Abstract:
A method includes receiving a direct current (DC) signal at an inverter control system from a bus. The inverter control system includes an inverter and an inverter controller. The received DC signal is compared to a reference value. Based at least in part on the comparison, the inverter controller determines whether to adjust a magnitude of the DC signal received through the bus. The DC signal is converted to an alternating current (AC) signal with the inverter, and the AC signal is provided to a load.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 61/129,620, filed on Jul. 8, 2008, the entire disclosure of which is incorporated herein by reference. 
    
    
     FIELD 
     The subject of the disclosure relates generally to a fuel cell system with independent power control. More specifically, the disclosure relates to a system and method for individually controlling fuel cell systems and the amount of power provided to one or more loads in electrical communication with the fuel cell systems. 
     BACKGROUND 
     Fuel cell systems can be used to provide electrical power to external loads such as buildings, appliances, lights, tools, air conditioners, heating units, factory equipment and machinery, power storage units, computers, security systems, electric grids, etc. In addition to providing power to external loads, the electricity produced by a fuel cell system can also be used internally by the fuel cell system. For example, the electricity produced by the fuel cell system can be used to maintain fuel cell system variables such as temperature, fuel flow rate, pressure, etc. Electricity produced by the fuel cell system can also be used to power auxiliary devices, control units, startup devices, monitoring devices, balance of plant (BOP) devices, etc. utilized by the fuel cell system. 
     SUMMARY 
     An exemplary method is provided. The method includes receiving a direct current (DC) signal at an inverter control system from a bus. The inverter control system includes an inverter and an inverter controller. The received DC signal is compared to a reference value. Based at least in part on the comparison, the inverter controller determines whether to adjust a magnitude of the DC signal received through the bus. The DC signal is converted to an alternating current (AC) signal with the inverter, and the AC signal is provided to a load. 
     An exemplary method for controlling a fuel cell arrangement includes receiving a direct current (DC) signal at a DC/DC converter system from a fuel cell system, where the DC/DC converter system includes a DC/DC converter. The received DC signal or an output signal from the DC/DC converter system is compared to a variable. A determination is made regarding whether a value, a threshold, or a setpoint for the variable is exceeded based at least in part on the comparison. A magnitude of the received DC signal or of the output signal is adjusted if the value, the threshold, or the setpoint is exceeded. 
     A system is also provided. The system includes a monitoring component, an inverter controller, and an inverter. The monitoring component is configured to compare a direct current (DC) signal to a variable, The inverter controller is configured to generate a control signal based at least in part on the comparison. The inverter is configured to receive the control signal from the inverter controller, increase or decrease a magnitude of the DC signal based at least in part on the control signal, convert the DC signal to an alternating current (AC) signal, and provide the AC signal to a load. 
     Another exemplary system for controlling a fuel cell arrangement includes a monitoring component, a DC/DC controller, and a DC/DC converter. The monitoring component is configured to receive a direct current signal from a fuel cell system or from the DC/DC converter and compare the DC signal to a variable, where the variable corresponds to an operating characteristic of the fuel cell system, a threshold, or a setpoint. The DC/DC controller is configured to generate a control signal based at least in part on the comparison. The DC/DC converter is configured to receive the control signal and adjust a magnitude of the DC signal based on the control signal. 
     Another exemplary method includes receiving a direct current (DC) signal at a DC/DC converter system from a fuel cell system, where the DC/DC converter system includes a DC/DC converter. The received DC signal or an output signal from the DC/DC converter is compared to a first variable. A determination is made regarding whether a value, a threshold, or a setpoint for the first variable is exceeded based at least in part on the comparison. A magnitude of the received DC signal or of the output signal is adjusted if the value, the threshold, or the setpoint is exceeded. An adjusted DC signal is received at an inverter control system from a bus, where the inverter control system includes an inverter and an inverter controller. The adjusted DC signal is compared to a second variable. The inverter controller is used to determine, based at least in part on the comparison to the second variable, whether to adjust a magnitude of the adjusted DC signal received through the bus. The adjusted DC signal is converted to an alternating current (AC) signal with the inverter. The AC signal is provided to a load. 
     Other principal features and advantages will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will hereafter be described with reference to the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a fuel cell arrangement with power control in accordance with an exemplary embodiment. 
