JP2006351280A - Fuel cell starter and starting method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell starter capable of starting a fuel cell in the shortest starting time without generating flooding even at low temperature. <P>SOLUTION: The fuel cell starter 3 is equipped with a produced water retention amount prediction part 31 predicting the temperature variation of a fuel cell stack 2 based on a taking out current value taken out of the fuel cell stack 2, predicting the variation of the produced water retention amount capable of retaining in the fuel cell stack, based on the temperature variation, an integrated produced water retention amount prediction part 32 predicting the variation of the integrated produced water retention amount capable of retaining in the fuel cell stack based on the taking out current value, and a current calculation part 33 calculating the maximum taking out current value out of taking out current values in which the predicted integrated produced water amount does not exceed the predicted produced water retention amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell starting device for controlling the starting of a fuel cell, and more particularly to a fuel cell starting device and a method for starting a fuel cell in a shortest starting time without causing flooding even at low temperatures.

  A fuel cell system is a device for directly converting chemical energy of a fuel into electrical energy, and supplies a fuel gas containing hydrogen to an anode of a pair of electrodes provided with an electrolyte membrane interposed therebetween. The oxygen agent gas containing oxygen is supplied to the cathode, and electric energy is extracted from the electrodes using the following electrochemical reaction that occurs on the electrolyte membrane side surface of the pair of electrodes.

Anode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode reaction: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
As a conventional example of such a fuel cell system, for example, JP-A-8-106914 (Patent Document 1) is disclosed.

  Here, there are known a method in which the fuel gas supplied to the anode is directly supplied from a hydrogen storage device, and a method in which a hydrogen-containing gas obtained by reforming a fuel containing hydrogen is supplied. Examples of the hydrogen storage device include a high-pressure gas tank, a liquefied hydrogen tank, and a hydrogen storage alloy tank. As the fuel containing hydrogen, natural gas, methanol, gasoline or the like can be considered. On the other hand, air is generally used as the oxygen agent gas supplied to the cathode.

  In the fuel cell described above, when power generation is performed below freezing point, the generated water generated by the electrochemical reaction prevents the oxidizing gas from being supplied to the catalyst, so power generation is possible until the generated water shuts off the gas supply. Only during.

In order to raise the temperature of the fuel cell stack, a method of raising the temperature of the fuel cell stack by heat generated by power generation by connecting the fuel cell stack to an external circuit, mainly an electric resistor, and supplying electric power is known. Yes. As a conventional example of such a fuel cell stack, US Pat. No. 5,798,186 (Patent Document 2) is disclosed. In this conventional example, the heat generated by water generated by power generation is used to raise the temperature of the fuel cell stack, and the temperature of the fuel cell stack having a large heat capacity is increased uniformly and quickly.
JP-A-8-106914 US Pat. No. 5,798,186

  However, in the conventional fuel cell stack described above, when the outside air temperature becomes low, such as below freezing point, the saturated water vapor pressure becomes extremely low and the water freezes. If it is not removed properly, it will remain in the reaction gas flow path and the gas diffusion layer, thereby inhibiting the diffusion of the reaction gas. This phenomenon is generally called flooding, and it prevents the reaction gas from reaching the catalyst, causing a decrease in power generation performance. Eventually, the reaction gas is not supplied to the catalyst and power generation is impossible. There was a problem.

  In order to solve the above-described problem, a fuel cell activation device according to the present invention is a fuel cell activation device that controls the activation of a fuel cell, and the temperature of the fuel cell is determined based on a current value taken out from the fuel cell. A generated water retention amount predicting means for predicting a change and predicting a change in the generated water retention amount that can be retained in the fuel cell based on the temperature change; and the fuel cell based on the extraction current value of the fuel cell. An integrated generated water amount predicting unit that predicts a change in the integrated generated water amount generated in step (a), and a current calculating unit that calculates a maximum extraction current value that does not exceed the generated water retained amount. It is characterized by that.

