Abstract:
A method of operating a power delivery system that has at least one power cell includes directing air into the power cells to cool them, receiving the air from the cells, directing the air to a cooling system, and recirculating the cooled air to the power cells. Each cell may include an air intake, an air output, a water-cooled heat sink, and optionally a plurality of capacitor connectors and/or a circuit board. The air may be directed through the air intake to the air output so that air passes over the capacitor connectors and/or the circuit board before passing over the heat sink.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application claims priority to, and incorporates by reference in its entirety, pending U.S. Provisional Patent Application No. 60/713,197, entitled “Packaging method for modular multilevel power cells and system infrastructure,” filed Aug. 31, 2005. This patent application is also related to U.S. patent application Ser. No. ______, entitled “Packaging system for modular power cells,” filed Aug. 29, 2006, which has attorney docket number 2005P15746US01-100530.00901. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT  
       [0003]     Not applicable.  
       INCORPORATION BY REFERENCE OF MATERIAL ON DISK  
       [0004]     Not applicable.  
       BACKGROUND  
       [0005]     1. Technical Field  
         [0006]     This application relates generally to the field of power delivery systems.  
         [0007]     2. Description of the Related Art  
         [0008]     In recent years, circuits for medium-voltage variable frequency drive (VFD) applications have received attention. Several novel methods have been introduced in the past decade. For example, in a circuit comprising series-connected inverters as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety, an inverter or power cell 110 includes a three-phase diode-bridge rectifier 112, one or more direct current (DC) capacitors 114, and an H-bridge inverter 116. The rectifier 112 converts the input 118 alternating current (AC) voltage to a substantially constant DC voltage that is supported by the capacitors 114 that are connected across the rectifier 112 output. The output stage of the inverter 110 includes an H-bridge inverter 116 that includes two poles, a left pole and a right pole, each with two devices. The inverter 110 transforms the DC voltage across the DC capacitors 114 to an AC output 120 using pulse-width modulation (PWM) of the semiconductor devices in the H-bridge inverter 116.  
         [0009]     Other circuits and drives for medium voltage and high voltage motor control are available. In general medium voltage refers to a rated voltage greater than 690 volts (V) and less than 69 kilovolts (kV). In some embodiments, medium voltage may be a voltage between about 1000 V and about 69 kV. High voltage ratings exceed such medium voltage ratings. In many such systems, modular power cells are used. Industry often seeks ways to reduce the size of such systems, increase the life and reliability of the systems, and permit the systems to keep operating under on or more fault conditions.  
         [0010]     The disclosure contained herein describes attempts to solve one or more of the problems described above.  
       SUMMARY  
       [0011]     In an embodiment, a power delivery system includes a plurality of removable power cells positioned within a housing structure. Each power cell includes a water cooled heat sink, an air intake, and an air output. The system also includes a heat exchanger. Each cell may be positioned to receive air into the air intake and expel the air into an air plenum. The heat exchanger may be positioned to receive the air from the air plenum, cool the air, and recirculate the cooled air to the cells via each cell&#39;s air intake. During operation, the air that is expelled into the air plenum by a cell may be warmer than the air that is received into the air intake of the cell. In addition, each cell&#39;s heat sink may be connected to a water intake and a water output, and during operation, the water that is expelled through the water output by a cell may be warmer than the water that is received into the water intake of the same cell. In some embodiments, each power cell includes a plurality of capacitor connectors and a plurality of transistors. The capacitor connectors may be positioned closer to the air intake when compared to the position of the heat sink, and the heat sink may be positioned closer to the air outlet when compared to the position of the capacitor connectors. During operation, most air circulating through the cell may contact the capacitor connectors before contacting the heat sink. Each power cell also may include a circuit board that is positioned closer to the air intake when compared to the position of the heat sink. The system also may include a back plane positioned between the cells and the air plenum, a plurality of power delivery busses positioned within the air plenum to deliver power to the cells, and a plurality of power return busses positioned within the air plenum to receive power from the cells and deliver the power to a load. The system also may include a water delivery manifold and a water return manifold, such that each manifold comprises a plurality of self-sealing connections, wherein each connection opens when a cell is connected to the connection and closes when a cell is removed from the connection.  
