WO2005008817A1

WO2005008817A1 - Fuel cell system and method for detecting running out of fuel in fuel cell

Info

Publication number: WO2005008817A1
Application number: PCT/JP2004/003887
Authority: WO
Inventors: Ryoichi Okuyama
Original assignee: Gs Yuasa Corporation
Priority date: 2003-07-18
Filing date: 2004-03-22
Publication date: 2005-01-27
Also published as: JPWO2005008817A1

Abstract

A fuel cell is connected with a secondary cell for backup and when the output from the fuel cell drops, the fuel cell is disconnected from a load and the load is driven with the secondary cell. When the residual capacity of the secondary cell lowers to below a first level, a fuel running out indication is turned on and when the residual capacity lowers to below second level, the secondary cell is also separated from the load.

Description

Specification

TECHNICAL FIELD The present invention relates to a fuel cell system and a method for detecting fuel shortage in a fuel cell.

The present invention relates to detection of running out of fuel in a fuel cell system using a proton conductive polymer solid electrolyte. Background art

Patent Document 1 Japanese Patent Application Laid-Open No. 2001-69610 (US Pat. No. 66 724 15) Patent Document 1 discloses a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for backup. It discloses a connected, in-vehicle fuel cell system. Such a fuel cell system is expected to have a wide range of applications not only for in-vehicle use but also for portable use, home use, and business use.

In a fuel cell system, it is necessary to detect the remaining amount of fuel. To do this, a pressure sensor (in the case of H2 fuel, etc.), a liquid level gauge using an ultrasonic sensor, float, optical sensor, etc. Case), a fuel sensor is required. If the fuel cell system is portable or domestic, providing a fuel sensor for detecting residual fuel is disadvantageous in terms of cost. When supplying fuel from a detachable cassette cylinder, it is impossible to attach a fuel sensor to a disposable cassette cylinder. Summary of the Invention

Problems to be solved by the invention

An object of the present invention is to make it possible to detect running out of fuel in a fuel cell without using a sensor for detecting remaining fuel.

An additional object of the present invention is to enable early notification of fuel replacement or addition.

An additional object of the present invention is to make it possible to use a fuel cassette which does not have a sensor for detecting residual fuel as a fuel cassette. Structure and effect of the invention

A fuel cell system according to the present invention includes a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for back-up, wherein the output of the fuel cell is monitored and the output is controlled to a predetermined value. Means for connecting a load to the secondary battery when the remaining capacity falls below the value, and monitoring the remaining capacity of the secondary battery, and when the remaining capacity falls below a predetermined value, notifies the fuel cell of running out of fuel. And means for performing the operation. To switch the connection to the load from the fuel cell to the secondary battery, for example, monitor the output voltage of the fuel cell and switch the connection with a switch, or use a switch such as a diode to switch between the fuel cell and the secondary battery. For example, connect the high output side to the load.

The method for detecting a fuel shortage in the fuel cell system according to the present invention includes detecting a fuel shortage in a fuel cell system including a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for backup. In the method, the output of the fuel cell is monitored without using a fuel sensor, and when the output drops below a predetermined value, a load is connected to the secondary battery, and the remaining capacity of the secondary battery is reduced to a predetermined value. It is characterized by the fact that the fuel cell runs out of fuel when it drops below.

In the present invention, there is no need to use a fuel sensor. Further, according to the present invention, when the output of the fuel cell decreases due to running out of fuel or the like, the load can be driven by the secondary battery, so that even if running out of fuel occurs, the load does not stop immediately. When the remaining capacity of the rechargeable battery falls below a predetermined value, the user is notified of running out of fuel.Before the load can no longer be driven, the user must take measures such as replacing the fuel cassette or adding fuel. Can be. The remaining capacity of the secondary battery can be detected using the output voltage of the secondary battery, the internal impedance, the temperature rise, the integrated value of the amount of charge and discharge, and the like. It is a standard equipment.

Preferably, a means for detecting a decrease in the output of the fuel cell is provided, and a means for displaying a warning signal of the fuel cell running out of fuel when the load is connected to the secondary battery is provided. Warning signal and the remaining capacity of the secondary battery The out-of-fuel signal at the time of drop is displayed so that the user can distinguish it.

In this way, the user can be notified of fuel shortage while the rechargeable battery has sufficient remaining capacity, so that the user can exchange the fuel cassette at a convenient time, which is convenient. In detecting the output decrease, the output of the fuel cell itself may be monitored, or which of the fuel cell and the secondary battery is connected to the load may be detected.

