JP2007115441A - FUEL CELL DIAGNOSIS METHOD AND FUEL CELL SYSTEM USING THE DIAGNOSIS METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lengthen a service life of a fuel cell by obtaining the advancing degree of carbon corrosion or the like after stop of power generation of a fuel cell. <P>SOLUTION: The diagnosis of the advancing degree of the deterioration of the fuel cell after the stop of power generation is conducted on the basis of a parameter relating to the advancing degree of deterioration of the fuel cell. As the parameter, the concentration of CO<SB>2</SB>in the outlet of a cathode can be used. Based on the diagnostic result, anode pressure is set higher than that during stop, or the temperature of cooling water of the fuel cell is set lower than that during stop. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell diagnosis method and a fuel cell system using the diagnosis method. More specifically, the present invention relates to an improvement in technology for suppressing deterioration of electrodes and the like of fuel cells.

  After the power generation of the fuel cell is stopped, the cathode electrode or the catalyst provided on the electrode may be deteriorated by the influence of the reaction gas (for example, hydrogen gas) remaining inside the fuel cell. Such deterioration of the electrodes and the like is undesirable because it leads to a decrease in power generation efficiency.

Therefore, conventionally, in order to prevent electrode degradation and power generation efficiency from being reduced, hydrogen consumption is continued inside the fuel cell even after power generation is stopped, and the process after power generation stop (stop processing) is performed to reduce the amount of residual gas. ) Is executed (see, for example, Patent Document 1).
JP 2005-85477 A

  However, the conventional stop processing is not sufficient from the following viewpoints.

  That is, although there is a desire to grasp the degree of progress of carbon corrosion after stopping, there has been no means for that purpose in the past. In other words, after power generation is stopped (for example, after the anode gas supply is stopped), the cathode electrode is prevented from deteriorating by consuming hydrogen, but the degree of progress of carbon corrosion or the like has not been fully understood. .

  Accordingly, the present invention provides a method for diagnosing a fuel cell that makes it possible to grasp the degree of progress of carbon corrosion after the power generation of the fuel cell is stopped, thereby improving the life of the fuel cell, and a fuel cell using the diagnostic method. The purpose is to provide a system.

  In order to solve this problem, the present inventor has made various studies. First, if the degree of progress of corrosion after power generation stoppage can be diagnosed and understood directly, the results can be used for processing after power generation stoppage (stopping processing), thereby extending the life of the electrode (prolonging life). Can be achieved. In addition, when examining the fuel cells that are actually used, not only there are individual differences by specification and manufacturing status, but naturally there are also individual differences in the usage status after manufacturing. It has been found that it is desirable to execute individual specific stop processing in consideration of the current state of individual fuel cells and individual differences, from the viewpoint of improving the service life, instead of executing specific stop processing.

Further, for example, if the exhaust state of the fuel cell is used as a parameter (specifically, for example, CO ₂ concentration is used as a parameter), the deterioration state is diagnosed, and processing for suppressing deterioration is executed as necessary based on the diagnosis result. As a result, the inventors have come to know that it is possible to extend the life of the fuel cell. According to this, it is possible not only to stop processing as in the prior art, but also to improve the life while reflecting the state of deterioration at that time individually and specifically.

The present invention is based on such knowledge, and the invention according to claim 1 is a fuel cell diagnosis method for diagnosing the degree of progress of deterioration of a fuel cell that proceeds after power generation is stopped, and the degree of progress of deterioration of the fuel cell. It is characterized by making a diagnosis based on parameters related to. The parameter in this case can be, for example, the concentration of CO ₂ at the outlet of the cathode electrode.

