JP2007165082A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately judge whether the starting of a system is continued or not, and prevent unnecessary stop of the system. <P>SOLUTION: Whether starting of a fuel cell stack of a fuel cell system is capable of continuing or not is diagnosed, based on the judgement whether the voltage of a fuel cell stack 4 reaches a prescribed voltage threshold value (VTh) or not within a prescribed time threshold value (Tth) from immediately after hydrogen and air are supplied to the fuel cell stack 4 to the temperature of the fuel cell stack 4 immediately after the fuel cell system is started and hydrogen and air are supplied to the fuel cell stack 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system for diagnosing whether or not activation is possible based on responsiveness of voltage rise after system activation.

  Conventionally, as a technique for diagnosing the operating state of a fuel cell system, for example, those described in the following documents are known (see Patent Documents 1 and 2). The technology described in Patent Document 1 divides a large number of cells of a fuel cell system into a plurality of cell groups, measures an output voltage for each cell group, averages output voltages, voltage variations in output voltages, and output voltages. Based on the above, excess water, drying of the electrolyte membrane, and insufficient supply of fuel gas are estimated. This makes it possible to accurately estimate the operating state of the fuel cell regardless of the temperature distribution in the fuel cell.

Further, in the technique described in Patent Document 2, from the viewpoint of suppressing deterioration of the fuel cell, at a low temperature where freezing may occur, the current is taken out after supplying the fuel gas and the oxidant gas to the fuel cell, and the voltage The optimum value of the current to be taken out from the fuel cell thereafter is determined based on the responsiveness at the time of starting up.
JP2004-127915 JP2005-071626

  In the technique described in Patent Document 1, the response when the output voltage rises after starting the fuel cell system has not been observed. For this reason, when the reaction gas of fuel gas and oxidant gas was supplied to the fuel cell stack at the time of low temperature startup of the system, it was not possible to detect the output voltage rise delay due to the low temperature part inside the fuel cell stack. . As a result, the rise delay of the output voltage may be erroneously determined as a system abnormality. If an erroneous determination occurs, it is determined that the system cannot be continuously started, and there is a possibility that the system is stopped even though no abnormality has occurred in the system.

  In addition, in the technique described in Patent Document 2, although the responsiveness when the output voltage rises is observed, this does not disclose a method for determining whether or not the start-up can be continued, and the rise characteristic of the voltage is not disclosed. In the case of determining whether or not the start-up can be continued, it may lead to an erroneous determination unless the voltage rising characteristics are properly determined.

  Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide a fuel cell system that accurately determines whether or not the system can continue to be activated and prevents unnecessary system stoppage. is there.

  In order to achieve the above object, a means for solving the problems of the present invention is to generate power by an electrochemical reaction between a fuel gas supplied by a fuel gas supply means and an oxidant gas supplied by an oxidant gas supply means. In a fuel cell system including a fuel cell to perform, a temperature measuring unit for measuring or estimating the temperature of the fuel cell, a voltage measuring unit for measuring a voltage of the fuel cell, and the fuel cell system is activated to start the fuel cell Immediately after the fuel gas and oxidant gas are supplied, the temperature of the fuel cell measured or estimated by the temperature measuring means and the rising characteristics of the voltage of the fuel cell measured by the voltage measuring means, Control means for diagnosing whether or not the start of the fuel cell system can be continued, and the control means supplies fuel gas and oxidant gas to the fuel cell. A diagnosis is made based on the rising characteristics of the voltage expressed by whether or not the voltage of the fuel cell has reached a predetermined first voltage threshold value within a predetermined time threshold immediately after The value and the voltage threshold value are variably set.

