JP5061594B2 - Fuel cell operation system - Google Patents

Description

  The present invention relates to a fuel cell operation system, and more particularly, to a fuel cell operation system that controls the water content of a fuel cell stack that is supplied with fuel gas and oxidant gas and generates power by a fuel cell chemical reaction.

  Since there is little impact on the environment, fuel cells are installed in vehicles. In the fuel cell, for example, a fuel gas such as hydrogen is supplied to the anode side of the fuel cell stack, a reaction gas containing oxygen such as air is supplied to the cathode side, and necessary electric power is taken out by a cell chemical reaction through the electrolyte membrane.

In this electrochemical reaction, protons (H ⁺ ) move in the electrolyte membrane and move in a hydrated state accompanied by water. Therefore, if the electrode substrate such as the anode is too dry, the accompanying water molecules are insufficient, the cell chemical reaction does not proceed, and the output of the fuel cell is reduced. Therefore, for example, a humidifier or the like is provided and monitored so that the water content of the electrolyte membrane becomes appropriate.

  For example, in Patent Document 1, as a fuel cell system that does not require humidification by an auxiliary device such as a bubbler or a mist generator, the water content is determined using the relationship between the internal pressure on the air electrode side of the fuel cell and the moisture content monitoring variable. It is disclosed that the back pressure valve on the air electrode side is controlled in accordance with a change in the rate monitoring variable. Here, as the moisture content monitoring variable, the internal temperature, output voltage, internal resistance, and off-gas relative humidity of the fuel cell can be used, and the relationship between the moisture content monitoring variable and the opening of the back pressure valve is a control map or a relational expression. Is described.

JP 2002-175821 A

  Patent Document 1 describes that the moisture content is controlled by adjusting the opening of the back pressure valve in accordance with the change in the moisture content monitoring variable of the fuel cell. However, since the internal temperature, output voltage, internal resistance, off-gas relative humidity, etc. of the fuel cell change depending on the degree of the electrochemical reaction, even if the fuel cell responds to these changes, it is already in these states. Has often changed, and the subsequent response will be repeated.

  An object of the present invention is to provide a fuel cell operation system capable of controlling the water content of an electrolyte membrane by predicting the drying of the electrolyte membrane in advance.

A fuel cell operation system according to the present invention includes a fuel cell stack that is supplied with a fuel gas and an oxidizing gas and generates power by a fuel cell chemical reaction, a control valve that controls the pressure of the oxidizing gas supplied to the fuel cell stack, A control unit that changes a set pressure of the control valve based on detection of an observed amount related to the moisture content of the stack, and the control unit is an observed amount threshold value that predicts a change in the moisture content leading to membrane drying. Under the first pressure of oxidant gas, the value of the observed amount when the power generation current of the fuel cell advances and increases in a range where the power generation efficiency is good is in a state before the predetermined target value is reached. Threshold value for a state of water content that does not cause membrane drying of the electrolyte, and does not cause membrane drying to such an extent that power generation efficiency is reduced to the value of the observed amount when the generated current reaches a predetermined target value. in advance constant as the observation amount Was set observations smaller value as the target value, if the value of the observed amount exceeds the threshold amount of observation, in a state where the water content is expected to membrane dryer lowered, the change in moisture content leading to membrane dryer And the pressure of the oxidizing gas is set to a second pressure higher than the first pressure so that the moisture content leading to film drying can be postponed accordingly.

Further, when the control unit exceeds the set observation amount range, the control valve is preferably set to the second pressure of the oxidizing gas that is higher than the first pressure of the oxidizing gas by a pressure difference that is arbitrarily set.

The control unit is preferably the ambient temperature on water temperature or the fuel cell stack cooling water of the fuel cell stack and observables.

  The control unit preferably uses the membrane impedance of the fuel cell stack as an observation amount.

