Abstract:
A method for controlling a fuel cell system, capable of quickly detecting the pressure rise caused by a faulted open anode injector, reducing pressure in the fuel cell stack when the fault occurs, and taking remedial action to allow continued operation of the fuel cell stack, and militate against a walk-home incident.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application is a continuation patent application of U.S. patent application Ser. No. 11/678,743 filed Feb. 26, 2007, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a method of operation of a fuel cell system. More particularly, this invention is directed to a method of operating a fuel cell system under faulted conditions caused by component failures. 
       BACKGROUND OF THE INVENTION 
       [0003]    In typical fuel cell systems, anode injectors provide hydrogen to the anode side of the fuel cell stack. A common mode of failure for the anode injectors is to fail in an open state. When the anode injectors fail open, undesirable and uncontrolled amounts of hydrogen is delivered to the anode side of the fuel cell stack. Often, the anode injectors do not signal a failure to the control system, consequently making it difficult to predict a pressure rise or the hydrogen flow in the anode side of the fuel cell stack. 
         [0004]    A faulted open injector may cause an increase of pressure on the anode side which can damage the fuel cell stack membrane, and affect the life of the fuel cell stack. The increase in pressure may also damage the fuel cell stack unless the pressure rise is detected and operation of the fuel cell system stopped quickly. Stopping the fuel cell system due to a faulted open injector typically results in the fuel cell being completely inoperable, and an operator being stranded when the fuel cell is powering a vehicle. 
         [0005]    It would be desirable to develop a method of operating a fuel cell system capable of detecting the pressure rise caused by a faulted open anode injector, reducing pressure in the fuel cell stack when the fault occurs, taking remedial action to allow continued operation of the fuel cell stack, and militate against a walk-home incident. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention, a method of operating a fuel cell system capable of quickly detecting the pressure rise caused by a faulted open anode injectors, reducing pressure in the fuel cell stack when the fault occurs, taking remedial action to allow continued operation of the fuel cell stack, and militate against a walk-home incident, has surprisingly been discovered. 
         [0007]    In one embodiment, the method for operating a fuel cell system, including the steps of providing a fuel cell stack having a plurality of anode injectors in fluid communication with an anode inlet of the fuel cell stack and a control system in electrical communication with the fuel cell stack and the anode injectors, determining if an anode injector has failed in an open state using the control system to monitor for a pressure at predetermined points in the fuel cell stack, and enabling the fuel cell stack to continue operation if an anode injector has failed in an open state using the control system to implement a remedial action. 
         [0008]    In another embodiment, the method for operating a fuel cell system, including the steps of providing at least one fuel cell stack having a plurality of anode injectors in fluid communication with an anode inlet of the fuel cell stack, a control system in electrical communication with the anode injectors, a vent valve disposed in a first conduit and in electrical communication with the control system, the first conduit in fluid communication with a fuel tank and the anode injectors, a cathode exhaust in fluid communication with a cathode outlet of the fuel cell stack by a second conduit and adapted to be controlled by the control system, a compressor in fluid communication with a cathode inlet of the fuel cell stack, and a motor mechanically coupled to the compressor and in electrical communication with the control system, controlling the pressure in the fuel cell stack to achieve a desired pressure at predetermined points by selectively controlling the anode injectors and the compressor using the control system, monitoring the actual pressure in the fuel cell stack in at least one predetermined location using the control system, determining if an anode injector has failed in an open state by comparing a desired pressure and the actual pressure in the fuel cell stack, and enabling the fuel cell stack to continue operation if an anode injector has failed in an open state using the control system. 
