JP5103851B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to control at the time of startup of the fuel cell system.

  In a fuel cell, for example, hydrogen containing hydrogen and oxygen containing oxygen are used as fuel, and electricity is generated by an electrochemical reaction and water is generated on the oxidizer electrode side. Discharged. In general, such a fuel cell has an optimum temperature of 70 to 80 ° C. for power generation, but it may take time for the fuel cell to reach the above temperature when starting at a low temperature. In the case of a fuel cell vehicle as a moving means, quick startability is required even at a low temperature. Therefore, after the fuel cell is started, the self-heating amount of the fuel cell is controlled to warm up the fuel cell in a short time. A method has been proposed (see, for example, Patent Document 1).

  Further, in the fuel cell system as described above, the water of the reaction product is discharged to the outside of the fuel cell together with the air as the oxidant, but a part of the generated water keeps the electrolyte membrane in a humidity atmosphere. A system that recirculates to the fuel cell inlet by a humidifier is often used. This is to prevent the electrolyte membrane from drying and the internal resistance from increasing and the output voltage of the fuel cell from decreasing. For this reason, the air side electrode which is an oxidant side electrode of a fuel cell contains much moisture. A part of the moisture in the air side electrode cross leaks to the hydrogen side electrode which is the fuel side electrode through the diffusion layer and the electrolyte membrane, so that the moisture is also contained in the hydrogen side electrode.

  If the fuel cell is placed in a low temperature environment after being stopped, the water remaining inside may freeze. If water freezes inside the fuel cell, particularly in a flow path through which air and hydrogen flow, there is a problem that the flow path is blocked and gas does not flow, and the fuel cell cannot be started. For this reason, it is predicted whether or not the outside air temperature will drop to the temperature at which freezing occurs in the fuel cell from the change in the outside air temperature while the fuel cell is stopped, and the outside air temperature is expected to drop to the temperature at which freezing occurs. In such a case, a method has been proposed in which a pump provided in a hydrogen recirculation system is started to remove water contained in the system and prevent water from freezing in the fuel cell (for example, Patent Documents). 2).

  For the problem of freezing of the air side electrode of the fuel cell, a scavenging treatment method is proposed in which when the fuel cell is stopped, air is sent into the fuel cell by an air compressor and the remaining water is discharged. (For example, see Patent Document 3).

JP 2002-313388 A Japanese Patent Laid-Open No. 2004-22198 JP 2006-190616 A

  However, since the gas flow path of the fuel cell is formed in a shape in which a narrow flow path is folded back many times, only a part of the gas flow path may freeze. In particular, the gas flow path of the end cell that is easily affected by a decrease in the outside air temperature may be locally frozen or blocked. In the prior art disclosed in Patent Document 2, water is discharged by starting the water discharging means in the hydrogen system, but whether or not freezing or blockage occurs in a part of the narrow gas flow path inside the fuel cell. I don't have a way to confirm. For this reason, for example, even when some gas flow paths in the end cell are frozen due to a rapid decrease in the outside air, the start after the stop is performed assuming that the moisture is removed. However, if such a partial hydrogen gas flow path freezes or closes, sufficient hydrogen gas is not supplied to that part, resulting in a partial shortage of hydrogen gas and deterioration of the fuel cell. There was a problem that. Further, the prior art described in Patent Document 3 is a method for scavenging the air side electrode, there is no description about a method for removing water from the hydrogen side electrode, and Patent Document 1 describes freezing and blockage of the gas flow path. There is no disclosure.

  Further, in a state where the hydrogen gas flow path is partially frozen or blocked, if the self-heating is controlled to accelerate the temperature rise of the fuel cell as in Patent Document 1, the partially frozen or blocked portion is generated. There is a problem that the shortage of the gas supply amount in the portion that has been increased becomes large, and the fuel cell may be further deteriorated.

  An object of the present invention is to reduce deterioration of a fuel cell even in an operation in which a part of a gas flow path in the fuel cell is frozen due to a decrease in outside air temperature.

