Abstract:
A dual power module architecture employing a high degree of modularity, that allows a base power module to be quickly, easily, and cost effectively configured to address a large variety of applications.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This disclosure is generally related to electrical power systems, and more particularly to power module architectures suitable for rectifying, inverting and/or converting electrical power between power sources and loads. 
   2. Description of the Related Art 
   Power modules are typically self-contained units that transform and/or condition power from one or more power sources for supplying power to one or more loads. Power modules commonly referred to as “inverters” transform direct current (DC) to alternating current (AC), for use in supplying power to an AC load. Power modules commonly referred to as a “rectifiers” transform AC to DC. Power modules commonly referred to as “DC/DC converters” step up or step down a DC voltage. An appropriately configured and operated power module may perform any one or more of these functions. The term “converter” is commonly applied generically to all power modules whether inverters, rectifiers and/or DC/DC converters. 
   There are a large variety of applications requiring power transformation and/or conditioning. For example, a DC power source such as a fuel cell system, battery and/or ultracapacitor may produce DC power, which must be inverted to supply power to an AC load such as a three-phase AC motor in an electric or hybrid vehicle. A photo-voltaic array may produce DC power which must be inverted to supply or export AC power to a power grid of a utility. An AC power source such as a power grid or micro-turbine may need to be rectified to supply power to a DC load such as a tool, machine or appliance. A high voltage DC source may need to be stepped down to supply a low voltage load, or a low voltage DC source may need to be stepped up to supply a high voltage load. Other applications will become apparent to those of skill in the art based on the teachings herein. 
   Addressing these various applications typically requires the custom design of a suitable power module. Custom designing of power modules results in excessive costs related to the design process, as well as, duplicative costs related to the creation of custom tooling, the manufacture of custom parts, and maintenance of separate inventories. Custom designing also reduces time to market. It would be desirable to have a power module that allows the investment in design, tooling, manufacturing and inventorying to be shared across many application specific products, and may shorten time to market. 
   SUMMARY OF THE INVENTION 
   The disclosure is directed to an architecture for a power module, employing a high degree of modularity, that allows a base power module to be quickly, easily, and cost effectively configured to address a large variety of applications by simply interchanging components, electrical connections, and/or software. 
   In one aspect, a power system comprises: a first power module comprising a module housing, a cold plate attached to the module housing, a first bus accessible from an exterior of the module housing, a second bus accessible from the exterior of the module housing, the second bus electrically isolated from the first bus, a first set of electrical terminals accessible from the exterior of the module housing, for each of the electrical terminals in the first set of electrical terminals, a number of first leg components electrically coupled between the electrical terminal and the first bus, and a number of second leg components electrically coupled between the electrical terminal and the second bus; a second power module comprising a module housing, a cold plate attached to the module housing, a first bus accessible from an exterior of the module housing, a second bus accessible from the exterior of the module housing, the second bus electrically isolated from the first bus, a first set of electrical terminals accessible from the exterior of the module housing, for each of the electrical terminals in the first set of electrical terminals, a number of first leg components electrically coupled between the electrical terminal and the first bus, and a number of second leg components electrically coupled between the electrical terminal and the second bus; and at least one external connector electrically coupling the first and the second buses of the first power module with respective ones of the first and the second buses of the second power module. 
   In another aspect, a power system comprises: a rectifier power module comprising a module housing, a cold plate attached to the module housing, a set of input terminals, a first output bus and a second output bus; an inverter power module comprising a module housing, a cold plate attached to the module housing, a first input bus, a second input bus, and a set of output terminals, wherein the cold pate of the inverter power module faces the cold plate of the rectifier power module; and at least one external connector electrically coupling each of the first and the second output buses of the rectifier with a respective one of the first and the second input buses of the inverter power module. 
