Abstract:
A power generation system including a housing defining a cavity and having an inlet for receiving a fluid that is used to cool and pressurize the cavity and an outlet for removing the fluid from the cavity. The system also may include a rotor having a first end positioned within the cavity of the housing and a second end, a plurality of bearings, positioned to contact the rotor, for providing radial support to the rotor, and a turbine connected to the second end of the rotor. Further, the system may include a heat sink positioned within the cavity and between the housing and the rotor, and an electronic component attached to the heat sink.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation-in-part of U.S. patent application Ser. No. 11/333,827, filed on Jan. 17, 2006 which was a continuation of U.S. patent Ser. No. 10/805,767, filed on Mar. 22, 2004 and issued as U.S. Pat. No. 7,019,415 on Mar. 28, 2006, both of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates generally to power generation systems for space applications such as re-useable launch vehicles, and more particularly to an electrical power generation system and method for mitigating corona discharge.  
         [0003]     Reusable space vehicles use power generation systems for providing power during launch and recovery. For example, the space shuttle uses hydrazine-fueled, turbine-driven, gearbox-mounted hydraulic pumps to provide power for thrust-vector and flight control actuation. Alternative electric power generation systems operate at high voltages in order to minimize their size and weight. During ascent and re-entry, these space vehicles are exposed to low ambient pressures.  
         [0004]     These systems, however, have several drawbacks. For example, these systems are very costly, complex and require many auxiliary systems, such as oil lubrication systems, to operate. In addition, these systems are dangerous to operate due to the need to handle highly toxic propellants such as hydrazine. Furthermore, these systems emit damaging corona discharge during ascent and re-entry.  
         [0005]     Thus, it should be appreciated that there is a need for a high-power electrical power generation system that does not use an oil lubrication system, use toxic propellants and emit corona discharge. The invention fulfills this need as well as others.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention relates to systems and methods for mitigating corona discharge. In one aspect of the invention there is provided a power generation system including a housing defining a chamber and having an inlet for receiving a fluid that is used to cool and pressurize the chamber and an outlet for removing the fluid from the cavity. The system also may include a rotor having a first end positioned within the cavity of the housing and a second end, a plurality of bearings positioned to provide radial support to the rotor, and a turbine connected to the second end of the rotor. The system may further include either a system for discarding of the fluid or a system for cooling and recycling the fluid back to the inlet, wherein the system for disposing of the fluid or the system for recycling the fluid back to the inlet is in fluid communication with the outlet. Further, the system may include a heat sink positioned within the cavity and between the housing and the rotor, and an electrical device (e.g., an electronic component) attached to the heat sink.  
         [0007]     In another aspect of the invention there is provided an electrical power generation system including an outer housing defining a chamber. The outer housing includes an input conduit for receiving a fluid that is used to cool and pressurize the chamber and an output conduit for removing the fluid from the chamber. The system may further includes a heat exchanger, the heat exchanger receiving the fluid from the output conduit, wherein the heat exchanger cools the fluid and a pump or compressor wherein the pump or compressor pumps the fluid from the heat exchanger to the input conduit. The system may also includes a turbine positioned adjacent to the outer housing, a rotor positioned within the chamber and connected to the turbine for rotating about a central axis, and an inner housing positioned within the chamber and between the outer housing and the rotor. Further, the system may include a plurality of electronic components attached to the inner housing and cooled by the fluid, a stator attached to the inner housing and adjacent to the rotor, and a plurality of bearings, positioned adjacent to the stator, for providing radial support to the rotor and cooled by the fluid.  
         [0008]     In a further aspect of the invention there is provided a method for mitigating corona discharge including introducing a fluid into a cavity defined by an outer housing, the fluid being used to pressurize the cavity and to cool a rotor, a stator, a plurality of bearings and a plurality of electrical components. The method may also include removing the fluid from the cavity and discarding thereof.  
