Fuel cell system and controlling method thereof

1. A fuel cell system, comprising:

a fuel cell stack coupled to a load for providing power;

a gas delivery system coupled to the fuel cell stack for providing fuel and oxygen to the fuel cell stack; and

a control system comprising:

a forward controller for generating a control instruction signal based on a command from the load; and

a correction controller for generating a control correction signal based on at least one measured signal from the fuel cell system,

wherein the control system is configured to generate a control signal based on the control instruction signal and the control correction signal, and to control the gas delivery system based on the generated control signal so as to operate the fuel cell stack within specific operating limits; and

wherein the correction controller is configured to predict whether the control instruction signal will violate the operational constraints of the fuel cell stack based on the at least one measured signal, and generate the control correction signal and add the generated control correction signal to the control instruction signal when it is predicted that the control instruction signal will violate operational constraints of the fuel cell stack.

2. The fuel cell system of claim 1 , wherein the correction controller uses a model predictive control to address the operational constraints of the fuel cell stack.

3. The fuel cell system of claim 1 , wherein the at least one measured signal comprises at least one of the following signals: an anode inlet gas pressure, an anode outlet gas pressure, a cathode inlet gas pressure, a cathode outlet gas pressure, an anode inlet flow rate, an anode outlet flow rate, a cathode inlet flow rate, and a cathode outlet flow rate of the fuel cell stack, one and more temperature measurements of the fuel cell stack, a voltage of a single fuel cell of the fuel cell stack, a current of the fuel cell stack, and ambient temperature, ambient pressure, and ambient humidity where the fuel cell system is located.

4. The fuel cell system of claim 1 , wherein the fuel cell system is a solid oxide fuel cell type system, and the fuel cell stack comprises a series of solid oxide fuel cells each of which has an anode, a cathode, solid electrolyte between the anode and the cathode and an interconnect.

5. The fuel cell system of claim 1 , wherein the control system further comprises:

a summator for summing the control instruction signal and the control correction signal to generate the control signal.

6. The fuel cell system of claim 5 , wherein the control instruction signal comprises a fuel flow rate instruction signal and an air flow rate instruction signal, the control correction signal comprises a fuel flow rate correction signal and an air flow rate correction signal, and the control signal comprises a fuel flow rate signal and an air flow rate signal, and wherein the summator comprises:

a first summator for summing the fuel flow rate instruction signal and the fuel flow rate correction signal to generate the fuel flow rate signal; and

a second summator for summing the air flow rate instruction signal and the air flow rate correction signal to generate the air flow rate signal.

7. The fuel cell system of claim 1 , wherein the command from the load comprises a power command and the forward controller comprises:

a scheduler for generating a scheduled current signal based on the power command; and

a converter for converting the scheduled current signal to the control instruction signal by multiplying a stoichiometry ratio.

8. The fuel cell system of claim 7 , wherein the scheduled current signal generated by the scheduler is based additionally on the power command and a current measurement from the fuel cell stack.

9. The fuel cell system of claim 8 , wherein the scheduler comprises:

a current calculation module for calculating a baseline current signal to meet the power command;

a compensation module for generating a compensation current signal based on the current measurement; and

a third summator for summing the baseline current signal and the compensation current signal to generate the scheduled current signal.

10. The fuel cell system of claim 1 , wherein the operational constraints of the fuel cell stack are user specified operational constraints associated with the life of the fuel cell stack.

11. The fuel cell system of claim 10 , wherein the operational constraints of the fuel cell stack comprise at least one of the following constraints: a voltage of a single fuel cell of the fuel cell stack, a resistance of the fuel cell stack, a pressure difference between anode gas pressure and cathode gas pressure of the fuel cell stack, maximal temperature difference in the fuel cell stack, an oxygen excess ratio which is a ratio of the oxygen supplied to a cathode of the fuel cell stack to the actually consumed oxygen, a fuel excess ratio which is a ratio of the fuel supplied to an anode of the fuel cell stack to the actually consumed fuel, a pressure difference between ambient pressure where the fuel cell system is located and anode inlet gas pressure of the fuel cell stack, a pressure difference between the ambient pressure and cathode inlet gas pressure of the fuel cell stack, cross leakage between the anode and the cathode, cross leakage between the anode and ambient environment where the fuel cell system is located, and cross leakage between the cathode and the ambient environment.

