JP2004119052A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To operate a fuel cell efficiently by maintaining moisture condition inside the fuel cell in superior condition. <P>SOLUTION: The incoming and outgoing water quantity Wb is calculated (S100-S130 ) by subtracting the outflow water quantity Wout brought out of the fuel cell by the off-gas of the air system of the fuel cell from the value of inflow water quantity Win brought into the fuel cell by the air supplied to the fuel cell as an oxidation gas added with the generated water quantity Wfc generated in connection with power generation of the fuel cell; and when the absolute value of the incoming and outgoing water quantity is larger than the threshold value Wref, the air flow rate Q is corrected by increasing and decreasing (S140-S150) using a value obtained by multiplying the incoming and outgoing water quantity Wb by a proportional constant k3. Since the increase and decrease of the air inflow rate Q have a larger increase and decrease of the outflow water quantity Wout compared with that of the inflow water quantity Win, the incoming and outgoing water quantity Wb is moved toward the value 0, thus, its absolute value is made to be the threshold value Wref or less. By this control, the moisture condition inside the fuel cell can be maintained in the superior condition. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly, to a fuel cell system including a fuel cell that receives power of a fuel gas and an oxidizing gas to generate power.
[0002]
[Prior art]
Conventionally, this type of fuel cell system includes a humidifier that humidifies the air supplied to the fuel cell by transferring moisture between air supplied to the fuel cell and exhaust gas of an air electrode system discharged from the fuel cell. Has been proposed (for example, see Patent Document 1). In this system, a bypass line for supplying air to the fuel cell by bypassing the humidifier is also provided. By supplying air to the fuel cell via the bypass line, pressure loss is reduced and the fuel cell is provided with a bypass line. The generated water is washed away.
[0003]
[Patent Document 1]
JP-A-2000-306595 (FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in such a fuel cell system, although the generated water accumulated in the fuel cell can be flushed with the air supplied to the fuel cell via the bypass line, it is necessary to prevent the generated water from accumulating in the fuel cell. Is not taken into account. It is also conceivable to supply air to the fuel cell through a bypass line in order to prevent generated water from accumulating in the fuel cell.However, when the amount of air is excessive, in a polymer electrolyte fuel cell, The wettability of the electrolyte membrane is impaired, leading to a decrease in battery performance.
[0005]
An object of the fuel cell system of the present invention is to improve the moisture condition in the fuel cell. Another object of the fuel cell system of the present invention is to operate a fuel cell efficiently.
[0006]
[Means for Solving the Problems and Their Functions and Effects]
The fuel cell system of the present invention employs the following means in order to achieve at least a part of the above objects.
[0007]
The fuel cell system of the present invention comprises:
A fuel cell system including a fuel cell that receives power of a fuel gas and an oxidizing gas and generates power,
Oxidizing gas supply means for supplying oxidizing gas to the fuel cell,
Humidifying means capable of humidifying the oxidizing gas by transferring water between the oxidizing gas supplied to the fuel cell by the oxidizing gas supplying means and an oxidizing gas-based exhaust gas discharged from the fuel cell;
From the input water amount calculated by adding the amount of oxidizing gas-containing water expected to be supplied to the fuel cell by the oxidizing gas and the amount of generated water expected to be generated with the power generation of the fuel cell, the fuel is discharged by the oxidizing gas-based exhaust gas. Control means for controlling the supply of gas or refrigerant to the fuel cell based on the balance water amount obtained by reducing the amount of output water expected to be taken out of the battery,
The gist is to provide
[0008]
In the fuel cell system of the present invention, the oxidizing gas-based water is calculated from the input water amount calculated by adding the oxidizing gas-containing water amount expected to be supplied to the fuel cell by the oxidizing gas to the generated water amount expected to be generated by the power generation of the fuel cell. The supply of gas or refrigerant to the fuel cell is controlled based on the amount of water that is obtained by reducing the amount of output water expected to be taken out of the fuel cell by the exhaust gas. That is, it is possible to control the water condition in the fuel cell to a favorable one by using the balance water amount as a control amount. As a result, the fuel cell can be operated more efficiently. Here, as the oxidizing gas-containing water amount and the output water amount, those calculated assuming that the oxidizing gas and the exhaust gas have a saturated steam pressure can be used. Further, as the amount of generated water, a value calculated based on the current taken out from the fuel cell can be used. Note that air can be used as the oxidizing gas.
