Abstract:
A system for providing back-up power to a load powered by a primary power source comprises: a fuel cell arrangement for generating back-up power for the load, a bridging power source for generating bridge power for the load, and a controller in operable communication with the fuel cell arrangement and the bridging power source. The controller is adapted to initiate application of the bridge power to the load upon detecting a deterioration of power from the primary power source, and is further adapted to initiate application of the back-up power to the load upon detecting a power capability of the back-up power to power the load.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation application of U.S. patent application Ser. No. 10/065,387 filed Oct. 11, 2002, which claims the benefit of U.S. Provisional Application No. 60/328,996, filed Oct. 12, 2001 and U.S. Provisional Application No. 60/410,412, filed Sep. 13, 2002; the contents of all of which are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     This disclosure relates generally to power systems, and especially relates to the storage and recovery of energy from a renewable power source and electrochemical cells.  
         [0003]     Geographically remote areas such as islands or mountainous regions are often not connected to main utility electrical grids due to the cost of installing and maintaining the necessary transmission lines to carry the electricity. Even in remote communities where the transmission lines are in place, it is not uncommon for frequent and extended power outages due to weather related faults. In either case, to prevent economic loss in times of an electrical outage, it is often necessary for these communities or industries in these regions to create local “micro” electrical grids to ensure a reliable and uninterruptible power system. This uninterruptible power system may be either a primary system where there is no connection to the main utility grid, or a backup system that activates when an outage occurs.  
         [0004]     Electrical power for the local grids comes from a variety of sources including hydrocarbon based and renewable power sources. Within a particular grid it is not uncommon to have multiple generation sources, such as diesel generators, natural gas generators, photovoltaic arrays, and wind turbines working in combination to meet the needs of the grid.  
         [0005]     Electrical demands placed on the local grid will vary during the course of a day, week, or season. Since it is not often practical or possible to turn generation sources on and off, inevitably excess power will be generated. This excess energy is typically converted into another form of energy such as heat for storage in another medium such as water. In cold climates, the heated water can then be used for other purposes such as heating buildings, cooking or maintaining temperature in equipment. As the load requirements of the grid increase, it is difficult or impossible to recapture the converted energy back into electrical energy for use in the electrical grid. Further complicating matters is that renewable power sources do not typically run continuously at full power and will experience extended periods of low to no energy output (e.g. night time or seasonal low wind periods).  
         [0006]     Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells or fuel cells commonly employed to address back-up power requirement when a grid fails or when a renewable energy source is unavailable. An electrolysis cell typically generates hydrogen by the electrolytic decomposition of water to produce hydrogen and oxygen gases, whereas in a fuel cell hydrogen typically reacts with oxygen to generate electricity. In a typical fuel cell, hydrogen gas and reactant water are introduced to a hydrogen electrode (anode), while oxygen gas is introduced to an oxygen electrode (cathode). The hydrogen gas for fuel cell operation can originate from a pure hydrogen source, methanol or other hydrogen source. Hydrogen gas electrochemically reacts at the anode to produce hydrogen ions (protons) and electrons, wherein the electrons flow from the anode through an electrically connected external load, and the protons migrate through a membrane to the cathode. At the cathode, the protons and electrons react with the oxygen gas to form resultant water, which additionally includes any reactant water dragged through the membrane to cathode. The electrical potential across the anode and the cathode can be exploited to power an external load.  
         [0007]     This same configuration is conventionally employed for electrolysis cells. In a typical anode feed water electrolysis cell, process water is fed into a cell on the side of the oxygen electrode (in an electrolytic cell, the anode) to form oxygen gas, electrons, and protons. The electrolytic reaction is facilitated by the positive terminal of a power source electrically connected to the anode and the negative terminal of the power source connected to a hydrogen electrode (in an electrolytic cell, the cathode). The oxygen gas and a portion of the process water exit the cell, while protons and water migrate across the proton exchange membrane to the cathode where hydrogen gas is formed. The hydrogen gas generated may then be stored for later use by an electrochemical cell.  
         [0008]     In certain arrangements, the electrochemical cells can be employed to both convert electricity into hydrogen, and hydrogen back into electricity as needed. Such systems are commonly referred to as regenerative fuel cell systems. Regenerative fuel cells may be used in power generation systems as either primary or secondary power sources. However, because regenerative fuel cell systems generally take a certain amount of time from the point of initial activation to delivering full power, there may be a brief delay of power attendant thereto when switching over from a primary power supply to backup power generated by a fuel cell supply. What is needed in the art is a cost effective apparatus and method for bridging short duration power interruptions.  
       SUMMARY OF INVENTION  
       [0009]     Disclosed herein is a power system, comprising: a primary power source in electrical communication with a bus and a bridging power source, wherein the bridging power source comprises at least one of a capacitor, a battery, and an electrolysis cell, and the bridging power source is in electrical communication with said the; and a secondary power source in electrical communication with the bus, wherein the secondary power source comprises a fuel cell.  
