WO2004105220A2

WO2004105220A2 - Power module system

Info

Publication number: WO2004105220A2
Application number: PCT/US2004/015259
Authority: WO
Inventors: Sayeed Ahmed; Fred Flett; Douglas K. Maly; Ajay V. Patwardhan
Original assignee: Ballard Power Systems Corporation
Priority date: 2003-05-16
Filing date: 2004-05-17
Publication date: 2004-12-02
Also published as: WO2004105220A3

Abstract

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.

Description

POWER MODULE SYSTEM

BACKGROUND OF THE INVENTION

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.

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. In one aspect, a power module commonly referred to as an inverter, transforms direct current (DC) to alternating current (AC), for use in supplying power to an AC load. In another aspect, a power module commonly referred to as a rectifier, transforms AC to DC. In a further aspect, power modules commonly referred to as a DC/DC converter 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

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.

Figure 1 is an isometric view of a power module comprising a housing, integrated cold plate, DC bus terminals, AC phase terminals, circuitry and a gate drive board. Figure 2A is an isometric view of the power module of Figure 1 with a cover removed and some portions broken or remove to show the DC bus, the AC bus, and the circuitry carried by a number of tiles carried by a substrate. Figure 2B is a top plan view of the power module of Figure 2A showing a representative sampling of wire bonds electrically connecting various circuit components, buses, and layers in the substrate as an inverter.

Figure 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.

Figure 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.

Figure 5 is a schematic view of 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.

Figure 6 is a schematic 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.

Figure 7 is a schematic 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.

Figure 8 is a schematic 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. Figure 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.

Figure 10 is a schematic view of the pair of power modules in back-to-back configuration of Figure 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.

Figure 11 is a schematic view of pair of power modules in back-to- back configuration of Figure 9 configured as two three phase inverters between a power source and a pair of loads, illustrating some aspects of the architecture of the power module and the topology of the substrate.

Figure 12 is a schematic view of the pair of power modules in back-to-back configuration of Figure 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.

Figure 13 is a schematic view of the pair of power modules in back-to-back configuration of Figure 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. Figure 14 is a schematic view of the pair of power modules in back-to-back configuration of Figure 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.

Figure 15 is a topological view of a single power module configured as a tri-level inverter between a power source and a three-phase load, illustrating some aspects of the architecture of the power module and the topology of the substrate.

Figure 16 is an electrical schematic view of a single-phase tri-level inverter (or one phase of a three-phase tri-level inverter). Figure 17 is a timing diagram illustrating example outputs produced by the tri-level inverter of Figure 16 in response to a particular series of control signals.

Figure 18 is a top view of a tri-level inverter implemented in the power module of Figure 1.

Figure 19 is an electrical schematic view of a three-phase tri-level inverter.

Figure 20 shows an isometric view of a power converter according to one embodiment, comprising a high frequency capacitor and bulk capacitor coupled across the DC bus of the base power converter, a second housing to receive the capacitors and first housing, and a gate driver.

Figure 21 is an exploded isometric view of the power converter of Figure 20.

Figure 22A is a partial isometric view of a portion of a low side of the power converter illustrating the surface mounting of snubber capacitors to a low side emitter area of the substrate.

Figure 22B is an isometric view of a portion of a high side of the substrate illustrating the surface mounting of the snubber capacitors to a high side collector area of the substrate. Figure 23 is an electrical schematic of the switches, freewheeling diodes, and snubber capacitors according to an illustrated embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth in order to provide a through 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 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

Figures 1 , 2A, and 2B 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; power semiconductor devices electrically coupled between the DC bus 16 and AC bus 18, forming a low side 20a and a high side 20b of the power module 10. The base power module 10 may further include one or more gate driver boards 22 for driving some of the power semiconductors 20 (see, Figures 20 and 21). The DC bus 16 includes 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 20b of a power source or load and the other set of DC bus terminals is 24 is electrically coupled to a negative voltage or low side 20a 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 28a, 28b, 30a, 30b, 32a, 32b, 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.

Figure 3 shows a schematic cross-sectional view of the power module 10 taken along section line 3-3 of Figure 2A. Figure 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 Figure 3. The integrated cold plate 14 comprises a metal base plate 39, a direct copper bonded (DCB) substrate 40 which attached to the metal base plate by a solder layer 41. A cooling header 42 including a number of cooling structures such as fins 42a, one or more fluid channels 42b, a fluid inlet 42c and a fluid outlet 42d for providing fluid connection flow to and from the fluid channels 42b, respectively.

The DCB substrate 40 typically comprises a first copper layer 40a, a ceramic layer 40b and a second copper layer 40c which are fused together. The second copper layer 40c 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 40c may be etched to form regions of emitter plating 43a and collector plating 44a on a low side 20a of the power module 10 (i.e., side connected to DC bus bar 34). Also for example, the second copper layer 40c may be etched to form regions of emitter plating 43b and collector plating 44b on the high side 20b of the power module 10 (i.e., side connected to DC bus bar 36.

A conductive strip 45 or wire bonds may extend between the collector plating 44a of the low side 20a and the emitter plating 43b of the high side 20b, 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 20a of the power module 10 to better illustrate the electrical connection with the collector plating 44a.

Power semiconductor devices 20 are attached to the various structures formed in the second copper layer 40c via a solder 47. The power semiconductor devices 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) 48. The power semiconductor devices may also include one or more diodes 50. The power semiconductor devices 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 44a, 44b by solder 47. Similarly, the cathodes of diodes 50 may be electrically coupled directly to the collector plating 44a, 44b by solder 47.