[0009]
In such a fuel cell system according to the present invention, the control means may be means for controlling the amount of the balance water to be zero. By doing so, it is possible to suppress an excessive increase or an excessive decrease in the amount of water in the fuel cell, and it is possible to operate the fuel cell more efficiently and favorably. In the fuel cell system according to the aspect of the present invention, the control means controls the gas supply amount to the fuel cell to increase when the balance water amount is a positive value, and the balance water amount is a negative value. Sometimes, the control means may be a means for controlling the gas supply amount to the fuel cell so as to decrease. Increasing the amount of gas supply to the fuel cell when the balance water amount is a positive value is because the input water amount and the output water amount increase due to the increase in the oxidizing gas-containing water amount. This is based on the fact that the amount of output water increases, so that the amount of income and expenditure can be reduced. The same applies to the case where the balance is negative.
[0010]
Further, in the fuel cell system of the present invention, the control means may be means for controlling the amount of the balance water to fall within a predetermined range including a value of zero. By doing so, it is possible to suppress an excessive increase or an excessive decrease in the amount of water in the fuel cell, and it is possible to operate the fuel cell more efficiently and favorably. In the fuel cell system according to the aspect of the present invention, the control unit may control the fuel supply when the amount of water supplied to the fuel cell is larger than the predetermined range and the amount of gas supplied to the fuel cell is smaller than the predetermined range. It may be a means for controlling the supply amount of gas to the battery to be reduced. Increasing the supply amount of the oxidizing gas when the balance water amount exceeds the predetermined range is because the input water amount and the output water amount also increase due to the increase in the oxidizing gas-containing water amount, but the output water amount is larger than the input water amount. This is based on the fact that the larger the increase, the smaller the amount of water balance. The same reason is applied when the amount of income and expenditure falls below the predetermined range.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described using examples. FIG. 1 is a configuration diagram schematically showing a partial configuration of a fuel cell system 20 according to one embodiment of the present invention. As shown in the figure, a fuel cell system 20 of the embodiment receives a supply of a hydrogen-rich fuel gas and air as an oxidizing gas containing oxygen to generate electric power, and supplies the fuel cell 22 with an air pump 24 to the fuel cell 22. A humidifier 28 attached to a supply pipe 26 of air to be discharged and a discharge pipe 27 of an air-based exhaust gas (hereinafter referred to as an air-based off-gas) discharged from the fuel cell 22 to humidify the air, and a whole system And an electronic control unit 30 for controlling.
[0012]
The fuel cell 22 is configured as, for example, a fuel cell stack in which a plurality of unit cells each including an electrolyte membrane and a cathode and an anode side electrode sandwiching the electrolyte membrane are stacked, and the air supplied to the cathode side electrode and The reaction with hydrogen supplied to the anode side generates power with the generation of water. A DC / DC converter, an inverter, and the like (not shown) are usually attached to a power line from an output terminal of the fuel cell 22 so that power (generated power) extracted from the fuel cell 22 can be adjusted. Further, the fuel cell 22 is provided with a circulating flow path for a cooling medium (for example, cooling water) for discharging heat generated by the power generation, and an electronic control unit so that the temperature becomes a temperature suitable for the power generation. It is adjusted by 30.
[0013]
In the humidifier 28, a supply pipe 26 and a discharge pipe 27 are attached to a supply gas passage 28a and a discharge gas passage 28b separated by a hollow fiber membrane having high water vapor selective permeability. The steam and heat of the air-based off-gas are supplied to the fuel cell 22 by bringing the high-temperature air-based off-gas containing water vapor discharged from the cathode into countercurrent contact with the air supplied to the fuel cell 22 by the air pump 24. Remove to air. Specifically, due to the difference in the partial pressure of water vapor generated between the air-based off gas containing water vapor and the air containing little water vapor, the water vapor of the air-based off gas moves through the hollow fiber membrane to the air, This is carried out by transferring the heat of the system off-gas to the room temperature air via the hollow fiber membrane.