         [0010]     Also disclosed herein is a method for operating a power system, comprising: monitoring a primary power source; if the primary power source exhibits selected characteristics, directing power from a bridging power source to a bus and initiating a secondary power source wherein the secondary power source comprises a fuel cell, and the bridging power source comprises at least one of a capacitor, a battery, and an electrolysis cell; and unless the secondary power source exhibits the selected characteristics, powering the bus with the secondary power source and ceasing the directing power from the bridging power source.  
         [0011]     Further, disclosed herein is a storage medium encoded with a machine-readable computer program code, said code including instructions for causing a computer to implement the abovementioned method for operating a power system.  
         [0012]     Further, disclosed herein is a computer data signal, said computer data signal comprising: instructions for causing a computer to implement the abovementioned method for operating a power system.  
         [0013]     Also disclosed herein in an exemplary embodiment is a method for operating a power system, comprising: if a primary power source exhibits first selected characteristics and a secondary power source comprising a fuel cell exhibits second selected characteristics, powering selected loads with an electrolysis cell. The first selected characteristics and the second selected characteristics, individually include at least one of, unavailable inoperable, inadequate to provide power at expected parameters, and unfueled.  
         [0014]     The above discussed and other features will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]     Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike:  
         [0016]      FIG. 1  is a block diagram of a power system featuring a power bridging power source;  
         [0017]      FIG. 2  is a block diagram of a power system featuring a power bridging power source including an electrolysis cell;  
         [0018]      FIG. 3  is a simplified block diagram of a power system featuring a power bridging power source and an electrolysis cell operably connected with a single power converter;  
         [0019]      FIG. 4  is a block diagram of a portion of a power system depicting an exemplary embodiment employing an electrolysis cell to maintain system loads;  
         [0020]      FIG. 5  is a block diagram of a portion of a power system depicting an exemplary embodiment employing an electrolysis cell to maintain system loads, eliminating a power supply;  
         [0021]      FIG. 6  is a block diagram of a portion of a power system depicting an exemplary embodiment employing an electrolysis cell to maintain system loads, eliminating an input power converter;  
         [0022]      FIG. 7  is a block diagram of a portion of a power system depicting an exemplary embodiment employing an electrolysis cell to maintain system loads, eliminating all power converters;  
         [0023]      FIG. 8  is a flowchart depicting an exemplary methodology of control of a portion of an exemplary power system;  
         [0024]      FIG. 9  is a flowchart depicting another exemplary methodology of control of a portion of an exemplary power system;  
         [0025]      FIG. 10  is a flowchart depicting yet another exemplary methodology of control of a portion of an exemplary power system;  
         [0026]      FIGS. 11A and 11B  are a pair of tables that illustrate the energy storage capacity for a 7,700 μF, and a 1,000 μF capacitor for a variety of different voltage ratings; and  
         [0027]      FIG. 12  is a graphical representation of the 7,700 μF capacitor energy storage versus charge voltage. 
     
    
     DETAILED DESCRIPTION  
       [0028]     The following description will provide specific examples with respect to the load and power source voltages for example only. It will also be understood that the method and apparatus for bridging short duration power interruptions may be used with different types of primary/secondary sources and/or other operating voltages, and is not limited to the implementations described herein. Various power sources can range from grid power to solar power, hydroelectric power, tidal power, wind power, fuel cell power, and the like, as well as combinations comprising at least one of the foregoing power sources (e.g., via solar panel(s), wind mill(s), dams with turbines, electrochemical cell systems, and the like).  
         [0029]      FIG. 1  depicts a block diagram of a portion of power system  10  having a primary power source  32  such as generated grid power or that from a renewable source, a secondary power source  100  and a load  36 , which load  36  is fed from a feeder bus  38 . In the example shown, the primary power source  32  provides power along a primary bus  40 ; e.g., 120/240 volts alternating current (VAC). It will be appreciated that the actual primary supply voltage is based upon the type of power source including, but not limited to other alternating current (AC) voltage sources, direct current (DC) sources renewable sources such as wind, solar and the like.  
         [0030]     Optionally, a conversion device  42  can be employed to rectify the power type (e.g., AC to DC, or DC to AC), or to transform the voltage level (e.g., 48 volts direct current (VDC) to 24 VDC). For example, rectifier  43  can convert 120/240 VAC supply voltage fed from the primary power source  32  to a 24 VDC supply, fed through feeder bus  38  to load  36 .  
         [0031]     A secondary power source  100  may comprise an electrochemical cell system. The electrochemical cell system may include a fuel cell  34 , or a regenerative fuel cell system comprising a fuel cell  34 , electrolysis cell  62 , an optional power converter  61 , optional associated hardware, optional storage devices  64 , controls, and the like. The size, i.e., the number of cells, of the fuel cell  34  and optional electrolysis cell  62 , and the desired hydrogen production of the electrolysis cell  62  is dependent upon the desired power output of the secondary power source  100  and specifically fuel cell  34 . For example, a secondary power source  100  can include a fuel cell  34  that provides about 50 to about 100 VDC output voltage for use by the load  36 .  