   In yet another aspect, a power system comprises: a first rectifier power module comprising a module housing, a cold plate attached to the module housing, a set of input terminals, a first output bus and a second output bus; a second rectifier power module comprising a module housing, a cold plate attached to the module housing, a set of input terminals, a first output bus and a second output bus, wherein the cold pate of the second rectifier power module faces the cold plate of the first rectifier power module; and at least one external connector electrically coupling each of the first and the second output buses of the first rectifier module with a respective one of the first and the second output buses of the second rectifier power module. 
   In still another aspect, a power system comprises: a first inverter power module comprising a module housing, a cold plate attached to the module housing, a first input bus and a second input bus, and a set of output terminals; a second inverter power module comprising a module housing, a cold plate attached to the module housing, a first input bus and a second input bus, and a set of output terminals, wherein the cold pate of the second inverter power module faces the cold plate of the first inverter power module; and at least one external connector electrically coupling each of the first and the second input buses of the first inverter input module with a respective one of the first and the second input buses of the second inverter power module. 
   In a further aspect, a method of forming a power system comprises: providing a first power module comprising a module housing, a cold plate attached to the module housing, a first bus accessible from an exterior of the module housing, a second bus accessible from the exterior of the module housing, the second bus electrically isolated from the first bus, a first set of electrical terminals accessible from the exterior of the module housing, for each of the electrical terminals in the first set of electrical terminals, a number of first leg components electrically coupled between the electrical terminal and the first bus, and a number of second leg components electrically coupled between the electrical terminal and the second bus; providing a second power module comprising a module housing, a cold plate attached to the module housing, a first bus accessible from an exterior of the module housing, a second bus accessible from the exterior of the module housing, the second bus electrically isolated from the first bus, a first set of electrical terminals accessible from the exterior of the module housing, for each of the electrical terminals in the first set of electrical terminals, a number of first leg components electrically coupled between the electrical terminal and the first bus, and a number of second leg components electrically coupled between the electrical terminal and the second bus; and externally electrically coupling the first and the second buses of the first power module with respective ones of the first and the second buses of the second power module. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings. 
       FIG. 1  is an isometric view of a power module comprising a housing, integrated cold plate, DC bus terminals, AC phase terminals, and power semiconductor devices. 
       FIG. 2A  is an isometric view of the power module of  FIG. 1  with a cover removed and some portions broken or removed to show the DC bus, the AC bus, and the power semiconductor devices carried by a number of regions carried by a substrate. 
       FIG. 2B  is a top plan view of the power module of  FIG. 2A  showing a representative sampling of wire bonds electrically connecting various power semiconductor devices, buses, and layers in the substrate as an inverter. 
       FIG. 3  is a schematic cross sectional view of one embodiment of the DC bus comprising a pair of L-shaped DC bus bars spaced by an electrical insulation. 
       FIG. 4  is a schematic cross sectional view of one embodiment of the DC bus comprising a pair of generally planar DC bus bars spaced by an electrical insulation. 
       FIG. 5  is a topological view a single power module configured as a power inverter between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 6  is a topological view of a single power module configured as an AC/AC power converter between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 7  is a topological view of a single power module configured as a half bridge rectifier between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 8  is a topological view of a single power module configured as an H-bridge rectifier between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 9  is an isometric view of a pair of power modules in back-to-back configuration and an external connector electrically coupling the DC buses of the power modules. 
       FIG. 10  is a topological view of the pair of power modules in back-to-back configuration of  FIG. 9  configured as a high power inverter between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 11  is a topological view of pair of power modules in back-to-back configuration of  FIG. 9  configured as two three phase inverters providing power to a pair of loads, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 12  is a topological view of the pair of power modules in back-to-back configuration of  FIG. 9  configured as a single three phase power inverter between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 13  is a topological view of the pair of power modules in back-to-back configuration of  FIG. 9  configured as a half bridge rectifier between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
       FIG. 14  is a topological view of the pair of power modules in back-to-back configuration of  FIG. 9  configured as an H-bridge rectifier between a power source and a load, illustrating some aspects of the architecture of the power module and the topology of the substrate. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. In other instances, well-known structures associated with power modules, power semiconductor devices and controllers have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention. 
   Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
   The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention. 
   Base Power Module 
     FIGS. 1 ,  2 A, and  2 B show a base power module  10 , generally comprising: a lead frame or housing  12 , an integrated cold plate  14  attached to the housing  12  via bushings  15 , a DC bus  16 , an AC bus  18 ; and power semiconductor devices  20  electrically coupled between the DC bus  16  and AC bus  18 , forming a high side  20   b  and a low side  20   a  of the power module  10 . The base power module  10  may further include one or more gate drivers  22  ( FIG. 9 ) for driving some of the power semiconductor devices  20 . 
   Two sets of DC bus terminals  24 ,  26  extend out of the housing  12 . As discussed in detail below, in some applications one set of DC bus terminals  26  is electrically coupled to a positive voltage or high side of a power source or load and the other set of DC bus terminals  24  is electrically coupled to a negative voltage or low side of the power source or load. In other applications, the DC bus terminals  24 ,  26  are electrically coupled to respective DC bus terminals  24 ,  26  on another power module. A set of AC phase terminals comprises three pairs of AC bus phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b , extending out of the housing  12 . As discussed in detail below, in some applications, one pair of AC phase terminals is coupled to a respective phase (A, B, C) of a three phase power source or load. In other applications, some of the AC phase terminals are interconnected across or between the pairs, and coupled to power sources or loads. 
     FIG. 3  shows a schematic cross-sectional view of the power module  10  taken along section line  3 — 3  of FIG.  2 A.  FIG. 3  is not an exact cross-sectional view, but has been modified to more accurately represent the electrical connections which would otherwise not be clearly represented in the FIG.  3 . 
   The integrated cold plate  14  comprises a metal base plate  39 , a direct copper bonded (DCB) substrate  40  which is attached to the metal base plate  39  by a solder layer  41 . A cooling header  42  includes a number of cooling structures such as fins  42   a , one or more fluid channels  42   b , and a fluid inlet  42   c  and a fluid outlet  42   d  for providing fluid connection flow to and from the fluid channels  42   b , respectively. 
   The DCB substrate  40  typically comprises a first copper layer  40   a , a ceramic layer  40   b  and a second copper layer  40   c  which are fused together. The second copper layer  40   c  may be etched or otherwise processed to form electrically isolated patterns or structures, as is commonly known in the art. For example, the second copper layer  40   c  may be etched to form regions of emitter plating  43   a  and collector plating  44   a  on a low side of the power module  10  (i.e., side connected to DC bus bar  34 ). Also for example, the second copper layer  40   c  may be etched to form regions of emitter plating  43   b  and collector plating  44   b  on the high side of the power module  10  (i.e., the side connected to DC bus bar  36 ). 
   A conductive strip  45  or wire bonds may extend between the collector plating  44   a  of the low side and the emitter plating  43   b  of the high side, passing through respective passages  46  formed under the DC bus bars  34 ,  36 . As illustrated, the conductive strip  45  has be exaggerated in length on the low side of the power module  10  to better illustrate the electrical connection with the collector plating  44   a.    
   The power semiconductor devices  20  are attached to the various structures formed in the second copper layer  40   c  via a solder  47 . The power semiconductor devices  20  may include one or more switches for example, transistors  48  such as integrated bipolar gate transistors (IGBTs) or metal oxide semiconductor field effect transistors (MOSFETS). The power semiconductor devices  20  may also include one or more diodes  50 . The power semiconductor devices  20  may have one or more terminals directly electrically coupled by the solder  47  to the structure on which the specific circuit element is attached. For example, the collectors of IGBTs  48  may be electrically coupled directly to the collector plating  44   a ,  44   b  by solder  47 . Similarly, the cathodes of diodes  50  may be electrically coupled directly to the collector plating  44   a ,  44   b  by solder  47 . 
