JP4759815B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system including a fuel cell that generates electric energy by a chemical reaction between hydrogen and oxygen, and is effective when applied to a moving body such as a vehicle, a ship, and a portable generator.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fuel cell system including a fuel cell that generates power using an electrochemical reaction between hydrogen and oxygen (air) is known. For example, in a polymer electrolyte fuel cell that is considered as a driving source for vehicles and the like, in a low temperature state of 0 ° C. or lower, moisture present in the vicinity of the electrode freezes and inhibits diffusion of reaction gas, There is a problem that the electrical conductivity of the film is lowered.
[0003]
[Problems to be solved by the invention]
When starting a fuel cell in such a low-temperature environment, the fuel gas may be supplied even if fuel gas is supplied due to clogging of the reaction gas path due to freezing or hindering the progress or arrival of the reaction gas (hydrogen and air) to the electrolyte membrane. There is a problem that the fuel cell cannot be started because the chemical reaction does not proceed. Furthermore, the gas path is also blocked due to the freezing of moisture condensed in the reaction gas path.
[0004]
In view of the above problems, an object of the present invention is to provide a fuel cell system that can remove moisture inside the fuel cell in a short time when the operation is stopped in a fuel cell system used in a low temperature environment. And
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a fuel cell system including a fuel cell (10) that generates electric energy by electrochemical reaction of hydrogen and oxygen, the fuel cell (10). Output current control means (13) for controlling the output current of the fuel cell, water content detection means (24, 34) for detecting the residual water content in the fuel cell (10), and water removal control in the fuel cell (10). Control means (50) for performing the operation, and when the normal operation of the fuel cell (10) is completed, the control means (50) is provided in the fuel cell (10) detected by the moisture amount detection means (24, 34). based on the residual water content sets a target current value, the output current of the output current control means (13) of the fuel cell (10) is characterized Rukoto is controlled so that the target current value.
[0006]
In this way, by controlling the output current of the fuel cell (10) based on the residual moisture amount in the fuel cell (10), the residual moisture amount and the evaporation rate are compared with the case where the current is controlled to be constant. Improvements can be achieved at the same time. Thereby, it becomes possible to remove the residual moisture in the fuel cell (10) efficiently in a short time.
[0007]
Specifically, as in the invention described in claim 2, the control unit (50) sets the target current value so as to decrease in accordance with the decrease in the residual moisture content in the fuel cell (10). At the start of the moisture removal control, the output current of the fuel cell (10) can be increased to improve the moisture evaporation rate, and the output current can be reduced in accordance with the decrease in the residual moisture amount to effectively reduce the residual moisture amount. .
[0008]
Control of the output current of the fuel cell (10) by the output current control means (13) is performed until the amount of residual moisture in the fuel cell decreases and falls below the range where freezing occurs in a low temperature environment.
[0009]
At this time, it is not necessary to make the residual moisture content below the freezing range for all the portions in each cell constituting the fuel cell (10), and it is sufficient that at least a partial residual moisture content in each cell is below the freezing range. If a part of each cell is dry, power generation can be started by supplying hydrogen and air to the dry part. If power generation is started in a part of the cell, the temperature of the other part can be raised by heat generated by the power generation, and power generation can be performed in the entire cell.
[0010]
Further, in the invention described in claim 3, the fuel cell (10) is provided with an oxygen supply means (21) for supplying oxygen to the fuel cell (10), and the control means (50) includes the fuel cell (10) in the oxygen supply means (21). to supply the air containing excess oxygen amount to the amount of oxygen required to output the target current value is characterized in Rukoto. Thereby, the water which exists in the state of a droplet in a fuel cell (10) with an airflow can be pushed out from the inside of a fuel cell (10).
[0011]
In the invention according to claim 4, the secondary battery (12) connected in parallel with the fuel cell (10) and the auxiliary machines (21, 22, 23, 32, 33, 41, 43, 45), and the control means (50) compensates for the output power of the fuel cell (10) when the fuel cell (10) is generated at the target current value. When surplus is generated for the power required for the operation of the machine, the surplus power is charged in the secondary battery, and the output power of the fuel cell (10) is insufficient for the power required for the operation of the auxiliary machine Is characterized by supplying insufficient power from the secondary battery to the auxiliary machine.
[0012]
As a result, the output current of the fuel cell (10) can be controlled to an optimum value for water removal in the fuel cell (10) regardless of the load of the auxiliary machine such as the blower (21), and moisture removal can be performed efficiently. It can be performed.
