, electric-only, or engine and electric propulsion. 
         [0011]    Regardless of the particular architecture, the electric machines of a Hybrid Electric Vehicle are typically operated by alternating current (AC). The electric machines may be of the synchronous or asynchronous variety. One example of a synchronous AC machine is a permanent magnet machine which utilizes permanent magnets in the rotor to induce an electric field. A typical asynchronous electric machine in a hybrid electric machine may be an AC induction machine that utilizes an AC current to induce the magnetic field in the rotor. 
         [0012]    Hybrid Electric Vehicles often utilizes an electrical energy storage device such as a battery, ultra-capacitor or the like. These energy storage devices store energy for usage by the electric machines. The ability to store electric energy and later use this energy to provide motive force, is one reason a Hybrid Electric Vehicle is more energy efficient than a conventional vehicle. The energy storage device typically transfers the stored electric energy to electric machines via direct current. 
         [0013]    The electric machines of a Hybrid Electric Vehicle are typically operated via 3-phase alternating current which energize poles of the stator causing the rotor to rotate. This 3-phase alternating current is typically provided by a power inverter which inverts the DC energy from the energy storage device into 3-phase AC for use by the electric machines. 
         [0014]    Power inverters may include several power modules which include several power devices. These power devices are switches which change the single phase direct current into 3-phase alternating current. The power devices may be one of an Insulated Gate Bipolar Transistor (IGBT), Metal Oxide Semiconductor Field-Effect Transistor (MOSFET), Schottky diode, etc. 
         [0015]    Power devices produce heat while operating that must be dissipated to maintain performance. Typically the excess heat is managed in order to maintain operation of the power device. Excess heat can cause premature failure of the power device or may cause the power device to operate inefficiently. 
         [0016]    Power electronic systems are typically cooled by heat sinks, water jackets, so-called cold plates and the like. Typically the power electronic systems dissipate heat via one of these devices to a fluid which carries the heat away from the power electronic device. These fluids may be gaseous (air for example) or liquid (water for example). 
         [0017]    As with many technologies, the trend in power electronics systems is to create higher power density devices with a smaller size. However, the increase in power density of the power electronic system also necessitates improvements in heat dissipation. 
         [0018]    Furthermore, increasing the thermodynamic efficiency is a common goal of many devices. One known means of increasing the thermodynamic efficiency of a system is through the use of thermoelectric devices. 
         [0019]    One application of a thermoelectric device is to provide electric power based on a temperature differential. When opposite junctions of a thermoelectric device are respectively heated and cooled, a voltage potential is created by the temperature differential. This “Seebeck” voltage can then be used as a power source. 
         [0020]    Land vehicles have utilized thermoelectric devices to make use of the Seebeck effect for the direct conversion of waste heat of a combustion engine into electricity. In particular, thermoelectric devices have been arranged in between an exhaust pipe and a heat sink in order to produce electricity. 
       SUMMARY OF THE INVENTION 
       [0021]    In an exemplary embodiment, a power module of a power electronics system of a hybrid electric vehicle includes a power device that switches electric power, a thermoelectric device that produces a harvested electric power, and a plate that dissipates heat produced by the power device. 
         [0022]    The thermoelectric device is provided in a first thermal path between the power device and the plate, such that a temperature differential across the thermoelectric device is formed between a respective top and bottom portions of the thermoelectric device. 
         [0023]    Furthermore, the harvested electric power is produced by the thermoelectric device based on the temperature differential. 
         [0024]    The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0026]      FIG. 1  is perspective view illustrating a first embodiment of the power electronics module including a thermoelectric device. 
           [0027]      FIG. 2  is a schematic view of the first embodiment illustrating the power electronics module and the thermoelectric device. 
           [0028]      FIG. 3  is schematic view illustrating a second embodiment of a power electronics module including a thermoelectric device. The power electronic module is shown utilizing wire (or ribbon) bonds. 
           [0029]      FIG. 4  is a schematic view illustrating a third embodiment of the power electronics module including a thermoelectric device. The power electronics module is shown utilizing a lead frame. 
           [0030]      FIG. 5  is a schematic view illustrating uses for the harvested electric power from the thermoelectric device of the preferred embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
       First Exemplary Embodiment 
       [0032]      FIG. 1  depicts a perspective view of a first exemplary embodiment of a power module  1  that includes power device  20 .  FIG. 2  schematically illustrates the first exemplary embodiment of the power module as seen from a front side view. The power device  20 , schematically depicted as a transistor, is a MOSFET but may be substituted with a similar device such as an IGBT. The power device  20  is mounted on a substrate  70  via a bonding layer  40 . The bonding layer  40  may be a solder layer, including for example, Tin Lead (SnPb), Gold Tin (AuSn), or Gold Germanium (AuGe). The bonding layer may also be a sintered layer, including for example nano-Silver (Ag). 