   The DC bus  16  comprises a pair of L-shaped or vertical DC bus bars  34   a ,  36   a . The upper legs of the L-shaped DC bus bars  34   a ,  36   a  are parallel and spaced from one another by the bus bar insulation  38 . The lower legs of the L-shaped DC bus bars  34 a,  36 a are parallel with respect to the substrate  40  to permit wire bonding to appropriate portions of the substrate. For example, the negative DC bus bar  34   a  may be wire bonded to the emitter plating  43   a  of the low side, while the positive DC bus bar  36   a  may be wire bonded to the collector plating  44   b  of the high side. The emitters of the IGBTs  48  and anodes of the diodes  50  may be wire bonded to the respective emitter plating  43   a ,  43   b . Wire bonding in combination with the rigid structure of the DC bus  16  and housing  12  may also eliminate the need for a hard potting compound typically used to provide rigidity to protect solder interfaces. For low cost, the copper layers  40   a  and  40   c  may be nickel finished or aluminum clad, although gold or palladium may be employed at the risk of incurring higher manufacturing costs. 
     FIG. 4  shows another embodiment of the DC bus  16  for use in the power module  10 , the DC bus  16  comprising a pair of generally planar DC bus bars  34   b ,  36   b  parallel and spaced from one another by a bus bar insulation  38 . The DC bus bars  34   b ,  36   b  are horizontal with respect to a substrate  40  (FIGS.  2 A and  2 B), with exposed portions to permit wire bonding to the various portions of the substrate  40 . 
   Because the DC bus bars  34 ,  36  are parallel, counter flow of current is permitted, thereby canceling the magnetic fields and their associated inductances. In addition the parallel DC bus bars  34 ,  36  and bus bar insulation  38  construct a distributed capacitance. As will be understood by one of ordinary skill in the art, capacitance dampens voltage overshoots that are caused by the switching process. Thus, the DC bus bars  34 ,  36  of the embodiments of  FIGS. 3 and 4  create a magnetic field cancellation as a result of the counter flow of current, and capacitance dampening as a result of also establishing a functional capacitance between them and the bus bar insulation  38 . 
   As best illustrated in  FIG. 2B , the power semiconductor devices  20  include a number of decoupling, high frequency capacitors  55  which are electrically coupled between the DC bus bars  34 ,  36  and ground to reduce EMI. In contrast to prior designs, the capacitors  55  are located on the substrate  40  inside the housing  12 . For example, some of the capacitors  55  are electrically coupled directly to the emitter plating  43   a  on the low side of the substrate  40  and some of the capacitors  55  are electrically coupled directly to the collector plating  44   b  on the high side of the substrate  40 . The capacitors  55  can be soldered in the same operation as the soldering of the substrate  40  to the cold plate  14 . 
   The power semiconductor devices  20  also include a number of snubber capacitors (not shown) electrically coupled between the DC bus bars  34 ,  36  to clamp voltage overshoot. For example, some of the snubber capacitors are electrically coupled directly to the emitter plating  43   a  on the low side of the substrate  40  and the collector plating  44   b  on the high side of the substrate  40 . Significant savings may be realized by effective clamping of voltage overshoot. For example, if switching transients are maintained below approximately 900V, a transformer may be eliminated. The snubber capacitors can be soldered in the same operation as the soldering of the substrate  40  to the cold plate  14 . 
   As best illustrated in  FIGS. 1 and 2A , the DC bus bars  34 ,  36  each include three terminals  24 ,  26 , spaced along the longitudinal axis, to make electrical connections, for example, to a DC power source. Without being restricted to theory, Applicants believe that the spacing of the terminals  24 ,  26  along the DC bus bars  34 ,  36  provides lower inductance paths within the DC bus bars  34 ,  36  and to the external DC voltage storage bank. 