[0013]
Further, in the invention described in claim 5, temperature control means (40 to 45) for controlling the temperature of the fuel cell (10) is provided, and the temperature control means (40 to 45) has a temperature of the fuel cell (10). The temperature control is performed so as to be between the predetermined upper limit temperature (Tmax) and the predetermined lower limit temperature (Tmin).
[0014]
As a result, it is possible to prevent the fuel cell temperature from exceeding the upper limit temperature Tmax and destroying the electrolyte membrane and the like inside the fuel cell, and the fuel cell temperature to be lower than the lower limit temperature Tmin to evaporate residual water. Can be prevented from decreasing.
[0015]
The output power control means can be a DC / DC converter (13) as in the invention described in claim 6, and the output voltage of the fuel cell (10) is controlled by the DC / DC converter (13). By doing so, the output current of the fuel cell (10) can be controlled.
[0016]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the present embodiment, the fuel cell system is applied to an electric vehicle (fuel cell vehicle) that runs using the fuel cell as a power source.
[0018]
FIG. 1 shows the overall configuration of the fuel cell system of the embodiment. As shown in FIG. 1, the fuel cell system of the present embodiment includes a fuel cell (FC stack) 10 that generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen. The FC stack 10 is configured to supply electric power to an electric device (load) 11 and a secondary battery 12 for driving the vehicle.
[0019]
In the FC stack 10, the following electrochemical reaction between hydrogen and oxygen occurs to generate electric energy.
(Negative electrode side) H ₂ → 2H ⁺ + 2e ⁻
(Positive electrode side) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O
In this embodiment, a solid polymer electrolyte fuel cell is used as the FC stack 10, and a plurality of cells serving as basic units are stacked. Each cell has a configuration in which an electrolyte membrane is sandwiched between a pair of electrodes.
[0020]
A DC / DC converter (output current control means) 13 that adjusts the output voltage value of the FC stack 10 is provided between the FC stack 10 and the secondary battery 12. FIG. 2 shows the relationship between the output voltage and the output current of the FC stack 10. As shown in FIG. 2, there is a correlation between the output voltage and output current of the FC stack 10, and the output voltage of the FC stack 10 decreases as the output current increases, and the output voltage increases as the output current decreases. It has the characteristics of Therefore, by controlling the output voltage of the FC stack 10 with the DC / DC converter 13, the output current of the FC stack 10 can be arbitrarily controlled.
[0021]
The FC stack 10 is provided with a temperature sensor 14 for detecting the temperature of the FC stack body. Further, the fuel cell system is provided with an outside air temperature sensor 15 that detects the outside air temperature.
[0022]
In the fuel cell system, an air path 20 for supplying air (oxygen) to the oxygen electrode (positive electrode) 10a side of the FC stack 10 and hydrogen for supplying hydrogen to the hydrogen electrode (negative electrode) 10b side of the FC stack 10 are provided. A hydrogen path 30 is provided. The air path 20 is provided with a blower (gas compressor) 21 for air supply for supplying air. Hydrogen is supplied to the hydrogen path 30 from a hydrogen supply device 31.
[0023]
For the electrochemical reaction during power generation, the electrolyte membrane in the FC stack 10 needs to be in a wet state containing moisture. Therefore, during normal operation, humidification is performed on the air in the air path 20 and the hydrogen in the hydrogen path 30 by a humidifier (not shown), and the humidified air and hydrogen are supplied to the FC stack 10. As a result, the inside of the FC stack 10 operates in a wet state. Further, moisture is generated by the electrochemical reaction on the oxygen electrode 10a side.
[0024]
In addition, during the moisture removal operation described later, dry air that is not humidified and dry hydrogen that is not humidified are supplied to the FC stack 10. In order to remove moisture remaining in the FC stack 10, it is desirable that these dry gases have as low a humidity as possible, and at least lower than the humidity in the FC stack 10.
[0025]
Shut valves 22 and 23 for blocking the air path 20 are provided at both ends of the air path 20. By closing these shut valves 22, 23, the inside of the FC stack 10 and the inside of the air path 20 can be shut off from the outside air. Similar shut valves 32 and 33 are provided at both ends of the hydrogen passage 30.
[0026]
The FC stack 10 is provided with moisture sensors 24 and 34 for detecting residual moisture present in the oxygen electrode 10a and the hydrogen electrode 10b inside the FC stack 10. In the present embodiment, humidity sensors are used as the moisture sensors 24 and 34. The humidity sensors 24 and 34 are desirably provided near the outlet of the FC stack 10 in the oxygen electrode 10a and the hydrogen electrode 10b in order to appropriately detect the humidity inside the FC stack 10.