  With the above configuration, the fuel cell operation system detects an observation amount related to the water content of the fuel cell stack, and when the detected observation amount is within the set observation amount range, the control valve is set to the oxidizing gas first pressure. When the set observation amount is exceeded, the change in the water content of the fuel cell stack is predicted, and the control valve is set according to the predicted change in the water content. Use gas pressure. Since the moisture content of the fuel cell stack can be controlled by the oxidant gas pressure, the ex-post response is repeated by setting the range of the set observation amount to a range where drying due to a change in the moisture content of the electrolyte membrane can be predicted in advance. In addition, the water content of the electrolyte membrane can be controlled to an appropriate level before the electrolyte membrane is dried.

  Further, when the detected observation amount exceeds the set observation amount range, the control valve is set to the oxidizing gas second pressure that is higher than the oxidizing gas first pressure by a pressure difference that is arbitrarily set. Since there is a predetermined pressure difference between the oxidizing gas first pressure and the oxidizing gas second pressure, when the detected observation amount exceeds the set observation amount range, the oxidizing gas pressure is changed in steps. As a result, the moisture content can be controlled in advance of drying of the electrolyte membrane.

  Further, the cooling water temperature of the fuel cell stack or the outside air temperature related to the fuel cell stack is used as an observation amount. It is known that when the cooling water temperature is high, the electrolyte membrane is easily dried, and when the outside air temperature is high, the electrolyte membrane is easily dried. Therefore, by setting these as the observed amounts and setting the range of the set observed amount to a range in which drying due to a change in the water content of the electrolyte membrane can be predicted in advance, the electrolyte membrane can be dried without repeating ex-post measures. In addition, the water content of the electrolyte membrane can be controlled appropriately.

  In addition, the membrane impedance of the fuel cell stack is used as an observation amount. It is known that the membrane impedance increases when the electrolyte membrane becomes dry. Therefore, by setting this as the observed amount, and setting the range of the set observed amount in advance so that the drying due to the change in the water content of the electrolyte membrane can be predicted, the electrolyte membrane can be dried without repeating the subsequent response. The water content of the electrolyte membrane can be controlled to an appropriate level.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a fuel cell operation system 10. The fuel cell operation system 10 includes an operation system main body 20 and a control unit 70 that controls each element of the operation system main body 20 as the entire system.

  The operation system main body 20 includes a fuel cell main body called a fuel cell stack 22 in which a plurality of fuel cells are stacked, elements for supplying hydrogen gas arranged on the anode side of the fuel cell stack 22, and a cathode side. It is comprised including each element for the air supply arrange | positioned.

  The fuel cell stack 22 is formed by laminating a plurality of unit cells in which separators are arranged and sandwiched on both outer sides of an MEA (Membrane Electrode Assembly) in which catalyst electrode layers are arranged on both sides of an electrolyte membrane. The fuel cell stack 22 has a function of supplying a fuel gas such as hydrogen to the anode side, supplying an oxidizing gas containing oxygen, for example, air, to the cathode side, generating power by a cell chemical reaction through the electrolyte membrane, and taking out necessary power. Have The generated power is detected by the FC generated power detection unit 68, and the data of the detected generated power is transmitted to the control unit 70.

  The anode-side hydrogen gas source 24 is a tank that supplies hydrogen as a fuel gas. The regulator 26 connected to the hydrogen gas source 24 has a function of adjusting the gas from the hydrogen gas source 24 to an appropriate pressure and flow rate. A pressure gauge 28 provided at the output port of the regulator 26 is a measuring instrument that detects the supply hydrogen pressure. The output port of the regulator 26 is connected to the anode side inlet of the fuel cell stack 22, and the fuel gas adjusted to an appropriate pressure and flow rate is supplied to the fuel cell stack 22.

  The flow divider 32 connected to the anode side outlet of the fuel cell stack 22 is for flowing the impurity gas concentration of the exhaust gas from the anode side outlet to the diluter 64 through the exhaust valve 34. The exhaust gas at this time is a hydrogen gas containing reaction product water in addition to nitrogen. The circulation booster 30 provided between the shunt 32 and the anode side inlet further has a function of increasing the hydrogen partial pressure of the gas returning from the anode side outlet and returning it to the anode side inlet for reuse. It has a hydrogen pump.