  According to the present invention, it is possible to prevent erroneous determination that the system is abnormal even when the rise of the voltage of the fuel cell is delayed at the time of low temperature startup of the system. As a result, unnecessary system stoppage due to erroneous determination can be avoided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. The system of the first embodiment shown in FIG. 1 is an electrochemical reaction between oxidant gas air (oxygen) supplied from an air supply device 1 and fuel gas hydrogen supplied from a hydrogen tank 2 via a hydrogen pressure regulator 3. A fuel cell stack 4 is provided that generates power by generating power through reaction, and the power obtained by power generation is supplied to the load device 9 via the power converter 12 and consumed.

  The air supply device 1 is composed of, for example, a compressor, and the pressure of air supplied to the fuel cell stack 4 by this compressor is adjusted and controlled by an air pressure regulating valve 10 provided on the outlet side of the air electrode of the fuel cell stack 4. . The temperature of the intake air of the compressor is measured by the temperature sensor 22, and the temperature of the exhaust air is measured by the temperature sensor 28. The pressure and temperature of air at the air electrode inlet of the fuel cell stack 4 are measured by a pressure sensor 18 and a temperature sensor 19 provided near the inlet, respectively.

  Cooling liquid is circulated and supplied to the compressor of the air supply device 1 by the cooling liquid pump 25, and the motor constituting the compressor is cooled by this cooling liquid. In the case of a fuel cell vehicle or the like, the circulatingly supplied coolant is supplied to a heat exchanger (HE) 26 composed of a radiator, a radiator fan or the like and cooled, and the temperature of the coolant is measured by a temperature sensor 27. Is done.

  The fuel cell stack 4 has a hydrogen circulation path, and unused hydrogen off-gas discharged from the fuel cell stack 4 by the hydrogen circulation pump 5 is returned to the hydrogen electrode inlet of the fuel cell stack 4 as circulating hydrogen and reused. That is, the hydrogen electrode inlet of the fuel cell stack 4 is supplied with a mixed hydrogen of hydrogen supplied from the hydrogen tank 2 and returned circulating hydrogen. The circulating hydrogen contains a lot of water vapor and is mixed with dry hydrogen supplied from the hydrogen tank 2 to humidify the hydrogen supplied to the fuel cell stack 4. The humidified hydrogen is supplied to the fuel cell stack 4. As a result, the electrolyte membrane is sufficiently humidified. Nitrogen accumulated in the hydrogen circulation system is discharged out of the system through a purge valve 11 that is appropriately controlled to be opened. The pressure and temperature of hydrogen at the hydrogen electrode inlet of the fuel cell stack 4 are measured by a pressure sensor 16 and a temperature sensor 17 provided near the inlet, respectively.

  The output voltage of the fuel cell stack 4 is measured by the voltage sensor 6, and the current flowing from the fuel cell stack 4 to the power converter 12 is measured by the current sensor 7. A cell voltage sensor 8 is provided in the fuel cell stack 4, and the cell voltage of the fuel cell stack 4 is measured by the cell voltage sensor 8. The cell voltage sensor 8 is provided for every cell of the fuel cell stack 4 or every predetermined cell, for example, every several cells. When the cell voltage sensor 8 is provided for each predetermined cell, the cell voltage of the cell not provided with the cell voltage sensor 8 is estimated based on the cell voltage measured by the cell voltage sensor 8, and the minimum cell voltage or the like is estimated. Is done.

  A temperature sensor 29 is provided in the fuel cell stack 4, and the temperature of the fuel cell stack 4 is estimated based on the temperature measured by the temperature sensor 29. A coolant is circulated and supplied to the fuel cell stack 4 by the coolant pump 21, and heat generated by power generation of the fuel cell stack 4 is removed by this coolant. Although not shown, in the case of a fuel cell vehicle or the like, this coolant is supplied to a heat exchanger composed of a radiator, a radiator fan, and the like to be cooled. The temperature of the coolant introduced into the fuel cell stack 4 is measured by the temperature sensor 23, and the temperature of the discharged coolant is measured by the temperature sensor 20.