         [0009]     In yet another aspect of the invention there is provided a method for mitigating corona discharge including introducing a fluid into a cavity defined by an outer housing, the fluid being used to pressurize the cavity and to cool a rotor, a stator, a plurality of bearings and a plurality of electrical components. The method may also include removing the fluid from the cavity, cooling the fluid removed from the cavity and reintroducing the cooled fluid into the cavity.  
         [0010]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a graph showing Paschen curves for air, carbon dioxide, helium, nitrogen, oxygen, hydrogen and neon gases at room temperature;  
         [0012]      FIG. 2A  is a perspective view of an electrical power generation system with its outer housing removed so that the components and electronics within the outer housing can be viewed according to an embodiment of the invention;  
         [0013]      FIG. 2B  is a perspective view of an electrical power generation system with its outer housing removed so that the components and electronics within the outer housing can be viewed according to an embodiment of the invention;  
         [0014]      FIG. 3  is a cross-sectional view illustrating the physical layout of the components and electronics of the electrical power generation system of  FIGS. 2A, 2B  according to a first embodiment of the invention;  
         [0015]      FIG. 4  is a block diagram illustrating an electrical system architecture of the power electronics and the signal electronics of the electrical power generation system of  FIGS. 2A, 2B  according to an embodiment of the invention;  
         [0016]      FIG. 5  is a block diagram illustrating an electrical power topology of the EMI filter, the inverter and the current sensors of the power electronics of  FIG. 4  according to an embodiment of the invention;  
         [0017]      FIG. 6  is a cross-sectional view illustrating the physical layout of the components and electronics of the electrical power generation system of  FIGS. 2A, 2B  according to a second embodiment of the invention; and  
         [0018]      FIG. 7  is a cross-sectional view illustrating the physical layout of the components and electronics of the electrical power generation system of  FIGS. 2A, 2B  according to a third embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.  
         [0020]     Systems and methods that implement the embodiments of the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. Reference in the specification to “one embodiment” or “an embodiment” is intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. In addition, the first digit of each reference number indicates the figure in which the element first appears.  
         [0021]     Referring now more particularly to the drawings,  FIG. 1  is a graph  100  showing Paschen curves  101 - 107  for air, carbon dioxide, helium, nitrogen, oxygen, hydrogen and neon gases at room temperature. The Paschen curves  101 - 107  identify the breakdown voltages between parallel plates of the various gases shown in  FIG. 1 . In particular, these Paschen curves  101 - 107  show the breakdown voltage of the gas (y-axis) as a function of the gas pressure times the spacing of the gap (x-axis), for example, between the parallel plates. The gap is generally measured to be the distance between the parallel plates across which the voltage is applied. The gap represents the maximum open distance parallel to an applied electric field. A characteristic of the Paschen curves  101 - 107  is that the breakdown voltage of the device is increased at any pressure by increasing the spacing of the gap. That is, in a fixed electric field, the breakdown voltage across the gap becomes smaller as the gap becomes smaller, and according to the Paschen curves  101 - 107 , this increases the breakdown voltage of the device. In the illustrated embodiment, hydrogen and oxygen gases are used as the coolants, lubricants and propellants for the electrical power generation system. However, one skilled in the art will be able to implement the invention using other gases including, but not limited to, the gases shown in  FIG. 1 . Alternatively, separate gases may be used where one gas may be used for the combined coolant and lubricant and a separate gas used as the propellant.  
         [0022]      FIGS. 2A, 2B  are perspective views of an electrical power generation system  200  with its outer housing  202  removed so that the components and electronics within the outer housing  202  can be viewed. The electrical power generation system  200  is typically a 270-volt dc electric power generation system used in space applications where a hydrogen gas is used as the turbine fuel. The outer housing  202  has a substantially air-tight chamber  204  for housing the components and electronics that make up the electrical power generation system  200 . The outer housing  202  may be made of aluminum, steel, titanium or other metallic material and is used to protect the components and high-voltage electronics (e.g., power electronics  206  and signal electronics  208 ) from external factors. The power electronics  206  are typically mounted on an outer surface  210  of a cold plate  212  (can also be referred to as an inner housing), the signal electronics  208  are typically mounted on a first side surface  214  of the outer housing  202  and a turbine wheel  216  is typically positioned adjacent to a second side surface  218  of the outer housing  202 . The first side surface  214  is generally positioned opposite the second side surface  218 .  