The DC bus 16 comprises a pair of L-shaped DC bus bars 34a, 36a. The upper legs of the L-shaped DC bus bars 34a, 36a are parallel and spaced from one another by the bus bar insulation 38. The lower legs of the L- shaped DC bus bars 34, 36 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 34a may be wire bonded to the emitter plating 43a of the low side 20a, while the positive DC bus bar 36a by be wire bonded to the collector plating 44b of the high side 20b. The emitters of the IGBTs 48 and anodes of the diodes 50 may be wire bonded to the respective emitter plating 43a, 43b. In contrast to soldering, the use of wire bonding allows for high volume manufacturing. 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 wire bonds 44 may be nickel finished or aluminum clad, although gold or palladium may be employed at the risk of incurring higher manufacturing costs. Figure 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 34b, 36b parallel and spaced from one another by a bus bar insulation 38. The DC bus bars 34b, 36b are horizontal with respect to a substrate 40 (Figures 2A and 2B), 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 Figures 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 Figure 2B, the power semiconductor devices include a number of decoupling capacitors 55 electrically coupled between the DC bus bars 34, 36 and ground to reduce EMI. In contrast to prior designs, the decoupling capacitors 55 are located on the substrate 40 inside the housing 12. For example, some of the decoupling capacitors 55 are electrically coupled directly to the emitter plating 43a on the low side 20a of the substrate 40 and some of the decoupling capacitors 55 are electrically coupled directly to the collector plating 44b on the high side 20b of the substrate 40. The decoupling capacitors 55 can be soldered in the same operation as the soldering of the substrate 40 to the cold plate 14. As best illustrated in Figures 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 smoother current flow within the DC bus bars 34, 36 and lower inductance paths 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 reliability. 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 bar 34, 36 may be integrally molded in the housing 12, or alternatively, the DC bus bar 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 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 large substrate 40 reduces or eliminates the need for jumpers, and consequently has the benefit of reducing inductance in the power module 10. The use of a cold plate 14 as the base plate, and the direct mounting of the power semiconductor devices thereto, enhances the cooling for the power semiconductor devices over other designs, producing a number of benefits such as prolonging the life of capacitors 55.

The power semiconductor devices are operable to transform and/or condition electrical power. As discussed above, the power semiconductor devices may include switches and/or diodes 50. The power semiconductor devices may also include other electrical and electronic components, for example, capacitors 55 and inductors. The power module 10 and power semiconductor devices may be configured and operated as an inverter (DC→7\C), rectifier (AC^DC), and/or converter (DC^DC; AC^AC). For example, the power module 10 and/or power semiconductor devices may be configured as full bridges, half bridges, and/or H-bridges, as suits the particular application.

Figure 5 schematically illustrates the layout of the substrate 40, employing twelve distinct regions of collector plating 44a, 44b, denominated collectively below as tiles 44. The tiles 44 are generally arranged in a low side 20a row of six areas of collector plating 44a and a high side 20b row of six areas of collector plating 44b. Each tile 44 can carry a variety of switches such as IGBTs 48 and/or a variety of diodes 50. The gate driver board(s) 22 (Figure 1) are coupled to control the power semiconductor devices, 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 tile 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 tile 44 may depend on the specific application. For example, a tile 44 may carry up to four IGBTs 48, or alternatively, up to eight diodes 50. Alternatively, a tile 44 may carry four diodes 50 and omit IGBTs 48, for example, where the power semiconductor devices on the tile 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 tile 44. The ability to add additional components of one type in the place of components of another type on a tile 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 tiles 44, which may carry more of less 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 44b on the high side 20b of the substrate 40. Current is then permitted to flow through one or more of the switching devices 48 and/or diodes 50 on the high side 20b to the emitter layer 43b. The current passes the emitter layer 43a on the low side 20a via the conductive strip 45 passing under the DC bus bars 34, 36. A phase terminal allows current to flow from the emitter layer 43a on the low side 20a 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 20a via the emitter layer 43a.

The overall design of the standard power module 10, including the position and structure of the DC and AC buses 16, 18, topology of the substrate 40, modularity of the tiles 44, and the inclusion of six phase terminals 28a, 28b, 30a, 30b, 32a, 32b 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

Figure 5 also shows the single power module 10 configured as a power inverter. The power inverter may be suitable, for example, for providing 300A 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 power bus 18. In particular, the phase terminals 28a, 28b, 30a, 30b, 32a, 32b, are electrically coupled in pairs, each pair supplying a respective phase of the power.

Single Power Module Power Converter

Figure 6 shows a single power module 10 configured as an AC/AC power converter. The power converter may be suitable, for example, for providing 300A at 1200V. Three of the AC phase terminals 28a, 28b, 30a are electrically coupled to respective phases (A, B, C) of a three phase AC power source 58, while the other three AC phase terminals 30b, 32a, 32b are electrically coupled respective phases of a three phase AC load 60. Single Power Module Half Bridge Rectifier

Figure 7 shows a single power module 10 configured as a half bridge rectifier. The half bridge rectifier may be suitable, for example, for providing 1800A at 1200V or 2400A at 600V. A typically use would employ a dedicated half bridge for each phase of the power source. All of the AC phase terminals 28a, 28b, 30a, 30b, 32a, 32b of the power module 10 are electrically coupled a phase (A, B, or C) of the three phase AC power source 62. The DC terminals 24, 26 are electrically coupled respective poles of a DC load 64.

As illustrated, the power module 10 is configured with IGBTs 50 for activation 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

Figure 8 shows a single power module 10 configured as an H bridge rectifier. The H bride rectifier may be suitable, for example, for providing 900A at 1200V, sufficient for home applications and furnaces such as induction heating. Three of the AC phase terminals 28a, 28b, 30a are electrically coupled to one line of an AC power source 62, while the other AC phase terminals 30b, 32a, 32b 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 62.

Dual Power Module Configurations

Figure 9 shows a pair of power modules 10a, 10b physically coupled back-to-back with the cold plates 14 facing each other. Alternatively, the power modules 10a, 10b may be physically coupled front-to-front, depending on orientation and specific topology.

A dielectric spacer 66 may positioned between the opposed faces (i.e., backs or fronts) of the first and second power modules 10a, 10b to form a capacitor 68. This takes advantage of the integrated cold plates 14 in the power modules 10a, 10b. Since the dielectric spacer 66 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 10a to respective ones of the of the DC bus bars 34, 36 of the second module 10b. In some embodiments, the external connector 70 may also function as a clamp, for biasing or holding the first and second power modules 10a, 10b together. The external connector 70 may conform to the exterior of a portion of the power modules 10a, 10b, 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 10a, 10b 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 material, for example, NOMEX® available from E.I. du Pont de Nemours and Company, Advanced Fibers Systems, Richmond, Virginia. 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.

High Power Inverter

Figure 10 shows a pair of power modules 10a, 10b physically coupled back-to-back similar to that of Figure 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 10a to respective ones of the of the DC bus bars 34, 36 of the second module 10b.

