Method of monitoring a fuel cell unit

• US 20050106426A1
• Filed: 09/13/2004
• Published: 05/19/2005
• Est. Priority Date: 09/12/2003
• Status: Active Grant

• Current Assignee: Daimler AG (Mercedes-Benz Group AG)
• Original Assignee: Daimler Chrysler Company LLC (Stellantis NV)
• Inventors: Weiss, Wolfgang, Engelhardt, Thorsten, Fosmoe, Richard
• Granted Patent: US 7,124,040 B2
• Time in Patent Office: Days
• US Class Current: 702/58
• CPC Class Codes: H01M 8/04552 of the individual fuel cell
• CPC Class Codes: H01M 8/04582 of the individual fuel cell
• CPC Class Codes: H01M 8/04671 of the individual fuel cell
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

In a method of monitoring a fuel cell unit, at least one pair of measured values, including a measured current value and a measured voltage value (I_actual, U_actual) are determined at the outputs of the fuel cell unit. The measured voltage value (U_actual) is compared with a limit value (P_G), which is a function of the measured current value (I_actual) by way of a limit characteristic polarization curve. It is concluded that the condition of the fuel cell unit is faulty when the measured voltage value (U_actual) or a function of the measured voltage value is smaller than or equal to a predefined threshold value.

Claims

1. A method of monitoring a fuel cell unit, comprising:

determining at least one pair of measured values comprising a measured current value and a measured voltage value at the outputs of the fuel cell unit;

comparing the measured voltage value with a limit value; and

drawing a conclusion that the fuel cell unit is faulty when one of the measured voltage value and a function of the measured voltage value is smaller than or equal to a predefined threshold value;

wherein,

the limit value is a function of the measured current value; and

a functional relationship between the limit value and the measured current value is given by a limit characteristic polarization curve of the fuel cell unit.

2. The method according to claim 1, wherein:

the measured voltage value is additionally compared with a starting value which is a function of the measured current value; and

a functional relationship between the starting value and the measured current value is determined based on a starting characteristic polarization curve of the fuel cell unit.

3. The method according to claim 1, wherein:

a distance (a) between the measured voltage value and the limit value is formed as a difference between the measured voltage value and the limit value; and

it is concluded that the condition of the fuel cell unit is faulty when the distance (a) or a function of the distance (a) is smaller than or equal to a predefined threshold value.

4. The method according to claim 2, wherein:

a distance (a) between the measured voltage value and the limit value is formed as a difference between the measured voltage value and the limit value; and

it is concluded that the condition of the fuel cell unit is faulty when the distance (a) or a function of the distance (a) is smaller than or equal to a predefined threshold value.

5. The method according to claim 3, wherein the difference is normalized for forming the distance (a).

6. The method according to claim 4, wherein the difference is normalized for forming the distance (a).

7. The method according to claim 3, wherein:

the distance (a) between the measured voltage value and the limit value is determined at each of a plurality of successive points in time;

an average value (z) of the determined distances (a) is formed; and

it is concluded that the condition of the fuel cell unit is faulty when the average value (z) of the distances (a) is smaller than or equal to a predefined threshold value.

8. The method according to claim 5, wherein:

the distance (a) between the measured voltage value and the limit value is determined at each of a plurality of successive points in time;

an average value (z) of the determined distances (a) is formed; and

it is concluded that the condition of the fuel cell unit is faulty when the average value (z) of the distances (a) is smaller than or equal to a predefined threshold value.

9. The method according to claim 7, wherein the averaging is performed in a sliding manner over a defined time interval.

10. The method according to claim 8, wherein the averaging is performed in a sliding manner over a defined time interval.

11. The method according to claim 6, wherein as a function of the time history of the average value (z), a prediction is made concerning at least one of a residual operating duration and a residual operating path of the fuel cell unit.

12. The method according to claim 10, wherein as a function of the time history of the average value (z), a prediction is made concerning at least one of a residual operating duration and a residual operating path of the fuel cell unit.

13. The method according to claim 3, wherein:

the distance (a) is determined at each of a plurality of successive points in time within a defined time interval; and

it is concluded that a condition of the fuel cell unit is faulty only when the distance values (a) or a function of the distance values (a) is smaller than or equal to a predefined threshold value with a frequency which exceeds a defined threshold frequency.

14. The method according to claim 5, wherein:

the distance (a) is determined at each of a plurality of successive points in time within a defined time interval; and

it is concluded that a condition of the fuel cell unit is faulty only when the distance values (a) or a function of the distance values (a) is smaller than or equal to a predefined threshold value with a frequency which exceeds a defined threshold frequency.