JP2012028221A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of a solid polymer electrolyte membrane by discharging a fuel cell stack in an appropriate timing while power generation is stopped.SOLUTION: A fuel cell system comprises; a fuel cell stack 2 which is formed by stacking a plurality of cells; an electric load 24 which consumes the electricity generated by the fuel cell stack 2; a switch 23; total voltage detection means which detects a total voltage of the fuel cell stack 2; and an electronic control unit 30. The electronic control unit 30 includes: a voltage variation calculation unit which calculates a voltage variation per predetermined time based on the total voltage value detected by the total voltage detection means; and a determination unit which determines whether or not the voltage variation has shifted from a positive value to 0 or to a negative value after the fuel cell stack 2 has stopped generating power. If the determination unit determines affirmative, the switch 23 is turned on to start the power supply to the electric load 24. If the total voltage value reaches a total voltage determination threshold or a lower value after the start of power supply, the switch 23 is turned off to stop the power supply to the electric load 24.

Description

  The present invention relates to a fuel cell system.

In a fuel cell having a solid polymer electrolyte membrane, in which hydrogen is supplied to the anode and air containing oxygen (oxidant) is supplied to the cathode to generate power, a solid polymer is used after power generation is stopped. When hydrogen and oxygen are present on both sides of the electrolyte membrane, an open circuit voltage is generated in each cell. When the voltage is generated in this way, the solid polymer electrolyte membrane may be deteriorated.
Therefore, a technique for reducing the voltage by discharging the fuel cell after stopping power generation has been proposed.

  For example, in the technique disclosed in Patent Document 1, when the fuel cell is stopped, the fuel cell is connected to an electric load, and the lowest value (hereinafter referred to as the minimum cell voltage) among all cell voltages (referred to as cell voltages). ) Is disconnected from the electric load when the voltage falls below the first predetermined voltage, and when all the cell voltages are equal to or lower than the second predetermined voltage after a certain period of time after the interruption, the fuel cell is again connected to the electric load. By connecting to, the voltage is lowered.

JP 2007-59120 A

By the way, as shown in FIG. 4, the voltage after the power generation stop of the fuel cell once falls (first period St1), rises again (second period St2), and then falls again (third period St3). It is known to have the characteristics of In FIG. 4, the vertical axis represents the total voltage obtained by summing the voltages of the cells. Here, in the first period St1, it is presumed that the cathode potential is lowered by hydrogen permeating from the anode to the cathode, and as a result, the total voltage (cell voltage) is lowered. In the second stage St2, the amount of hydrogen permeated from the anode to the cathode is reduced, and oxygen is diffused from the atmosphere to the cathode, so that the cathode potential rises, and as a result, the total voltage (cell voltage) is estimated to rise. Is done. In the third period St3, it is presumed that the anode potential increases due to the permeation of oxygen from the cathode to the anode, and as a result, the total voltage (cell voltage) decreases.
When the high voltage state is maintained in the second stage St2 (A in the figure), and in the third stage St3 in which hydrogen and oxygen are mixed on the anode side and a radical reaction occurs, the solid polymer electrolyte membrane Degradation occurs.

  However, in the above-described discharge control disclosed in Patent Document 1, only reconnection with the electric load is determined based on the cell voltage after a certain time after the connection with the electric load is cut off. Since it is not determined after grasping the voltage rising state after the power generation has stopped and the subsequent voltage decreasing state after power generation stop, it is possible to execute the discharge of the fuel cell at an appropriate timing. The solid polymer electrolyte membrane could not be prevented from being deteriorated.