The phase terminals of the first power module 10a 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 10a is operated as a starter inverter (i.e., rectifier) while a second power module 10b functions as a main inverter. Note that the IGBTs 48 have been removed from the tiles 44 of the first power module 10a, since the IGBTs are not necessary for the rectification, thus significantly reducing the cost of the inverter.

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

Figure 11 shows a pair of power modules 10a, 10b physically coupled back-to-back similar to that of Figure 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 1800A at 1200V or 2400A 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 10a to respective ones of the of the DC bus bars 34, 36 of the second module 10b. 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 28a, 28b, 30a, 30b, 32a, 32b of the first power module 10a are electrically coupled to provide respective phases (A, B, or C) to a first three phase AC power load 60. Pairs of the AC phase terminals 28a, 28b, 30a, 30b, 32a, 32b of the second power module 10b 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 Figure 12 shows a pair of power modules 10a, 10b physically coupled back-to-back similar to that of Figure 9, and electrically coupled as a single three phase inverter. The inverter may be suitable, for providing power to two three phase AC loads. The inverter may be suitable, for example, for providing 1800A at 1200V or 2400A 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 10a to respective ones of the of the DC bus bars 34, 36 of the second module 10b. 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 28a, 28b of the first power module 10a are electrically coupled to a first pair 32a, 32b of the AC phase terminals of the second power module 10b, and to provide a first phase (A) to a three phase AC power load 60. A second pair of the AC phase terminals 30a, 30b of the second power module 10b are electrically coupled to a second pair of AC phase terminals 30a, 30b of the second power module 10b and to provide a second phase (B) to the three phase AC load 60. A third pair of the AC phase terminals 32a, 32b of the first power module 10a are electrically coupled to a third pair of the AC phase terminals 28a, 28b of the second power module 10b and to provide a third phase (C) to the three phase AC load 60.

Dual Power Module Half Bridge Rectifier

Figure 13 shows a pair of power modules 10a, 10b physically coupled back-to-back similar to that of Figure 9, and electrically coupled as a half bridge. The half bridge may be suitable, for example, for providing 1800A at 1200V, or 2400A at 600V. In typically use, a separate half bridge will be provided for each phase.

All of the AC phase terminals 28a, 28b, 30a, 30b, 32a, 32b of the first power module 10a are electrically coupled to one line of an AC power source 62. All of the AC phase terminals 28a, 28b, 30a, 30b, 32a, 32b of the second power module 10b are electrically coupled to one line of an AC load 60 to provide one phase (A).

Dual Power Module H Bridge Rectifier

Figure 14 shows a pair of power modules 10a, 10b physically coupled back-to-back similar to that of Figure 9, and electrically coupled as an H bridge. The H bride may be suitable, for example, for providing 900A at 1200V.

Three of the AC phase terminals 28a, 28b, 30a of the first power module 10a are electrically coupled to one line of an AC power source 62, while the other three AC phase terminals 30b, 32a, 32b of the first power module 10a are electrically coupled to the other line of the AC power supply 62. Three of the AC phase terminals 28a, 28b, 30a of the second power module 10b are electrically coupled to one line of an AC load 60, while the other AC phase terminals 30b, 32a, 32b of the second power module 10b are electrically coupled to the other line of the AC load 60.

Tri-Level Inverter

Figures 15-19 illustrate tri-level inverters that take advantage, inter alia, of the inclusion of two terminals per phase in the design of the base power module 10. This approach reduces the size and cost over prior tri-level inverters which employ two separate bi-level modules for each phase, requiring fairly complex external coupling schemes.

Figure 15 shows an embodiment of a tri-level inverter 170 implemented with the base power module 10. One phase terminal 28a, 30a, 32a in each pair of phase terminals is coupled to a neutral line in the housing 12 of the power module 10, to provide a reference to a respective phase 164a, 164b, 164c of a three-phase load 164, such as a motor. The other terminal 28b, 30b, 32b of each pair of phase terminals is electrically coupled to provide the first, second, and third voltages V-i, V₂, V₃ across the respective phase 164a, 164b, 164c of the three-phase load 164. Figure 16 is an electrical schematic of a single-phase tri-level inverter 170, or one phase of a three-phase tri-level inverter. The collector 172 of a first transistor Q1 is coupled to a positive DC supply line P. The emitter 174 of the first transistor Q1 is connected to a first node 176. A first anti- parallel diode D1 is connected between the collector 172 and the emitter 174 of the first transistor Q1. The base 178 of the first transistor Q1 is coupled to a first control line G1. The first node 176 is coupled to a first control reference line EK

The collector 182 of a second transistor Q2 is coupled to the first node 176. The emitter 184 of the second transistor Q2 is connected to a second node 186. A second anti-parallel diode D2 is connected between the collector 182 and the emitter 184 of the second transistor Q2. The base 188 of the second transistor Q2 is coupled to a second control line G2. The second node 186 is coupled to a second control reference line EK2.

The collector 192 of a third transistor Q3 is coupled to the second node 186. The emitter 194 of the third transistor Q3 is connected to a third node 196. A third anti-parallel diode D3 is connected between the collector 192 and the emitter 194 of the third transistor Q3. The base 198 of the third transistor Q3 is coupled to a third control line G3. The third node 196 is coupled to a third control reference line EK3. The collector 102 of a fourth transistor Q4 is coupled to the third node 196. The emitter 104 of the fourth transistor Q4 is connected to a fourth node 106. A fourth anti-parallel diode D4 is connected between the collector 102 and the emitter 104 of the fourth transistor Q4. The base 108 of the fourth transistor Q4 is coupled to a fourth control line G4. The fourth node 106 is coupled to a fourth control reference line EK4 and to a negative DC supply line N.

A fifth diode D5 is coupled between the first node 176 and a fifth node 116. A sixth diode D6 is coupled between the fifth node 116 and the third node 196. The second node 186 provides a phase-output of the tri-level inverter 170 and the fifth node 116 provides a neutral line for the phase output. For improved performance characteristics, parallel components may be used. For example, each transistor illustrated in Figure 16 may actually represent two or more parallel transistors.

