Method for fast and reliable fuel cell system start-ups
A method for providing a fast and reliable start-up of a fuel cell system. The method uses a stack voltage response to a load to assess if hydrogen and oxygen are being sufficiently distributed to all of the fuel cells by coupling an auxiliary load to the fuel cell stack until a predetermined minimum cell voltage has been reached or a first predetermined time period has elapsed. The method then determines whether a minimum cell voltage has dropped to a first predetermined voltage and, if so, reduces the maximum power allowed to be below the first predetermined voltage value, determines whether the minimum cell voltage in the stack is below a second predetermined voltage, or determines whether the minimum cell voltage drop rate is greater than a predetermined voltage drop rate. If none of these conditions are met, the method returns to loading the stack with system components.
1. A method for starting a fuel cell system, said method comprising:
starting a compressor for providing cathode air to a fuel cell stack;
determining whether the fuel cell stack is filled with air and requires an anode flush;
starting an anode flow to an anode side of the fuel cell stack;
coupling an auxiliary load to the fuel cell stack until a predetermined minimum cell voltage has been reached by a fuel cell in the stack or a first predetermined period of time has elapsed;
coupling the fuel cell stack to system loads;
loading the stack with system components to a predetermined maximum level for a second predetermined period of time; and
determining whether a minimum cell voltage in the stack is below a first predetermined voltage value.
2. The method according to claim 1 further comprising reducing the maximum power allowed from the stack if the minimum cell voltage is below the first predetermined voltage value, determining whether the minimum cell voltage in the stack is below a second predetermined voltage value or the minimum cell voltage drop rate is greater than a predetermined voltage drop rate.
3. The method according to claim 2 further comprising returning to loading the stack with the system components if the minimum cell voltage is not below the second predetermined voltage value or the minimum cell voltage drop rate is not greater than the predetermined voltage drop rate.
4. The method according to claim 2 further comprising determining whether a maximum stack power allowed is less than a predetermined power value if the minimum cell voltage is greater than the first predetermined voltage value.
5. The method, according to claim 4 further comprising determining whether a battery can support another start-up sequence if the maximum amount of power is less than the predetermined power value, the minimum cell voltage is below the second predetermined voltage value, or the minimum cell voltage drop rate is greater than the predetermined voltage drop rate.
6. The method according to claim 5 further comprising limiting the power drawn from the battery to a predetermined minimum value or a maximum battery power available, whichever is smaller, if the battery can support another start-up sequence.
7. The method according to claim 5 further comprising putting the fuel cell system in a reduced performance mode if the battery cannot support another start-up sequence.
8. The method according to claim 1 further comprising providing an anode side flush using hydrogen gas.
9. The method according to claim 8 further comprising by-passing the cathode air around the stack for approximately one-half of an anode flow volume if the stack has been flushed with hydrogen gas.
10. The method according to claim 1 wherein the fuel cell stack is split fuel cell stacks that employ anode flow-shifting, and wherein beginning an anode flow to the stack includes delivering the same amount of gas flow to both of the split stacks simultaneously.
11. The method according to claim 2 wherein the first predetermined voltage value is about 400 mV, the second predetermined voltage value is about 200 mV and the predetermined cell voltage drop rate is about 1000 mV/sec.
12. The method according to claim 1 wherein the predetermined minimum cell voltage is about 700 mV and the first predetermined period of time is about 10 seconds.
13. The method according to claim 1 wherein the auxiliary load is a resistor.
14. A method for a start-up sequence for a fuel cell system including first and second split stacks, said method comprising:
starting a compressor for providing cathode input air to the cathode side of the split stacks;
determining whether the split stacks are filled with air and require an anode flush;
simultaneously starting an anode flow to the anode side of the first and second split stacks;
determining whether the start-up sequence is in a first loop and the anode flush has been performed;
by-passing the split stacks with the cathode air if it is the first time through the start-up sequence loop and the anode flush has been performed for a predetermined number of anode flow volumes;
flowing the cathode air through the cathode side of the split stacks if it is not the first start-up sequence loop or the anode flush has not been performed;
coupling an auxiliary load to the split stacks until a predetermined minimum cell voltage has been reached by a fuel cell in the split stacks or a first predetermined period of time has elapsed;
coupling the split stacks to system loads;
loading the split stacks with system components to a predetermined maximum level for a second predetermined period of time;
determining whether a minimum cell voltage in the split stacks is below a first predetermined voltage value;
determining whether a maximum stack power allowed is less than a predetermined power value if the minimum cell voltage is greater than the first predetermined voltage value; and
updating a look-up table that identifies how many anode volumes of hydrogen gas have been flowed into the anode of the split stacks if the maximum stack power allowed is greater than the predetermined power value.
15. The method according to claim 14 further comprising reducing the maximum power allowed if the minimum cell voltage is below the first predetermined voltage value, determining whether the minimum cell voltage in the split stacks is below a second predetermined voltage value or the minimum cell voltage drop rate is greater than a predetermined voltage drop rate.
16. The method according to claim 14 further comprising returning to loading the split stacks with the system components if the minimum cell voltage is not below the second predetermined voltage value or the minimum cell voltage drop rate is not greater than the predetermined drop rate.
17. The method according to claim 14 further comprising determining whether a battery can support another start-up sequence if the maximum amount of power is less than the predetermined power value, the minimum cell voltage is below the second predetermined voltage value, or the minimum cell voltage drop rate is greater than the predetermined voltage drop rate.
18. The method according to claim 17 further comprising limiting the power drawn from the battery to a predetermined minimum value or a maximum battery power available, whichever is smaller, if the battery can support another start-up sequence.
19. The method according to claim 17 further comprising putting the fuel cell system in a reduced performance mode if the battery cannot support another start-up sequence.
20. The method according to claim 15 wherein the first predetermined voltage value is about 400 mV, the second predetermined voltage value is about 200 mV and the predetermined cell voltage drop rate is about 1000 mV/sec.
21. The method according to claim 14 wherein the predetermined minimum cell voltage is about 700 mV and the first predetermined period of time is about 10 seconds.
22. The method according to claim 14 wherein the auxiliary load is a resistor.