Based on the above knowledge, the present inventor has come up with the idea of knowing the state of the fuel cell as a parameter, for example, the amount of CO _{2 in} the exhaust gas. That is, after knowing that the CO ₂ concentration becomes high as an example after the power generation stop (operation stop) of the fuel cell, the idea of diagnosing the degree of progress of deterioration using this CO ₂ as a parameter has been obtained. In such a case, it is possible to diagnose and grasp the deterioration state of the fuel cell every time the power generation stop process, in other words, to learn the deterioration state of each fuel cell and to carry out optimal control. It is possible to suppress the progress of deterioration after absorbing individual differences in the fuel cell. Moreover, since the deterioration value can be detected and grasped, a reference value can be set according to the detection result, and processing for extending the life (or extending the life) can be performed. Very suitable. Note that “power generation stop” in this specification means a state where power generation is stopped (or after that), and is a concept including, for example, stop of gas supply for power generation.

In this diagnosis method, as described in claim 3, it is preferable to make a diagnosis based on the cumulative value of CO ₂ . Based on the accumulated value, it becomes possible to execute the processing after the power generation is stopped in consideration of the accumulated situation, not the instantaneous situation of the fuel cell.

  Furthermore, the fuel cell system according to the invention described in claim 4 performs processing for suppressing deterioration of the fuel cell based on a diagnosis result by the fuel cell diagnosis method according to any one of claims 1 to 3. It is to execute.

  In this case, as described in claim 5, the back pressure after the next power generation stop can be reset. For example, it is possible to further suppress deterioration by controlling the hydrogen consumption pressure that causes the cathode pressure to decrease during hydrogen consumption. Furthermore, in this case, as described in claim 6, it is preferable to reset the anode pressure in the fuel cell to a value higher than that in the previous stop process. By resetting the anode pressure to a higher value according to the specific situation in the fuel cell, the backflow of air to the anode side in the fuel cell is prevented to suppress oxidation, and the electrode deteriorates and the power generation efficiency decreases. Can be suppressed.

Further, when executing the process for suppressing deterioration of the fuel cell, as described in claim 7, the temperature of the cooling water for the fuel cell after the next power generation stop can be reset. In this case, it is preferable to reset the coolant temperature of the fuel cell to a value lower than that in the previous stop process. For example, when the cooling water temperature is lowered, the amount of CO ₂ generated can be suppressed, and as a result, the life of the fuel cell can be extended.

  According to a ninth aspect of the present invention, the processing in the fuel cell system according to any one of the fourth to eighth aspects is performed after the scavenging process is performed after the power generation of the fuel cell is stopped.

  According to the fuel cell diagnosis method and the fuel cell system using the diagnosis method as described above, it is possible to grasp the degree of progress of carbon corrosion and the like after the fuel cell power generation is stopped, thereby improving the life of the fuel cell. It becomes possible.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

  1 to 5 show an embodiment of a fuel cell system according to the present invention. The fuel cell system according to the present embodiment performs diagnosis based on parameters related to the degree of progress of deterioration of the fuel cell, and executes processing for suppressing deterioration based on the result of the diagnosis. In the following, the outline of the fuel cell system 10 in the present embodiment will be described first. In the following, the fuel cell may be expressed as “FC”.

  FIG. 1 shows a schematic configuration of a fuel cell system 10 according to the present embodiment. The fuel cell system 10 shown in the present embodiment can be used as, for example, an on-vehicle power generation system of a fuel cell vehicle (FCHV; Fuel Cell Hybrid Vehicle), but is not limited to this, and various mobile objects (for example, ships) Naturally, it can also be used as a power generation system mounted on a self-propelled device such as a robot or a robot. A fuel cell stack (hereinafter also referred to as “fuel cell stack” or simply “fuel cell”) 20 has a stack structure in which a plurality of single cells are stacked in series. For example, a solid polymer electrolyte type It consists of a fuel cell and the like.

  In addition, the fuel cell system 10 according to the present embodiment includes a fuel cell (hereinafter referred to as a fuel cell stack, which is indicated by reference numeral 20 in the drawing) that generates power upon receiving the supply of fuel gas, and fuel gas is supplied to the fuel cell stack 20. A fuel gas system 3 to be supplied and discharged, a pressure regulating valve provided in the fuel gas system 3, a pressure sensor for detecting pressure in a closed space formed in the fuel gas system 3, and a fuel gas system 3 are formed. The system includes a gas leakage determination unit that determines gas leakage in a closed space (see FIG. 1).