         FIG. 2  is a block diagram illustrating a DC/DC converter system in accordance with an exemplary embodiment. 
         FIG. 3  is a block diagram illustrating an inverter system in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In a traditional fuel cell arrangement, a plurality of fuel cell systems may be connected in parallel or series to generate a desired amount of power. The plurality of fuel cell systems are generally controlled as a single power source having a single output. However, each of the plurality of fuel cell systems may vary slightly in operation, and may produce a different amount of power at any given time. The inventors have perceived that controlling a plurality of fuel cell systems as a single unit may decrease overall system efficiency and may result in fuel cell degradation. As such, the inventors have perceived a need for a fuel cell arrangement in which fuel cell systems can be individually monitored and controlled to improve system performance and life. 
     Traditional fuel cell arrangements may also include an inverter to convert a direct current (DC) generated by the fuel cell systems into an alternating current (AC) for delivery to one or more AC loads. The inverter may automatically provide all of the received AC power to the one or more loads regardless of the state of the fuel cell arrangement. The inventors have perceived that automatically distributing all available power to the load(s) can decrease efficiency and increase deterioration of the fuel cell arrangement. As such, the inventors have perceived a need for a fuel cell arrangement with an inverter that is configured to intelligently distribute generated power among one or more loads based on the monitoring of one or more internal processes. 
       FIG. 1  is a block diagram illustrating a fuel cell arrangement with power control in accordance with an exemplary embodiment. The fuel cell arrangement includes a first fuel cell system  100 , a second fuel cell system  105 , a third fuel cell system  110 , and a fourth fuel cell system  115 . Fuel cell systems  100 ,  105 ,  110 , and  115  can produce a direct current (DC) signal as known to those of skill in the art. In alternative embodiments, fewer or additional fuel cell systems can be included in the system. In an exemplary embodiment, a fuel cell system can include one or more fuel cell columns, each of which may contain one or more fuel cell stacks, such as solid oxide fuel cell stacks. A fuel cell stack can refer to a plurality of individual fuel cells which are electrically connected in series. Alternatively, a fuel cell system can refer to a single fuel cell stack. The number of individual fuel cells which make up a given fuel cell system can depend on the amount of electrical power which the given fuel cell system is intended to generate. 
     In alternative embodiments, fuel cell systems  100 ,  105 ,  110 , and  115  can include any other configuration, arrangement, and/or number of individual fuel cells, and may be arranged in a modular configuration, where the power supply system is comprised of separate fuel cell modules or systems and associated power conditioning modules and fuel pre-processing modules. An exemplary fuel cell system is described in U.S. patent application Ser. No. 11/797,707 (filed May 7, 2007 and entitled Ripple Cancellation), the disclosure of which is incorporated herein by reference in its entirety. 
     The fuel cell arrangement also includes a DC/DC converter system  120 , a DC/DC converter system  125 , a DC/DC converter system  130 , and a DC/DC converter system  135 . Fuel cell system  100  can be in electrical communication with DC/DC converter system  120 , fuel cell system  105  can be in electrical communication with DC/DC converter system  125 , fuel cell system  110  can be in electrical communication with DC/DC converter system  130 , and fuel cell system  115  can be in electrical communication with DC/DC converter system  135 . As used herein, electrical communication can refer to any direct or indirect electrical connection. In an exemplary embodiment, each of DC/DC converter systems  120 ,  125 ,  130 , and  135  can include a DC/DC converter, a DC/DC controller, and one or more monitoring components. The monitoring components, which can be implemented in hardware and/or software, can be used to monitor one or more fuel cell system variables. An exemplary monitoring component can be a comparator, and exemplary fuel cell system variables can include output current, output voltage, output power, etc. 
