JP2005044748A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system operable under a broad range of operating conditions while having high fuel utilization efficiency. <P>SOLUTION: A newly supplied hydrogen line 6 supplies a newly supplied hydrogen gas from a high pressure gas tank 2 the pressure of which is adjusted by a pressure adjusting valve 3 to an ejector 4. The ejector 4 mixes a surplus hydrogen gas exhausted from a fuel cell stack 1 with the newly supplied hydrogen gas to supply the mixed hydrogen gas to the fuel cell stack 1. A hydrogen gas line 8 for ejector circulation leads the surplus hydrogen gas exhausted from a fuel electrode outlet to the suction opening of the ejector 4. A hydrogen line 9 for pump circulation leads the surplus hydrogen gas exhausted from the fuel electrode outlet to the downstream of an ejector exhaust port, and a gas circulation pump 5 capable of forcibly circulating a gas is disposed in the middle of the line. A controller 15 determines a water blocking state based on the detected value of a cell voltage sensor 14, and the gas circulation pump 5 is intermittently operated until the blocking state is canceled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly, to a fuel cell system including a gas circulation device that circulates fuel gas or oxidant gas discharged from a fuel cell stack to the fuel cell stack again.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and air containing oxygen to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and the only exhaust material is water.

  Since the electromotive force of a single cell is as low as about 1 [V], the fuel cell is usually configured as a fuel cell stack in which a large number of cells are stacked. In order to maintain high power generation efficiency in all the cells of this fuel cell stack, the amount of reaction gas larger than the amount of reaction gas actually required for the electrochemical reaction is supplied to the fuel cell stack, and the cells at the end of the fuel cell stack It is common practice to distribute the reaction gas up to At this time, surplus gas will be discharged from the fuel cell stack outlet side, but this is not thrown away wastefully, but by providing a gas circulation path and returning it to the fuel cell stack inlet side again, A method of ensuring the amount of reaction gas flowing into the fuel cell stack without deteriorating the fuel consumption rate is employed.

As a gas circulation device of the fuel cell system, there is a fuel circulation type fuel cell system disclosed in Patent Document 1, for example, in which an ejector and a pump are used in combination. According to this system, an ejector that is a type of jet pump that uses the negative pressure of a high-speed fluid and a fuel pump to which power is supplied from the outside are arranged in parallel or in series. The unreacted fuel gas discharged from the stack is sent again to the fuel cell stack.
JP 2003-151588 A (page 4, FIG. 1)

  However, in the above conventional fuel cell system, in order to separate and remove nitrogen that has entered the fuel circulation channel through the fuel cell and excess water discharged from the fuel cell, it branched from the fuel circulation channel. A purge valve is provided in the purge piping, and the purge valve is periodically opened to perform hydrogen purge, so that fuel gas is wasted out of the system, leading to a decrease in fuel cell performance of the fuel cell. was there.

  In order to solve the above problems, the present invention provides a fuel cell stack having at least one unit cell in which an electrolyte membrane is disposed between a fuel electrode and an oxidant electrode, and a fuel that supplies fuel gas to the fuel electrode. A supply pipe, a fuel discharge pipe for discharging surplus fuel gas to the outside of the fuel cell stack, an oxidant supply pipe for supplying oxidant gas to the oxidant electrode, and a surplus oxidant gas outside the fuel cell stack. An oxidant discharge pipe to be discharged into the fuel cell, and the fuel gas or oxidant gas once discharged out of the fuel cell stack from the fuel discharge pipe or the oxidant discharge pipe to the fuel supply pipe or the oxidant supply pipe again as a circulation gas A first circulation path to be fed, an ejector that mixes the newly supplied fuel gas or oxidant gas and the circulation gas, and a parallel arrangement with the first circulation path; A second circulation path for sending fuel gas or oxidant gas once discharged out of the fuel cell stack from the oxidant discharge pipe to the fuel supply pipe or the oxidant supply pipe as a circulation gas, and a second circulation path in the second circulation path A gas circulation pump capable of forcibly circulating gas; a water blockage state detecting means for directly or indirectly detecting a water blockage state of the gas passage in the fuel cell stack; and And a control means for controlling the gas circulation pump to intermittently operate until the water blockage state is improved when it is detected.

