Method for operating a fuel cell stack

Abstract

A method for operating a fuel cell stack (12), the method comprising: Determining (106) when a vehicle (10) powered by the fuel cell stack (12) is in a stationary state; Calculating (114) an O2 concentration of an assumed closed space (14) over time while the vehicle (10) is in the stationary state; Establishing a set of O2 concentration problem levels (98, 100) comprising a first O2 concentration problem level (98) being less than a standard O2 concentration and a second O2 concentration problem level (100) being less than the first O2 concentration problem level (98); Comparing (126, 136) the O2 concentration of the assumed closed space (14) over time with the set of O2 concentration problem levels (98, 100); and Operating the fuel cell stack (12) without restriction when the vehicle (10) is in the stationary state as long as the O2 concentration of the assumed enclosed space (14) remains greater than the first O2 concentration problem level (98); the method further comprising operating (132) the fuel cell stack, BZS, in a low power state when the O2 concentration of the assumed enclosed space (14) is equal to or less than the first O2 concentration problem level (98) but greater than the second O2 concentration problem level (100).

Description

[0001] The present description relates to operating a fuel cell stack (FCS) for a vehicle that may be enclosed by a surrounding structure such as an enclosed garage or other confined space. More particularly, the present description provides methods for operating the FCS according to a conditional operating mode that assumes the vehicle is in an enclosed space when certain vehicle operating conditions are met. The conditional operating mode is designed such that, when the vehicle is actually in an enclosed space, the operation of the FCS is modified so that the FCS does not over-deplete the available oxygen in that space beyond an acceptable level. The conditional operating mode also attempts to avoid unnecessary changes to the operation of the FCS when the vehicle is not actually in an enclosed space but the conditional operating mode is triggered anyway.

[0002] A proton exchange membrane fuel cell (PAM fuel cell) is an electrochemical device containing a membrane electrode assembly with an anode catalyst layer and a cathode catalyst layer on opposite sides of a proton-conducting solid polymer electrolyte. The anode catalyst layer receives hydrogen gas, and the cathode catalyst layer receives oxygen or air. The hydrogen gas is dissociated in the anode catalyst layer to produce free protons and electrons. The protons migrate through the electrolyte, and the electrons are passed through a load to perform work. The protons and the electrode eventually reach the cathode catalyst layer, where they react with oxygen to produce water. A PAM fuel cell comprises a plurality of similar PAM fuel cells separated by bipolar plates and connected to common gas sources of hydrogen and oxygen or air.

[0003] The cathode catalyst layers of the FCS are supplied with oxygen from the surrounding environment and consume this oxygen to support the ongoing operation of the FCS. If the vehicle is in an enclosed space during FCS operation—for example, if the vehicle is running in a closed garage to warm the passenger compartment—the amount of available oxygen within the enclosed space can be depleted faster than it can be replaced by air exchange from outside the enclosed space into the enclosed space. Under these circumstances, a decrease in the oxygen concentration within the enclosed space can begin.

[0004] EP 2 546 912 A1 describes a fuel cell system comprising: a fuel cell having an anode to which fuel is supplied and a cathode to which oxidant is supplied; an operation control unit for controlling the operation of the fuel cell; oxygen consumption amount detection means for detecting an amount of oxygen consumed in the fuel cell, and at least one of a first alarm means and a first stop command means, wherein the first alarm means is configured to output an alarm when the amount of oxygen consumed is equal to or greater than a first reference value, and the first stop command means is configured to output a stop command for stopping power generation by the fuel cell to the operation control unit when the amount of oxygen consumed is equal to or greater than a second reference value.

[0005] JP 2006 - 73 309 A describes a correction of the oxygen concentration in the interior and the oxygen concentration outside the vehicle by using temperature correction coefficients based on the interior temperature and the outside temperature, as well as an atmospheric pressure correction coefficient based on the atmospheric pressure. When a vehicle is operating, the oxygen concentration in the interior is compared with the threshold values, and if the oxygen concentration in the interior has dropped, this is reported or the system is stopped. When the vehicle is not operating, the corrected oxygen concentration outside the vehicle is compared with the threshold values, and if the oxygen concentration outside the vehicle has dropped, this is reported or the system is stopped.

[0006] JP 2016 - 80 328 A describes a simple structure for preventing the interior of a garage from becoming oxygen-deficient. An air supply fan supplies outside air to a garage. A CT sensor measures the power consumption on the side of a residential building when the residential building is powered by a hydrogen fuel cell vehicle parked in the garage. A control ECU calculates an oxygen consumption amount in the garage based on the power consumption amount measured by the CT sensor and the vehicle information stored in a storage unit, and controls the operation of the air supply fan so that oxygen corresponding to the calculated oxygen consumption amount is supplied to the garage.

[0007] It is therefore an object of the invention to provide a conditional operating mode for a FCS which can address the problem of a falling oxygen concentration within an enclosed space when certain operating conditions of the vehicle indicate that the vehicle could be located in an enclosed space, without, of course, unnecessarily disturbing the operation of the FCS when it is assumed that the vehicle is located in such an enclosed space but this is not actually the case.