The fuel cell system of the present invention includes a fuel cell for driving a vehicle that generates electric power by an electrochemical reaction between a fuel gas and an oxidant gas, a temperature sensor that detects an atmospheric temperature outside the fuel cell, and an output from the fuel cell. A fuel cell system comprising: an output current regulator that regulates a current; and a control unit that receives a temperature signal detected by the temperature sensor and outputs an output current command to the output current regulator. The unit calculates an atmospheric temperature decrease rate calculation method for calculating an atmospheric temperature decrease rate during the stop of the fuel cell from an atmospheric temperature detected by the temperature sensor during the stop of the fuel cell and an elapsed time from the stop of the fuel cell. And an atmospheric temperature at the time of startup following the stop of the fuel cell is lower than a predetermined temperature, and an atmospheric temperature decrease rate during the stop of the fuel cell is larger than a predetermined decrease rate In case, in the start-up process of the fuel cell, have a, and an output current limiting means for limiting the output current from the said fuel cell below a predetermined limit current, the limiting current, the atmosphere during the stop of the fuel cell characterized Rukoto a smaller temperature drop rate is high. Further, the limiting current, the ambient temperature in the fuel cell following the stop start that is the lower the smaller, may be used as the, before SL output current regulator to regulate the output voltage of from the fuel cell It is good also as an output voltage regulator which adjusts the output current from the fuel cell by the above, and it has a secondary battery, and the output current regulator is between the fuel cell and the secondary battery. It may be an attached DC / DC converter.

  The present invention has an effect that deterioration of the fuel cell can be reduced even in an operation in which a part of the gas flow path in the fuel cell is frozen due to a decrease in the outside air temperature.

  Hereinafter, a preferred embodiment for carrying out the present invention will be described with reference to FIG. FIG. 1 is a schematic system diagram showing an embodiment according to the fuel cell system 10 of the present invention. In FIG. 1, a solid line indicates an electric system, a double line indicates a gas system such as air or hydrogen, and a one-dot chain line indicates a control system. As shown in FIG. 1, the fuel cell system 10 of the present embodiment uses air containing oxygen as the oxidant gas and hydrogen as the fuel gas. Air, which is an oxidant gas, is sucked into the air compressor 15 from the air through the air suction line 19 via the intake flow meter and the air filter, and the discharge air pressurized by the air compressor 15 is the oxidant of the fuel cell 11. It flows into the air side electrode 12 which is a pole. In the air that has entered the fuel cell from the air side electrode 12 of the fuel cell 11, oxygen is reduced by a power generation reaction with hydrogen supplied from the hydrogen system. The product water, which is a product of the reaction, increases in the air as water vapor or water droplets. The air whose water content has increased after the reaction is discharged to the air discharge pipe 24 of the fuel cell 11.

  Hydrogen gas as fuel gas is stored in the hydrogen tank 31. Hydrogen is supplied from a hydrogen tank 31 to a hydrogen side electrode 13 which is a fuel side electrode of the fuel cell 11 through a hydrogen supply line 33. A part of the hydrogen supplied to the fuel cell 11 is consumed by reacting with oxygen in the air, which is an oxidant supplied to the air side electrode 12, but the unconsumed hydrogen enters the hydrogen system due to cross leak. After being discharged from the hydrogen discharge pipe 34 of the hydrogen side electrode 13 together with moisture etc., the hydrogen circulation pump 36 provided in the hydrogen circulation pipe 35 connecting the hydrogen discharge pipe 34 and the hydrogen supply pipe 33 is used. Recirculated to the hydrogen supply line 33. The hydrogen content consumed by power generation is replenished from the hydrogen tank 31 through the hydrogen supply line 33. The amount of hydrogen gas to be replenished is adjusted by the hydrogen gas supply control valve 32.

  As described above, since the hydrogen system is a circulation system, impurities such as moisture that cross-leak from the air side electrode 12 are concentrated when the hydrogen system is operated for a long time. Therefore, when such impurities have been concentrated to some extent, the hydrogen-based discharge valve 38 of the hydrogen-based atmospheric discharge line 39 connected to the hydrogen discharge line 34 is opened, and a predetermined amount of hydrogen gas after the reaction is supplied. The hydrogen partial pressure in the hydrogen system is increased by discharging the hydrogen-based atmospheric discharge line 39 to the outside air.