   In contrast to typical power modules, the DC bus bars  34 ,  36  are internal to the housing  12 . This approach results in better utilization of the bus voltage, reducing inductance and consequently permitting higher bus voltages while maintaining the same margin between the bus voltage and the voltage rating of the various devices. The lower inductance reduces voltage overshoot, and problems associated with voltage overshoot such as device breakdown. The increase in bus voltage permits lower currents, hence the use of less costly devices. The bus bar insulation  38  between the DC bus bars  34 ,  36  may be integrally molded as part of the housing  12 , to reduce cost and increase structural rigidity. The DC bus bars  34 ,  36  may be integrally molded in the housing  12 , or alternatively, the DC bus bars  34 ,  36  and bus bar insulation  38  may be integrally formed as a single unit and attached to the housing  12  after molding, for example, via post assembly. 
   The power semiconductor devices  20  are directly mounted on the substrate  40  which is directly attached to the cold plate  14  via solder layer  41 , the resulting structure serving as a base plate. The use of a cold plate  14  as the base plate, and the direct mounting of the power semiconductor devices  20  thereto, enhances the cooling for the power semiconductor devices  20  over other designs, producing a number of benefits such as prolonging the life of capacitors  55 . 
   The power semiconductor devices  20  are operable to transform and/or condition electrical power. As discussed above, the power semiconductor devices  20  may include switches  48  and/or diodes  50 . The power semiconductor devices  20  may also include other electrical and electronic components, for example, capacitors  55  and inductors, either discrete or formed by the physical layout. The power module  10  and power semiconductor devices  20  may be configured and operated as an inverter (DC→AC), rectifier (AC→DC), and/or converter (DC→DC; AC→AC). For example, the power module  10  and/or power semiconductor devices  20  may be configured as full three phase bridges, half bridges, and/or H-bridges, as suits the particular application. 
     FIG. 5  topographically illustrates the layout of the substrate  40 , employing twelve distinct regions of collector plating  44   a ,  44   b , denominated collectively below as regions  44 . The regions  44  are generally arranged in a low side row of six areas of collector plating  44   a  and a high side row of six areas of collector plating  44   b . Each region  44  can carry a variety of switches such as IGBTs  48  and/or a variety of diodes  50 . The gate drivers  22  ( FIG. 9 ) are coupled to control the power semiconductor devices  20 , particularly the switches  48 , based on signals received from a controller  52  via a signal bus  54 , which may also be integrated into the power module  10  or which may be provided separately therefrom. 
   A base or standard region  44  typically carries two IGBTs  48  and four diodes  50 . However, the inclusion of specific component types (switches such as IGBTs  48  and/or diodes  50 ) and the number of each component on a region  44  may depend on the specific application. For example, a region  44  may carry up to four IGBTs  48 , or alternatively, up to eight diodes  50 . Alternatively, a region  44  may carry four diodes  50  and omit IGBTs  48 , for example, where the power semiconductor devices  20  on the region  44  will act as a rectifier. The ability to eliminate components where the specific application does not require these components provides significant cost savings. For example, eliminating IGBTs  48  can save many dollars per region  44 . The ability to add additional components of one type in the place of components of another type on a region  44  provides some flexibility in adjusting the current and/or voltage rating of the power module  10 . Thus, this modular approach reduces costs, and provides flexibility in customizing to meet demands of a large variety of customers. Of course other sizes of regions  44 , which may carry more or fewer components, are possible. 
   In at least one described embodiment, the power module  10  comprises three half bridges combined into a single three-phase switching module, or single half bridge modules that may be linked together to form a three phase inverter. As would be understood by one of ordinary skill in the art, the same DC to AC conversion may be accomplished using any number of half bridges, which correspond to a phase, and each switching pair may contain any number of switching devices. For simplicity and clarity, many of the examples herein use a common three phase/three switching pair configuration, although this should not be considered limiting. 
   In at least one described embodiment, current flows from the power source through the positive DC bus bar  36  to the collector plating  44   b  on the high side of the power module  10 . Current is then permitted to flow through one or more of the switching devices  48  and/or diodes  50  on the high side to the emitter layer  43   b . The current passes to the collector layer  44   a  on the low side via the conductive strip  45  passing under the DC bus bars  34 ,  36 . A phase terminal allows current to flow from the collector layer  44   a  on the low side to a load such as a three phase AC motor. Similarly, the negative DC bus bar  34  couples the load to the switching devices  48  and/or diodes  50  on the low side via the emitter layer  43   a.    