         [0009]    In another embodiment, the method for operating a fuel cell system, including the steps of providing at least one fuel cell stack having a plurality of anode injectors in fluid communication with an anode inlet of the fuel cell stack, a control system in electrical communication with the anode injectors, a vent valve disposed in a first conduit and in electrical communication with the control system, the first conduit in fluid communication with a fuel tank and the anode injectors, a cathode exhaust in fluid communication with a cathode outlet of the fuel cell stack by a second conduit and adapted to be controlled by the control system, a compressor in fluid communication with to a cathode inlet of the fuel cell stack, and a motor mechanically coupled to the compressor and in electrical communication with the control system, controlling the pressure in the fuel cell stack to achieve a desired pressure at predetermined points by selectively controlling the anode injectors and the compressor using the control system, monitoring the actual pressure in the fuel cell stack in at least one predetermined location using the control system, determining if an anode injector has failed open when a difference between a desired pressure and an actual pressure is greater than a predetermined calibrated constant and all the anode injectors are commanded to zero flow, opening the vent valve to decrease a pressure in the fuel cell stack when a failed open anode injector has been determined, controlling the pressure to achieve a desired cathode pressure calculated as the difference of the actual pressure and a delta pressure above atmospheric pressure when a failed open anode injector has been determined, and increasing a flow of air to a cathode side of the fuel cell stack by increasing a speed of the compressor. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
           [0011]      FIG. 1  is a schematic illustration of a fuel cell system according to an embodiment of the invention; 
           [0012]      FIG. 2  is a graph showing actual fuel cell pressure and desired fuel cell pressure during normal operation and following a failure of an anode injector; and 
           [0013]      FIG. 3  is a flow diagram illustrating a method of operation of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
         [0015]    Referring now to  FIG. 1 , a basic layout of a fuel cell system  1  with associated components is shown. In practice many variants are possible. A schematic representation of a first fuel cell stack  10  and a second fuel cell stack  11  integrated into the fuel cell system  1  is shown. Each of the first fuel cell stack  10  and the second fuel cell stack  11  includes a plurality of individual fuel cells (not shown). The Anode sides (not shown) of all individual fuel cells of the fuel cell stacks  10 ,  11  are connected in a manner commonly known in the art. In a similar manner, cathode sides (not shown) of the fuel cells of the stacks  10 ,  11  are connected in a manner commonly known in the art. Remaining structure and operation of various types of fuel cell systems are commonly known in the art. One embodiment can be found in commonly owned U.S. Pat. No. 6,849,352, hereby incorporated herein by reference in its entirety. Therefore, only the structure and operation of a fuel cell system as pertinent to this invention will be explained in the description. 
         [0016]    In the exemplary embodiment described herein, the fuel cell system includes a control system  16 . The control system  16  is in electrical communication with a plurality of anode injectors  20  via an electrical connection  18 . The electrical connection  18  may be any conventional means of electrical communication. 
         [0017]    The anode injectors  20  are in fluid communication with a fuel tank  2  via a conduit  4 . The anode injectors  20  are also in fluid communication with an anode inlet  24  of the first fuel cell stack  10  and the second fuel cell stack  11 . The anode inlets  24  are in fluid communication with anode outlets  12 . A conduit  15  fluidly connects the anode outlet  12  of the first fuel cell stack  10  with the anode outlet  12  of the second fuel cell stack  11 . A vent valve  6  is disposed in the conduit  15 , and is in electrical communication with the control system  16  via an electrical connection  8 . 
         [0018]    The control system  16  is in electrical communication with a motor  34  via an electrical connection  32 . The motor  34  is coupled with a compressor  36 . The compressor  36  is in fluid communication with a cathode inlet  25  of the fuel cell stacks  10 ,  11  via an air supply conduit  23 . The conduit  23  can be any conventional conduit providing a sealed passageway. 
         [0019]    The cathode sides (not shown) of the fuel cell stacks  10 ,  11  include a plurality of cathodes (not shown) of the fuel cells connected in a manner commonly known in the art. Each of the fuel cells has a plurality of channels between the cathode inlet  25  and a cathode outlet  26 . 
         [0020]    The cathode outlets  26  of the fuel cell stacks  10 ,  11  are in fluid communication with the cathode exhaust valve  30  via a conduit  28 . The cathode exhaust valve  30  is in fluid communication with the vent valve  6  via a conduit  13 . The control system  16  is in electrical communication with the cathode exhaust valve  30  via an electrical connection  22 . 
         [0021]    In operation, air is supplied from a source of air (not shown) via a conduit  42 , compressed by the compressor  36 , and supplied via the conduit  23  to the cathode inlets  25  of the fuel cell stacks  10 ,  11 . The control system  16  can influence the speed of rotation of the air compressor  36  by controlling the motor  34 , and thus, the air flow delivered by the air compressor  36 . By influencing the air flow delivered on the cathode side (not shown) of the fuel cell system  1 , the control system  16  can facilitates reaching a desired air flow and a desired air pressure in the cathode side (not shown) of the fuel cell system  1 . 
         [0022]    The control system  16  monitors an actual gas pressure at predetermined points. The points may include the anode outlets  12  and the cathode outlets  26  via means commonly known in the art, such as a pressure sensor (not shown), for example. A delta pressure is calculated using the difference between the gas pressure at the anode outlets  12 , and the cathode outlets  26 . 
         [0023]    Hydrogen gas is stored in the fuel tank  2 , supplied to the anode injectors  20  via the conduit  4 , and selectively injected into the anode inlets  24 . Typically, the vent valve  6  is closed during normal operation. The control system  16  can influence the rate of hydrogen delivery to the anode inlets  24  by controlling the position of the anode injectors  20  via the connection  18 . 
         [0024]    The control system  16  generates and transmits an anode injector signal to each anode injector  20  individually in order to maintain a desired anode pressure in the fuel cell stacks  10 ,  11 . In flow shifting fuel cell systems  1 , the control system  16  selectively controls the anode injectors  20  for the first fuel cell stack  10  and the anode injectors  20  for the second fuel cell stack  11  to achieve a desired flow of hydrogen through the fuel cell system, using an anode shift algorithm. It may be desirable to alternate the direction of the flow of hydrogen through the fuel cell system  1  at predetermined time intervals, although other switching times can be used as desired. It is further understood that additional methods of control can be implemented without departing from the scope of the invention. 