  From the air side electrode 12 and the hydrogen side electrode 13 of the fuel cell 11, the generated power of the fuel cell 11 is output by power output lines 41 a and 41 b, respectively. The power output lines 41a and 41b are connected to an inverter device 47, and the DC power supplied from the fuel cell 11 is converted into a driving three-phase AC and supplied to the vehicle driving motor 46. A DC / DC converter 43 is connected to the power output lines 41 a and 41 b between the fuel cell 11 and the inverter device 47, and a secondary battery 45 is connected to the DC / DC converter 43. The DC / DC converter 43 controls charging to the secondary battery 45 and discharging from the secondary battery 45, and controls the output voltage and current of the fuel cell 11 by controlling the voltage of the power output lines 41a and 41b. .

  A temperature sensor 26 for measuring the atmospheric temperature is attached to the outside of the fuel cell 11. The temperature sensor 26 may be a thermocouple or an electric resistance type as long as it can continuously measure the atmospheric temperature.

  The state quantities of the temperature sensor 26, the control valves 32 and 38, the fuel cell 11 and the state quantities of the air compressor 15 and the hydrogen circulation pump 36 are all connected to the control unit 61. Control of the fuel cell system 10 as a whole is performed by outputting the opening commands of the valves 32 and 38, the rotation command of the air compressor 15 and the hydrogen circulation pump 36, and the control signals to the inverter device 47 and the DC / DC converter 43. The control unit 61 includes a CPU and a storage unit, and may be configured to perform overall control by software, or may be configured to perform control by combining electric circuits. Further, data from the vehicle such as the running state of the vehicle and the required required load may be input to the control unit 61. A storage unit 63 that holds control data such as a control map necessary for the control operation is connected to the control unit 61 via a data bus 65.

  The operation of this embodiment will be described with reference to FIG. As shown in step S <b> 101 of FIG. 2, when the driver sets the ignition key of the fuel cell vehicle to the OFF position, the control unit 61 outputs a stop command to each device of the fuel cell system 10. As shown in step S102 of FIG. 2, the stop command stops the air compressor 15 and the hydrogen circulation pump 36, the control valves 32 and 38 are closed, and the power generation of the fuel cell 11 is stopped. Then, as shown in step S <b> 103 of FIG. 2, after the power generation from the fuel cell 11 is stopped, the atmospheric temperature outside the fuel cell 11 is acquired from the temperature sensor 26. The acquired atmospheric temperature is stored in the storage unit 63 as the initial atmospheric temperature.

  As shown in step S104 of FIG. 2, the control unit 61 is also stopped after the acquisition of the atmospheric temperature outside the fuel cell and the storage of data, but the real time provided in the control unit 61 constituted by the CPU. The clock continues to operate even after the control unit 61 stops. Then, as shown in step S105 of FIG. 2, when a predetermined time, for example, 1 hour elapses from the measurement of the atmospheric temperature at the time of stopping, a wakeup signal is output from the real time clock. When this wakeup signal is input to the control unit 61, the control unit 61 is activated as shown in step S106 of FIG.

  As shown in step S <b> 107 of FIG. 2, when the control unit 61 is activated, the control unit 61 acquires the atmospheric temperature when the fuel cell 11 is stopped measured by the temperature sensor 26. Then, as shown in step S108 in FIG. 2, the control unit 61 determines the atmospheric temperature as 1 from the difference between the initial atmospheric temperature stored in the storage unit and the measured atmospheric temperature and the time difference of each temperature measurement. Calculate the atmospheric temperature decrease rate, which is the temperature decrease per hour. As shown in step S <b> 109 of FIG. 2, the control unit 61 stores the measured atmospheric temperature and the calculated atmospheric temperature decrease rate in the storage unit 63. Then, as shown in step S110 of FIG. 2, the control unit 61 stops after the data storage is completed. As shown in step S111 of FIG. 2, the real-time clock continues to operate even when the control unit 61 is stopped. When a predetermined time, for example, 1 hour elapses from the previous measurement of the atmospheric temperature, a wakeup signal is output again. The signal is input to the control unit 61. Then, as shown in step S106 of FIG. 2, the control unit 61 is activated again, and the above operation is repeated. Then, the measured value of the atmospheric temperature and the temperature drop rate of the atmospheric temperature are stored in the storage unit 63 at regular time intervals.

