This disclosure generally relates to fuel cell power plants and more particularly to controlling an operating condition of a fuel cell power plant.
Fuel cell power plants are well known. Cell stack assemblies and other known components operate in a known manner to provide electrical power. The applications for fuel cell power plants vary. Depending on the installation, different features and functions are required of different fuel cell power plants.
It has been proposed to include a voltage limiting device in a fuel cell power plant assembly for managing an operating condition of the assembly. One approach includes using different devices for different operating condition controls. For example, one voltage limiting device may be used during a start up operation while a different voltage limiting device may be used during a shutdown operation. While that approach has proven useful, there are limitations.
For example, adding additional devices to a fuel cell power plant introduces additional cost. It is therefore not possible to add such devices in an unlimited manner. Additionally, such voltage limiting devices tend to be designed for one particular type of fuel cell power plant and for only one operating condition. Further, such voltage limiting devices do not address the needs of all conditions within an operating scenario for which the device is intended. For example, a fixed voltage limiting device during a start up operation does not provide the ability to avoid non-recoverable decay as some of the cells go negative.
U.S. Pat. No. 6,887,599 shows one approach to adding an auxiliary load to control voltage levels during start up and shut down procedures. U.S. Pat. No. 7,041,405 shows an approach for cyclically switching an auxiliary load into and out of a fuel cell stack external circuit.
Even with such improvements, there is a desire in the industry to be able to provide more customized control over various operating conditions in a fuel cell power plant.
An exemplary method of controlling operation of a fuel cell power plant using a variable resistive device includes selectively varying an electrical resistance of the variable resistive device responsive to an operating condition of the fuel cell power plant.
In one example, the electrical resistance is selectively varied responsive to a condition of a cell stack assembly within the fuel cell power plant.
For different operating conditions, a single variable resistive device can be controlled to introduce a different resistance depending on the operating condition. Using such a device and a control strategy consistent with the examples disclosed in this description provides the ability to customize the control of various operating conditions of a fuel cell power plant while minimizing additional cost because there is no need for multiple devices to achieve the multiple functions.
An exemplary fuel cell power plant includes a cell stack assembly. At least one other component is operationally associated with the cell stack assembly. A variable resistive device is operationally associated with at least one of the cell stack assembly or the other component. A controller selectively controls an electrical resistance of the variable resistive device responsive to an operating condition of the fuel cell power plant.
Various features and advantages will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
The disclosed examples relate to customized control of various operating conditions or functions in a fuel cell power plant. In a disclosed example, a single variable resistive device is used to provide a variety of control functions. By selecting the resistance based upon the operating condition, the disclosed examples allow for realizing a variety of control functions for various fuel cell power plant operating conditions in an economical manner.
The example of
In the illustrated example, the controller 32 has the ability to control the electrical resistance of the variable resistive device in a plurality of different manners. As schematically shown at 46, the electrical resistance may be selected and maintained at a steady value throughout the current operating condition. Alternatively, as schematically shown at 48, the controller 32 dynamically varies the electrical resistance within a particular operating condition. In such an example, not only does the controller vary the resistance to different electrical resistance values for different operating conditions, but also has the ability to vary the electrical resistance value within a particular operating condition.
For example, during a start-up condition the electrical resistance of the variable resistive device 30 in one example is dynamically varied to maintain a constant, low voltage during start-up fuel introduction. In one example this is accomplished by monitoring the voltage on all the cells of the CSA 22 and responsively varying the electrical resistance of the variable resistive device 30 to ensure that the voltage on all of the cells remains positive. This approach facilitates reducing any non-recoverable decay that is otherwise associated with a start-up operating condition.
The ability to dynamically vary the resistance during an operating condition may be based upon dynamically determining characteristics of the cell stack assembly 22, for example. One example includes a sensor arrangement to provide the appropriate information to the controller 32. In one example, empirical testing is done to determine particular voltage profiles and associated decay characteristics. The controller 32 is provided with a database or information such as a look up table that includes corresponding resistance values that should be selected by the controller 32 during appropriate portions of a start-up operation to achieve a desired decay characteristic, for example.
The example of
Another feature available from the illustrated example is to provide a thawing function, which may be needed for some freeze capable fuel cell power plant installations, for example. At 52, the controller 32 determines whether thawing is needed. By having the selectively variable resistive device 30 appropriately situated within the power plant 20, it is possible to use that device as a heater, for example, for providing a thawing function. When thawing is needed, the controller 32 selects an appropriate resistance at 44.
Another function available from the illustrated example is a freeze protection function. The controller 32 makes a determination at 54 whether freeze protection is desired during operation or subsequent to operation of a fuel cell power plant before freezing may have occurred. When freeze protection is desired, an appropriate resistance for the variable resistive device 30 is selected and utilized.
A voltage trim function is available at 56. There are various operating conditions where trimming a voltage of one or more cells in the CSA 22, for example, may be desired. The controller 32 in one example is programmed to determine when such a condition exists and to control the variable resistive device 30 in a corresponding manner to achieve the desired effect.
At 58, the controller 32 is able to determine whether a power plant turn down operating condition exists or is desired. If so, the controller 32 makes an appropriate resistance selection at 44 to control the variable resistive device 30 to achieve the desired effect.
A voltage limiting device can be useful during a shutdown procedure of a fuel cell power plant. The example of
Another function available in the example of
It may be possible for each of the resistance determinations in the example of
As can be appreciated, a single variable resistive device 30 and an appropriate control strategy allows for providing a variety of functions to achieve various desired characteristics of different operating conditions for a fuel cell power plant. The illustrated example, therefore, provides the advantage of minimizing expense by minimizing the number of components required to provide a variety of advantageous control functions within a fuel cell power plant assembly.
In one example, the variable resistive device 30 is operationally associated directly with the CSA 22 as schematically shown in
In one example, the controller 32 uses a control signal to selectively vary the electrical resistance of the variable resistive device. In an illustrated example as schematically shown in
In an example where the controller can dynamically change the electrical resistance even during a particular operating condition or responsive to a particular characteristic or condition of the CSA 22, a control strategy as schematically shown in
In one example, the variable resistive device 30 comprises a resistor and a plurality of switches such as MOSFETs that are arranged to respond to a control signal from the controller 32 such that operating the different switches based upon the selected pulse width modulation achieves the desired resistance provided by the variable resistive device 30. Given this description, those skilled in the art will be able to select an appropriate variable resistive device and an appropriate control arrangement to meet their particular needs.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art. The scope of legal protection can only be determined by studying the following claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US06/61271 | 11/28/2006 | WO | 00 | 3/31/2009 |