JP2006196402A - Control device for fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control unit of a fuel cell system capable of operating continuously, even if an anode off-gas treatment function fails. <P>SOLUTION: The anode off-gas dilution device 10 dilutes the anode off-gas exhausted from a purge valve 9, by the air introduced from a dilution air inlet fan 11 to less than a prescribed concentration and exhausts to the outside of the system. When a controller 19 detects the failure of the dilution air inlet fan 11, the purge valve 9 is closed and the current extracted from the fuel cell 2 is restricted and the operation of the fuel cell 2 is continued. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a fuel cell system capable of continuing operation even when a hydrogen concentration reducing means for reducing the hydrogen concentration in an anode off-gas discharged from a fuel cell fails or when the performance is reduced.

  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 many polymer electrolytes used in polymer electrolyte fuel cells do not exhibit good cation conductivity unless they are in a wet state, hydrogen gas or oxidant gas (hereinafter referred to as both) supplied to the fuel cell. The reaction gas is also called humidified. In addition, in order to increase power generation efficiency, more gas than the mass flow rate of the reaction gas required from the output current of the fuel cell is supplied, and surplus hydrogen gas is circulated to the anode (hydrogen electrode) inlet through the hydrogen circulation path. Yes.

  In such a fuel cell system, the inert gas (nitrogen, argon, etc.) in the air that leaks the electrolyte membrane from the cathode (air electrode) to the anode accumulates in the anode circulation path to reduce the hydrogen partial pressure, Reduce power generation efficiency. Further, when the by-product hydrogen gas of the chemical industry is used as the fuel gas of the fuel cell, impurities in the fuel gas are similarly accumulated in the anode circulation path. Furthermore, the generated water generated by the electrochemical reaction of power generation becomes liquid water and accumulates in the gas passage, obstructing gas distribution and gas diffusion, leading to a decrease in power generation efficiency and power generation stoppage. In order to sweep out such impurity gas and liquid water from the gas passage, a purge valve is provided for releasing the anode-off gas discharged from the anode out of the circulation path.

Usually, a dilution device and a catalytic combustion device are provided downstream of the purge valve as a waste hydrogen treatment device. The diluting device dilutes the hydrogen concentration in the purge gas below the limit concentration with air and discharges it outside the system. The catalytic combustion apparatus burns hydrogen in the purge gas with a platinum catalyst or the like and releases it as water vapor outside the system (for example, Patent Document 1).
JP 2002-289237 A (page 7, FIG. 1)

  However, in the above-described conventional technology, no consideration is given to a case where the exhaust hydrogen treatment apparatus malfunctions or performance is deteriorated, and the hydrogen concentration in the exhaust gas may exceed the limit value. There was a problem that the operation of the fuel cell had to be stopped only by failure or performance degradation.

  In order to solve the above problems, the present invention provides a fuel cell that generates electricity by an electrochemical reaction between hydrogen supplied to an anode and an oxidant gas supplied to a cathode, and a hydrogen supply that supplies hydrogen to the fuel cell. Means, an anode offgas circulation means for circulating the anode offgas discharged from the anode outlet of the fuel cell to the anode inlet, an oxidant gas supply means for supplying an oxidant gas to the fuel cell, and a desired output current Reactive gas supply amount adjusting means for adjusting gas supply amounts from the hydrogen supply means and the oxidant gas supply means, anode offgas discharge means for discharging the anode offgas out of the circulation path, and anode offgas discharge Means for reducing the hydrogen concentration in the anode off-gas discharged by the means, and an output for limiting the output current of the fuel cell A fuel cell system control device comprising: a limiting means; and a failure detection means for detecting a failure or a performance drop of the hydrogen concentration lowering means, wherein the failure detection means detects a failure or a performance drop of the hydrogen concentration reduction means. When detected, the gist is to limit the discharge of the anode offgas from the anode offgas discharge means and to limit the output current of the fuel cell by the output restriction means.