  Further, the fuel cell system 10 includes a fuel gas circulation supply system (this is referred to as “fuel gas system” in this specification) 3 and an oxidizing gas supply system 4 connected to the fuel cell stack 20. Among these, the fuel gas system 3 supplies and discharges fuel gas to and from the fuel cell stack 20. For example, in this embodiment, the fuel gas supply source 30, the fuel gas supply path 31, and the fuel gas circulation The structure includes the passage 32 and the anode off-gas passage 33 (see FIG. 1).

  The fuel gas supply source 30 is configured by a hydrogen storage source such as a high-pressure hydrogen tank or a hydrogen storage tank, for example. The fuel gas supply path 31 is a gas flow path for guiding the fuel gas discharged from the fuel gas supply source 30 to the anode (fuel electrode) of the fuel cell stack 20, and the tank valve extends from upstream to downstream in the gas flow path. H201, high pressure regulator H9, low pressure regulator H10, hydrogen supply valve H200, and FC inlet valve H21 are provided. The fuel gas compressed to a high pressure is reduced to a medium pressure by a high pressure regulator H9 and further reduced to a low pressure (normal operating pressure) by a low pressure regulator H10.

  The fuel gas circulation path 32 is a return gas flow path for returning unreacted fuel gas to the fuel cell stack 20, and the gas flow path includes an FC outlet valve H22, a hydrogen pump 63, and a check valve from upstream to downstream. Each H52 is disposed. The low-pressure unreacted fuel gas discharged from the fuel cell stack 20 is appropriately pressurized by the hydrogen pump 63 and guided to the fuel gas supply path 31. The check valve H52 suppresses the backflow of the fuel gas from the fuel gas supply path 31 to the fuel gas circulation path 32. The anode off-gas flow path 33 branched in the middle of the fuel gas circulation path 32 is a gas flow path for exhausting the hydrogen off-gas discharged from the fuel cell stack 20 to the outside of the system, and the gas flow path includes a purge valve. H51 is provided.

  The tank valve H201, the hydrogen supply valve H200, the FC inlet valve H21, the FC outlet valve H22, and the purge valve H51 described above are used to supply or shut off the fuel gas to the gas flow paths 31 to 33 or the fuel cell stack 20. For example, an electromagnetic valve is used. As such an electromagnetic valve, for example, an on / off valve or a linear valve capable of linearly adjusting the valve opening degree by PWM control is suitable.

  The oxidizing gas supply system 4 of the fuel cell stack 20 includes an air compressor (oxidizing gas supply source) 40, an oxidizing gas supply channel 41, and a cathode off-gas channel 42 (see FIG. 1). The air compressor 40 compresses air taken from outside air through the air filter 61 and supplies the compressed air as an oxidizing gas to the cathode (oxygen electrode) of the fuel cell stack 20. The oxygen off-gas after being subjected to the cell reaction of the fuel cell stack 20 flows through the cathode off-gas flow path 42 and is exhausted outside the system. Since this oxygen off gas contains moisture generated by the cell reaction in the fuel cell stack 20, it is in a highly moist state. The humidification module 62 exchanges moisture between the low wet state oxidizing gas flowing through the oxidizing gas supply path 41 and the high wet state oxygen off gas flowing through the cathode off gas flow path 42, and is supplied to the fuel cell stack 20. Humidify the gas moderately. The back pressure of the oxidizing gas supplied to the fuel cell stack 20 is regulated by a pressure regulating valve A4 disposed near the cathode outlet of the cathode offgas passage 42. Further, the cathode offgas passage 42 communicates with the diluter 64 downstream thereof. Further, the anode off-gas passage 33 communicates with the diluter 64 downstream thereof, and is configured to exhaust the hydrogen off-gas outside the system after being mixed and diluted with the oxygen off-gas.

