Patent Publication Number: US-10326378-B2

Title: Inverter assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/841,520, filed Aug. 31, 2015. This application is related to U.S. patent application Ser. No. 14/841,526, filed Aug. 31, 2015, and U.S. patent application Ser. No. 14/841,532, filed Aug. 31, 2015. The subject matter of the aforementioned applications is incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE PRESENT DISCLOSURE 
     The present disclosure relates generally to an inverter assembly and, more specifically, but not by limitation, to an inverter assembly comprising structures configured to convert a DC input to a three phase AC output. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     According to various embodiments, the present disclosure may be directed to an inverter assembly, comprising: (a) a housing that encloses: (i) a DC input bus bar sub-assembly; (ii) a three phase output AC bus bar sub-assembly; (iii) a DC link capacitor electrically coupled to the DC input bus bar sub-assembly; (iv) a second DC bus bar sub-assembly that electrically couples the DC link capacitor with a plurality of power modules, wherein the plurality of power modules can be electrically coupled to the three phase output AC bus bar sub-assembly; and (v) a cooling sub-assembly associated with the plurality of power modules. 
     According to some embodiments, the present disclosure may be directed to an inverter assembly, comprising: (a) a housing that encloses: (i) a DC input bus bar sub-assembly; (ii) a three phase output AC bus bar sub-assembly having symmetrically aligned output tabs that each carry a unique phase of an AC power signal; (iii) a DC link capacitor electrically coupled to the DC input bus bar sub-assembly; (iv) a gate drive circuit board; (v) a plurality of power modules mounted to the gate drive circuit board, the plurality of power modules producing the AC power signal; and (vi) a second DC bus bar sub-assembly that electrically couples the DC link capacitor with the plurality of power modules, wherein the plurality of power modules can be electrically coupled to the three phase output AC bus bar sub-assembly. 
     According to some embodiments, the present disclosure may be directed to an inverter assembly, comprising: (a) a housing that can comprise a cover and a lower enclosure, wherein the lower enclosure receives: (i) a DC input bus bar sub-assembly mounted to a sidewall of the lower enclosure of the housing; (ii) a DC link capacitor electrically coupled to the DC input bus bar sub-assembly with a pair of connectors that extend upwardly to the DC input bus bar sub-assembly, the DC link capacitor being potted into a void in the housing; (iii) a gate drive circuit board; (iv) a plurality of power modules mounted an underside of the gate drive circuit board, the plurality of power modules producing an AC power signal from DC power received from the DC link capacitor; (v) a second DC bus bar sub-assembly that electrically couples the DC link capacitor with the plurality of power modules, wherein the second DC bus bar sub-assembly bridges above the gate drive circuit board and the DC link capacitor; and (vi) a three phase output AC bus bar sub-assembly comprising three bus bars which can be physically separated from one another, the three bus bars comprising linearly aligned power module tabs that electrically couple with linearly aligned output terminals of the plurality of power modules, wherein the three bus bars further comprise output tabs that each carry a unique phase of the AC power signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the present disclosure are illustrated by the accompanying figures. It will be understood that the figures are not necessarily to scale and that details not necessary for an understanding of the technology or that render other details difficult to perceive may be omitted. It will be understood that the technology is not necessarily limited to the particular embodiments illustrated herein. 
         FIG. 1  is a perspective view of an exemplary drive train that can comprise inverter assemblies of the present disclosure. 
         FIG. 2  is a perspective view of an exemplary inverter assembly. 
         FIG. 3  is an exploded perspective view of the exemplary inverter assembly of  FIG. 2 . 
         FIG. 4  is a top down view of the exemplary inverter assembly with a top cover removed. 
         FIGS. 5A, 5B, and 5C  are various views of an exemplary DC bus bar sub-assembly. 
         FIG. 6  is a perspective view of a portion of another exemplary DC bus bar sub-assembly. 
         FIG. 7  is a perspective view of the exemplary DC bus bar sub-assembly connected to power cables. 
         FIG. 8  is a top elevation view that illustrates an exemplary DC link capacitor of the inverter assembly, where the DC link capacitor may comprise a capacitor bank. 
         FIG. 9A  is a perspective view of an exemplary DC input bus bar that couples the DC link capacitor with power modules. 
         FIG. 9B  is an exploded perspective view of another exemplary DC input bus bar of  FIG. 9A . 
         FIG. 9C  is a cross sectional view of the exemplary DC input bus bar of  FIGS. 9A and 9B . 