         [0032]     In order to provide backup power for the load  36 , a controller/DC-DC power supply  44  may be used to convert the power from the secondary power source  100  to a power receivable by the feeder bus  38 . For example, the input from the fuel cell  34  is converted to an output that is connected to feeder bus  38 , wherein a smooth output is an uninterrupted power that has an average voltage fluctuation of less than or equal to about 10% over several seconds. An uninterrupted power is a less than or equal to about 0.005 second delay between cease of power supply from primary power source  32  and introduction of power from controller/DC-DC power supply  44 .  
         [0033]     During operation with a regenerative fuel cell system, the primary power source  32  provides power via optional power converter  61  to an electrolysis cell  62  e.g., an electrolyzer, which generates hydrogen gas. When the optional power converter  61  is not employed, the electrolysis cell  62  may be directly connected to the primary bus  40  via line  65 . The hydrogen generated by the electrolysis cell  62  is stored in an appropriate storage device  64  for later use. At such a point in time as required for operation such as outages of the primary power source  32  and the like, or for a renewable power source, during the day or season where the power generation capability of the renewable power source declines (e.g., night time), the primary power source  32  or secondary power source  100  will need to offset the loss in capacity. The hydrogen previously stored in storage device  64  is supplied to a hydrogen electrochemical device, e.g., fuel cell  34 , which converts the hydrogen into electricity to supply to the load  36 . Power generation will continue until the hydrogen in the storage device  64  is exhausted or the power is no longer required. Reasons for ending power generation may include, for example, the restoration of the grid power, restoration of renewable energy sources (such as solar, wind, wave power, or the like), and/or the determination that peak-shaving is no longer cost effective or no longer required.  
         [0034]     Once the amount of hydrogen in the hydrogen storage device  64  decreases below a pre-determined level, the electrolysis cell  62  engages to replenish the hydrogen supply. Preferably, hydrogen will be replenished whenever the hydrogen storage level in the hydrogen storage device  64  is less than full, and there is power available from the primary power source  32  for the electrolysis operation to ensure the longest possible operational duration capability for the secondary power source  100 , e.g., the fuel cell  34 . Alternatively, hydrogen may be replenished with the addition of hydrogen from another source. For example, another hydrogen generating means, or replacement, replenishment, or supplementation of the existing hydrogen storage device  64 .  
         [0035]     Returning to  FIG. 1  once again, and to discussion of the secondary power source  100 , because fuel cell systems generally take a certain amount of time from the point of initial activation to delivering full power, there may be a brief delay of power attendant thereto when switching over a primary power source  32  to secondary power source  100  and power generated by a fuel cell  34 . To address this time lapse, a power system may employ a bridging power source  46 . The bridging power source  46  stores electrical energy and temporarily provides power to load  36  in the event of any gap or delay between the transfer of power delivery from the primary power source  32  to the power delivery from the secondary power source  100 , namely, fuel cell  34 . For example, power system  10  may include a monitor of the primary power source  32  (e.g., a grid, solar power, another electrochemical system, and the like); and upon a cease in power from the primary power source  32 , start-up an secondary power system  100  and introduce power from the bridging power source  46  during the time lapse. The bridging power source  46  may comprise a capacitor  48  and/or battery  49  and optionally a power converter  50 .  
         [0036]     Charging of the capacitor  48  and/or battery  49  may be accomplished in various fashions, depending upon the type of primary power source  32  and the voltage of feeder bus  38  or primary bus  40 , accordingly. The capacitor  48  or battery  49  can be charged with power from primary bus  40  via optional power converter  50 . Power converter  50  converts the voltage from the bus voltage on feeder bus  38  (or primary  40  depending upon the implementation) to the capacitor/battery voltage. Meanwhile, a conversion device  42  can be employed, if desired, to adjust the voltage of primary bus  40  to the desired voltage for the feeder bus  38 . Alternatively, the power can pass from primary bus  40  through conversion device  42 , to feeder bus  38 . Power converter  50  may alternatively convert voltages from feeder bus  38  to charge to the capacitor  48  and/or battery  49 . Finally, it will be appreciated, that capacitor  48  and/or battery  49  may be operably connected to either primary bus  40  or feeder bus  38  directly. In this embodiment, power from primary bus  40  can be converted from AC to DC, and/or the DC voltage of the feeder bus  38  may be converted to the desired capacitor voltage via power converter  50 . For example, the energy used to charge capacitor  48  or battery  49  can come from the output of rectifier  43  that converts 120 (or 240) VAC on primary bus  40  to 24 VDC on feeder bus  38 . The power converter  50  then converts the low voltage (e.g., 24 VDC) input into an appropriate voltage output, which is then used to charge capacitor  48  and/or battery  49 .  
         [0037]     The output of capacitor  48  and/or battery  49  is connected to controller/DC-DC power supply  44 . When capacitor  48  and/or battery  49  is used to bridge the gap in power between a switch-over from primary power source  32  to the secondary power source  100 , the controller/DC-DC power supply  44  may be employed to convert the power from the power level of the capacitor  48  to the power level of the feeder bus  38 . Preferably, power is supplied by capacitor  48  and/or battery  49  for the period of time from a cease in the power supply from primary power source  32  until commencement of power supply from fuel cell  34  (i.e., when the fuel cell  34  attains operating conditions and begins to supply a predetermined amount of power).  