[0014]
The electronic control unit 30 is configured as a microprocessor mainly including a CPU 32, and includes, in addition to the CPU 32, a ROM 34 for storing a processing program, a RAM 36 for temporarily storing data, and an input / output port (not shown). The electronic control unit 30 has an air flow rate Q, which is a flow rate of air supplied to the fuel cell 22 by the air pump 24 detected by a flow meter 40 attached to the supply pipe 26, and a flow rate to the fuel cell 22 in the supply pipe 26. Temperature Tin as an air temperature detected by a temperature sensor 42 mounted near the inlet of the fuel cell, and a temperature of the air-based off-gas detected by a temperature sensor 44 mounted near the outlet of the fuel cell 22 in the discharge pipe 27. , An output temperature Tout, a generated current i from a current sensor 46 attached to a power line from the fuel cell 22, and the like are input via an input port. From the electronic control unit 30, a drive signal to the air pump 24 and a drive signal for adjusting a supply amount of the fuel gas to a fuel gas supply unit (not shown) for supplying the fuel gas to the fuel cell 22 are output through an output port. Output.
[0015]
Next, the operation of the fuel cell system 20 according to the embodiment configured as described above, particularly, the operation in adjusting the supply amount of air to the fuel cell 22 and the humidification of air will be described. FIG. 2 is a flowchart illustrating an example of the humidification processing routine executed by the electronic control unit 30. This routine is repeatedly executed at predetermined time intervals (for example, every 0.1 seconds, every 1 second, etc.). When the humidification processing routine is executed, the CPU 32 of the electronic control unit 30 first detects the inlet temperature Tin of the air supplied to the fuel cell 22 detected by the temperature sensor 42 and the air-based off-gas detected by the temperature sensor 44. Processing for reading the outlet temperature Tout from the fuel cell 22, the air flow rate Q as the flow rate of the air supplied to the fuel cell 22 detected by the flow meter 40, the generated current i of the fuel cell 22 detected by the current sensor 46, and the like. Is executed (step S100).
[0016]
Subsequently, based on the read inlet temperature Tin and the air flow rate Q, the inflow water amount Win, which is the amount of water brought into the fuel cell 22 per unit time by the air supplied to the fuel cell 22, is calculated by the following equation (1). At the same time, based on the outlet temperature Tout and the air flow rate Q, the outflow water amount Wout, which is the amount of water waiting from the fuel cell 22 per unit time by the air-based off-gas per unit time, is calculated by equation (2) (step S110). Based on i, the generated water amount Wfc generated with the power generation of the fuel cell 22 is calculated (step S120). In the embodiment, the inflow water amount Win is calculated assuming that the air supplied to the fuel cell 22 contains saturated steam at the inlet temperature Tin. That is, the amount of water per unit volume of air supplied to the fuel cell 22 is obtained from the saturated water vapor pressure at the inlet temperature Tin (function f1 in the equation (1)), and is multiplied by the air flow rate Q and the conversion coefficient k1. It is. Here, the conversion coefficient k1 is set to reflect the flow rate that increases due to humidification by the humidifier 28. In the embodiment, the outflow water amount Wout is also calculated assuming that the air-based off-gas from the fuel cell 22 contains saturated steam at the outlet temperature Tout. That is, similarly to the inflow water amount Win, the water amount per unit volume of the air-based off-gas is obtained from the saturated steam pressure at the outlet temperature Tout, and the water amount per unit volume of the air-based off-gas is multiplied by the air flow rate Q and the conversion coefficient k2. Here, the conversion coefficient k2 is calculated based on the amount of oxygen consumed in the air consumed by the power generation of the fuel cell 22 and the increase due to water vapor when the generated water generated by the power generation of the fuel cell 22 is vaporized. Is set to reflect the
[0017]
(Equation 1)
Win = k1 · Q · f1 (Tin) (1)
Wout = k2 · Q · f1 (Tout) (2)
[0018]
When the inflow water amount Win, the outflow water amount Wout, and the generated water amount Wfc are calculated, the outflow water amount Wout is calculated by subtracting the outflow water amount Wout from the sum of the inflow water amount Win and the generated water amount Wfc as shown in the following equation (3). (Step S130). As can be seen from the calculation formula (1), the balance water amount Wb indicates a certain state in which water tends to accumulate in the fuel cell 22 when its value is positive, and indicates the state where water in the fuel cell 22 tends to accumulate when the value is negative. Shows some degree in a state that tends to dry.