         FIG. 10  is a perspective view of the exemplary DC input bus bar installed into the inverter assembly. 
         FIG. 11  is a partial exploded perspective view of exemplary power modules. 
         FIG. 12  is a perspective view of an exemplary three phase output AC bus bar sub-assembly. 
         FIG. 13  is another perspective view of the exemplary three phase output AC bus bar sub-assembly. 
         FIG. 14  is a perspective view of the exemplary three bus bars of the three phase output AC bus bar sub-assembly. 
         FIG. 15  is a top down view of the exemplary three phase output AC bus bar sub-assembly installed into the inverter assembly. 
         FIG. 16  is a perspective view of the exemplary three phase output AC bus bar sub-assembly coupled with power cables. 
         FIG. 17  is an exploded view of an exemplary cooling assembly. 
         FIGS. 18A-C  illustrate an exemplary alternative cooling assembly. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     While this technology is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail several specific embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the technology and is not intended to limit the technology to the embodiments illustrated. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that like or analogous elements and/or components, referred to herein, may be identified throughout the drawings with like reference characters. It will be further understood that several of the figures are merely schematic representations of the present disclosure. As such, some of the components may have been distorted from their actual scale for pictorial clarity. 
     In general, the present disclosure is directed to inverter assemblies and their methods of manufacture and use. An example inverter assembly can comprise a symmetrical structure configured to convert DC input power to AC output power. 
     Some embodiments can include a symmetrical DC input section, a symmetrical AC output section, a gate drive circuit board, and a controller. The gate drive circuit board and controller can be associated with two inverter power modules coupled in parallel. The power modules can provide currents significantly exceeding 400 amps RMS (root mean squared) and in various embodiments, each can comprise an IGBT (insulated gate bipolar transistor), or other suitable element, for switching the direct current into an alternating current. The total RMS current may exceed that which may be typically available by a single commercially available power module. The DC input section can include a DC input bus and a DC bus sub-assembly. The DC bus sub-assembly can have a symmetrical structure with a layered design, including a positive plate and a negative plate substantially overlapping each other. The positive plate can be coupled to the positive terminal of the DC input bus through a plurality of positive input tabs. The negative plate can be coupled to the negative terminal of the DC input bus through a plurality of negative input tabs. The positive plate can have two or more positive output tabs and two or more negative output tabs coupled to the input terminals of the two inverter power modules. 
     The AC output section can include a plurality of output bus bars, each having a symmetrical structure. In an embodiment, the AC output section can provide a three-phase AC power signal. Each of the output bus bars can correspond to a channel (phase) of the three-phase AC power signal. Each bus bar can include two input tabs coupled to output terminals of each channel of the two inverter power modules and an output tab coupled to an AC output terminal of the inverter. The output tab may be disposed at substantial equal distances from the two input tabs of each AC bus bar. These and other advantages of the present disclosure will be described in greater detail infra with reference to the collective drawings. 
     Referring now to  FIG. 1 , which illustrates the positioning of two inverter assemblies, such as exemplary inverter assembly  102 . The inverter assemblies can be disposed on an exemplary drive train  104 . 
       FIGS. 2 and 3  collectively illustrate the exemplary inverter assembly  102  which can comprise a housing  106  that can comprise a lower enclosure  108  and a cover  110 . 
       FIG. 4  is a top down view of the exemplary inverter assembly  102  with the cover  110  removed to expose internal components of the inverter assembly  102 . In some embodiments, the inverter assembly  102  can comprise a DC bus sub-assembly (referred to herein as “DC bus bar  112 ”), a DC link capacitor  114  (which may comprise a capacitor bank and also be referred to as DC link capacitor bank  114 ), a DC input bus bar sub-assembly  170 , a gate drive circuit board  116 , and a three phase output AC bus bar sub-assembly  118 . 
       FIGS. 5A-C  collectively illustrate the example DC bus bar  112  that can comprise a pair of bus bars, namely a positive bus bar  120  and a negative bus bar  122 . Each of the bus bars can comprise an input tab and an output tab. For example, positive bus bar  120  may comprise a positive input tab  124  and a positive output tab  126 , while negative bus bar  122  may comprise a negative input tab  128  and a negative output tab  130 . 
     Both the positive bus bar  120  and the negative bus bar  122  can have a bar body that spans between their respective input tab and output tab. In one embodiment, the positive bus bar  120  can have a positive bar body  132  and the negative bus bar can comprise a negative bar body  134 . 