  According to the present invention, the water blockage of the gas passage in the fuel cell stack can be eliminated by intermittent operation of the gas circulation pump without opening the purge valve and releasing the fuel gas to the outside. As a result, the drivability and fuel efficiency of the fuel cell system can be improved.

  Next, the best embodiment of the present invention will be described with reference to the drawings. In the following embodiments, a second circulation gas line is provided in parallel with the first circulation gas line passing through the ejector, and a gas circulation pump capable of forced circulation is provided in the middle of the second circulation gas line. A fuel cell system will be described in which when a water blockage state of a battery stack is detected, a gas circulation pump is intermittently operated to eliminate the water blockage state without wasting a reactive gas out of the system. These embodiments improve the drivability and economy of the fuel cell system and are suitable for fuel cell vehicles.

  FIG. 1 is a schematic configuration diagram illustrating Example 1 of a fuel cell system according to the present invention. In this embodiment, an example will be described in which hydrogen is used as the fuel gas and air is used as the oxidant gas.

  1, the fuel cell system includes a fuel cell stack 1 having at least one fuel cell in which an electrolyte membrane is disposed between a fuel electrode and an oxidant electrode, a high-pressure hydrogen gas tank 2 that stores high-pressure hydrogen gas, A pressure adjusting valve 3 for adjusting the pressure of the hydrogen gas supplied from the high-pressure hydrogen gas tank 2, a new supply hydrogen line 6 for supplying a new supply hydrogen gas pressure-adjusted by the pressure adjustment valve 3 to the ejector 4, and the new An ejector 4 that sucks surplus hydrogen gas discharged from the fuel cell stack 1 using the supplied hydrogen gas as a driving source and supplies the hydrogen gas, which is a mixture of the surplus hydrogen gas and the newly supplied hydrogen gas, to the fuel cell stack, and the ejector 4 The stack supply hydrogen line 7 connecting the exhaust port of the fuel cell stack and the fuel electrode inlet of the fuel cell stack, and excess hydrogen gas discharged from the fuel electrode outlet A gas circulation pump 5 that can circulate in a controlled manner, an ejector circulation hydrogen line 8 that guides surplus hydrogen gas discharged from the fuel electrode outlet to the suction port of the ejector 4, and a gas circulation pump 5 that is disposed on the way from the fuel electrode outlet A pump circulation hydrogen line 9 that leads the discharged excess hydrogen gas downstream of the ejector exhaust port, an oxidant supply line 10 that supplies oxidant gas to the oxidant electrode inlet of the fuel cell stack, and an oxidant electrode outlet Based on the oxidant discharge line 11 for deriving the oxidant gas, the cell voltage sensor 14 (water blockage state detecting means) for detecting the cell voltage of the fuel cell stack, and the water blockage state detection result by the cell voltage sensor 14, A controller 15 (control means) that drives the gas circulation pump 5 to eliminate the water blockage state is provided.

  Although not shown, the fuel cell system includes a pressure pickup that detects the pressure of the stack supply hydrogen line 7 and a pressure pickup that detects the pressure of the pump circulation hydrogen line 9, and the controller 15 detects these pressure pickups. A function of controlling the operation of the gas circulation pump 5 according to the value is also provided.

Next, the operation of the fuel cell system having the above configuration will be described.
The high pressure hydrogen gas taken out from the high pressure hydrogen gas tank 2 is depressurized to an appropriate pressure by the pressure regulating valve 3 and supplied to the supply port of the ejector 4 through the new supply hydrogen line 6.

  In the ejector 4, a negative pressure is generated by creating a high-speed gas flow with an internal nozzle, and surplus hydrogen gas discharged from the suction port through the ejector circulation hydrogen line 8 from the suction port using the negative pressure. Inhale. The ejector 4 discharges the newly supplied hydrogen gas flow and surplus hydrogen gas from the exhaust port while mixing them, and supplies the mixed hydrogen gas to the fuel cell stack 1 via the stack hydrogen supply line 7.

  On the other hand, air is sent from the compressor (not shown) to the fuel cell stack 1 through the oxidant supply line 10, and excess air that has not been used in the fuel cell stack passes through the oxidant discharge line 11 and a pressure control valve (not shown). It is discharged outside the fuel cell stack 1.