  A part of the DC power generated by the fuel cell stack 20 is stepped down by the DC / DC converter 53 and charged to the battery (secondary battery) 54. The traction inverter 51 and the auxiliary inverter 52 convert the DC power supplied from the fuel cell stack 20 and / or the battery 54 into AC power and supply the AC power to the traction motor M3 and the auxiliary motor M4, respectively. To do. Incidentally, the auxiliary motor M4 is a generic expression of a motor M2 for driving a hydrogen circulation pump 63, which will be described later, a motor M1 for driving the air compressor 40, and the like, and therefore may function as the motor M1. This means that it may function as the motor M2.

  The control unit 50 obtains the system required power (the sum of the vehicle travel power and the auxiliary power) based on the accelerator opening detected by the accelerator sensor 55, the vehicle speed detected by the vehicle speed sensor 56, etc., and the fuel cell stack 20 Control the system to match Specifically, the control unit 50 adjusts the rotation speed of the motor M1 that drives the air compressor 40 to adjust the supply amount of the oxidizing gas, and adjusts the rotation speed of the motor M2 that drives the hydrogen pump 63 to adjust the fuel gas. Adjust the supply amount. Further, the control unit 50 controls the DC / DC converter 53 to adjust the operation point (output voltage, output current) of the fuel cell stack 20 and adjust the output power of the fuel cell stack 20 to match the target power. .

  High pressure section (tank valve H201 to hydrogen supply valve H200), low pressure section (hydrogen supply valve H200 to FC inlet valve H21), FC section (stack inlet valve H21 to FC outlet valve H22), circulation section (FC outlet valve H22) To each of the check valves H52) are pressure sensors P6, P7, P9, P61, P5, P10, P11 for detecting the pressure of the fuel gas and temperature sensors T6, T7, T9, T61 for detecting the temperature of the fuel gas. , T5, T10 are arranged. The description of the role of each pressure sensor is as follows. That is, the pressure sensor P6 detects the fuel gas supply pressure of the fuel gas supply source 30. The pressure sensor P7 detects the secondary pressure of the high pressure regulator H9. The pressure sensor P9 detects the secondary pressure of the low pressure regulator H10. The pressure sensor P61 detects the pressure in the low pressure portion of the fuel gas supply path 31. The pressure sensor P10 detects the pressure on the input port side (upstream side) of the hydrogen circulation pump 63. The pressure sensor P11 detects the pressure on the output port side (downstream side) of the hydrogen circulation pump 63.

  Further, the fuel cell system 10 is provided with a fuel electrode pressure detecting means for detecting the pressure at the anode (fuel electrode). For example, in the case of the present embodiment, a pressure gauge (hereinafter referred to as “pressure sensor”) P5 provided as a sensor for detecting the pressure in the closed space formed in the fuel gas system 3 is the fuel electrode pressure detection means. Is functioning as The pressure sensor P5 of the present embodiment detects the pressure in the above-described FC section (stack inlet valve H21 to FC outlet valve H22), and thus, for example, the stack inlet, more specifically, the fuel cell stack 20 and the FC inlet valve H21. (See FIG. 1). According to the pressure sensor P5, it is possible to detect and capture a change in pressure in the closed space (in the case of the present embodiment, the above-described FC unit).

Further, an ECU (Electric Computer Unit) 13 is connected to the fuel cell stack 20 (see FIG. 1). The ECU 13 of the present embodiment can detect the CO ₂ concentration at the cathode (oxygen electrode) outlet of the fuel cell stack 20 based on the measurement result by the CO ₂ sensor (not shown).

  Further, a cooling path 73 for circulating the cooling water is provided at the inlet / outlet of the cooling water (LLC) of the fuel cell stack 20. In the cooling path 73, a temperature sensor T1 that detects the temperature of the cooling water drained from the fuel cell stack 20, a radiator (heat exchanger) C2 that radiates the heat of the cooling water to the outside, and the cooling water is pressurized and circulated. A temperature sensor T2 that detects the temperature of the cooling water supplied to the pump C1 and the fuel cell stack 20 is provided. The radiator C2 is provided with a cooling fan C13 that is rotationally driven by a motor.