         [0023]     The components are generally contained within the outer housing  202  and the power electronics  206  are generally mounted to the cold plate  212 . In one embodiment, the components and the electronics are housed within the outer housing  202 . The cold plate  212  may be made of aluminum, steel, titanium or other metallic material and functions and serves as a common heat exchanger or heat sink. In the illustrated embodiment, the power electronics  206  are mounted around a hexagonal shaped cold plate  212  and the signal electronics  208  are mounted on the first side surface  214  of the outer housing  202 .  
         [0024]      FIG. 3  is a cross-sectional view illustrating the physical layout of the components and electronics of the electrical power generation system  200  of  FIGS. 2A, 2B . The electrical power generation system  200  includes a rotor  300  that may be cylindrical in shape and that has a first end  302  and a second end  304  wherein the first end  302  is positioned within the chamber of the outer housing, a thrust disc  306  that is connected to the first end  302  of the rotor  300 , the turbine wheel  216  that is connected to the second end  304  of the rotor  300  and a set of turbine blades  308  that are attached about the circumference of the turbine wheel  216 . The electrical power generation system  200  further includes a first set of journal bearings  310  that are circumferentially positioned around the first end  302  of the rotor  300  and a second set of journal bearings  312  that are circumferentially positioned around the second end  304  of the rotor  300 . The first and second sets of journal bearings  310 ,  312  provide radial support to the rotor  300 . The rotor  300  is mounted or rotates on the first and second sets of journal bearings  310 ,  312 . The first and second sets of journal bearings  310 ,  312  are used to assist the rotor  300  in rotating concentrically about a central axis  314 . In one embodiment, the first and second sets of journal bearings  310 ,  312  are radially spaced from the central axis  314 . The turbine wheel  216  is mounted in a fixed orientation, without any gears, to the rotor  300 . In one embodiment, the turbine wheel  216  may be an axial-impulse turbine wheel or any other type of turbine wheel.  
         [0025]     The electrical power generation system  200  also includes a plurality of thrust bearings  316  that are circumferentially positioned around an outer portion  318  of the thrust disc  306  to provide axial support to the rotor  300 . The thrust disc  306  is mounted or rotates on the plurality of thrust bearings  316 . The plurality of thrust bearings  316  are radially spaced around the central axis  314  and are used to maintain the rotor axial position. The rotor  300 , the thrust disc  306 , the turbine wheel  216 , and the turbine blades  308  are configured to rotate about the central axis  314  at substantially the same revolutions per minute. In one embodiment, the first and second sets of journal bearings  310 ,  312  and the plurality of thrust bearings  316  are self-acting, hydrodynamic foil bearings. Hence, the rotor  300  and the thrust disc  306  may be mounted on foil bearings. When foil bearings are used, no oil lubrication for the bearings is required. Other types of bearings such as externally pressurized hydrostatic bearings, gas cooled ceramic ball bearings, magnetic bearings with a pressurized cooling fluid or any other types of bearings can be used.  
         [0026]     A ring-shaped turbine seal  320  is positioned around the second end  304  of the rotor  300  to provide a substantially air tight seal between the rotor  300  and the housing  202 . The ring-shaped turbine seal  320  provides a seal so that the gas inside the chamber  204  is maintained within the chamber  204 . The ring-shaped turbine seal  320  may be a floating ring seal or similar device.  
         [0027]     The electrical power generation system  200  also includes a stator  322  attached to an inner surface  324  of the cold plate  212 . The stator  322  is positioned around the rotor  300  and between the first and second sets of journal bearings  310 ,  312 . The stator  322  is mounted in a stationary position relative to the cold plate  212 .  