  Accordingly, the present invention provides a fuel cell system capable of reliably discharging at an appropriate timing after stopping the power generation of the fuel cell stack and preventing deterioration of the solid polymer electrolyte membrane.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 is a fuel cell stack formed by stacking a plurality of cells that generate power by supplying an anode gas containing hydrogen to the anode and a cathode gas containing oxygen to the cathode (for example, an embodiment described later) A fuel cell stack 2), an electrical load connected to the fuel cell stack and consuming electricity generated by the fuel cell stack (for example, a battery 22 and an electrical load 24 in the embodiments described later), and the fuel cell stack Discharge control means for controlling power supply to the electric load (for example, a DC / DC converter 21 and a switch 23 in an embodiment described later) and total voltage detection means for detecting the total voltage of the fuel cell stack (for example, described later) And an electronic control unit 30) and a control unit for controlling the discharge control means (for example, an embodiment to be described later) An electronic control device 30), and the control unit calculates a voltage change amount per predetermined time based on the total voltage value detected by the total voltage detecting means (for example, described later). Step S103 in the embodiment, and a determination unit that determines whether or not the voltage change amount calculated by the voltage change amount calculation unit has shifted from positive to zero or negative after power generation stop of the fuel cell stack (for example, Step S104) in an embodiment to be described later, and when the determination unit makes an affirmative determination, operates the discharge control means to start supplying power to the electric load, and after the power supply starts, the total voltage value is When the total voltage determination threshold (for example, a first predetermined value V1 in an embodiment to be described later) estimated to have consumed oxygen in the anode of the fuel cell stack is less than or equal to The fuel cell system of the discharge control means in the inoperative, characterized in that stops power supply to the electrical load (e.g., the fuel cell system 1 in the embodiment) is.

  The invention according to claim 2 is the invention according to claim 1, further comprising cell voltage detection means (for example, a cell voltage sensor 20 in an embodiment described later) for detecting the voltage of each cell of the fuel cell stack. The control unit is configured such that, after the power supply starts, before the total voltage value becomes equal to or lower than the total voltage determination threshold value, a minimum value among the voltages of each cell detected by the cell voltage detection unit is a cell voltage determination threshold value. When it becomes below, when the said minimum value becomes below the said cell voltage determination threshold value, the said discharge control means is deactivated and the electric power supply to the said electric load is stopped, It is characterized by the above-mentioned.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, temperature detecting means for detecting the temperature of the fuel cell stack when the power generation of the fuel cell stack is stopped (for example, in an embodiment described later) A temperature sensor 8), humidity detection means for detecting the humidity in the fuel cell stack, and pressure detection means for detecting the pressure of the anode of the fuel cell stack. A standby time (for example, a standby time T1 in an embodiment to be described later) is determined based on a detection value of the detection means, and after the standby time has elapsed since the generation stop, the voltage change amount calculation unit calculates the voltage change amount. The execution of the calculation process is started.

  According to a fourth aspect of the present invention, there is provided the invention according to any one of the first to third aspects, wherein the fuel cell stack is predicted to have no hydrogen in a predetermined time (for example, an embodiment described later). Until the predetermined time T2) elapses, the control of the discharge control means by the control unit is repeated.

  According to the first aspect of the present invention, the discharge of the fuel cell stack is executed when the voltage change amount of the total voltage of the fuel cell stack during the stop of power generation shifts from positive to 0 or negative. The discharge can be executed when the total voltage becomes the highest in the process of the voltage once decreasing and increasing again, and the discharge can be surely executed at the optimum timing. As a result, it is possible to reliably prevent deterioration of the solid polymer electrolyte membrane of the fuel cell stack.

  According to the invention of claim 2, when there is an abnormal cell in the fuel cell stack and the cell voltage of the cell is lower than the cell voltage of other normal cells, the discharge of the fuel cell stack is stopped. The fuel cell stack can be protected.

  According to the third aspect of the invention, the voltage change amount calculation process is not executed until the standby time elapses after the power generation is stopped, so that the load on the control unit can be reduced and the power consumption can be reduced. it can.

  According to the fourth aspect of the present invention, the voltage change amount need not be monitored unnecessarily, the load on the control unit can be reduced, and the power consumption can be reduced.

It is a schematic block diagram in the Example of the fuel cell system concerning this invention. It is a flowchart of the discharge control in the electric power generation stop in the fuel cell system of the said Example. It is the discharge time chart in the power generation stop in the fuel cell system of the said Example. It is a time chart which shows the change of the total voltage of the fuel cell stack during power generation stop.

Embodiments of a fuel cell system according to the present invention will be described below with reference to the drawings of FIGS.
FIG. 1 is a schematic configuration diagram of a fuel cell system according to the present invention. In this embodiment, the fuel cell system 1 is mounted on a fuel cell vehicle and includes a solid polymer electrolyte membrane type fuel cell stack 2.