   The overall design of the standard power module  10 , including the position and structure of the DC and AC buses  16 ,  18 , topology and modularity of substrates  40  and the inclusion of six phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  in the AC bus  16  provides great flexibility, allowing the standard power module  10  to be customized to a variety of applications with only minor changes and thus relatively small associated costs. A number of these applications are discussed below. 
   Single Power Module Power Inverter 
     FIG. 5  also shows a single power module  10  configured as a power inverter. The power inverter may be suitable, for example, for providing 600 A at 1200V. A DC power supply  58  supplies power to the power module  10  via the terminals  24 ,  26  of the DC power bus  16 . The power module  10  supplies three phase AC power to a three phase AC load  60  via the AC bus  18 . In particular, the phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b , are electrically coupled in pairs, each pair supplying a respective phase of the power. 
   Single Power Module Power Converter 
     FIG. 6  shows a single power module  10  configured as an AC/AC power converter. The power converter may be suitable, for example, for providing 300 A at 1200V. Three of the AC phase terminals  28   a ,  28   b ,  30   a  are electrically coupled to respective phases (A, B, C) of a three phase AC power source  62 , while the other three AC phase terminals  30   b ,  32   a ,  32   b  are electrically coupled respective phases of a three phase AC load  60 . 
   Single Power Module Half Bridge Rectifier 
     FIG. 7  shows a single power module  10  configured as a half bridge rectifier. The half bridge rectifier may be suitable, for example, for providing 1800 A at 1200V or 2400 A at 600V. A typical use would employ a dedicated half bridge for each phase of the power source. All of the AC phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  of the power module  10  are electrically coupled to one phase (A, B, or C) of the three phase AC power source  62 . The DC bus terminals  24 ,  26  are electrically coupled to respective poles of a DC load  64 . 
   As illustrated, the power module  10  is configured with IGBTs  48  for active rectification. In an alternative embodiment, the power module  10  may employ passive rectification, omitting the IGBTs  48 , and thereby reducing parts count and costs. 
   Single Power Module H-Bridge Rectifier 
     FIG. 8  shows a single power module  10  configured as an H-bridge rectifier. The H-bridge rectifier may be suitable, for example, for providing 900 A at 1200V, sufficient for industrial applications and furnaces such as induction heating. Three of the AC phase terminals  28   a ,  28   b ,  30   a  are electrically coupled to one line of an AC power source  62 , while the other AC phase terminals  30   b ,  32   a ,  32   b  are electrically coupled to the other line of the AC power source  62 . The DC terminals  24 ,  26  are electrically coupled to respective poles of a DC load  64 . 
   As illustrated, the power module  10  is configured with IGBTs  48  for active rectification. In an alternative embodiment, the power module  10  may employ passive rectification, omitting the IGBTs  48 , and thereby reducing parts count and costs. 
   Dual Power Module Configurations 
     FIG. 9  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back with the cold plates  14  facing each other. Alternatively, the power modules  10   a ,  10   b  may be physically coupled front-to-front, depending on orientation and specific topology. 
   A capacitor  68  may positioned between the opposed faces (i.e., backs or fronts) of the first and second power modules  10   a ,  10   b  to form a capacitor  68 . This takes advantage of the integrated cold plates  14  in the power modules  10   a ,  10   b . Since the capacitor  68  is adjacent the cold plates  14  cooling of the capacitor will be enhanced. Thus, the high power inverter may employ a smaller capacitor than would otherwise be necessary. This may allow the use of a film capacitor (i.e., one or more layers) rather than the typical electrolytic capacitor, further enhancing and contributing to the form function of the power module  10 . Film capacitors are available commercially from a variety of sources, including EPCOS AG of Munich, Germany. 