  Next, a stop processing system when power generation is stopped in the fuel cell system 10 of the present embodiment will be described (see FIG. 2 and the like).

In the present embodiment, for example, in diagnosing the progress degree of deterioration of the fuel cell 20 that proceeds after the operation stop due to gas supply stop (hereinafter referred to as power generation stop as an expression including these), it is related to the deterioration progress degree of the fuel cell. Diagnosis based on the parameters to be performed. In the following, an embodiment in which the progress of deterioration is diagnosed using the CO ₂ concentration at the outlet of the cathode electrode (oxygen electrode) as a parameter will be described. In this case, the CO ₂ concentration may be a cumulative value. Moreover, it is also preferable to perform the process for suppressing deterioration shown below after the scavenging process is performed after the power generation of the fuel cell 20 is stopped.

  The processing procedure in this embodiment is as follows (see FIG. 2). First, the fuel cell 20 is stopped and a stop process is started (step 1). For example, when the fuel cell 20 is used as an on-vehicle power generation system of a fuel cell vehicle (FCHV), the operation of turning off the ignition key of the vehicle corresponds to the stop of the fuel cell 20 here.

After the start of the stop process (step 1), (in the present embodiment the storage value for this anode pressure P _A and display) the stored value of the anode pressure at the previous stop process to keep the (Step 2). The stored value P _A is that the pressure values stored in ECU 13, in this stopping process is currently in progress will perform stop processing the stored value P _A as a reference value (see FIG. 2 ). For example, if the pressure value used in the previous stop process is stored as it is without being updated, the pressure value is also used this time.

Then, it waits until predetermined time passes (step 3). Here, the predetermined time is a time until the CO ₂ concentration in the vicinity of the cathode outlet becomes stable to some extent or sufficiently. That is, since the CO ₂ concentration is unstable and the value is likely to fluctuate until a predetermined time elapses after the operation of the fuel cell 20 is stopped, the concentration measurement is performed after a stable state is reached. Is preferred. For example, in this embodiment, the CO ₂ concentration is measured after 2 hours have passed as one guide (see FIG. 2).

After a predetermined time (2 hours in the present embodiment) has elapsed since the stop of power generation (step 3), the CO ₂ concentration at the cathode outlet is measured (step 4). In the present embodiment, the measured value obtained as a result is set as C _B (see FIG. 2).

Subsequently, using a map (see FIG. 3), an anode pressure P _B corresponding to this value is obtained from the concentration value C _B obtained by measurement (step 5). In general, there is a correlation between the CO ₂ concentration at the cathode outlet and the anode pressure, and there is a relationship that the anode pressure increases as the CO ₂ concentration increases (in FIG. This is just a rough relationship that is roughly proportional, and does not necessarily match the actual relationship). Therefore, in this embodiment, this relationship is used, and the anode pressure P _B is obtained from a map representing the relationship (see FIG. 3).

Thereafter, the pressure value P _A of the stored the reference value described above, the comparison between the pressure value P _B determined from the map (step 6). As a result, if is larger pressure value P _A (No in step 6), the pressure value P _A, which is the storage is the current reference value and to utilize it the next time (step 7). In other words, carry-over it without updating the pressure values P _A on the basis at this stop process, and be used as a reference pressure value even when the next stop process, and ends the stop processing (step 9).

On the other hand, as a result of the comparison, if the pressure value P _B is larger than the pressure value P _A (Yes in step 6), the pressure value P _A that is the reference value for the current stop process is rewritten, and the pressure value P _B Is the reference pressure value from the next time (step 8). In other words, the stored value is updated (overwritten), in other words, the back pressure is reset, and P _B that is data reflecting the current state of the fuel cell system 1 is used as a reference value for the next stop process. When the stored value is updated, the stop process is terminated (step 9).