[0027]
The FC stack 10 generates heat with power generation. For this reason, the fuel cell system is provided with cooling systems 40 to 45 so that the FC stack 10 is cooled and the operating temperature becomes an appropriate temperature (about 80 ° C.) for the electrochemical reaction.
[0028]
The cooling system is provided with a cooling water path 40 that circulates cooling water (heat medium) through the FC stack 10, a water pump 41 that circulates the cooling water, and a radiator 42 that includes a fan 43. The radiator 42 and the fan 43 constitute a cooling unit. The heat generated in the FC stack 10 is discharged out of the system by the radiator 42 through the cooling water.
[0029]
The cooling water path 40 is provided with a bypass path 44 in parallel with the radiator 44 for bypassing the cooling water to the radiator 42. The flow path of the cooling water is switched to the radiator 43 side and the bypass passage 44 side by the cooling water switching valve 45.
[0030]
With such a cooling system, the cooling amount control of the FC stack 10 can be performed by the circulation flow rate control by the water pump 41, the air volume control by the radiator 42 and the fan 43, and the bypass flow rate control by the cooling water switching valve 45.
[0031]
The fuel cell system of this embodiment is provided with a control unit (ECU) 50 that performs various controls. The control unit 50 receives a required power signal from the load 11, a temperature signal from the temperature sensor 12, an outside air temperature signal from the outside air temperature sensor 15, a residual moisture amount signal from the moisture sensors 24 and 34, and the like. The control unit 50 is configured to output control signals to the secondary battery 12, the DC / DC converter 13, the blower 21, the water pump 41, the radiator fan 43, the cooling water switching valve 45, and the like.
[0032]
Next, the moisture removal control of the fuel cell system having the above configuration will be described with reference to FIGS. FIG. 3 is a flowchart showing the water removal control of this embodiment.
[0033]
First, it is determined whether or not to stop the operation of the FC stack 10 (step S10). The operation stop determination is performed by detecting a key-off signal from the driver. If the key-off signal is not detected, normal operation is continued (step S11). When the key-off signal is detected, it is determined whether or not moisture removal (moisture purge) in the FC stack 10 is necessary (step S12).
[0034]
The determination of whether or not to remove moisture is performed in consideration of the environmental temperature (outside temperature) at the time of operation stop, seasonal information, and the like. That is, the necessity for the water removal operation is determined based on the condition that the environmental temperature is 0 ° C. or lower, or that the temperature is predicted to decrease in winter. Naturally, moisture operation is not necessary because there is no risk of freezing in conditions such as summer.
[0035]
Further, when the operation of the FC stack 10 is stopped, an expected time of the FC stack 10 stop time by the driver may be input. This is because even if the environmental temperature is below the freezing point when the FC stack 10 is stopped, the FC stack 10 does not immediately drop below the freezing point because the FC stack 10 is sufficiently preheated, and the high temperature is maintained for a while. It is to be done. Therefore, it is not necessary to remove the residual water when the operation is stopped within the stop time of about 10 hours (all day and night).
[0036]
If it is determined that moisture removal is necessary, the moisture sensors 24 and 34 detect the residual water amount in the FC stack 10 (step S13), and determine whether the residual water amount is within the range of freezing in a low temperature environment. Determination is made (step S14). As a result, when the residual moisture content exceeds the freezing range, the output current value (target current value) of the FC stack 10 is determined based on the residual moisture content (step S15).
[0037]
Here, a method of determining the FC stack output current value necessary for removing residual moisture in the FC stack 10 will be described with reference to FIGS.
[0038]
FIG. 4 shows the relationship between the output current, the calorific value, and the generated water amount of the FC stack 10. As shown in FIG. 4, when the output current of the FC stack 10 increases, the amount of heat generation increases, so that it is possible to promote the removal of residual moisture in the FC stack 10. On the other hand, since water is generated by the electrochemical reaction, the generated water increases when the output current of the FC stack 10 increases.
[0039]
FIG. 5 shows the relationship between the output current of the FC stack 10 and the residual moisture content. The vertical axis represents the residual moisture content, and the horizontal axis represents time. I _{0 to} I ₃ indicate the amount of residual moisture when the output current of the FC stack 10 is constant. I ₀ has the largest current value and I ₃ has the smallest current value. W _{0 to} W ₃ are saturated residual moisture amounts that cannot be reduced below that at a specific current value, and W _{0 to} W ₃ correspond to I _{0 to} I ₃ , respectively.
[0040]
As shown in FIG. 5, when the output current is large, the residual water removal rate is fast, while the amount of generated water is large and the residual water amount is saturated at a high value. When the output current is small, the residual water removal rate is high. On the other hand, since the amount of generated water is small, the saturation value of the residual water amount becomes small. Therefore, when the amount of residual moisture in the FC stack 10 is large, the output current value of the FC stack 10 is increased to quickly remove the residual moisture, and the output current value is decreased as the residual moisture amount is reduced. As much as possible, residual moisture can be efficiently removed.
