JP2006324213A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the concentration of exhausting hydrogen to less than a prescribed value by consuming hydrogen leaked from an anode to a cathode by reaction at the starting of operation, and shorten the time starting power generation by quickening the supply of an oxidant to a fuel cell. <P>SOLUTION: A fuel cell system is equipped with a first bypass passage 33 extending from a compressor 16 to the upstream part of an air pressure control valve 22 and a second bypass passage 34 extending from the compressor 16 to the downstream part of the air pressure control valve 22. At the starting of operation, a first bypass valve 33 is opened, a second bypass valve 34 and the air pressure control valve 22 are closed. Then, the operation of the compressor 16 is started, and air is supplied from the inlet and outlet of a cathode 4. Hydrogen leaked from the anode 3 to the cathode 4 during the stop of operation quickly reacts with oxygen in air supplied from the inlet and outlet of the cathode 4 and is consumed. After the concentration of the hydrogen is decreased, the first bypass valve 35 is closed, and the second bypass valve 34 and the air pressure control valve 22 are opened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system capable of shortening startup time.

  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 has a hydrogen storage device and a hydrogen generator mounted on the vehicle, and hydrogen supplied from the vehicle and oxygen-containing air are sent to the fuel cell to react with each other, and electric energy extracted from the fuel cell is used. It drives the motor connected to the drive wheels, and is the ultimate clean vehicle that only emits water.

  In such a fuel cell vehicle, an idle stop similar to that of the internal combustion engine vehicle can be considered. In the low load region or no load region where the power generation efficiency of the fuel cell is low, the power generation of the fuel cell is temporarily stopped and the required power is supplied from the secondary battery. Then, when the fuel cell has power generation capacity, charging the secondary battery improves the overall fuel efficiency (for example, Patent Document 1).

  In such a fuel cell vehicle that performs idle stop, hydrogen (cross leak hydrogen) that has permeated the electrolyte membrane from the fuel electrode to the oxidizer electrode during idle stop must be discharged out of the system at a concentration lower than the specified concentration when the operation is resumed. . For this reason, a technique for reducing the amount of oxidant electrode exhaust gas by reducing the air supply flow rate at the time of starting the fuel cell or intermittently operating the air supply compressor is known (for example, Patent Document 2).

In addition, in order to make the hydrogen concentration discharged from the fuel cell system less than the specified concentration, the air supply pump is once reversely rotated when the operation is resumed, and the air is sucked into the oxidant electrode from the oxidant electrode outlet. A technique for oxidizing and consuming hydrogen trapped in an oxidant electrode catalyst is known (for example, Patent Document 3).
Japanese Patent Laying-Open No. 2001-307758 (page 12, FIG. 5) JP 2004-172027 A (page 8, FIG. 3) JP 2004-87313 A (page 8, FIG. 3)

  However, in the prior art described in Patent Document 2 or 3, in order to suppress the release of cross leak hydrogen at the time of restarting operation, the air supply amount is suppressed or the compressor is temporarily reversely rotated. There was a problem that it took a long time until the fuel cell was able to generate power later.

  In order to solve the above problems, the present invention provides a fuel cell having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode, an oxidant supply means for supplying an oxidant to the fuel cell, an oxidant supply means, An oxidant supply path that connects the oxidant electrode inlet, an oxidant discharge path that connects to the oxidant electrode outlet, and an oxidant pressure control means that controls the flow rate of the oxidant discharged from the oxidant discharge path. In the fuel cell system, a first auxiliary flow path connecting the oxidant supply path and an upstream portion of the oxidant pressure control means of the oxidant discharge path, the oxidant supply path and the oxidant discharge path of the oxidant supply path The gist of the invention is that it includes a second auxiliary flow path connecting the downstream portion of the oxidant pressure control means.