  The fuel cell activation method of the present invention is a fuel cell activation method for controlling the activation of the fuel cell, and predicts a change in temperature of the fuel cell based on a current value taken out from the fuel cell. And a generated water holding amount prediction stage for predicting a change in the generated water holding amount that can be held in the fuel cell based on the temperature change, and the fuel cell generated based on the extraction current value of the fuel cell. An integrated generated water amount prediction stage for predicting a change in the integrated generated water amount, and a current calculation stage for calculating a maximum extraction current value in which the integrated generated water amount does not exceed the generated water retention amount. .

  In the fuel cell starting device and the fuel cell starting method according to the present invention, the maximum extracted current value among the extracted current values that does not exceed the generated water retention amount that can be retained by the fuel cell. Since the value is calculated and the fuel cell is started with this maximum extracted current value, the fuel cell can be started with the shortest start-up time without causing flooding even under the freezing point.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a fuel cell system including a fuel cell activation device according to the present embodiment.

  As shown in FIG. 1, the fuel cell system 1 of the present embodiment includes a fuel cell stack 2 that is supplied with fuel gas and an oxidant gas and generates power through an electrochemical reaction, and a fuel that controls the start-up of the fuel cell stack 2. Battery starter 3, temperature sensor 4 for detecting the temperature of fuel cell stack 2, current sensor 5 for detecting a current value taken out from fuel cell stack 2, and heating device 6 for heating fuel cell stack 2 at low temperatures And.

  In the fuel cell system 1 configured as described above, in the fuel cell stack 2, hydrogen gas as a fuel gas is supplied to the anode, and air as an oxidant gas is supplied to the cathode to generate power by an electrochemical reaction. Yes.

  Here, the structure of the fuel cells constituting the fuel cell stack 2 will be described with reference to FIG. As shown in FIG. 2, the fuel cell 21 has a pair of electrode catalyst layers 23 disposed on both sides of a solid polymer electrolyte membrane 22, and a pair of gas diffusion layers 24 disposed on the outside thereof. An anode separator 25 having a gas flow path for supplying a fuel gas on the surface thereof is attached to the outside of the fuel cell, and a gas flow path for supplying an oxidant gas is provided on the surface of the oxidizer electrode. A cathode separator 26 is attached. Both of the gas channels have a shape generally called a straight channel in which the channel is almost linear from the gas supply port to the gas discharge port. With such a shape, the generated water can be discharged out of the fuel cell in the liquid phase by the gas flow. In the present embodiment, a case where hydrogen gas is used as the fuel gas and air is used as the oxidant gas will be described. Further, since a perfluorosulfonic acid film is used as the solid polymer electrolyte membrane 22, a perfluorosulfonic acid polymer is used in consideration of bonding properties.

  The fuel cell activation device 3 controls the activation of the fuel cell stack 2, and a generated water retention amount prediction unit (predicted generated water retention amount prediction) that predicts a change in the generated water retention amount that can be retained in the fuel cell stack 2. Means) 31, an integrated generated water amount prediction unit (integrated generated water amount predicting means) 32 for predicting a change in the integrated generated water amount generated in the fuel cell stack 2, and an extraction in which the integrated generated water amount does not exceed the generated water retention amount A current calculation unit (current calculation means) 33 for calculating a maximum extraction current value among the current values is provided.

  The temperature sensor 4 detects the temperature of the fuel cell stack 2 and outputs the detected value to the fuel cell activation device 3.

  The current sensor 5 detects the extracted current value extracted from the fuel cell stack 2 and outputs the detected value to the fuel cell activation device 3.

  The heating device 6 is a device for heating the fuel cell stack 2 such as a heater, and performs heating based on a command from the fuel cell starting device 3 at a low temperature.

  Next, the properties of the above-described fuel cell stack 2 during low temperature startup will be described with reference to FIGS.