     The DC/DC controller can be used to control the power drawn by the DC/DC converter from the fuel cell system. The DC/DC controller can control the DC/DC converter based at least in part on the monitored system variables. As an example, a monitoring component of DC/DC converter system  130  may indicate that a direct current produced by fuel cell system  110  has exceeded a current threshold. In response to the exceeded threshold, a DC/DC controller of DC/DC converter system  130  can cause a DC/DC converter of DC/DC converter system  130  to draw less current from fuel cell system  110 . Similarly, a second monitoring component of DC/DC converter system  130  may be used to monitor and control an output of the DC/DC converter associated with DC/DC converter system  130 . An exemplary DC/DC converter system is described in more detail with reference to  FIG. 2 . The DC/DC converters can also be used to increase (i.e., boost) the voltage of the DC signals received from the fuel cell systems. For example, the DC/DC converter of DC/DC converter system  120  can be used to increase the voltage of the DC signal received from fuel cell system  100 , the DC/DC converter of DC/DC converter system  125  can be used to increase the voltage of the DC signal received from fuel cell system  105 , and so on. In an alternative embodiment, the DC/DC converters of DC/DC converter systems  120 ,  125 ,  130 , and  135  may be used to decrease the voltage of the DC signals produced by fuel cell systems  100 ,  105 ,  110 , and  115 . In another alternative embodiment, DC/DC converters may not be used. 
     The fuel cell arrangement also includes a fuel cell system controller  140 . In an exemplary embodiment, fuel cell system controller  140  can be used to determine individual reference values for each of fuel cell systems  100 ,  105 ,  110 , and  115 . The reference values can be current values, voltage values, power values, etc. which represent desired operating thresholds of the respective fuel cell systems. As illustrated in  FIG. 1 , fuel cell system controller  140  can determine a first reference value  142  corresponding to fuel cell system  100 , a second reference value  144  corresponding to fuel cell system  105 , a third reference value  146  corresponding to fuel cell system  110 , and a fourth reference value  148  corresponding to fuel cell system  115 . Reference values  142 ,  144 ,  146 , and  148  can be determined based on performance characteristics of fuel cell systems  100 ,  105 ,  110 , and  115 , respectively. As such, each fuel cell system may have a different reference value. 
     The monitoring components in DC/DC converter systems  120 ,  125 ,  130 , and  135  can compare the reference values from fuel cell system controller  140  to corresponding measured values from fuel cell systems  100 ,  105 ,  110 , and  115 . The DC/DC controllers can be used to adjust the amount of current, voltage, power, etc. produced by fuel cell systems  100 ,  105 ,  110 , and  115  based on the comparisons. As an example, fuel cell system controller  140  can determine a reference current for fuel cell system  105  based on performance characteristics of fuel cell system  105 . A comparator of DC/DC converter system  125  can be used to compare the reference current to a measured current from the output of fuel cell system  105 . If the measured current is greater than the reference current, a DC/DC controller of DC/DC converter system  125  can cause a DC/DC converter of DC/DC converter system  125  to draw less current from fuel cell system  105 . If the measured current is less than the reference current, the DC/DC controller can cause the DC/DC converter to draw more current from fuel cell system  105 . Fuel cell systems  100 ,  110 , and  115  can be similarly controlled such that individual fuel cell system control is achieved. 
     As illustrated in  FIG. 1 , positive and negative outputs of the DC/DC converter systems  120 ,  125 ,  130 , and  135  are combined to form a spit bus. The split bus includes a positive bus  150 , a negative bus  155 , and a neutral bus  160 . Positive bus  150  is formed with a positive output  162  from DC/DC converter system  120  and a positive output  164  from DC/DC converter system  125 . Negative bus  155  is formed with a negative output  166  from DC/DC converter system  130  and a negative output  168  from DC/DC converter system  135 . Neutral bus  160  is formed with a negative output  170  from DC/DC converter system  120 , a negative output  172  from DC/DC converter system  125 , a positive output  174  from DC/DC converter system  130 , and a positive output  176  from DC/DC converter system  135  (such that the positive and negative outputs combine to form a neutral output for neutral bus  160 ). In alternative embodiments, the split bus may be formed by any other combinations of the outputs of DC/DC converter systems  120 ,  125 ,  130 , and  135 . In one embodiment, the split bus configuration described in U.S. application Ser. No. 11/797,707, filed on May 7, 2007 and incorporated herein by reference in its entirety may be used. In another alternative embodiment, a split bus configuration may not be used. 