  The fuel cell stack 2 is formed by stacking a plurality of cells formed by sandwiching a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane between an anode and a cathode from both sides, and hydrogen gas as fuel is supplied to the anode. When (anode gas) is supplied and air containing oxygen as an oxidizing agent (cathode gas) is supplied to the cathode, hydrogen ions generated by the catalytic action at the anode move through the solid polymer electrolyte membrane to the cathode. Water is generated by generating electricity by causing an electrochemical reaction with oxygen at the cathode.

  Hydrogen stored in the high-pressure hydrogen tank 3 is supplied to the anode of the fuel cell stack 2 through the hydrogen supply channel 4, and unreacted hydrogen that has not been consumed in the fuel cell stack 2 is supplied from the fuel cell stack 2 to the hydrogen. It is discharged to a diluter (not shown) through the discharge channel 5. The hydrogen supply flow path 4 and the hydrogen discharge flow path 5 are provided with shut-off valves 6 and 7, and a hydrogen discharge flow is provided in the hydrogen discharge flow path 5 upstream of the shut-off valve 7 and immediately downstream of the fuel cell stack 2. A temperature sensor (temperature detection means) 8 for detecting the gas temperature in the passage 5 is provided. In this embodiment, the gas temperature detected by the temperature sensor 8 is regarded as the temperature in the fuel cell stack 2. In addition, you may comprise so that the unreacted hydrogen which was not consumed with the fuel cell 2 may be returned to the hydrogen supply flow path 4 with an ejector or a hydrogen pump, and may be circulated.

  The air is pressurized to a predetermined pressure by the air pump 10 and supplied to the cathode of the fuel cell stack 2 through the air supply passage 11. After the air supplied to the fuel cell stack 2 is used for power generation, it is discharged from the fuel cell stack 2 together with the generated water, and is discharged to the diluter through the air discharge passage 12. The air discharge channel 12 is provided with a pressure control valve 13 for adjusting the air pressure at the cathode of the fuel cell stack 2. In the diluter, the hydrogen discharged from the fuel cell stack 2 is diluted by the air discharged from the fuel cell stack 2.

The fuel cell stack 2 is provided with a cell voltage sensor (cell voltage detection means) 20 for detecting the cell voltage of each cell.
The fuel cell stack 2 is connected to a battery 22 via a DC / DC converter (discharge control means) 21, and electricity generated by the fuel cell stack 2 can be stored in the battery (electric load) 22.
Further, the fuel cell stack 2 is connected to an electric load 24 via a switch (discharge control means) 23 so that electricity generated by the fuel cell stack 2 can be consumed by the electric load 24 as necessary. It has become. In addition, the electric load 24 can be comprised by an electrical resistance, for example.
In this embodiment, the battery 22 and the electric load 24 can be said to be an electric load that consumes electricity generated by the fuel cell stack 2, and the DC / DC converter 21 and the switch 23 supply power to these electric loads. It can be said that the discharge control means controls.

  The fuel cell system 1 includes an electronic control device (control unit) 30, and the electronic control device 30 controls the shutoff valves 6 and 7, the air pump 10, the pressure control valve 13, the DC / DC converter 21, and the switch 23. Is done. In addition, in order to perform discharge control while the power generation of the fuel cell stack 2 is stopped, which will be described later, an electrical signal corresponding to the detected value is input from the temperature sensor 8 and the cell voltage sensor 20 to the electronic control unit 30. The electronic control unit 30 calculates the total voltage of the fuel cell stack 2 by adding up the cell voltages based on the electric signal input from the cell voltage sensor 20. In this embodiment, the electronic control unit 30 constitutes a total voltage detecting means for detecting the total voltage of the fuel cell stack 2.

Next, the discharge control during power generation stop of the fuel cell system 1 will be described.
In this fuel cell system 1, the shutoff valves 6 and 7 are fully closed to close the anode gas flow path system of the fuel cell stack 2, the air pump 10 is stopped, and the supply of air to the fuel cell stack 2 is stopped. As a result, the power generation stop of the fuel cell stack 2 is executed.

