Patent Abstract:
Heat from a safe high energy density fuel, such as aluminum, is used to generate electrical power. In some applications, the fuel may use seawater as an oxidizer. Additionally, the hybrid power system uses a highly efficient and silent thermoacoustic power converter (TAPC) to convert the thermal energy from the oxidation of aluminum to AC electrical energy. The AC electrical energy is converted to DC energy and stored in a battery. In situations demanding low power, the battery can provide power while the fuel combustion process is suspended.

Full Description:
TECHNICAL FIELD 
     An embodiment of the present invention relates to the field of energy conversion, more particularly to the field of converting thermal energy to electrical energy. 
     BACKGROUND 
     Safe power generation and flexible power storage is desirable in extended power consumption systems for mobile vehicles, especially underwater vehicles. In many applications it is desirable to have high energy density fuels for extended missions. Examples include submarines where safety and silence are important. Generating useful power without coming to the surface is very important. This class of system is usually called “Air Independent Power” or “Air Independent Propulsion” 
     In the past, vehicle power systems generated too much noise and were relatively inefficient. Additionally, the power systems were not flexible enough to efficiently satisfy a wide dynamic range of power requirements. In these systems, heat from a hydrocarbon fuel&#39;s oxidation was used to drive a turbine, which in turn drove a generator to generate electrical energy. The use of hydrocarbon based fuel introduced additional drawbacks. This type of fuel was dangerous due to the potential for explosion, and in underwater applications, the oxidizer was carried on board and thereby limited the space available for fuel. Only nuclear steam plants which are very large, expensive, and requiring highly trained operators, solved these problems for the world&#39;s most advanced Navies. 
     SUMMARY 
     An embodiment of the present invention provides a hybrid power system that is silent, highly efficient and can address a wide dynamic range of power requirements. It uses heat from a safe high energy density fuel, such as aluminum, to generate electrical power. The fuel uses water as an oxidizer and thereby provides additional fuel storage by freeing up space that was used to store oxidizer. Additionally, the hybrid power system uses a highly efficient and silent thermoacoustic power converter (TAPC) to convert the thermal energy from the oxidation of aluminum to AC electrical energy. The AC electrical energy is either used directly to power the vehicle, or is converted to DC energy and stored in a battery. This embodiment&#39;s use of a battery provides power over a wide dynamic range of power requirements. For example, in situations demanding low power, the battery can provide power while the fuel combustion process is suspended. In a period of very high demand, the TAPC can be run in parallel with the battery, generating very high power levels. 
     In another embodiment of the present invention, an aluminum combustor is thermally connected to a thermoacoustic power converter. The thermoacoustic power converter generates electrical power from the thermal energy received from the aluminum combustor. 
     In yet another embodiment of the present invention, a heat source is thermally connected to a thermoacoustic power converter. The thermoacoustic power converter generates electrical power from thermal energy received from the heat source using dual alternators. The electrical power obtained from the thermoacoustic power converter is stored in an electrical energy storage device. 
     In still another embodiment of the present invention, an aluminum combustor is thermally connected to a thermoacoustic power converter. The thermoacoustic power converter generates electrical power from the thermal energy received from the aluminum combustor. A battery stores the electrical power obtained from the thermoacoustic power converter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an embodiment that includes a distiller and hydrogen capture system; 
         FIGS. 2A and 2B  illustrate a TAPC; 
         FIG. 3  illustrates an embodiment that includes an energy storage unit; 
         FIG. 4  illustrates an embodiment that includes a battery; and 
         FIG. 5  illustrates a load equalizer. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates hybrid power system  100 . System  100  includes combustor  110 , TAPC  112  and load equalizer  114 . Combustor  110  generates the thermal energy that is used by TAPC  112 . 
     Combustor  110  oxidizes aluminum received at input  116  using water received at input  118 . The oxygen in the water is the oxidizer that is used to combust the aluminum to produce aluminum oxide and thermal energy. The combustion process is started through the use of plasma jet  120 . The combustion may be implemented within a temperature range of approximately 3400° C. and 900° C., and a pressure range of approximately 200 to 300 psi. In underwater applications, the source of water to input  118  may be seawater. It is also possible to include distiller  122  to remove salt or other contaminants from the water. Distiller  122  may receive water at input  124  and provide distilled water to combustor  110  via output  126 . The thermal energy is provided to distiller  122  via heat pipes  128  and  130 . Heat pipes  128  and  130  may contain phase change materials or liquid salts to convey the thermal energy from combustor  110  to distiller  122 . In this example, the liquid salt flows from combustor  110  to distiller  122  via heat pipe  128  and returns to combustor  110  via heat pipe  130 . The oxidation or combustion process produces hydrogen gas as byproduct. The hydrogen gas is removed from the combustor by output  132 , and can be stored for later processing, or vented directly to the external environment. The hydrogen gas may be simply vented to the atmosphere or to the water in underwater applications. It is also possible use hydrogen capture system  134  to make use of the hydrogen byproduct. Hydrogen capture system  134  may be, for example, a tank to hold the hydrogen, a material that absorbs hydrogen for later release, or a fuel cell that can be used to produce additional electrical energy. 