The rewriting of the reference value from P _A → P _{B in} step 8 will be described as follows. That is, there is a correlation between the CO ₂ concentration and the anode pressure at the cathode outlet is as described above, in this embodiment, the CO ₂ concentration at the measurement (step 4), the CO ₂ concentration than the previous Is increased from C _A to C _B, for example, according to this increase, the reference pressure value (the reference value at the time of stop processing) corresponds to C _B from P _A corresponding to C _A. Rewrite to increase to P _B (step 8). That is, the reference value of the anode pressure is increased by a predetermined amount using the CO ₂ concentration as a parameter (in some cases, a trigger). By going through this series of processing, the fuel cell system 1 is in a state of learning about the pressure reference value, and can perform processing based on the pressure value after learning in the next power generation stop processing. Expressed another way, by the CO ₂ concentration amount corresponding pressure reference value corresponding to the increase of also increasing, Based on the situation that the CO ₂ concentration increases, it is possible to set the reference value most conformity with the current situation It has become. Moreover, in the present embodiment, since the series of processes as described above are performed every time the fuel cell system 1 is stopped, the latest situation in the fuel cell system 1 can always be reflected.

According to the fuel cell system 1 having the so-called learning function as described above, the following effects can be obtained. That is, in general, even if the fuel cell system 1 has the same specifications, it is inevitable that individual differences will occur depending on the production time, operating environment, etc., and therefore the anode pressure reference value is determined uniformly. However, in this respect, in the fuel cell system 1 of the present embodiment, since learning is performed for each individual fuel cell system, each fuel cell 20 or each fuel cell system 1 It is possible to absorb the solid difference and set an appropriate anode pressure reference value. Moreover, if the CO ₂ concentration does not increase, it is determined that there is no need to increase the pressure reference value, and the pressure reference value is not updated and can continue to be used thereafter. As described above, it is possible to prevent backflow of air in the fuel cell 20 to suppress oxidation, and to suppress deterioration of the electrode and reduction in power generation efficiency.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the example using the relationship between the CO ₂ concentration at the cathode outlet and the anode pressure has been described. However, this is only a preferable example, and other relationships or relationships are used to store the memory pressure. It is also possible to learn the value. For example, instead of the CO ₂ concentration, the anode pressure value can be set by using the cell voltage after stopping the power generation of the fuel cell 20 as a parameter (in some cases, a trigger). That is, the cell voltage in the fuel cell 20 once decreases after power generation is stopped, then starts to increase, and shows a tendency to become maximum in a time zone where the CO ₂ concentration is stabilized (see FIG. 4). A relationship close to the map shown in FIG. 3 is recognized between the anode pressure value and the anode pressure value (see FIG. 5). Therefore, a chart is not particularly shown here, but based on such a map, the value of the anode pressure is obtained by using the value of the cell voltage after power generation is stopped as a parameter (or a trigger in some cases), and updated as necessary. It is possible to implement the process. In addition, when such a process is adopted, there is an advantage that the cost can be reduced because at least the CO ₂ sensor is unnecessary. The cell voltage referred to here includes a total cell voltage that is a voltage of the entire cell.

  Up to this point, the actual form of learning for each fuel cell system and resetting the reference value of the anode pressure as necessary has been described, but this is from the viewpoint of suppressing electrode deterioration and power generation efficiency reduction. For example, other elements can be used as parameters (in some cases, triggers). Hereinafter, still another embodiment of the present invention will be described.

6 to 7 show another embodiment of the fuel cell system according to the present invention. The fuel cell system in the present embodiment measures components and gas concentrations in exhaust gas, detects deterioration of the fuel cell, and controls the cooling water temperature as necessary. That is, until now there has been a technique for detecting a change in the concentration of the fuel gas (hydrogen gas) on the cathode side, whereas in this embodiment, the CO ₂ concentration on the cathode side is detected, By controlling the cooling water temperature based on the relationship with the CO ₂ concentration, electrode deterioration and power generation efficiency reduction are suppressed.