  As shown in FIG. 4, the total voltage of the fuel cell stack 2 when power generation is stopped temporarily decreases in the first period St1, rises again in the second period St2, and decreases again in the third period St3, as time passes. As described above, it has the characteristic of performing. When the high voltage state is maintained in the second stage St2 (A in the figure), and in the third stage St3 in which hydrogen and oxygen are mixed on the anode side and a radical reaction occurs, the solid polymer electrolyte membrane It has been found that degradation of Therefore, deterioration of the solid polymer electrolyte membrane can be prevented by preventing the high voltage state from continuing during the power generation stop of the fuel cell stack 2 and shortening the state where hydrogen and oxygen are mixed on the anode side as much as possible.

  Therefore, in this fuel cell system 1, when the voltage rise reaches the end point (start point A in the figure), the discharge of the fuel cell stack 2 is started and the voltage is lowered so that the high voltage state does not continue. The state where hydrogen and oxygen are mixed on the anode side is shortened. As a means for determining that the voltage increase has reached the end point, the amount of voltage change per predetermined time of the total voltage of the fuel cell stack 2 is monitored, and the amount of voltage change has shifted from a positive value to zero or negative. The time was determined to be the end point of the voltage rise.

  As described above, when the discharge start timing of the fuel cell stack 2 during power generation stop is determined, the discharge can be started when the total voltage becomes the highest. When the total voltage becomes the highest, it is presumed that the diffusion of oxygen from the atmosphere to the cathode side of the fuel cell stack 2 is uniformly performed in all the cells, and therefore depends on the stacking position of the cells in the fuel cell stack 2. It is estimated that there is very little variation in cell voltage.

  Further, the monitoring of the voltage change amount is started in accordance with the start timing of the increase in the total voltage of the fuel cell stack 2 (boundary between St1 and St2 in FIG. 4), so that the load of the electronic control unit 30 is unnecessarily increased. Can be prevented from increasing, and power consumption can be reduced. It is known that the start timing of the increase in the total voltage of the fuel cell stack 2 is determined by the amount of hydrogen permeated from the anode to the cathode, and the amount of hydrogen in the anode system and the solid used in the fuel cell stack 2 It is determined by the permeation characteristics of the polymer electrolyte membrane and the state quantities (temperature, humidity, anode pressure, etc.) in the fuel cell stack 2.

Next, the discharge control during power generation stop in the fuel cell system 1 will be described with reference to the flowchart of FIG. 2 and the time chart of FIG.
The discharge control shown in FIG. 2 is started by stopping the power generation of the fuel cell stack 2. First, in step S101, based on the gas temperature in the hydrogen discharge flow path 5 (temperature in the fuel cell stack 2) detected by the temperature sensor 8, power generation is stopped and voltage change monitoring is started. Time (hereinafter referred to as standby time).

As described above, the start timing of the increase in the total voltage of the fuel cell stack 2 includes the amount of hydrogen in the anode system of the fuel cell stack 2, the permeation characteristics of the solid polymer electrolyte membrane used in the fuel cell stack 2, As described above, it is determined by the state quantity (temperature, humidity, anode pressure, etc.) in the fuel cell stack 2.
Here, the amount of hydrogen in the anode system of the fuel cell stack 2 immediately after the stop of power generation is known in advance by the configuration of the fuel cell system 1 including the fuel cell stack 2, and the fuel after the discharge stop during the power generation stop described later. The amount of hydrogen remaining in the anode system of the battery stack 2 can be estimated empirically (experimental) by the configuration of the fuel cell system 1, the permeation characteristics of the solid polymer electrolyte membrane are also known, and the fuel cell stack 2 Only the state quantity is a variable.

In this embodiment, the temperature start is used as the state quantity in the fuel cell stack 2 to estimate the rise start timing of the total voltage, and this is set as the standby time T1. The relationship between the temperature in the fuel cell stack 2 and the waiting time T1 is as follows. The higher the temperature in the fuel cell stack 2, the more easily hydrogen permeates the solid polymer electrolyte membrane, the first St1 period is shortened, and the second St2 is shifted earlier (in other words, the voltage rises faster). ). Therefore, the higher the temperature in the fuel cell stack 2, the shorter the waiting time T1.
The relationship between the temperature in the fuel cell stack 2 and the standby time T1 is mapped and stored in advance in the storage unit of the electronic control unit 30, and the standby corresponding to the temperature detected by the temperature sensor 8 in step S101. Time T1 is obtained.

