JP2014073003A - Fuel cell, fuel cell system including lead storage battery and charging method - Google Patents

Abstract

An object of the present invention is to shorten the charging time without increasing the cost of the fuel cell system, to extend the life of a lead storage battery used in the fuel cell system, and to improve the power generation efficiency of the fuel cell. Allow at least one.
The charging method includes a step of supplying a fuel cell with an oxidant at a first predetermined flow rate AQ, a step of supplying a fuel at a second predetermined flow rate FQ, and charging a lead storage battery with a constant charging current Ib. When the output current If increases to the upper limit current value UI so as to increase the output current If of the fuel cell and decrease the output voltage Ef as the battery voltage Eb increases, the output current If is increased to the upper limit current The step of gradually decreasing the charging current Ib according to the increase of the battery voltage Eb so as to be equal to or less than the value UI, and every time the battery voltage Eb reaches the first reference voltage ER1, the charging current Ib is changed to the first current Ib. The method includes a step (n-1) stepwise reduction from (1) to the nth current Ib (n).
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to charge control of a fuel cell system for charging a lead storage battery with electric power generated by the fuel cell and supplying it to the outside.

  As mobile devices such as mobile phones, notebook PCs, and digital cameras become more sophisticated, polymer electrolyte fuel cells using polymer electrolyte membranes are expected as their power sources. Among polymer electrolyte fuel cells (hereinafter simply referred to as “fuel cells”), direct oxidation fuel cells that supply liquid fuel such as methanol directly to the anode as fuel are suitable for miniaturization and weight reduction. It is being developed as a power source for power generation and a portable generator.

  Furthermore, since the fuel cell has high power generation efficiency and less noise and vibration than a general generator, it is expected to be an energy source for a medium-sized power supply device for consumer use that requires quietness. For example, it is considered to use a fuel cell for a power supply device used for outdoor activities. Since fuel cells have high power generation efficiency, the amount of fuel to be carried can be kept to a minimum, and noise during power generation is low, so it can be used at night in environments close to residential areas. .

  In order to effectively use the power generated by the fuel cell, the power supply device including the fuel cell preferably includes a secondary battery. Fuel cells may have reduced power generation efficiency from the time they are started until the operating state stabilizes, and even during power generation, it may be difficult to adjust the amount of power generated in response to load fluctuations. It is.

  For example, in the case of a medium-sized power supply device used for outdoor activities, it is preferable to use a lead storage battery as a secondary battery included in the fuel cell system. Such a power supply device requires the use of a high-capacity, high-energy density lithium-ion secondary battery or the like because the demand for downsizing is not as great as that for portable electronic devices such as mobile phones. The cost is reduced by using a lead storage battery.

  While lead-acid batteries do not have a memory effect, they are subject to rapid deterioration when subjected to deep discharge, and if used in such a way, they may become unusable after several uses. For this reason, in order to avoid overdischarge, it is desirable that the lead storage battery is charged immediately after use and always satisfies the charge capacity.

  Regarding the above points, in the conventional system for charging a lead storage battery with a fuel cell, as shown in Patent Documents 1 and 2, it has been proposed to charge the lead storage battery by constant current / constant voltage charging.

JP 2006-5979 A JP 2006-236610 A

  However, when storing a lead storage battery using the fuel cell as an energy source, it may be difficult to charge the lead storage battery to a fully charged state only by charging with a normal constant current / constant voltage charge. In constant current charging, the battery voltage (charging voltage) increases as charging progresses. For this reason, as the charging progresses, the load of the fuel cell gradually increases in the constant current charging. At this time, if the load of the fuel cell exceeds the rated output, the power generation efficiency is greatly reduced. In order to avoid this, it becomes necessary to use a fuel cell having a larger rated output, and as a result, the cost of the power supply device increases.

  In order to avoid the inconvenience described above, there is a need to terminate constant current charging at an earlier time in constant current / constant voltage charging and switch to constant voltage charging. However, as the proportion of constant voltage charging in the amount of electricity required for charging to a fully charged state increases, the charging time increases accordingly. For the above reasons, when it is attempted to reduce the cost of the power supply device, it takes a long time to charge the lead storage battery to the fully charged state by the fuel cell. As a result, it is difficult to sufficiently improve the cycle life of the lead-acid battery.