[0008] The object of the invention is achieved by means of a method for operating a fuel cell stack comprising several steps. One step comprises determining when a car supplied with energy by the fuel cell stack is in a stationary state. In a further step, an O2 concentration of an assumed enclosed space is calculated over time while the vehicle is in the stationary state. In a further step, a set of O2 concentration problem levels is established, which includes a first O2 concentration problem level being less than a standard O2 concentration and a second O2 concentration problem level being less than the first O2 concentration problem level. In a further step, the O2 concentration of the assumed enclosed space is compared over time with a set of O2 concentration problem levels.In yet another step, the fuel cell stack is operated without restriction when the vehicle is in the stationary state, as long as the O2 concentration of the assumed enclosed space remains greater than the first O2 concentration problem level. The method further comprises operating the fuel cell stack, BZS, in a low power state when the O2 concentration of the assumed enclosed space is equal to or less than the first O2 concentration problem level, but greater than the second O2 concentration problem level.

[0009] According to one embodiment, the step of determining when the vehicle powered by the fuel cell stack is in a stationary state comprises determining that a speed of the vehicle is less than or equal to five km / h.

[0010] According to another embodiment, the step of determining when the vehicle powered by the fuel cell stack is in a stationary state comprises determining whether the vehicle is stationary.

[0011] According to another embodiment, the step of determining when the vehicle powered by the fuel cell stack is in a stationary state includes determining that the vehicle is stationary and that GPS coordinates of the vehicle indicate that the vehicle is not on a road.

[0012] According to another embodiment, the step of calculating the O2 concentration of the assumed enclosed space over time comprises setting the O2 concentration of the assumed enclosed space at atmospheric standard O2 concentration when first determining that the vehicle is in the stationary state, and thereafter setting the O2 concentration of the assumed enclosed space based on an amount of O2 consumed by the fuel cell stack over time and an amount of O2 replaced over time in the assumed enclosed space.

[0013] According to another embodiment, the amount of O2 consumed by the fuel cell stack may include an amount of O2 consumed due to current generation of the fuel cell stack, an amount of O2 consumed due to cathode catalytic heating (CCH), and an amount of O2 consumed due to stack voltage recovery (SVR), and the amount of O2 replaced in the enclosed space may be based on 0.03 air exchanges / hour.

[0014] According to another embodiment, the first O2 concentration problem level is less than 21 mol% and more than 19 mol%, and separately the second O2 concentration problem level is less than 20 mol% and more than 18 mol%.

[0015] According to a further embodiment, the first O2 concentration problem level is 20 mol% and the second O2 concentration problem level is 19 mol%.

[0016] According to another embodiment, the step of operating the fuel cell stack includes, without limitation, operating the fuel cell stack with activated cathode catalytic heating, CCH, and stack voltage recovery, SVR, processes.

[0017] According to a further embodiment, the method further comprises the additional step of operating the FCS in a low power state when the O2 concentration of the assumed enclosed space is equal to or less than the first O2 concentration problem level but greater than the second O2 concentration problem level.

[0018] According to another embodiment, the method further comprises the step of shutting down the fuel cell stack when the O2 concentration of the assumed enclosed space is equal to or less than the second O2 concentration problem level.

[0019] According to the invention, a further method for operating a fuel cell stack is also provided, which comprises several steps. One step comprises determining when a car powered by the fuel cell stack is in a stationary state. In a further step, an O2 concentration of an assumed enclosed space is calculated over time while the vehicle is in the stationary state. In a further step, the O2 concentration of the assumed enclosed space is compared over time to a set of O2 concentration problem levels, which includes a first O2 concentration problem level and a second O2 concentration problem level. The first O2 concentration problem level is less than a standard O2 concentration, and the second O2 concentration problem level is less than the first O2 concentration problem level.In yet another step, the fuel cell stack is operated when the vehicle is in the stationary state according to a conditional operating mode. The conditional operating mode includes (1) operating the fuel cell stack without restriction as long as the O2 concentration of the assumed enclosed space remains greater than the first O2 concentration problem level; (2) operating the fuel cell stack in a low power state when the O2 concentration of the assumed enclosed space is equal to or less than the first O2 concentration problem level but greater than the second O2 concentration problem level; and (3) shutting down the fuel cell stack when the O2 concentration of the assumed enclosed space is equal to or less than the second O2 concentration problem level.

[0020] According to one embodiment, the step of determining when the vehicle powered by the fuel cell stack is in a stationary state comprises determining that the vehicle is stationary. As a further step, the step of determining when the vehicle powered by the fuel cell stack is in a stationary state comprises determining that the vehicle is stationary and that GPS coordinates of the vehicle indicate that the vehicle is not on a road.

[0021] According to another embodiment, the step of calculating the O2 concentration of the assumed enclosed space over time comprises setting the O2 concentration of the assumed enclosed space at atmospheric standard O2 concentration when first determining that the vehicle is in a stationary state, and thereafter setting the O2 concentration of the assumed enclosed space based on an amount of O2 consumed by the fuel cell stack over time and an amount of O2 replaced over time in the assumed enclosed space.The amount of O2 consumed by the fuel cell stack includes an amount of O2 consumed due to the generation of a current of the fuel cell stack, an amount of O2 consumed due to the cathode catalytic heating (CCH), and an amount of O2 consumed due to the SVR, and the amount of O2 replaced in the enclosed space may be based on 0.03 air exchanges / hour.