  Hereinafter, a stop processing system at the time of power generation stop in the fuel cell system 10 of the present embodiment will be described (see FIG. 6 and the like). First, after the fuel cell 20 is stopped, processing after power generation stop (stop processing) for reducing the residual gas amount is started (step 11). For example, when the fuel cell 20 is used as an in-vehicle power generation system of a fuel cell vehicle (FCHV), the operation of turning off the ignition key of the vehicle corresponds to the start of the stop process of the fuel cell 20 here.

After starting the stop processing (step 11), cooling the fuel cell 20 while maintaining the stored value of the coolant temperature at the previous stop process (in the present embodiment to display the stored values for the cooling water temperature and T _A) (Step 12). This stored value T _A with the values stored in ECU 13, in the current stop processing is carried out cooling the stored value T _A as a reference value. For example, the temperature value is the current is also used if it is stored without cooling water temperature T _A used in the previous stop processing is updated.

Thereafter, the CO ₂ concentration is measured until a predetermined time has elapsed (step 14) (step 13). Here, the predetermined time is, for example, the time until the CO ₂ concentration in the vicinity of the cathode outlet becomes to a certain level or sufficiently stable, and for example, about 2 hours as in the above-described embodiment. It is preferable that

After a predetermined time (2 hours in the present embodiment as an example) has elapsed since the stop of power generation, the coolant temperature corresponding to the measured maximum value of CO ₂ concentration is obtained from the map (see FIG. 7) (step 15). For example, if the maximum value of the CO ₂ concentration was C _B, it is T _B is determined as the cooling water temperature corresponding to the density value C _B (see FIG. 7). Here, the fact that there is a correlation between the CO ₂ concentration at the cathode outlet and the coolant temperature of the fuel cell 20 is used. That is, regarding the CO ₂ concentration and the fuel cell life, there is a relationship in which the peak of the increase in CO ₂ concentration after power generation is stopped increases as the fuel cell deteriorates. ₂ Concerning the concentration, when the cooling water temperature is lowered, the catalyst degradation reaction is suppressed by reducing the activity of the entire cell, and the amount of CO ₂ generated can be suppressed (however, the fuel cell is below a certain temperature). Then, since the power generation performance is reduced, the cooling water temperature is not infinitely lowered). Therefore, in this embodiment, to create a map of these relationships representing the relationships CO ₂ concentration and the cooling water temperature, is set to ask the cooling water temperature from the CO ₂ concentration by utilizing the map (Fig. 7). In FIG. 7, the relationship between the two is represented by a straight line as a primary one, but this is merely an approximate relationship in the form of a first order and is consistent with the actual relationship. Not necessarily.

Subsequently, the cooling water temperature T _B determined from the map, the comparison between the cooling water temperature reference value T _A stored in advance (step 16). As a result, the smaller the better the temperature T _A (Yes in step 16), the temperature T _A that is the storage is the current reference value and to utilize it the next time (step 17). That is, the cooling water temperature T _A used as a reference in the current stop process is carried over without being updated, and the stop process is terminated by using it as a reference temperature value in the next stop process (step 19).

On the other hand, the result of the comparison, the smaller the better the temperature T _B than the temperature T _A (No in step 16), rewrites the temperature T _A was the reference value of the current stop process, the temperature T _B for Future A reference temperature value is set (step 18). In other words, it performs updating of the stored value (overwriting), the T _B which is a data that reflects the current state of the fuel cell system 1 as the reference value to be used in the next time stop process. When the stored value is updated, the stop process is terminated (step 19).