  According to the present invention, when the failure detection means detects a failure or performance degradation of the hydrogen concentration lowering means, hydrogen gas of a specified concentration or more is released by stopping the discharge of the anode off-gas or limiting the discharge amount. In addition, the power generation is continued without limiting the output current of the fuel cell and degrading the fuel cell.

  The hydrogen concentration lowering means may decrease the hydrogen concentration by burning the anode off gas with a combustion catalyst, or may decrease the hydrogen concentration by diluting the anode off gas with air.

  According to the present invention, when the failure detection means detects a failure of the hydrogen concentration lowering means or a decrease in performance, the anode offgas discharge is stopped or the discharge amount is restricted, and the operation can be performed in that state. Since the output current of the fuel cell is limited to the output, it is possible to continue the power generation of the fuel cell without discharging hydrogen gas having a predetermined concentration or more. If the vehicle is powered by a fuel cell, the speed will be limited even if a failure occurs in the hydrogen concentration reduction means, but it will move to the garage, service factory, etc. by itself (referred to as limp home travel). )be able to.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a fuel cell system for a vehicle provided with a first embodiment of a control device for a fuel cell system according to the present invention.

  In FIG. 1, a fuel cell system 1 includes a solid polymer fuel cell 2 having an anode (fuel electrode, hydrogen electrode) 2a and a cathode (oxidant electrode, air electrode) 2b, and supplies air as an oxidant to the cathode 2b. An air compressor 3, an air pressure control valve 4 for controlling the air pressure of the cathode 2b, a hydrogen tank 5 for storing hydrogen gas as fuel, a hydrogen pressure control for controlling the hydrogen pressure and flow rate supplied from the hydrogen tank 5 to the anode 2a Valve 6, anode off-gas containing unreacted hydrogen gas discharged from the outlet of the anode 2 a is pumped to the inlet of the anode 2 a via the hydrogen circulation path 8, and the anode off-gas is removed from the system from the hydrogen circulation path 8. The purge valve 9 to be discharged, the anode off-gas diluting device 10 for reducing the hydrogen concentration in the gas discharged from the purge valve 9, and the anode off-gas A dilution air introduction fan 11 for introducing dilution air into the treatment apparatus 10, a cooling water path 12, a heat exchanger 13, a cooling water pump 14, pressure sensors 15 and 16, temperature sensors 17 and 18, and a controller 19 are provided. It is configured.

  The controller 19 includes a pressure sensor 15 for detecting the inlet pressure of the cathode 2b, a pressure sensor 16 for detecting the inlet pressure of the anode 2a, a temperature sensor 18 for detecting the temperature of the cooling water inlet of the fuel cell 2, and cooling of the fuel cell 2. A temperature sensor 17 for detecting the temperature of the water outlet is connected as an input device. The controller 19 is connected with an air compressor 3, an air pressure control valve 4, a hydrogen pressure control valve 6, a hydrogen circulation pump 7, a purge valve 9, a dilution air introduction fan 11, and a cooling water circulation pump 14 as output devices.

  The controller 19 controls the opening of the air pressure control valve 4 based on the pressure value detected by the pressure sensor 15 to control the pressure of the cathode 2b to a pressure corresponding to the load. Further, the controller 19 controls the hydrogen pressure control valve 6 based on the pressure value detected by the pressure sensor 16 to control the pressure of the anode 2a to a pressure corresponding to the load.

  The purge valve 9 is provided on the exhaust piping of the anode of the fuel cell 2 and is normally closed. The controller 19 determines that water clogging has occurred in the fuel cell 2 when the amount of generated power or the generation time since the start of the fuel cell 2 reaches a certain value, or when a decrease in the cell voltage of the fuel cell 2 is detected. When this occurs, the purge valve 9 is opened, and impurities such as moisture and nitrogen are discharged together with hydrogen.