         [0033]    Also attached to the substrate  70  is the power device bottom side terminal  22 . The power device bottom side terminal  22  may consist of Aluminum (Al), Copper (Cu), or alloys thereof. The power device bottom side terminal  22  communicates with a first electrical bus, not shown. The power device bottom side terminal  22  also communicates with the power device  20  via circuitry of the substrate, not shown, and the bonding layer  40 . Accordingly, it is advantageous for the power device bottom side terminal  22  and the bonding layer  40  to each be capable of conducting electricity. 
         [0034]    A portion of the top side of the power device  20  contacts the power device top side terminal  21 . Similar to the power device bottom side terminal  22 , the power device top side terminal  21  may consist of Aluminum (Al), Copper (Cu), or alloys thereof. The power device top side terminal  21  communicates with a second electrical bus, not shown. The power device top side terminal  21  may communicate directly with the power device  20  or may communicate via a conductive layer. 
         [0035]    One of the power device top side terminal  21  and the power device bottom side terminal  22  is an electrical input for the power device  20 . The other of the power device top side terminal  21  and the power device bottom side terminal  22 , is an output of the power device  20 . Based on a control process, the power device  20  switches a conductive path between the power device top side terminal  21  and the power device bottom side terminal  22 . 
         [0036]    A bottom portion of the substrate  70  contacts an insulation layer  31 . The insulation layer  31  includes an electrically insulating material. The insulation layer  31  advantageously is a dielectric layer. Furthermore, the insulation layer  31  advantageously has a high thermal conductivity. Accordingly, the insulation layer  31  is an electric insulator and a thermal conductor. Typical materials for the insulation layer  31  may be Epoxy Resin, Alumina Cement (Al 2 O 3 ), Aluminum Nitride (AlN), Aluminum Silicon Carbide (AlSiC), or similar. 
         [0037]    Below the insulation layer  31 , in a direction opposite of the power device  20 , is a base plate  50  which communicates with the insulation layer  31 . The base plate  50  is advantageously a thermally conductive material such that heat may be dissipated away from the power device  50 . The base plate  50  may be made of Aluminum, Copper, or an alloy such as Aluminum Silicon Carbide. 
         [0038]    The base plate  50  also advantageously exhibits low coefficient of thermal expansion. In particular, a base plate  50  including Aluminum Silicon Carbide exhibits properties of both high thermal conductivity and low coefficient of thermal expansion. The ceramic Silicon Carbide particles have a low coefficient of thermal expansion. Whereas, the Aluminum matrix which supports the Silicon Carbide has high thermal conductivity. 
         [0039]    An insulation layer  30  contacts a top portion of the power device top side terminal  21 . The insulation layer  30 , like the insulation layer  31 , is advantageously electrically insulating and thermally conductive. The insulation layer  30  may also be made of Epoxy Resin, Alumina Cement (Al 2 O 3 ), Aluminum Nitride (AlN), Aluminum Silicon Carbibe (AlSiC), or the like. The insulation layer  30  covers the power device top side terminal  21  and prevents an electric current from flowing in an unintended electrical path, i.e. a path other than the second electrical bus, not pictured. 
         [0040]    The insulation layer  30  is provided between the power device  20  and a thermoelectric device terminal  11 . The thermoelectric device terminal  11  advantageously includes a thermally conductive material such as Copper or Aluminum. The thermoelectric device terminal  11  is also advantageously electrically conductive. 
         [0041]    A thermoelectric device  10  is provided to contact the thermoelectric terminal  11 . The thermoelectric device  10  is a device that produces electrical power when opposite sides of the device have a thermal differential. As can be seen in  FIG. 1 , the thermoelectric device  10  includes a positive (+) junction  10   a  and a negative (−) junction  10   b . Further, the thermoelectric device  10  is advantageously a Bismuth Antimony Telluride (BiSbTe) device. However, similar thermoelectric device materials may also used. 
         [0042]    A bottom portion the thermoelectric device  10  is in communication with the thermoelectric terminal  11 . Moreover, the thermoelectric device  10  is in electric and thermal communication with the thermoelectric terminal  11 . Furthermore, the thermoelectric device  10  is in thermal communication with the power device  20 . Specifically, a bottom portion of thermoelectric device  10  is in thermal communication with the power device  20  via the power device top side terminal  21 , the insulation layer  30 , and the power device terminal  11 . Accordingly, the bottom portion of the thermoelectric device  10  is warmed by heat produced by the power device  20 . 