         [0012]     In an alternate embodiment a method of operating a power delivery system that has at least one power cell includes directing air into a power cell to cool the cell, and receiving the air from the power cell. The air received from the cell is warmer than the air directed into the cell. The method also includes cooling the received air to a desired temperature, such as 55° C. or any other temperature that is lower than the temperature of air that is expected to be expelled from the cell, and recirculating it to the power cell. The cell may be contained within a support structure having an air plenum. In such an embodiment, the cooling may be provided by a heat exchanger, and the receiving may include directing air through the air plenum from the cell to the heat exchanger. The cell may include an air intake, an air output, a water-cooled heat sink, and optionally a plurality of capacitor connectors and/or a circuit board. The air may be directed through the air intake to the air output so that air passes over the capacitor connectors and/or the circuit board before passing over the heat sink. The cell&#39;s heat sink may be connected to a water intake and a water output. During operation, water that is expelled through the water output by the cell may be warmer than water that is received into the water intake of the cell. The recirculating may reduce air ionization.  
         [0013]     In an alternate embodiment, a method of operating a power delivery system having multiple power cells includes directing air into the power cells. Each cell includes an air intake, an air output, a water-cooled heat sink, and a plurality of capacitor connectors. The directing includes, for each cell, directing the air through the air intake, and passing the air over the water-cooled heat sink and the capacitor connectors so that the air passes over the capacitor connectors before passing over the heat sink. The air is receiving the each power cell, cooled and recirculated to the power cells. The cells may be contained within a support structure having an air plenum. The cooling may be provided by a heat exchanger, and the receiving may include directing air through the air plenum from the cells to the heat exchanger. Optionally, each cell&#39;s heat sink may be connected to a water intake and a water output. During operation, water that is expelled through the water output by each cell may be warmer than water that is received into the water intake of the cell. Each cell also may include a circuit board, and the passing may include passing the air over the circuit board before the air passes over the heat sink of each cell. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a circuit diagram illustrating exemplary features of a prior art power cell.  
         [0015]      FIG. 2  depicts a circuit comprising a plurality of power cells connected to a load.  
         [0016]      FIG. 3A  is a rear perspective view and  FIG. 3B  is a front perspective view of an exemplary power cell housing structure, while  FIGS. 3C and 3D  illustrate exemplary connecting members for the power cell structure.  
         [0017]      FIG. 4  illustrates an exemplary power cell internal structure.  
         [0018]      FIG. 5  illustrates an exemplary support structure for multiple power cells.  
         [0019]      FIG. 6  illustrates an exemplary power cell system in a housing.  
         [0020]      FIG. 7  illustrates an exemplary water delivery system. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Before the present methods, systems and materials are described, it is to be understood that this disclosure is not limited to the particular methodologies, systems and materials described, as these may vary. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope. For example, as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. In addition, the term “comprising” is intended to mean “including but not limited to.” Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.  
         [0022]     In various embodiments, a multi-level power circuit a plurality of power cells to drive a load.  FIG. 2  illustrates an exemplary embodiment of a circuit having such power cells. In  FIG. 2 , a transformer  210  delivers three-phase, medium-voltage power to a load  230  such as a three-phase induction motor via an array of single-phase inverters (also referred to as power cells). The transformer  210  includes primary windings  212  that excite a number of secondary windings  214 - 225 . Although primary winding  212  is illustrated as having a star configuration, a mesh configuration is also possible. Further, although secondary windings  214 - 225  are illustrated as having a mesh configuration, star-configured secondary windings are possible, or a combination of star and mesh windings may be used. Further, the number of secondary windings illustrated in  FIG. 2  is merely exemplary, and other numbers of secondary windings are possible. The circuit may be used for medium voltage applications or, in some embodiments, other applications.  