  The oxidant gas source 40 on the cathode side can actually use the atmosphere. The atmospheric air as the oxidizing gas source 40 is supplied to the cathode side through the filter 42. The flow meter 44 provided after the filter 42 is a flow meter that detects the total supply flow rate from the oxidizing gas source 40. The oxidizing gas thermometer 46 provided after the filter 42 has a function of detecting the temperature of the gas from the oxidizing gas source 40.

  The air compressor (ACP) 48 is a gas booster that compresses the volume of oxidizing gas by the motor 50 to increase its pressure. In addition, the ACP 48 has a function of providing a predetermined amount of oxidizing gas by changing the rotation speed (the number of rotations per minute) under the control of the control unit 70. That is, when the required flow rate of the oxidizing gas is large, the rotational speed of the motor 50 is increased. Conversely, when the required flow rate of the oxidizing gas is small, the rotational speed of the motor 50 is decreased. The ACP power consumption detection unit 52 is a measuring instrument having a function of detecting the power consumption of the ACP 48, specifically, the power consumption of the motor 50. The motor 50 increases power consumption when the rotation speed is increased, and decreases power consumption when the rotation speed is decreased. Therefore, the power consumption is closely related to the motor rotation speed or the oxidizing gas flow rate.

  The humidifier 54 has a function of appropriately humidifying the oxidizing gas and efficiently performing the fuel cell reaction in the fuel cell stack 22. The oxidizing gas appropriately moistened by the humidifier 54 is supplied to the cathode side inlet of the fuel cell stack 22 and exhausted from the cathode side outlet. At this time, water as a reaction product is also discharged together with the exhaust. Since the fuel cell stack 22 is heated to a high temperature by the reaction, the discharged water is water vapor, and this water vapor is supplied to the humidifier 54 to appropriately wet the oxidizing gas. As described above, the humidifier 54 has a function of appropriately giving water vapor to the oxidizing gas, and a gas exchanger using a so-called hollow fiber can be used.

  Here, the flow path connecting the oxidizing gas source 40 and the cathode side inlet of the fuel cell stack 22 can be referred to as an inlet side flow path. Correspondingly, the flow path connected from the cathode side outlet of the fuel cell stack 22 to the exhaust side can be called an outlet side flow path. The oxidizing gas path 66 that is an oxidizing gas path enters the fuel cell stack 22 from the inlet side channel through the humidifier 54 from the oxidizing gas source 40, and passes through the humidifier 54 from the outlet side channel. Extends to the open air.

  The pressure gauge 56 provided at the cathode side outlet of the outlet side channel has a function of detecting the gas pressure at the cathode side outlet. The pressure regulating valve 60 provided in the outlet side flow path is also referred to as a back pressure valve, and is a valve having a function of adjusting the gas pressure at the cathode side outlet and adjusting the flow rate of the oxidizing gas to the fuel cell stack 22. A valve that can adjust the effective opening of the flow path, such as a valve, can be used. Since the output port of the pressure regulating valve 60 is connected to the humidifier 54 described above, the gas that has exited the pressure regulating valve 60 supplies water vapor to the humidifier 54 and then returns to enter the diluter 64 and then to the outside. Discharged.

  The diluter 64 collects the waste water containing hydrogen from the exhaust valve 34 on the anode side and the exhaust gas containing hydrogen leaking through the MEA due to the water vapor on the cathode side, and discharges it to the outside as an appropriate hydrogen concentration. It is a buffer container.

  Further, in FIG. 1, a cooling water flow path 80 for cooling the fuel cell stack 22 is indicated by a broken line. The cooling water channel 80 is a channel for circulating cooling water between the radiator and the fuel cell stack 22 (not shown), and a circulation pump is provided in the channel.

  The cooling water thermometer 82 is temperature detection means for detecting the temperature of the cooling water flowing through the cooling water flow path 80. The cooling water thermometer 82 is provided in the cooling water flow path 80 downstream of the fuel cell stack and upstream of the radiator (not shown). The detection data of the cooling water thermometer 82 is transmitted to the control unit 70 as an observation amount for predicting MEA film drying.