Switched voltage states for the tri-level inverter 170 of Figure 16 can be realized as follows. A first voltage state of zero volts across the second node 186 and the fifth node 116 can be achieved by (a) applying a low signal (for example, zero volts) to the first control line G1 with respect to the first control reference line EK1 ; (b) applying a high signal (for example, 15 volts DC) to the second control line G2 with respect to the second control reference line EK2; (c) applying a high signal (for example, 15 volts DC) to the third control line G3 with respect to the third control reference line EK3; and (d) applying a low signal (for example, zero volts) to the fourth control line G4 with respect to the fourth control reference line EK4.

A second output state of P volts (a positive voltage) across the second node 186 and the fifth node 116 can be achieved by (a) applying a high signal (for example, 15 volts DC) to the first control line G1 with respect to the first control reference line EK1 ; (b) applying a high signal (for example, 15 volts DC) to the second control line G2 with respect to the second control reference line EK2; (c) applying a low signal (for example, zero volts) to the third control line G3 with respect to the third control reference line EK3; and (d) applying a low signal (for example, zero volts) to the fourth control line G4 with respect to the fourth control reference line EK4.

A third output voltage state of N volts (a negative output voltage) across the second node 186 and the fifth node 116 can be achieved by (a) applying a low signal (for example, zero volts) to the first control line G1 with respect to the first control reference line EK1 ; (b) applying a low signal (for example, zero volts) to the second control line G2 with respect to the second control reference line EK2; (c) applying a high signal (for example, 15 volts DC) to the third control line G3 with respect to the third control reference line EK3; and (d) applying a high signal (for example, 15 volts DC) to the fourth control line G4 with respect to the fourth control reference line EK4.

By controlling the first through fourth transistors Q1-Q4 using the first through fourth control lines G1-G4 and the first through fourth control reference lines EK1-EK4, an output can deliver an alternating voltage with three values: P, zero and N. After reviewing the specification, one of skill in the art will recognize that it is the difference in potential between respective control lines and control reference lines that controls the operation of the transistors Q1-Q4. Appropriate control signals may be generated by the controller 52 (see Figure 5).

The tri-level inverter 170 when connected to a typical load (see Figure 15), such as a motor (not shown), can be controlled so as to supply an approximately sinusoidal alternating current output for particular load conditions. This principle is illustrated in Figure 17, which is a timing diagram for the tri-level inverter 170 of Figure 16 illustrating an example output voltage between a time period to and a time period t|. Voltage level U1 shows the voltage applied to the first control line G1 with respect to the first control reference line EK1. Voltage level U2 shows the voltage applied to the second control line G2 with respect to the second control reference line EK2. Voltage level U3 shows the voltage applied to the third control line G3 with respect to the third control reference line EK3. Voltage level U4 shows the voltage applied to the fourth control line G4 with respect to the fourth control reference line EK4.

Figure 18 illustrates a top view of an embodiment of the single- phase tri-level inverter 170 of Figure 16 implemented in the base power module 10 of Figure 1. The lead 30a of the base power module 10 is coupled to the fifth node 116 of the tri-level inverter 170 and the phase lead 30b of the base power module 10 is coupled to the second node 186 of the tri-level inverter 170. Figure 19 is an electrical schematic of a three-phase, tri-level inverter 170. It comprises three phase circuits 170U, 170V, 170W, each of which is a single-phase tri-level inverter circuit as described in Figure 16. The three neutral lines neutral U, neutral V, neutral W may be coupled together to a single neutral bus (not shown). After reviewing the specification, one of skill in the art will recognize that other multi-level inverters, such as an inverter configured to operate in four, non-loaded voltage states, may be employed.

High Power Devices Employing A Capacitor Across A DC Bus

Figures 20 and 21 show an embodiment of the base power converter 10 configured with a high frequency capacitor 200 and a bulk capacitor 202, suitable for a variety of high power applications, for example, as a 600V, 800A inverter. Figures 20 and 21 also illustrate a gate driver board 22 (not shown in Figures 1 and 2A so as to illustrate the structure under the gate driver board 22). As illustrated in Figures 20 and 21 , a second housing 216 receives the first housing 12, as well as both the high frequency capacitor 200 and the bulk capacitor 202. The second housing 216 may provide an enclosure or channels to provide liquid cooling in the cold plate 14.

The high frequency capacitor 200 may be a film capacitor, rather than an electrolytic capacitor. This provides a tightly coupled, low impedance path for high frequency components of current. The high frequency capacitor 200 may be physically coupled adjacent the gate driver board 22 via various clips, clamps, and/or fasteners 204, 206. The high frequency capacitor 200 may overlay a portion of the first housing 12, and may be electrically coupled to the DC bus bars 34, 36 (Figure 2A) via the terminals 24, 26, respectively. The bulk capacitor 202 may be an electrolytic capacitor or a film capacitor such as a polymer film capacitor, and may be physically coupled adjacent the gate driver board 22 via various clips, clamps, and/or fasteners 208. The bulk capacitor 202 may be electrically coupled to the DC bus bars 34, 36 via the terminals 24, 26, respectively. Alternatively, the anode of the bulk capacitor 202 may be electrically coupled to the anode of the high frequency capacitor 200 and the cathode of the bulk capacitor 202 may be electrically coupled to the cathode of the high frequency capacitor 200 via DC interconnects.

The second housing 216 is provided to physically receive the high frequency capacitor 200, the bulk capacitor 202, the base power converter 10 and first housing 12. The second housing 216 further accepts the cold plate 14, containing an inlet aperture 260 and outlet aperture 262 for liquid cooling of the cold plate 14. The cold plate 14 may take the form of a pin finned aluminum silicone carbide (ALSIC) plate. The use of ALSIC plate closely matches the thermal expansion properties of the substrate 40, thus reducing cracking and the void formation associated with thermal cycling. This particular embodiment employs liquid cooling of the cold plate 14 via inlet 260 and outlet 262.

Tightly coupling the bulk capacitor 202 and high frequency capacitor 200 to the DC bus bars 34, 36, avoids bus bar problems typically associated with DC bus bars 34, 36, and may allow the elimination of overvoltage (i.e., snubber) capacitors. The high frequency capacitor 200 provides a very low impedance path for the high-frequency components of the switched current. The prior art of high-frequency paths (sometimes called "decoupling" or "snubber" paths) placed a discrete package external to the module. Since this path included a significant stray inductance, the discrete package was large. For example, in one embodiment, the discrete capacitor is 1 uF. However, the inclusion of the high frequency capacitor 200 serves the purpose better, but with only 50nF (5% of the capacitance). Further, this makes the capacitor so small it did not impact the size of the power module 10, thus completely eliminating the need for external hardware and volume requirements.