  It is also possible to determine the rise start timing of the total voltage using the pressure in the anode system, that is, the anode pressure, as the state quantity in the fuel cell stack 2, and to set this as the standby time. In this case, a pressure sensor (pressure detection means) is installed in the hydrogen discharge flow path 5 instead of the temperature sensor 8, and the pressure detected by this pressure sensor is used as the anode pressure. The relationship between the anode pressure and the waiting time T1 is as follows. The higher the anode pressure, the greater the amount of hydrogen remaining in the anode system, and the longer it takes for the hydrogen to be consumed. Therefore, the period of the first period St1 becomes longer, and the transition to the second period St2 is delayed. (In other words, the voltage rise slows down). Accordingly, the higher the anode pressure, the longer the waiting time T1.

  It is also possible to determine the start timing of the increase of the total voltage using humidity as the state quantity in the fuel cell stack 2, and to set this as the standby time. In this case, a humidity sensor (humidity detection means) is installed in the hydrogen discharge channel 5 instead of the temperature sensor 8, and the humidity detected by this humidity sensor is used as the humidity in the fuel cell stack 2. The relationship between the humidity in the fuel cell stack 2 and the waiting time T1 is as follows. The higher the humidity in the fuel cell stack 2, the higher the water content of the solid polymer electrolyte membrane, so the hydrogen permeability is higher, the period of the first period St1 is shortened, and the process proceeds to the second period St2 earlier (in other words, , The voltage rises early). Accordingly, the higher the humidity in the fuel cell stack 2, the shorter the waiting time T1.

  As described above, the standby time T1 can be determined using any one of the temperature, humidity, and anode pressure in the fuel cell stack 2 as the state quantity in the fuel cell stack 2, but the temperature in the fuel cell stack 2 It is also possible to determine the waiting time T1 based on appropriate two of humidity and anode pressure, or based on all three.

After determining the standby time T1 in step S101, the process proceeds to step S102, and it is determined whether or not the power generation stop time is equal to or longer than the standby time T1.
If the determination result in step S102 is “NO”, the process returns to step S102 and waits until the power generation stop time reaches the standby time T1.
If the determination result in step S102 is “YES”, the process proceeds to step S103, where the cell voltage sensor 20 detects the cell voltage of each cell of the fuel cell stack 2, and sums the cell voltages to add the fuel cell stack 2. And a change amount of the total voltage per predetermined time (for example, per minute) (hereinafter referred to as a voltage change amount).
Thus, since the process of step S103 (voltage change amount calculation process) is not executed until the standby time elapses after the power generation is stopped, the load on the electronic control device 30 can be reduced and the power consumption can be reduced. be able to.
In this embodiment, the voltage change amount calculation unit is realized by the electronic control device 30 executing step S103.

Next, proceeding to step S104, the voltage change amount calculated in the previous step S103 (hereinafter referred to as the previous voltage change amount) is positive (> 0), and the voltage change amount calculated in the current step S103 (hereinafter referred to as the current voltage change amount). It is determined whether the voltage change amount is 0 or negative (≦ 0). In this embodiment, the determination unit is realized by the electronic control device 30 executing step S104.
If the determination result in step S104 is “NO”, the process proceeds to step S105. If the determination result in step S104 is “YES”, the process proceeds to step S107.

If the determination result in step S104 is “NO”, the voltage state of the fuel cell stack 2 is the state of the first period St1 in FIG. 4 or the voltage continues to increase in the second period St2. . Therefore, in this case, the process proceeds to step S105, the voltage change amount calculation cycle is set to a predetermined constant time t (for example, 1 minute), the process further proceeds to step S106, and the voltage change amount is calculated in step S103. It is determined whether or not the predetermined time t has elapsed, and if the determination result in step S106 is “NO”, the process returns to step S106 and waits until the predetermined time t elapses, and the determination in step S106 If the result is “YES”, the process returns to step S103, the cell voltage sensor 20 detects the cell voltage of each cell of the fuel cell stack 2 again, and sums the cell voltages to obtain the total voltage of the fuel cell stack 2. And the voltage change amount is calculated.
That is, the voltage change amount calculation process in step S103 and the voltage change amount transition determination process in step S104 are performed only when the predetermined time t has elapsed, and both processes are not performed during the elapse of the predetermined time t. As a result, the load on the electronic control unit 30 can be prevented from being increased unnecessarily, and power consumption can be reduced.