The fuel may be a gaseous fuel such as hydrogen or a liquid fuel such as methanol that has been processed by a reformer. It is particularly important to supply the liquid fuel directly to the fuel cell. Among the direct fuel cells, it is particularly important to supply liquid fuel from a detachable fuel cassette, since providing a fuel sensor such as a liquid level gauge on a disposable cassette is cost-prohibitive. Therefore, preferably, the fuel cell is a direct fuel cell that supplies liquid fuel directly to the fuel cell, and the liquid fuel is supplied from a detachable fuel power set. The cassette may be used as it is as a fuel tank, or may be used to supply liquid fuel to a separate fuel tank. Brief Description of Drawings

FIG. 1 is a block diagram of the fuel cell system according to the embodiment.

FIG. 2 is a flowchart showing the fuel exhaustion detection algorithm according to the embodiment.

FIG. 3 is a flowchart following FIG. 2 and illustrating an algorithm for detecting a fuel shortage. FIG. 4 is a diagram schematically illustrating the operation characteristics of the fuel cell system according to the example. Example

1 to 4 show a fuel cell system 2 according to an embodiment. In the figure, reference numeral 4 denotes a fuel cell main body, which is provided with a fuel electrode using a Pt-Ru catalyst or the like and an air electrode using a Pt catalyst or the like on both surfaces of a proton conductive polymer solid electrolyte membrane. Gas fuel such as hydrogen or liquid fuel such as water-methanol mixed fuel is supplied to the electrode side, and oxidizing gas such as air is supplied to the air electrode side. A single cell is composed of a solid polymer electrolyte membrane, a fuel electrode, an air electrode, and a separator for supplying fuel and oxidizing gas to these, and a plurality of single cells are connected in series to form a fuel cell. A predetermined voltage is obtained as the main body 4. So that

6 is a fuel power set, for example, 3 wt. /. This is a cassette that contains liquid fuel such as methanol-water mixed fuel and isopropanol-water and butanol-water. In the embodiment, the cassette 6 is used as it is as the liquid fuel tank. However, the fuel cassette may be set in a fuel tank (not shown) and the fuel may be transferred into the tank. In addition to the fuel cassette, a cassette for accommodating exhaust fuel may be provided. In place of the above liquid fuel, hydrogen may be supplied from a hydrogen cylinder L, or hydrogen obtained by reforming the liquid fuel in the fuel cassette 6 with a reformer may be supplied to the fuel cell body 4. good. However, the direct fuel cell system in which the liquid fuel from the fuel cassette 6 is directly supplied to the fuel cell body 4 is particularly important.

Reference numeral 7 denotes a cassette attaching / detaching mechanism, which makes the fuel cassette 6 detachable. The fuel cassette 6 is, for example, disposable, and does not have a fuel sensor for detecting a liquid level in the fuel cassette 6. Reference numeral 8 denotes a valve, 10 denotes a fuel pump, and when the valve 8 is opened and the fuel pump 10 is operated, fuel is supplied to the fuel cell body 4 to generate power. In addition, an air pump and a pump for collecting exhaust fuel may be provided. If these auxiliary pumps and their associated auxiliary valves are provided, their operation is synchronized with valve 8 and fuel pump 10. Reference numeral 12 denotes a charger, which charges the secondary battery 14 with the output from the fuel cell body 4. Instead of the output of the fuel cell body 4, the battery may be charged via a charger 12 from a commercial power supply or the like (not shown). Reference numeral 16 denotes a remaining capacity detection unit which detects the remaining capacity of the secondary battery 14 using the output voltage impedance of the secondary battery 14, temperature change, integrated value of charge / discharge electricity, and the like. The remaining capacity detection unit 16 may be a battery that is normally provided in a secondary battery 14 or an electronic device including the same.

Reference numeral 18 denotes a control unit which opens the valve 8 using the secondary battery 14 when the fuel cell system 2 is started, operates the fuel pump 10 and starts the fuel cell body 4. At the same time, the switch 26 is closed, and the load 30 such as a portable personal computer is operated by the secondary battery 14. When the fuel cell main body 4 is activated and a predetermined time has elapsed, or when the fuel cell main body 4 detects that the fuel cell main body 4 has reached a stable state from a temperature change or the like, through the protection switch 20, the fuel cell main body 4 is activated. Connected to load 30 Then, the rechargeable battery 14 is charged from the charger 12 at an appropriate timing. The control unit 18 detects the output voltage from the fuel cell body 4 and the output voltage from the secondary battery 14 using, for example, the potential at any one of points A to C in FIG. At point A, the output voltage of the fuel cell body 4 can be measured, at point B, the voltage applied to the load 30 can be detected, and at point C, the output voltage of the secondary battery 14 can be detected. it can. By inputting these potentials to the control unit 18, if the voltage drops of the diodes 21, 22, and 23 and the voltage drop of the charger 12 are ignored, for example, the potential at point A (VA)> If the potential is at the point C (Vc), it can be seen that a current flows from the fuel cell body 4 to the load 30, and a charging current for the secondary battery 14 also flows from the fuel cell body 4. If the potential at point A (VA) and the potential at point C (Vc), current flows from the secondary battery 14 to the load 30, and no charging current flows to the secondary battery 14. You can see that. Therefore, it is possible to monitor the state of rotation of the fuel cell body 4 and the secondary battery 14.

