Abstract: A method for creating an oxygen depleted gas in a fuel cell system, including operating a fuel cell stack at a desired cathode stoichiometry at fuel cell system shutdown to displace a cathode exhaust gas with an oxygen depleted gas. The method further includes closing a cathode flow valve and turning off a compressor to stop the flow of cathode air.

Abstract: A fuel cell system is provided having a fuel cell stack including a plurality of fuel cells. The fuel cell system includes an anode supply manifold in fluid communication with the plurality of fuel cells, the anode supply manifold adapted to deliver a anode supply stream to the plurality of fuel cells; an anode exhaust manifold in fluid communication with the anodes of the plurality of fuel cells, the anode exhaust manifold adapted to receive an anode exhaust stream from the plurality of fuel cells; a first valve in fluid communication with the anode supply manifold; and a second valve in fluid communication with the anode exhaust manifold. A method of starting the fuel cell system is also provided. The fuel cell system and method militates against a non-uniform distribution of the anode supply stream to the anodes of the plurality of fuel cells.

Abstract: A method for reconditioning a fuel cell stack. The method includes periodically increasing the relative humidity level of the cathode input airflow to the stack to saturate the cell membrane electrode assemblies to be greater than the relative humidity levels during normal stack operating conditions. The method also includes providing hydrogen to the anode side of the fuel cell stack at system shut down while the membrane electrode assemblies are saturated without stack loads being applied so that the hydrogen crosses the cell membranes to the cathode side and reacts with oxygen to reduce stack contaminants.

Abstract: A system and method for detecting a low performing cell in a fuel cell stack using measured cell voltages. The method includes determining that the fuel cell stack is running, the stack coolant temperature is above a certain temperature and the stack current density is within a relatively low power range. The method further includes calculating the average cell voltage, and determining whether the difference between the average cell voltage and the minimum cell voltage is greater than a predetermined threshold. If the difference between the average cell voltage and the minimum cell voltage is greater than the predetermined threshold and the minimum cell voltage is less than another predetermined threshold, then the method increments a low performing cell timer. A ratio of the low performing cell timer and a system run timer is calculated to identify a low performing cell.

Abstract: A fuel cell system including a fuel cell stack having a plurality of fuel cells is provided. An anode supply manifold and an anode exhaust manifold are in fluid communication with the anodes of the plurality of fuel cells. A first valve is in fluid communication with the anode supply manifold and a second valve is in fluid communication with the anode exhaust manifold. A pressure sensor is adapted to measure an anode pressure. In operation, the first valve and the second valve are controlled in response to the anode pressure, thereby militating against an undesired exhausting of an anode supply stream.

Abstract: A fuel cell system including a fuel cell stack having a plurality of fuel cells, each of the fuel cells including an electrolyte membrane disposed between an anode and a cathode, an anode supply manifold in fluid communication with the anodes of the fuel cells, the anode supply manifold providing fluid communication between a source of hydrogen and the anodes, an anode exhaust manifold in fluid communication with the anodes of the fuel cells, and a fan in fluid communication with the anodes of the fuel cells, wherein the fan controls a flow of fluid through the anodes of the fuel cells after the fuel cell system is shutdown.

Abstract: A method of estimating minimum voltage of fuel cells, and a product using same.

Abstract: A system and method for increasing the temperature of a fuel cell stack quickly, especially at cold stack start-up. The method includes determining whether the fuel cell stack is below a first predetermined temperature threshold, and, if so, starting a cooling fluid flow through the stack and engaging a shorting circuit across the stack to short circuit the stack and cause the stack to operate inefficiently. The method then determines a desired heating rate of the fuel cell stack and calculates a cathode airflow to the fuel cell stack based on the desired heating rate. The method reduces the flow of cathode air to the stack if a minimum cell voltage is below a predetermined minimum cell voltage threshold and disengages the shorting circuit and applies vehicle loads to the stack when the stack temperature reaches a predetermined second temperature threshold.

Abstract: A fuel cell system that employs a technique for reducing MEA degradation during system shut-down that occurs as a result of the hydrogen and air being present in the fuel cell stack flow channels. The fuel cell system includes a non-linear load element, such as a positive temperature coefficient resistor, electrically coupled to each fuel cell in the fuel cell stack. The non-linear element operates such that it has high electrical conduction at low cell voltages and low electrical conduction at high cell voltages. During system shut-down, the voltage that is generated as a result of the hydrogen and air interaction in the fuel cells that creates a low cell voltage is drawn from the fuel cell and dissipated by the element. During system operation, the fuel cell potentials are relatively high and the resistance of the element goes up so that less current flows through the element, thus reducing electrical losses.

Abstract: A fuel cell system is provided that includes a fuel cell stack with a plurality of fuel cells and a power converter in electrical communication with the fuel cell stack. The power converter is configured to selectively regulate a power of the fuel cell stack and short circuit the fuel cell stack, as desired. A method for starting the fuel cell stack is also described including the steps of causing a short circuit of the fuel cell stack by placing the power converter in a short circuit mode; introducing a hydrogen to the anodes of the fuel cell stack to displace a quantity of air on the anodes; and placing the power converter in a power regulation mode. A degradation of the fuel cell stack during start-up is thereby militated against.

