The present invention relates to a device to measure individual or grouped cell voltages to monitor fuel cell performance for diagnostic or control purposes. More particularly, the present invention involves a device to make attachments to individual cells or groups of cells of a fuel cell stack which measures the voltage of these individual cells or groups of cells and uses these measurements, the change in these measurements, or the time response of these measurements to report on the performance of the fuel cell stack and to control fuel cell system parameters or isolate poorly performing cell groups based on this performance data. The present invention also provides a method to measure a plurality of voltages at a plurality of points around the perimeter of cells or cell groups to realize a non-invasion measurement of disproportionate current density distribution across the surface of these cells. The present invention further extends to an associated device in communication with the said measuring device to modulate fuel cell stack current to allow dynamic performance measurements of individual or grouped cells.
Generally speaking a fuel cell is a device that uses an electrochemical process to generate electrical power utilizing the reaction of hydrogen and oxygen. A typical fuel cell is comprised of a multitude of individual fuel cells electrically connected in series to provided a practical voltage output, a voltage equal to the sum of all the individual fuel cells. This arrangement of a multitude of individual cells is referred to as a xe2x80x9cfuel cell stackxe2x80x9d and each individual cell a xe2x80x9ccell.xe2x80x9d A fuel cell stack typically consists of 10 to 100 cells to realize a total output voltage that is practical for use as an electrical power generation device.
A typical fuel cell system can comprise a fuel cell stack, control or regulating devices for either or both of the reactant fluids (oxygen or air and hydrogen), control or regulating devices for humidification of either or both of the reactant fluids (oxygen or air and hydrogen), control or regulating devices for the cooling fluids (water or air), and a electronic controller to monitor fuel cell stack parameters and adjust control and regulating parameters accordingly.
Since the output voltage of the fuel cell stack equals the sum of all of the individual cells electrically connected in series, the overall performance of the fuel cell stack is an average of the performance of each individual cell. Furthermore, since all these individual cells are electrically connected in series a failure of one individual cell could possibly compromise the performance of the entire fuel cell stack. Therefore to insure the overall performance of the fuel cell stack it is important to monitor the performance of individual cells or groups of cells.
Additionally it is desirable to measure any variation in current density across the plane of cells. A disproportionate current density distribution will manifest itself as differences in cell voltage as measured at different points around the perimeter of a cell. The present invention can allow for voltage measurements to be made at two or more points of the outside perimeter and interpreting these voltage differences and displaying such in a manner to provide an effective determination of a disproportionate current density and hence an operational problem.
It is common for existing control devices to monitor fuel cell stack performance based on the sum of all the cells, but since this voltage is much greater than that of individual cells and the cell voltages have some degree of uncertainty it is impossible to monitor the performance of individual cells and determine performance degradations of individual cells.
It is also desirable for the control system to isolate individual cells or cell groups that are performing poorly and whose performance has not been corrected by control means.
Accordingly, what is needed is a new and useful device and method for measuring individual or grouped cell voltages to monitor fuel cell stack performance for diagnostic or control purposes.
The prior art includes U.S. Pat. No. 6,281,684 to James which is directed to a method and apparatus for measuring cell voltages of a fuel cell stack using different ground references. The apparatus includes scanning units coupled to a fuel cell stack to measure and indicate a voltage of each selected fuel cell in response to a selection signal.
U.S. Pat. No. 6,281,684 to James also discloses a method for measuring cell voltages of a fuel cell stack which similarly includes scanning units coupled to a fuel cell stack.
U.S. Pat. No. 5,170,124 to Blair discloses a method and apparatus for the measurement and comparison of fuel cell performance indicators, such as voltage, in groups of cells connected in series.
The citation of any reference herein should not be construed as an admission that such reference is available as xe2x80x9cPrior Artxe2x80x9d to the instant application.
There is provided, in accordance with the present invention, a new, useful, and unobvious device for measuring individual or grouped cell voltages to monitor fuel cell performance for diagnostic or control purposes. Such a device allows performance data to be collected on each individual cell or on groups of cells of the fuel cell stack for stack performance analysis and fuel cell system control.
Broadly, the present invention extends to a device for measuring individual or grouped cell voltages to monitor fuel cell performance for diagnostic or control purposes, wherein the device comprises a contact arrangement which is associated with the fuel cell stack, which makes electrical connections to individual cells of the fuel cell stack and measures the voltages of said individual cells or cell groups. A device of the invention also comprises a monitor and/or controller, which uses these measurements to report on the performance of the fuel cell stack and to control fuel cell system parameters, based on this performance data.
The present invention further extends to an associated device in communication with the said measuring device and in electrical connection with the said fuel cell stack to modulate fuel cell stack current to allow dynamic performance measurements of individual or grouped cells, such as current voltage relationships, voltage transient response, and voltage frequency response.
The present invention further extends to performing said measurements at a multitude of points around the perimeter of individual cells or cell groups. Thus providing a non-invasive method to determine a disproportionate current density distribution across the plane of an individual cell or cell group.
The present invention further extends to associated apparatus in communication with the said measuring device and in electrical connection with individual cells or cell groups in that the said measuring device can instruct said associated apparatus to electrically isolate individual cells or cell groups which could compromise the performance of the entire fuel cell stack.
The present invention finds application in numerous types of fuel cells including, but certainly not limited to PEM (proton exchange membrane), Phosphoric Acid, and Molten Carbonate.
The present invention also finds application in numerous applications of fuel cells including, but certainly not limited to vehicular power, residential cogeneration, power generation, UPS (uninterruptible power supply), backup power, battery replacement, battery charging, and portable power.
These and other objects of the present invention will be better appreciated and understood by those skilled in the art by reference to the following drawings and Detailed Description.