[0041]
FIG. 6 shows the relationship between the residual moisture content in the FC stack 10 and the target current value of the FC stack 10. In the present embodiment, as shown in FIG. 6, until the residual water content is W ₀ the output current I _0, until a residual water content of the W ₁ the output current I _1, the residual water content of W ₂ The output current is set to I ₂ until the residual water amount reaches W ₃ , and the output current is set to I ₃ until the residual water content reaches W ₃ .
[0042]
In this way, by controlling the output current value of the FC stack 10 to the optimum value based on the amount of residual moisture in the FC stack 10, the residual moisture in the FC stack 10 can be quickly increased as shown by Iv in FIG. And can be effectively reduced.
[0043]
Next, the amount of hydrogen and the amount of oxygen necessary to generate the target current value determined as described above are calculated, and air (oxygen) and hydrogen are supplied to the FC stack 10 by the blower 21 and the hydrogen supply device 31. (Step 16). At this time, air and hydrogen are not humidified, dry air is supplied to the oxygen electrode 10a of the FC stack 10, and dry hydrogen is supplied to the hydrogen electrode 10b.
[0044]
In the fuel cell system of this embodiment, the FC stack 10 is configured to supply an excessive amount of air with respect to the amount of air necessary for power generation of the target control current value. As a result, moisture existing in the form of droplets in the FC stack 10 can be pushed out (blown out) from the FC stack 10 by the air flow.
[0045]
Next, the output current is controlled so that the output current value of the FC stack 10 becomes the target control current (step S17). Specifically, as described with reference to FIG. 2, the output current of the FC stack 10 is controlled by the DC / DC converter 13 to control the output current.
[0046]
At this time, the output current of the FC stack 10 is controlled to be an optimum value for removing moisture inside the FC stack 10. Therefore, the electric power generated by the FC stack 10 may be larger or smaller than the electric power necessary for operating the auxiliary devices such as the blower 21, the water pump 41, and the flow path switching valve 45. For this reason, when the power of the FC stack 10 is larger than the auxiliary machine operating power, the surplus power is charged in the secondary battery 12, and conversely, when the power generation amount of the FC stack 10 is smaller than the auxiliary machine operating power, the power is insufficient. Is supplied from the secondary battery 12 to the auxiliary machine. Thereby, the output current of the FC stack 10 can be controlled to an optimum value for removing moisture in the FC stack 10 regardless of the load of the auxiliary machine, and moisture removal can be performed efficiently.
[0047]
Next, temperature control of the FC stack 10 is performed. The FC stack 10 generates heat by power generation. When the FC stack temperature becomes equal to or higher than the upper limit temperature Tmax, the electrolyte membrane or the like inside the FC stack 10 is destroyed. Further, when the FC stack temperature becomes equal to or lower than the lower limit temperature Tmin, the evaporation amount of residual moisture in the FC stack 10 decreases. For this reason, the temperature control of the FC stack 10 is performed by the cooling systems 40 to 45 so that the temperature of the FC stack 10 falls within a predetermined temperature range. In the present embodiment, the upper limit temperature Tmax of the FC stack 10 is set to about 120 ° C., and the lower limit temperature Tmin is set to about 60 ° C.
[0048]
First, the temperature of the FC stack 10 is detected by the temperature sensor 14 (step S18), and it is determined whether the FC stack temperature needs to be cooled (step S19). As a result, if the FC stack temperature exceeds the upper limit temperature Tmax, the cooling water is circulated to the radiator 42 side to cool the FC stack 10 (step S20). If the FC stack temperature is lower than the lower limit temperature Tmin, the cooling water is circulated to the bypass path 44 side, or the water pump 41 is stopped to temporarily stop the cooling of the FC stack 10 (step S21). As a result, the FC stack temperature can be controlled within the range between the upper limit temperature Tmax and the lower limit temperature Tmin.
[0049]
Next, returning to step S13, the residual moisture content in the FC stack 10 is detected, and it is determined whether or not the residual moisture content is within the freezing range. As a result, if the residual water content is below the freezing range, the shut valves 22, 23, 32, 33 provided at both ends of the air path 20 and the hydrogen path 30 are closed (step S21). As a result, the inside of the FC stack 10, the inside of the air path 20, and the inside of the hydrogen path 30 are blocked from the outside air, and moisture intrusion from the external environment can be prevented. Thereafter, the fuel supply to the FC stack 10 is stopped, and the FC stack 10 is completely stopped.
