Abstract:
A method for operating a fuel cell system includes electrically coupling a fuel cell stack to an energy storage device and an electrical demand by a load device. A controller is coupled to the fuel cell stack, the energy storage device, and the load device via a communications connection. The controller obtains information relative to an operation of at least one of the fuel cell stack and the energy storage device and the controller controls an operation of the load device based on the information.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional patent application No. 61/577,777 filed on Dec. 20, 2011, entitled “Fuel Cell-Vehicle Communications Systems and Methods”, the entire disclosure of which is incorporated herein by reference. 
         [0002]    This application is also related to U.S. Ser. No. 13/665,248 filed on Oct. 31, 2012, entitled “Method to Control Current in a Fuel Cell System”, which claims priority to U.S. Provisional Application No. 61/553,656 filed on Oct. 31, 2011, the entire disclosures of which are incorporated herein by reference 
     
    
     TECHNICAL FIELD 
       [0003]    This invention relates generally to fuel cells and fuel cell systems, more particularly to methods for communication between a fuel cell system and a vehicle such as an industrial electric vehicle. 
       BACKGROUND OF THE INVENTION 
       [0004]    Fuel cells electrochemically convert fuels and oxidants to electricity and heat and can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid or solid polymer) used to accommodate ion transfer during operation. Moreover, fuel cell assemblies can be employed in many (e.g., automotive, aerospace, industrial, residential) environments, for multiple applications. 
         [0005]    A Proton Exchange Membrane (hereinafter “PEM) fuel cell converts the chemical energy of fuels such as hydrogen and oxidants such as air directly into electrical energy. The PEM is a sold polymer electrolyte that permits the passage of protons (i.e., H+ ions) from the “anode” side of the fuel cell to the “cathode” side of the fuel cell while preventing passage there through of reactant fluids (e.g., hydrogen and air gases). The membrane electrode assembly is placed between two electrically conductive plates, each of which has a flow passage to direct the fuel to the anode side and oxidant to the cathode side of the PEM. 
         [0006]    Two or more fuel cells can be connected together to increase the overall power output of the assembly. Generally, the cells are connected in series, wherein one side of a plate serves as an anode plate for one cell and the other side of the plate is the cathode plate for the adjacent cell. Such a series of connected multiple fuel cells is referred to as a fuel cell stack. The stack typically includes means for directing the fuel and the oxidant to the anode and cathode flow field channels, respectively. The stack also usually includes a means for directing a coolant fluid to interior channels within the stack to absorb heat generated by the exothermic reaction of hydrogen and oxygen within the fuel cells. The stack also generally includes means for exhausting the excess fuel and oxidant gases, as well as product water. 
         [0007]    In some fuel cell systems, the fuel cell is coupled in parallel with an energy storage device (e.g., battery, capacitor, etc.) which is then coupled to a load. Commonly referred to as a hybrid system, peak power from the system is supplied by the energy storage device while the fuel cell provides the average power needs of the application. In most hybrid systems a voltage converter is used to convert the fuel cell stack voltage to the energy storage device voltage. In these types of systems, the fuel cell can operate independently from the energy storage device. 
         [0008]    Another type of hybrid system eliminates the need for the voltage converter and couples the fuel cell stack directly to the energy storage device. In this system the fuel cell stack voltage, energy storage device voltage and load voltage are equal. The current output of the fuel cell is therefore dictated by the polarization curve of the fuel cell being used. Therefore, the voltage of the system controls the current output of the fuel cell. 
         [0009]    In addition to the energy storage device, many fuel cell systems include a balance of plant that supplies the necessary reactant and cooling fluids for a fuel cell or fuel cell stack. The balance of plant may include devices such as pumps, air compressors, blowers, fans, valves, and sensors. These devices function cohesively to provide power to a load, such as a stationary device or an industrial electric vehicle (e.g., a forklift truck). 
         [0010]    An electronic system controller conditions the signals from the sensors and commands the actuators in order to operate the fuel cell system. The software in the system controller is typically designed to optimize one or more aspects of the fuel cell system, such as output power, efficiency, safety, fuel cell life, battery life, etc. In the case of a load such as an industrial electric vehicle, these optimizations can be achieved more easily if the fuel cell system has some knowledge of, or control over, the load. 
         [0011]    Thus, there is a need for a means to allow the fuel cell system to communicate with a load, such as an industrial electric vehicle, in order to optimize the operation of the combined fuel cell and vehicle system. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a method to allow the communication of information between a fuel cell system and an industrial electric vehicle in order to optimize system performance and safety. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will be readily understood from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  is a block diagram of a fuel cell system and vehicle in accordance with the invention 
           [0015]      FIG. 2  is an example of system optimization using a communication protocol 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    An example of a fuel cell system which incorporates the novel features of the present invention is depicted in  FIG. 1-2  and described in detail herein. 