  A load device 9 is connected to the fuel cell stack 4 via the power conversion device 12, and the load device 9 sets a power generation amount and takes out a load current from the fuel cell stack 4. The load device 9 is composed of, for example, a drive motor, and the electric power obtained by power generation is converted into energy by the inverter of the power conversion device 12, supplied to the drive motor, and consumed. When the fuel cell system is applied to, for example, a fuel cell vehicle, the drive motor is used as power for driving the vehicle.

  A battery 13 is connected to the fuel cell stack 4 via a power conversion device 12, and the battery 13 stores power obtained by power generation, while the stored power is, for example, when the system is started up. And is supplied to the air supply device 1 and the like as auxiliary equipment, and bears a part of electric power for driving the compressor. The voltage and current input / output to / from the battery 13 are measured by the voltage sensor 14 and the current sensor 15, respectively.

  Although not shown, the fuel cell system includes a control unit. The control unit functions as a control center for controlling the operation of the system, and is provided with resources such as a CPU, a storage device, and an input / output device necessary for a computer that controls various operation processes based on a program, for example, a microcomputer Etc. The control unit reads signals from the sensors (not shown) that collect information necessary for operation of the system, such as the above-mentioned sensors and other pressures, temperatures, concentrations, voltages, currents, etc. that cannot be obtained by these sensors. Based on the various signals read and control logic (program) stored in advance, commands are sent to the components that require control of this system, including each valve, and the responsiveness of the generated voltage at system startup described below All operations necessary for the operation / stop of this system including the determination process are managed and controlled. In addition, the control unit has a measurement function for measuring a time from a system stop to the next start to be described later and an elapsed time of a time threshold value in order to execute a determination process of the responsiveness of the generated voltage.

  Next, with reference to the flowchart of FIG. 2, a procedure for determining whether to continue the activation of the system will be described. Here, in the process shown below, the temperature of the fuel cell stack 4 estimated based on the temperature measured by the temperature sensor 29 is referred to, and then the temperature inside the fuel cell stack 4 is low (approximately 5 ° C. or less). Run at low temperatures where parts can occur. Needless to say, the temperature at which this processing is executed is appropriately changed according to the system specifications and the operating environment.

  In FIG. 2, the start of the fuel cell system is first started, and the supply of air and hydrogen to the fuel cell stack 4 is started (step S20). In the first embodiment, the hydrogen circulation pump 5 is provided in the hydrogen system so as to maintain a high hydrogen stoichiometric ratio. Therefore, the hydrogen circulation pump 5 also starts to be driven at this time. The purge valve 11 is started in a closed state, but the nitrogen accumulated in the hydrogen electrode of the fuel cell stack 4 is periodically discharged by periodically opening and closing the purge valve 11 after starting.

  The hydrogen supplied to the fuel cell stack 4 is maintained at a target pressure by the hydrogen pressure regulator 3, and the air supplied to the fuel cell stack 4 is the rotational speed of the compressor constituting the air supply device 1 and the valve opening of the air pressure regulating valve 10. Adjust the degree to maintain the target flow rate and target pressure.

  Further, driving of the coolant pump 25 is started to start circulation of coolant for cooling the compressor motor, and control is performed so that the outlet coolant temperature of the compressor motor becomes the target temperature. At the time of low temperature startup, the circulation of the coolant that circulates through the fuel cell stack 4 is not yet performed here.

  After the system is started in this way, it is observed whether or not a voltage is generated in the fuel cell stack 4. When there is no abnormality in the system, the voltage set during normal operation is generated by power generation, but when that voltage does not occur, it is determined that there is some abnormality in the system and it is impossible to continue the startup (stopping the startup ( Shut down).

  In such a determination, the rising response of the voltage at which the voltage reaches a predetermined value after the reaction gas is supplied to the fuel cell stack 4 depends on the state of the fuel cell stack 4. That is, when the temperature of the fuel cell stack 4 is low, for example, when the fuel cell stack 4 is started at a low temperature, the electrochemical reaction in the fuel cell stack 4 is slow, so that the voltage rise is delayed. Therefore, in this embodiment, in the rising response of the voltage after supplying the reaction gas to the fuel cell stack 4, the rising voltage (voltage threshold, Vth) and the time until rising to this voltage threshold (time threshold) , Tth) (determination condition) is selectively set according to preset requirements (step S21), and the system abnormality due to the rising response of the voltage is determined. The determination conditions are set based on the flowcharts shown in FIGS.