One aspect of the present invention is a fuel cell system including a fuel cell and a lead storage battery, and is a charging method for charging the lead storage battery with power generated by the fuel cell,
Supplying an oxidant at a first predetermined flow rate AQ to the fuel cell;
Supplying fuel at a second predetermined flow rate FQ to the fuel cell;
Charging the lead storage battery with a constant charging current Ib by the power generated by the fuel cell;
A step of increasing the output current If of the fuel cell and decreasing the output voltage Ef of the fuel cell as the battery voltage Eb of the lead storage battery increases.
When the output current If increases to the upper limit current value UI or the output voltage Ef decreases to the lower limit voltage value DE, the output current If is set to be equal to or lower than the upper limit current value UI, or the output voltage Ef Step of decreasing the charging current Ib in response to an increase in the battery voltage Eb so that is equal to or higher than the lower limit voltage value DE, and
Each time the battery voltage Eb reaches the first reference voltage ER1, the charging current Ib of the lead storage battery is changed stepwise (n-1) times from the first current Ib (1) to the nth current Ib (n). In which n is an integer equal to or greater than 2 and Ib (1)> Ib (2)>.

Another aspect of the present invention is a fuel cell;
A first current sensor for detecting an output current If of the fuel cell;
A first voltage sensor for detecting an output voltage Ef of the fuel cell;
A lead-acid battery that is charged by the output power of the fuel cell and an output terminal of the fuel cell, and the output voltage Ef is transformed to set a charging current Ib that charges the lead-acid battery. A DC / DC converter that outputs generated power to the lead-acid battery;
A second current sensor for detecting the charging current Ib;
A second voltage sensor for detecting a battery voltage Eb of the lead acid battery;
A charge control unit that sets a transformation ratio PS of the DC / DC converter so as to adjust a charging current Ib of the lead storage battery according to the battery voltage Eb;
The charging control unit sets the transformation ratio PS so as to keep the charging current Ib constant while the battery voltage Eb is lower than the first reference voltage, and the output current If reaches the upper limit current value UI. When the output voltage Ef increases or decreases to the lower limit voltage value DE, the output current If is set to be equal to or lower than the upper limit current value UI, or the output voltage Ef is set to be equal to or higher than the lower limit voltage value DE. Set the transformation ratio PS,
Furthermore, the charge control unit relates to a fuel cell system that sets the transformation ratio PS so that the charge current Ib is reduced stepwise when the battery voltage Eb reaches a first reference voltage.

  According to the present invention, the charging time is shortened without increasing the cost of the fuel cell system, the life of the lead storage battery used in the fuel cell system is extended, and the power generation efficiency of the fuel cell is improved. At least one of the above is possible.

1 is a block diagram schematically showing a fuel cell system according to an embodiment of the present invention. It is sectional drawing which shows roughly the cell of the fuel cell used for the fuel cell system. It is a graph which shows the outline | summary of the charging process by the fuel cell system. It is a graph which shows the output characteristic of the fuel cell used for the fuel cell system. It is a flowchart which shows the procedure of the charging process in the fuel cell system.

  The present invention relates to a fuel cell system including a fuel cell and a lead storage battery, and relates to a charging method for charging a lead storage battery with power generated by the fuel cell. In this method, a step of supplying an oxidant at a first predetermined flow rate AQ to a fuel cell, a step of supplying a fuel at a second predetermined flow rate FQ to the fuel cell, a lead storage battery, and a constant charging current Ib by the generated power of the fuel cell The step of charging and the step of increasing the output current If of the fuel cell and decreasing the output voltage Ef of the fuel cell as the battery voltage Eb of the lead storage battery increases so as to obtain the maximum output power of the fuel cell When the output current If increases to the upper limit current value UI, or the output voltage Ef decreases to the lower limit voltage value DE, the output current If is set to the upper limit current value UI or less, or the output voltage Ef is set to the lower limit voltage value. A step of gradually decreasing the charging current Ib according to the increase of the battery voltage Eb so as to be equal to or higher than DE is included. Here, the first predetermined flow rate AQ and the second predetermined flow rate FQ can be set to be larger by a predetermined amount than a value corresponding to the rated output of the fuel cell, for example.