     Heat pipes  140  and  142  are used to conduct thermal energy from combustor  110  to TAPC  112 . Heat pipes  140  and  142  may contain phase change materials or liquid salts to convey thermal energy from combustor  110  to TAPC  112 . In this example, the liquid salt flows from combustor  110  to TAPC  112  using heat pipe  140  and returns from TAPC  112  to combustor  110  using heat pipe  142 . 
     TAPC  112  uses thermal energy received from combustor  110  to cause a gas, such as helium, contained within the TAPC to expand and contract in an oscillatory fashion. As the gas expands and contracts, it drives flexible membranes that are attached to magnets. The oscillatory expansion and contraction of the helium gas causes the flexible membranes and their attached magnets to oscillate within a wire coil to generate AC power. In this embodiment, there are two sets of flexible membranes, magnets and coils to produce AC outputs AC 1  and AC 2 . These assemblies are set in opposing motion, greatly reducing noise and vibration. 
     Outputs AC 1  and AC 2  are provided to load equalizer  114 . Load equalizer  114  load balances each of TAPC outputs AC 1  and AC 2  using adjustable reactive shunt loads. The output impedance of each TAPC output is matched to the load impedance seen by each output. Equalized outputs AC 1 E and AC 2 E are then available for use or storage. It should be noted that by equalizing the outputs from TAPC  112 , vibrational noise generated by TAPC  112  is minimized. This is desirable in underwater applications where silence is important. The reduction in vibration also increases reliability and lifespan of the system. 
       FIGS. 2A and 2B  illustrate an embodiment of TAPC  112 .  FIG. 2A  is a cross-section of TAPC  112  and  FIG. 2B  is a side view of TAPC  112 . TAPC  112  may be implemented using other well-known thermoacoustic power converters; however, in this embodiment a dual alternator TAPC is used. TAPC  112  includes thermal buffer tube  210  and inertance tube  212 . Positioned between tube  212  and tube  210  is heat exchanger  214 . Heat exchanger  214  receives thermal energy from combustor  110  through heat pipes  140  and  142 . Tubes  210 ,  212  and working volume  216  are filled with a working gas such as helium gas. Heat from heat exchanger  214  heats the helium gas and causes it to expand, which drives membranes  218  and  220  in the direction of arrows  222  and  224 , respectively. The expansion of the gas causes a cooling which results in the gas contracting which then allows membranes  218  and  220  to move in the direction of arrows  226  and  228 , respectively. This motion causes magnets  230  and  232  to oscillate within wire coils  234  and  236 , respectively. This oscillatory motion produces the AC current that is provided from TAPC  112  to load equalizer  114 . The combination of membrane, magnet and wire coil may be viewed as an alternator. It should be noted that the movement of the alternators expands the working fluid, cooling it, generating the resonance needed to drive the TAPC. It should also be noted that the alternators are arranged opposed to each other, which helps to minimize vibrational noise. 
       FIG. 3  illustrates an embodiment that includes an energy storage unit. Heater  300  provides thermal energy to TAPC  112 , which provides AC power to AC to DC converter  310 . AC to DC converter  310  provides DC power to storage unit  312 . 
     Heater  300  may be a combustor such as combustor  110  which oxidizes aluminum or it may be used in some applications to combust or oxidize hydrocarbons. It is also possible to implement heater  300  as a collector of solar energy. The thermal energy from heater  300  is conveyed to TAPC  112  using heat pipes  314  and  316 . Heat pipes  314  and  316  may contain phase change materials or liquid salts to convey thermal energy from heater  300  to TAPC  112 . In this example, the liquid salt flows from heater  300  to TAPC  112  using heat pipe  314  and returns from TAPC  112  to heater  300  using heat pipe  316 . 
     TAPC  112  provides AC power to AC to DC converter  310 . AC to DC converter  310  converts the two AC outputs from TAPC  112  into DC power, which is provided to storage unit  312 . Storage unit  312  may be implemented using embodiments such as a capacitor, and/or batteries such as lithium-ion batteries or zinc-air batteries. 