  On the other hand, if the driver turns on the ignition key before a predetermined time until the wake-up signal is output, as shown in step S112 of FIG. 2, a fuel cell start command is output, As shown in step S113 of FIG. 2, the control unit 61 is activated by this command. When activated, the controller 61 obtains the atmospheric temperature at the time of activation from the temperature sensor 26 as shown in step S114 of FIG. 2, calculates the atmospheric temperature decrease rate as shown in step S115 of FIG. Store the data in the storage unit. Then, as shown in step S <b> 116 of FIG. 2, the control unit 61 reads the data of the atmospheric temperature decrease rate during the stop of the fuel cell 11 stored in the storage unit 63. At this time, when there are a plurality of data on the atmospheric temperature decrease rate, the average atmospheric temperature decrease rate may be used as judgment data, the maximum atmospheric temperature decrease rate may be used, or the lowest temperature You may use the atmospheric temperature fall rate just before reaching.

As shown in step S117 of FIG. 2, the control unit 61 determines that the read determination data of the atmospheric temperature decrease rate is equal to or higher than a predetermined value, and the atmospheric temperature data measured at the time of activation is equal to or lower than the predetermined value. After setting the output current limit value I _limit from the fuel cell 11 as shown in step S118 of 2, the start command for the fuel cell 11 is output as shown in step S119 of FIG. In response to the start command of the fuel cell 11, the air compressor 15 is started, air flows into the air side electrode 12, hydrogen from the hydrogen tank 31 is supplied to the hydrogen side electrode 13, and the hydrogen circulation pump 36 is started. Power generation begins. On the other hand, when the read determination data of the atmospheric temperature decrease rate is equal to or lower than a predetermined value, or the atmospheric temperature data measured at the time of activation is equal to or higher than a predetermined value, as shown in step S118 of FIG. Without setting the output current limit value I _limit , a start command for the fuel cell 11 is output as shown in step S119 of FIG.

Here, as the predetermined values of the atmospheric temperature and the atmospheric temperature decrease rate, for example, the atmospheric temperature at startup is −5 ° C. or less and the atmospheric temperature decrease rate is set to a constant value such as 10 ° C./hr. May be. Further, the output current limit value I _limit from the fuel cell 11 may be set as a constant value, for example, 50A. In this case, when the atmospheric temperature at the start of the fuel cell 11 is −5 ° C. or lower and the atmospheric temperature decrease rate is 10 ° C./hr or higher, the output current limit value I _{limit of} 50 A is set, and the atmospheric temperature Is -5 ° C. or higher, or when the atmospheric temperature decrease rate is 10 ° C./hr or lower, the output current limit value I _limit is not set. The set value of the output current of the fuel cell 11 may be changed according to the output capacity of the fuel cell 11 or the like.

Further, the output current limit value I _limit may be changed according to the temperature drop rate of the atmospheric temperature at the time of startup or the atmospheric temperature when the fuel cell is stopped. In this case, since the possibility that freezing has occurred and the region is large as the atmospheric temperature at the time of startup is low, the output current limit value I _limit can be changed so as to decrease as the atmospheric temperature decreases. Is preferred. Even at the same atmospheric temperature, the larger the atmospheric temperature decrease rate while the fuel cell 11 is stopped, the greater the possibility that freezing has occurred and the region, so the output current increases as the atmospheric temperature decrease rate increases. It is preferable to change the limit value I _{limit to} be small. Further, if the atmospheric temperature at the time of start-up and the atmospheric temperature decrease rate while the fuel cell 11 is stopped are associated with each other and the atmospheric temperature decrease rate is small even if the atmospheric temperature decreases, the output current limit value I _limit is not so small. It is also preferable to do so.