         [0023]     Any number of ranks of power cells are connected between the transformer  210  and the load  230 . A “rank” is considered to be a three-phase set, or a group of power cells established across each of the three phases of the power delivery system. Referring to  FIG. 2 , rank  250  includes power cells  251 - 253 , rank  260  includes power cells  261 - 263 , rank  270  includes power cells  271 - 273 , and rank  280  includes power cells  281 - 283 . Fewer than four ranks, or more than four ranks, are possible. A central control system  295  sends command signals to local controls in each cell over fiber optics or another wired or wireless communications medium  290 .  
         [0024]     The power cells described in  FIG. 2  provide a modular, multilevel system that allows cells to be replaced as needed to accommodate different design requirements, or to replace a failed cell.  FIG. 3A  illustrates a rear perspective view and  FIG. 3B  illustrates a front perspective view of exemplary power cell structure  310 . The power cell  310  includes a chassis  312  and a plurality of power input/output connectors  325 .  
         [0025]     Referring to  FIG. 3C , power connector  325  for the power cell may include a conducting arm  371  that extends from a mounting block  370 . Referring to  FIG. 3D , conducting arm  371  may be sized to make a secure electrical connection with a power connector  380  for the power bus. For example, conducting arm  371  may fit between and contact a pair of conducting arms  381 ,  382  of the power bus connector  380 . In some embodiments, power bus connector  380  may include a support  383  that helps to make a substantially rigid connection. Other power connector configurations are possible. In addition, in some embodiments a structure similar to power bus connector  380  may be included with the power cell, while a structure similar to  325  may be included with the power bus.  
         [0026]     Returning to  FIGS. 3A and 3B , the chassis  312  encloses various components of the electronic module  310 , such as one or more capacitors, printed circuit boards, heat sinks, etc. The chassis  312  may be fabricated from any suitable material, such as galvanized steel or another metal, that both mechanically and electromagnetically isolates the power cell from other power cells in the system during both normal operation and many abnormal operating conditions. The chassis  312  may serve to protect internal components of the electronic module  310  from damage during shipping and handling, and it may be configured in a manner such that the electronic module  310  can be placed on any of its sides without causing any damage to the components of the electronic module  310 . According to various embodiments, the chassis  312  may be comprised of several portions connected together, and one or more portions of the chassis  312  may be removable. In addition, the chassis  312  may be of a thickness sufficient to prevent any debris resulting from a failure of the internal components of the electronic module  310  from exiting the space enclosed by the chassis  312 , thereby preventing any collateral damage to other components in the vicinity of the electronic module  310 . The chassis  312  may also serve to provide a low impedance path for arcing faults within the chassis to minimize potential damage caused thereby.  
         [0027]     Exemplary internal components of the cell may include an electronics assembly that may include current-controlling devices or switches such as insulated gate bipolar transistor (IGBT) modules, other transistors, thyristors and one or more rectifier modules. The IGBTs may be separated for I/O bus locations and to increase thermal performance. The cell may include one or more control boards or other electronic devices that may be positioned near the front end  311  of the cell, with an optional access opening  315  covered by a door or panel that may be opened or removed. The interior front area of the cell may include a plurality of capacitor connectors  330  that receive capacitors for cell operation. The capacitors (not shown) may extend from the capacitor connectors toward the rear  321  of the cell or in another direction. The lower portion of the cell, where the capacitors are positioned, may be covered by a housing that serves as a lower portion (not shown) of chassis  312 .  
         [0028]     The cell  312  may contain a water cooling system to remove heat from the cell during operation. The cell&#39;s internal water cooling pipes may contain a water inlet connection  330  and water outlet connection  332  to receive cool water into the cell and expel water from the cell, respectively, via one or more hoses or conduits.  
         [0029]     Referring to  FIG. 4 , the hose connections may deliver water to and receive water from input water conduit  410  and output water conduit  412  that are connected to deliver fluid to and from a water cooled heat sink  416 , which is a sealed container that holds cooling water at a position that is effective to absorb heat from components of the cell, such as a location under IGBT devices connected to busses  422 ,  423  and  424  and other components of the cell. Busses  422 ,  423  and  424  may be electrically connected to one or more power plugs  325  (see  FIG. 3 ). A bus may be any electrically conductive delivery device, such as a wire, rigid or flexible piece of metal, conductive polymer, or another material. Referring to  FIG. 3 , the heat sink and IGBTs are typically located near the rear  321  of the cell. The water for the heat sink may cool the IGBTs. Deionized water is preferred, and the water may be recirculated to an air-to-water or water-to-water heat exchanger that is located external to the cell.  