     In some embodiments, the positive bus bar  120  and the negative bus bar  122  can be shaped similarly to one another. Both the positive bus bar  120  and negative bus bar  122  can have a first section and a second section. For example, the positive bus bar  120  can have a first section  136  and a second section  138 . In some embodiments, the first section  136  and the second section  138  can be positioned relative to one another at a substantially right angle configuration. That is, the first section  136  may extend perpendicularly from the second section  138 . 
     The negative bus bar  122  can comprise a first section  140  and a second section  142 . In some embodiments, the first section  140  and second section  142  can be positioned relative to one another at a substantially right angle. 
     The input tabs on both the positive bus bar  120  and the negative bus bar  122  extend from their respective bar body. For example, the positive input tab  124  can extend in linear alignment with the first section  136  of the positive bar body  132 . The positive output tab  126  can extend rearwardly from the second section  138  of the positive bus bar  120 . 
     The positive bus bar  120  and the negative bus bar  122  can be placed into mating relationship with one another such that the positive bus bar  120  may be nested within the negative bus bar  122  with both being electrically isolated from one another. A space can exist between the positive bar body  132  and the negative bar body  134 . The size of this space can be minimized, which can reduce inductance through the DC bus bar  112  and can minimize noise pick-up from stray fields within the inverter enclosure. 
     In one embodiment, the negative output tab  130  of the negative bus bar  122  may be offset to a side of the second section  142  of the negative bar body  134 . Conversely, the positive output tab  126  of the positive bus bar  120  may be offset to a side of the second section  138  of the positive bar body  132 . In one embodiment, the negative output tab  130  and the positive output tab  126  can be spaced apart from one another due to their positioning on their respective sides of their associated bar body. Similarly, the positive input tab  124  and the negative input tab  128  can be spaced apart from one another and can be individually secured to a terminal block, which is described in greater detail below. 
     In some embodiments, the space between the positive bar body  132  and the negative bar body  134  can be filled with an electrical insulator such as a Mylar™ film. Likewise, surfaces of the positive bar body  132  and the negative bar body  134  that face one another can be coated with a layer of an electrically insulating material rather than disposing an electrically insulating layer therebetween. 
     In some embodiments, the first section  136  of positive bar body  132  and the first section  140  of the negative bar body  134  can be surrounded, at least partially, with an input core  149 . The input core  149  may be configured to contact a terminal block  146  onto which the pair of bus bars can be installed. 
     For example, the terminal block  146  can provide a mounting surface that supports the DC bus bar  112 . The terminal block  146  can mount to the inner sidewall of the lower enclosure  108  and a lower support  148  of the lower enclosure  108 . 
     In some embodiments, the input core  149  may be secured to the terminal block  146  using a compression plate  150 . A spacer  152  can be disposed between the input core  149  and the compression plate  150 . In one embodiment, the spacer  152  may be a silicon foam block, although other materials that would be known to one of ordinary skill in the art can also likewise be utilized in accordance with the present disclosure. 
     Another example of a DC bus bar  112  is illustrated in  FIG. 6 . In this embodiment, the input tabs  141  and  143  can angle upwardly and outwardly from the bar bodies along reference line A, rather than in linear alignment. Also, the input tabs  141  and  143  can extend from a side edge of the bar bodies, while output tabs  145  and  147  can extend in alignment with reference line B. To be sure, reference line A and reference line B can be substantially perpendicular to one another. 
     Turning to  FIG. 7 , the positive input tab  124  and negative input tab  128  can be illustrated as being coupled with input power cables  158  and  160 , respectively. 
       FIG. 8  is a top elevation view that illustrates the exemplary DC link capacitor  114  of the inverter assembly, where the DC link capacitor may comprise a capacitor bank. As illustrated in  FIG. 8 , in some embodiments, the DC bus bar  112  may be electrically coupled to the DC link capacitor  114  through a first connector  154  and a second connector  156 . (The first connector and second connector  156  may variously be positive and negative connectors depending on the arrangement of the polarities provided by the DC bus bar  112 .) According to some embodiments, the first connector  154  and second connector  156  can be coupled or embedded within the DC link capacitor  114 . To be sure, the DC link capacitor  114  can be potted into place within the lower enclosure  108 ; the first connector  154  and second connector  156  being embedded into the DC link capacitor  114  during the potting process. 