Reference numerals 21 to 23 denote protection diodes. If the diodes 21 and 22 are provided, or if at least the diode 21 is provided, the switch 20 need not be provided. That is, when the diode 21 is provided, the voltage obtained by subtracting the level shift of the diode 21 from the output voltage of the fuel cell body 4 and the level shift of the diode 23 are obtained from the output voltage of the secondary battery 14 The voltages are compared and only the battery with the higher voltage is connected to load 30. Further, if the diode 22 is provided, it is possible to prevent the power of the secondary battery 14 from flowing into the fuel cell body 4 via the charger 12 when the output of the fuel cell body 4 is reduced. Can be. However, if charger 12 has an input voltage detection circuit, diodes 22 are unnecessary.

When the control unit 18 detects that the output of the fuel cell body 4 has decreased, the control unit 18 opens the switch 20 to disconnect the fuel cell body 4 from the load 30, and the load 30 receives the current from the secondary battery 14. Is supplied, the valve 8 is closed, the fuel pump 10 and the like are stopped, and the fuel cell body 4 is stopped (signal D). If there are an air pump, an exhaust fuel recovery pump, etc. in addition to the fuel pump 10, these pumps are also stopped. In detecting the output drop, the output voltage of the fuel cell body 4 may be corrected by the load or the like, or the moving average or the maximum value within a predetermined time may be used. good. When the diodes 21 and 23 are provided, the output voltage of the fuel cell body 4 decreases, and when the output voltage of the secondary battery 14 becomes higher than that, a current flows from the secondary battery 14 to the load 30, The main body 4 and the secondary battery 14 are in the same state as separated. In this case, if the fuel cell main body 4 is stopped due to a temporary overload or the like, a restart is required.Therefore, with the switch 20 closed, simply use the diodes 21 and 23 to switch to the higher output voltage battery. The load 30 may be driven. Further, when the diodes 21 and 23 are used, the load 30 can be driven by connecting the fuel cell body 4 and the secondary battery 14 in parallel at the time of overload.

The control unit 18 controls the LEDs 24 and 25 for displaying a fuel shortage or the like. For example, the LED 24 is green and the LED 25 is red. When the fuel cell unit 4 is disconnected from the load 30, the control unit 18 changes the display of the green LED 24 from the previous on state to the on / off state of flashing to notify that the fuel needs to be changed. . At this point, the red LED 25 is turned off. The remaining capacity of the secondary battery 14 should be sufficient to drive the load 30 further. The remaining capacity is detected by the remaining capacity detection unit 16. When the remaining capacity drops to the first level or less, the fuel shortage display is turned on. In this display, for example, the green LED 24 is turned off, and the red LED 25 is turned on / off. The remaining capacity detection unit 16 further monitors the remaining capacity of the secondary battery 14, and when the remaining capacity drops below the second level, opens the switch 26 and disconnects the load 30 from the secondary battery 14. It is preferable that the second level is a remaining capacity that is larger than the remaining capacity at which the fuel cell body 4 can be restarted.The first level is, for example, 10 minutes before the remaining capacity decreases to the second level. A level that can drive the load for about 1 hour.

In the embodiment, the LEDs 24 and 25 are used for the indication of running out of fuel or the like.However, an LCD or the like may be used. Is also good. In the embodiment, it is difficult to directly discriminate between the fuel shortage and the fuel cell failure. Therefore, for example, even if the fuel is exchanged and the fuel cell system 2 is restarted in response to the out-of-fuel indication, the out-of-fuel indication is not turned off, so that the user can recognize that the fuel cell has failed.

Fig. 2 to Fig. 4 show the operation algorithm of the embodiment (Figs. 2 and 3) and the state based on it. The change of state (Fig. 4) is shown. When the fuel cell system 2 is started, for example, the valve 8 is opened with electric power from the secondary battery 14, the pump 10 is driven, and the fuel cell main body 4 is started by the secondary battery 14 (step 1). Wait for a predetermined time of about 30 seconds to 2 minutes after startup, check the output voltage (FC voltage) from the fuel cell body 4 (step 2), and if the FC voltage is less than the predetermined value, go to step 8 from connector 8. To turn on the fuel-out display and finish. Note that the output check from the fuel cell main body 4 at the time of startup may be performed by monitoring the temperature rise of the fuel cell main body 4 instead of monitoring the FC voltage. However, monitoring the FC voltage eliminates the need for a temperature sensor.