   An external connector  70  electrically couples the DC bus bars  34 ,  36  of the first power module  10   a  to respective ones of the of the DC bus bars  34 ,  36  of the second module  10   b . In some embodiments, the external connector  70  may also function as a clamp, for biasing or holding the first and second power modules  10   a ,  10   b  together. The external connector  70  may conform to the exterior of a portion of the power modules  10   a ,  10   b , contributing to the small footprint of the device. For example, the external connector  70  may be approximately U-shaped, as illustrated, including a pair of arms that are sufficiently spaced apart to receive the power modules  10   a ,  10   b  therebetween. 
   The external connector  70  may be a laminate structure formed from at least two conductive layers and a number of insulating layers, at least one of the insulating layers spacing and electrically insulating the two conductive layers. Portions of the insulating layers are removed to expose portions of the conductive layers to allow the electrically connections to the respective DC bus bars  34 ,  36 . Insulating layers may be formed from a variety of commercially available materials, for example, NOMEX® available from E.I. du Pont de Nemours and Company, Advanced Fibers Systems, Richmond, Va. 
   This modular approach takes advantage of the unique topology of the standard power module  10  to provide a simple, cost effective, form factor solution to meet a large variety of customer demands, as discussed in detail below. 
   Starter/Main Inverter Combination 
     FIG. 10  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back similar to that of  FIG. 9 , and electrically coupled to create a first embodiment of a power converter. The first power module  10   a  is operated as a starter inverter while a second power module  10   b  functions as a main inverter. Note that the IGBTs  48  have been removed from the regions  44  of the first power module  10   a , since the IGBTs are not necessary for the rectification, thus significantly reducing the cost of the inverter. A dielectric  66  is interposed between the cold plates of the first and the second power module. 
   This modular approach takes advantage of the unique topology of the standard power module  10  to provide a simple, cost effective, form factor solution to customer demands for various levels of power. 
   Dual Power Module Dual 3 Phase Inverter 
     FIG. 11  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back similar to that of  FIG. 9 , and electrically coupled as two three phase inverters. The inverter may be suitable for providing power to two three phase AC loads. The inverter may be suitable, for example, for providing 600 A at 1200V or 800 A at 600V for each load. 
   The external connector  70  (illustrated as separate DC+ and DC− connectors for clarity), electrically couples the DC bus bars  34 ,  36  of the first power module  10   a  to respective ones of the DC bus bars  34 ,  36  of the second module  10   b . The external connector  70  further couples the DC bus bars  34 ,  36  to a DC power source DC+, DC−. 
   Pairs of the AC phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  of the first power module  10   a  are electrically coupled to provide respective phases (A, B, or C) to a first three phase AC load  60 . Pairs of the AC phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  of the second power module  10   b  are electrically coupled to provide respective phases (A′, B′, or C′) to a second three phase AC load  72 . 
   Dual Power Module Single 3 Phase Inverter 
     FIG. 12  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back similar to that of  FIG. 9 , and electrically coupled as a single three phase inverter. The inverter may be suitable for providing power to a single three phase AC loads. The inverter may be suitable, for example, for providing 1200 A at 1200V or 1600 A at 600V. 
   The external connector  70  (illustrated as separate DC+ and DC− connectors for clarity), electrically couples the DC bus bars  34 ,  36  of the first power module  10   a  to respective ones of the DC bus bars  34 ,  36  of the second module  10   b . The external connector  70  further couples the DC bus bars  34 ,  36  to a DC power source DC+, DC−. 
   A first pair of the AC phase terminals  28   a ,  28   b  of the first power module  10   a  is electrically coupled to a first pair  32   a ,  32   b  of the AC phase terminals of the second power module  10   b , and to provide a first phase (A) to a three phase AC load  60 . A second pair of the AC phase terminals  30   a ,  30   b  of the second power module  10   b  is electrically coupled to a second pair of AC phase terminals  30   a ,  30   b  of the second power module  10   b  and to provide a second phase (B) to the three phase AC load  60 . A third pair of the AC phase terminals  32   a ,  32   b  of the first power module  10   a  is electrically coupled to a third pair of the AC phase terminals  28   a ,  28   b  of the second power module  10   b  and to provide a third phase (C) to the three phase AC load  60 . 