  First, the time change of the stack temperature and the accumulated amount of water generated when the fuel cell stack 2 is started will be described with reference to FIG. FIG. 3 is a diagram showing a case where the fuel cell stack 2 is heated from below freezing point (for example, −20 ° C.) to 0 ° C. by heat generation by power generation. As shown in FIG. 3, when the fuel cell stack 2 starts to generate electricity and outputs a current i0 that is taken out, the stack temperature rises. On the other hand, a certain amount of generated water is generated in the fuel cell stack 2 by this power generation, and the integrated generated water amount obtained by integrating the generated water increases.

  However, since the gas temperature is low until the stack temperature reaches 0 ° C. or higher, the amount of generated water generated by power generation is very little discharged out of the fuel cell stack 2 as water vapor, and since it is a freezing point atmosphere, it is used as liquid water. It cannot be discharged.

  However, it has been found that by providing a generated water holding mechanism for holding generated water in the electrolyte membrane, the electrode catalyst layer, the gas diffusion layer, and the gas flow path, constant power generation can be continuously performed. The generated water retention mechanism is a mechanism for trapping generated water. 1. pore part of catalyst part and gas diffusion layer part; 2. polymer material (ionomer); Includes water adsorbents such as zeolite, silica gel, activated alumina, and activated carbon.

  FIG. 4 is a diagram showing the sensitivity of the generated water retention amount with respect to the stack temperature in the generated water retention mechanism of a certain specification. As shown in FIG. 4, it can be seen that the generated water retention amount is sensitive to the stack temperature in the same specification, and the generated water retention amount tends to increase as the stack temperature increases.

  Next, prediction performed after the fuel cell stack 2 is activated by the generated water retention amount prediction unit 31 and the integrated generation water amount prediction unit 32 will be described with reference to FIG.

  FIG. 5 is a diagram in which the fuel cell stack 2 is predicted to be heated from a low temperature (for example, −20 ° C.) to 0 ° C. by heat generation by power generation. As shown in FIG. 5, after the fuel cell stack 2 is started, the take-out current i increases until time t1, and accordingly, the total amount of generated water, the amount of generated water retained, and the stack temperature start increasing. . Then, after time t1, the generated water retention amount prediction unit 31 and the integrated generation water amount prediction unit 32 make predictions when the extraction current i is constant. First, the generated water retention amount prediction unit 31 predicts a change in the stack temperature based on the extracted current value i, and predicts a change in the generated water retention amount based on the change in the stack temperature. Next, the integrated water generation amount prediction unit 32 predicts a change in the integrated water generation amount based on the extracted current value i. Thus, the prediction of the generated water retention amount and the accumulated generated water amount as shown by the broken line in FIG. 5 is calculated.

  In the case of FIG. 5, since the accumulated amount of generated water does not exceed the amount of retained water, if the power generation is continued at this extraction current value i, the generated water generated by the power generation is retained in the water retention mechanism and flooded. It shows that it is possible to continue power generation without generating it.

  On the other hand, FIG. 6 is a diagram showing a case where the start of the fuel cell stack 2 is started at a lower stack temperature than the case shown in FIG. As shown in FIG. 6, in this case, since the accumulated amount of generated water exceeds the amount of retained water at time t2, when the power generation is actually continued after time t1, the diffusion of gas as it approaches time t2. As a result, the output drops and power generation becomes impossible. Therefore, in order to calculate the maximum extraction current value among the extraction current values in which the accumulated generation water amount does not exceed the generation water retention amount, the start-up control process of the fuel cell stack 2 is performed.

  Here, the startup control processing of the fuel cell stack 2 by the fuel cell startup device 3 of the present embodiment will be described based on the flowchart of FIG. As shown in FIG. 7, first, when the fuel cell stack 2 is activated and the process is started (S701), the extraction current value i is set (S702). The extraction current value at the beginning of startup is i0.

  Then, a change in the stack temperature is predicted from the amount of heat generated when constant current power generation is continuously performed with the set extraction current value i (S703), and a change in the generated water retention amount is predicted from the change in the stack temperature. Then, a prediction line of the generated water retention amount is calculated (S704). In the prediction of the generated water retention amount, the relationship between the stack temperature and the generated water retention amount shown in FIG. 4 may be mapped and stored, or an experimental arrangement formula or the like may be prepared.