  Inside the fuel cell stack 1, the chemical energy of hydrogen and oxygen is converted into electrical energy by an electrochemical reaction between hydrogen gas and oxygen in the air. Excess hydrogen gas that has not been involved in the electrochemical reaction is discharged from the fuel cell stack 1. In this embodiment, the surplus hydrogen gas is removed from the two systems of the ejector circulation hydrogen line 8 and the pump circulation hydrogen line 9. It can be recirculated through gas piping.

  Of these, surplus hydrogen gas is returned to the suction port of the ejector 4 by the ejector circulation hydrogen line 8 and can be sent out again into the stack supply hydrogen line by suction and pressure-increasing action by the ejector 4.

  The other is a pump circulation hydrogen line 9, whereby surplus hydrogen gas can be returned to the suction port of the gas circulation pump 5 and sent out again into the stack supply hydrogen line 7 by suction and pressure increase by the gas circulation pump 5.

  As shown in the figure, the surplus hydrogen gas discharged from the gas circulation pump 5 has a piping layout such that it flows as a flow toward the stack downstream from the exhaust port of the ejector 4.

  A configuration of a unit cell battery in a solid polymer electrolyte fuel cell (PEFC) used as the fuel cell stack 1 will be described with reference to FIG.

  An anode electrode 129 and a cathode electrode 130 are disposed across a solid polymer film 128 having hydrogen ion conductivity, and an oxidant gas is supplied to a fuel gas supply groove 131 for supplying fuel gas to the anode electrode 129 and a cathode electrode 130. Oxidant gas supply grooves 132 for supplying gas, conductive gas-impermeable anode separator 133 on the outside of each supply groove, cathode separator 134, and on the outer side of anode separator 133, there is conductivity. A gas and water impervious water separator 135 and a cooling water supply groove 136 through which stack cooling water flows to maintain the fuel cell stack temperature appropriately by removing excess heat generated during power generation are provided. The unit cell battery 137 is composed of 128 to 136.

  In the solid polymer electrolyte fuel cell as described above, when a fuel gas is supplied to the anode electrode 129 and an oxidant gas is supplied to the cathode electrode 130, an electrochemical reaction occurs between the pair of electrodes of the unit cell battery as follows. Thus, an electromotive force is generated.

(Chemical formula 1)
Anode reaction: H ₂ → 2H ⁺ + 2e ⁻
Cathode reaction: 2H ⁺ + (1/2) O ₂ + 2e ⁻ → 2H ₂ O
Usually, hydrogen is used as the fuel gas supplied to the anode, and air is used as the oxidant gas supplied to the cathode. First, when hydrogen is supplied to the anode electrode 129 and air is supplied to the cathode electrode 130, the supplied hydrogen is dissociated into hydrogen ions and electrons at the anode electrode 129. Then, hydrogen ions pass through the solid polymer film 128, and electrons move to the cathode electrode 130 through the external circuit.

  On the other hand, in the cathode electrode 130, oxygen in the supplied air, the hydrogen ions, and electrons react to generate water. At this time, electrons passing through the external circuit become current and can supply power. That is, the reaction shown in the above chemical reaction formula proceeds at the anode electrode 129 and the cathode electrode 130, respectively. The generated water is discharged out of the battery together with the unreacted gas.

  Incidentally, since the electromotive force of the unit cell battery 137 is as low as 1 [V] or less, the fuel cell stack 1 has several tens to several hundreds of unit cells 137 stacked thereon.

The polymer film 128 having hydrogen ion conductivity as used herein, for example, perfluorocarbon sulfonic acid (Nafion ^R, manufactured by DuPont) is known as a proton exchange membrane. This membrane has a hydrogen ion exchange group in the molecule and functions as a hydrogen ion conductive electrolyte by saturated water content, and also has a function of separating fuel and oxidant. Conversely, when the water content of the membrane decreases, the ionic resistance increases and a crossover occurs in which the fuel and oxidant that permeate the membrane are mixed, making it impossible to generate electricity in the battery. For this reason, it is desirable that the solid polymer film be saturated with water.

  When hydrogen ions separated at the anode electrode by power generation move to the cathode electrode through the solid polymer film, water also moves together, so that the solid polymer film tends to dry on the anode electrode side. Further, when the supplied fuel or air contains less water vapor, the solid polymer membrane tends to dry near the respective reaction gas inlets.

  For the above reasons, the fuel cell stack 1 is supplied with fuel and oxidizer that have been humidified in advance, or is wetted with water generated by reaction in the fuel cell.