  According to the present invention, when the fuel cell system is started, the oxidant is supplied to the oxidant electrode inlet via the oxidant supply channel, and the oxidant is also supplied from the oxidant electrode outlet via the first auxiliary channel. By supplying and reacting the supplied oxidant and cross-leakage hydrogen, the concentration of discharged hydrogen can be reduced below a predetermined value, and the supply of oxidant to the fuel cell can be accelerated to generate electricity. There is an effect that time until it becomes possible can be shortened.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In addition, although each Example demonstrated below is not specifically limited, it is an Example which applied this invention to the fuel cell vehicle.

  FIG. 1 is a schematic diagram showing the overall configuration of a first embodiment of a fuel cell system according to the present invention. The fuel cell system 1 includes, for example, a fuel cell 2 in which a solid polymer electrolyte is sandwiched between an anode (fuel electrode, negative electrode) 3 and a cathode (oxidant electrode, positive electrode) 4.

  The hydrogen supply device 5 supplies hydrogen as fuel to the anode 3 by a fuel reformer, a hydrogen storage device, or the like. The hydrogen shut-off valve 6 shuts off the hydrogen supply when operation is stopped or when an abnormality occurs. The hydrogen supply valve 7 reduces the hydrogen pressure supplied by the hydrogen supply device 5 to the operating pressure of the fuel cell 2, and supplies it to the anode 3 through the hydrogen supply pipe 8. The anode pressure sensor 9 detects the fuel pressure at the anode inlet. The hydrogen circulation pipe 10 is a path for circulating the fuel gas discharged from the outlet of the anode 3 to the inlet of the anode 3 through the hydrogen circulation pump 11.

  When impurities accumulate in the fuel gas in the hydrogen circulation system constituted by the anode 3, the hydrogen circulation pipe 10 and the hydrogen circulation pump 11, the purge valve 12 is opened and the fuel gas is supplied from the hydrogen discharge pipe 13 to the exhaust hydrogen treatment device 31. Is discharged.

  The exhaust hydrogen treatment device 31 regulates the concentration of hydrogen discharged to the outside by diluting hydrogen in the fuel gas by using separately supplied air, or reacting hydrogen with oxygen in the air via a combustion catalyst. Less than the concentration.

  The compressor (oxidant supply means) 16 supplies air as an oxidant gas to the cathode 4. Impurities in the outside air taken in by the compressor 16 are removed by the filter 14, and the air flow rate is measured by the air flow meter 15. The air compressed by the compressor 16 is supplied to the inlet of the cathode 4 via an air supply pipe (oxidant supply path) 19, and the pressure is measured by the cathode pressure sensor 20.

  Excess air discharged from the outlet of the cathode 4 is reduced in flow rate by the air pressure regulating valve 22 and discharged from the air discharge pipe (oxidant discharge path) 21 to the exhaust hydrogen treatment device 31. The air pressure adjustment valve 22 is an oxidant pressure control means for adjusting the pressure of the cathode 4 by controlling the flow rate of the air discharge pipe 21.

  In addition, the fuel cell system 1 includes a DC / DC converter 23 that converts the output voltage of the fuel cell 2 into a voltage of the battery 24, a battery that is charged from the DC / DC converter 23 and that discharges when the output of the fuel cell 2 is insufficient. 24, an SOC detector 25 that detects the state of charge (SOC) of the battery 24, a DC / DC converter 23 and / or an inverter 26 that converts direct current from the battery 24 into alternating current, and a vehicle drive motor that operates with the alternating current of the inverter 26 27.

  Further, the fuel cell system 1 includes a voltage sensor 28 that detects the output voltage of the fuel cell 2, and a cell voltage sensor 29 that detects each cell voltage of the fuel cell 2 or each cell group in which a predetermined number of cells are connected in series. A controller (ECU) 30 for controlling the entire fuel cell system 1 is provided.