[0022] According to one embodiment, the first O2 concentration problem level is less than 21 mol% and more than 19 mol%, and the second O2 concentration problem level is less than 20 mol% and more than 18 mol%. Furthermore, the step of operating the fuel cell stack in the low power state may include deactivating the CCH and SVR of the fuel cell stack. Fig. 1 is a schematic representation of a fuel cell stack enclosed by an assumed enclosed space showing various oxygen consumption methods and an oxygen replenishment method that can be used to calculate a calculated O2 concentration of the assumed enclosed space over time according to the practices of the present description; Fig. Figure 2 is a graphical representation illustrating four different scenarios in which the operation of a fuel cell stack can affect the calculated O2 concentration of the assumed enclosed space according to the practices of the present description, where the y-axis is the calculated O2 concentration in mole percent and the x-axis is time in seconds; Fig. 3 is a flowchart illustrating an approach for determining whether a vehicle is in a stationary state according to the practices of the present description; Fig. 4 is a flowchart illustrating another approach for determining whether a vehicle is in a stationary state, in accordance with the practices of the present description; Fig. 5 is a graphical representation plotting the calculated O2 concentration within the assumed enclosed space over time for comparing the calculated O2 concentration against a set of established O2 concentration problem levels while the vehicle remains in the stationary state according to the practices of the present description, where the y-axis is the calculated O2 concentration in mole percent and the x-axis is time in seconds; Fig. 6 is also a graphical representation plotting the calculated O2 concentration within the assumed enclosed space over time for comparing the calculated O2 concentration against a series of established O2 concentration problem levels while the vehicle remains in the stationary state according to the practices of the present description, where the y-axis is the calculated O2 concentration in mole percent and the x-axis is time in seconds; and Fig. 7 is a flowchart illustrating how the described method including the conditional operating mode of the fuel cell stack may be performed by the vehicle.

[0023] Hydrogen is an attractive fuel for powering a vehicle because it is clean and can be used to efficiently generate electricity in a fuel cell. A number of individual PAM fuel cells, which consume hydrogen as part of an electrochemical reaction that produces electrical power, are typically combined in a fuel cell stack (FCS) to produce the desired power to power a vehicle. For example, a typical FCS for a vehicle may have two hundred or more stacked PAM fuel cells. The FCS typically receives a stream of hydrogen gas and a stream of an oxidizer gas, such as air or oxygen, and then distributes each of these reactant gases to the anode catalyst layers and cathode catalyst layers, respectively, of the various PAM fuel cells via bipolar plates separating the PAM fuel cells.The FCS therefore consumes both hydrogen and oxygen during normal operation.

[0024] In some types of enclosed spaces (e.g., a garage), oxygen from the air in the local environment may be consumed by the FCS faster than it is replenished. To address this problem, a method including a conditional operating mode of the FCS may be implemented when a vehicle 10 powered by a FCS 12 is in a stationary state, as schematically shown in Fig. 1. In particular, and as shown in the diagram of Fig. 1, the conditional mode of operation requires that the vehicle 10 be treated as if it were contained within an enclosed space, referred to herein as a "presumed enclosed space" and identified by reference numeral 14, whenever the vehicle 10 is determined to be in a stationary state. The presumed enclosed space 14 is thus a virtual enclosure with a volume that may or may not be large enough to contain the vehicle 10. This space 14 is used to model the amount of O2 in the volume of the presumed enclosed space 14 based on the operation of the FCS 12 and the pressure and temperature of the presumed enclosed space 14, which may be estimated, measured, or simply assigned.In this regard, the assumed enclosed space 14 and the calculated amount of O2 within that space 14 is designed to conservatively model what would happen if the vehicle 10 were actually contained within an enclosed space, such as a garage, although this is not always the case, and to perform response actions based on the O2 concentration calculated within the assumed enclosed space 14 to ensure that the O2 concentration in an actual enclosed space is not overly depleted.

[0025] Fig. Figure 1 schematically illustrates how oxygen is consumed and replenished in the assumed enclosed space 14, which may be sized to be just large enough to surround the vehicle 10 according to the definition of a "small garage" in SAE J 2578, 3rd Edition (August 2014). The size and volume of the assumed enclosed space 14 may vary depending on the size of the vehicle 10. Instead of the SAE J 2578 standard, other standards (e.g., ISO standard, JIS standard, local regulations, etc.) may be used to define the size of the assumed enclosed space 14, if desired, or the assumed enclosed space 14 may be an approximation of an actual surrounding enclosure, the dimensions of which can be evaluated and estimated using machine vision systems or LIDAR. Furthermore, the assumed enclosed space 14 may simply be predefined.However, in many cases, regardless of how the assumed enclosed space 14 and its volume are determined, the assumed enclosed space 14 may have a volume of 5 m. 3 up to 200 m 3 or, more precisely, from 20 m 3 up to 50 m 3 Additionally, a temperature and pressure in the space 14 may be calibrated or assigned based on measured atmospheric ambient conditions to account for the amount and concentration of O2 to be modeled in the assumed enclosed space 14. For example, in one implementation, the temperature and pressure of the assumed enclosed space may be set to 60°C and 1 atmosphere for simplicity.