         [0028]     As shown in  FIG. 3 , the power electronics  206 , the signal electronics  208 , the cold plate  212 , the rotor  300 , the thrust disc  306 , the first and second sets of journal bearings  310 ,  312 , the plurality of thrust bearings  316  and the stator  322  are contained within or housed inside the outer housing  202 . The outer housing  202  includes one or more inlets or input conduits  326  for allowing a fluid to enter the chamber  204  and one or more outlets or output conduits  328  for allowing the fluid to exit the chamber  204 . In one embodiment, a first conduit  326   a  is positioned to direct the fluid into the chamber  204  to cool and pressurize the chamber  204  and the power electronics  206  and a second conduit  326   b  is positioned to direct the fluid toward or into the cold plate  212  to cool the cold plate  212 . Cooling the cold plate  212  also cools the power electronics  206  and the stator  322 , which are attached to the cold plate  212 .  
         [0029]     The output conduit  328  allows the fluid to be removed from the chamber  204  and the cold plate  212 . In one illustrative embodiment, the fluid exiting the chamber  204  may be directed to a reaction chamber  330  through the output conduit  328  where it may be combined with another fluid supplied through a first reaction chamber conduit line  332 , where the fluids are reacted to produce power to operate the turbine wheel  216 . Alternatively, the fluid removed from chamber  204  may be directed toward either a system for discarding of the fluid or a system for recycling the fluid back to the first and second input conduits  326   a,    326   b.  The system for discarding the fluid and/or the system for recycling the fluid may be in fluid communication with output conduit  328 . In an illustrative embodiment, the fluid exiting chamber  204  may be discarded by venting overboard or to a waste receptacle through the output conduit  328  to overboard vent  350  ( FIG. 6 ). A third fluid may then be directed to the reaction chamber  330  through a second reaction chamber conduit line  360 . In yet another illustrative embodiment, the fluid exiting chamber  204  may be cooled by some external means such as, but not limited to, a heat exchanger  354  and then pumped back into the chamber  204  through first and second conduits  326   a,    326   b  by a pump or compressor  356  ( FIG. 7 ). In either of the latter two illustrative embodiments, it may be beneficial to include a flow restricting orifice or back-pressure regulator  352  in the output conduit  328  exiting the chamber to maintain the pressure in the chamber  204 . The input conduits  326   a,b  are generally located at one end of the outer housing  202  and the output conduit  328  is generally located at an opposite end of the outer housing  202  to ensure that the fluid travels throughout the chamber  204  to cool all the components within the chamber  204 . In one embodiment, the fluid is constantly fed into the input conduits  326   a,b,  travels through the chamber  204  to cool and pressurize the components, the power electronics  206  and the signal electronics  208  within the chamber  204 , and may travel through the output conduit  328  to either the reaction chamber  330 , or through the pressure restricting orifice or backpressure regulator  352  to either the overboard vent  350  or via the external heat exchanger  354  and pump  356  back to the chamber  204 . The pressure within outer housing  202  is maintained at a substantially constant pressure value by metering the flow of fluid into the chamber  204  via the input conduits  326   a,b.    
         [0030]     The fluid may be a gas such as a hydrogen gas, helium gas, nitrogen gas or oxygen gas; a liquid such as alcohol, liquid rocket propellant, liquid hydrogen, liquid nitrogen or liquid oxygen; or combinations thereof. The fluid can be used as a bearing process fluid to lubricate the first and second sets of journal bearings  310 ,  312  and the plurality of thrust bearings  316 , a cooling fluid to cool the components (e.g., the cold plate  212 , the rotor  300 , the thrust disc  306 , the first and second sets of journal bearings  310 ,  312 , the plurality of thrust bearings  316  and the stator  322 ) and the high-voltage electronics contained within the housing  202 , and a pressurizing fluid to pressurize the chamber  204 , which in turn pressurizes the high-voltage electronics. Hence, the same fluid is advantageously used as a lubricant, coolant, and pressurizer for the electrical power generation system  200 . Therefore, separate fluids are not required for each of these different purposes. In one illustrative embodiment, the fluid may also be used as a fuel, being supplied to the reaction chamber  330  after being used to lubricate, cool and pressurize the electrical power generation system  200 . The fluid may be cooling, reaction and pressurization gases such as, but not limited to, fuels such as hydrogen, methane, butane, or other light hydrocarbons; or oxidizers such as oxygen or nitrous oxide. Other reactive gases might also be contemplated. Alternatively, cooling and reaction fluids might include any of the cooling reaction and pressurization gases but could also include liquid fuels such as liquid hydrogen, jet fuel or RP1; and liquid oxidizers such as liquid oxygen, hydrogen peroxide, nitrogen tetraoxide or nitric acid. Other reactive fluids might also be considered.  