  FIG. 2 is a diagram for explaining the role of the gas circulation pump in the first embodiment of the fuel cell system according to the present invention.

  In the fuel cell system as in the present embodiment, the amount of hydrogen supplied from upstream to the ejector 4 is the amount of hydrogen consumed by the fuel cell stack 1 (corresponding to the operating load) in order to generate electric power constantly. Although the suction force generation at the ejector 4 has a mechanism in which the internal negative pressure increases according to the flow rate (velocity) of the nozzle jet, and the suction flow rate (circulation flow rate) increases. When only the ejector is used as the gas circulation device, the supply hydrogen amount and the circulation hydrogen amount basically have a one-to-one relationship as shown by the broken line in FIG.

  In contrast, in this embodiment, the gas circulation line by the gas circulation pump is arranged in parallel, so when the circulation flow rate of the gas circulation pump is maximized with respect to the circulation hydrogen flow rate realized by using only the ejector, A circulating hydrogen flow rate as shown by the solid line in FIG. 2 can be obtained. Furthermore, since the output of the gas circulation pump is variable, it is possible to achieve a circulating hydrogen flow rate that can realize the entire region indicated by the oblique lines in FIG.

  With the above-described configuration, while ensuring gas circulation in the ejector, even when the operating load of the fuel cell system is constant, that is, even when the amount of hydrogen supplied to the ejector is constant, only the gas circulation flow rate is independent. Because it becomes possible to control the fuel cell system, the operability of the fuel cell system can be improved, and the gas purge operation for throwing the fuel gas out of the system as in the conventional fuel cell system is unnecessary. Therefore, the economic efficiency of the fuel cell system can be improved.

  FIG. 6 is a diagram for explaining a method of operating the gas circulation pump according to the water clogging state signal of the fuel cell stack in the fuel cell system of the first embodiment.

  If any of the cells constituting the fuel cell stack 1 is blocked by water in the in-cell gas flow path, the supply flow rate of fuel gas or oxidant gas to the cell decreases and the generated voltage of the cell decreases. To do. For this reason, it can be determined whether it is in a water blockage state by measuring each cell voltage of a fuel cell stack, and judging the variation.

  In this embodiment, a cell voltage sensor 14 for detecting each cell voltage of the fuel cell stack 1 is provided, and each cell voltage detected by the cell voltage sensor 14 is input to the controller 15. The controller 15 generates a water clogging state signal for determining whether any cell of the fuel cell stack 2 is in a water blocking state from the cell voltage distribution.

  The water clogging state signal is generated when the difference ΔV (= Vav−Vmin) between the average value Vav of the cell voltages and the cell voltage Vmin having the lowest voltage exceeds a predetermined value. It is the determined signal. Alternatively, the dispersion value Vσ of the cell voltage may be calculated, and water clogging may occur when the dispersion value Vσ exceeds a predetermined value. Furthermore, when the number of cells constituting the fuel cell stack is large, the determination accuracy is lowered, but the cell voltage sensor 14 does not detect the voltage for each cell, but for each of a certain number of cells connected in series. The voltage may be measured and the controller 15 may make the same determination.

  When the degree of water clogging is output as a water clogging level signal, ΔV or Vσ may be used as the water clogging level signal indicating the degree of clogging.

  In the present embodiment, when the water clogging state signal becomes defective (water clogging occurs), the rotation speed of the gas circulation pump is varied at a certain period as shown in FIG. Thereby, pulsation can be given to the amount of gas (gas flow velocity) flowing into the fuel cell stack.

  FIG. 7 is a flowchart for controlling the movement of the gas circulation pump in the fuel cell system of this embodiment, and the algorithm will be described below.

  First, in step S21, the clogged state of the gas passage in the fuel cell stack is obtained from the detection value of the cell voltage sensor. In step S22, it is determined whether the current level of water clogging is bad or good, and if it is determined to be good, the process returns to step S21, and the water clogging state is captured again. . If it is determined to be defective, the process proceeds to step S23, where the operation rotational speed of the pump starts to change, and the removal of the adhering water inside the gas passage in the stack is started.

  Next, in step S24, it is determined whether or not the level of the clogged state has been improved by the intermittent operation of the pump and returned to good. If the level is still defective, the process returns to step S23 and the pump is intermittently connected. Continue driving. When it returns to good, it is no longer necessary to perform intermittent operation, and the pump is returned to normal operation in step S25.