A method for this so that the output current limit value I _limit the atmospheric temperature decrease rate of the atmospheric temperature and the fuel cell 11 is stopped at the time of start in relation to change the output current limit value I _limit is are many ways, for example 3, a set value map of the output current limit value I _limit with respect to the atmospheric temperature at the time of activation and the atmospheric temperature decrease rate while the fuel cell 11 is stopped as shown in FIG. There is a method of obtaining the value of the output current limit value I _limit based on the set value map shown in FIG. Here, the setting value map in FIG. 3, the atmospheric temperature decrease rate on the horizontal axis takes the output current limit value I _limit the vertical axis, and a graph of output current limit value I _limit for ambient temperature decrease rate for each atmospheric temperature Is. As shown in this figure, the output current limit value I _limit decreases from the minimum value I ₁ to the output current limit value I ₂ corresponding to each atmospheric temperature as the atmospheric temperature decrease rate decreases from D ₂ to D _1. increases to I ₆ from the output current limit value when the atmospheric temperature decrease rate of D ₁ or less is as constant at I ₆ from the I ₂ for each temperature. Even when the atmospheric temperature is low, the output current limit value I _limit when the atmospheric temperature decrease rate is small is larger than when the atmospheric temperature is higher and the atmospheric temperature decrease rate is larger than that. There are cases. For example, in FIG. 3, the output current limit value I _limit when the atmospheric temperature is −25 ° C. and the atmospheric temperature decrease rate D ₁ is I ₂ , and the output current limit when the atmospheric temperature is −5 ° C. and the atmospheric temperature decrease rate D _2. The value I _limit is larger than I ₁ . As described above, when the output current limit value I _limit is set in association with the atmospheric temperature at the time of startup and the atmospheric temperature decrease rate while the fuel cell 11 is stopped, the output current limit value I _limit is set to be lower than the minimum value I _1. Since the temperature can be set large and the temperature rise due to self-heating is increased in the startup process, the startup time can be shortened.

In the above embodiment, the setting value map has been described on the assumption that the horizontal axis represents the atmospheric temperature decrease rate and the vertical axis represents the output current limit value I _limit , but the format of the setting value map is not limited to this graph, If the set value of the output current limit value I _limit can be output by associating the ambient air temperature with the atmospheric temperature decrease rate while the fuel cell 11 is stopped, the horizontal axis is the temperature and corresponds to each atmospheric temperature decrease rate It is possible to have a plurality of curves, or a database in tabular format.

With reference to FIGS. 4 and 5, the operation when the fuel cell is started by setting the output current value from the fuel cell 11 to the output current limit value I _limit will be described. When the control unit 61 sets the output current limit value I _limit based on the above set value map, the control unit 61 sets the output current between the output current and the output voltage of the fuel cell 11 stored in the storage unit 63 as shown in FIG. On the basis of the characteristic curve, the set output current limit value I _limit is converted into a voltage set value. As shown in FIG. 4, when the output current limit value I _limit is I ₁ , the control voltage V is set to V ₆ , and when the output current limit value I _limit is I ₆ , the control voltage V is set to V ₁ . Set. That is, the control voltage increases as the output current limit value I _limit decreases. Then, the control unit 61 outputs this control voltage setting command to the DC / DC converter 43. The DC / DC converter 43 performs control so that the voltage of the power output lines 41a and 41b becomes the control voltage in accordance with this command.

As described above, when the output current limit value I _limit at the time of start-up is set, the power output from the fuel cell 11 is reduced as compared with the normal case. For this reason, while the output current limit value I _limit is set, the amount of power generated by the fuel cell 11 is limited, and the degree of deterioration of the fuel cell 11 caused by gas shortage even when the gas flow path is partially blocked. Can be reduced. Then, the temperature of the fuel cell 11 is gradually increased by performing the warm-up operation in an operation state in which the deterioration of the fuel cell 11 does not increase. As shown in FIG. 5, the temperature of the fuel cell 11 is slowly increased from time 0 to time t ₁ when the temperature of the fuel cell 11 reaches the thawing temperature T ₁ . When the temperature of the fuel cell 11 reaches the thawing temperature T ₁ at time t ₁ , the setting of the output current limit value I _limit is released assuming that the flow path blockage due to the freezing of the fuel cell 11 has been eliminated, as shown in FIG. The warm-up operation is continued while outputting the required power based on the characteristic curve between the output current and the output voltage of the fuel cell 11. As shown in FIG. 5, when the temperature of the fuel cell 11 reaches the warm-up completion temperature T _{2 at} time t ₂ , the control unit 61 switches the operation of the fuel cell 11 from the warm-up operation to the normal operation, thereby changing the normal operation temperature. Normal startup control is performed until