  FIG. 3 shows a means for setting the voltage threshold. In FIG. 3, first, referring to a map 31 showing the relationship between the temperature of the fuel cell stack 4 and the voltage threshold value (Vth1> 0), the voltage threshold value (Vth1) is set based on the temperature of the fuel cell stack 4. Set. The map 31 is prepared in advance by experiments or desktop examinations and stored in the storage device of the control unit. The map 31 has a characteristic that the voltage threshold (Vth1) decreases as the temperature of the fuel cell stack 4 decreases, and the voltage threshold becomes a constant value above a predetermined positive temperature.

  Further, referring to the map 32 showing the relationship between the time from when the system was last stopped until this time it is started and the correction coefficient k1 (0 <k1 <1) for correcting the voltage threshold (Vth1), The correction coefficient k1 is set based on the time after the stop. The map 32 is prepared in advance by experiments or desktop examinations and stored in the storage device of the control unit. In this map 32, the correction coefficient becomes smaller as the time after the previous stop becomes longer, and the correction coefficient k1 has a constant value over a predetermined time. When the correction coefficient k1 is set, the voltage threshold (Vth2) set as the product (Vth1 × k1) of the previous voltage threshold (Vth1) and the correction coefficient k1 is calculated by the calculation means 34 of the control unit. Is done.

  Further, with reference to a map 33 showing the relationship between the no-load voltage (OCV) immediately after the reaction gas is supplied and the voltage threshold (Vth3), the voltage threshold (Vth3) based on the no-load voltage (OCV) Set. The map 33 is prepared in advance by experiments or desktop examinations and stored in the storage device of the control unit. The map 33 has a characteristic that the voltage threshold (Vth3) decreases as the no-load voltage (OCV) decreases, and the voltage threshold becomes a constant value above a predetermined positive power generation voltage.

  When three voltage threshold values (Vth1, Vth2, Vth3) corresponding to the respective requirements are obtained in this way, the voltage threshold value having the lowest value among these voltage threshold values is selected by the selection means 35. Selected. The selected voltage threshold is provided to the lower limiter 36 to determine whether the selected voltage threshold is appropriate. That is, when the selected voltage threshold value is larger than the lower limit value, it is determined to be appropriate, and the selected voltage threshold value is used as the voltage threshold value (Vth) for determining the voltage rising response. . On the other hand, if it is small, it is determined that the voltage threshold value obtained in the above calculation is inappropriate, and the lower limit value is used as the voltage threshold value (Vth) for determining the voltage rising response.

  Here, the lower limiter value is a parameter determined in advance by experiment or the like, and is set to a value that can be determined that there is some abnormality at a voltage equal to or lower than a certain value. For example, about 300 mV may be adopted as the cell voltage. Thus, by providing the lower limit value, it is possible to determine the rising response of the voltage even when an inappropriate voltage threshold value is calculated by the calculation of the voltage threshold value.

  FIG. 4 shows the means for setting the time threshold. In FIG. 4, first, a time threshold value (Tth1) is set based on the temperature of the fuel cell stack 4 with reference to a map 41 showing the relationship between the temperature of the fuel cell stack 4 and the time threshold value (Tth1). . The map 41 is prepared in advance by an experiment or a desktop study and is stored in the storage device of the control unit. This map 41 has a characteristic that the time threshold (Tth1) becomes longer as the temperature of the fuel cell stack 4 becomes lower, and the time threshold becomes a constant value above a predetermined positive temperature.

