Abstract:
A method and system for calibrating a fuel cell test station. The fuel cell test station has an interface for connection to at least one of a fuel cell, a fuel cell stack and a fuel processor to measure a plurality of physical characteristics associated therewith to obtain a plurality of station measurements. The method and system involve: (a) concurrently measuring the plurality of physical characteristics to obtain a plurality of measurements; (b) storing the plurality of measurements; and, (c) comparing the plurality of measurements with the plurality of station measurements to obtain an aggregate calibration of the fuel cell test station.

Description:
FIELD OF THE INVENTION  
         [0001]    This application relates to a portable apparatus for verifying the accuracy and consistency of test data produced by fuel cell test stations and for simulating some of the physical characteristics of a fuel cell. The apparatus can be used to calibrate each test station to a pre-defined test standard, and to experiment with new test setups without fear of damaging an expensive fuel cell.  
         BACKGROUND OF THE INVENTION  
         [0002]    Test stations are used by developers and manufacturers of fuel cell systems to test new designs and materials and to monitor product life cycles. Such test stations include numerous subsystems, such as gas mixing modules, humidification units, water management systems, load banks, measuring devices and system controllers. Test stations control the physical characteristics of the reactants and cooling fluid entering a fuel cell, to simulate the various conditions that a fuel cell would encounter during real world operation. Typically, all fuel cells require three material inputs to operate: a fuel, an oxidant and a cooling fluid. The fuel (typically hydrogen) and oxidant (typically air) are delivered to the fuel cell in the form of heated, and humidified gas. The gas temperature, pressure, flow rate and humidity are all controlled from the test station. The coolant (typically de-ionized water) is delivered to the fuel cell for thermal control. Controllable properties of the coolant include temperature, pressure, flow rate, and conductivity.  
           [0003]    With the delivery of the following inputs, a fuel cell produces an electric potential across its terminals, from which current can be drawn. The test stations apply varying electrical loads, and measure the subsequent fuel cell voltage. Test stations may also include integrated data acquisition and reporting hardware and software for analyzing test results.  
           [0004]    The data generated by test stations is relied upon by product development engineers to test assumptions and hypotheses, and to assist in making product design decisions. Accordingly, if the data generated by a test station is faulty, this may result in flawed design or production decisions having potentially serious and expensive consequences. It is therefore imperative that test station data be as accurate and reliable as possible.  
           [0005]    Many fuel cell developers and manufacturers employ multiple fuel cell test stations located at different locations on site. Often such test stations are manufactured by different suppliers and comprise different combinations of testing equipment. However, despite their design differences, fuel cell test stations generally control and measure many of the same properties. Problems can arise if a product designer suspects that some of the test stations are not producing accurate and consistent results (and hence the data generated by different stations is not readily comparable). Prior to the present invention there was no way to verify that the instrumentation of each test station was calibrated to the same standard and hence it was difficult to compare and characterize fuel cell stacks tested at different stations. Previously, data output verification could only be performed on one type of device measuring one physical characteristic on one station. For example, if an operator suspected that a flow meter was faulty, it would be necessary to physically remove the flow meter from the test station and conduct bench tests to verify its accuracy. Alternatively, diverter valves would be required to isolate the instrument from the rest of the test station. In either case instrument verification and re-calibration was a painstaking and time consuming exercise.  
           [0006]    The present invention has been developed to provide an integrated testing apparatus for quickly verifying the accuracy of data outputted by fuel cell test stations. Additionally, the invention can be used to simulate the behavior of an actual fuel cell allowing for the development of fuel cell tests. This avoids risking a valuable fuel cell during test development. The apparatus is portable so that it may be conveniently transported between the different test station locations.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with aspects of the invention, a fuel cell test station verification, calibration and simulation apparatus is provided. The apparatus includes a plurality of inlets for connecting to the fuel cell stack or fuel processor interface of a test station. For example, the apparatus is connectable to the fuel supply, oxidant supply, nitrogen supply and coolant supply of the test station. The apparatus also includes a plurality of outlets, which are connectable to corresponding test station inlets, such as fuel, oxidant and coolant inputs. The apparatus comprises high quality, traceable instrumentation and a data acquisition and recording system. Depending upon the test results, data correction factors may be calculated for adjusting previously recorded test station data. The invention may also comprise a computer model of a simulated fuel cell and a means for changing the model&#39;s parameters.  