[0050]
When the residual moisture content exceeds the freezing range, the above steps S15 to S21 are repeated.
[0051]
As described above, based on the amount of residual moisture in the FC stack 10 as in the present embodiment, the output current of the FC stack 10 is increased at the start of control to improve the moisture evaporation rate, and the output current is reduced according to the amount of residual water. By doing so, compared to the case where the current is controlled to be constant, it is possible to achieve both improvement of the residual water content and the evaporation rate. Thereby, it becomes possible to remove the residual moisture in the FC stack 10 efficiently in a short time.
[0052]
(Other embodiments)
In the above embodiment, the humidity sensors are used as the moisture sensors 24 and 34 for detecting the residual moisture amount in the FC stack 10. However, the present invention is not limited to this. For example, the electrical resistance of the electrolyte membrane in the FC stack 10 as a moisture sensor. The residual moisture content inside the FC stack 10 can also be detected by measuring this change.
[0053]
Further, it is sufficient that at least a part of the water is removed from each cell constituting the FC stack 10. If a part of the cell is dry, power generation can be started by supplying hydrogen and air to the dry part. If power generation is started in a part of the cell, the temperature of the other part can be raised by heat generated by the power generation, and power generation can be performed in the entire cell.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an overall configuration of a fuel cell system according to the embodiment.
FIG. 2 is a characteristic diagram showing a relationship between an output current and an output voltage of a fuel cell.
FIG. 3 is a flowchart showing water removal control of the fuel cell system according to the embodiment.
FIG. 4 is a characteristic diagram showing the relationship between the output current, the calorific value, and the generated water amount of the fuel cell.
FIG. 5 is a characteristic diagram showing the relationship between the output current of the fuel cell and the residual moisture content.
FIG. 6 is a characteristic diagram showing the relationship between the amount of residual water and the control current value of the fuel cell according to the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell (FC stack), 12 ... Secondary battery, 13 ... DC / DC converter (current control means), 20 ... Air passage, 22, 23 ... Shut valve, 24 ... Humidity sensor (moisture sensor), 30 ... Hydrogen passage, 32, 33 ... shut valve, 34 ... humidity sensor (moisture sensor), 50 ... control unit.

Claims (6)

A fuel cell system comprising a fuel cell (10) for generating electric energy by electrochemical reaction of hydrogen and oxygen,
Output current control means (13) for controlling the output current of the fuel cell (10);
Water content detection means (24, 34) for detecting the residual water content in the fuel cell (10) ;
Control means (50) for performing moisture removal control in the fuel cell (10) ,
The control means (50) is based on the residual water content in the fuel cell (10) detected by the water content detection means (24, 34) when the normal operation of the fuel cell (10) ends. fuel cell system sets a target current value, and wherein the Rukoto is controlled so that the output current of the fuel cell the output current control means (13) (10) becomes the target current value. Wherein said control means (50), a fuel cell system according to claim 1, set to said Rukoto to decrease in accordance with the target current value to decrease the residual water content of the fuel cell (10) . Oxygen supply means (21) for supplying oxygen to the fuel cell (10);
The control means (50) is configured to supply the oxygen supply means (21) with air containing an excessive amount of oxygen relative to the amount of oxygen required for the fuel cell (10) to output the target current value. the fuel cell system according to claim 1 or claim 2, characterized in Rukoto was supplied. A secondary battery (12) connected in parallel with the fuel cell (10);
An auxiliary machine (21, 22, 23, 32, 33, 41, 43, 45) that operates with electric power supplied from the fuel cell (10),
When the fuel cell (10) is generated at the target current value , the control means (50) causes the output power of the fuel cell (10) to be surplus with respect to the power required for the operation of the auxiliary machine. Is generated, the surplus power is charged into the secondary battery, and when the output power of the fuel cell (10) is insufficient with respect to the power required for the operation of the auxiliary machine, the insufficient power is The fuel cell system according to any one of claims 1 to 3, wherein a secondary battery is supplied to the auxiliary machine. Temperature control means (40 to 45) for controlling the temperature of the fuel cell (10),
It said temperature control means (40-45) are claims, characterized in that the temperature of the fuel cell (10) control the temperature to be between a predetermined upper limit temperature (Tmax) of a predetermined minimum temperature (Tmin) 5. The fuel cell system according to any one of 1 to 4.   The output power control means is a DC / DC converter (13), and the output of the fuel cell (10) is controlled by controlling the output voltage of the fuel cell (10) by the DC / DC converter (13). The fuel cell system according to any one of claims 1 to 5, wherein the current is controlled.

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