   High Power Inverter 
     FIG. 13  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back similar to that of  FIG. 9 , and electrically coupled to create a high power inverter (e.g., twice the power of an inverter based on a single power module). 
   The external connector  70  (illustrated as separate DC+ and DC− connectors for clarity), electrically couples the DC bus bars  34 ,  36  of the first power module  10   a  to respective ones of the DC bus bars  34 ,  36  of the second module  10   b.    
   The phase terminals of the first power module  10   a  are electrically coupled in pairs to respective phases of a three phase AC power source  62 . The phase terminals of the main inverter are electrically coupled in pairs to a three phase AC load  60 . 
   The first power module  10   a  is operated as a rectifier while a second power module  10   b  functions as a main inverter. Note that the IGBTs  48  have been removed from the regions  44  of the first power module  10   a , since the IGBTs are not necessary for the rectification, thus significantly reducing the cost of the inverter. 
   Dual Power Module H-Bridge Rectifier 
     FIG. 14  shows a pair of power modules  10   a ,  10   b  physically coupled back-to-back similar to that of  FIG. 9 , and electrically coupled as a half bridge. The half bridge may be suitable, for example, for providing 1800 A at 1200V, or 2400 A at 600V. In typical use, a separate half bridge will be provided for each phase. 
   The external connector  70  (illustrated as separate DC+ and DC− connectors for clarity), electrically couples the DC bus bars  34 ,  36  of the first power module  10   a  to respective ones of the DC bus bars  34 ,  36  of the second module  10   b . The external connector  70  further couples the DC bus bars  34 ,  36  to a DC power source DC+, DC−. 
   All of the AC phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  of the first power module  10   a  are electrically coupled to one line of an AC power source  62 . All of the AC phase terminals  28   a ,  28   b ,  30   a ,  30   b ,  32   a ,  32   b  of the second power module  10   b  are electrically coupled to the other line of an AC source  62 . 
   Although specific embodiments of and examples for the power module and method of the invention are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein of the invention can be applied to power module and power converters, rectifiers and/or inverters not necessarily the exemplary power module and systems generally described above. 
   While elements may be describe herein and in the claims as “positive” or “negative” such denomination is relative and not absolute. Thus, an element described as “positive” is shaped, positioned and/or electrically coupled to be at a higher relative potential than elements described as “negative” when the power module  10  is coupled to a power source. “Positive” elements are typically intended to be coupled to a positive terminal of a power source, while “negative” elements are intended to be coupled to a negative terminal or ground of the power source. Generally, “positive” elements are located or coupled to the high side of the power module  10  and “negative” elements are located or coupled to the low side of the power module  10 . 
   The power modules described above may employ various methods and regimes for operating the power modules  10  and for operating the switches (e.g., IGBTs  48 ). The particular method or regime may be based on the particular application and/or configuration. Basic methods and regimes will be apparent to one skilled in the art, and do not form the basis of the inventions described herein so will not be discussed in detail for the sake of brevity and clarity. 
   The various embodiments described above can be combined to provide further embodiments. All of the above U.S. patents, patent applications and publications referred to in this specification, including but not limited to: Ser. Nos. 60/233,992; 60/233,993; 60/233,994; 60/233,995 and 60/233,996 each filed Sep. 20, 2000; Ser. No. 09/710,145 filed Nov. 10, 2000; Ser. Nos. 09/882,708 and 09/957,047 both filed Jun. 15, 2001; Ser. Nos. 09/957,568 and 09/957,001 both filed Sep. 20, 2001; Ser. No. 10/109,555 filed Mar. 27, 2002; and Ser. No. 60/471,387 filed May 16, 2003, are incorporated herein by reference, in their entirety, as are the sections which follow this description. Aspects of the invention can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments of the invention. 
   These and other changes can be made to the invention in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all power modules, rectifiers, inverters and/or converters that operate or embody the limitations of the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.