           [0008]    An object of a first aspect of the present invention is to provide an improved fuel cell testing station verification, calibration and simulation system.  
           [0009]    In accordance with this first aspect of the present invention there is provided a system for calibrating a fuel cell test station. The fuel cell test station has an interface for connection to at least one of a fuel cell, a fuel cell stack and a fuel processor to measure a plurality of physical characteristics associated therewith to obtain a plurality of station measurements. The system comprises: (a) a plurality of inlets for connecting to a plurality of interface outlets of the interface to receive a plurality of inflows therefrom; (b) a plurality of outlets for connecting to a plurality of interface inlets of the interface for discharging a plurality of outflows thereto; (c) a plurality of sensors associated with the plurality of inlets and plurality of outlets for measuring the plurality of physical characteristics of the plurality of inflows and the plurality of outflows to obtain a plurality of measurements for comparison with the plurality of station measurements; and, (d) a data processor for receiving and storing the plurality of measurements from the plurality of sensors and for comparing the plurality of measurements with the plurality of station measurements, the data processor being connected to the plurality of sensors by data transfer means  
           [0010]    An object of a second aspect of the present invention is to provide an improved fuel cell testing station verification, calibration and simulation system.  
           [0011]    In accordance with this second aspect of the present invention there is provided a method of calibrating a fuel cell test station. The fuel cell test station has an interface for connection to at least one of a fuel cell, a fuel cell stack and a fuel processor to measure a plurality of physical characteristics associated therewith to obtain a plurality of station measurements. The method comprises: (a) concurrently measuring the plurality of physical characteristics to obtain a plurality of measurements; (b) storing the plurality of measurements; and, (c) comparing the plurality of measurements with the plurality of station measurements to obtain an aggregate calibration of the fuel cell test station. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    In drawings which illustrates an embodiment of the invention but which should not be construed as restricting the spirit or scope of the invention in any way,  
         [0013]    [0013]FIG. 1 is a piping and instrumentation diagram for a test station verification, calibration and simulation device according to one embodiment of the invention;  
         [0014]    [0014]FIG. 2 is a schematic view showing a possible arrangement for the device of FIG. 1 (i.e. a Verification Test Cart (VTC)) adapted to interface with a fuel cell test station (i.e. Test Station (T/S));  
         [0015]    [0015]FIG. 3 is a schematic diagram of a test station providing a context for implementing different aspects of the invention;  
         [0016]    [0016]FIG. 4 is a schematic diagram of a fuel line of a test station verification, calibration and simulation device according to a second aspect of the invention;  
         [0017]    [0017]FIG. 5 is a schematic diagram of an oxidant line of the test station verification, calibration and simulation device of FIG. 4; and  
         [0018]    [0018]FIG. 6 is a schematic diagram of a coolant line of the test station verification, calibration and simulation device of FIG. 4 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    As shown schematically in FIG. 1, this application relates to a test station verification, calibration and simulation apparatus  10 . Apparatus  10  is connectable to the fuel cell stack interface of a test station  40  (FIG. 3). In particular, apparatus  10  comprises a plurality of inlets  12  for receiving fuel, oxidant, nitrogen and coolant supplies from the test station  40  and a plurality of outlets  13  for delivering precisely measured amounts of physical characteristics to the test station  40 , such as fuel, oxidant, coolant and current inputs.  
         [0020]    The apparatus  10  includes a plurality of high quality, traceable instrumentation for simultaneously or sequentially controlling, measuring and recording different physical characteristics. For example, as shown in FIG. 1, apparatus  10  may comprise manual or solenoid valves  14 , thermocouples  16 , pressure transducers  18 , dew point meters  20 , flow meters  22 , and resistivity meters  24 . Other physical parameter measuring devices may be provided, such as gas sample ports  25  and analyzers  26  (e.g. gas chromatographs). The various power inputs and outputs of a fuel cell are measured and controlled from the apparatus, as shown schematically in FIG. 2. As the reactant gases are provided to a fuel cell, a voltage is produced across the plates of each cell. This apparatus could provide a variable controlled DC power supply, connected to a resistor ladder to simulate the individual cell voltages of a fuel cell stack. An accurate current measuring device such as a shunt could be placed in the apparatus to test the current drawing calibration of the test station load box.  