[0026] When the vehicle 10 containing the FCS 12 is in the stationary state, the FCS 12 can consume oxygen in several ways, which can reduce the O2 concentration in the assumed enclosed space 14. In a first method 16, the FCS 12 consumes O2 from the volume of the assumed enclosed space 14 while simultaneously consuming H2 to generate an electric current. The general cathode half-reaction for consuming O2 and generating water, the general anode half-reaction for consuming H2 and generating an electron flow, and the overall reaction of the fuel cells in the FCS 12 are shown below: Anode: 2H2 → 4H + + 4e - Cathode: O2 + 4H + + 4e - → 2H2O Total: 2H2 + O2 → 2H2O

[0027] For this purpose, the molar flow of O2 (ṅ O2) required to support the generation of a given electrical current (I) by the FCS 12 for the operation of the various vehicle systems can be calculated continuously over time while the vehicle 10 is in the stationary state by the following equation: n˙O2=I∗CELL4∗F I: Stack current N ZELLE : Number of cells in the stack 4: Number of electrons per O2 molecule F: Faraday's constant, 96485 C / mol

[0028] In a second process 18, the FCS 12 consumes O2 from the volume of the assumed enclosed space 14 to support the cathode catalytic heating (CCH) of the FCS 12. During CCH, H2 is circulated around the polymer electrolytes and delivered along with O2 to the cathode catalyst layers of the FCS 12 to facilitate the combustion of the H2. The heat generated at the cathode catalyst layers as a result of the combustion of H2 is then used to heat the FCS 12 to its optimal operating temperature range and, if desired, also to heat the passenger compartment of the vehicle 10. The CCH is thus useful when the vehicle 10 is started, particularly in cold or subzero temperatures after the vehicle 10 has been in an inoperative state for an extended period. The molar flow rate of O2 (ṅ O2) required to support the CCH can be calculated continuously over time while the vehicle 10 is in the stationary state by the following equation: n˙O2=Q∗0.5LHVH2 Q: Heat generation LHV L2 : Lower heating value of hydrogen (242 kJ / mol) 0.5: Number of O2 molecules per H2 molecule

[0029] In a third method 20, the FCS 12 consumes O2 from the volume of the assumed enclosed space 14 to support stack voltage recovery (SVR) of the FCS 12. During SVR operation, the FCS 12 runs at a low voltage to remove pollutant deposits and / or contaminants from the catalyst layers and / or the solid polymer electrolyte within the stack (e.g., sulfate deposition). Water then flushes away the contaminants. An SVR cycle is typically implemented during vehicle start-up, and the molar flow of O2 (ṅ O2 ) required to support one SVR cycle can be calculated continuously over time while the vehicle 10 is in the stationary state, using the same equation as set forth above for drawing electrical current (I).

[0030] Other factors can also affect the amount of O2 present within the assumed enclosed space 14, besides the direct consumption of O2. For example, in some cases, the O2 concentration in the assumed enclosed space 14 may be further reduced based on the output of unreacted H2 from the FCS 12, which can dilute the O2 and lower its concentration. The effect of O2 dilution is generally negligible compared to the direct consumption of O2 by stack power generation, CCH, and SVR and, for this reason, can normally be ignored when calculating the O2 of the assumed enclosed space 14 over time, although provisions can be made to account for O2 dilution as part of the overall process if necessary.

[0031] The assumed enclosed space 14 is also enriched with air from an air / exchange ratio 22 located outside the assumed enclosed space 14. The air / exchange rate 22 can be set to any value to adjust the modeling of the O2 concentration within the assumed enclosed space 14 as desired. In one embodiment, according to the incorporated SAE J 2578 standard, the air / exchange rate 22 can be 0.03 air exchanges / hour, which means that 3% of the air by volume in a given space is renewed every hour. Of course, the air / exchange rate 22 is calibratable and can be set higher or lower than 0.03 air exchanges / hour.By knowing the volume, temperature, pressure, and original O2 concentration of the assumed enclosed space 14, as well as the amount of O2 consumed by the processes 16, 18, 20 and renewed by the air / exchange rate 22, the amount and concentration of O2 in the assumed enclosed space 14 during the time the vehicle 10 is in the stationary state can be calculated or modeled over time, and the FCS 12 is operated using the ideal gas law or another suitable equation or algorithm. This information can be used to communicate the conditional operating mode of the FCS 12 and to trigger certain actions related to the operation of the FCS 12 when the modeled O2 concentration of the assumed enclosed space 14 exceeds certain predetermined O2 concentration problem levels.

[0032] With current reference to Fig. Figure 2 shows a graphical representation illustrating several different operating scenarios of the FCS 12, where the y-axis represents a calculated O2 concentration in mole percent of the assumed enclosed space 14 and the x-axis represents time in seconds. The volume of the assumed enclosed space 14 is that specified in the SAE J 2578 standard. Additionally, the air exchange rate 22 is set to 0.03 air exchanges / hour, the temperature and pressure within the assumed enclosed space 14 are set to 60°C and 1 atmosphere, respectively, and the O2 concentration of the assumed enclosed space 14 is set to the standard atmospheric O2 concentration of 21 mole percent at the time the vehicle 10 incorporating the FCS 12 is determined to be in the stationary state.It is assumed that the power generation process 16, the CCH process 18, and the SVR process 20 all consume O2 from the assumed enclosed space 14, as described above. The graphical representation here is intended to illustrate how certain operating scenarios of the FCS 12 can consume the modeled O2 concentration within the assumed enclosed space 14 and how quickly such depletion can occur.

