JP2005353511A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fuel cell system capable of holding a secondary battery in an appropriate charged state by the output of the fuel cell and capable of stably using the fuel cell or the secondary battery for a long period of time.
In a fuel cell system including a fuel cell 1 using a proton conductive polymer solid electrolyte and a secondary battery 2 for backup, a charging path 30 for charging the secondary battery 2 by the output of the fuel cell. A fuel cell output path 10 for supplying the output of the fuel cell to a load, and a secondary battery output path 20 for supplying the output of the secondary battery to the load. , connected in a direction in which the discharge current of the secondary battery through the diode D _2, when the output current of the fuel cell 1 is lower than the rated output current is controlled so that the output voltage of the charging circuit 30 is floating charge voltage.
[Selection] Figure 1

Description

  The present invention provides a fuel cell system using a proton conductive polymer solid electrolyte in a place where there is no power source, such as a power source for camping, an emergency power source for disasters, a power source for remote observation equipment, and a power source for robots. More particularly, the present invention relates to a fuel cell system that combines a fuel cell and a secondary battery.

  Fuel cells, which directly extract the reaction energy of fuel and oxidant as electrical energy, are less noticeable as noise and vibration, and are clean as exhaust gas. In general, such a fuel cell is often used as a system in which a secondary battery is used as a buffer for load fluctuations, and is mainly used for applications where the power supply to the load is intermittent or the fluctuation range is large. .

  In the above application, the load is always connected to the system, and the secondary battery is charged by continuing the operation of the fuel cell unless it is overcharged, and the charge is stopped when overcharged. However, in preparation for the case where the secondary battery needs to be charged, the fuel cell can be quickly restarted.

  However, when a lead-acid battery is used for the secondary battery described above, if the charging is stopped by opening the charging path, the output voltage of the fuel cell rises at light load, causing erosion of the constituent materials of the fuel cell. There was a problem of letting. Further, if the charging is stopped by stopping the operation of the fuel cell, there is a problem that the temperature of the fuel cell is lowered and it is difficult to restart the operation quickly.

JP-A 63-175352

  In Patent Document 1, in a fuel cell power supply system using a fuel cell using methanol as a fuel and a storage battery, when the storage battery reaches overcharge, the connection between the fuel cell and the storage battery is turned off and the fuel cell and the dummy battery are connected. When the resistor connection is turned ON and the overcharge state continues after a certain time, the OFF and ON are reversed to turn ON and OFF, and the supply of the oxidant to the fuel cell is stopped, and further fixed When the overcharge state continues over time, supply of fuel to the fuel cell is stopped, and when the overcharge state continues over a certain time, the fuel in the fuel tank is held at a predetermined temperature by the temperature maintaining means, A configuration is disclosed that returns to the initial state when the overcharge state is avoided in any of the stages.

  In the case where a dummy resistor is connected to the output of the fuel cell described above, there is a problem that loss due to current flowing through the dummy resistor is large.

  In order to solve the above-mentioned problems, a first aspect of the present invention provides a fuel cell system including a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for backup, wherein the secondary battery is a fuel cell. A charging path for charging by the output of the fuel cell, a fuel cell output path for supplying the output of the fuel cell to the load, and a secondary battery output path for supplying the output of the secondary battery to the load. A diode is connected to the battery output path in the direction in which the discharge current of the secondary battery flows, and the output voltage of the charging path is controlled to be a floating charge voltage when the output current of the fuel cell is equal to or lower than the rated output current. It is characterized by that. According to a second aspect of the present invention, in the fuel cell system according to the first aspect, a function of transmitting a start signal of the fuel cell activated by the secondary battery, or a reduction in one of the output voltage of the fuel cell or the secondary battery. And a start / stop section having at least one of a function of sending a stop signal for stopping the operation of the fuel cell and stopping the supply of output from the secondary battery to the load. According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect, a stabilization circuit for stabilizing the output voltage or an inverse conversion circuit for inversely converting the output voltage is provided.

  According to the invention described in the above claims, the secondary battery can be held in an appropriate charged state by the output of the fuel cell, and an overcharge or overdischarge state can be prevented. In addition, even during light loads, the fuel cell can supply an output current to the load and a floating charging current to the secondary battery, so that an increase in the output voltage of the fuel cell can be suppressed.

  FIG. 1 shows a circuit diagram of a fuel cell system according to the present invention.