Voltage Overshoot Limiting

Current flowing through various inductive paths within the module transiently stores energy which increases energy loss, reduces efficiency, and generates heat. When the flow of current changes, as in such a high frequency switching environment, large voltage overshoots often result, further decreasing efficiency. These large voltage overshoots typically reduce the power rating of the power module or require the use of circuitry devices with higher ratings than would otherwise be required, thus significantly increasing the cost of the power module.

To minimize the negative effects of current gradients, noise and voltage overshoots associated with the switching process of the module, large capacitors are generally placed in a parallel arrangement between the positive and negative DC connections or from each DC connection to a ground or chassis. These large capacitors are commonly referred to as "X" or "Y" capacitors. Relatively large external capacitors of about around 100 micro Farads are needed. By "external" it is meant that the element referred to is located outside of a power module. High frequency noise, and voltage overshoots that are initiated in the module by the switching process travel away from the source of the noise and voltage overshoots. A low impedance network may be used to provide a return path for the high frequency energy associated with noise and voltage overshoots. The further the energy travels, the more difficult it is to provide a low impedance network to return the energy. Therefore, capacitors attached between the positive and negative DC connections or from the DC connections to ground must be relatively large to minimize the impact of noise, and voltage overshoots. In addition, these external capacitors typically cause stray inductance, which renders the capacitor ineffective at frequencies higher than about 10 kHz.

These and other problems are avoided and numerous advantages are provided by the method and device described herein.

As best illustrated in Figures 22A, 22B and 23, the power semiconductor devices include a number of snubber capacitors 53 that are electrically coupled between the DC bus bars 34, 36 to clamp voltage overshoot. For example, some of the snubber capacitors 53 are electrically coupled directly (i.e., surface mounted) to the emitter plating 43a on the low side 20a of the power module 10 and are electrically coupled directly (i.e., surface mounted) to the collector plating 44b on the high side 20b of the power module 10. While the Figures show two snubber capacitors for each switching pair combination, the power module 10 may include fewer or a greater number of snubber capacitors as suits the particular application. Significant savings may be realized by effective clamping of voltage overshoot. For example, if switching is maintained below approximately 900V, a transformer may be eliminated. The snubber capacitors 53 can be soldered in the same operation as the soldering of the substrate 40 to the cold plate 14, or the soldering of other elements of the power semiconductor devices to the substrate 40, simplifying manufacturing and reducing costs. 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 20b of the power module 10 and "negative" elements are located or coupled to the low side 20a 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. 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.

Claims

1. A power system, comprising: 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.

2. The power system of claim 1 wherein the first and the second power modules are arranged back-to-back with the cold plate of the first power module facing the cold plate of the second power module.

3. The power system of claim 2, further comprising: a dielectric interposed between the cold plates of the first and the second power modules.

4. The power system of claim 1 wherein the first and the second buses of the first power module comprises a first bus bar and a second bus bar substantially parallel to and spaced from the first bus bar by a first dielectric, each of the first and the second bus bars having at least two terminals extending out of the module housing of the first power module to provide access to the first and the second buses externally from the module housing, and wherein the first and the second buses of the second power module comprises a first bus bar and a second bus bar substantially parallel to and spaced from the first bus bar by a second dielectric, each of the first and the second bus bars having at least two terminals extending out of the module housing of the second power module to provide access to the first and the second buses externally from the module housing.

5. The power system of claim 1 wherein the external connector is approximately U-shaped.

6. The power system of claim 1 wherein the external connector is formed as a laminate comprising a first conducting layer, a second conducting layer and at least one electrically insulating layer electrically isolating the first conducting layer from the second conducting layer.

7. The power system of claim 1 wherein the first and the second leg components comprise at least one of an integrated gate bipolar transistor, a metal oxide semiconductor field effect transistor, and a diode.

8. The power system of claim 1 wherein the first power module is operable to passively rectify an alternating current received at the first set of electrical terminals of the first power module and the second power module is operable to invert a direct current received at the first and the second buses of the second power module.

9. The power system of claim 1 wherein the first power module is operable to actively rectify an alternating current received at the first set of electrical terminals of the first power module and the second power module is operable to invert a direct current received at the first and the second buses of the second power module.

10. The power system of claim 1 wherein the first power module is operable to rectify an alternating current received at the first set of electrical terminals of the first power module to provide a direct current on the first and the second buses of the first power module, and wherein the second power module is operable to rectify an alternating current received at the first set of electrical terminals of the second power module to provide a direct current at the first and the second buses of the second power module.

11. The power system of claim 10 wherein the first set of electrical terminals of the first power module comprises six electrical terminals where a first three of the electrical terminals are electrically connected together and a second set of three electrical terminals electrically connected together, and wherein the first set of electrical terminals of the second power module comprises six electrical terminals where a first three of the electrical terminals are electrically connected together and a second three of the electrical terminals are electrically connected together.

12. The power system of claim 10 wherein the first power module comprises six electrical terminals in the first set of electrical terminals where the six electrical terminals are electrically connected together, and wherein the second power module comprises six electrical terminals in the first set of electrical terminals where the six electrical terminals are electrically connected together.

13. The power system of claim 1 wherein the first power module is operable to invert a direct current received at the first and second buses of the first power module to provide an alternating current at the first set of terminals of the first power module, and wherein the second power module is operable to invert a direct current received at the first and second buses of the second power module to provide an alternating current at the first set of terminals of the second power module.

14. The power system of claim 13 wherein each of the electrical terminals of the first power module is electrically connected to a respective phase of a first load, and each of the electrical terminals of the second power module is electrically connected to a respective phase of a second load.

15. The power system of claim 13 wherein each of the electrical terminals of the first power module is electrically connected to a respective one of the electrical terminals of the second power module.

16. A power system, comprising: 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.

17. The power system of claim 16, further comprising: a dielectric interposed between the cold plates of the first and the second power modules.

18. The power system of claim 17 wherein the external connector is formed as an approximately U-shaped laminate comprising a first conducting layer, a second conducting layer and at least one electrically insulating layer electrically isolating the first conducting layer from the second conducting layer, the external connector comprising a first arm and a second arm spaced from the first arm sufficiently to receive the rectifier power module and the inverter power module therebetween.