  Next, with reference to a map 42 showing the relationship between the time from the previous system shutdown to the current startup and the correction coefficient m1 (0 <m1 <1) for correcting the time threshold (Tth1), The correction coefficient m1 is set based on the time since the previous stop. The map 42 is prepared in advance by experiments or desktop examinations and stored in the storage device of the control unit. In this map 42, the correction coefficient m1 increases as the time after the previous stop increases, and the correction coefficient m1 has a constant value over a predetermined time. When the correction coefficient m1 is set, the time threshold value (Tth2) set as the product (Tth1 × m1) of the previous time threshold value (Tth1) and the correction coefficient m1 is calculated by the calculation means 46 of the control unit. Is done.

  Next, immediately after the reaction gas is supplied, a predetermined current is taken out from the fuel cell stack 4, and the lowest cell voltage is set to a voltage threshold (here, for example, 0 V) used to set a time threshold (Tth3). The time threshold value (Tth3) is set based on the time when the minimum cell voltage reaches 0V with reference to the map 43 showing the relationship between the time until reaching the setting) and the time threshold value (Tth3). The map 43 is prepared in advance by experiments or desktop examinations and stored in the storage device of the control unit. This map 43 has a characteristic that the time threshold value (Tth3) becomes longer as the time for the lowest cell voltage to reach 0V is longer.

  In the first embodiment, the time threshold (Tth3) is set longer as the time during which the minimum cell voltage is 0 V or more is longer. In addition, the voltage of the fuel cell stack 4 is set to a predetermined value. The time threshold (Tth3) may be set longer as the time until the voltage threshold is exceeded is longer. Here, the voltage threshold value to be compared with the voltage of the fuel cell stack 4 is preferably set to a value smaller than the voltage threshold value (Vth) set in the process shown in FIG.

  Next, referring to a map 44 showing the relationship between the absolute value of the minimum cell voltage and the time threshold (Tth4) when a predetermined current is taken out from the fuel cell stack 4 immediately after the reaction gas is supplied, the minimum cell A time threshold value (Tth4) is set based on the absolute value of the voltage. The map 44 is prepared in advance by an experiment or a desktop study and is stored in the storage device of the control unit. This map 44 has a characteristic that the time threshold value (Tth4) becomes longer as the absolute value of the lowest cell voltage increases.

  Next, with reference to the map 45 showing the relationship between the no-load voltage (OCV) of the fuel cell stack 4 and the time threshold value (Tth5) immediately after the reaction gas is supplied, the time is determined based on the no-load voltage (OCV). A threshold value (Tth5) is set. The map 45 is prepared in advance by experiment or desktop examination and stored in the storage device of the control unit. This map 45 has a characteristic that the time threshold value (Tth5) becomes longer as the no-load voltage (OCV) is lower.

  Note that the current taken from the fuel cell stack 4 when setting the time threshold value (Tth3) and the time threshold value (Tth4) may be a very small value, and may be about several amperes. In the first embodiment, for example, it is about 1 ampere. If a large current is used, a cell whose cell voltage is slow to reach 0V or a cell having the lowest cell voltage is emphasized. However, since there is a variation in the distribution of the reaction gas to each cell, there is a risk of shortage of hydrogen in some cells immediately after hydrogen supply. If a large amount of current is taken out in such a state, the fuel cell stack 4 will deteriorate. May be promoted. For this reason, the current to be extracted is set as small as possible.

  Thus, when five time threshold values (Tth1 to Tth5) corresponding to the respective requirements are obtained, the longest time threshold value among these time threshold values is selected by the selection means 47. . The selected time threshold is provided to the upper limiter 48 to determine whether the selected time threshold is appropriate. That is, when the selected time threshold value is shorter than the upper limit value, it is determined to be appropriate, and the selected time threshold value is used as the time threshold value (Tth) for determining the voltage rising response. . On the other hand, if it is long, it is determined that the time threshold value obtained in the above calculation is inappropriate, and the upper limit value is used as the time threshold value (Tth) for determining the voltage rising response.