         [0043]    A top portion of the thermoelectric device  10  is in communication with electrically and thermally conductive layer  12 . The conductive layer  12  electrically connects positive junction  10   a  and negative junction  10   b  of the thermoelectric device  10 . Accordingly a current path is formed between positive junction  10   a  and negative junction  10   b.    
         [0044]    A thermally conductive and electrically isolating insulation layer  13  is provided between the conductive layer  12  and heat pipe  60 . The insulation layer  13  electrically isolates the conductive layer  12  from the heat pipe  60  and conducts heat from the conductive layer  12  to the heat pipe  60 . 
         [0045]    The heat pipe  60  is made of a thermally conductive material such as Copper or Aluminum. As can be seen in  FIG. 2 , the heat pipe  60  is also in communication with the base plate  50 . Accordingly, there is a thermally conductive path between the thermal electric device  10  and the base plate  50 , via conductive layer  12 , insulation layer  13 , and heat pipe  60 . 
         [0046]    The first exemplary embodiment includes a thermally conductive path in which the thermoelectric device  10  is connected in series between the power device  20  and the base plate  50 . The base plate  50  in this exemplary embodiment is designed to dissipate heat produced by the power device  20 . Due to this communication with the base plate  50 , via the heat pipe  60 , a top portion of the thermoelectric device  10  is comparatively cooler that the bottom portion of the thermoelectric device  10 . 
         [0047]    As described above, the top portion of the thermoelectric device  10  is in thermal communication with the base plate  50  and the bottom portion of the thermoelectric device  10  in thermal communication with the power device  20 . Further, the power device  20  produces heat while in operation. Accordingly, a temperature differential is formed across the thermoelectric device  10  when the power device  20  is in operation. 
         [0048]    This temperature differential in the thermoelectric device  10  causes the thermoelectric device  10  to produce a voltage potential due to the Seebeck effect. This voltage potential is present at the thermoelectric device terminal  11 . When this voltage potential is attached to a load, then electric power is produced as a result of the temperature differential across the thermoelectric device  10 . 
         [0049]    Therefore, as described above, electric power may be produced by the thermoelectric device placed in thermal series between the power device  20  and the base plate  50 . This “harvested” electric power is produced from the waste heat produced by the power device  20 . Accordingly, the thermoelectric device  10  increases the thermodynamic efficiency of the power module  1 . 
         [0050]    The thermoelectric device  10  of the first embodiment is assumed to have a conversion efficiency of 10 percent. If a temperature differential of approximately 60 degrees Celsius is attained across the thermoelectric device  10 , a single thermoelectric device  10  may produce 0.25 W Accordingly, a power module  1  including twenty-two thermoelectric devices  10  as described in the first exemplary embodiment, may produce 5.5 W of harvested power. 
       Second Exemplary Embodiment 
       [0051]      FIG. 3  illustrates a second exemplary embodiment of a power module  1 . The power module  1  includes a power device  20  which is schematically shown as a transistor (MOSFET, IGBT, etc.) and diode pair. 
         [0052]    The a bottom portion of the power device  20  is in communication with a substrate  70 . The substrate  70  is a stacked structure which includes an electrical insulating layer between electrically conductive layers. The substrate  70  advantageously is a direct bonded aluminum (DBA) substrate. The substrate  70  may include a circuit pattern formed in the bottom layer. The substrate  70  could also be made of direct bonded copper (DBC) or the like. The substrate  70  is furthermore thermally conductive. 
         [0053]    A top portion of the power device  20  is in communication with wire  80 . The wire  80  can be a single wire or plurality of wires. The wire  80  may also be an electrically conductive ribbon or tape. The wire  80  is bonded to the top portion of the power device  20 . The bond may be a solder bond [i.e. Tin Lead (SnPb), Gold Tin (AuSn), or Gold Germanium (AuGe)] or a sintered bond [nano-Silver (Ag)]. 
         [0054]    The substrate  70  is in communication with an electric lead  71 . The electric lead  71  is also electrically connected with the wire  80  via an electric connection  81 . Therefore the substrate  70  in electric communication with the wire  80 , via electric lead  71 , and electric connection  81 . 
         [0055]    The substrate  70  is also in communication with cooling jacket  51 . The cooling jacket  51  allows a fluid to flow within an internal structure. The fluid may advantageously be water or a liquid coolant such as glycol mixed with water. The fluid flowing within the cooling jacket dissipates heat produced by the power device  20 . 
         [0056]    Between the substrate  70  and the cooling jacket  51  there is a thermal interface  52 . The thermal interface  52  transfers heat from the substrate  70  to the cooling jacket  51 . Embedded within the thermal interface  52  are a plurality of thermoelectric devices  10 . The thermoelectric devices  10  include a positive (+) junction  10   a  and a negative (−) junction  10   b . The thermoelectric devices  10  are advantageously made of Bismuth Antimony Telluride (BiSbTe). 
