# US 7,608,351 B2 · System and method for controlling cathode stoichiometry to minimize RH excursions during transients > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,608,351 B2 - Document ID: US7608351B2 - Status: Granted - Kind: B2 - Application number: 11/245,755 - Filed: 2005-10-07 - Published: 2007-04-12 - Granted: 2009-10-27 - Earliest claimed: 2005-10-07 - Assignees: GM Global Technology Operations LLC - Inventors: Manish Sinha; David A. Arthur; Matthew K. Hortop - Web page: https://patentgrep.com/patent/US7608351B2 ## CPC - H01M 8/04089: of gaseous reactants - H01M 8/04589: {of fuel cell stacks} - H01M 8/04753: {of fuel cell reactants} - H01M 8/04798: {of fuel cell reactants} - H01M 8/04835: {of fuel cell reactants} - H01M 2250/20: Fuel cells in motive systems, e.g. vehicle, ship, plane - Y02E 60/50: Fuel cells - Y02T 90/40: Application of hydrogen technology to transportation, e.g. using fuel cells - H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract A system and method for providing dynamic cathode stoichiometry control in a fuel cell during stack load transients to minimize relative humidity excursions. Particularly, changes in the cathode stoichiometry is controlled as a function of time in response to a decrease or increase in stack current density. Thus, if the stack current density drops to a predetermined current density, the dynamic stoichiometry logic will monitor the low power condition and determine if the condition is sustained, i.e., for an extended period of time. If the low power condition is not sustained, then the cathode stoichiometry does not change, but if it is sustained, then the cathode stoichiometry is increased. The same delay in changing the cathode stoichiometry can be provided for a transition from a low power condition to a high power condition. ## Claims ### Claim 1 A method for controlling the cathode stoichiometry of a fuel cell stack, said method comprising: monitoring the current density generated by the fuel cell stack; monitoring time if the current density goes above or below a predetermined range; maintaining the cathode stoichiometry constant for a predetermined period of time after the current density goes below the predetermined range; and increasing the cathode stoichiometry after the predetermined period of time that the current density has remained below the predetermined range so as to compensate for any mismatch in thermal dynamics caused by the change in current density. ### Claim 2 (depends on 1) The method according to claim 1 wherein the predetermined period of time is about 30 seconds. ### Claim 3 (depends on 1) The method according to claim 1 wherein increasing the cathode stoichiometry includes increasing the cathode stoichiometry to about 6. ### Claim 4 A method for controlling the cathode stoichiometry of fuel cell stack, said method comprising: defining different operating ranges of the current density generated by the fuel cell stack; identifying a desired cathode stoichiometry for each of the low power range, the mid-power range and the high power range; determining which range the current density generated by the stack is in; determining that the current density generated by the stack has changed from one range to another range for an extended period of time; and maintaining the cathode stoichiometry for the one range for a predetermined period of time after the current density generated by the stack has changed to the other range. ### Claim 5 (depends on 4) The method according to claim 4 wherein defining different operating ranges includes defining a low power range, a mid-power range and a high power range. ### Claim 6 (depends on 5) The method according to claim 5 wherein the low power range is 0-0.3 A/cm2, the mid-power range is 0.3-0.6 A/cm2 and the high power range is 0.6-2 A/cm2. ### Claim 7 (depends on 5) The method according to claim 5 wherein the cathode stoichiometry for the low power range is about 6, the cathode stoichiometry for the mid-power range is about 4 and the cathode stoichiometry for the high power range is about 2. ### Claim 8 (depends on 4) The method according to claim 4 wherein the predetermined period of time is about 30 seconds. ### Claim 9 (depends on 4) The method according to claim 4 wherein maintaining the cathode stoichiometry includes maintaining a maximum cathode stoichiometry based on compressor limitations when the current density of the stack goes from a lower current density range to a higher current density range. ### Claim 10 A fuel cell system comprising: a fuel cell stack generating a current density; a compressor for providing an airflow to the fuel cell stack; and a controller for controlling the compressor for providing a desirable cathode stoichiometry, said controller determining that the current density generated by the stack has changed from one current density range to another current density range, maintaining the cathode stoichiometry that is desirable for the one range for a predetermined period of time after the current density generated by the stack has changed to the other range, and then increasing or decreasing the cathode stoichiometry to a desirable value for the other range so as to compensate for any mismatch in thermal dynamics caused by the change in current density. ### Claim 11 (depends on 10) The system according to claim 10 wherein the predetermined period of time is about 30 seconds. ### Claim 12 (depends on 10) The system according to claim 10 wherein the controller maintains a maximum cathode stoichiometry based on compressor limitations when the current density of the stack goes from a lower current density range to a higher current density range. ### Claim 13 (depends on 9) The system according to claim 9 wherein the fuel cell system is on a vehicle. ### Claim 14 A fuel cell system comprising: a fuel cell stack generating a current density; a compressor for providing an airflow to the fuel cell stack; and a controller for controlling the compressor for providing a desirable cathode stoichiometry, wherein the controller defines a low power range, a mid-power range and a high power range of the current density generated by the fuel cell stack and identifies a desirable cathode stoichiometry for each of the low power range, the mid-power range and the high power range, said controller determining which range the current density generated by the stack is currently operating in, determining that the current density generated by the stack has changed from one range to another range, and maintaining the cathode stoichiometry of the one range for a predetermined period of time after the current density generated by the stack has changed to the other range. ### Claim 15 (depends on 14) The system according to claim 14 wherein the low power range is 0-0.3 A/cm2, the mid-power range is 0.3-0.6 A/cm2 and the high power range is 0.6-2 A/cm2. ### Claim 16 (depends on 14) The system according to claim 14 wherein the cathode stoichiometry for the low power range is about 6, the cathode stoichiometry for the mid-power range is about 4 and the cathode stoichiometry for the high power range is about 2. ### Claim 17 (depends on 14) The system according to claim 14 wherein the predetermined period of time is about 30 seconds. ### Claim 18 (depends on 14) The system according to claim 14 wherein the controller maintains a maximum cathode stoichiometry based on compressor limitations when the current density of the stack goes from a lower current density range to a higher current density range. ### Claim 19 (depends on 14) The system according to claim 14 wherein the fuel cell system is on a vehicle.