19. The power system of claim 16 wherein the rectifier power module comprises a number of transistors electrically coupled to actively rectify an alternating current received at the set of input terminals.

20. A power system, comprising: 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.

21. The power system of claim 20, further comprising: a dielectric interposed between the cold plates of the first and the second power modules.

22. The power system of claim 21 wherein the external connector is formed as an approximately U-shaped laminate comprising a first conducting layer, a second conducting layer and at least one electrically insulating layer electrically isolating the first conducting layer from the second conducting layer.

23. The power system of claim 22 wherein the first and the second rectifiers are configured as an H bridge.

24. The power system of claim 22 wherein the first and the second rectifiers are configured as a half bridge.

25. The power system of claim 22 wherein the at least one of the first and the second rectifier power modules comprises a number of transistors electrically coupled to actively rectify an alternating current received at the respective set of input terminals.

26. A power system, comprising: 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.

27. The power system of claim 26, further comprising: a dielectric interposed between the cold plates of the first and the second power modules.

28. The power system of claim 27 wherein the external connector is formed as an approximately U-shaped laminate conforming to at least a portion of an exterior of the first and the second inverter power modules, the U-shape laminate comprising a first conducting layer, a second conducting layer and at least one electrically insulating layer electrically isolating the first conducting layer from the second conducting layer.

29. The power system of claim 28 wherein at least a first, a second and a third one of the output terminals of the first inverter power module is electrically coupled to supply a respective phase of three phase AC power to a first load and at least a first, a second and a third one of the output terminals of the second inverter power module is electrically coupled to supply a respective phase of three phase AC power to a second load.

30. The power system of claim 28 wherein at least a first one of the output terminals of each of the first and the second inverter modules are electrically coupled to supply a first phase of a three phase AC power to a first load, at least a second one of the output terminals of each of the first and the second inverter modules are electrically coupled to supply a second phase of three phase AC power to the first load, and at least a third one of the output terminals of each of the first and the second inverter modules are electrically coupled to supply a third phase of three phase AC power to the first load.

31. A method of forming a power system, comprising: 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.

32. The method of claim 31 wherein 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 comprises attaching an external connector between the first buses of the first power module and the second power module and attaching the external connector between the second buses of the first and the second power modules.

33. The method of claim 31 wherein 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 comprises attaching an approximately U shaped external laminate connector conforming to an exterior of the first and the second power modules between the first buses of the first power module and the second power module and attaching the external connector between the second buses of the first and the second power modules.

34. A power module, comprising: a module housing; a set of DC terminals accessible from an exterior of the module housing; at least three pairs of AC terminals accessible from the exterior of the module housing; and an inverter circuit contained within the module housing, the inverter circuit configurable to selectively switch between at least three output states and electrically coupled between the set of DC terminals and at least one of the pairs of AC terminals.

35. The power module of claim 34, further comprising a set of control terminals accessible from the exterior of the module housing and electrically coupled to the inverter circuit.

36. The power module of claim 34, wherein the inverter circuit comprises at least three pairs of output nodes each electrically coupled to a respective one of the pairs of AC terminals.

37. A power module, comprising: a housing; an inverter, the inverter comprising: a first node for electrically coupling to a first supply voltage; a second node; a first transistor electrically coupled between the first node and the second node, the first transistor comprising a control terminal for electrically coupling to a first control signal; a first diode electrically coupled in anti-parallel across the first transistor; a third node for providing an output; a second transistor electrically coupled between the second node and the third node, the second transistor comprising a control terminal for electrically coupling to a second control signal; a second diode electrically coupled in anti-parallel across the second transistor; a fourth node; a third transistor electrically coupled between the third node and the fourth node, the third transistor comprising a control terminal for electrically coupling to a third control signal; a third diode electrically coupled in anti-parallel across the third transistor; a fifth node for electrically coupling to a second supply voltage; a fourth transistor electrically coupled between the fourth node and the fifth node, the fourth transistor comprising a control terminal for electrically coupling to a fourth control signal; a fourth diode electrically coupled in anti-parallel across the fourth transistor; a sixth node for providing an output; a fifth diode electrically coupled between the second node and the sixth node; and a sixth diode electrically coupled between the sixth node and the fourth node; a first DC terminal accessible from an exterior of the housing and electrically coupled to the first node; a second DC terminal accessible from the exterior of the housing and electrically coupled to the fifth node; a first output terminal accessible from the exterior of the housing and electrically coupled to the third node; and a second output terminal accessible from the exterior of the housing and electrically coupled to the sixth node.

38. The power module of claim 37, further comprising a control-signal bus accessible from the exterior of the housing and coupled to the control terminal of the first transistor.

39. The power module of claim 37, further comprising: third, fourth, fifth and sixth output terminals accessible from the exterior of the housing.

40. A power module, comprising: an inverter, comprising at least three phase circuits, each of the phase circuits comprising: a first node for electrically coupling to a first supply voltage; a second node; a first transistor electrically coupled between the first node and the second node, the first transistor comprising a control terminal for electrically coupling to a first control signal; a first diode electrically coupled in anti-parallel across the first transistor; a third node for providing a phase output; a second transistor electrically coupled between the second node and the third node, the second transistor comprising a control terminal for electrically coupling to a second control signal; a second diode electrically coupled in anti-parallel across the second transistor; a fourth node; a third transistor electrically coupled between the third node and the fourth node, the third transistor comprising a control terminal for electrically coupling to a third control signal; a third diode electrically coupled in anti-parallel across the third transistor; a fifth node for electrically coupling to a second supply voltage; a fourth transistor electrically coupled between the fourth node and the fifth node, the fourth transistor comprising a control terminal for electrically coupling to a fourth control signal; a fourth diode electrically coupled in anti-parallel across the fourth transistor; a sixth node for providing a neutral output; a fifth diode electrically coupled between the second node and the sixth node; and a sixth diode electrically coupled between the sixth node and the fourth node; a housing; a first DC terminal accessible from an exterior of the housing and electrically coupled to the first node of each phase circuit; a second DC terminal accessible from the exterior of the housing and electrically coupled to the fifth node of each phase circuit; a first AC terminal accessible from the exterior of the housing and electrically coupled to the third node of a first phase circuit; a second AC terminal accessible from the exterior of the housing and electrically coupled to the sixth node of the first phase circuit; a third AC terminal accessible from the exterior of the housing and electrically coupled to the third node of a second phase circuit; a fourth AC terminal accessible from the exterior of the housing and electrically coupled to the sixth node of the second phase circuit; a fifth AC terminal accessible from the exterior of the housing and electrically coupled to the third node of a third phase circuit; and a sixth AC terminal accessible from the exterior of the housing and electrically coupled to the sixth node of the third phase circuit.