  Here, the upper limit value is a parameter determined in advance by experiment or the like, and is set to a value that can be determined that there is some abnormality in a time longer than a certain value. For example, about 30 seconds may be adopted. In this manner, by providing the upper limit value, it is possible to determine the rising response of the voltage even when an inappropriate time threshold value is calculated by the time threshold value calculation.

  Next, returning to FIG. 2, when the voltage threshold value (VTh) and the time threshold value (Tth) are set in this way, after the reactive gas is supplied to the fuel cell stack 4, the generated voltage As shown in the timing chart of FIG. 5 showing the change in the generated voltage when the absolute value of the minimum cell voltage is small (indicated by symbol a) and large (indicated by symbol b), the above-mentioned time threshold value is set. It is determined whether or not the generated voltage has reached a voltage equal to or higher than the set voltage threshold (Vth) within the time (Tth) (step S22). As a result of the determination, if the above determination requirements are satisfied, the startup operation so far is continued and warm-up power generation is started (step S23).

  After the warm-up power generation is started, the coolant pump 21 is driven to circulate the coolant in the fuel cell stack 4. In the first embodiment, the circulation of the coolant is started after the predetermined power generation is continued for a predetermined time. That is, the coolant is circulated in advance in a state where the inside of the fuel cell stack 4 is warmed by power generation so that the inside of the fuel cell stack 4 is not cooled by circulation of the coolant and the generated water generated by power generation is not frozen. After the coolant is circulated, if the outlet coolant temperature of the fuel cell stack 4 reaches a predetermined temperature, for example, about 20 ° C., the warm-up power generation is terminated and the startup process is terminated (step S24).

  On the other hand, if the determination result does not satisfy the determination requirement, it is determined that the activation is impossible, and a process for stopping the activation (shutdown) is started (step S25). Is stopped (step S26).

  In step S22, after reaching the voltage threshold voltage within the time threshold time, whether or not the state has continued for a predetermined diagnosis time may be added to the determination requirement. . Here, immediately after the reaction gas is supplied to the air electrode and the hydrogen electrode of the fuel cell stack 4, respectively, the larger the absolute value of the minimum cell voltage when a predetermined current is taken out from the fuel cell stack 4, the higher the value of the fuel cell stack 4 becomes. The longer it takes for the voltage (minimum cell voltage in the first embodiment) to exceed the voltage threshold for setting the time threshold (0 V in the first embodiment), and the air in the fuel cell stack 4 The predetermined diagnosis time for determining the continuation may be set longer as the no-load voltage (OCV) immediately after supplying the reaction gas to the electrode and the hydrogen electrode is lower.

  As described above, in the above embodiment, it is diagnosed whether or not a low temperature portion is generated inside the stack of the fuel cell stack 4 based on the temperature response of the fuel cell stack 4 and the rising response characteristics of the cell voltage. Here, it is diagnosed whether or not the generated voltage reaches or exceeds the predetermined voltage threshold within a predetermined time threshold immediately after the supply of the reaction gas to the fuel cell stack 4 is started. Since the threshold value and the voltage threshold value are variably set, it is possible to appropriately determine the rising response characteristic of the voltage. Thereby, for example, even when the electrochemical reaction becomes dull at a low temperature and the voltage rises slowly, it is possible to prevent erroneous determination that the system is abnormal.

  By prolonging the time until it is determined whether the generated voltage reaches or exceeds the predetermined voltage threshold, the electrochemical reaction becomes dull at low temperatures, the voltage rises slowly, and the voltage is low. It becomes possible not to judge.

  Since the rising characteristic of the voltage at low temperature is detected by the time until the power generation voltage exceeds the predetermined voltage threshold, the response becomes dull at low temperatures before starting the power generation after starting up. Whether the rise is slow can be detected.