12. The fuel cell system of claim 11 , wherein the specific operating limit of the voltage of a single fuel cell of the fuel cell stack is in the range of about 0.55 to 1.0V, the specific operating limit of the pressure difference between the anode gas pressure and the cathode gas pressure of the fuel cell stack is in the range of about −40 Kpa to 40 Kpa, the specific operating limit of the oxygen excess ratio is in the range of 2 to 6, the specific operating limit of the fuel excess ratio is in the range of 1.5 to 6, the specific operating limit of the pressure difference between ambient pressure and the anode inlet gas pressure of the fuel cell stack is in the range of about 0 Kpa to 40 Kpa and the specific operating limit of a pressure difference between the ambient pressure and the cathode inlet gas pressure of the fuel cell stack is in the range of 0 Kpa to 40 Kpa.

13. A method for controlling a fuel cell system, comprising:

generating a control instruction signal based on a command from a load in a fuel cell system, wherein the fuel cell system comprises a fuel cell stack coupled to the load for providing power, and a gas delivery system coupled to the fuel cell stack for providing fuel and oxygen to the fuel cell stack;

predicting whether the control instruction signal will violate operational constraints of the fuel cell stack based on the at least one measured signal;

generating a control correction signal to based on at least one measured signal from the fuel cell system and adding the generated control correction signal to the control instruction signal when it is predicted that the control instruction signal will violate the operational constraints of the fuel cell stack;

generating a control signal based on the control instruction signal and the control correction signal; and

controlling the gas delivery system based on the generated control signal to operate the fuel cell stack within specific operating limits.

14. The method of claim 13 , wherein generating the control signal comprises:

summing the control instruction signal and the control correction signal to generate the control signal.

15. The method of claim 13 , wherein generating the control correction signal further comprises:

pre-specifying the operational constraints of the fuel cell stack; and

pre-establishing a predictive model that describes behavior of the fuel cell stack.

16. The method of claim 13 , wherein the operational constraints of the fuel cell stack comprise at least one of the following constraints: a voltage of a single fuel cell of the fuel cell stack, a resistance of the fuel cell stack, a pressure difference between anode gas pressure and cathode gas pressure of the fuel cell stack, maximal temperature difference in the fuel cell stack, an oxygen excess ratio which is a ratio of the oxygen supplied to a cathode of the fuel cell stack to the actually consumed oxygen, a fuel excess ratio which is a ratio of the fuel supplied to an anode of the fuel cell stack to the actually consumed fuel, a pressure difference between ambient pressure where the fuel cell system is located and anode inlet gas pressure of the fuel cell stack, a pressure difference between the ambient pressure and cathode inlet gas pressure of the fuel cell stack, cross leakage between the anode and the cathode, cross leakage between the anode and ambient environment where the fuel cell system is located, and cross leakage between the cathode and the ambient environment.

17. The method of claim 13 , wherein the at least one measured signal comprises at least one of the following signals: an anode inlet gas pressure, an anode outlet gas pressure, a cathode inlet gas pressure, a cathode outlet gas pressure, an anode inlet flow rate, an anode outlet flow rate, a cathode inlet flow rate, and a cathode outlet flow rate of the fuel cell stack, one and more temperature measurements of the fuel cell stack, a voltage of a single fuel cell of the fuel cell stack, a current of the fuel cell stack, and ambient temperature, ambient pressure, and ambient humidity where the fuel cell system is located.

18. The method of claim 13 , wherein the command from the load comprises a power command and generating the control instruction signal comprises:

generating a scheduled current signal based on the power command; and

converting the scheduled current signal to the control instruction signal by multiplying a stoichiometry ratio.

19. The method of claim 18 , wherein generating the scheduled current signal comprises:

generating the scheduled current signal is further based on the power command and a current measurement from the fuel cell stack.

20. The method of claim 19 , wherein generating the scheduled current signal comprises:

calculating a baseline current signal to meet the power command;

generating a compensation current signal based on the current measurement; and

summing the baseline current signal and the compensation current signal to generate the scheduled current signal.