  With the configuration and control method as described above, the effect of quickly removing the adhering water in the gas passage causing water clogging is obtained by pulsating the flow of gas passing through the fuel cell stack. As a result, the operability and reliability of the fuel cell system can be further improved.

FIG. 3 is a schematic configuration diagram of the fuel cell system according to the second embodiment.
In this embodiment, the backflow prevention valve B-13 is arranged on the exhaust side of the ejector 4 so as to prevent the backflow to the inside of the ejector, and the backflow prevention valve is arranged on the discharge side of the gas circulation pump 5 so as to prevent the backflow inside the pump. Since A-12 is installed and the configuration other than the above is the same as that of the above-described first embodiment, the same components are assigned the same reference numerals and redundant description is omitted.

  FIG. 4 is a diagram for explaining the relationship among the rotational speed, the pressure increase amount, and the discharge amount of the gas circulation pump in the fuel cell system of the present embodiment.

  As a general characteristic when a gas having high leakage such as hydrogen gas is used for a gas circulation pump (compressor) that uses gas as a working fluid, the pressure increase amount increases even at the same pump rotation speed. On the contrary, the discharge amount tends to decrease. If the pump is rotated at a higher speed, it is possible to increase both the pressure increase amount and the discharge amount, but there is often a maximum value for the pressure increase amount. The main factor is that the internal leakage in the minute gap inside the pump appears prominently in the case of a gas with low viscosity such as hydrogen and a small molecule.

  Therefore, when the operating condition of the gas circulation pump required in the fuel cell system exceeds the above maximum pump boost value due to the relationship between the pump discharge amount and the boost amount (corresponding to the stack operation pressure), the pump is Even if the pump is in operation, the entire amount sucked in the pump is leaking internally, so there is no point in operating the pump. Therefore, control is performed to stop the gas circulation pump.

  FIG. 5 is a flowchart of a controller controlled by the gas circulation pump in the fuel cell system of this embodiment, and the algorithm will be described below.

  First, in step S11, the supply pressure Pin and the exhaust pressure Pout of the hydrogen gas to the fuel cell stack 1 are combined with the stack supply hydrogen line 7, the pump circulation hydrogen line 9 (or the ejector circulation hydrogen line 8, or 8 and 9 respectively). Measured and taken in with a pressure pickup or the like arranged upstream of the point. Next, in step S12, the current pump boost amount ΔP (= Pin−Pout) is calculated from Pin and Pout. Moving to step S13, it is determined whether or not the current pressure increase amount ΔP has reached the pump maximum pressure increase value ΔPmax described above. If it has not yet reached the maximum value, the effect of internal leakage in the pump is determined in step S15. Continue pumping as if is still small, or start if pump is stopped.

  On the other hand, if the maximum value is reached in the determination in step S13, the operation jumps to step S14, and the influence of the internal leakage of the pump is sufficiently large and the meaning of operating the pump is lost. To stop.

  Further, in the present embodiment, based on the detection result of the cell voltage sensor 14, the controller 15 determines whether any cell of the fuel cell stack 2 is in a water-blocked state from the cell voltage distribution. A clogged state signal is generated. When the controller 15 determines that a water clogging state has occurred according to the water clogging state signal, the controller 15 controls the gas circulation pump 5 to intermittently operate until the water clogging state signal does not indicate the water clogging state. At this time, control is performed so that the backflow prevention valve 12 is opened and the backflow prevention valve 13 is closed. Other controls by the controller 15 are the same as those described with reference to FIGS. 6 and 7 in the first embodiment.

  With the configuration as described above, even if the balance between the pressure increase amount at the ejector and the pressure increase amount at the gas circulation pump is temporarily lost due to a transition period of operation load change, the pressure increase from the ejector. This prevents a part of the discharged gas flow from flowing back in the gas circulation pump, or a part of the gas flow boosted and discharged from the gas circulation pump to flow back in the ejector. As a result, it becomes possible to circulate gas to the fuel cell stack more efficiently and without waste. As a result, the operation stability of the fuel cell system is increased, and the power for driving the gas circulation pump is increased. A reduction effect can be expected.

  Further, if the control method is as described above, it is possible to cut wasteful power consumption in the gas circulation pump further than in the first embodiment, which leads to further improvement in the power supply / demand balance of the entire fuel cell system.