  The outside air thermometer 84 is temperature detecting means for detecting the outside air temperature T around the fuel cell stack 22. Since the detection of the outside air temperature T of the fuel cell stack 22 is used for the prediction of MEA membrane drying, it is preferable to provide an outside air thermometer 84 at a location that affects the membrane drying. For example, it can be provided near the gas inlet / outlet port of the fuel cell stack 22. Moreover, it is good also as what arrange | positions the external temperature thermometer 84 in several places. The detection data of the outside air thermometer 84 is transmitted to the control unit 70 as an observation amount for predicting MEA film drying.

  The control unit 70 controls the above-described elements of the operation system main body unit 20 as a whole system, and is sometimes called a so-called fuel cell CPU. For example, the control unit 70 has a function of controlling the rotational speed of the ACP 48 and controlling the pressure regulating valve 60 based on the required power generation amount and the generated power data transmitted from the FC generated power detection unit 68. Have. Here, in particular, it has a function of controlling the moisture content of the membrane drying prevention for predicting the membrane drying of the MEA based on the detection result of the observation amount and adjusting the opening degree of the pressure regulating valve 60. These functions can be realized by software, specifically, by executing a corresponding fuel cell operation program or the like. Some of these functions can also be realized by hardware.

  The operation of the above configuration, in particular, the function of the control unit 70 for controlling the moisture content of the membrane drying prevention will be described using FIGS. In the following, description will be made using the reference numerals in FIG. FIG. 2 is a flowchart showing a procedure for controlling the moisture content of the membrane drying prevention. Each procedure corresponds to each processing procedure in the membrane dry prevention water content control part of the fuel cell operation program.

In the procedure for controlling the moisture content of the membrane drying prevention, first, it is determined whether or not the cooling water temperature θ as an observation amount is in a range equal to or lower than a preset threshold water temperature θ ₀ (S10). The cooling water temperature θ is obtained from the detection data of the cooling water thermometer 82. The threshold water temperature θ ₀ is set to a temperature at which the water content of the MEA can be reduced to predict membrane drying. As the operation of the fuel cell stack 22 proceeds and the generated current increases, the cooling water temperature θ increases, the water content decreases, and membrane drying is predicted. Therefore, the value just before the generated current reaches a predetermined target value. The cooling water temperature can be set to the threshold water temperature θ ₀ . Assuming that the water temperature when the power generation efficiency is within a good range and the generated current is a predetermined target value is 65 ° C., for example, the threshold water temperature θ ₀ can be 60 ° C. Of course, other water temperatures can be set as the threshold water temperature θ ₀ .

When it is determined that the cooling water temperature θ is in the range equal to or lower than the threshold water temperature θ ₀ , the oxidizing gas pressure is set to a predetermined pressure P ₁ (S12). In general, it is known that the lower the oxidizing gas pressure supplied to the fuel cell stack 22, the higher the water content of MEA and the less likely membrane drying occurs. That is, the moisture content of MEA can be controlled by the oxidizing gas pressure. Therefore, the oxidizing gas pressure P ₁ is set to a sufficiently low pressure at which the water content of MEA is high and film drying does not occur at the cooling water temperature at the threshold water temperature θ ₀ . The oxidant gas pressure is set by setting the opening of the pressure regulating valve 60 described with reference to FIG.

On the other hand, when it is determined that the cooling water temperature θ exceeds the threshold water temperature θ ₀ , it is determined that the water content is reduced and film drying is predicted (S14), and the oxidizing gas pressure is higher than the pressure P ₁ in S12. A high pressure P ₂ is set (S16). If the oxidizing gas pressure P ₁ is called the oxidizing gas first pressure, the oxidizing gas pressure P ₂ can be called the oxidizing gas second pressure. The oxidizing gas second pressure P ₂ is set to a pressure at which the water content of the MEA can be maintained in an appropriate range and film drying does not occur even when the cooling water temperature θ significantly exceeds the threshold water temperature θ ₀ . Therefore, the oxidizing gas second pressure P ₂ is set to a stepwise higher pressure than the oxidizing gas first pressure P ₁ , thereby further increasing the cooling water temperature at which the water content of the MEA decreases and the membrane may be dried. It is possible to provide a sufficient margin for prevention of film drying.