  By estimating the characteristics that the voltage rises toward the positive voltage and then reaches a certain voltage threshold as the absolute value of the lowest cell voltage of the generated voltage increases, the response becomes dull at a low temperature in advance. It is possible to detect whether the rise is slow.

  Since a predetermined current is taken out from the fuel cell stack 4 to determine the voltage rising characteristic, it is possible to accurately distinguish the fuel cell having a slow voltage rising.

  Even if the power generation reaction becomes dull and the power generation voltage becomes low by setting the voltage threshold value for determining whether or not the operation state of the system is normal as the fuel cell temperature becomes low, the power generation reaction becomes slow at low temperatures. It is possible to prevent erroneous determination as abnormal.

  Even if the no-load voltage is low and the no-load voltage is low by setting the voltage threshold to determine whether the system operating state is normal as the no-load voltage is low, It is possible to prevent erroneous determination as a system abnormality.

  The longer the time from system shutdown to startup, the lower the voltage threshold that determines whether or not the system is operating normally, so the period from the previous system shutdown to the current startup is longer. Even when the air that has filled the hydrogen electrode is not completely replaced with hydrogen, it is possible to prevent erroneous determination as a system abnormality when the voltage rises slowly and the voltage is low.

  When the no-load voltage is lowered, the voltage threshold that determines whether the system operating state is normal is set low so that the power generation reaction is slow at low temperatures, the voltage rises slowly, and the no-load voltage decreases. Even so, it is possible to prevent erroneous determination as a system abnormality.

  The longer the period from the previous stop of the system to the current start, the longer the time it takes to determine whether the generated voltage reaches or exceeds the predetermined voltage threshold. Even if the time to start this time is long and the air that has filled the hydrogen electrode is not completely replaced with hydrogen, it will not be mistaken as a system error when the voltage rises slowly and the voltage is low. can do.

  By extending the time (diagnosis time) for determining whether or not the generated voltage has been continuously maintained at a predetermined voltage threshold value or higher for a predetermined period, there is a low-temperature portion in the fuel cell stack 4. Even in a case where a general freezing is likely to occur, it is possible to detect a case where the voltage is lowered due to refreezing.

It is a figure which shows the structure of the fuel cell system which concerns on Example 1 of this invention. It is a flowchart which shows the procedure of the operation | movement which concerns on Example 1 of this invention. It is a figure which shows the setting procedure of a voltage threshold value. It is a figure which shows the setting procedure of a time threshold value. It is a timing chart of operation concerning Example 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Air supply device 2 ... Hydrogen tank 3 ... Hydrogen pressure regulator 4 ... Fuel cell stack 5 ... Hydrogen circulation pump 6, 14 ... Voltage sensor 7, 15 ... Current sensor 8 ... Cell voltage sensor 9 ... Load device 10 ... Air pressure regulation valve DESCRIPTION OF SYMBOLS 11 ... Purge valve 12 ... Power converter 13 ... Battery 16, 18 ... Pressure sensor 17, 19, 20, 22, 23, 27, 28, 29 ... Temperature sensor 21, 25 ... Coolant pump 34, 46 ... Calculation means 35 , 47 ... selection means 36, 48 ... lower limit limiter

Claims (14)