  Further, upstream of the purge valve 9 is connected to one end of a hydrogen circulation path 8 for circulating the anode off gas to the inlet of the anode 2 a, and the other end is downstream of the hydrogen pressure control valve 6 via the hydrogen circulation pump 7. It is connected. The anode off-gas discharged from the outlet of the anode 2a is circulated to the inlet of the anode 2a by an anode off-gas circulation means constituted by the hydrogen circulation pump 7 and the hydrogen circulation path 8.

  The cooling water path 12 is a flow path through which cooling water for cooling the main body of the fuel cell 2 flows. The cooling water path 12 includes a heat exchanger 13 and a cooling water pump 14 for flowing cooling water. Is provided. The temperature sensor 17 detects the temperature of the coolant outlet of the fuel cell 2, and this temperature detection value is used as the temperature of the fuel cell together with the cooling control.

  The anode off-gas diluting device 10 mixes the air introduced from the diluted air introduction fan 11 and the anode off-gas discharged from the purge valve 9, lowers the hydrogen concentration below a specified concentration, and discharges it to the outside.

  Hereinafter, the operation in the first embodiment will be described with reference to the control flowchart of FIG.

  First, in step (hereinafter, step is abbreviated as S) 10, it is determined whether or not the anode off-gas dilution device 10 has failed. For example, in the system of FIG. 1, a method may be considered in which a failure is determined when the actual rotational speed of the dilution air introduction fan 11 falls below a specified value by a predetermined value or more.

  When a catalytic combustor is used as the hydrogen concentration reducing means, for example, when a temperature abnormality is detected by a temperature sensor provided in the catalytic combustor, it can be determined that the catalytic combustor is out of order.

  If it is determined in S10 that the anode off-gas diluting device 10 has failed, the process proceeds to S12 and the purge valve is completely closed.

  Then, the process proceeds to S14, and the upper limit value of the fuel cell take-out current is set to the limit current Ib in FIG. The limiting current Ib is a current value at which the current-voltage characteristic of the fuel cell becomes the lower limit voltage when the purge valve is fully closed.

  On the other hand, if it is not determined in S10 that the anode off-gas diluting device has failed (during normal operation), the process proceeds to S16 and the purge valve 9 is normally controlled. For example, as shown in FIG. 3, the nitrogen gas permeability of the membrane electrode assembly (MEA) increases as the fuel cell temperature rises, so the opening time of the purge valve 9 per unit time may be increased. Then, in S18, the upper limit value of the fuel cell take-out current is set to the maximum current Ia in FIG.

  FIG. 3 shows an example of the purge valve opening time per unit time with respect to the fuel cell temperature. When the anode off-gas dilution device is normal, the purge valve opening time is increased in proportion to the fuel cell temperature. Let

  FIG. 4 shows current-voltage characteristics of the fuel cell when the purge valve is fully closed and when it is normal. When the purge valve is fully closed, the current-voltage characteristic after the time required for limp home travel (for example, 2 hours) has elapsed is generally indicated by a characteristic B. In this characteristic, the point that does not fall below the lower limit voltage is defined as the limiting current Ib, and the upper limit current of the fuel cell extraction current when the purge valve is closed. On the other hand, a current-voltage characteristic when the purge valve can be normally opened and closed is indicated by a characteristic A.

  According to the present embodiment described above, when the failure detection means detects a failure of the hydrogen concentration lowering means or a performance drop, the anode offgas discharge is limited to stop the discharge of the anode offgas or limit the discharge amount. Since the configuration is such that the output current of the fuel cell is limited to an output that can be operated in the above manner, there is an effect that the power generation of the fuel cell can be continued without discharging hydrogen gas having a predetermined concentration or more. In particular, in the case of a vehicle using a fuel cell as a power source, even if a failure occurs in the hydrogen concentration lowering means, the speed is limited, but there is an effect that limp home traveling that moves to a garage or a service factory by self-propulsion can be performed. .

  The operation of the second embodiment will be described below with reference to the control flowchart of FIG. The schematic configuration of the fuel cell system of the second embodiment is the same as that of the first embodiment shown in FIG. 1, but vehicle speed detection means (not shown) is provided, and the detection signal is connected to the controller 19.