         [0030]     In addition to a water cooling structure, referring back to  FIG. 3 , each cell may include an air inlet  340  and an air outlet  342  that directs air through the cell  310  so that the air flows over components such as capacitor connections, electronics and control boards, power switches, bus connectors, and/or the busses themselves. Each of the air intake and output may be covered by a filter or grill in some embodiments. Preferably, the cell  310  components are positioned so that air flows first over the capacitor connections, and/or circuit boards, with air flow over the heat sink occurring later in the air stream. This occurs by positioning capacitor connections  330  and circuit boards (under opening  315 ) near the front of the cell, while positioning the heat sink  416  near the air outlet  342  or rear area  321  of the cell. Thus, the air may be cooler when it passes across components that are not also near the water-cooled heat sink, while air may be warmer in areas where the heat sink also provides cooling capability.  
         [0031]      FIG. 5  illustrates an exemplary support structure  544  for multiple power cells, such as nine cells, within a housing wherein each power cell or other electronic module is positioned on one or more mounting rails  546  so that the rear of each cell faces a backplane  548  and the cell&#39;s power plugs contact the cell power connections  521 - 525  within an air plenum. The backplane  548  may be fabricated from any suitable non-conductive material, such as a high-strength non-conductive laminate material, and it separates the air plenum from the heat exchange system that removes heat from the individual cells.  
         [0032]      FIG. 6  illustrates an exemplary power cell system  600  containing any number of replaceable power cells  310  connected to power input/output buswork  605  via connecting buswork  620 . Back plane  548  separates the power cells  310  from the air plenum  610 . As air moves into the front of a cell, the air may absorb heat from the components of the cell. The air that leaves the cell at its rear and passes through an opening in the back plane  548  is typically warmer than the air that entered the cell. A heat exchanger  640  receives the warm or hot air from the air plenum  610 , cools the air and returns cooled air to the front of the cells via an air delivery space  630  that is located within system housing  650 . Any suitable air cooling system may be used as the heat exchanger  640 . Preferably, heat exchanger  640  is located on or near the top of the housing  650 , although other locations are possible. Thus, the system may direct air from the rear of the cells, through the heat exchanger in a constant, recirculating manner. In the forced air delivery system described herein, in some embodiments the recirculation of air may reduce ionization of the air and the arcing faults associated with such ionization.  
         [0033]      FIG. 7  illustrates a water delivery system that also may be included within the housing. Each cell  310  has input and output hose connections  330  and  332  that are connected to water delivery  740  and return  742  manifolds via connecting conduits  710  and  712 . Water manifolds and conduits may be made of any material suitable for delivering hot and cold water, such as noncorrosive metal, rubber, silicon, PVC, plastic or any other suitable material. The connections between hose connections  330  and  332  and connecting conduits  710  and  712  may be self-sealing so that an individual power cell can be removed from the system without breaking the water paths to other cells. Any suitable sealing device, such as a valve that opens upon connection and closes upon disconnection, may be used for this purpose. Water delivery  740  and return  742  manifolds may be located within the air plenum  610  of the power delivery system  600  (referring to  FIG. 6 ). Water, preferably deionized, may be circulated to or from an external heat exchanger to be cooled.  
         [0034]     In medium voltage systems, the air entering the cell may be controlled to a temperature of approximately 55° C., while the water delivered to the cells may be controlled to a temperature of approximately 47° C. Other temperatures are possible. The air and water may absorb heat while inside the cells, and the air and water exiting the cell may, in some embodiments, be several degrees warmer than the air and water that enters the cells.  
         [0035]     Still other embodiments will become readily apparent to those skilled in this art from reading the above-recited detailed description and drawings of certain exemplary embodiments. It should be understood that numerous variations, modifications, and additional embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the spirit and scope of this application.