     Monitor  320  monitors the level of charge within storage unit  312 . By monitoring the charge stored within storage unit  312 , it is possible to control heater  300  so that the heating process can be suspended when additional electrical energy is not required or cannot be stored within storage unit  312 . Suspending the heating process when additional electrical energy is not required conserves fuel. 
     It should be noted that in order to minimize vibration produced by TAPC  112  a load equalizer  114  maybe placed between TAPC  112  and AC to DC converter  310 . 
       FIG. 4  illustrates an embodiment that includes an aluminum combustor and a battery. Aluminum combustor  110  provides thermal energy to TAPC  112  using heat pipes  140  and  142 . The two AC outputs from TAPC  112  are provided to load equalizer  114 . The AC outputs from load equalizer  114  are provided to AC to DC converter  310 , which provides DC electrical energy to battery  410  for storage. Battery  410  may be implemented using batteries such as lithium-ion batteries or zinc-air batteries. The charge level of battery  410  is monitored by monitor  320 , which is used to control combustor  110 . Monitor  320  suspends the combustion process when additional electrical energy is not required or cannot be stored within battery  410 . Suspending the combustion process when system power requirements can be met by the energy stored within battery  410  conserves the fuel used by combustor  110 . It is possible for hysteresis to be built in to the operation of monitor  320 . For example, monitor  320  may activate combustor  110  when battery  410  has a voltage of less than 10 V and will deactivate combustor  110  when battery  410  has a voltage greater than 12 V. 
     It should be noted that the embodiment a  FIG. 4  may include distiller  122  and its associated thermal connections to combustor  110 , and it may also include hydrogen capture system  134 . 
       FIG. 5  illustrates an example of an embodiment of load equalizer  114 . Each of TAPC outputs AC 1  and AC 2  are connected to adjustable reactive shunt load  510  and  512 , respectively. Each of TAPC outputs AC 1  and AC 2  are load balanced using the adjustable reactive shunt loads. The output impedance of TAPC output AC 1  is matched to the load impedance seen by output AC 1 E by adjusting reactive shunt load  510 . Likewise, the output impedance of TAPC output AC 2  is matched to the load impedance seen by output AC 2 E by adjusting reactive shunt load  512 . Controller  520  matches the output impedance to the load impedance by monitoring the current and voltage on output AC 1 E, and then by adjusting reactive shunt load  510  to maximize the power transfer to the load seen by output AC 1 E. Likewise, controller  520  matches the output impedance to the load impedance by monitoring the current and voltage on output AC 2 E, and then by adjusting reactive shunt load  512  to maximize the power transfer to the load seen by output AC 2 E. Controller  520  may be implemented, for example, using a programmable processor or computer that executes a program stored in a memory or other non-transitory medium. 
     Controller  520  operates in real time in order to compensate for variations in load impedance that may occur as a result of changing conditions such as changes in power demands, number of loads or changes in temperature. By managing the reactive loads, controller  520  minimizes system noise and vibration, and maximizes overall efficiency. 
     In another embodiment, it is also possible to minimize system noise and vibration, and increase overall efficiency by providing sensor input  524  to controller  520 . Sensor input  524  may include information such as a vibration level of TAPC  112 , the temperature of the working fluid within TAPC  112 , or other parameters. For example, as the vibration level increases, controller  520  may incrementally change the reactive shunt loads to decrease the vibration. Controller  520  may use a search algorithm to minimize the vibration by, for example, increasing the reactive shunt loads by 0.01% and then determining if the vibration decreases, if it decreases, controller  520  will continue to incrementally increase the reactive shunt loads in order to minimize vibration. If increasing the reactive shunt loads causes vibration to increase, controller  520  will incrementally decrease the reactive shunt loads in order to minimize vibration. Controller  520  may act in a similar manner when sensor input  524  indicates an increase in the temperature of the working fluid within TAPC  112 . In this case, for example, the search algorithm may start by incrementally decreasing the reactive shunt loads by 0.01% and then determining if the temperature decreases, if it decreases, controller  520  will continue to incrementally decrease the reactive shunt loads in order to minimize the temperature. If decreasing the reactive shunt loads causes the temperature to increase, controller  520  will incrementally increase the reactive shunt loads in order to decrease the temperature. It is possible to use other algorithms to adjust the reactive shunt loads, and it is also possible to adjust the reactive shunt loads in parallel or individually when minimizing the vibration or temperature. 
     The methods or functions described hereinabove may be executed through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor or controller, the corresponding methods or functions may be provided by a single dedicated processor or controller, by a single shared processor or controller, or by a plurality of individual processors or controllers, some of which may be shared. Processors or controllers may be implemented as hardware capable of executing software, and may also be implemented using devices that include, for example and without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), operation specific hardware such as multipliers or adders, read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage.

Technology Classification (CPC): 5