     Positive bus  150 , negative bus  155 , and neutral bus  160  are in electrical communication with an inverter system  180 . Inverter system  180  can include an inverter, an inverter controller, and one or more monitoring components. The inverter of inverter system  180  can be any electrical device configured to receive a direct current and convert the received direct current into an alternating current for provision to an external load  185  and an internal load  190 . External load  185  and internal load  190  can be in electrical communication with the inverter. In alternative embodiments, any number of internal and/or external loads may be provided with an AC signal from the inverter. The AC signal from the inverter to the loads can be a three-phase AC signal. Alternatively, any other AC signal may be used. External load  185  can be an electrical grid to which electrical power is being provided by the fuel cell arrangement. Alternatively, external load  185  can be a building, an appliance, an air conditioner, a heating unit, a computer, a security system, etc. Internal load  190  can be a power auxiliary device, a control unit, a startup device, a monitoring device, a balance of plant (BOP) device, etc. 
     The monitoring components of inverter system  180 , which can be implemented in hardware and/or software, can be used to monitor one or more internal variables. An exemplary monitoring component can be a comparator, and exemplary internal variables can include a split bus current, a positive split bus voltage, a negative split bus voltage, etc. The internal variables can also include load thresholds. The inverter controller of inverter system  180  can be used to control the amount of power drawn from the split bus based on the monitored variables. The inverter controller can also be used to control the distribution of power between external load  185  and internal load  190 . 
     As an example, a monitoring component of inverter system  180  can monitor a voltage on positive bus  150  of the split bus. If the voltage on positive bus  150  drops below a predetermined threshold, the inverter controller of inverter system  180  can increase the power drawn from the split bus. If the voltage on positive bus  150  exceeds the predetermined threshold, the inverter controller can decrease the power drawn from the split bus. As such, the inverter controller can be used to maintain the split bus at a desired voltage, current, etc. The inverter controller can also distribute power received from the split bus. In one embodiment, the inverter controller can provide sufficient power to internal load  190 . The inverter controller can provide all excess power to external load  185 . An exemplary inverter system is described in more detail with reference to  FIG. 3 . 
       FIG. 2  is a block diagram illustrating a DC/DC converter system in accordance with an exemplary embodiment. The DC/DC converter system includes a DC/DC converter  200 , a DC/DC controller  205 , a comparator  210 , a comparator  215 , a comparator  217 , and a comparator  220 . In alternative embodiments, DC/DC converter system may include fewer, additional, and/or different components. The DC/DC converter system can be used to control the amount of power drawn from a fuel cell system  225 . Fuel cell system  225  can be any of fuel cell systems  100 ,  105 ,  110 , or  115  described with reference to  FIG. 1 . DC/DC controller  205  can receive inputs from comparator  210 , comparator  215 , and comparator  220 . Based on the inputs, DC/DC controller  205  can provide a control signal to DC/DC converter  200 . DC/DC converter  200  can draw power from fuel cell system  225  based on the control signal. In an exemplary embodiment, the output of DC/DC converter  200  can be determined at least in part by the load(s) being provided with power through an inverter in electrical communication with DC/DC converter  200 . As such, the inverter may treat DC/DC converter  200  as a current source. 
     Comparators  210 ,  215 ,  217 , and  220  can be implemented in hardware and/or software, and can be any type of comparators known to those of skill in the art. Comparator  210  is used to compare an output of fuel cell system  225  to a reference value  230 . Reference value  230  can be an output voltage of fuel cell system  225 , an output current of fuel cell system  225 , and/or any other operating characteristic of fuel cell system  225 . Reference value  230  can be determined and provided by a fuel cell system controller such as fuel cell system controller  140  described with reference to  FIG. 1 . The fuel cell system controller can determine reference value  230  based on one or more performance characteristics of fuel cell system  225 . Performance characteristics can include an internal temperature of fuel cell system  225 , an external temperature of the environment, a fuel flow rate of fuel cell system  225 , one or more load demands, a measured voltage of fuel cell system  225 , etc. Reference value  230  can be any measured, stored and/or calculated value. Based on the comparison, comparator  210  can provide an output to DC/DC controller  205 . 