         [0038]     In order to determine when, and for what period, to draw power from capacitor  48 , sensing lines  52  and  54  are connected from the primary bus  40  and the output of the secondary power source  100  to the controller/DC-DC power supply  44 . In this manner, controller/DC-DC power supply  44  can monitor the status of the primary power source  32  and the secondary power source  100  so that the switching to an appropriate power source may be determined and controlled. It will easily be appreciated that in controller/DC-DC power supply  44 , the DC-DC power supply may optionally be separated from the controller.  
         [0039]     During a normal mode of operation, the power supplied from primary power source  32  (e.g., 120/240 VAC or optionally a DC source) on primary bus  40  is converted (in the depicted configuration) to a DC voltage by rectifier  43  of conversion device  42 . The load  36  draws current from feeder bus  38 , regardless of the source of the power thereto. During the normal mode, bridging power source  46  maintains stored electrical energy in the event of a temporary power interruption.  
         [0040]     In the event of a loss of power from the primary power source  32 , controller/DC-DC power supply  44  senses the loss on the primary bus  40  through sensing line  52 . A signal is then sent by controller/DC-DC power supply  44  to the secondary power source  100  (through line  56 ) to begin generating backup power for feeder bus  38 . Because of the inherent time delay of a fuel cell  34  in producing full power, controller/DC-DC power supply  44  converts the output voltage of capacitor  48  and/or battery  49  to voltage that is directed to feeder bus  38  until the secondary power source  100 , and more specifically the fuel cell  34  is ready to take over so that load  36  sees an uninterrupted supply of power.  
         [0041]     Once controller/DC-DC power supply  44  senses that the fuel cell  34  is generating a desired amount of power, the capacitor  48  and/or battery  49  may be disconnected (circuit broken) from feeder bus  38  and backup power is now directed from the secondary power source  100  and more specifically the fuel cell  34 , through controller/DC-DC power supply  44 , and onto feeder bus  38 . Optionally, at the same time, capacitor  48  and/or battery  49  may be recharged through line  58  from feeder bus  38  and power converter  50 . The connecting and disconnecting of the capacitor  48  and/or battery  49  to the DC-DC converter within controller/DC-DC power supply  44  may be accomplished with one or more device(s) such as a power field effect transistor(s) (FET; not shown), transistor(s), thyrister(s), relay(s), switching device(s), and the like, as well as combinations including at least one of the foregoing. Optionally, controller/DC-DC power supply  44  may leave capacitor  48  and/or battery  49  in the circuit but draw essentially no power therefrom. If power from the primary power source  32  is subsequently restored, this will be sensed by controller/DC-DC power supply  44 . This time, however, there is no need to discharge capacitor  48  and/or battery  49 , since controller/DC-DC power supply  44  may seamlessly switch from the secondary power source  100  and fuel cell  34  back to primary power source  32  by deactivating the fuel cell  34 .  
         [0042]     Either during operation of the secondary power source  100  (via feeder bus  38 ) and/or after reconnection to primary power source  32  (via primary bus  40 ), the bridging power source  46 , namely the capacitor  48  and/or battery  49  may be charged (or recharged, as is appropriate). During charging, current supplied from feeder bus  38  is sent through line  60  to power converter  50 , which converts the voltage of feeder bus  38  to that appropriate to charge capacitor  48  and/or battery  49 . It should be noted, that once capacitor  48  and/or battery  49  is/are charged, no significant current would be drawn by power converter  50  (if used) from feeder bus  38 . Alternatively, it will be further appreciated that in an implementation where primary power source  32  and primary bus  40  comprise a VDC power source, power may be optionally be drawn directly from the primary bus  40  (or optionally through the power converter  50 ) to charge the capacitor  48  and/or battery  49 .  
         [0043]     Moreover, the power converter  50  may, be configured as an AC/DC converter (rectifier) coupled directly to the primary power source  32  and primary bus  40 . In addition, for yet another alternative embodiment, the output voltage of controller/DC-DC power supply  44  may be generated at a slightly lower value than that resultant from the conversion device  42  (e.g., by about 1 to about 3 volts). In so doing, any current flow from controller/DC-DC power supply  44  onto feeder bus  38  would be limited until such time as the primary power source  32  is unavailable.  
         [0044]     Referring now to  FIGS. 11A and 11B , there is shown a pair of tables, which illustrate the energy storage capacity for a 7,700 μF (microfarad), and a 1,000 μF capacitor for a variety of different voltage ratings. (Also see the graphical representation of  FIG. 12 ) Such a capacitor as depicted in the figure may be employed as capacitor  48  in an exemplary embodiment as described herein. In an exemplary embodiment, the capacitor exhibits a capacitance range of about 1,000 μF (microfarad) to about 7,700 μF at of voltage range of about 450 VDC. Naturally, the higher the capacitance and the voltage ratings, the more energy is stored and the more power delivery capability. Likewise, it will be appreciated that various capacitances and voltage ranges may be employed to suit a selected implementation. While a capacitance of about 1,000-7,700 μF at a voltage of about 450 VDC has been disclosed, these values are purely illustrative. Many other values are conceivable both larger and smaller and at higher or lower voltages. The voltages for charging the capacitor  48  may be selected as desired for ease of implementation, in an exemplary embodiment, the voltage for capacitor  48  is selected to be about 5 to 10 times the voltage of the feeder bus  38 .  