         [0031]     If the fluid is not used as a fuel source, cooling and pressurizations gases may be, but not limited to, any of the cooling, reaction and pressurization gases listed above, as well as nitrogen gas, helium gas, or other inert gases such as argon on xenon. The use of other cooling gases may also be contemplated.  
         [0032]     Locating the power electronics  206  and the signal electronics  208  within the chamber  204  advantageously allows the fluid to be used to cool and pressurize the components and electronics. The design may also be advantageous for also allowing the fluid to be used as a propellant (i.e., fuel) and/or reactant for the reaction chamber  330 . An additional advantage includes providing corona mitigation with little to no additional complexity and cost and thus virtually eliminating the need for more complex systems or methods of corona mitigation. Furthermore, the electrical power generation system  200  does not require a separate cooling system, housing or pressure vessel or pressurization system for the power electronics  206 .  
         [0033]     The electrical power generation system  200  may include a supply conduit  332  for supplying a second fluid into the reaction chamber  330 . The second fluid may be one which is capable of being chemically reacted with the first fluid. For example, if the first fluid is a hydrogen gas, the second fluid might be an oxygen gas. The reaction chamber  330  mixes the fluid (e.g., a hydrogen gas) and the second fluid (e.g., an oxygen gas) and reacts them to produce reaction products, which may then be used to produce thrust or drive a turbine wheel. Other propellant combinations can be used to produce combustion reaction products. The combustion reaction products are discharged through a discharge port  333  of the reaction chamber  330  to a turbine exhaust port  334  causing the turbine blades  308  and the turbine wheel  216  to rotate about the central axis  314 . Hence, the combustion reaction products are used as the propellant for the turbine wheel  216 . The rotation of the turbine wheel  216  generates power for the electrical power generation system  200 .  
         [0034]      FIG. 4  is a block diagram illustrating an electrical system architecture of the power electronics  206  and the signal electronics  208  of the electrical power generation system  200  of  FIGS. 2A, 2B . The power electronics  206  may include an electromagnetic interference (EMI) filter  402 , a bleed resistor  403 , an inverter  404 , a gate driver  406  and current sensors  408 . The signal electronics  208  may include a signal EMI filter  410 , a power supply  412  and a controller  414  (e.g., a digital or analog controller). The power electronics  206  and the signal electronics  208  may be referred to as electrical components. The combination of the rotor  300  and the stator  322  can be referred to as a high-reactance permanent-magnet generator (HRPMG)  416 . The power electronics  206  and the signal electronics  208  are mounted to the outer housing  202  and are located within the chamber  204 . The current sensors  408  measure the current between the power electronics  206  and the HRPMG  416 . One skilled in the art will be able to make the electrical power generation system  200  using the electrical schematic shown in  FIG. 4 .  
         [0035]      FIG. 5  is a block diagram illustrating an electrical power topology of the EMI filter  402 , the inverter  404  and the current sensors  408  of the power electronics  206  of  FIG. 4 . One skilled in the art will be able to make the electrical power generation system  200  using the electrical schematic shown in  FIG. 5 .  
         [0036]     Although an exemplary embodiment of the invention has been shown and described, many other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, may be made by one having skill in the art without necessarily departing from the spirit and scope of this invention. Accordingly, the present invention is not intended to be limited by the preferred embodiments, but is to be defined by reference to the appended claims.