As described above, when the output current limit value I _limit at the time of start-up is set, the power output from the fuel cell 11 is also reduced compared to the normal case, so that the amount of power generated by the fuel cell 11 is limited, Even if the gas flow path in the fuel cell is partially blocked by freezing due to a decrease in the outside air temperature, it is possible to reduce the deterioration of the fuel cell 11 caused by gas shortage.

In the above embodiment, the voltage of the power output lines 41 a and 41 b connected to the fuel cell 11 is increased by the DC / DC converter 43 in order to reduce the output current from the fuel cell 11. A current control device capable of reducing current may be connected to the power output lines 41a and 41b together with a capacitor or the like to directly limit the current value to the output current limit value I _limit .

1 is a schematic system diagram showing an embodiment of a fuel cell system according to the present invention. 5 is a flowchart showing an operation in the embodiment of the fuel cell system according to the present invention. In embodiment of the fuel cell system which concerns on this invention, it is a control map which shows the relationship between the fall rate of atmospheric temperature and atmospheric temperature, and a limiting current. 4 is a graph showing the relationship between the output current and voltage of the fuel cell in the embodiment of the fuel cell system according to the present invention. 5 is a graph showing changes in the temperature of the fuel cell during the startup process in the embodiment of the fuel cell system according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell system, 11 Fuel cell, 12 Air side electrode, 13 Hydrogen side electrode, 15 Air compressor, 19 Air suction line, 23 Air supply line, 24 Air discharge line, 26 Temperature sensor, 31 Hydrogen tank, 32 Hydrogen supply control valve, 33 Hydrogen supply line, 34 Hydrogen discharge line, 35 Hydrogen circulation line, 36 Hydrogen circulation pump, 38 Hydrogen-based discharge valve, 39 Hydrogen-based atmospheric discharge line, 41a, 41b Power output line, 43 DC / DC converter, 45 secondary battery, 47 inverter device, 49 vehicle drive motor, 61 control unit, 63 storage unit, 65 data bus D ₁ , D ₂ atmospheric temperature decrease rate, I ₁ , I ₆ , I _limit output current limit value, T _1, T ₂ temperatures, t _1, t ₂ hours, V, V _1, V ₆ control voltage.

Claims (4)

A fuel cell for driving a vehicle that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas;
A temperature sensor for detecting an atmospheric temperature outside the fuel cell;
An output current regulator for adjusting an output current from the fuel cell;
A control unit for inputting a temperature signal detected by the temperature sensor and outputting an output current command to the output current regulator;
A fuel cell system comprising:
The control unit calculates an air temperature decrease rate during the stop of the fuel cell from an air temperature detected by the temperature sensor during the stop of the fuel cell and an elapsed time from the stop of the fuel cell. Rate calculation means,
In the start-up process of the fuel cell, when the atmospheric temperature at the time of start-up following the stop of the fuel cell is lower than a predetermined temperature and the air temperature decrease rate during the stop of the fuel cell is larger than a predetermined decrease rate And an output current limiting means for limiting an output current from the fuel cell to a predetermined limit current or less ,
The fuel cell system according to claim 1, wherein the limiting current decreases as the atmospheric temperature decrease rate during stoppage of the fuel cell increases . The fuel cell system according to claim 1, wherein
The limit current is smaller as the atmospheric temperature is lower during startup following the stop of the fuel cell,
A fuel cell system. The fuel cell system according to claim 1 or 2 ,
The output current regulator is an output voltage regulator that regulates an output current from the fuel cell by adjusting an output voltage from the fuel cell;
A fuel cell system. The fuel cell system according to any one of claims 1 to 3 ,
A secondary battery,
The output current regulator is a DC / DC converter attached between the fuel cell and the secondary battery;
A fuel cell system.

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