[0033] In Fig. 2 illustrates four specific operating scenarios of the FCS 12. In a first scenario, identified by reference numeral 30, a 200-second warm-up cycle 32 is performed using the CCH process 18, followed by an idle period 34 of more than 1200 seconds without executing the CCH or SVR processes 18, 20. In this scenario 30, the O2 concentration of the assumed enclosed space 14 dropped by approximately 0.7 mol% during the warm-up cycle 32, but then decreased only slightly by a further 0.1 mol% to 0.2 mol% over the longer idle period 34. In a second scenario, indicated by reference numeral 36, a 200-second warm-up cycle 38 is performed in the same manner as in the first scenario 30, followed by an idle period 40 of 1200 seconds in which the CCH method 18 was used to provide 8 kW of cabin heating.In this scenario 36, the O2 concentration of the assumed closed space 14 fell by more than 2.5 mol% after 1400 seconds.

[0034] In a third scenario, indicated by reference numeral 42, a 200-second warm-up cycle 44 is performed in the same manner as in the first and second scenarios 30, 36, followed by a 30-second SVR cycle 46 and then an idle period 48 of 820 seconds, during which the CCH process 18 was used to provide 8 kW of cabin heating. Here, the O2 concentration of the assumed enclosed space 14 dropped by more than 3.0 mol% after 1100 seconds. Finally, in a fourth scenario, indicated by reference numeral 50, two 30-second SVR cycles 52 are performed, followed by an idle period 54 of more than 1100 seconds, without executing the CCH or SVR processes 18, 20.In this scenario 50, the O2 concentration of the assumed enclosed space 14 decreased by about 0.5 mol% during each SVR cycle 20, but then decreased only slightly by a further 0.1 mol% to 0.2 mol% over the longer idle period 54.

[0035] Given the various ways in which the FCS 12 can consume O2 and actually affect the O2 concentration in the assumed enclosed space 14 over time, the conditional mode of operation relies on a set of programmed O2 concentration problem levels to ensure that the calculated O2 concentration of space 14 does not drop too low. However, to trigger the conditional mode of operation, the vehicle 10 powered by the FCS 12 is first determined to be in a stationary state. This can be achieved by observing certain available parameters of the vehicle 10, including its speed and / or position (using GPS coordinates), as well as by using proximity sensor(s), vision systems, and / or LIDAR to observe the surroundings of the vehicle 10, to name a few possibilities.After determining that the vehicle is in the stationary state, an O2 concentration of the assumed enclosed space 14 is calculated over time as described above in connection with the . Fig. 1-2, while the vehicle 10 is in the stationary state. The calculated O2 concentration of the assumed enclosed space 14 is then compared over time to a set of predetermined O2 concentration problem levels. Based on this ongoing comparison, the conditional operating mode can limit certain operations of the FCS 12, as further explained below.

[0036] Determining whether the vehicle 10 is in a stationary state may be performed by taking into account the speed of the vehicle 10. For example, and with reference to Fig. 3, an approach 60 for determining when the vehicle 10 is in a stationary state is shown in a flowchart. The approach 60 begins at box 62. At box 64, the approach 60 includes determining whether the vehicle is moving at a speed indicative of a stationary state. In one embodiment, a speed less than or equal to 5 km / h may be programmed to indicate a stationary state. In another, narrower embodiment, the vehicle 10 may only be considered to be in a stationary state when the vehicle is stationary (i.e., a speed of 0 kilometers / hour). If the stationary state speed condition is not met, the approach 60 proceeds via arrow 66 to box 68 where it is determined that the vehicle 10 is not in a stationary state and, therefore, the conditional mode of operation is not initiated.If the speed condition for a stationary state is met, the approach proceeds through arrow 70 to box 72 where it is determined that the vehicle 10 is in a stationary state and the conditional operating approach is initiated until the vehicle 10 is no longer in a stationary state.

[0037] Another more robust approach 74 for determining when the vehicle 10 is in a stationary state, which in Fig. 4 as a flow chart, may be carried out taking into account the speed and position of the vehicle 10. This approach begins in box 76. In box 78, the approach includes determining whether the vehicle is moving at a speed indicating a stationary condition, in the same manner as before in connection with Fig. 3. If the speed condition for a stationary state is not met, the approach 74 proceeds via arrow 80 to box 82, where it is determined that the vehicle 10 is not in a stationary state and the conditional operating mode is therefore not initiated. However, if the speed condition for a stationary state is met, the approach 74 proceeds via arrow 84 to box 86, where GPS coordinates of the vehicle 10 are referenced to determine if the vehicle 10 is on a road (e.g., a highway). If the vehicle 10 is on a road, the approach proceeds via arrow 88 to box 90, where it is determined that the vehicle 10 is not in a stationary state and the conditional operating mode is therefore not initiated.If the vehicle 10 is not on a road, the approach proceeds via arrow 92 to box 94 where it is determined that the vehicle 10 is in a stationary state and the conditional operating approach is initiated until the vehicle 10 is no longer in the stationary state.