  Furthermore, the fuel cell system 1 includes, as a characteristic component of the present invention, a first bypass flow path (first auxiliary flow) that branches from the air supply pipe 19 and reaches the air discharge pipe 21 upstream of the air pressure adjustment valve 22. Path) 33, the second bypass flow path (second auxiliary flow path) 34 that branches from the air supply pipe 19 and reaches the downstream side of the air pressure adjustment valve 22, and opens / closes or controls the flow rate of the first bypass flow path 33. A first bypass valve (first auxiliary flow path control means) 35 and a second bypass valve (first auxiliary flow path control means) 36 that performs opening / closing or flow rate control of the second bypass flow path 34 are provided.

  The anode pressure sensor 9, the air flow sensor 15, the cathode pressure sensor 20, the voltage sensor 28, the cell voltage sensor 29, and the hydrogen concentration sensor 32 are each connected to the input terminal of the controller 30, and each detection signal is input to the controller 30. .

  Further, the hydrogen shutoff valve 6, the hydrogen supply valve 7, the hydrogen circulation pump 11, the purge valve 12, the compressor 16, the air pressure adjustment valve 22, the first bypass valve 35, and the second bypass valve 36 are respectively connected to the output terminals of the controller 30. It is connected and controlled by a control signal output from the controller 30.

  The controller 30 determines the operation state of the fuel cell 2 from the input signals of the sensors, controls the operation of the entire fuel cell system 1, and controls the operation / stop of the fuel cell system. When starting the fuel cell system, the controller 30 supplies air from the compressor 16 to the inlet of the cathode 4 via the air supply pipe 19 and opens the first bypass valve 35 so that the outlet of the cathode 4 also goes to the cathode 4. Control to supply air.

  Further, the controller 30 is not particularly limited. In the present embodiment, the controller 30 is constituted by a microprocessor having a CPU, a ROM preliminarily storing control parameters such as a control program and a control map, a working RAM, and an input / output interface. Has been.

  FIG. 2 is a flowchart for explaining the control contents performed by the controller 30 when the fuel cell system 1 is started and when the fuel cell system 1 is returned from idle stop (hereinafter referred to as operation start). This flowchart is called and executed at the start of operation of the fuel cell system.

  First, in step (hereinafter, step is abbreviated as S) 10, the first bypass valve 35 is opened, the second bypass valve 36 is closed in S12, and the air pressure adjustment valve 22 is closed in S14. Next, the operation of the compressor 16 is started. Thereby, air supply is started from the inlet and outlet of the cathode 4 of the fuel cell 2. Next, the operation of the timer built in the controller 30 is started in S18, and the elapsed time from the start of air supply is measured.

  Next, in S20, the hydrogen supply valve 7 is opened to start supplying hydrogen, and in S22, the operation of the hydrogen circulation pump 11 is started. Next, the fuel cell state is detected. In this state detection, the cathode pressure sensor 20 for detecting the pressure of the cathode 4, the voltage sensor 28 for detecting the voltage of the fuel cell 2, the hydrogen concentration sensor 32 for detecting the hydrogen concentration of the cathode 4, and the air flow rate sucked by the compressor 16 are detected. That is, the controller 30 reads each detected value from the air flow rate sensor 15 and the like, and the DC / DC converter 23 starts taking out the current from the fuel cell 2.

  Next, in S26, the timer for measuring the elapsed time is updated, and the integrated value obtained by multiplying the detection value (mass flow rate per unit time) of the air flow rate sensor 15 by the cycle time (repetition time) in which S24 is executed is obtained. It updates and calculates the supply air amount from the time of compressor operation start of S16.

  Next, in S28, it is determined whether or not the condition for ending the air supply from the first bypass channel is satisfied. This condition is that any of the following six conditions (1) to (6) is satisfied.

  (1) The pressure of the cathode 4 detected by the cathode pressure sensor 20 exceeds a predetermined value. The predetermined value of the pressure is, for example, a value set to be less than the pressure resistance value of the cathode 4 and the anode 3 of the fuel cell 2 or the pressure resistance value of the sealant between the cathode 4 and the outside of the fuel cell 2.