  When the hydrogen concentration lowering means has failed, the purge valve is completely closed in the first embodiment. However, in this embodiment, the traveling wind of the vehicle is used for anode off-gas dilution, and the purge valve is opened and closed according to the vehicle speed. It is characterized in that it performs control.

  In FIG. 5, first, in S20, it is determined whether or not the anode off-gas dilution device has failed. For example, in the system of FIG. 1, a method may be considered in which a failure is determined when the actual rotational speed of the dilution air introduction fan 11 falls below a specified value by a predetermined value or more.

  If it is determined in S20 that the anode off-gas diluting device has failed, the process proceeds to S22, and the opening time (ratio) of the purge valve 9 is controlled according to the vehicle speed as shown in FIG.

  Next, in S24, the ratio of the purge valve opening time from the present time to a predetermined time before is calculated based on the purge valve opening time. In S26, the limit current Ib, which is the upper limit of the current taken out from the fuel cell 2, is calculated according to the ratio of the opening time of the purge valve from the current time calculated in S24 to a predetermined time before.

  On the other hand, if it is not determined in S20 that the anode off-gas diluting device has failed (normal), the process proceeds to S28 and the purge valve is normally controlled. For example, as shown in FIG. 3, the purge valve opening time per unit time may be increased as the fuel cell temperature rises. Next, in S30, the upper limit value of the fuel cell extraction current is set to the maximum current Ia in FIG.

  FIG. 6 shows an example of the purge valve opening time per unit time with respect to the vehicle speed. Until the vehicle speed reaches the first speed, the running wind is weak and the anode off gas dilution effect is low, so the purge valve opening time is set to 0 (closed). When the vehicle speed exceeds the first speed, the purge valve is opened in proportion to the excess of the first speed of the vehicle speed, and more anode off-gas can be discharged. When the vehicle speed further increases and reaches the second speed, sufficient purge can be performed. Therefore, even if the vehicle speed further increases, the purge valve opening time is set to a fixed time. The first speed and the second speed have different values depending on the structure of the vehicle and the fuel cell system, but can be obtained by numerical simulation, cavity experiment, actual running experiment, or the like.

  FIG. 7 shows current-voltage characteristics of the fuel cell when the purge valve is fully closed and when it is normal. A current-voltage characteristic when the anode off-gas diluting device is normal is indicated by a characteristic A. A current-voltage characteristic after a time (for example, 2 hours) necessary for general limp home traveling in a state where the purge valve is completely closed is indicated by a characteristic B.

  In this characteristic B, the point of the lower limit voltage is defined as a limit current Ib2. Time required for general limp home travel (for example, 2 hours) Based on the limit current Ib2 when the purge valve is fully closed, the purge valve opening time ratio depending on the vehicle speed (from here to 2 hours before the current time) As the purge valve opening time ratio increases, the limit current Ib (Ib2≤Ib≤Ib1) is calculated so as to increase the limit current to Ib1 (= Ia), and the calculation result is taken out from the fuel cell in S26. The upper limit value of the current.

  According to the present embodiment described above, the anode off gas can be diluted by the traveling wind blown into the vehicle, and the discharge amount of the anode off gas is increased as the vehicle speed increases. The inert gas concentration can be lowered, and there is an effect that the operation can be continued at a higher output than in the first embodiment.

  The third embodiment will be described below with reference to the control flowchart of FIG. The schematic configuration of the fuel cell system of the third embodiment is the same as that of the first embodiment shown in FIG. 1. However, as in the second embodiment, vehicle speed detection means (not shown) is provided, and the detection signal is sent to the controller 19. It is connected. The feature of this embodiment is that the anode off-gas circulation amount by the hydrogen circulation pump is increased from the normal time when the anode off-gas diluting device fails.