     Additionally, a positive output bus bar  162  may be embedded into the DC link capacitor  114 , along with a negative output bus bar  164 . Both the positive output bus bar  162  and the negative output bus bar  164  comprise a plurality of output tabs. For example, the positive output bus bar  162  can comprise positive output tabs  166 A-C, while negative output bus bar  164  can comprise negative output tabs  168 A-C. In some embodiments, the positive output tabs  166 A-C and the negative output tabs  168 A-C can be positioned in linear alignment with one another. The positive output tabs  166 A-C and the negative output tabs  168 A-C can also be alternatingly positioned such that negative output tab  168 A may be positioned between positive output tab  166 A and positive output tab  166 B, just as an example. 
     The DC link capacitor  114  can be potted into a void  169 , in some instances. In one embodiment, the DC link capacitor  114  is secured within the void  169  with a potting material that can include a mixture of polyol and isocyanate. The potting material can include 100 parts polyol to 20 parts isocyanate, in some embodiments. The DC link capacitor material may be poured into the void  169  to a height of 45 to 50 mm below an upper edge of the void  169 . The DC link capacitor material can be cured at 25 degrees centigrade for 24 hours, at 60 degrees centigrade for two hours, or also at 100 degrees centigrade for 20-30 minutes, in various embodiments. 
     Referring now to  FIGS. 9A-10 , which illustrate an example DC input bus bar sub-assembly  170 . The DC input bus bar sub-assembly  170  can also be referred to as a “second DC bus bar sub-assembly” or “DC input bus bar  170 ”. The DC input bus bar  170  can comprise a positive bus bar  174  and a negative bus bar  176 , which can be arranged into a mating relationship with one another similarly to the DC bus bar  112  described above. 
     The positive bus bar  174  can comprise a plurality of positive input tabs  178 A-C and the negative bus bar  176  can comprise a plurality of negative input tabs  180 A-C. When installed, the positive bus bar  174  can couple with the positive output bus bar  162  of the DC link capacitor  114  by connecting the plurality of positive input tabs  178 A-C of the positive bus bar  174  with the positive output tabs  166 A-C of the positive output bus bar  162  of the DC link capacitor  114 . Likewise, the negative bus bar  176  can couple with the negative output bus bar  164  of the DC link capacitor  114  by connecting the plurality of negative input tabs  180 A-C of the negative bus bar  176  with the negative output tabs  168 A-C of the negative output bus bar  164  of the DC link capacitor  114 . 
     The plurality of positive input tabs  178 A-C and the plurality of negative input tabs  180 A-C can be arranged in an alternating and linear configuration. 
     The positive bus bar  174  and negative bus bar  176  can be placed in an overlaid mating relationship with one another. A space  175  may be provided between the positive bus bar  174  and negative bus bar  176 , which can be filled with an electrically insulating material, in some embodiments. The space  175  between the positive bus bar  174  and negative bus bar  176  can allow for low inductance of current through the DC input bus bar sub-assembly  170 . 
     The positive bus bar  174  can comprise a pair of positive output tabs  182 A and  182 B, while the negative bus bar  176  can comprise a pair of negative output tabs  184 A (shown in  FIG. 10 ) and  184 B. The pair of positive output tabs  182 A and  182 B can be disposed on opposing sides of the positive bus bar  174  relative to one another. The pair of negative output tabs  184 A and  184 B can also be disposed on opposing sides of the negative bus bar  176  relative to one another. The pairs of negative and positive output tabs can be arranged such that positive output tab  182 A may be placed in proximity to negative output tab  184 A, while positive output tab  182 B may be placed in proximity to negative output tab  184 B. 
     As illustrated best in  FIG. 10 , the DC input bus bar  170  can provide electrical connectivity between the DC link capacitor  114  and the power modules of the gate drive circuit board  116 , which will be described in greater detail below. In one embodiment, the positive output tab  182 A and negative output tab  184 A can be coupled, through an opening in the gate drive circuit board  116 , to a first power module  188 . The positive output tab  182 B and negative output tab  184 B can be coupled to a second power module  186 . 
       FIG. 11  is a partial exploded perspective view illustrating exemplary first and second power modules  186  and  188 , with the gate drive circuit board removed, as well as the various bus bars and the DC link capacitor described above. Each of the first and second power modules  186  and  188  can comprise a pair of positive and negative input terminals. For example, first power module  186  can include positive terminal  190  and negative terminal  192 . Each of the power modules can be coupled to a bottom of the lower enclosure  108  with a gasket, such as gasket  194 . In various embodiments, the gaskets can serve to create a fluid impermeable seal that keeps fluid from a cooling sub-assembly from entering the lower enclosure  108 . As will be discussed in greater detail herein, heat sinks of the power modules  186  and  188  can be exposed to a coolant fluid by the cooling sub-assembly. The coolant fluid can remove excess heat from the power modules increasing their performance. 