  (2) The voltage of the fuel cell 2 detected by the voltage sensor 28 exceeds a predetermined value. The predetermined value of the voltage is, for example, a voltage value at which it can be determined that the hydrogen concentration in the cathode 4 has sufficiently decreased and the voltage of the fuel cell 2 has risen, and is a value determined experimentally.

  (3) The hydrogen concentration in the cathode 4 detected by the hydrogen concentration sensor 32 is below a predetermined value. This predetermined value of the hydrogen concentration is a value that becomes less than the prescribed hydrogen concentration when the air containing hydrogen in the cathode 4 is discharged to the outside through the exhaust hydrogen treatment device 31 thereafter. It is determined according to the air supply characteristics to the processing apparatus 31 and the type and characteristics of the exhaust hydrogen processing apparatus.

  (4) The elapsed time after the start of air supply by the compressor 16 timed by the timer has exceeded a predetermined time. This predetermined time is when the hydrogen in the cathode 4 is sufficiently reacted and consumed after the air supply is started, and the air containing hydrogen in the cathode 4 is discharged to the outside through the exhaust hydrogen treatment device 31. This is the time during which the hydrogen concentration is below the specified level, and is determined experimentally.

  (5) The DC / DC converter 23 has started taking out current from the fuel cell 2. This current extraction is notified from the DC / DC converter 23 to the controller 30 through a signal line (not shown in FIG. 1). When current extraction is started from the fuel cell 2, oxygen in the air is consumed for power generation at the cathode 4, and the oxygen concentration decreases. Therefore, air is supplied from the inlet of the cathode 4, and excess air is supplied to the cathode 4. The air supply from the cathode outlet is terminated in order to allow the oxygen supply necessary for power generation to be discharged from the outlet of the cathode.

  (6) The integrated air flow rate (air amount) calculated in S26 exceeds a predetermined value. The predetermined value of the air amount is such that the hydrogen in the cathode 4 is sufficiently reacted and consumed after the air supply is started, and the air containing the hydrogen in the cathode 4 is discharged to the outside through the exhaust hydrogen treatment device 31. In some cases, the amount of air is less than the specified hydrogen concentration and is determined experimentally.

  If the condition is not satisfied in the determination of S28, the process returns to S24. If even one condition is satisfied in the determination of S28, the air supply from the first bypass flow path 33 to the cathode outlet is terminated by the processing of S30 and subsequent steps. In S30, the first bypass valve 35 is closed, and in S32, the second bypass valve 36 is opened at an appropriate opening, and air supply from the compressor 16 to the exhaust hydrogen treatment device 31 is started via the second bypass flow path 34. .

  Next, in S34, the air pressure adjusting valve 22 controls the cathode pressure according to the output current of the fuel cell 2, and in S36, the opening of the hydrogen supply valve 7 is controlled, so that the anode according to the output current of the fuel cell 2 is controlled. After that, the fuel cell is in a normal operation state.

  FIG. 2 is a schematic diagram showing the overall configuration of a second embodiment of the fuel cell system according to the present invention. The difference from the first embodiment is that a three-way valve 37 is used instead of the first bypass valve 35 and the second bypass valve 36 of the first embodiment. Other configurations are the same as those of the first embodiment.

  The three-way valve 37 includes (a) a state in which both the first bypass channel 33 and the second bypass channel 34 are closed, (b) a state in which the air supply pipe 19 and the first bypass channel 33 are communicated, and (c). This is a valve that can take three states, that is, a state in which the air supply pipe 19 and the second bypass passage 34 are communicated with each other. The three-way valve 37 can control the first bypass flow path 33 and the second bypass flow path 34 as in the first embodiment.

1 is a system configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. FIG. 2 is a control flowchart at the start of fuel cell operation in Embodiment 1. It is a system block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention.