  In FIG. 1, reference numeral 1 denotes a fuel cell, which is provided with a fuel electrode using a Pt-Ru catalyst and an air electrode using a Pt catalyst on both sides of a proton conductive polymer solid electrolyte membrane. Gas fuel such as hydrogen or liquid fuel such as methanol-water mixed fuel is supplied, oxidizing gas such as air is supplied to the air electrode side, the polymer solid electrolyte membrane, the fuel electrode, the air electrode, and these A single battery cell is constituted by a separator or the like for supplying fuel and an oxidizing gas, and a plurality of single battery cells are connected in series so that a predetermined voltage can be obtained as the fuel cell 1. As the fuel, for example, a fuel cassette containing liquid fuel such as about 3% by weight of methanol-water mixed fuel, isopropanol-water, butanol-water, etc. is detachably provided in the fuel cell 1 and supplied from this fuel cassette. Alternatively, a liquid fuel tank 6 containing the liquid fuel may be provided and supplied through a pipe. Instead of the above liquid fuel, hydrogen may be supplied from a hydrogen cylinder, or hydrogen obtained by reforming the liquid fuel in the fuel cassette with a reformer may be supplied to the fuel cell 1. However, this embodiment is suitable for a direct fuel cell system in which the liquid fuel in the fuel cassette is supplied directly to the fuel cell 1. In addition, you may provide the waste fuel cassette for accommodating waste fuel separately from the above-mentioned fuel cassette.

A fuel cell system according to the present invention includes the above-described fuel cell 1 and a backup secondary battery 2, and includes a charging path 30 for floatingly charging the secondary battery 2 with the output of the fuel cell 1, and the fuel cell 1. The fuel cell output path 10 for supplying the output of the secondary battery 2 to the load 3, and the secondary battery output path 20 for supplying the output of the secondary battery 2 to the load 3. The charging path 30 is provided with a diode 12 and a charger 12 whose output voltage is set to the floating charging voltage V _bf of the secondary battery 2, and the fuel cell output path 10 is provided with a diode 21. The secondary battery output path 20 is provided with a diode 23 in the direction in which the discharge current of the secondary battery 2 flows, and the output voltage of the charger 12 when the output current of the fuel cell 1 is less than the rated output current. Is controlled to be the floating charging voltage of the secondary battery 2.

The fuel cell system described above, as shown in FIG. 2, the operation of the following A region rated output current I _a of the fuel cell 1 is the current flowing through the load 3, B region or C exceeds the rated output current I _a Driven with the area.

The region A is a region where the output voltage V _fc of the fuel cell 1> the floating charging voltage V _bf of the secondary battery 2. On the left side of the region A in FIG. 2, the current flowing through the fuel cell output path 10 to the load 3 is small, the output voltage V _fc of the fuel cell 1 is high, and the output voltage of the charger 12 is the secondary battery 2. When the floating charging voltage V _bf is controlled, the charging current flowing through the secondary battery 2 increases. On the other hand, on the right side of the region A in FIG. 2, a large amount of current flows to the load 3 through the fuel cell output path 10, the output voltage V _fc of the fuel cell 1 decreases, and the output voltage of the charger 12 decreases. When the floating charging voltage V _bf of the secondary battery 2 is controlled, the charging current flowing through the secondary battery 2 decreases.

The region B is a region where the floating charging voltage V _bf of the secondary battery 2 cannot be obtained from the output voltage V _fc of the fuel cell 1, and the charging current disappears and all of the output current of the fuel cell 1 flows to the load 3. Since the output voltage V _fc of the fuel cell 1 ≧ the open circuit voltage V _bo of the secondary battery 2, this is a region where the diode 23 is reverse-biased. In the region B, the secondary battery 2 is not discharged, and the fuel cell 1 supplies output following the load 3 until the output voltage V _fc drops to the open circuit voltage V _bo of the secondary battery 2.

The C region is a region where the output voltage V _fc of the fuel cell 1 <the open circuit voltage V _bo of the secondary battery 2. In this C region, the diode 23 becomes forward biased, the current flowing from the fuel cell 1 to the load 3 starts to decrease and the secondary battery 2 starts to discharge, and the voltage further decreases from the open circuit voltage _Vbo. The discharge voltage V _bd is lowered to the discharge end voltage V _bt and continues until the discharge is terminated.

  In the fuel cell system described above, as shown in FIG. 1, one of the function of sending a start signal for starting the control unit 40 by the secondary battery 2 or the output voltage of the fuel cell 1 or the secondary battery 2 is provided. A start / stop unit 4 having at least one of a function of detecting a decrease and sending a stop signal for stopping the operation of the fuel cell or stopping the supply of output from the secondary battery 2 to the load is provided.

For example, the start / stop unit 4 is connected in parallel to the series connection circuit of the secondary battery 2 and the secondary battery output path 20 and detects an HLV relay 41 that detects a low voltage, and this HLV. A series connection circuit of the first A contact 42 _a1 , the second A contact 42 _a2 and the control unit 40 of the X relay 42 connected in parallel to the relay 41, and the first A contact 42 _a1 and the second A contact of the X relay 42 The push button switch 43 is connected in parallel to the series connection circuit 42 a ₂ , and the B contact 41 _b of the HLV relay 41 and the series connection circuit of the X relay 42 are connected in parallel to the control unit 40. The load 3 is connected in parallel with the second A contact 42 _a2 of the X relay 42 and the series connection circuit of the control unit 40, with the load disconnect switch 5 connected in series.