  On the other hand, if the determination result in step S104 is “YES”, it can be determined that the voltage increase in the second period St2 has reached the end point and the total voltage of the fuel cell stack 2 has leveled out or has started to decrease. it can. Therefore, in this case, the process proceeds to step S107 and the fuel cell stack 2 is discharged. The discharge of the fuel cell stack 2 may be executed by operating the DC / DC converter 21 to charge the battery 22, or by turning on the switch 23 and consuming electric power by the electric load 24. Also good.

Then, the process proceeds from step S107 to step S108, where the total voltage of the fuel cell stack 2 is equal to or lower than the first predetermined value V1, or the lowest value (hereinafter referred to as the lowest cell voltage) of the cell voltages of all cells is the second. It is determined whether or not any of the predetermined value V2 or less is satisfied.
When the determination result in step S108 is “NO”, that is, when the total voltage of the fuel cell stack 2 is larger than the first predetermined value V1 and the minimum cell voltage is larger than the second predetermined value V2. Returns to step S108 and continues to discharge the fuel cell stack 2 until the determination result in step S108 becomes "YES".
On the other hand, when the determination result in step S108 is “YES”, that is, the total voltage of the fuel cell stack 2 is equal to or lower than the first predetermined value V1, or the minimum cell voltage is equal to or lower than the second predetermined value V2. In some cases, the process proceeds to step S109, and the discharge of the fuel cell stack 2 is stopped by disabling the DC / DC converter 21 or turning off (inactive) the switch 23.

  That is, in step S108, it is determined whether or not the discharge stop condition is satisfied. There are two discharge stop conditions, and the discharge is stopped when one of the conditions is satisfied. One of the discharge stop conditions is that the total voltage of the fuel cell stack 2 is not more than a first predetermined value V1 (for example, 0 volts), and the other is that the minimum cell voltage is not more than the second predetermined value V2. is there.

  As in this embodiment, when the discharge of the fuel cell stack 2 is started when the previous voltage change amount is positive (> 0) and the current voltage change amount is 0 or negative (≦ 0), The discharge can be started when the voltage becomes the highest. As described above, when the total voltage becomes the highest, it is presumed that the diffusion of oxygen from the atmosphere to the cathode side of the fuel cell stack 2 is performed uniformly in all cells, and the cells in the fuel cell stack 2 It is estimated that there is very little variation in cell voltage depending on the stacking position. Therefore, the discharge stop timing can be determined based on the total voltage of the fuel cell stack 2. The first predetermined value V1 is a total voltage when it is estimated that oxygen in the anode of the fuel cell stack 2 (that is, oxygen permeated from the cathode to the anode through the solid polymer electrolyte membrane) is consumed, For example, it can be set to 0 volts.

  However, the reason why the discharge stop timing can be determined based on the total voltage of the fuel cell stack 2 is based on the assumption that all the cells are normal. If there is an abnormal cell and the abnormal cell has a lower cell voltage than other normal cells, the discharge stop timing is determined based on the total voltage of the fuel cell stack 2, and the abnormal cell This will damage the solid polymer electrolyte membrane. Therefore, basically, the discharge stop timing is determined based on the total voltage of the fuel cell stack 2, but even if the total voltage is not less than or equal to the first predetermined value V1, the minimum cell voltage is the second predetermined value V2. In the following cases, it is determined that the cell having the lowest cell voltage is abnormal, and the discharge is stopped to protect the fuel cell stack 2. Note that the second predetermined value V2 can be set to, for example, approximately 0 V (a value in consideration of sensor error so that the true value of the cell voltage does not become 0 V or less).