  Next, the accumulated amount of generated water calculated and stored by the processing up to immediately before is acquired (S705), and the sum of the acquired accumulated water amount and the amount of generated water when power is generated with the extraction current i is obtained. A change in the accumulated water volume is predicted, and a prediction line for the accumulated water volume is calculated (S706).

  When the prediction line for the accumulated product water amount and the prediction line for the product water retention amount are calculated in this way, it is calculated whether or not these prediction lines have solutions, that is, whether they have intersections (S707).

  For example, FIG. 8 is a diagram illustrating changes in the stack temperature, the accumulated amount of generated water, and the amount of retained water when the current value at the initial stage of startup is i0 and power generation is continued at this current value. As shown in FIG. 8, the accumulated amount of generated water rises and becomes tangent to the amount of retained water after time t0. In the prediction after time t1, when the power generation is continued with the extraction current i0, the prediction line L1 for the generated water retention amount and the prediction line L′ 1 for the integrated generation water amount do not intersect. Therefore, the prediction line L1 of the generated water retention amount and the prediction line L′ 1 of the integrated generation water amount have no solution.

  Therefore, when it is determined that there is no solution in stage S707, it is determined that the accumulated generated water amount does not exceed the generated water holding amount and power generation cannot be stopped even if the extraction current i is increased after time t1. The current i is increased by a predetermined minute current Δi, i1 = i0 + Δi is set (S708), the process returns to the stage S702, and the above-described processing is repeated.

  When the prediction line for the generated water retention amount and the prediction line for the integrated generation water amount are calculated again, the prediction line L2 for the generation water retention amount and the prediction line L′ 2 for the integration water generation amount are slightly closer as shown in FIG. However, since there is no solution yet, in step S708, the current is increased by the minute current Δi again and the above-described processing is repeated.

  By repeatedly performing such processing, the extraction current becomes in + 1 = in + Δi, and the prediction line of the integrated water generation amount approaches the prediction line of the generation water retention amount, and finally, as shown in FIG. The prediction line of the accumulated water generation amount is a tangent to the prediction line of the generation water retention amount.

  In this way, if it is determined in stage 707 that the integrated water generation amount and the generated water retention amount have solutions, it is next determined whether the number of solutions, that is, the number of intersections is one or two (S709).

  If the number of intersections is one, it is determined that the maximum extraction current value in which the integrated water generation amount does not exceed the generated water retention amount has been calculated, and the process ends (S710). If the fuel cell stack 2 is started up with the maximum extracted current value calculated here, the accumulated amount of generated water does not exceed the amount of generated water retained, so flooding does not occur, and the maximum current value is started. Therefore, the fuel cell stack 2 can be started up in the shortest time.

  On the other hand, when the number of intersections is two, the accumulated amount of generated water exceeds the amount of generated water retained and the fuel cell stack 2 cannot be started, so that the extraction current i is reduced by a predetermined minute current Δi. I = i−Δi (S711).

  Then, it is determined whether or not the extraction current i is equal to or less than a predetermined extraction current value imin. When the extraction current i is larger than imin, the process returns to the stage S702 and the above-described process is repeated.

  On the other hand, when the reduced extraction current i is equal to or less than the predetermined extraction current value imin, it is determined that the time required for starting the fuel cell stack 2 is too long and it is difficult to start the self-sustained operation. Is turned on (S713), the start control process of the fuel cell stack 2 by the fuel cell starter 3 of the present embodiment is ended (S714), and the process proceeds to a process for controlling the output of the heating device 6 and the like.

  In addition, the above-described processing is recalculated and resetting the current value at an arbitrary interval, and if the interval is reduced, it is possible to perform an ideal startup in which the integrated water generation amount and the generated water retention amount are asymptotic. However, since calculation processing increases, it is desirable to carry out at an appropriate interval.