The rewriting of the reference value T _A → T _{B in} step 18 will be described as follows. That is, as described above, there is a correlation between the CO ₂ concentration at the cathode outlet and the cooling water temperature. In the present embodiment, the result of the CO ₂ concentration measurement (step 14) indicates that the CO ₂ concentration is higher than the previous time. _{2 If,} for example, the concentration increases from C _A to C _B , on the contrary, the reference cooling water temperature value (the reference value at the time of stop processing) is determined from T _A corresponding to C _A. rewrites in order to lower to T _B corresponding to C _B (step 8). That is, the cooling water temperature is set to a low temperature by a predetermined amount using the CO ₂ concentration as a parameter (trigger in some cases). By going through this series of processing, the fuel cell system 1 is in a state of learning about the cooling water temperature, and can perform processing based on the temperature after the learning at the next power generation stop processing. In other words, by setting the reference value of the cooling water temperature to the opposite level by the amount corresponding to the increase in the CO ₂ concentration, the reference value that best suits the current situation is set based on the situation of increasing CO ₂ concentration. It is possible to do. Conventionally, even if there is a stop processing technique for detecting the deterioration of the fuel cell 20 by measuring the concentration of the exhaust gas of the fuel cell 20, a measure for improving the life of the fuel cell after detecting the deterioration However, if the cooling water temperature is lowered as described above, it is possible to suppress the amount of CO ₂ generated, and as a result, the life of the fuel cell can be extended. It becomes. Moreover, in the present embodiment, since the series of processes as described above are performed every time the fuel cell system 1 is stopped, the latest situation in the fuel cell system 1 can always be reflected.

  In actual control for lowering the cooling water temperature, for example, by controlling the number of rotations of the cooling fan C13 or by controlling the pressure of the pump C1 that pressurizes and circulates the cooling water. The operation of lowering the temperature (for example, about 5 ° C. to 10 ° C.) is performed.

Further, here, the magnitudes of the temperatures T _A and T _B have been compared, but instead, the determination is also made by comparing the magnitudes of C _A and C _B obtained as a result of the CO ₂ concentration measurement. be able to. In the above-described embodiment, the CO ₂ concentration on the cathode side is measured. On the contrary, it is also possible to measure the CO ₂ concentration on the anode side and use the measurement result.

It is the schematic which shows the structure of the fuel cell system concerning this embodiment. It is a flowchart which shows an example of the diagnostic method of the deterioration progress after a power generation stop of a fuel cell, and the process for the deterioration suppression based on this. Is a map showing a schematic relationship between the CO ₂ concentration and the anode pressure at the cathode outlet. It is a graph which shows the example of a change after the power generation stop of the cell voltage after the power generation stop of a fuel cell. It is a map which shows the rough relationship between the cell voltage and anode pressure after the power generation stop of a fuel cell. It is a flowchart which shows the other example of the diagnostic method of the deterioration progress degree after the power generation stop of a fuel cell, and the process for deterioration suppression based on this. Is a map showing a schematic relationship between the temperature of the cooling water of the CO ₂ concentration and the fuel cell at the cathode outlet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 20 ... Fuel cell stack (fuel cell)

Claims (9)

A fuel cell diagnosis method for diagnosing the degree of progress of deterioration of a fuel cell that proceeds after power generation is stopped,
A diagnosis method for a fuel cell, characterized in that a diagnosis is made based on a parameter related to the degree of deterioration of the fuel cell. _2. The fuel cell diagnostic method according to claim 1, wherein the parameter is a concentration of CO2 at the outlet of the cathode electrode. The fuel cell diagnosis method according to claim 2, wherein diagnosis is performed based on the cumulative value of CO ₂ .   4. A fuel cell system, wherein a process for suppressing deterioration of the fuel cell is executed based on a diagnosis result obtained by the method for diagnosing a fuel cell according to claim 1.   5. The fuel cell system according to claim 4, wherein the back pressure after power generation is stopped after the next time is reset.   6. The fuel cell system according to claim 5, wherein the anode pressure in the fuel cell is reset to a value higher than that in the previous stop process.   5. The fuel cell system according to claim 4, wherein the temperature of the cooling water for the fuel cell is reset after the next power generation stop.   8. The fuel cell system according to claim 7, wherein the coolant temperature of the fuel cell is reset to a value lower than that during the previous stop process. The fuel cell system according to any one of claims 4 to 8, wherein the processing is executed after scavenging processing is performed after power generation of the fuel cell is stopped.

Images