[0019]
(Equation 2)
Wb = Win + Wfc-Wout (3)
[0020]
Then, it is determined whether or not the absolute value of the balance water amount Wb is larger than the threshold value Wref, that is, whether or not the balance amount Wb is within a predetermined range set by the positive and negative threshold values Wref including the value 0 (step S140). Here, the threshold value Wref sets a range of a favorable state in which water does not accumulate in the fuel cell 22 or the inside of the fuel cell 22 is not too dry, that is, a state in which the fuel cell 22 can continue generating power satisfactorily. It is determined by the size of the fuel cell 22 and the like. When the balance water amount Wb is equal to or less than the threshold value Wref, the condition of the water in the fuel cell 22 is good and the humidification state of the supplied air is also determined to be good, and this routine is terminated. When the balance water amount Wb is greater than the threshold value Wref, A new air flow rate Q is set by adding a value obtained by multiplying the balance water amount Wb by the proportionality constant k3 to the air flow rate Q (step S150), and this routine ends. Here, the air flow rate Q is set so that the air flow rate Q is increased when the balance water amount Wb is a positive value, and is set so as to decrease when the balance water amount Wb is a negative value. This is because the temperature of the air-based off-gas (outlet temperature Tout) is usually higher than the temperature of the air supplied to the fuel cell 22 (inlet temperature Tin) and the function of the above-described equations (1) and (2). This is based on the fact that the amount of water per unit volume obtained by f1 is calculated based on the saturated steam pressure using temperature as a variable. That is, since f1 (Tout) is larger than f1 (Tin) in the equation (1), if the air flow rate Q is increased when the balance water amount Wb is a positive value and larger than the threshold value Wref, the air flow rate Q increases. If the amount of outflow water Wout is larger than the increase of the amount of inflow water Win based on the following formula, and the amount of generated water Wfc is the same, the amount Wb of income and expenditure becomes smaller from equation (3), and the value becomes less than or equal to the threshold value Wref. Become. If the air flow rate Q is reduced when the balance water amount Wb is a negative value and smaller than the threshold value Wref, the decrease in the outflow water amount Wout is larger than the decrease in the inflow water amount Win based on the decrease in the air flow amount Q. If the generated water amount Wfc is the same, the balance water amount Wb increases from the equation (3), and its value becomes equal to or larger than the threshold value Wref (the absolute value of the value is equal to or smaller than the threshold value Wref).
[0021]
According to the fuel cell system 20 of the embodiment described above, the water state in the fuel cell 22 is maintained in a good state by adjusting the air flow rate Q so that the absolute value of the water balance Wb is equal to or less than the threshold value Wref. Can be. As a result, the fuel cell can be operated efficiently.
[0022]
In the fuel cell system 20 of the embodiment, the air flow rate Q is adjusted when the balance water amount Wb is not within the predetermined range set by the threshold value Wref. However, the balance water amount Wb falls within the predetermined range set by the threshold value Wref. The air flow rate Q may be adjusted irrespective of whether the air flow rate is within the range.
[0023]
In the fuel cell system 20 of the embodiment, the air flow rate Q is adjusted so that the balance water amount Wb falls within a predetermined range set by the threshold value Wref. However, the fuel gas supply amount to the fuel cell 22 is adjusted. By adjusting the supply amount of the refrigerant to the fuel cell 22, the balance water amount Wb may be adjusted to be within a predetermined range set by the threshold value Wref. Further, a radiator for radiating heat of the refrigerant to the fuel cell 22 is provided, and the amount of heat radiated by the radiator is adjusted (for example, on / off control of a fan) to adjust the temperature of the fuel cell 22 so that the amount of water Wb is adjusted to a threshold value. The value may be within a predetermined range set by Wref.
[0024]
In the fuel cell system 20 of the embodiment, the entire amount of the air-based off-gas is supplied to the humidifier 28 to transfer the water vapor and heat of the air-based off-gas to the air supplied to the fuel cell 22 through the supply pipe 26. 3, a bypass pipe 50 for bypassing the humidifier 28 is provided in a discharge line 27 of the air-based off-gas, and a control valve 52 is provided in the bypass pipe 50. The humidification amount of the air supplied to the fuel cell 22 may be adjusted by controlling the opening / closing of the 52 to bypass a part of the air-based off-gas.