         [0021]    Power supplies for delivering precisely measured current or voltages to the test station may also be employed to simulate fuel cell stack voltages. On board heater hose  28  or other heaters are provided to heat gases or other reactants.  
         [0022]    Preferably apparatus  10  includes computer hardware and software (FIG. 2) for recording a historical log of test data for each station including computer algorithms for calculating corrective factors if the test station data output is inaccurate. That is, the manual or solenoid valves  14 , thermocouples  16 , pressure transducers  18 , dew point meters  20 , flow meters  22 , and resistivity meters  24  are all connected to the computer system of FIG. 2, such that at any time the readings received provide an overall “snap shot” of the state of the test station. The historical data can also be used to track degradation of test instrumentation and controls over time so that test instruments can be replaced or recalibrated when readings deviate from predetermined standards beyond an acceptable range. Computer algorithms may also be provided for diagnosing problems with the test station based on a pattern of errors received. If the accuracy quotient falls outside a tolerable range the test station could be replaced or removed from service for replacement of faulty instrumentation or controls.  
         [0023]    Referring to FIG. 2, there is illustrated in a block diagram a computer system  78  linked to the apparatus  10  by I/O system  88  The computer system  78  includes a verification test cart (VTC) data acquisition control and analysis PC  86  having a PC monitor  87 . The PC operates software, which controls the state of the apparatus  10  such that verification or fuel cell simulation can take place. During verification and calibration of the apparatus  10 , the PC  86  logs pertinent data points and automatically calculates corrective calibration values required for a particular test station. This calibration data can then be stored for historical purposes, used in comparison with an established calibration baseline, or compared to similar data taken from other test stations. In fuel cell simulation mode, the PC controls the various apparatus outputs to physically simulate the response conditions of a programmed fuel cell computer model (a virtual fuel cell). Various models simulating different types of fuel cells can be stored and retrieved to run the test station through a number of different scenarios.  
         [0024]    As described above, all sensors and control information in the apparatus  10  are connected to the PC monitor via VTC instrumentation and control I/O system, which relays data to the PC  86 . Specifically, all of the instruments for controlling controllable physical characteristics of the flow, such as heaters, flow rate controllers, humidifiers and pressure controllers are connected to the I/O  88  to receive control inputs from the PC  86 .  
         [0025]    Most fuel cell stations contain a load bank, shown as T/S load bank  80  in FIG. 2. Typically, load banks are used to simulate an electrical load, such as an electric motor or the power supplied to a home. In effect, a load bank is a large variable resistor. Similarly, most fuel cell test stations include a cell voltage monitor (CVM) such as T/S CVM  82  as shown in FIG. 2. Such cell voltage monitors typically measure the voltage outputted from each cell of a fuel cell stack being tested. These elements of the test station are linked to elements of the computer system. Specifically, a DC current supply  83   a  provides a controllable DC current to verify the accuracy of the T/S load bank  80  or to calibrate the T/S load bank  80 . In addition, the DC current supply  83   a  may also be controlled via I/O  88  from PC  86  to simulate an electrical current produced from a fuel cell.  
         [0026]    Similarly, the DC voltage supply and resistor ladder  83   b  provides a controllable DC voltage supply that can be used to simulate the electric potential created by a fuel cell. This voltage can be passed through a resistor ladder to simulate the voltages of the individual cells in a fuel cell stack. As all fuel cell test stations measure cell voltages using a CVM, a controllable DC supply can be used to calibrate the test station CVM  82 . Furthermore, the voltage supplied by the DC voltage supply  83   b  can be controlled and varied as part of a fuel cell stack simulation.  