[0038] If it is determined that the vehicle is in a stationary state, either by one of the approaches 60, 74 described above or by another approach, the O2 concentration of the assumed enclosed space 14 is calculated over time while the vehicle 10 remains in the stationary state. This may involve first adjusting the O2 concentration of the assumed enclosed space 14 to the standard atmospheric O2 concentration of 21 mol% at the time the vehicle 10 including the FCS 12 is determined to be in a stationary state, and subsequently adjusting the O2 concentration of the assumed enclosed space 14 based on the amount of O2 consumed by the FCS 12 over time and the amount of O2 renewed in the assumed enclosed space 14 over time.The amount of O2 consumed by the FCS 12 over time and an amount of O2 renewed into the assumed enclosed space 14 over time can be readily calculated using the O2 consumption method 16, 18, 20 and the air / exchange rate 22 described above in conjunction with the . Fig. 1-2. Furthermore, by knowing the volume, temperature, and pressure of the assumed enclosed space 14—each of which can be specified in various ways as explained above—the O2 concentration within the assumed enclosed space 14 can be continuously calculated.

[0039] Referring to Fig. 5, the calculated O2 concentration within the assumed enclosed space 14 is compared over time with a set of established O2 concentration problem levels, as long as the vehicle 10 remains in the stationary state. Here, in this figure, the calculated O2 concentration (y-axis) is labeled with the reference numeral 96 and is plotted against time in seconds (x-axis). The set of O2 concentration problem levels is also shown in this figure and includes a first O2 concentration problem level 98 and a second O2 concentration problem level 100. The first O2 concentration problem level 98 is less than a standard O2 concentration (i.e., less than 21%), and the second O2 concentration problem level 100 is less than the first O2 concentration problem level 98.For example, the first O2 concentration problem level 98 may be less than 21 mol% and more than 19 mol%, and the second O2 concentration problem level 100 may be less than 20 mol% and more than 18 mol%. In a specific example, as shown, the first O2 concentration problem level 98 may be set to 20 mol% and the second O2 concentration problem level 100 may be set to 19 mol%.

[0040] The conditional operating mode of the BZS 12 performs its function based on the comparison of the calculated O2 concentration 96 within the assumed enclosed space 14 against the set of established O2 concentration problem levels. As long as the calculated O2 concentration 96 within the assumed enclosed space 14 remains above the first O2 concentration problem level 98, which is Fig. 5 between 0 seconds and approximately 340 seconds, the FCS 12 may be operated without restriction, meaning that all of its oxygen-consuming processes 16, 18, 20 are enabled and may be operated individually or in combination to support the requirements of the vehicle 10. In particular, the power generation process 16 may supply any required current (I) required by the vehicle 10, warm-up and cabin heating may be performed as enabled by the CCH process 18, and cycles of the SVR process 20 may be performed as desired.

[0041] If the calculated O2 concentration 96 at a time reaches the first O2 concentration problem level 98, which is Fig. 5 occurs at approximately 340 seconds, the BZS 12 is limited to operating in a low power state where the BZS 12 outputs no more than 15% of its maximum power output in order to slow the rate at which the calculated O2 concentration 96 decays. This may result in the BZS 12 being limited to a maximum power output of 8 kW. In a particular example of a low power state, the BZS 12 may be at idle. At idle, the BZS 12 provides current (I) to drive its associated prime mover, typically an electric motor, which may or may not be coupled to an internal combustion engine, and its accessories without any applied loads. Essentially, the power generation method 16 is ready for operation so that the BZS 12 can supply enough current (I) to drive the prime mover while the prime mover is not coupled to the driveline and the foot pedal is not depressed.Each of the CCH method 18 and the SVR method 20 may also be deactivated. Operating the FCS 12 in the low power state, particularly in idle mode with the CCH and SVR methods 18, 20 deactivated, results in a fairly constant and minimal reduction in the calculated O2 concentration 96 over time and allows the calculated O2 concentration 96 to remain above the second O2 concentration problem level 100 for a longer period of time. In the example of FIG. Fig. 5, for example, the calculated O2 concentration 96 will not reach the second O2 concentration problem level 100 for approximately another 9,000 seconds (~ 2.6 hours or 9,350 seconds since the vehicle entered the stationary state) when the vehicle 10 is idling and the CCH and SVR methods 18, 20 are deactivated.

[0042] Should the calculated O2 concentration 96 reach the second O2 concentration problem level 100, which as mentioned in the example of Fig. 5 occurs at approximately 9,350 seconds, the BZS 12 is shut down to stop all oxygen-consuming processes 16, 18, 20 and thus prevent a further decrease in the calculated O2 concentration 96. In this regard, since only the air exchange rate 22 affects the amount of O2 in the assumed enclosed space 14, the calculated O2 concentration 96 should begin to rise until it eventually reaches the standard atmospheric O2 concentration of 21 mol%.By operating the FCS 12 in a low power state when the calculated O2 concentration 96 is equal to or less than the first O2 concentration problem level 98 but greater than the second O2 concentration problem level 100, and shutting down the FCS 12 when the calculated O2 concentration 96 is equal to or less than the second O2 concentration problem level 100, the conditional mode of operation of the FCS 12 provides an orderly and controlled method to ensure that the FCS 12 does not over-deplete the available O2 in an actual enclosed space, such as a garage, if and when the vehicle 10 is in such a space, while at the same time not burdening the use of the FCS 12 with disruptive actions when the vehicle 10 is not in an actual enclosed space, but is nevertheless in a stationary state.