FIG. 3 is a diagram showing a state of the processing of FIG. In FIG. 3, the horizontal axis represents the cooling water temperature, and the vertical axis represents the oxidizing gas pressure. Figure 3 is a oxidizing gas pressure in the range coolant temperature threshold temperature theta ₀ or less P _1, when the coolant temperature exceeds a threshold temperature theta _0, oxidizing gas pressure and P ₂ is higher stepwise It will be shown.

As an example of these values, the threshold water temperature θ ₀ is 60 ° C., P ₁ = 140 kPa, and P ₂ = 200 kPa as in the above example. In this example, at an oxidizing gas pressure of P ₁ = 140 kPa, the water content does not cause membrane drying to such an extent that the power generation efficiency of the fuel cell stack 22 decreases until the cooling water temperature reaches 65 ° C., and P ₁ = At an oxidizing gas pressure of 200 kPa, the values of θ ₀ , P ₁ , and P ₂ are set so that the water content does not cause film drying to such an extent that the power generation efficiency of the fuel cell stack 22 decreases to a cooling water temperature of 75 ° C. To be elected. In other words, the threshold water temperature θ ₀ is an observed amount threshold value for predicting a change in water content leading to membrane drying under the oxidizing gas first pressure P ₁ , and the fuel cell stack 22 causes membrane drying at that water temperature. It is the cooling water temperature in a state having a moisture content of no degree. Then, when the cooling water temperature reaches the threshold water temperature θ ₀ , the oxidizing gas second pressure P ₂ predicts a change in the water content that leads to film drying, and accordingly becomes the water content that leads to film drying. The oxidant gas pressure is set to a higher value in order to further advance the operation. Therefore, the pressure difference between the oxidizing gas second pressure P ₂ and the oxidizing gas first pressure P ₁ = P ₂ −P ₁ is a state where the moisture content reaches the membrane drying based on the prediction of the membrane drying due to the change in the moisture content. Can be set on the basis of how much to postpone. In the above example, the setting is performed so that the power generation efficiency of the fuel cell stack 22 does not decrease until the coolant temperature reaches 75 ° C. These values are illustrative examples, and of course other values can be used.

  In the above, the cooling water temperature is used as the observation amount related to the water content of the MEA of the fuel cell stack 22. As the observation amount related to the water content of the MEA, the outside air temperature related to the fuel cell stack 22 can be used instead of the cooling water temperature. As the outside air temperature related to the fuel cell stack 22, the outside air temperature T detected by the outside air thermometer 84 can be used.

FIG. 4 is a diagram showing the state of the oxidizing gas pressure control for controlling the moisture content of the membrane drying prevention when the outside air temperature is used as the observed amount related to the moisture content of the MEA. The vertical axis in FIG. 4 is the same as that in FIG. 3, and the horizontal axis is the outside air temperature. As shown in FIG. 4, a threshold temperature T ₀ is set for the outside air temperature. When the outside air temperature is equal to or lower than the threshold temperature T ₀ , the oxidizing gas pressure is P ₁ , and the outside air temperature exceeds the threshold temperature T ₀ . the oxidizing gas pressure is P ₂ is higher stepwise is shown.

The method of setting the threshold temperature T ₀ , the oxidizing gas pressure P ₁ , and the oxidizing gas pressure P ₂ is the same as when the observation amount is the cooling water temperature, and the cooling water temperature may be replaced with the outside air temperature. Omitted. The oxidizing gas pressures P ₁ and P ₂ may be different from the values for the cooling water temperature.

  Further, as the observation amount related to the water content of the MEA, the membrane impedance of the MEA of the fuel cell stack 22 can be used instead of the cooling water temperature and the outside air temperature. A known AC impedance method can be used for measuring the membrane impedance. For example, the membrane impedance can be calculated by adding an arbitrary sine wave signal to the output current of the operating fuel cell stack 22 and performing FFT conversion on the output current and the output voltage. The impedance may be calculated only for the real part, that is, the resistance component, or may be calculated by an effective value that is the square root of the square sum of the real part and the imaginary part.