41. The power module of claim 40, further comprising a control-signal bus accessible from the exterior of the housing and electrically coupled to the control terminal of the first transistor of the first phase circuit.

42. The power module of claim 40, further comprising a controller for generating control signals for applying to the control terminal of the first through fourth transistors of the first phase circuit.

43. The power module of claim 40, wherein the second, fourth and sixth AC terminals are electrically coupled together.

44. A power system, comprising: a DC power supply; a power module, comprising: a housing; a pair of input terminals accessible from an exterior of the housing, the input terminals electrically coupled to the DC power supply; a DC bus electrically coupled to the pair of input terminals; three pairs of output terminals accessible from the exterior of the housing; an AC bus electrically coupled to at least one of the three pairs of output terminals; and an inverter circuit configurable to selectively operate in one of at least three output states and electrically coupled between the DC bus and the AC bus; and a controller to generate control signals to control the inverter circuit.

45. The power system of claim 44 wherein the controller is contained within the housing of the power module.

46. The power system of claim 44, further comprising: a load, wherein each pair of output terminals is electrically coupled to the AC bus to supply a respective phase of three-phase AC power to the load.

47. The power system of claim 44, further comprising: a number of loads, wherein each pair of output terminals is electrically coupled to the AC bus to supply AC power to a respective one of the loads.

48. A power module, comprising: a housing; multi-level inverter means for selectively converting a direct current to an alternating current, the multi-level inverter means configurable to provide at least three nominal output voltage levels; means for externally coupling a DC power source to the multilevel inverter means; means for externally coupling the multi-level inverter means to a first, a second, and a third load.

49. The power module of claim 48 wherein the multilevel inverter means is configured to convert a direct current to an alternating current of at least three phases.

50. A method of supplying AC power to a load, comprising: electrically coupling a DC power supply to a DC bus of a power module; electrically coupling the DC bus to an inverter contained within the power module; converting the DC power to AC power by selectively switching the inverter between at least three nominal output voltage levels; electrically coupling the inverter to an AC bus of the power module; and electrically coupling the AC bus to at least two exterior terminals of the power module.

51. The method of claim 50 wherein converting the DC power to AC power comprises generating at least three alternating currents and wherein electrically coupling the AC bus to at least two exterior terminals of the power module comprises coupling the AC bus to at least six exterior terminals of the power module.

52. The method of claim 50 wherein converting the DC power to AC power comprises generating first, second and third phases of an alternating current.

53. A power module, comprising: a housing; a first DC bus structure; a second DC bus structure electrically isolated from the first DC bus structure; a circuit electrically coupled between the first and the second DC bus structures; a high frequency capacitor comprising an anode and a cathode, the anode electrically coupled to the first DC bus structure and the cathode electrically coupled to the second DC bus structure; and a bulk capacitor comprising an anode and a cathode, the anode electrically coupled to the first DC bus structure and the cathode electrically coupled to the second DC bus structure.

54. The power module of claim 53 wherein the first DC bus structure comprises a first DC bus bar comprising a number of terminals and the second DC bus structure comprises a second DC bus bar comprising a number of terminals and wherein the housing comprises a lead frame, the lead frame supporting the first and the second DC bus structures.

55. The power module of claim 53 wherein the first and the second DC bus structures are received in the housing with at least one terminal of each of the first and the second DC bus structures extending from the housing.

56. The power module of claim 53 wherein the circuit comprises a number of semiconductor switches and a number of semiconductor diodes electrically coupled as a bi-directional converter circuit.

57. The power module of claim 53 wherein the high frequency capacitor is a film capacitor.

58. The power module of claim 53 wherein the high frequency capacitor is an electrolytic capacitor.

59. The power module of claim 53 wherein the bulk capacitor is a film capacitor.

60. The power module of claim 53 wherein the bulk capacitor is an electrolytic capacitor.

61. The power module of claim 53 wherein the high frequency capacitor has a capacitance of approximately 500 μF and the bulk capacitor has a capacitance of approximately 800 μF.

62. A power module, comprising: a first housing; a first DC bus bar comprising a number of terminals, at least a portion of the first DC bus bar received in the first housing with the terminals accessible from an exterior of the first housing; a second DC bus bar comprising a number of terminals, the second DC bus bar received in the first housing with the terminals accessible from the exterior of the first housing; a bridge circuit received in the first housing and electrically coupled between the first and the second DC bus bars; a high frequency capacitor comprising an anode and a cathode, the anode electrically coupled to at least one terminal of the first DC bus bar and the cathode electrically coupled to at least one terminal of the second DC bus bar; and a bulk capacitor comprising an anode and a cathode, the anode electrically coupled to at least one terminal of the first DC bus bar and the cathode electrically coupled to at least one terminal of the second DC bus bar.

63. The power module of claim 62 further comprising: a second housing receiving the first housing, the bulk capacitor, and the high frequency capacitor.

64. The power module of claim 62 further comprising: a gate driver board physically coupled to the first housing.

65. The power module of claim 64 wherein the terminals of the first and the second DC bus bars extend through apertures formed in the gate driver board and the high frequency capacitor is adjacent the gate driver board.

66. The power module of claim 62 wherein the high frequency capacitor overlies at least a portion of the first housing.

67. The power module of claim 62 wherein the second housing comprises a cold plate with an inlet aperture and an outlet aperture for cooling of the cold plate.

68. A power module, comprising: a first housing; a substrate received in the first housing, the substrate comprising a number of regions; a first DC bus bar comprising a first set of terminals, the first DC bus bar received at least partially in the first housing with the first set of terminals accessible from an exterior thereof; a second DC bus bar comprising a second set of terminals, the second DC bus bar received at least partially in the first housing with the second set of terminals accessible from an exterior thereof; a number of switches mounted to at least some of the regions of the substrate and electrically coupled to one another to form a bridge circuit electrically coupled between the first and the second DC bus bars; a first film capacitor electrically coupled across the terminals of the first and the second DC bus bars; and a second film capacitor electrically coupled across the terminalsof the first and the second DC bus bars.