  FIG. 8 is a diagram illustrating a method for operating the gas circulation pump in accordance with the water clogging state signal of the fuel cell stack in the fuel cell system according to the third embodiment of the present invention.

  In this embodiment, a signal that can know the degree of water clogging in the gas passage inside the fuel cell stack continuously or stepwise can be estimated and output from the behavior of the generated voltage of each cell of the fuel cell stack. Except for this, it is the same as the previous embodiments.

  In this embodiment, when the water clogging state signal level exceeds a predetermined threshold value, it is determined that it is necessary to eliminate clogging of the gas passage in the fuel cell stack, and the gas circulation pump intermittent operation is started. However, the frequency of fluctuation of the pump rotation speed is changed according to the level of the clogged state. Thereby, the frequency of the pulsation given to the gas amount (gas flow velocity) flowing into the fuel cell stack can be changed according to the level of the clogged state.

  FIG. 9 is a diagram for explaining the relationship between the water clogging state level signal of the fuel cell stack and the frequency of rotation fluctuation of the gas circulation pump in the fuel cell system of the present embodiment.

  When the water clogging state level is below the threshold value, it is not necessary to vary the rotational speed of the gas circulation pump, so normal operation is performed at a constant rotational speed. However, the intermittent operation of the gas circulation pump is started from the time when the water clogging level exceeds the threshold value, and a relationship is set such that the frequency at which the pump rotation speed is changed increases as the water clogging state level deteriorates.

  In other words, the higher the level of clogged water, the higher the frequency at which the rotational speed of the gas circulation pump is changed (the fluctuation period is shortened), thereby discharging droplets that have clogged the fuel cell stack. On the contrary, if the degree of water clogging is low, the frequency that fluctuates the rotation speed of the gas circulation pump is lowered (the fluctuation period is increased), so that both the ejector and the gas circulation pump supply the stack. It is set as the characteristic which prevents that the total amount of gas to perform falls and an electric power generation output falls.

  FIG. 10 is a flowchart for controlling the movement of the gas circulation pump in the fuel cell system of this embodiment, and the algorithm will be described below.

  First, in step S31, a clogged state level signal indicating the degree of clogged state of the gas passage in the fuel cell stack is obtained from the monitored value of the cell voltage. In step S32, the degree of the current water clogging state is determined by determining whether or not the water clogging state level signal is equal to or less than a predetermined threshold value. If it is determined in step S32 that the threshold value is equal to or less than the threshold value, the process returns to step S31, and the water clogging state level signal is captured again. If it is determined that the threshold value is exceeded, the process proceeds to step S33, and the frequency corresponding to the water clogging state level signal is read from the pump rotation speed fluctuation frequency table corresponding to FIG. The rotation speed fluctuation operation of the pump at the repetition frequency read in is started.

  Next, in step S35, it is determined whether or not the water clogging state level signal has been improved by the intermittent operation of the pump and has fallen below the threshold value. The water clogging state level signal is updated and the frequency of the corresponding pump rotation speed fluctuation operation is read again. If it is determined that the value has recovered below the threshold value, the process proceeds to step S36, and the pump is returned to normal operation because it is no longer necessary to perform intermittent operation.

  With the configuration and the control method as described above, the repetition frequency of the intermittent operation of the gas circulation pump can be changed according to the degree of water clogging, that is, the optimum pulsation of the gas flow under the conditions can be set in the fuel cell stack. It can be given to the flow of gas passing therethrough, and the action of efficiently removing the adhering moisture in the gas passage can be obtained. As a result, the effect of further improving the operability and reliability of the fuel cell system can be expected.

  The preferred embodiments have been described above, but the present invention is not limited by the descriptions and drawings that form part of the disclosure of the present invention. That is, it is a matter of course that all other embodiments and operation techniques made by those skilled in the art based on these embodiments are included in the scope of the present invention.

  For example, in the embodiment, the example in which the water blockage state is indirectly detected by the cell voltage has been described. However, the gas flow rate sensor for each cell is directly provided to measure the gas flow rate for each cell, and the measured gas flow rate decreases. It is also possible to use a direct water blockage state detecting means for determining a cell that has been closed as a water blockage state.

  As such a gas flow rate sensor, there is a micromechanical hot film type gas flow rate sensor, which can detect a mass flow rate (for example, Bosch Automobile Handbook 1st Edition, p118, Sankaido, 1999.3.31). .