  As described above, in the fuel cell activation device 3 of the present embodiment, the integrated amount of generated water generated by the fuel cell stack 2 is the maximum of the extracted current that does not exceed the amount of generated water retained that can be retained by the fuel cell stack 2. Since the extraction current value is calculated and the fuel cell stack 2 is activated with this extraction current, the fuel cell can be activated in the shortest activation time without causing flooding even when the temperature is below freezing. 3 effect).

  Further, in the fuel cell starting device 3 of the present embodiment, when the calculated maximum extraction current value is equal to or less than the predetermined value imin, the fuel cell stack 2 is heated by the heating device 6, so that the temperature of the fuel cell stack 2 is low. Therefore, even when the time required for starting becomes too long and it is difficult to start independently, it is possible to start the fuel cell stack 2 by heating with the heating device 6 (effects of claims 2 and 4). .

  Although the fuel cell system of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

  The present invention relates to a fuel cell activation device for controlling the activation of a fuel cell, and is extremely useful as a technique for activating a fuel cell in the shortest activation time without causing flooding even at a low temperature.

It is a block diagram which shows the structure of the fuel cell system provided with the fuel cell starting device which concerns on embodiment of this invention. It is sectional drawing for demonstrating the structure of a fuel battery cell. It is a figure which shows the time change of stack temperature at the time of starting of a fuel cell stack, and the amount of integrated production water. It is a figure which shows the relationship between the temperature of a fuel cell stack, and the amount of produced water retention. It is a figure which shows the time change of the stack temperature at the time of starting of a fuel cell stack, an integrated production | generation water amount, and a production | generation water retention amount. It is a figure which shows the time change of the stack temperature at the time of starting of a fuel cell stack, an integrated production | generation water amount, and a production | generation water retention amount. It is a flowchart which shows the starting control process of the fuel cell stack by the fuel cell starting apparatus which concerns on embodiment of this invention. It is a figure which shows the time change of the stack temperature at the time of starting of a fuel cell stack, an integrated production | generation water amount, and a production | generation water retention amount. It is a figure which shows the time change of the stack temperature at the time of starting of a fuel cell stack, an integrated production | generation water amount, and a production | generation water retention amount. It is a figure which shows the time change of the stack temperature at the time of starting of a fuel cell stack, an integrated production | generation water amount, and a production | generation water retention amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell stack 3 Fuel cell starting device 4 Temperature sensor 5 Current sensor 6 Heating device 31 Generated water retention amount prediction unit (generated water retention amount prediction means)
32 Accumulated water generation prediction unit (integrated water generation prediction means)
33 Current calculation unit (current calculation means)

Claims (4)

A fuel cell activation device for controlling the activation of a fuel cell,
A generated water retention amount that predicts a change in the temperature of the fuel cell based on a current value extracted from the fuel cell and predicts a change in the retained water amount that can be retained in the fuel cell based on the temperature change. Prediction means,
Integrated production water amount prediction means for predicting a change in the amount of integrated production water generated in the fuel cell based on a current value taken out of the fuel cell;
A fuel cell starting device, comprising: a current calculating unit that calculates a maximum extraction current value in which the integrated generated water amount does not exceed the generated water retention amount.   2. The fuel cell starting device according to claim 1, wherein when the maximum extraction current value calculated by the current calculation unit is equal to or less than a predetermined value, the fuel cell is heated by the heating unit. A fuel cell activation method for controlling the fuel cell activation,
A generated water retention amount that predicts a change in the temperature of the fuel cell based on a current value extracted from the fuel cell and predicts a change in the retained water amount that can be retained in the fuel cell based on the temperature change. The prediction stage;
An integrated water generation prediction stage for predicting a change in the integrated water generation amount generated in the fuel cell based on a current value taken out of the fuel cell;
And a current calculation stage for calculating a maximum extraction current value in which the integrated water generation amount does not exceed the generated water retention amount.   4. The method of starting a fuel cell according to claim 3, further comprising a heating stage for heating the fuel cell by a heating means when a maximum extraction current value calculated by the current calculation stage is equal to or less than a predetermined value. .

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