When the control unit 40 depresses the push button switch 43 when the fuel cell 1 is activated, the secondary battery 2 passes through the diode 23 and passes through the push button switch 43 → the control unit 40 and the B contact 41 _{b of the} HLV relay 41. And the X relay 42 is discharged through the path of the series connection circuit, whereby the first A contact 42 _a1 and the second A contact 42 _a2 of the X relay 42 are turned on and self-held, and the valve 8 is connected to the fuel cell 1. Is opened, and a start signal for operating the fuel pump 7 is sent. At the same time, the load separation switch 5 is turned on, and the load 3 such as a portable personal computer is operated by discharging the secondary battery 2 through the diode 23. When the fuel cell 1 is activated by the activation signal and a predetermined time elapses or when the fuel cell 1 reaches a stable state and the output voltage of the fuel cell 1 rises, the load 3 passes through the diode 21 from the fuel cell 1. Supply of output is started. Then, the output current to the load 3 increases, and the floating charge voltage is applied to the secondary battery 2 until the transition from the A region to the B region, and until the transition from the B region to the C region, the fuel cell 1 The output is supplied from the load 3 to the load 3. In the C region, when the discharge voltage V _{bd of the} secondary battery decreases to the discharge end voltage V _bt , the HLV relay 41 is not excited, the B contact 41 _b of the HLV relay 41 is turned off, and the X relay 42 Is no longer excited, the first A contact 42 _a1 and the second A contact 42 _a2 of the X relay 42 are both turned off, the discharge of the secondary battery is stopped, and the operation of the control unit 40 is also stopped and the fuel cell 1 is stopped. Stop the operation and send a stop signal.

The HLV relay 41 is operated by detecting the voltage at the connection point between the diode 21 and the diode 23 in FIG. 1. However, if the voltage on the anode side of the diode 21 is detected, the output voltage of the fuel cell 1 is increased. When the voltage detected on the anode side of the diode 23 is detected, the output voltage of the secondary battery 2 is detected, and the detected voltage is reduced to a predetermined value ( The above-described operation can be performed when the discharge end voltage V _bt ) is lowered. Further, by combining the voltage detection at each point, it is possible to determine whether the output is supplied from the fuel cell 1 to the load 3 or whether the secondary battery 2 is discharged. The operating state of the battery 2 can be monitored. If the charger 12 has an input voltage detection circuit, the diode 22 can be dispensed with or can be used as the diode 21.

  Further, in the fuel cell system described above, a stabilization circuit for stabilizing the output voltage is provided in addition to the start / stop unit 4 or in place of the start / stop unit 4 to improve the accuracy of the voltage applied to the load 3. It can also be made. Further, when the load 3 is driven by alternating current, an inverse conversion circuit that reversely converts the output voltage may be provided to obtain an alternating current output.

  In the fuel cell system described above, the description is omitted. However, when the fuel is a gas, the fuel cell 1 is provided with a pressure sensor for detecting the remaining amount of the fuel, or in the case of a liquid, the ultrasonic sensor. Alternatively, a fuel sensor such as a liquid level gauge using a float, an optical sensor, or the like may be provided. When the fuel cell system is portable or household, it is disadvantageous in cost to provide such a fuel sensor for detecting the remaining amount of fuel, and the fuel is supplied from a detachable cassette or cylinder. It is difficult to attach the above-described fuel sensor to a disposable cassette or cylinder, and it may be determined as necessary as necessary.

Further, in the A region, if the operation of the fuel pump 7 is controlled when the current flowing through the load 3 decreases so that the output voltage V _fc of the fuel cell 1 does not increase, the charger 12 Loss can also be reduced.

  According to the present invention, the secondary battery can be maintained in an appropriate charged state by the output of the fuel cell, and an overcharge or overdischarge state can be prevented. In addition, even during light loads, the fuel cell can supply an output current to the load and a floating charging current to the secondary battery, so that an increase in the output voltage of the fuel cell can be suppressed. Therefore, since the fuel cell and the secondary battery can be used stably over a long period of time, industrial applicability is great.

1 is a circuit diagram of a fuel cell system according to the present invention. It is a figure for demonstrating operation | movement of the fuel cell system which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Secondary battery 3 Load 4 Startup stop part 5 Load separation switch 6 Liquid fuel tank 7 Fuel pump 8 Valve

Claims (3)

In a fuel cell system comprising a fuel cell using a proton conductive polymer solid electrolyte and a secondary battery for backup, a charging path for floatingly charging the secondary battery by the output of the fuel cell, and an output of the fuel cell A secondary battery output path for supplying the output of the secondary battery to the load, and a discharge current of the secondary battery flows in the secondary battery output path The fuel cell system is characterized in that when the output current of the fuel cell is equal to or lower than the rated output current, control is performed so that the output voltage of the charging path becomes a floating charge voltage. A function of transmitting a start signal of the fuel cell, which is started by the secondary battery, or a stop signal for stopping the operation of the fuel cell by detecting a decrease in one of the output voltages of the fuel cell or the secondary battery or the secondary battery 2. The fuel cell system according to claim 1, further comprising a start / stop unit having at least one of a function of stopping supply of output from the power source to the load. 3. The fuel cell system according to claim 1, further comprising a stabilization circuit for stabilizing the output voltage or an inverse conversion circuit for inversely converting the output voltage.

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