  S40 to S46, S50, and S52 in FIG. 8 are the same as S20 to S26, S28, and S30 of the second embodiment shown in FIG. In this embodiment, S48 and S54 are added processing steps.

  8 controls the hydrogen circulation pump 7 in FIG. 1 to the maximum rotation. On the other hand, in S54, the circulation pump speed is set to a speed at which normal control, in other words, a stoichiometric ratio (hydrogen excess ratio) necessary for power generation can be secured.

  FIG. 9 shows the hydrogen concentration distribution in the anode passage when the hydrogen circulation pump rotation speed is maximum when the purge valve is closed, and the hydrogen circulation pump rotation speed normal control when the purge valve is closed (when the purge valve is normally controlled). This is a hydrogen concentration distribution in the anode flow path in the same hydrogen circulation pump rotation speed control). At the time of failure of the anode off-gas diluting device, it is impossible to purge every certain amount of generated power or periodically, so that the nitrogen concentration in the anode flow path tends to increase.

  Here, when the rotation speed of the hydrogen circulation pump is normally controlled, sufficient anode off-gas circulation cannot be performed due to an increase in the gas weight accompanying an increase in the nitrogen concentration. As a result, as shown in FIG. The variation in distribution becomes large. For this reason, since the anode off gas having a high hydrogen concentration may be discharged depending on the purge timing, it is necessary to control the discharge amount of the anode off gas with a small amount.

  However, by maximizing the number of revolutions of the hydrogen circulation pump, variations in the hydrogen concentration distribution in the anode flow path can be reduced and the margin for dilution can be reduced when discharging the anode off-gas. The off-gas can be discharged, and impurities in the anode circulation path can be effectively discharged. It should be noted that a simple effect can be obtained by simply increasing the rotational speed of the hydrogen circulation pump without increasing the rotational speed.

  According to the present embodiment, utilizing the fact that the anode off gas can be diluted by the driving wind blown into the vehicle, the anode off gas discharge amount is increased as the vehicle speed increases, and a circulation device such as a hydrogen circulation pump for circulating the anode off gas is provided. Since the operation is performed in a direction in which the circulation ratio becomes higher, the inert gas concentration distribution in the anode channel can be made uniform. As a result, since the margin for dilution can be reduced when discharging the anode off gas, more anode off gas can be discharged, and the inert gas concentration in the anode and the hydrogen circulation path can be lowered.

  Hereinafter, the fourth embodiment will be described with reference to the control flowchart of FIG. The schematic configuration of the fuel cell system of the fourth embodiment is the same as that of the first embodiment shown in FIG. 1. However, as in the second embodiment, vehicle speed detection means (not shown) is provided, and the detection signal is sent to the controller 19. It is connected. The feature of this embodiment is that the hydrogen pressure supplied from the hydrogen supply means to the anode 2a of the fuel cell 2 is increased from the normal time when the anode off-gas diluting device fails.

  In FIG. 10, first, in S60, it is determined whether or not the anode off-gas dilution device has failed. For example, in the system of FIG. 1, a method may be considered in which a failure is determined when the actual rotational speed of the dilution air introduction fan 11 falls below a specified value by a predetermined value or more.

  If it is determined in S60 that the anode off-gas diluting device has failed, the process proceeds to S62, and as shown in FIG. 11, the hydrogen pressure control valve 6 is set so that the gas pressure at the anode 2a becomes the maximum value regardless of the take-out current of the fuel cell. To control. It should be noted that more impurities can be discharged during the same purge time by simply increasing the gas pressure of the anode 2a than when the gas pressure is normal. Since S64 to S68 of the next step after S62 are the same as S22 to S26 of the second embodiment, description thereof will be omitted.

  On the other hand, if it is not determined in S60 that the anode off-gas diluting device has failed (normal), the process proceeds to S70, and the pressure of the anode 2a is controlled normally according to the fuel cell take-out current. Since S72 and subsequent steps of the next step after S70 are the same as S28 and subsequent steps of the second embodiment, the description thereof is omitted.