         [0045]     The tables of  FIGS. 11A and 11B  further illustrate the “hold up” or discharge time of the capacitor  48  at a power output of 10 kW. Again, the more energy that is stored, the longer it takes for the capacitor  48  to discharge and hence the longer the bridging power source  46  will be able to bridge power between the primary power source  32  and the secondary power source  100 . It should be noted that the actual hold up time of capacitor  48  would be reduced as a function of normal inefficiencies associated with the controller/DC-DC power supply  44  and other system components and interconnections.  
         [0046]     Employing a system comprising an electrochemical system in conjunction with a high voltage, medium-sized capacitor as part of a power bridging power source, a cost-effective uninterrupted power supply system is realized. This is especially the case when one or more of the sources have an inherent power-up time associated therewith, such as secondary power source  100  including a fuel cell  34 . It should also be noted that the number of components employed may be reduced as disclosed by employing commonality in selected components, e.g., using a common the DC-DC power supply  44  connected to both the capacitor  48  and/or battery  49  and the fuel cell  34  instead of multiple power supplies.  
         [0047]     Referring now to  FIG. 2  there is depicted an alternative embodiment of the power system described above and as depicted in  FIG. 1 .  FIG. 2  depicts a block diagram of a portion of a power system  10   a , very similar to power system  10  of  FIG. 1 , again, having a primary power source  32  such as generated grid power or that from a renewable source, a secondary power source  100  and a load  36 , which load  36  is fed from a feeder bus  38 .  
         [0048]     As described earlier, to provide backup power for the load  36 , the controller/DC-DC power supply  44  is used to convert the power from the secondary power source  100  to a power receivable by the feeder bus  38 . Likewise, during operation with a regenerative fuel cell system, the primary power source  32  provides power via optional power converter  61  to an electrolysis cell  62 , e.g., an electrolyzer, which generates hydrogen gas. The hydrogen generated by the electrolysis cell  62  is stored in an appropriate storage device  64  for later use.  
         [0049]     The hydrogen previously stored in storage device  64  is supplied to a hydrogen electrical generator e.g. fuel cell  34 , which converts the hydrogen into electricity to supply the load  36 . Power generation will continue until the hydrogen in the storage device  64  is exhausted or the power is no longer required.  
         [0050]     As previously discussed, due to the inherent delay in start-up of the secondary power source  100  and the fuel cell  34 , in addition to the fuel cell  34 , a bridging power source  46   a  may be employed to enable the uninterrupted supply of power to load  36 . In this exemplary embodiment, the bridging power source  46   a  may comprise the electrolysis cell  62  (operating as an electrical source to replace or supplement capacitor  48  and/or battery  49 ) and optionally a power converter  50  and/or power converter  61 .  
         [0051]     Continuing with  FIG. 2 , the electrical input to the electrolysis cell  62  may be disconnected from the primary bus  40  of primary power source  32  and/or the optional power converter  61  and instead connected as an output to supply electrical power as depicted via line  63 . During bridging, the electrolysis cell  62  may be employed to generate electricity by utilizing the hydrogen remaining within the electrolysis cell  62  to generate and supply bridging power to feeder bus  38  (via controller/power supply  44 ). Depending upon the amount of hydrogen available within the electrolysis cell  62 , electricity may be supplied for the duration of the above mentioned power interruption between loss of the primary power source  32  and the generation of power from the secondary power source  100 , more specifically fuel cell  34 . In an exemplary embodiment, an electrolysis cell  62  may supply about 30 watts decaying to about 1 watt of power over about 10 minutes.  
         [0052]     In an exemplary embodiment, the electrolysis cell  62  is operably connected to controller/DC-DC power supply  44  in a manner to facilitate the electrolysis cell  62  supplying current to controller/DC-DC power supply  44 . When the electrolysis cell  62  is used to bridge the gap in power between a switch-over from primary power source  32  to the secondary source  100 , the controller/DC-DC power supply  44  may optionally be employed to convert the voltage from the voltage level output by the electrolysis cell  62  to the voltage level of the feeder bus  38 . Preferably, power is supplied by electrolysis cell  62  for the period of time from a cease in the power supply from primary power source  32  until commencement of power supply from the secondary power source  100  (i.e., when the fuel cell  34  attains operating conditions and begins to supply a predetermined amount of power). Otherwise the electrolysis cell  62  may, as described earlier be supplemented with a capacitor  48  and/or battery  49 . It will be appreciated, that employing the electrolysis cell  62  in this manner will facilitate elimination of the capacitor  48  and/or battery  49  from the power system  10 . Alternatively, the size of the capacitor  48  and/or battery  49  may be reduced because of the net increase in bridge power available with the electrolysis cell  62 . Finally, the addition of the electrolysis cell  62  to the bridging power source  46   a  may result in reduced maintenance and replacement for storage components such as the capacitor  48  and/or battery  49 .  