In a fuel cell system including a fuel cell that generates power by an electrochemical reaction between a fuel gas supplied by a fuel gas supply unit and an oxidant gas supplied by an oxidant gas supply unit,
Temperature measuring means for measuring or estimating the temperature of the fuel cell;
Voltage measuring means for measuring the voltage of the fuel cell;
Immediately after the fuel cell system was started and fuel gas and oxidant gas were supplied to the fuel cell, the temperature of the fuel cell measured or estimated by the temperature measuring means and the voltage measuring means were measured. Control means for diagnosing whether or not it is possible to continue the start of the fuel cell system based on the rising characteristics of the voltage of the fuel cell,
The control means determines whether or not the voltage of the fuel cell has reached a predetermined first voltage threshold value within a predetermined time threshold immediately after the fuel gas and oxidant gas are supplied to the fuel cell. A fuel cell system characterized in that a diagnosis is made based on a rising characteristic of a voltage expressed and the time threshold value and the voltage threshold value are variably set. 2. The fuel cell system according to claim 1, wherein the time threshold is set longer as the temperature of the fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell. The time threshold is set longer as the time until the voltage of the fuel cell becomes equal to or higher than a predetermined second voltage threshold smaller than the first voltage threshold is increased. The fuel cell system according to claim 1 or 2. Immediately after fuel gas and oxidant gas are supplied to the fuel cell, the time threshold is set longer as the absolute value of the minimum cell voltage of the fuel cell when a predetermined current is taken out from the fuel cell is larger. The fuel cell system according to claim 2 or 3, characterized in that: Immediately after the fuel gas and oxidant gas are supplied to the fuel cell, when a predetermined current is taken out from the fuel cell, the voltage of the fuel cell is lower than the first voltage threshold value. 5. The fuel cell system according to claim 2, wherein the time threshold value is set to be longer as the time until the voltage threshold value of 2 or more is increased. 6. The first voltage threshold value is set lower as the temperature of the fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell is lower. The fuel cell system according to claim 1. 6. The first voltage threshold value is set lower as the no-load voltage of the fuel cell immediately after the fuel gas and oxidant gas are supplied to the fuel cell is lowered. The fuel cell system according to any one of the above. The first voltage threshold value is set to be lower as the time from the previous stop of the fuel cell system to the next startup becomes longer and the temperature of the fuel cell becomes lower. Item 6. The fuel cell system according to any one of Items 2 to 5. 6. The time threshold value is set longer as the no-load voltage of the fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell is reduced. 2. The fuel cell system according to item 1. The time threshold is set longer as the time from the previous stop of the fuel cell system to the next startup becomes longer and the temperature of the fuel cell becomes lower. The fuel cell system according to any one of 5. The control means is configured so that the voltage of the fuel cell reaches or exceeds a predetermined first voltage threshold value within a predetermined time threshold immediately after the fuel gas and the oxidant gas are supplied to the fuel cell. 2. The fuel cell system according to claim 1, wherein the fuel cell system is diagnosed based on a voltage rising characteristic expressed by whether or not a predetermined diagnosis time has continued. Immediately after the fuel gas and oxidant gas are supplied to the fuel cell, the larger the absolute value of the minimum cell voltage of the fuel cell when a predetermined current is taken out from the fuel cell, the higher the voltage of the fuel cell becomes. The fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell as the time until it becomes a predetermined second voltage threshold value that is smaller than the voltage threshold value of 1 becomes longer. The fuel cell system according to claim 11, wherein the predetermined diagnosis time is set longer as the no-load voltage becomes lower. The first voltage threshold is a value set based on the temperature of the fuel cell immediately after the fuel gas and oxidant gas are supplied to the fuel cell, and the fuel gas and oxidant gas are in the fuel cell. The smallest value among the values set based on the no-load voltage of the fuel cell immediately after being supplied, and the values set based on the time from the previous shutdown of the fuel cell system to the next startup. The fuel cell system according to any one of claims 2 to 12, wherein is selected. The time threshold is a value set based on the temperature of the fuel cell immediately after the fuel gas and oxidant gas are supplied to the fuel cell, from the previous shutdown of the fuel cell system to the next startup. When the predetermined current is taken out from the fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell, the voltage of the fuel cell is the first voltage. A value set based on a time until a predetermined second voltage threshold value that is smaller than the threshold value is reached, and immediately after the fuel gas and oxidant gas are supplied to the fuel cell, Based on the value set based on the absolute value of the minimum cell voltage of the fuel cell when the current is taken out, based on the no-load voltage of the fuel cell immediately after the fuel gas and the oxidant gas are supplied to the fuel cell Set The fuel cell system according to any one of claims 2 to 13 in which of the values, characterized in that the highest value is selected.

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