         [0057]    A bottom portion of the thermoelectric device  10  is in communication with electrically and thermally conductive layer  12 . In particular, the conductive layer  12  electrically connects positive junction  10   a  and negative junction  10   b  of the thermoelectric device  10 . Accordingly a current path is formed between positive junction  10   a  and negative junction  10   b.    
         [0058]    A thermally conductive and electrically isolating insulation layer  13  is provided between the conductive layer  12  and cooling jacket  51 . The insulation layer  13  electrically isolates the conductive layer  12  from the cooling jacket  51  and conducts heat from the conductive layer  12  to the cooling jacket  51 . 
         [0059]    The thermoelectric devices  10  are also in communication with the substrate  70  via a thermoelectric device terminal  11 . Furthermore, the thermoelectric devices  10  are in communication with the wire  80  via the thermoelectric device terminal  11 , the substrate  70 , the electric lead  71 , and the electric connection  81 . This electric path facilitates energy recovery from the thermoelectric devices  10 . 
         [0060]    Accordingly, the thermoelectric devices  10  which are embedded in the thermal interface  52  are part of a thermal path between the power device  10  and the cooling jacket  51  via the substrate  70 , the thermoelectric terminal  11 , the thermoelectric device  10 , the conductive layer  12 , and the insulation layer  13 . As such, a top side of a representative thermoelectric device  10 , which is in communication with the power device  20  is respectively warmer than a bottom side of the thermoelectric device  10  which is communication with the cooling jacket  51 . Therefore, a temperature differential is formed across the thermoelectric device  10  when heat is produced by the operation of the power device  10 . 
         [0061]    In accordance with the Seebeck effect, this temperature differential causes the thermoelectric device  10  to create a voltage potential. The voltage potential is present at the thermoelectric device terminal  11 . Accordingly, electric power produced due to the temperature differential is transferred from the thermoelectric device  10  to the substrate  70  via the thermoelectric device terminal  11 . 
       Third Exemplary Embodiment 
       [0062]      FIG. 4  illustrates a third exemplary embodiment of a power module  1 . The power module  1  includes a power device  20  which is schematically shown as a transistor (MOSFET, IGBT, etc.) and diode pair. 
         [0063]    The power module of the third exemplary embodiment includes the cooling jacket  51 , substrate  70 , the thermoelectric device terminal  11 , the conductive layer  12 , the insulation layer  13 , and the thermal interface  52  as discussed above with regard to the second exemplary embodiment. Furthermore, similar to the second embodiment, a plurality of thermoelectric devices  10  are embedded within the thermal interface  52 . 
         [0064]    As shown in  FIG. 4 , the third exemplary embodiment includes a lead frame  91  which communicates with the top portion of the power device  20 . Furthermore, the lead frame  91  communicates with the electric lead  71 . Accordingly, an electric path between the lead frame and the thermoelectric device is formed via the thermoelectric device terminal  11 , the substrate  70 , and the electric lead  71 . 
         [0065]    Similar to the second exemplary embodiment, the thermoelectric devices  10  embedded in the thermal interface  52  are part of a thermal path between the power device  10  and the cooling jacket  51 . When the power device  20  operates, heat is produced. Accordingly, a top side of a representative thermoelectric device  10 , which is in communication with the power device  20  is respectively warmer than a bottom side of the thermoelectric device  10  which is communication with the cooling jacket  51 . Therefore, a temperature differential is formed across the thermoelectric device  10  which produces a voltage potential at the thermoelectric device terminal  11 . 
         [0066]    Exemplary Uses of the Harvested Electric Power 
         [0067]    As described in the above embodiments, a thermoelectric device placed in thermal series between a power device and cooling medium produces electric power. This electric power harvested by the thermoelectric device  10  has several advantageous uses within a hybrid electric vehicle. 
         [0068]      FIG. 5  illustrates some of these potential uses. For example, the power produced by the thermoelectric device  10  may be used to energize power module sensors such as a current sensor  90  or temperature sensor  91  which are used in the control of the power module  1 . The harvested electric power could also be used to operate a printed circuit board (PCB) controller  92  which controls the power module  1 . The power produced by the thermoelectric device  10  may also be input into an energy storage device  93  for later use by the power module  1 . The energy storage device  93  may advantageously be a battery, capacitor, or the like. 
         [0069]    Furthermore, as described above with respect to the preferred embodiments, thermoelectric devices may increase the thermodynamic efficiency of a power module of a hybrid electric vehicle. Accordingly, less fuel in consumed by the vehicle which has environmental and economical benefits. 
         [0070]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.