  In the embodiment, the example in which the gas circulation pump is provided in the fuel gas system has been described. However, in the fuel cell system used in outer space or in the sea, the air taken in from the atmosphere is different from the fuel cell used on the ground. Cannot be used as an oxidant gas. For this reason, the oxidant gas stored in the storage means is used, and a gas circulation pump is provided in the oxidant gas system as in the fuel gas system, and the same control as in the fuel gas system can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram explaining the structure of Example 1 of the fuel cell system based on this invention. It is a figure of the supply hydrogen flow rate with respect to the circulation hydrogen flow rate explaining the effect | action of the gas circulation pump in Example 1. FIG. It is a schematic block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention. It is a figure explaining the relationship between the rotational speed of the gas circulation pump in this invention, pressure | voltage rise amount, and discharge amount. 6 is a flowchart for controlling a gas circulation pump in the fuel cell system of Example 2. It is a figure explaining (a) water clogging state flag, (b) gas circulation pump rotational speed, and (c) stack supply gas amount in the fuel cell system of Example 1. 2 is a flowchart for controlling a gas circulation pump in the fuel cell system according to the first embodiment. It is a figure explaining (a) water clogging state level, (b) gas circulation pump rotational speed, and (c) stack supply gas amount in the fuel cell system of Example 3. It is a figure explaining the example of a table which calculates | requires a gas circulation pump rotation fluctuation frequency from the water clogging state level in Example 3. FIG. 6 is a flowchart for controlling a gas circulation pump in a fuel cell system according to a third embodiment. It is a schematic diagram explaining the structure of the unit cell in a polymer electrolyte fuel cell (PEFC).

Explanation of symbols

1: Fuel cell stack 2: High-pressure hydrogen gas tank 3: Pressure regulating valve 4: Ejector 5: Gas circulation pump 6: New supply hydrogen line 7: Stack supply hydrogen line 8: Ejector circulation hydrogen line 9: Pump circulation hydrogen line 10: Oxidant supply line 11: Oxidant discharge line 12: Backflow prevention valve A
13: Backflow prevention valve B
14: Cell voltage sensor (water blocking state detecting means)
15: Controller

Claims (4)

A fuel cell stack having at least one unit cell in which an electrolyte membrane is disposed between the fuel electrode and the oxidant electrode;
A fuel supply pipe for supplying fuel gas to the fuel electrode;
A fuel discharge pipe for discharging excess fuel gas to the outside of the fuel cell stack;
An oxidant supply pipe for supplying an oxidant gas to the oxidant electrode;
An oxidant discharge pipe for discharging excess oxidant gas out of the fuel cell stack;
A first circulation path for sending fuel gas or oxidant gas once discharged out of the fuel cell stack from the fuel discharge pipe or the oxidant discharge pipe to the fuel supply pipe or the oxidant supply pipe again as a circulation gas;
An ejector for mixing the newly supplied fuel gas or oxidant gas and the circulating gas;
The fuel supply pipe or the oxidant is arranged again in parallel with the first circulation path and once discharged from the fuel discharge pipe or the oxidant discharge pipe to the outside of the fuel cell stack as a circulation gas. A second circulation path that feeds into the supply pipe;
A gas circulation pump capable of forcibly circulating the gas in the second circulation path;
A water blocking state detecting means for directly or indirectly detecting a water blocking state of the gas passage in the fuel cell stack;
Control means for controlling the gas circulation pump to intermittently operate until the water blockage state is improved when the water blockage state detection unit detects the water blockage state;
A fuel cell system comprising: A first backflow prevention valve is provided on the outlet side of the gas circulation pump in a direction to prevent backflow to the gas circulation pump,
2. The fuel cell according to claim 1, wherein a second backflow prevention valve is provided between the outlet of the ejector and a junction with the outlet of the gas circulation pump so as to prevent backflow to the outlet of the ejector. system.   The control means stops the operation of the gas circulation pump when the actual required pressure increase is larger than the maximum pressure increase possible with the gas circulation pump. The fuel cell system according to claim 1 or 2. The water blockage state detection means detects the degree of water blockage of the gas passage in the fuel cell stack,
The control unit performs control to increase the frequency of intermittent operation of the gas circulation pump as the degree of water blockage detected by the water blockage state detection unit deteriorates. 4. The fuel cell system according to any one of 3.

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