[0043] The capacity of the conditional operating mode of the BZS 12 to avoid disruptive actions - especially unnecessary shutdowns of the BZS 12 - is in Fig. 6. Here, the calculated O2 concentration 96 of the assumed enclosed space 14 is plotted against time when it has been determined that the vehicle 10 is in a stationary state, even though the vehicle 10 is not actually parked in an actual enclosed space, but is instead in a traffic jam where shutdown of the FCS 12 is not desired. And since the program managing the overall process, including the conditional operation mode of the FCS 12, may not be able to distinguish between parking in an actual garage or being in a traffic jam, since the speed of the vehicle 10 may be 0 km / h in both cases, the FCS 12 is subjected to the conditional operation mode by default, even though the reason for implementing the conditional operation mode is not given.

[0044] As can be seen, and with further reference to Fig. 6, it is determined that the vehicle 10 is in a stationary state due to a traffic jam at approximately 60 seconds, which is more likely if determining a stationary state is based on the speed of the vehicle 10, as in connection with Fig. 3. The FCS 12 operates in a traffic jam without restriction for approximately another 190 seconds (just over three minutes) until the calculated O2 concentration 96 of the assumed enclosed space 14 reaches the first O2 concentration problem level 98, which has been set to 20 mol%. At this time, and if the vehicle 10 is still in the stationary state due to a traffic jam, the FCS 12 is limited to operation in the low power state and is preferably idled with the CCH and SVR methods 18, 20 deactivated until such time as the vehicle 10 moves to release its stationary status, which occurs after approximately another 400 seconds.In fact, the idle operation of the FCS 12 during this 400-second (just under 7 minutes) period slowed the rate of decrease of the calculated O2 concentration 96 to such an extent that the FCS 12 would be far from shutting down due to the calculated O2 concentration 96 reaching the second O2 concentration problem level 100, which was set at 19 mol%. Indeed, the FCS 12 could be idle for at least several hours before the calculated O2 concentration 96 approached the second O2 concentration problem level 100.Consequently, the use of the first O2 concentration problem level 98 to trigger the restrictive operation of the FCS 12 in the low power state should prevent a nuisance shutdown of the FCS 12, since the amount of time the FCS 12 can operate in such a state before triggering a shutdown will almost certainly outlast any period of time that the vehicle 10 may be in a stationary state due to traffic congestion or otherwise.

[0045] The various operations required to manage the overall process, including the conditional operating mode of the BZS 12, can be programmed into a standard vehicle electronic control unit or other control system that controls the operation of the vehicle and / or the BZS 12. Such programming can, for example, be Fig. 7. In the flowchart shown, a program that executes the overall method begins in box 102. In box 104, the program calculates the volume of the assumed enclosed space 14 to be used to carry out the method. Subsequently, in box 106, the program determines whether the vehicle 10 is in a stationary state, such as described above in connection with the Fig. 3-4. If it is determined that the vehicle 10 is not in a stationary state, the program proceeds to box 110 by arrow 108. In box 110, the program resets the O2 concentration of the assumed enclosed space 14 to the standard atmospheric concentration of 21 mol%, thereby avoiding the conditional mode of operation, and then proceeds through boxes 106 and 110 until it is determined that the vehicle 10 is in a stationary state.

[0046] If it is determined in box 106 that the vehicle 10 is in a stationary state, the program follows arrow 112 to box 114, where the calculated O2 concentration 96 of the assumed enclosed space 14 is calculated based on a series of sub-calculations, including calculating the consumption of O2 in the assumed enclosed space 14 due to the power generation method 16, box 116, calculating the consumption of O2 in the assumed enclosed space 14 due to the CCH method 18, box 118, calculating the consumption of O2 in the assumed enclosed space 14 due to the SVR method 20, box 120, and calculating the replenishment of O2 in the assumed enclosed space 14 due to the air / exchange rate 22, box 122, all using a selected temperature (e.g., 60°C) and a selected print (e.g.1 atmosphere) of the assumed enclosed space 14 and an initial O2 concentration corresponding to the standard atmospheric O2 concentration (e.g., 21 mol%). The program then follows arrow 124 to box 126, where the calculated O2 concentration 96 of the assumed enclosed space 14 is compared with the first O2 concentration problem level 98. If the calculated O2 concentration 96 of the assumed enclosed space 14 is greater than the first O2 concentration problem level 98, the program advances through arrow 128 and continues to cycle through boxes 106, 114, and 126, thereby operating the FCS 12 without restriction until the program indicates in box 124 that the calculated O2 concentration 96 has reached the first O2 concentration problem level 98.