After stopping the discharge in step S109, the process proceeds to step S110, and it is determined whether or not the elapsed time since the power generation of the fuel cell stack 2 is stopped is equal to or longer than the predetermined time T2. The predetermined time T2 is a time when it is predicted that hydrogen will not exist in the anode system of the fuel cell stack 2, and is experimentally obtained in advance as an experimental value.
When the determination result in step S110 is “NO”, the process returns to step S101 and the series of discharge control in steps S101 to S110 is continued.
If the determination result in step S110 is “YES”, since there is no hydrogen in the anode system of the fuel cell stack 2, it is determined that no voltage drop will occur thereafter, and the execution of this discharge control routine is terminated. To do. Thereby, it is not necessary to continuously monitor the voltage change amount, the load on the electronic control device 30 can be reduced, and the power consumption can be reduced.

  According to the fuel cell system 1 of this embodiment, the discharge start condition of the fuel cell stack 2 when power generation is stopped is not managed by the voltage value of the fuel cell stack 2, but is managed by the voltage change amount. Can be executed. For example, if the discharge start condition is managed by a voltage value, depending on the hydrogen pressure and temperature at the time of stop, the voltage value does not rise to the discharge start threshold in the second period St2, and it may occur that the discharge cannot be performed. When the discharge start condition is managed by the voltage change amount, the discharge is started when the voltage value becomes the highest in the second period St2, so that the discharge can be surely executed at an appropriate timing.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, in the above-described embodiment, the temperature detection means for detecting the temperature of the fuel cell stack is constituted by the temperature sensor for detecting the temperature in the anode system. Instead, the temperature inside the fuel cell stack is detected. You may comprise with a temperature detection means, and you may comprise with the temperature detection means which detects the temperature in the cathode system of a fuel cell stack.
Further, in the above-described embodiment, the humidity detecting means for detecting the humidity in the fuel cell stack is configured by the humidity sensor for detecting the humidity in the anode system, but instead, the humidity sensor in the cathode system of the fuel cell stack is configured. You may comprise with the humidity detection means to detect humidity.

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell stack 8 Temperature sensor (temperature detection means)
20 cell voltage sensor (cell voltage detection means)
21 DC / DC converter (discharge control means)
22 Battery (electric load)
23 switch (discharge control means)
24 Electric load 30 Electronic control device (control unit, total voltage detection means)

Claims (4)

A fuel cell stack formed by stacking a plurality of cells that generate electricity by supplying an anode gas containing hydrogen to the anode and a cathode gas containing oxygen to the cathode;
An electric load connected to the fuel cell stack and consuming electricity generated by the fuel cell stack;
Discharge control means for controlling power supply from the fuel cell stack to the electric load;
Total voltage detecting means for detecting the total voltage of the fuel cell stack;
A control unit for controlling the discharge control means;
With
The control unit calculates a voltage change amount per predetermined time based on the total voltage value detected by the total voltage detection means, and calculates the voltage change amount after the fuel cell stack stops generating power. And a determination unit that determines whether or not the voltage change amount calculated by the means has shifted from positive to zero or negative, and when the determination unit makes an affirmative determination, the discharge control unit is operated to the electric load. When the total voltage value is equal to or lower than the total voltage determination threshold estimated to have consumed oxygen in the anode of the fuel cell stack after the power supply is started, the discharge control means is turned off. A fuel cell system which is activated to stop power supply to the electric load. Cell voltage detection means for detecting the voltage of each cell of the fuel cell stack;
The control unit is configured such that, after the power supply starts, before the total voltage value becomes equal to or lower than the total voltage determination threshold value, a minimum value among the voltages of each cell detected by the cell voltage detection unit is a cell voltage determination threshold value. The power supply to the electric load is stopped by disabling the discharge control means when the minimum value is equal to or less than the cell voltage determination threshold value when the value is below. The fuel cell system described in 1. Temperature detecting means for detecting the temperature of the fuel cell stack when power generation of the fuel cell stack is stopped; humidity detecting means for detecting the humidity in the fuel cell stack; and detecting the pressure of the anode of the fuel cell stack. Comprising at least one detection means of pressure detection means,
The control unit determines a standby time based on a detection value of the detection unit, and starts executing a voltage change amount calculation process by the voltage change amount calculation unit after the standby time has elapsed since the power generation was stopped. The fuel cell system according to claim 1 or 2, wherein   The control of the discharge control means by the control unit is repeated until a predetermined time when it is predicted that no hydrogen exists in the fuel cell stack elapses. The fuel cell system according to item.

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