     Comparator  215  is used to compare an output of DC/DC converter  200  to an output threshold  235 . In one embodiment, output threshold  235  can be a maximum output current for DC/DC converter  200 . The maximum output current can be based on a desired operating condition, the current capacity of DC/DC converter  200 , the current capacity of fuel cell system  225 , or any other factor. Alternatively, output threshold  235  can be any other variable associated with the output of DC/DC converter  200 . Output threshold  235  can be a stored value, a measured value, and/or a calculated value based on any parameters. Based on the comparison, comparator  215  can provide an output to DC/DC controller  205 . Comparator  220  is used to compare an output of comparator  217  to an output setpoint  240 . The output of comparator  217  is based on a comparison of the outputs from DC/DC converter  200 . As such, comparator  217  can generate an output based on an output voltage, output current, output power, etc. of DC/DC converter  200 . In an exemplary embodiment, output setpoint  240  can be a desired voltage to be output by DC/DC converter  200 . In another exemplary embodiment, output setpoint  240  can be 390 Volts. The desired voltage can be based on a desired operating condition, a number of loads in electrical communication with the system, the type of load(s) in electrical communication with the system, a desired split bus voltage, the type of inverter used in the system, etc. Alternatively, output setpoint  240  can be any other variable associated with the output of DC/DC converter  200 . Based on the comparison, comparator  220  can provide an output to DC/DC controller  205 . In an alternative embodiment, any other number of comparators may be used and/or any other number of variables, thresholds, etc. may be monitored and controlled. In another alternative embodiment, comparators may not be used, and the monitoring may be implemented using any other type of hardware/software known to those of skill in the art. For example, in one embodiment, summers may be used instead of comparators. 
     Direct current/direct current (DC/DC) controller  205  can provide a control signal to DC/DC converter  200  based on the inputs received from comparators  210 ,  215 , and  220 . As an example, comparator  210  may indicate that the output of fuel cell system  225  exceeds or is below reference value  230 . In response, DC/DC controller  205  can provide a control signal to DC/DC converter  200  such that less or more power is drawn from fuel cell system  225 . DC/DC controller  205  can similarly control DC/DC converter  200  based on inputs received from comparators  215  and  220  if an output of DC/DC converter  200  exceeds or is below output threshold  235  and/or output setpoint  240 . In an exemplary embodiment, DC/DC controller  205  can be a proportional-integral (PI) controller as known to those of skill in the art. Alternatively, any other type(s) of controllers may be used. For example, DC/DC controller  205  may be a proportional-integral-derivative (PID) controller, a proportional-derivative (PD) controller, a proportional (P) controller, an integral (I) controller, etc. DC/DC controller  205  can be implemented in hardware and/or software, depending on the embodiment. 
     In an alternative embodiment, fuel cell system  225  may be replaced with an alternative DC power source. The alternative DC power source can be a solar cell system, a wind turbine system, a hydroelectric system, a battery, a generator, or any other type of DC source. The power provided from the alternative DC source can be monitored and controlled using DC/DC controller  205  and DC/DC converter  200  as described above with reference to fuel cell system  225 . As such, DC power sources can be efficiently added to and incorporated within an existing fuel cell arrangement. 
       FIG. 3  is a block diagram illustrating an inverter system in accordance with an exemplary embodiment. The inverter system includes an inverter  300 , an inverter controller  305 , a comparator  310 , a comparator  315 , a comparator  320 , and a comparator  325 . In alternative embodiments, the inverter system may include fewer, additional, and/or different components. The inverter system can be used to control the amount of power drawn from a split bus having a positive bus  330 , a negative bus  335 , and a neutral bus  340 . Split bus  330 ,  335 , and  340  may be the same as split bus  150 ,  155 , and  160  described with reference to FIG.  1 . As such, the inverter system can maintain the split bus at a desired current, a desired voltage, etc. In alternative embodiments, a split bus configuration may not be used. The inverter system can also be used to distribute power to an internal load  345  and an external load  350 . Internal load  345  and external load  350  may be the same as internal load  190  and external load  185  described with reference to  FIG. 1 . In alternative embodiments, power may be distributed to any number of loads in electrical communication with inverter  300 . 