[0047] When the calculated O2 concentration 96 reaches the first O2 concentration problem level 98, as indicated in box 124, the program proceeds by arrow 130 to box 132. In box 132, the FCS 12 operates in a low power state, as described above, which may include idling the FCS 12 and deactivating both the CCH process 18 and the SVR process 120. The program then proceeds by arrow 134 to box 136, where the calculated O2 concentration 96 is compared to the second O2 concentration problem level 100.If the calculated O2 concentration 96 of the assumed enclosed space 14 is greater than the second O2 concentration problem level 100, the program proceeds by arrow 138 and continues to cycle through boxes 106, 114, 126, and 136, limiting the operation of the FCS 12 to the low power state until the program indicates in box 136 that the calculated O2 concentration 96 has reached the second O2 concentration problem level 100. When the calculated O2 concentration 96 has reached the second O2 concentration problem level 100, as indicated in box 136, the program proceeds by arrow 140 to box 142. In box 142, the FCS 12 is shut down.If at any time in box 106 the program determines that the vehicle 10 is no longer in a stationary state and the FCS 12 has not been shut down, full unrestricted operation of the FCS 12 is restored and the calculated O2 concentration 96 of the assumed enclosed space 14 is reset to the standard atmospheric concentration of 21 mol%.

[0048] The system(s) and methods discussed herein offer advantages over simple timing systems that perform a specific action (e.g., turn off the FCS) after a certain time. Calculating the estimated O2 concentration of the assumed enclosed space 14 over time and comparing this value to the set of O2 concentration problem levels 98, 100 allows for corrective actions to be taken regarding the operation of the FCS 12 that would not be available with a simple countdown-type timing system. Additionally, a countdown-type timing system may result in nuisance shutdowns of the FCS 12, which can be avoided by the method described herein.

Claims

[1] A method for operating a fuel cell stack (12), the method comprising: Determining (106) when a vehicle (10) powered by the fuel cell stack (12) is in a stationary state; Calculating (114) an O2 concentration of an assumed closed space (14) over time while the vehicle (10) is in the stationary state; Establishing a set of O2 concentration problem levels (98, 100) comprising a first O2 concentration problem level (98) being less than a standard O2 concentration and a second O2 concentration problem level (100) being less than the first O2 concentration problem level (98); Comparing (126, 136) the O2 concentration of the assumed closed space (14) over time with the set of O2 concentration problem levels (98, 100); and Operating the fuel cell stack (12) without restriction when the vehicle (10) is in the stationary state as long as the O2 concentration of the assumed enclosed space (14) remains greater than the first O2 concentration problem level (98); the method further comprising operating (132) the fuel cell stack, BZS, in a low power state when the O2 concentration of the assumed enclosed space (14) is equal to or less than the first O2 concentration problem level (98) but greater than the second O2 concentration problem level (100). [2] The method of claim 1, wherein the step of determining when the vehicle (10) powered by the fuel cell stack (12) is in a stationary state comprises determining that a speed of the vehicle (10) is less than or equal to five km / h. [3] The method of claim 2, wherein the step of determining when the vehicle (10) powered by the fuel cell stack (12) is in a stationary state comprises determining whether the vehicle (10) is stationary. [4] The method of claim 1, wherein the step of determining when the vehicle (10) powered by the fuel cell stack (12) is in a stationary state comprises determining that the vehicle (10) is stationary and that GPS coordinates of the vehicle (10) indicate that the vehicle (10) is not on a road. [5] The method of claim 1, wherein the step of calculating the O2 concentration of the assumed enclosed space (14) over time comprises setting the O2 concentration of the assumed enclosed space (14) at atmospheric standard O2 concentration when first determining that the vehicle (10) is in a stationary state, and thereafter setting the O2 concentration of the assumed enclosed space (14) based on an amount of O2 consumed by the fuel cell stack (12) over time and an amount of O2 replaced over time in the assumed enclosed space (14). [6] The method of claim 1, wherein the first O2 concentration problem level (98) is less than 21 mol% and more than 19 mol%, and the second O2 concentration problem level (100) is less than 20 mol% and more than 18 mol%. [7] The method of claim 1, wherein the step of operating the fuel cell stack (12) comprises, without limitation, operating the fuel cell stack (12) with activated cathode catalytic heating, CCH, and stack voltage recovery, SVR, processes. [8] The method of claim 1, further comprising shutting down the fuel cell stack (12) when the O2 concentration of the assumed enclosed space (14) is equal to or less than the second O2 concentration problem level (100). [9] A method for operating a fuel cell stack (12), the method comprising: Determining (106) when a car (10) powered by a fuel cell stack (12) is in a stationary state; Calculating (114) an O2 concentration of an assumed closed space (14) enclosing the vehicle (10) over time while the vehicle (10) is in the stationary state; Comparing (126, 136) the O2 concentration of the assumed enclosed space (14) over time with a set of O2 concentration problem levels (98, 100) comprising a first O2 concentration problem level (98) and a second O2 concentration problem level (100), wherein the first O2 concentration problem level (98) is less than 21 mol% and more than 19 mol% and the second O2 concentration problem level (100) is less than 20 mol% and more than 18 mol%; and Operating the fuel cell stack (12) when the vehicle (10) is in the stationary state according to a conditional operating mode, comprising: Operating the fuel cell stack (12) without restriction when the vehicle (10) is in the stationary state as long as the O2 concentration of the assumed enclosed space (14) remains greater than the first O2 concentration problem level (98); Operating the fuel cell stack (12) at idle when the O2 concentration of the assumed enclosed space (14) is equal to or less than the first O2 concentration problem level (98) but greater than the second O2 concentration problem level (100); and Switching off (142) the fuel cell stack (12) when the O2 concentration of the assumed closed space (14) is equal to or less than the second O2 concentration problem level (100).

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