         [0027]    The computer system also includes a shunt  84 . The shunt  84  is highly calibrated resistor, which can accurately measure current when placed in series with a current source. In the setup of FIG. 2, the T/S load bank  80  can use the shunt  84  to verify the accuracy and calibrate its load drawing capabilities.  
         [0028]    In general, apparatus  10  employs very precise instrumentation to accurately measure the same physical characteristics as are commonly outputted from a test station. The test data can then be compared for calibration purposes, verification of control, and comparison to the calibration of another test station. Apparatus  10  makes it possible to easily calibrate each test station to a pre-defined test standard to ensure reliable and consistent test results. Apparatus  10  is preferably mounted on a mobile cart having caster wheels so that it may be easily transported between test sites.  
         [0029]    Referring to FIG. 3, there is illustrated in a schematic diagram a test station  40  providing a suitable context in which to implement the present invention. As shown in FIG. 3, a fuel cell  42  may be linked to the test station for testing. Alternatively, the apparatus  10  may be linked to the test station  40  to test or calibrate the test station  40 , or, alternatively, to simulate a fuel cell in a test run of the test station  40 .  
         [0030]    As shown in FIG. 3, the test station  40  comprises a fuel supply  44  for supplying fuel (hydrogen) to a fuel line  43 . Fuel line  43  includes a fuel flow control valve  45  for controlling the flow of fuel, a humidifier  46  for providing a desired level of humidification to the fuel and a heater  48  for heating the fuel to a desired temperature. The fuel is then supplied to the fuel cell (or, alternatively, to a fuel inlet in the plurality of inlets of the apparatus  10 ) at a test station fuel outlet  49   a . Fuel discharged from the fuel cell  42  (or, alternatively, discharged from the fuel outlet of the apparatus  10 ) is received in a fuel outlet line  51  at a test station fuel inlet  49   b . The pressure of this fuel is measured by a fuel pressure sensor  50 , before the fuel is discharged at fuel exhaust  52 .  
         [0031]    Similarly, oxidant is supplied to oxidant input line  53  by oxidant supply  54 . The rate of flow of the oxidant (air) is controlled by oxidant flow controller  55 . The humidity and temperature of the oxidant are controlled by oxidant humidifier  56  and oxidant heater  58  respectively before the oxidant input line  53  supplies the oxidant to the fuel cell at a test station oxidant outlet  59   a . The fuel cell discharges the oxidant into oxidant outlet line  61  at a test station oxidant inlet  59   b . The pressure of the oxidant is measured by pressure sensors  60  before the oxidant is discharged at oxidant exhaust  62 . Similarly, coolant (water) is supplied to the coolant input line  63  by coolant supply  64 . The temperature and rate of flow of the coolant are then controlled by heater  66  and coolant flow controller  65  respectively before the coolant is provided to the fuel cell  42  at a test station coolant outlet  69   a . The coolant discharged from the fuel cell  42  is received by the coolant outlet line  71  at a test station coolant inlet  69   b . A portion of the coolant in the coolant output line  71  is redirected to a coolant reservoir  70  which reconnects to the coolant inlet line  63  upstream from the heater  66  and coolant flow controller  65  The remainder of the coolant is discharged at the coolant drain  72 .  
         [0032]    According to another aspect of the invention, the behavior of an actual fuel cell can be simulated allowing for the development of fuel cell tests. This avoids risking a valuable fuel cell during test development. To this end, the invention may comprise a computer model of a simulated fuel cell as well as means for changing the model&#39;s parameter.  
         [0033]    Referring to FIGS. 4, 5 and  6  there are illustrated in schematic diagrams a fuel supply line, an oxidant supply line and a coolant supply line respectively of a an apparatus in accordance with a further aspect of the invention. The fuel supply line receives fuel (hydrogen) from a fuel inlet  100 . The fuel passes through an isolation valve  102 , which, if desired, can be closed to shut off fuel flow, while permitting flow of oxidant and coolant. The pressure, temperature and humidity of the fuel are measured by pressure sensor  104 , temperature sensor  106 , and humidity sensor  108  respectively. The rate of flow of fuel is controlled by first flow control valve  110 , and this rate of flow is then measured by flow meter  112 . The first flow control valve  110  can be used to simulate varying pressure drops associated with different fuel cell architectures. This enables users of the test station to tune pressure control loops under different conditions without fear of damaging the fuel cell.  