         [0017]    In the embodiment depicted in  FIG. 1 , a fuel cell system  10  is referred to as the assembled, or complete, system that, together with all parts thereof, produces electricity and typically includes a fuel cell  20  and an energy storage device  30 . The fuel cell is supplied with fuel, for example, hydrogen, through a fuel inlet  46 . Excess fuel is exhausted from the fuel cell through a fuel exhaust  48 . Oxidant, for example, air, is supplied through an oxidant inlet  40  and excess oxidant is exhausted from an oxidant exhaust  42 . The fuel cell reactants and a cooling fluid  44  are supplied by a fuel supply  60  and other components of balance of plant  50 , which may include compressors, pumps, valves, fans and sensors. A controller  90  uses feedback from sensors in balance of plant  50  and fuel supply  60  to control actuators in balance of plant  50  and fuel supply  60 . 
         [0018]    Referring to  FIG. 1 , an electrical demand or load  100 , for example an industrial electric vehicle (e.g., an electrically powered forklift truck), is connected to energy storage device  30  and fuel cell  20  in parallel by electrical connection  80 . Depending on the demand, power may flow from energy storage device  30 , fuel cell  20  or both to the load. In times of high demand in excess of the maximum power output of the fuel cell  20 , power will flow from both the fuel cell  20  and energy storage device  30 . In times of low demand, power can flow to load  100  from fuel cell  20 , while excess power from fuel cell  20  can flow into energy storage device  30  to recharge it when required. In the case of loads that can source power, such as regenerative braking, power may flow from load  100  to energy storage device  30 . 
         [0019]    System controller  90  communicates with the load  100  through a communication connection  110 . The connection may be a hard wire, wireless connection (e.g., via a Wi-Fi, Bluetooth or cellular connection, or both. The signals in the connection may be digital or analog. A communication protocol such as RS-232, RS-485, Controller Area Network (CAN) or wireless protocol may be used to transfer information bi-directionally. 
         [0020]    Communication connection  110  allows fuel cell system  10  and load  100  to identify each other and communicate operating limits before and during operation. These limits may include, but are not limited to, operating voltage limits, maximum power draw, maximum allowable regenerative current (i.e., current flowing from load  100  to energy storage device  30 ), range (i.e., run time using fuel in fuel supply  60  based on fuel level as read by fuel sensor  70 ), and any active faults that may affect operation. 
         [0021]    Communication connection  110  may also be used to transmit a status of fuel cell system  10  to load  100  and/or controller  90 . The status may include, but is not limited to, an operating state (e.g., startup, running, fueling), fuel level remaining, energy remaining, maximum allowable power draw, output voltage, active faults, balance of plant sensor readings (e.g., coolant temperature, oxidant flow rate), and current configuration (e.g., software versions, installed options). This information may be displayed on a user interface (e.g., dashboard of an industrial electric vehicle) of the load or downloaded through the load&#39;s service port. The feedback on the load&#39;s user interface may be visible (e.g., warning light), audible (e.g., buzzer) or tactile (e.g., vibration of control surfaces). 
         [0022]    Conversely, the load may use connection  110  to transmit its status to the fuel cell system. The status may include, but is not limited to, operating state (e.g., startup, running, emergency stop), active faults codes, current configuration (e.g., software versions, installed options), and state of user inputs (e.g., gas pedal depressed, key switch in start position, emergency stop button depressed). Using this information, fuel cell system  10  may react in the appropriate way, for example starting up when the key switch is moved to the start position or shutting down when the emergency stop button is depressed. 
         [0023]    Communication connection  110  may be used to improve the safety of system  10 . For example, during fueling of the fuel cell system  10 , the system may communicate its state (i.e., fueling) to load  100 , e.g., an industrial electric vehicle, and/or controller  90 . The vehicle may then place itself in a safe state for fueling or controller  90  may send a message to the vehicle to cause the vehicle to be placed in such a safe state. This state may prevent the operator from moving the vehicle while the system is fueling. The safe state may also cause the vehicle electrical system to be de-energized to eliminate ignition sources during the transfer of fuel to the fuel cell system. In one example, fuel cell system  10  may be coupled to controller  90  such that controller  90  receives an indication that fueling is occurring and thus may control the vehicle (e.g., preventing motion or ignition sources) during the fueling of fuel cell system  10 . 
