Shutdown and storage method for fuel cell system at below freezing temperatures

Patent metadata

Field	Value
Publication number	US-10170781-B2
Application number	US-201615258141-A
Country	US
Kind code	B2
Filing date	Sep 7, 2016
Priority date	Sep 19, 2015
Publication date	Jan 1, 2019
Grant date	Jan 1, 2019

Abstract

Improved methods are disclosed for shutting down and storing a fuel cell system, particularly for below freezing temperature conditions. The methods comprise stopping power production from the fuel cell stack, monitoring the amount of energy remaining in an energy supply, monitoring the stack temperature, and repeatedly performing a predetermined warming operation if the stack temperature falls to a normal threshold temperature and if the amount of energy remaining exceeds a certain minimum amount. In the improved methods, when the amount of remaining energy is less than or equal to the minimum amount, a final warming operation is performed that differs from the predetermined warming operation.

First claim

What is claimed is:

1. A keep-warm method for shutting down and storing a fuel cell system at below freezing temperatures, the fuel cell system prior to shutting down comprising a fuel cell stack that is producing power and an energy supply for heating the fuel cell stack, the method comprising:
stopping power production from the fuel cell stack;
monitoring the amount of energy remaining in the energy supply, wherein the energy supply is selected from the amount of fuel available for producing power in the fuel cell stack and the amount of electricity in a battery for operating an electric heater;
monitoring the temperature of the fuel cell stack;
specifying an amount of energy necessary to perform a final warming operation;
performing, when the temperature of the fuel cell stack drops to a normal threshold temperature, an initial warming operation to keep the fuel cell system above the normal threshold temperature, said warming operation selected from the group consisting of producing power from said fuel cell stack and heating the fuel cell stack with said electric heater;
subsequently performing, each time the fuel cell system temperature drops to the normal threshold temperature, a predetermined warming operation to keep the fuel cell system above the normal threshold temperature, so long as the amount of energy remaining exceeds a minimum amount, said minimum amount being that amount adequate to perform a final warming operation;
and
in the event the stack temperature falls to the normal threshold temperature and the amount of energy remaining is less than or equal to the minimum amount, performing a final warming operation;
wherein the final warming operation differs from the predetermined warming operation.

2. The method of claim 1 wherein the normal threshold temperature is less than 0° C.

3. A keep-warm method for shutting down and storing a fuel cell system at below freezing temperatures, the fuel cell system prior to shutting down comprising a fuel cell stack that is producing power and an energy supply for heating the fuel cell stack, the method comprising:
stopping power production from the fuel cell stack;
monitoring the amount of energy remaining in the energy supply, wherein the energy supply is selected from the amount of fuel available for producing power in the fuel cell stack and the amount of electricity in a battery for operating an electric heater;
monitoring the temperature of the fuel cell stack;
specifying an amount of energy necessary to perform a final warming operation;
performing, when the temperature of the fuel cell stack drops to a normal threshold temperature, an initial warming operation to keep the fuel cell system above the normal threshold temperature, said warming operation selected from the group consisting of producing power from said fuel cell stack and heating the fuel cell stack with said electric heater;
subsequently performing, each time the fuel cell system temperature drops to the normal threshold temperature, a predetermined warming operation to keep the fuel cell system above the normal threshold temperature, so long as the amount of energy remaining exceeds a minimum amount, said minimum amount being that amount adequate to perform a final warming operation; and
in the event the stack temperature falls to the normal threshold temperature and the amount of energy remaining is less than or equal to the minimum amount, performing a final warming operation;
wherein each predetermined warming operation heats the stack to a predetermined target temperature, the final warming operation heats the stack to a final target temperature, and the predetermined target temperature is less than the final target temperature.

4. A keep-warm method for shutting down and storing a fuel cell system at below freezing temperatures, the fuel cell system prior to shutting down comprising a fuel cell stack that is producing power and an energy supply for heating the fuel cell stack, the method comprising:
stopping power production from the fuel cell stack;
monitoring the amount of energy remaining in the energy supply, wherein the energy supply is selected from the amount of fuel available for producing power in the fuel cell stack and the amount of electricity in a battery for operating an electric heater;
monitoring the temperature of the fuel cell stack;
specifying an amount of energy necessary to perform a final warming operation;
performing, when the temperature of the fuel cell stack drops to a normal threshold temperature, an initial warming operation to keep the fuel cell system above the normal threshold temperature, said warming operation selected from the group consisting of producing power from said fuel cell stack and heating the fuel cell stack with said electric heater;
subsequently performing, each time the fuel cell system temperature drops to the normal threshold temperature, a predetermined warming operation to keep the fuel cell system above the normal threshold temperature, so long as the amount of energy remaining exceeds a minimum amount, said minimum amount being that amount adequate to perform a final warming operation; and
in the event the stack temperature falls to the normal threshold temperature and the amount of energy remaining is less than or equal to the minimum amount, performing a final warming operation;

wherein each predetermined warming operation heats the stack for a predetermined time period, the final warming operation heats the stack for a final time period, and the predetermined time period is less than the final time period.

5. The method of claim 1 wherein said final warming operation comprises supplying at least one reactant gas selected from fuel and oxidant to the fuel cell stack and producing power in the fuel cell stack, and wherein the relative humidity of the reactant gas supplied to the fuel cell stack is lower during the final warming operation than during the predetermined warming operation.

6. The method of claim 1 wherein said final warming operation comprises supplying at least one reactant gas selected from fuel and oxidant to the fuel cell stack and producing power in the fuel cell stack, and wherein the flow rate of the reactant gas supplied to the fuel cell stack is greater during the final warming operation than during the predetermined warming operation.

7. The method of claim 1 wherein said final warming operation comprises supplying at least one reactant gas selected from fuel and oxidant to the fuel cell stack and producing power in the fuel cell stack, and wherein the pressure of the reactant gas supplied to the fuel cell stack is lower during the final warming operation than during the predetermined warming operation.

8. The method of claim 1 wherein:
the predetermined warming operation comprises:
heating the stack for a predetermined time period; and
performing a predetermined purge after the predetermined time period;

the final warming operation comprises:
heating the stack for a final time period; and
performing a final purge after the final time period; and

wherein the final purge is longer than the predetermined purge.

9. The method of claim 1 wherein the steps of performing the predetermined and the final warming operations are selected from the group consisting of producing power from the fuel cell stack and heating the fuel cell stack with an electric heater.

Assignees

• Daimler Ag
• Ford Motor Co
• Nissan Motor

Inventors

• Procter Michael
• Fukuyama Yosuke
• Fellows Richard
• Shiomi Takeshi

Classifications

• H01M8/04037

  Electrical heating · CPC title

• H01M8/04303

  applied during shut-down · CPC title

• H01M8/04228

  during shut-down · CPC title

• H01M8/0432

  Temperature; Ambient temperature · CPC title

• H01M8/04619

  of fuel cell stacks · CPC title