Explanation of symbols

1: Fuel cell system 2: Fuel cell 3: Anode (fuel electrode)
4: Cathode (oxidant electrode)
5: Hydrogen supply device 6: Hydrogen shutoff valve 7: Hydrogen supply valve 8: Hydrogen supply pipe 9: Anode pressure sensor 10: Hydrogen circulation pipe 11: Hydrogen circulation pump 12: Purge valve 13: Hydrogen discharge pipe 14: Filter 15: Air Flow sensor 16: Compressor (oxidant supply means)
19: Air supply pipe 20: Cathode pressure sensor 21: Air discharge pipe 22: Air pressure regulating valve (oxidant pressure control means)
23: DC / DC converter 24: battery 25: SOC detector 26: inverter 27: vehicle drive motor 28: voltage sensor 29: cell voltage sensor 30: controller 31: exhaust hydrogen treatment device 32: hydrogen concentration sensor 33: first Bypass channel (first auxiliary channel)
34: Second bypass channel (second auxiliary channel)
35: First bypass valve (first auxiliary flow path control means)
36: Second bypass valve (second auxiliary flow path control means)

Claims (12)

A fuel cell having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode;
An oxidant supply means for supplying an oxidant to the fuel cell;
An oxidant supply path connecting the oxidant supply means and the oxidant electrode inlet;
An oxidant discharge path connected to the oxidant electrode outlet;
In a fuel cell system comprising an oxidant pressure control means for controlling the pressure of the oxidant electrode by controlling the flow rate of the oxidant discharged from the oxidant discharge path,
A first auxiliary flow path connecting the oxidant supply path and the upstream portion of the oxidant pressure control means of the oxidant discharge path;
A second auxiliary flow path connecting the oxidant supply path and the downstream portion of the oxidant pressure control means of the oxidant discharge path;
A fuel cell system comprising:   2. The fuel cell system according to claim 1, further comprising first auxiliary flow path control means for controlling opening / closing or flow rate of the first auxiliary flow path.   At the start of supplying the oxidant to the fuel cell, the oxidant is supplied to the oxidant electrode inlet via the oxidant supply path, and the first auxiliary flow path control means is opened so that the oxidant is also supplied from the oxidant electrode outlet. The fuel cell system according to claim 2, wherein the fuel cell system is supplied. Comprising second auxiliary flow path control means for controlling the opening and closing or flow rate of the second auxiliary flow path,
4. The fuel cell system according to claim 3, wherein the second auxiliary flow path is closed by the second auxiliary flow path control means at the start of supplying the oxidant to the fuel cell. 5.   The fuel cell system according to any one of claims 1 to 4, wherein the oxidant pressure control means is closed when oxidant supply to the fuel cell is started.   The fuel cell according to any one of claims 1 to 5, wherein the first auxiliary flow path control means is closed if a predetermined condition is satisfied after the supply of the oxidant to the fuel cell is started. system. An oxidant electrode pressure detecting means for detecting the pressure of the oxidant electrode;
7. The fuel cell system according to claim 6, wherein the predetermined condition is that the pressure detected by the oxidant electrode pressure detection means exceeds a predetermined value. Voltage detecting means for detecting the voltage of the fuel cell;
7. The fuel cell system according to claim 6, wherein the predetermined condition is that the voltage detected by the voltage detecting means exceeds a predetermined value. Comprising a fuel concentration detection means for detecting the fuel concentration in the oxidant electrode;
7. The fuel cell system according to claim 6, wherein the predetermined condition is that the fuel concentration detected by the fuel concentration detection means falls below a predetermined value.   The fuel cell system according to claim 6, wherein the predetermined condition is that an elapsed time from the start of supply of the oxidant to the oxidant electrode exceeds a predetermined time.   The fuel cell system according to claim 6, wherein the predetermined condition is that current extraction is started from the fuel cell. An oxidant supply amount detection means for detecting an oxidant amount supplied from the oxidant supply means;
7. The fuel cell system according to claim 6, wherein the predetermined condition is that the amount of oxidant detected by the oxidant supply amount detection means exceeds a predetermined value.

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