         [0024]    The information transmitted through communication connection  110  may also be used to adjust the operating envelope of the combined fuel cell and load system in situ (i.e., fuel cell system  10  and load  100 ). For example, fuel cell system  10  may be coupled to an industrial electric vehicle represented by load  100  where the vehicle has the ability to reduce its power draw by entering a “limp” mode in which a top speed of the vehicle is reduced. Furthermore, the vehicle may have regenerative braking and the ability to turn off its regenerative braking on command. Also, commands may be sent from the fuel cell system  10  to load  100  (e.g., the industrial electric vehicle). 
         [0025]    In an example depicted in  FIG. 2 , fuel cell system  10  determines an amount of energy remaining (energy storage level) in energy storage device  30 . If the level is not greater than a predetermined maintenance level (e.g., 50%), the fuel cell system proceeds to step  202 . If the energy storage level is not greater than a predetermined cut-off level (25%), the system enters step  204  and the fuel cell system (e.g., controller  90 ) sends an “Enable Limp Mode” command to load  100  (e.g., an industrial electrical vehicle) using communication connection  110 . The load receives this command and limits its top speed to 50% of the maximum value, or another reduced speed to conserve energy. This reduces the load on fuel cell system  10 , allowing energy storage device  30  to recharge. The process returns to step  200  and continues to return to step  204  until the energy storage level in energy storage device  30  is greater than the cut-off level (e.g., 25%). The system then cycles between steps  200  and  202  until the energy storage level exits the 25%-50% range (i.e., the range including the cut-off level and the predetermined maintenance level). This provides hysteresis for the “limp” mode commands. 
         [0026]    If the energy storage level in energy storage device  30  exceeds the maintenance level (e.g., 50%), fuel cell system  10  proceeds to step  206  and sends the “Disable Limp Mode” command to load  100 , such as an industrial electric vehicle. The load then changes its top speed limit to the maximum value. Fuel cell system  10  continues to step  208 . If the energy storage level in energy storage device  30  is not less than a desired maintenance level (e.g., 90%), the fuel cell system proceeds to step  210 . If the energy storage level is not less than a maximum level (e.g., 95%), the fuel cell system sends the “Disable Regenerative Braking” command. In response, the load or vehicle disables regenerative braking to avoid overcharging energy storage device  30 . When the energy storage level is not less than the desired maximum (e.g., 95%), the fuel cell system returns to step  208  through steps  200  and  206 . If the energy storage level is less than the desired maintenance level (e.g., 90%), the fuel cell system proceeds to step  212  and sends the “Enable Regenerative Braking” command. If the energy storage level is between 90% &amp; 95%, the system cycles between steps  200  and  210  (passing through steps  206  &amp;  208 ). This provides hysteresis for the regenerative braking command. If the energy storage level is less than 90%, the fuel cell system sends the “Enable Regenerative Braking” command. In response, the load or vehicle enables regenerative braking. Fuel cell system  10  then returns to step  200 . 
         [0027]    Various aspects of the fuel cell system described above (e.g., fuel cell system  10 ), such as a fuel cell stack, energy storage device, electrical demand, and a controller, may include various sensors utilized to determine various parameters relative to the aspects of the fuel cell system which may be coupled to a controller (e.g., controller  90 ) and/or the other aspects (e.g., fuel cell stack  20 , energy storage device  30 , and load  100 ) of the fuel cell system to allow control of the fuel cell system by the controller. 
         [0028]    The controller (i.e., controller  90 ) described above, could be any type of computing unit (e.g., a personal computer operating a WINDOWS operating system or Apple OSX operating system, a Unix system, a microprocessor (which may or may not utilize a BIOS or operating system) or a mobile computing device such as a tablet computer or smart phone) configured to communicate with a fuel cell (fuel cell  20 ), an energy storage device (energy storage device  30 ), a balance of a plant (e.g., balance of plant  50 ), fuel supply (e.g., fuel supply  60 ), and/or a load (e.g., load  100 ). Further, the controller (e.g., controller  90 ) could be a unit separate from the fuel cell stack, energy storage device, and load device. Further, such a controller could be part of one or more of these components (e.g., a fuel cell, load device, and energy storage device) or could be distributed between these devices and other connected systems, such as balance of plant  50  while the distributed portions of such controller could be coupled to each other to allow communication therebetween. 
         [0029]    The load (e.g., load  100 ) described above could be any type of stationary or moveable load device, such as an industrial electrical vehicle or forklift truck. The fuel cell (e.g., fuel cell stack  20 ) could be any type of fuel cell such as a proton exchange membrane fuel cell, solid oxide fuel cell, or any other fuel cell as would be known by one of ordinary skill in the art. The energy storage device (e.g., energy storage device  30 ) described above could be any type of battery or other way of storing energy such as a lithium ion battery, lead acid battery, air compression energy storage device, water storage device, capacitor, ultra-capacitor, or any other device for storing energy. 
         [0030]    Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.