     Each of the exemplary power modules  186  and  188  can comprise three output terminals that each can output a different phase of an AC power signal that can be generated by the power module. For example, first power module  186  can comprise output terminals  187 A,  187 B, and  187 C and second power module  188  can comprise output terminals  189 A,  189 B, and  189 C. 
       FIGS. 12 and 13  collectively illustrate an example three phase output AC bus bar sub-assembly (hereinafter “AC bus bar  118 ”). In some embodiments, the AC bus bar  118  can comprise three bus bars such as a first bus bar  202 , a second bus bar  204 , and a third bus bar  206 . 
     Each of the first, second and third bus bars  202 ,  204 ,  206  can comprise a bar body. For example, first bus bar  202  can comprise a bar body  208 , the second bus bar  204  can comprise a bar body  210 , and the third bus bar  206  can comprise a bar body  212 . Each of the first, second and third bus bars  202 ,  204 ,  206  can comprise a front and back surface. For example, the bar body  208  of the first bus bar  202  can comprise a front surface  214  and a back surface  216 . The bar body  210  of the second bus bar  204  can comprise a front surface  218  and a back surface  220 , while the bar body  212  of the third bus bar  206  can comprise a front surface  222  and a back surface  224 . 
     In one embodiment, the first, second and third bus bars  202 ,  204 ,  206  can be spaced apart from one another while being positioned in a nested configuration. Thus, a space  205  can exist between the front surface  214  of the first bus bar  202  and the back surface  216  of the second bus bar  204 . Likewise, the third and second bus bars can be spaced apart from one another to form a space  207  between the front surface  214  of the second bus bar  204  and the back surface  220  of the third bus bar  206 . The spaces  205  and  207  can each be filled with an electrically insulating material. In other embodiments, the front and/or back surfaces of the bus bars  202 ,  204 ,  206  can be coated with an insulating layer of material that can be adapted to provide electrical insulation. 
     Each of the first, second and third bus bars  202 ,  204 ,  206  also can comprise a plurality of power module tabs that can electrically couple each of the bus bars with both the first and second power modules  186  and  188  (see  FIG. 11 ). For example, the first bus bar  202  can comprise power module tabs  226  and  228 , while the second bus bar  204  can comprise power module tabs  230  and  232 . The third bus bar  206  can comprise power module tabs  234  and  236 . The power module tabs of any one of the bus bars can be spaced apart from one another so as to allow for the bus bar to connect with each of the power modules. 
     The plurality of power module tabs of each of the bus bars can extend away from the back surface of their respective bar body. The plurality of power module tabs  226 ,  228 ,  230 ,  232 ,  234 , and  236 , can be coplanar and aligned with one another along a longitudinal axis of alignment Ls (see  FIG. 13 ). 
     In some embodiments, the first, second and third bus bars  202 ,  204 ,  206  can be placed into a nested but offset relationship with one another. For example, second bus bar  204  can be disposed in front of first bus bar  202 , while third bus bar  206  can be disposed in front of second bus bar  204 . Also, the bus bars can be staggered or offset from one another. The second bus bar  204  can be offset from the first bus bar  202 , and the third bus bar  206  can be offset from the second bus bar  204 . In this configuration, the power module tab  230  of the second bus bar  204  can be positioned between the power module tab  226  of the first bus bar  202  and the power module tab  234  of the third bus bar  206 . Power module tab  234  of the third bus bar can be positioned between the power module tab  230  of the second bus bar  204  and the power module tab  228  of the first bus bar  202 . Power module tab  228  of the first bus bar  202  may be positioned between the power module tab  234  of the third bus bar  206  and the power module tab  232  of the second bus bar  204 . Power module tab  232  may be positioned between the power module tab  228  of the first bus bar  202  and the power module tab  236  of the third bus bar  206 . 
     In some embodiments, a length of the power module tabs ( 234 ,  236 ) of the third  206  of the three bus bars may be greater than a length of the power module tabs ( 230 ,  232 ) of the second  204  of the three bus bars. Also, the length of the power module tabs ( 230 ,  232 ) of the second  204  of the three bus bars can be greater than a length of the power module tabs ( 226 ,  228 ) of the first  202  of the three bus bars. 