         [0053]     During a normal mode of operation, in this embodiment, the power supplied from primary power source  32  (e.g., 120/240 VAC if an AC source) on primary bus  40  is converted (in the depicted configuration) to a DC voltage by rectifier  43  of conversion device  42 . The load  36  draws current from feeder bus  38 , regardless of the source of the power thereto. During the normal mode, bridging power source  46   a  maintains stored electrical energy in the event of a temporary power interruption, while the electrolysis cell  62  is operatively configured to receive electrical power and generate hydrogen for storage if needed. Moreover, preferably, the electrolysis cell  62  has fully filled the hydrogen storage device  64  and therefore the electrolysis cell  62  is idle but configured to provide an electrical output to controller/DC-DC power supply  44  and thereby the feeder bus  38 . It will be further appreciated that the electrical connection and configuration could be arranged such that the electrolysis cell  62  supplies only a subset of the full load on the feeder bus  38 . For example, the load of the feeder bus  38  may be logically partitioned as needed to support various priority loading schemes. Moreover, the load may be further partitioned in consideration of the available backup or bridging power available. For example, the load partition could be modified as backup power storage capability is diminished, providing additional protection for the critical system components and interfaces, such as system controllers, monitors, or watchdog circuits.  
         [0054]     As stated above, in the event of a loss of power from the primary power source  32 , here again, controller/DC-DC power supply  44  senses the loss on the primary bus  40  through sensing line  52 . A signal is then sent by controller/DC-DC power supply  44  to the secondary power source  100  and fuel cell  34  (through line  56 ) to begin generating backup power for feeder bus  38 . Because of the inherent time delay of a fuel cell  34  in producing full power, controller/DC-DC power supply  44  converts the output voltage of electrolysis cell  62  (and/or capacitor  48  and/or battery  49 ) to voltage that is directed to feeder bus  38  and appropriate partitions thereof, until the secondary power source  100 , and more specifically the fuel cell  34  is ready to take over so that load  36  sees an uninterrupted supply of power.  
         [0055]     Once controller/DC-DC power supply  44  senses that the fuel cell  34  is generating a desired amount of power, electrolysis cell,  62 , and/or the capacitor  48  and/or battery  49  are disconnected and backup power is now directed from the secondary power source  100  and more specifically the fuel cell  34 , through controller/DC-DC power supply  44 , and onto feeder bus  38 . Optionally, at the same time, capacitor  48  and/or battery  49  may be recharged through feeder bus  38  and power converter  50 . The connecting and disconnecting of the electrolysis cell  62 , and/or capacitor  48 , and/or battery  49  to the DC-DC converter within controller/DC-DC power supply  44  may be accomplished with a device such as a power field effect transistor (FET; not shown), or the like. Optionally, controller/DC-DC power supply  44  may leave capacitor  48  and/or battery  49  in the circuit but draw essentially no power therefrom. If power from the primary power source  32  is subsequently restored, this will be sensed by controller/DC-DC power supply  44  facilitating a seamless switch from the secondary power source  100  and fuel cell  34  back to primary power source  32  by deactivating the fuel cell  34 .  
         [0056]     Employing a power system including an electrolysis cell  62  as part of a bridging power source  46   a , a cost-effective uninterrupted power supply system is realized. This is especially the case when one or more of the sources have an inherent power-up time associated therewith, such as secondary power source  100  including a fuel cell  34 .  
         [0057]     Turning now to  FIG. 3 , a power system  10   b  similar once again to the power system  10  and  10   a  from  FIGS. 1 and 2  respectively is depicted to illustrate yet another exemplary embodiment where the electrolysis cell  62  is operably connected to provide power for system control and/or load applications. In this embodiment, as depicted in the figure, it will be appreciated that a bridging power source  46   b  no longer includes optional power converter  61  and thereby power system  10   b  is simplified. The electrolysis cell  62  in this instance (as it could also be for the embodiments disclosed above) is configured to be operably connected to optional power converter  50 . Once again, it will also be appreciated that while in an exemplary embodiment a DC/DC power converter is disclosed the power converter  50  may be selected to address the configuration of the primary power source  32  whether AC grid power or DC such as from a renewable source, such as wind power generators, photovoltaic and the like as well as a battery bus and so on.  
         [0058]     Continuing now with  FIG. 3 , the electrical input to the electrolysis cell  62  may be disconnected from the primary bus  40  of primary power source  32  ( FIG. 2 ) and/or the optional power converter  50  and instead connected as an output to supply electrical power as depicted via line  63 . The electrolysis cell  62  utilizes the remaining internal hydrogen to generate and supply bridging power to feeder bus  38  (via controller/DC-DC power supply  44 ) for the duration of the above mentioned power interruption between loss of the primary power source  32  and the generation of power from the secondary power source  100 , more specifically fuel cell  34 . Operation of the power system  10   b  is similar to that described for power systems  10  and  10   a  for  FIGS. 1 and 2  respectively. Only specific differences are address here. It will be appreciated that the  FIG. 3  provides a depiction intended to illustrate the operation of power system  10   b  in the absence of power converter  61 .  