         [0034]    A bleed line  113  can be used to draw some of the fuel off from the fuel line. This is controlled by a second flow control valve  114 , and is used to simulate the normal consumption of fuel by the chemical reaction within the fuel cell. Combined with the first control valve  110 , this provides the feedback required to tune the pressure control loop of a test station. The bleed line  113  can also be connected to a gas chromatograph and used to verify the composition of the fuel.  
         [0035]    A heater  116  is provided in the fuel line downstream from the branch where the bleed line  113  bleeds off fuel. This heater can be used to simulate the additional heat added to the system by the exothermal chemical reactions taking place within a fuel cell. Furthermore, the heater  116  can be used to prevent condensation from forming within the apparatus lines. Downstream from heater  116 , the fuel is discharged to the test station at a fuel outlet  118 .  
         [0036]    Referring to FIG. 5, the oxidant supply line is illustrated. The oxidant supply line receives oxidant (air) from an oxidant inlet  120 . The oxidant passes through an isolation valve  122 , which, if desired, can be closed to shut off oxidant flow, while permitting flow of fuel and coolant. The pressure, temperature and humidity of the oxidant are measured by pressure sensor  124 , temperature sensor  126 , and humidity sensor  128  respectively. The rate of flow of oxidant is controlled by first flow control valve  130 , and this rate of flow is then measured by flow meter  132 . The first flow control valve  130  can be used to simulate varying pressure drops associated with different fuel cell architectures. This enables users of the test station to tune pressure control loops under different conditions without fear of damaging the fuel cell.  
         [0037]    A bleed line  133  can be used to draw some of the oxidant off from the oxidant line. This is controlled by a second flow control valve  134 , and is used to simulate the normal consumption of oxidant by the chemical reaction within the fuel cell. Combined with the first control valve  130 , this provides the feedback required to tune the pressure control loop of a test station. The bleed line  133  can also be connected to a gas chromatograph and used to verify the composition of the oxidant.  
         [0038]    A heater  136  is provided in the oxidant line downstream from the branch where the bleed line  113  bleeds off oxidant. This heater  136  can be used to simulate the additional heat added to the system by the exothermal chemical reactions taking place within a fuel cell. Furthermore, the heater  136  can be used to prevent condensation from forming within the apparatus lines. Downstream from heater  136 , the oxidant is discharged to the test station at an oxidant outlet  138 .  
         [0039]    Referring to FIG. 6, the coolant supply line is illustrated. The coolant supply line receives coolant (water) from a coolant inlet  140 . The coolant passes through an isolation valve  142 , which, if desired, can be closed to shut off coolant flow, while permitting flow of fuel and oxidant. The pressure, temperature and conductivity of the coolant are measured by pressure sensor  146 , temperature sensor  148 , and conductivity sensor  144  respectively. The rate of flow of coolant is controlled by first flow control valve  150 , and this rate of flow is then measured by flow meter  152 . The first flow control valve  150  can be used to simulate varying pressure drops associated with different fuel cell architectures. This enables users of the test station to tune pressure control loops under different conditions without fear of damaging the fuel cell. A heater  154  is provided in the coolant line downstream from flow meter  152 . This heater  154  can be used to simulate the additional heat added to the system by the exothermal chemical reactions taking place within a fuel cell. Downstream from heater  154 , the coolant is discharged to the test station at a coolant outlet  156 .  
         [0040]    Other variations and modifications of the invention are possible. For example, to reduce the number of components required, thereby reducing the cost and weight of the apparatus, different lines may be combined into one line. That is, the line for the oxidant and fuel might be combined into one line, such that only one set of sensors and control devices is required for both the oxidant and fuel. Isolation valves upstream of this common line would be provided for both the fuel feeder line and the oxidant feeder line to shut off the flow of fuel, say, when the testing station was being calibrated relative to the physical characteristics of the oxidant. All such modifications or variations are believed to be within the sphere and scope of the invention as defined by the claims appended hereto.