[0025]
In the fuel cell system 20 of the embodiment, the inflow water amount Win and the outflow water amount Wout were calculated on the assumption that the air supplied to the fuel cell 22 and the air-based off-gas from the fuel cell 22 contained saturated steam. Assuming that the humidity of the air near the inlet of the fuel cell 22 in the pipe 26 and the humidity of the air-based off-gas near the outlet of the fuel cell 22 in the discharge pipe 27 are detected, the inflow water amount Win and the outflow water amount Wout are calculated. Is also good.
[0026]
In the fuel cell system 20 of the embodiment, the inflow water amount Win and the outflow water amount Wout are calculated based on the air flow rate Q detected by the flow meter 40 provided in the supply pipe 26 between the air pump 24 and the humidifier 28. However, a flowmeter is attached near the inlet of the fuel cell 22 in the supply pipe 26 and near the outlet of the fuel cell 22 in the discharge pipe 27, and the inflow water amount Win and the outflow water amount Wout are determined using the values from the flowmeter. It may be calculated.
[0027]
As described above, the embodiments of the present invention have been described using the examples. However, the present invention is not limited to these examples, and may be implemented in various forms without departing from the gist of the present invention. Obviously you can get it.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing a configuration of a part of a fuel cell system 20 according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating an example of a humidification process routine executed by an electronic control unit 30 of the embodiment.
FIG. 3 is a configuration diagram schematically showing a configuration of a part of a fuel cell system 20B according to a modification.
[Explanation of symbols]
Reference Signs List 20 fuel cell system, 22 fuel cell, 24 air pump, 26 supply line, 27 discharge line, 28 humidifier, 30 electronic control unit, 32 CPU, 34 ROM, 36 RAM, 40 flow meter, 42, 44 temperature sensor, 46 current sensor, 50 bypass pipe, 52 control valve.

Claims (8)

A fuel cell system including a fuel cell that receives power of a fuel gas and an oxidizing gas and generates power,
Oxidizing gas supply means for supplying oxidizing gas to the fuel cell,
Humidifying means capable of humidifying the oxidizing gas by transferring water between the oxidizing gas supplied to the fuel cell by the oxidizing gas supplying means and an oxidizing gas-based exhaust gas discharged from the fuel cell;
From the input water amount calculated by adding the amount of oxidizing gas-containing water expected to be supplied to the fuel cell by the oxidizing gas and the amount of generated water expected to be generated with the power generation of the fuel cell, the fuel is discharged by the oxidizing gas-based exhaust gas. Control means for controlling the supply of gas or refrigerant to the fuel cell based on the balance water amount obtained by reducing the amount of output water expected to be taken out of the battery,
A fuel cell system comprising: The fuel cell system according to claim 1, wherein the control unit is a unit that controls the amount of the balance water to be zero. The control means controls the gas supply amount to the fuel cell to increase when the balance water amount is a positive value, and controls the gas supply amount to the fuel cell when the balance water amount is a negative value. 3. The fuel cell system according to claim 2, wherein the fuel cell system is means for controlling the fuel cell system to decrease. 2. The fuel cell system according to claim 1, wherein the control unit is a unit that controls the balance water amount to be within a predetermined range including a value of zero. The control means may be configured such that when the amount of the balance water exceeds the predetermined range, the amount of gas supply to the fuel cell increases, and when the amount of the balance water is less than the predetermined range, the amount of gas supply to the fuel cell decreases. 5. The fuel cell system according to claim 4, which is means for controlling the fuel cell system. The fuel cell system according to any one of claims 1 to 5, wherein the control unit is a unit that calculates and uses an oxidizing gas content flow rate and an output water amount assuming that the oxidizing gas and the exhaust gas have a saturated steam pressure. The fuel cell system according to any one of claims 1 to 6, wherein the control unit is a unit that calculates and uses the generated water amount based on a current drawn from the fuel cell. 8. The fuel cell system according to claim 1, wherein said oxidizing gas is air.

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