         [0059]     Turning now to  FIG. 4 a  portion of the power system  10  from  FIGS. 2 and 3  is depicted to illustrate an exemplary embodiment where the electrolysis cell  62  is operably connected to provide power for system control and/or load application. It is note worthy to appreciate that in an embodiment as depicted the electrolysis cell  62  may under certain configurations be utilized entirely to provide bus power in the absence of the primary power source  32 .  
         [0060]     Turning now to  FIG. 5 , in yet another exemplary embodiment a portion of the power system  10   b  from  FIG. 3  is depicted to illustrate an exemplary embodiment where the electrolysis cell  62  is operably connected to provide power for system control and load applications. It is note worthy to appreciate that in an embodiment as depicted, the electrolysis cell  62  may be configured and utilized to provide bus power to a load without employing a DC/DC power supply  44  on the output of the electrolysis cell  62  in the absence of the primary power source  32 . In such a configuration, the electrolysis cell  62  and/or selected loads may be configured to facilitate operable interconnection between the electrolysis cell  62  and selected loads. For example, the system may be configured to limit the loads applied to the electrolysis cell  62  to the most essential loads (such as system control, monitoring, and diagnostics) and those loads may be configured to operate directly from the voltage output by the electrolysis cell  62 . It will be appreciated, that depending upon the power available, loads may be added and deleted as desired.  
         [0061]     Turning now to  FIG. 6 , in yet another exemplary embodiment a portion of the power system  10  from  FIGS. 2 and 3  is depicted to illustrate an exemplary embodiment where the electrolysis cell  62  is operably connected to provide power for system control and load application. In this embodiment as depicted, the electrolysis cell  62  is configured to be interfaced with and may be operably connected to the primary power source  32  without the intervening power converter  50  as described earlier. In such a configuration, once again the electrolysis cell  62  is utilized to provide bus power to the feeder bus  38 , and thereby to a load  36  in the absence of the primary power source  32 . Once again, in such a configuration, the elimination of the power converter  50  provides for additional system simplification and reduced cost.  
         [0062]     Optionally, it will be appreciated that the embodiment described above may be further simplified to include the elimination of the controller/DC-DC power supply  44  for conversion of the voltage from the electrolysis cell  62  to the feeder bus  38  and loads  36 . Once again, in such a configuration as depicted in  FIG. 7 , the electrolysis cell  62  may be operably connected to receive power directly from the primary power source  32  e.g. a renewable source with a DC output. Furthermore, the electrolysis cell  62  and/or selected loads may be configured to facilitate operable interconnection between the electrolysis cell  62  and selected loads directly.  
         [0063]     Continuing now with  FIGS. 1, 2 , and  3  and turning as well to  FIG. 8 , a flow chart depicting an exemplary method of a control process  200  for a power system is depicted. The process  200  initiates with monitoring and evaluation of the power source at block  210 . Such monitoring may include evaluation of the voltage on the primary bus  40  ( FIGS. 1, 2 , and  3 ), or as depicted in this instance, wind speed or light level for a renewable power source as the primary power source  32 . As disclosed earlier, such a renewable power source ( FIGS. 1, 2 , and  3 ) includes solar wind, tidal, geothermal resources, and the like as well as combinations including at least one of the foregoing. Decision block  212  includes a determination that the primary power source  32  is adequate for electrolysis. For example, is the input power available from the primary power source greater than or equal to about 500 watts. If so, a determination is made at a second decision block  214  as to whether the electrolysis cell  62  is already operating. If so, a determination is made to continue generation of hydrogen with the electrolysis cell  62  as depicted at block  216  and thereafter the processing returns to block  210 . If the electrolysis cell  62  is not operating, yet there is adequate power from the primary power source  32 , the selected ancillary/parasitic loads may be started and added as the load. For example as loads added to feeder bus  38 . Additionally, the electrolysis cell  62  is powered to generated hydrogen and recharge any depleted hydrogen. The addition of loads is depicted at blocks  218  and  220  respectively. Processing then returns to the initial functions at block  210 .  
         [0064]     Returning to decision block  212 , if there is inadequate power at the primary power source  32 , e.g., low light, no wind, grid interruption, and the like, a determination is made at decision block  222  as to whether there is any portion of the system operable, e.g., any power available from any source to operate as opposed to all sources depleted. For example, insufficient power available for electrolysis and yet still electrolyzing. If so, an orderly elimination of loads is initiated at block  224  with the termination of electrolysis, and thereafter shedding of ancillary loads as shown at  226 . Finally, block  228  depicts operating the electrolysis cell  62  (denoted E/C) as an electrical power source to power control circuitry and monitoring. Processing thereafter returns to block  210  to repeat the cycle.  