     Each of the first, second and third bus bars  202 ,  204 ,  206  also can comprise an output tab, which can extend from a front surface of their respective bar body. For example, the first bus bar  202  can comprise an output tab  238 , the second bus bar  204  can comprise an output tab  240 , and the third bus bar  206  can comprise an output tab  242 . 
     In one embodiment, the output tabs  238 ,  240 , and  242  can be arranged so as to be symmetrical in their positioning relative to one another. Due to spacing of the output terminals of each of the power modules (described above), and in order to maintain symmetry of the output tabs  238 ,  240 , and  242 , output tab  240  can have a substantially serpentine shaped section  244  that can position the output tab  240  in between output tabs  238  and  242 . 
     In some embodiments, the bus bars  202 ,  204 ,  206  can be held in their respective positions using a mounting plate  246  (see  FIG. 12 ). The mounting plate  246  may be adapted with apertures. The output tabs  238 ,  240 , and  242  can each extend through these apertures. In one embodiment, the output tabs  238 ,  240 , and  242  can be secured in place on the mounting plate  246  with locking members, such as locking member  248 . 
     The mounting plate  246  can be coupled to the second and the third of the three bus bars (see example shown in  FIG. 12 ). 
     Referring now to  FIGS. 14 and 15  (and  FIGS. 11, 12, and 13 ), according to some embodiments, power module tabs  226  and  228  of the first bus bar  202  (see  FIG. 12 ) can connect with output terminal  187 A (see also  FIG. 11 ) of first power module  186  and output terminal  189 A of second power module  188 . The second bus bar  204  may connect with output terminal  187 B of first power module  186  and output terminal  189 B of second power module  188 . The third bus bar  206  can couple with output terminal  187 C of first power module  186  and output terminal  189 C of second power module  188 . 
     In  FIG. 16 , a plurality of power cables, such as power cable  250  can be coupled with the output tabs  238 ,  240 , and  242  (see  FIGS. 14-15 ) of the AC bus bar  118 . 
       FIG. 17  illustrates an example cooling sub-assembly  252  that can comprise a cooling cavity  254 , a gasket  256 , cover plate  258 , an inlet port  260 , an outlet port  262 , and a purge port  264 . In general, the cooling cavity  254  may be formed by a sidewall  266  formed into a lower enclosure  108  of the housing. Heat sinks  268  and  270  of the power modules  186  and  188 , respectively, can be exposed to the cooling cavity  254 . As mentioned above, the power modules  186  and  188  can be isolated with gaskets so as to prevent fluid inside the cooling cavity  254  from entering the housing. 
     When the cover plate  258  may be joined to the lower enclosure  108  of the housing, a fluid, such as a coolant can be pumped into the cooling cavity  254  through the inlet port  260  and can be extracted through the outlet port  262  using a pump (not shown). The purge port  264  can be used to purge trapped air from the cooling cavity  254  if needed. 
     In one embodiment, the inlet and outlet ports  260  and  262  can be disposed near a center of the housing which can help promote equal flow rate of fluid to each cooling cavity. 
       FIGS. 18A-C  collectively illustrate another embodiment of a cooling sub-assembly. In one embodiment, the first and second power modules  186  and  188  can be mounted to a plate  280 . A sidewall (See e.g.,  266  in  FIG. 17 ) defines a cooling cavity (See e.g.,  254  in  FIG. 17 ). The heat sinks  268  and  270  can be positioned within the cooling cavity  254 . An inlet port  286  may be positioned on one end of the cooling cavity  254  and the outlet port  288  may be positioned on the opposing end of the cooling cavity  254 . As fluid may be introduced into the inlet port  286  and removed from the outlet port  288 , the fluid can remove heat from the first and second power modules  186  and  188  as it communicates over the heat sinks  268  and  270 , for providing a substantially equal share of coolant to each power module. In some other embodiments (see e.g.,  FIG. 17 ) the inlet port may be positioned substantially midway between heat sinks  268  and  270  such that coolant may be communicated from the substantially midway point so coolant can flow bidirectionally, over the heat sink  268  in one direction and heat sink  270  in the other direction, and be collected substantially in the middle, for providing substantially equal share of coolant to each power module, with less thermal differential across the power modules. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. The descriptions are not intended to limit the scope of the technology to the particular forms set forth herein. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments. It should be understood that the above description is illustrative and not restrictive. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the technology as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art. The scope of the technology should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.