Electrochemical impedance spectroscopy (“EIS”) analyzer and method of using thereof
Systems, methods, and devices of the various embodiments provide a hardware and software architecture enabling electrochemical impedance spectroscopy (“EIS”) to be performed on multiple electrochemical devices, such as fuel cells, at the same time without human interaction with the electrochemical devices and to use EIS to dynamically monitor the performance of a fuel cell system. Embodiment methods may include determining an impedance of a set of fuel cells using electrochemical impedance spectroscopy, determining an ohmic polarization of the set of fuel cells from the impedance, determining a concentration polarization of the set of fuel cells from the impedance, comparing the ohmic polarization of the set of fuel cells to a first threshold, comparing the concentration polarization of the set of fuel cells to a second threshold, and initiating a corrective action when the ohmic polarization is above the first threshold or when the concentration polarization is below the second threshold.
1. A method of monitoring a fuel cell system performed by a controller, comprising:
determining a first frequency range to apply to a set of fuel cells, wherein the slope of the real impedance of the set of fuel cells versus frequency in the first frequency range is substantially the same as the slope of the real impedance of the set of fuel cells versus frequency of a second frequency range outside the first frequency range;
determining the real impedance of the set of fuel cells over the first frequency range using electrochemical impedance spectroscopy;
comparing the real impedance of the set of fuel cells to a first threshold; and
initiating a corrective action when the real impedance crosses the first threshold.
2. The method of claim 1 , further comprising determining ohmic resistance of the set of fuel cells from the real impedance.
3. The method of claim 2 , wherein determining ohmic resistance of the set of fuel cells for the second frequency range from the real impedance of the first frequency range comprises determining a relationship between the real impedance of the set of fuel cells and frequency.
4. The method of claim 3 , wherein the relationship between the real impedance of the set of fuel cells and frequency is determined through a log or linear fit equation.
5. The method of claim 3 , wherein the relationship between the real impedance of the set of fuel cells and frequency is determined through a lookup table.
6. The method of claim 2 , further comprising:
comparing the ohmic resistance of the set of fuel cells to a second threshold; and
initiating the corrective action when the ohmic resistance crosses the second threshold.
7. The method of claim 1 , wherein the real impedance of the set of fuel cells over the first frequency range has more dependence on ohmic resistance than on operational parameters.
8. The method of claim 7 , wherein the operational parameters include at least one of fuel utilization and air utilization.
9. The method of claim 1 , wherein the set of fuel cells comprises a fuel cell module, a fuel cell column, or a fuel cell segment.
10. The method of claim 1 , wherein the first frequency range is within the range of 10 hertz to 1000 hertz.
11. The method of claim 1 , wherein the second frequency range is within the range of 1000 hertz to 100,000 hertz.
12. The method of claim 1 , wherein the corrective action comprises one or more of initiating a stack recovery sequence, varying fuel supplied to the set of fuel cells, varying output current from the set of fuel cells, adjusting a component in the fuel cell system, and sounding an alarm for an operator to take action.
13. The method of claim 1 , further comprising:
determining imaginary impedance of the set of fuel cells at a single frequency using electrochemical impedance spectroscopy;
comparing the imaginary impedance of the set of fuel cells to a third threshold; and
initiating the corrective action when the imaginary impedance crosses the third threshold.
14. The method of claim 1 , wherein a DC/DC converter in the set of fuel cells is measured to determine the real impedance in the first frequency range while the set of fuel cells is generating power.