         [0065]     Continuing now with  FIGS. 1, 2 , and  3  and turning as well now to  FIG. 9 , an alternative embodiment is depicted showing exemplary process  201  and control for the power system  10  when experiencing a brief power loss. Such a brief power loss may include but not be limited to, cloud cover for solar systems, wind droop for wind systems, momentary and short grid interruptions, and the like. Processing in this embodiment is similar to that described for process  200  in association with  FIG. 8  except that following the block  224  to halt hydrogen generation from the electrolysis cell  62  a decision block,  230  is added to determine if the power interruption is expected or anticipated. For example, in a solar power system, to ascertain if an interruption is due to cloud cover as opposed to sunset. If the interruption satisfies selected criteria for an unexpected interruption, then the process transfers to block  232 . Selected criteria may include, but not be limited to a time duration based upon time of day, date, current conditions, weather conditions, geographic position, and the like, as well as combinations including one or more of the foregoing.  
         [0066]     Continuing with  FIG. 9  at block  232  a timer is initiated to track the duration of the brief loss of the primary power source  32 , once again, in this instance a renewable power source. During this time interval, the ancillary system may be powered using the electrolysis cell  62  (denoted E/C) as a source of electricity as depicted at block  234 . The status of the primary power source  32  is monitored to determine the availability of the primary power source  32 , namely the return to desirable power generation as depicted at block  236 . Should the primary power return to acceptable parameters within a selected time-frame, as depicted at decision block  238  the process  201  transfers to block  220  for initiation hydrogen generation with the electrolysis cell  62 . If the primary power source in not available within the selected window, the process  201  transfers to block  226  to shut down ancillary loads as described earlier. Similarly, returning to decision block  230 , if the interruption of the power source does not satisfy selected criteria for an expected interruption, then the process  201  also transfers to block  226  to shut down as described earlier.  
         [0067]     Continuing once again with  FIGS. 1, 2 , and  3  and turning to  FIG. 10 , yet another alternative embodiment is depicted showing exemplary control process  202  for the power system  10  employing various configurations of selected power converters e.g., conversion device  42 , power converters  50  and  61 , and controller/DC-DC power supply  44 , to facilitate control of the electrolysis cell  62  as well as the loads applied thereto. More specifically, this embodiment address an optional configuration of the power systems described earlier where the electrolysis cell  62  and loads are connected to a single conversion device  42  (or power converter  50 ) and the operation of the conversion device  42  as a power converter in light of such a connection. Additionally, in this embodiment, evaluation of the availability of power or a resource is monitored to facilitate determination of the appropriate control action. For example, the process  202  may evaluate the presence of a primary power source  32  such as from a grid, availability of a secondary power source  100 , or the status of renewable sources such as wind, light, tidal, geothermal, and the like, as well as combinations including at least one of the foregoing.  
         [0068]     Turning to the figure, the process  202  is initiated at block  210  as described earlier, and continues with a decision block  240 . Decision block  240  includes a determination that the primary power source  32  (once again, in this instance, a renewable power source, e.g., solar, wind) is adequate for powering selected systems and loads. If not, the process  202  transfers to decision block  214  and thereafter block  224 ,  226  and  228  as described earlier. Returning to decision block  240 , if there is adequate power for other loads the process  202  transfers to decision block  212  where a determination is made as to whether adequate power is available to generate hydrogen with the electrolysis cell  62 . If so, similar to previous embodiments, the process  202  transfers to decision block  214 , where a determination is made as to whether the electrolysis cell  62  (denoted E/C) is operating. If so, a determination is made to continue generation of hydrogen for the electrolysis cell  62  as depicted at block  216  and thereafter the processing returns to block  210 . If the electrolysis cell  62  is not operating, as determined at decision block  214 , yet there is adequate power from the primary power source, e.g.,  32 , the selected ancillary/parasitic loads may be started and added as a load as depicted at decision block  242  and block  218 . Moreover, as depicted at block  244 , the conversion device  42  may be operated in a current regulation mode to facilitate powering the electrolysis cell  62  and thereby generation of hydrogen to storage in the storage device  64 . Process  202  thereafter returns to block  210  to continue.  
         [0069]     Returning to decision block  212 , if it is determined that there is inadequate power available for electrolysis and hydrogen generation, the process  202  transfers to block  244  where the regulation of the conversion device  42  is set to voltage control mode for controlling selected loads. The process  202  then continues to block  246  were the conversion device  42  regulates and limits the voltage from the primary power source  32  to less than a selected value. Such a configuration facilitates operating various loads without providing sufficient excitation to the electrolysis cell  62  to promote hydrogen generation. In an exemplary embodiment, this voltage would be less than or equal to about 1.4 VDC per cell of the cell stack of the electrolysis cell  62 . Preferably, less than 1 VDC per cell. In an exemplary embodiment employing a 20 cell stack in the electrolysis cell  62 , the potential across the cell stack of the electrolysis cell  62  would be less than or equal to 10 VDC. The process  202  thereafter continues to block  218  where ancillary load are started and powered. Finally, process  202  returns to block  210  to continue the control cycle.  
         [0070]     The disclosed invention can be embodied in the form of computer or controller implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media  70 , such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the invention. The present invention may also be embodied in the form of computer program code or signal  72 , for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.  
         [0071]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.