After the FC voltage reaches the specified value and waits for the specified time, connect the load (Step 3). At this time, if the FC voltage drops below the predetermined value (step 4), the process moves from the connector ② to step 7, turns off the load, turns on the fuel-out display, and ends. If the FC voltage is sufficient to drive the load, the operation shifts to the steady operation (Step 5). If the operation is terminated by the user on the way, the operation moves from Step 6 to the connector ③ to disconnect the load. If, for example, the secondary battery 14 does not need to be charged, the fuel cell is stopped (step 9). If the FC voltage drops below the monitoring level during steady operation,

(Step 10) The control unit 18 disconnects the fuel cell body 4 from the load or the like, closes the valve 8, stops the pump 10, and stops the operation of the fuel cell (Step 11). As a result, the FC voltage increases, for example, as indicated by the chain line in FIG.

Even if the output of the fuel cell body 4 decreases, the secondary battery should have remaining capacity, and the load is driven by the secondary battery 14 (step 12). The voltage indicated by the broken line in FIG. 4 is the output voltage of the secondary battery 14. Then, the remaining capacity is detected in steps 13 and 15, and when the remaining capacity falls below the first level, a fuel shortage display is performed (step 14), and a replacement of the fuel cassette is requested. When the remaining capacity falls below the second level, the load is disconnected and the operation of the fuel cell system is terminated (step 16).

The fuel cell system of the present invention is particularly important in the case of a direct fuel cell using a liquid fuel such as methanol-water as a fuel. The inventors have found that when the fuel cell whose output has been reduced due to running out of fuel or the like is further operated, the Ru catalyst in the fuel electrode elutes into the fuel. This phenomenon occurs, for example, when the potential of the fuel electrode is Occurred above +50 O mV. This phenomenon occurred when a liquid fuel such as methanol-water was used as the fuel, and did not occur with hydrogen gas fuel. Furthermore, this phenomenon was irreversible, and when this phenomenon occurred, the exhaust fuel turned black and a large amount of Ru was detected in the exhaust fuel.

In a direct fuel cell using methanol water fuel, the fuel electrode is exposed to the acidic electrolyte due to formic acid generated by partial oxidation of methanol. Generally, a Pt—Ru composite catalyst is used for the fuel electrode to prevent poisoning by CO. Here, it is considered that when the potential of the fuel electrode becomes, for example, +50 OmV or more with respect to the air electrode, the elution potential of Ru is exceeded, and Ru elutes into the fuel as the electrolyte.

This problem is further complicated in the fuel cell body 4 because a plurality of unit cells are generally connected in series and driven. For example, when the fuel supply is insufficient in some of the cells, the output from the other cells causes current to flow through the cells with insufficient fuel, and the potential of the fuel electrode becomes abnormal with respect to the air electrode. And Ru is easily eluted. Thus, the output voltage of the fuel cell main body is monitored, and when the output drops below a predetermined value, the fuel cell can be protected by stopping the fuel cell main body.

In this embodiment, the fuel cell can be protected by detecting the fuel shortage without using a fuel sensor for detecting the remaining fuel amount. Even after the output drops, the load can be driven using the secondary battery for backup, and the running out of fuel can be displayed at an appropriate timing to request replacement of the fuel cassette. In this embodiment, a secondary battery 14 whose output voltage greatly decreases at the end of discharge, for example, a lithium ion battery using hard carbon is assumed, but a type in which the output voltage gradually decreases at the end of discharge. However, for example, a Ni-MH battery / a lithium ion battery using soft carbon can also be used in the same manner by detecting a change in the integrated value of charge / discharge electricity, a change in internal impedance, or a temperature rise.

Claims

The scope of the claims

1. In a fuel cell system including a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for backup,

Means for monitoring the output of the fuel cell and connecting a load to the secondary battery when the output drops below a predetermined value;

Means for monitoring the remaining capacity of the secondary battery and notifying the fuel cell of running out of fuel when the remaining capacity drops below a predetermined value.

2. A means for detecting a decrease in the output of the fuel cell is provided, and a means for displaying a notice signal for running out of fuel of the fuel cell when a load is connected to the secondary battery is provided. The fuel cell system according to claim 1, wherein

3. A direct fuel cell in which the fuel cell directly supplies a liquid fuel to the fuel cell, wherein the liquid fuel is supplied from a detachable fuel cassette. 2. The fuel cell system according to paragraph 2.

4. In a fuel cell system equipped with a fuel cell using a proton-conductive polymer solid electrolyte and a secondary battery for back-up, in the method of detecting fuel shortage, the output of the fuel cell is used without using a fuel sensor. When the output drops below a predetermined value, a load is connected to the secondary battery,

A method of detecting fuel shortage in a fuel cell system, wherein when the remaining capacity of the secondary battery falls below a predetermined value, the fuel cell is notified of fuel shortage.