69. The power module of claim 68 wherein the first film capacitor is disposed in the exterior of the first housing.

70. The power module of claim 69 wherein the second film capacitor is disposed in the exterior of the first housing.

71. The power module of claim 70 further comprising: a first DC interconnect electrically coupling an anode of the first film capacitor to an anode of the second capacitor; and a second DC interconnect electrically coupling a cathode of the first capacitor to a cathode of the second film capacitor.

72. The power module of claim 71 further comprising: a second housing receiving the first housing, the first film capacitor and the second film capacitor.

73. A power module for supplying power to loads from power sources, the power module comprising: a lead frame forming at least a portion of a module housing; a first set of terminals accessible from an exterior of the lead frame; a second set of terminals accessible from the exterior of the lead frame; a positive DC bus received at least partially in the module housing; a negative DC bus received at least partially in the module housing; a number of high side switches received in the module housing and selectively electrically coupling a first one of the first set of terminals to respective ones of the second set of terminals; a number of low side switches received in the module housing and selectively electrically coupling a second one of the first set of terminals to respective ones of the second set of terminals; and at least one capacitor received in the lead frame and electrically coupled between the positive DC bus and the negative DC bus.

74. The power module of claim 73, further comprising: at least one substrate coupled to the lead frame, the at least one substrate comprising a high side and a low side; a number of high side collector plating areas formed on the high side of the at least one substrate; and a number of low side emitter plating areas formed on the low side of the at least one substrate, where the at least one capacitor is surface mounted to at least one of the high side collector plating areas and the low side emitter plating areas.

75. The power module of claim 73, further comprising: at least one substrate coupled to the lead frame, the at least one substrate comprising a high side and a low side; a number of high side collector plating areas formed on the high side of the at least one substrate; and a number of low side emitter plating areas formed on the low side of the at least one substrate, where a first pole of the at least one capacitor is surface mounted to one of the high side collector plating areas and where a second pole of the at least one capacitor is surface mounted to one of the low side emitter plating areas.

76. The power module of claim 73, further comprising: at least one substrate coupled to the lead frame, the at least one substrate comprising a high side and a low side; a number of high side collector plating areas formed on the high side of the at least one substrate; and a number of low side emitter plating areas formed on the low side of the at least one substrate, where for each of the number of high side collector plating areas at least one capacitor is surface mounted to one of the high side collector plating areas and is surface mounted to a respective one of the low side emitter plating areas.

77. The power module of claim 73 wherein the positive DC bus comprises a positive DC bus bar and the negative DC bus comprises a negative DC bus bar, the negative DC bus bar comprising at least a portion parallel to and spaced from a portion of the positive DC bus bar by a dielectric material.

78. The power module of claim 77, further comprising: at least one substrate coupled to the lead frame, the at least one substrate comprising a high side and a low side; a number of high side collector plating areas formed on the high side of the at least one substrate; and a number of low side emitter plating areas formed on the low side of the at least one substrate, where for each of the number of high side collector plating areas at least one capacitor is surface mounted to one of the high side collector plating areas and is surface mounted to a respective one of the low side emitter plating areas, each of the capacitors passing through at least one of a number of passages formed in the positive and the negative DC bus bars.

79. A power module, comprising: a lead frame; a plurality of electrical terminals carried by the lead frame; a first bus bar coupled to the lead frame; a second bus bar coupled to the lead frame; a high side substrate coupled to the lead frame, the high side substrate comprising a number of electrically conductive high side collector areas and a number of electrically conductive high side emitter areas, the high side emitter areas electrically isolated from the high side collector areas; a low side substrate coupled to the lead frame, the low side substrate comprising a number of electrically conductive low side collector areas and a number of electrically conductive low side emitter areas, the low side emitter areas electrically isolated from the low side collector areas; a number of high side switches physically coupled to the high side substrate; a number of low side switches physically coupled to the low side substrate; and a number of capacitors received in the lead frame, each of the capacitors electrically coupled between one of the high side collector areas and one of the low side emitter areas.

80. The power module of claim 79 wherein .each of the capacitors is surface mounted to the respective high side collector area.

81. The power module of claim 79 wherein each of the capacitors is surface mounted to the respective low side emitter area.

82. The power module of claim 79 wherein each of the capacitors is surface mounted to the respective high side collector area and is surface mounted to the respective low side emitter area.

83. The power module of claim 79 wherein at least a portion of the first bus bar and at least a portion of the second bus bar are parallel to one another, and spaced from one another by a dielectric material.

84. The power module of claim 79 wherein the first and the second bus bars comprise a number of passages and the capacitors extend through the passages between the high side substrate and the low side substrate.

85. A method of forming a power module, the method comprising: providing a lead frame; coupling a substrate comprising a high side and a low side to the lead frame, the high side comprising a number of high side collector areas and a number of high side emitter areas electrically isolated from the high side collector areas, the low side comprising a number of low side collector areas and a number of low side emitter areas electrically isolated from the low side collector areas; mounting a number of high side switches to the high side of the substrate; mounting a number of low side switches to the low side of the substrate; surface mounting at least one capacitor to one of the low side emitter areas; and surface mounting the at least one capacitor to one of the high side collector areas.

86. The method of claim 85, further comprising: for each of the high side switches, surface mounting a collector of the high side switch to one of the high side collector areas; and for each of the low side switches, surface mounting a collector of the low side switch to one of the low side collector areas.

87. The method of claim 86, further comprising: for each of the high side switches, wire bonding an emitter of the high side switch to one of the high side emitter areas; and for each of the low side switches, wire bonding an emitter of the low side switch to one of the low side emitter areas.

88. The method of claim 86, further comprising: electrically coupling each of the high side emitter areas to a respective one of the low side collector areas.

89. The method of claim 86, further comprising: providing a first bus structure; providing a second bus structure; electrically coupling each of the high side emitter areas to a respective one of the low side collector areas through a number of passages formed in the first and the second bus structures.

90. The method of claim 86, further comprising: providing a first bus structure; providing a second bus structure; and providing a number of conductive straps electrically coupling each of the high side emitter areas to a respective one of the low side collector areas through a number of passages formed in the first and the second bus structures.