FIG. 5 is a diagram showing the state of the oxidizing gas pressure control for controlling the moisture content of the membrane drying prevention when the membrane impedance is used as the observation amount related to the moisture content of the MEA. 5 is the same as FIG. 3 and FIG. 4, and the horizontal axis is the membrane impedance. As shown in FIG. 5, when the threshold impedance R ₀ for the membrane impedance is set, the oxidizing gas pressure is P ₁ in the range where the outside temperature is equal to or less than the threshold impedance R ₀ , and the outside temperature exceeds the threshold impedance R ₀ , the oxidizing gas pressure is P ₂ is higher stepwise is shown.

The threshold impedance R ₀ , the oxidizing gas pressure P ₁ , and the oxidizing gas pressure P ₂ are set in the same manner as when the observation amount is the cooling water temperature or the outside air temperature, and the cooling water temperature or the outside air temperature may be replaced with the membrane impedance. Therefore, detailed description is omitted. The oxidizing gas pressures P ₁ and P ₂ may be different from the values for the cooling water temperature.

1 is a configuration diagram of a fuel cell operation system in an embodiment according to the present invention. FIG. In embodiment which concerns on this invention, it is a flowchart which shows the procedure of film | membrane dry prevention water content control. In embodiment which concerns on this invention, it is a figure which shows the mode of the oxidation gas pressure control for film | membrane dry prevention water content control, when using a cooling water temperature as an observation amount relevant to the water content of MEA. In embodiment which concerns on this invention, it is a figure which shows the mode of the oxidizing gas pressure control for film | membrane dry prevention water content control, when using outside temperature as an observation amount relevant to the water content of MEA. In embodiment which concerns on this invention, it is a figure which shows the mode of the oxidation gas pressure control for film | membrane dry prevention water content control, when using a membrane impedance as an observation amount relevant to the water content of MEA.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell operation system, 20 Operation system main-body part, 22 Fuel cell stack, 24 Hydrogen gas source, 26 Regulator, 28 Pressure gauge, 30 Circulation booster, 32 Shunt, 34 Exhaust valve, 40 Oxidation gas source, 42 Filter, 44 flow meter, 46 oxidizing gas thermometer, 48 ACP, 50 motor, 52 ACP power consumption detection unit, 54 humidifier, 56 pressure gauge, 60 pressure regulating valve, 64 diluter, 66 oxidizing gas path, 68 FC generated power detection unit , 70 control unit, 80 cooling water flow path, 82 cooling water thermometer, 84 outside air thermometer.

Claims (4)

A fuel cell stack that is supplied with a fuel gas and an oxidizing gas and generates power by a fuel cell chemical reaction; and
A control valve for controlling the pressure of the oxidizing gas supplied to the fuel cell stack;
A control unit that changes the set pressure of the control valve based on detection of an observed amount related to the water content of the fuel cell stack;
With
The control unit
A threshold for the amount of observation that predicts a change in water content leading to membrane drying, and under the first pressure of the oxidizing gas, a power generation current that increases as the power generation of the fuel cell proceeds in a range where power generation efficiency is good is predetermined. It is the value of the observed amount in the state before the target value, and yet the value of the observed amount does not cause the electrolyte membrane to dry, and power generation is performed up to the value of the observed amount when the generated current becomes the predetermined target value. Set a value smaller than the observation value that is a predetermined target value as a threshold observation amount in a state having a water content that does not cause membrane drying to a degree that reduces efficiency,
When the observed value exceeds the threshold observed value, the moisture content decreases and the membrane drying is predicted.As a result, the change in the moisture content leading to membrane drying is predicted, and the moisture content leading to membrane drying is adjusted accordingly. The fuel cell operating system is characterized in that the pressure of the oxidizing gas is set to a second pressure that is higher than the first pressure so that it can be postponed. The fuel cell operation system according to claim 1,
The control unit sets the control valve to a second pressure of the oxidizing gas that is higher than the first pressure of the oxidizing gas by a pressure difference arbitrarily set when exceeding the range of the threshold observation amount. Driving system. The fuel cell operation system according to claim 1,
The control unit uses the temperature of the cooling water of the fuel cell stack or the outside air temperature related to the fuel cell stack as an observation amount. The fuel cell operation system according to claim 1,
The control unit uses the membrane impedance of the fuel cell stack as an observation amount.

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