         [0025]    Typically, when the fuel cell system  1  is operating under normal conditions, the desired anode pressure is equal to the sum of the actual pressure at the cathode outlet  26  and a desired delta pressure determined by the control system  16 . 
         [0026]    A reaction known per se in the art occurs between the air in the cathode sides (not shown) and the hydrogen in the anode sides (not shown) of the fuel cell stacks  10  that releases electrons which can be drawn by an external circuit and/or vehicle (not shown). 
         [0027]    During operation, the anode injectors  20  may fail in an open state. When the anode injectors  20  fail, an undesirable and uncontrolled quantity of gas is delivered to the anode inlets  24 . Thus, even when flow is desired to be zero, hydrogen continues to flow into the anode inlets  24 , resulting in an excess of pressure on the anode side (not shown) of the fuel cell stacks  10 ,  11 . The pressure increase is directly influenced by the position of the failed anode injectors  20 . 
         [0028]      FIG. 2  is a graph showing an actual fuel cell pressure  52  and a desired fuel cell pressure  54  before and after an anode injector failure  50 . When the anode injectors  20  are operating correctly, the desired pressure  54  and the actual pressure  52  are maintained within a calibrated constant. In the embodiment shown, the desired pressure  54  and the actual pressure  52  are typically maintained within a calibrated constant of  3  kPa. After the anode injector failure  50 , the actual pressure  52  is greater than the desired pressure  54  and diverges therefrom. In the embodiment shown, the pressure diverges within a time span of about three seconds. It may be desirable for the calibrated constant to be calculated using factors such as a controllability of the anode pressure controls, a fuel cell system  1  pressure drop, and a fuel cell system  1  protection pressure. 
         [0029]    There is no known adaptive or real time correction method to correct the anode injector failure  50 . If the fuel cell system  1  is shut down after the anode injector failure  50 , an operator of the fuel cell system  1  or vehicle (not shown) is stranded, 
         [0030]      FIG. 3  is a logic flow diagram illustrating a method of operation of the present invention. After a start point  60 , the desired pressure  54  set point is entered  62 . The control system  16  then monitors the difference between the desired pressure  54  and the actual pressure  52 . If the difference between the desired pressure  54  and the actual pressure  52  is greater than the calibrated constant  66 , and at least one anode injector  20  is commanded to zero flow  64 , then the anode injector failure  50  has occurred. The logic flow diagram facilitates a detection of the anode failure  50  by the control system  16 , despite the anode injectors  20  being commanded to zero flow  64 . 
         [0031]    The control system  16  of the current invention detects the anode failure  50 , which allows initiation of a remedial action  70  to enable a continued operation of the fuel cell stacks  10 ,  11 . In the embodiment shown, the remedial action  70  is an opening of the anode vent valve  6  to expose the anode outlet  12  of the fuel cell stacks  10 ,  11  to a pressure in the cathode exhaust  30 . The exposure to the pressure in the cathode exhaust  30  reduces the pressure in the anode sides (not shown). Reducing the pressure in the anode sides (not shown) militates against possible damage to the fuel cell stacks  10 ,  11 . As a result, the uncontrolled hydrogen delivered to the anode sides (not shown) of the fuel cell stacks  10 ,  11  by the failed open anode injectors  20  vents through the cathode exhaust  30 . A remedial desired cathode pressure is determined by the control system  16 . The remedial desired cathode pressure is the atmospheric pressure plus the difference between the actual pressure  52  and the desired delta pressure. The remedial desired cathode pressure enables the continued operation of the fuel cell system  1  by controlling the pressure in the cathode sides (not shown) to account for exposure of the fuel cell stacks  10 ,  11  to the atmospheric pressure, and the venting of fresh hydrogen through the cathode exhaust  30 . The control system  16  then increases the speed of the compressor  22  above a normal operating speed to create a higher flow of air through the cathode exhaust  30 . Thus, emissions from the fuel cell system are minimized by diluting the fresh hydrogen being vented from the fuel cell system. It may be further desirable for the control system  16  to activate at least one of a check engine light (not shown) and a service engine now light (not shown), which will prompt the operator to replace the anode injector  20 , and notify the operator that fresh hydrogen is being released from the vehicle. It is understood that other remedial actions can be taken, as desired. 
         [0032]    It may be further desirable, in fuel cell systems using anode shift methods, to stop the operation of the anode shift algorithm and not change direction of the flow. Instead, hydrogen flow into the fuel cell stacks  10 ,  11  should be balanced in equal percentages, and both the anode injectors for the first fuel cell stack  10  and second fuel cell stack  11  should be in operation. 
         [0033]    From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.