  According to this embodiment, when the anode off-gas dilution device fails, the anode pressure is increased, so that more anode off-gas can be discharged even with the same purge valve opening time than when the pressure is not increased. Impurities accumulated in the anode gas circulation path while the valve is closed can be efficiently discharged.

1 is a schematic configuration diagram of a fuel cell system to which a control device of the present invention is applied. 3 is a control flowchart for explaining the operation of the first embodiment. It is a figure which shows the example of a characteristic of the purge valve opening time at the time of normal of an anode off gas dilution apparatus. FIG. 3 is a fuel cell current-voltage characteristic diagram illustrating an example of output current limitation of the fuel cell in the first embodiment. 6 is a control flowchart for explaining the operation of the second embodiment. It is a figure which shows the example of a characteristic of the purge valve opening time with respect to the vehicle speed of Example 2. FIG. 6 is a fuel cell current-voltage characteristic diagram showing an example of output current limitation of a fuel cell in Example 2. FIG. 10 is a control flowchart for explaining the operation of the third embodiment. It is a figure explaining the appearance frequency distribution of the hydrogen density | concentration in an anode flow path with respect to the hydrogen circulation pump rotation speed in Example 3. FIG. 10 is a control flowchart for explaining the operation of the fourth embodiment. 14 is an example of a control map of a target anode gas pressure with respect to a target output current in Example 4.

Explanation of symbols

1: Fuel cell system 2: Fuel cell 2a: Anode 2b: Cathode 3: Air compressor 4: Air pressure control valve 5: Hydrogen tank 6: Hydrogen pressure control valve 7: Hydrogen circulation pump 8: Hydrogen circulation path 9: Purge valve 10 : Anode off-gas diluting device 11: Diluted air introduction fan 12: Cooling water path 13: Heat exchanger 14: Cooling water pump 15, 16: Pressure sensor 17, 18: Temperature sensor 19: Controller

Claims (4)

A fuel cell that generates electricity by an electrochemical reaction between hydrogen supplied to the anode and an oxidant gas supplied to the cathode;
Hydrogen supply means for supplying hydrogen to the fuel cell;
Anode offgas circulation means for circulating anode offgas discharged from the anode outlet of the fuel cell to the anode inlet;
An oxidant gas supply means for supplying an oxidant gas to the fuel cell;
A reaction gas supply amount adjusting means for adjusting a gas supply amount from the hydrogen supply means and the oxidant gas supply means according to a desired output current;
Anode off-gas discharge means for discharging the anode off-gas out of the circulation path;
Hydrogen concentration lowering means for lowering the hydrogen concentration in the anode offgas discharged by the anode offgas discharging means;
Output limiting means for limiting the output current of the fuel cell;
A control device for a fuel cell system comprising a failure detection means for detecting a failure of the hydrogen concentration reduction means or a performance drop,
When the failure detection means detects a failure or performance degradation of the hydrogen concentration reduction means, the anode offgas discharge from the anode offgas discharge means is restricted and the output current of the fuel cell is restricted by the output restriction means. A control apparatus for a fuel cell system. Vehicle speed detection means for detecting the speed of the vehicle on which the fuel cell system is mounted, and discharge amount determination means for determining the discharge amount discharged by the anode off-gas discharge means according to the detected vehicle speed,
When the failure detection unit detects a failure or performance degradation of the hydrogen concentration reduction unit, the discharge amount from the anode off-gas discharge unit is controlled based on the result of the discharge amount determination unit. The fuel cell system control device according to claim 1.   3. The fuel cell system according to claim 2, wherein when the failure detection unit detects a failure or a performance decrease of the hydrogen concentration reduction unit, the amount of circulation by the anode off-gas circulation unit is increased from the normal time. Control device.   3. The fuel cell system according to claim 2, wherein when the failure detection unit detects a failure or a performance decrease of the hydrogen concentration reduction unit, the hydrogen pressure supplied by the hydrogen supply unit is increased from the normal time. Control device.

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