     Inverter controller  305  can receive inputs from comparators  320  and  325 . Comparator  320  receives an input from comparator  310  which is in electrical communication with positive bus  330  and neutral bus  340 . As such, comparator  310  can generate an output based on a voltage, current, power, etc. of positive bus  330 . The output from comparator  310  is provided to comparator  320  for a comparison with a reference value  355 . In an exemplary embodiment, reference value  355  can be a minimum desired voltage of positive bus  330 . In one embodiment, reference value  355  may be +380 Volts. Alternatively, reference value  355  may be any other value. Based on the comparison, an output is provided from comparator  320  to inverter controller  305 . Inverter controller  305  can control the amount of power drawn from the split bus based at least in part on the input from comparator  320 . Similarly, comparator  325  receives an input from comparator  315 , which is in electrical communication with negative bus  335  and neutral bus  340  of the split bus. As such, comparator  315  can generate an output based on a voltage, current, power, etc. of negative bus  335 . The output from comparator  315  is provided to comparator  325  for a comparison with a reference value  360 . In an exemplary embodiment, reference value  360  can be a minimum desired voltage of negative bus  335 . In one embodiment, reference value  360  can be a voltage of −380 Volts. Alternatively, reference value  360  may be any other value. Based on the comparison, an output is provided from comparator  325  to inverter controller  305 . Inverter controller  305  can control the amount of power drawn from the split bus based at least in part on the input from comparator  325 . In another exemplary embodiment, reference values  355  and  360  can be less than output setpoint  240  described with reference to  FIG. 2 . 
     Comparators  310 ,  315 ,  320  and  325  can be implemented in hardware and/or software, and can be any type of comparators known to those of skill in the art. In an alternative embodiment, any other number of comparators may be used and/or any other number of variables, thresholds, etc. may be monitored and controlled. In another alternative embodiment, comparators may not be used, and the monitoring may be implemented using any other type of hardware/software known to those of skill in the art. For example, in one embodiment, summers may be used instead of comparators. 
     Inverter controller  305  can also receive a load threshold  365 . Load threshold  365  can be a desired power to be delivered to internal load  345 , a desired power to be delivered to external load  350 , a maximum power to be delivered to internal load  345 , a maximum power to be delivered to external load  350 , etc. As an example, load threshold  365  can indicate that a maximum power of 25,000 Watts can be provided to external load  350 . In such an example, inverter controller  305  can control inverter  300  such that the power provided to external load  350  does not exceed 25,000 Watts. In an alternative embodiment, inverter controller  305  may receive a plurality of load thresholds corresponding to one or more loads. In an exemplary embodiment, using the control signal from inverter controller  305 , inverter  300  can track the maximum power that can be supplied to external load  350 . 
     Based on the inputs from comparator  320 , comparator  325 , and load threshold  365 , inverter controller  305  can provide a control signal to inverter  300  to control the amount of power drawn from the split bus and/or the amount of power distributed to internal load  345  and external load  350 . As an example, comparator  320  may indicate that the voltage of positive bus  330  is less than reference value  355 . In response, inverter controller  305  can reduce the amount of power drawn from the split bus such that a desired voltage of the split bus is maintained. Inverter controller  305  can also include an algorithm for distributing available power among a plurality of loads. As an example of a simple algorithm, inverter controller  305  may be configured to provide a first amount of power to internal load  345  and a second amount of power to external load  350 , where the second amount of power is equal to the total received power less the first amount of power. Inverter controller  305  can also ensure that the second amount of power provided to external load does not exceed load threshold  365 . 
     In one embodiment, inverter  300  can be implemented with no control wires. In such an embodiment, inverter  300  can calculate the amount of power to be drawn based at least in part on an output impedance of the source. Inverter  300  can determine the output impedance of the source by monitoring split bus  330 ,  335 , and  340 . Inverter  300  can also include an input voltage loop configured to correct the power supplied to the internal load  345  and external load  350  based at least in part on the control signal received from inverter controller  305 . In another exemplary embodiment, inverter controller  305  can be a proportional-integral (PI) controller as known to those of skill in the art. Alternatively, any other type(s) of controllers may be used. For example, inverter controller  305  may be a proportional-integral-derivative (PID) controller, a proportional-derivative (PD) controller, a proportional (P) controller, an integral (I) controller, etc. Inverter controller  305  can be implemented in hardware and/or software, depending on the embodiment. 
     As described above, the control systems described herein can be implemented with hardware and/or software (or logic), depending on the embodiment. In one embodiment, the system can be implemented at least in part as instructions stored in a computer-readable medium. Upon execution of the instructions by a processor, the instructions can cause the processor to perform operations of a fuel cell load controller. 
     The foregoing description of exemplary embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.