Abstract: Processes to shut down a fuel cell system are described. In one implementation (300), a load (215) is cyclically engaged and disengaged across a fuel cell stack (205) so as to deplete the fuel available to the system's fuel cells (205). Voltage and/or current thresholds may be used to determine when to engage and disengage the load (215) and when to terminate the shutdown operation. In another implementation (500), a variable load (405) is engaged and adjusted so as to deplete the fuel available to the system's fuel cells (205). As before, voltage and/or current thresholds may be used to determine when to adjust the load (405) and when to terminate the shutdown process. In still another implementation, a load (215 or 405) may be periodically engaged and disengaged during some portion of the shutdown process and engaged but adjusted during other portions of the shutdown process.

Abstract: A method for providing a current density set-point for a fuel cell stack in response to a power request from the stack where the set-point is determined based on system parameters that identify the life and degradation of the stack. The method includes dividing a current density range of the fuel cell stack into a predetermined number of sample regions, and selecting the sample regions in order from low to high during the current set-point analysis. The method calculates an average cell voltage for the current density of the selected sample region, and stack power from the average cell voltage. The method then determines whether a power request signal is less than the stack power for the selected sample region and greater than the calculated power for the previous sample region, and if so, calculates the current density set-point at the requested power based on these values.

Abstract: An algorithm for determining the maximum net power available from a fuel cell stack as the stack degrades over time using an online adaptive estimation of a polarization curve of the stack. The algorithm separates the current density range of the stack into sample regions, and selects a first sample region from the far left of the estimated polarization curve. The algorithm then calculates the cell voltage for that current density sample region, and determines whether the calculated cell voltage is less than or equal to a predetermined cell voltage limit. If the calculated cell voltage is not less than the cell voltage limit, then the algorithm selects the next sample region along the polarization curve. When the calculated cell voltage does reach the cell voltage limit, then the algorithm uses that current density for the sample region being analyzed to calculate the maximum power of the fuel cell stack.

Abstract: A system and method for detecting and predicting low performing cells in a fuel cell stack. When the fuel cell stack is running and certain data validity criteria have been met, an algorithm collects the data, such as stack current density, average cell voltage and minimum cell voltage. This information is used to estimate predetermined parameters that define the stack polarization curve. The system defines a predetermined minimum current density that is used to identify a low performing cell. The system then calculates an average cell voltage and a minimum cell voltage at the minimum current density set-point, and calculates a cell voltage difference between the two. If the cell voltage difference is greater than a predetermined low voltage threshold and the minimum cell voltage is less than a predetermined high voltage threshold, the algorithm sets a flag identifying a potential for a low performing cell.

Abstract: 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.

Abstract: A fuel cell system including a fuel cell stack having a plurality of fuel cells is provided. An anode supply manifold and an anode exhaust manifold are in fluid communication with the anodes of the plurality of fuel cells. A first valve is in fluid communication with the anode supply manifold and a second valve is in fluid communication with the anode exhaust manifold. A pressure sensor is adapted to measure an anode pressure. In operation, the first valve and the second valve are controlled in response to the anode pressure, thereby militating against an undesired exhausting of an anode supply stream.

Abstract: A fuel cell system is provided having a fuel cell stack including a plurality of fuel cells. The fuel cell system includes an anode supply manifold in fluid communication with the plurality of fuel cells, the anode supply manifold adapted to deliver a anode supply stream to the plurality of fuel cells; an anode exhaust manifold in fluid communication with the anodes of the plurality of fuel cells, the anode exhaust manifold adapted to receive an anode exhaust stream from the plurality of fuel cells; a first valve in fluid communication with the anode supply manifold; and a second valve in fluid communication with the anode exhaust manifold. A method of starting the fuel cell system is also provided. The fuel cell system and method militates against a non-uniform distribution of the anode supply stream to the anodes of the plurality of fuel cells.

Abstract: A control strategy for bleeding an anode side of fuel cell stack in a fuel cell system that improves water management and addresses durability and performance concerns. The method includes determining when to begin the anode bleed, typically by estimating or measuring the amount of nitrogen in the anode side of the stack. The method also includes determining when to end the anode bleed based on the volume of gas that has been bled. The method determines the mole flow rate of the anode gas flowing through a bleed valve, integrates the mole flow rate to get the number of moles of the gas that have passed through the bleed valve, determines a desired amount of moles to be bled, and ends the bleed when the actual number of moles of the gas equals the desired number of moles of the gas.

Abstract: A fuel cell system is provided including a fuel cell stack having a fuel cell having an anode, an anode outlet, an anode inlet, and a cathode. The fuel cell system further includes a hydrogen pump in communication with the anode outlet and the anode inlet. The hydrogen pump features a proton exchange membrane disposed between a first electrode and a second electrode. The first electrode is configured to accept an anode outlet stream from the anode outlet, the anode outlet stream including a hydrogen gas and an inert gas, the first electrode being configured to exhaust the inert gas. In one embodiment, the hydrogen pump is in communication with a PROX unit and configured to provide the hydrogen gas to the fuel cell stack. Further provided are methods employing the hydrogen pump wherein a start-stop degradation of the fuel cell is militated against and a hydrogen feed stream is humidified.

Abstract: An algorithm for determining a polarization curve of a fuel cell stack. When the fuel cell stack is running and certain data validity criteria have been met, the algorithm goes into a data collection mode where it collects stack data, such as stack current density, average cell voltage and minimum cell voltage. When the stack is shut down, the algorithm uses a cell voltage model to solve a least squares problem to estimate predetermined parameters that define the polarization curve. If the estimated parameters satisfy certain termination criteria, then the estimated parameters are stored to be used by a system controller to calculate the polarization curve of the stack.