  With the above configuration, the fuel cell generates power at a point where the maximum or near output power can always be obtained with respect to the actual amount of fuel consumed, and the fuel cell generates power greatly exceeding the rated output, for example. Therefore, the power generation efficiency can be improved. This is because, as shown in FIG. 4, the fuel cell can obtain the maximum output power P, that is, the output current If and the output voltage Ef at which the maximum power generation efficiency can be obtained. Note that the graph of the output characteristic curve E-I and the output power P shown in FIG. 4 shows a state when the fuel cell is generating power at the rated output.

  Further, according to the present invention, every time the battery voltage Eb of the lead storage battery reaches the first reference voltage Er1, the charging current Ib of the lead storage battery is changed from the first current Ib (1) to the nth current Ib (n) (n -1) including a step-by-step reduction process. However, n is an integer equal to or greater than 2, and Ib (1)> Ib (2)>. Here, “every time the battery voltage Eb of the lead storage battery reaches the first reference voltage Er1” means that when the charging current Ib is switched to a low current, the battery voltage (charging voltage) Eb once decreases when switching. Furthermore, it means that the battery voltage Eb rises again to the first reference voltage Er1 from the lowered voltage.

  By reducing the charging current Ib stepwise as described above, constant current charging can be executed immediately before the lead storage battery is fully charged or until the point where the lead storage battery is fully charged. As a result, the amount of electricity to be charged by constant voltage charging can be minimized. Therefore, the charging time can be shortened.

  In a preferred embodiment of the present invention, the first predetermined flow rate AQ and the second predetermined flow rate are reduced as the charging current Ib is reduced stepwise from the first current Ib (1) to the nth current Ib (n). The concentration of the fuel supplied to the FQ or the fuel cell is gradually reduced. When the charging current Ib is reduced stepwise, the load on the fuel cell is also reduced stepwise, and the amount of fuel and oxidant actually consumed is also reduced. Accordingly, it becomes possible to reduce the fuel supply amount and the oxidant supply amount, and by actually reducing the fuel supply amount and the oxidant supply amount, the auxiliary pumps such as the fuel pump and the oxidant pump (air pump) Power consumption can be reduced. As a result, the efficiency of the entire system can be improved.

  In a further preferred embodiment of the present invention, when the charging current Ib is reduced to the nth current Ib (n), the lead acid battery is used with the nth current Ib (n) until the battery voltage Eb reaches the second reference voltage ERmax. Is charged. However, ERmax> ER1. Thereby, compared with the case where the lead storage battery is charged to a fully charged state or a state close thereto, for example, by charging at a constant voltage, it is possible to charge with a large current and to charge in a short time. Moreover, since a fully charged state or a state close to it can always be maintained, the life of the lead storage battery can be extended. Here, in a lead storage battery (for example, nominal voltage 12V), the first reference voltage ER1 is set to a voltage of 14.4 ± 0.1V, and the second reference voltage ERmax is 14.5V to 18.0V (however, ERmax > ER1). Even if the battery voltage Eb does not reach the second reference voltage ERmax, the battery is charged with the nth current (n) for a predetermined time (for example, 0.25 to 5.0 hours, preferably 1.5 to 2.5 hours). Then, charging can be terminated.

  Moreover, the lead acid battery has one or a plurality of cell chambers inside a battery case (not shown). In the cell chamber, an electrode group and an electrolytic solution are respectively accommodated. When the lead storage battery has a plurality of cell chambers, the electrode groups are connected in series and / or in parallel. If the nominal voltage NV is 2V, 4V, 6V, etc., for example, the first reference voltage ER1 can be set to a voltage value of NV × 1.2 ± 0.1V, and the second reference voltage Ermax is It can be set to a voltage value larger than the first reference voltage ER1 and not more than NV × 1.5 (V).

  The present invention also provides a fuel cell, a first current sensor for detecting the output current If of the fuel cell, a first voltage sensor for detecting the output voltage Ef of the fuel cell, and lead charged by the output power of the fuel cell. DC / DC connected to the storage battery and the output terminal of the fuel cell, and transforming the output voltage Ef to output the generated power of the fuel cell to the lead storage battery so as to set the charging current Ib for charging the lead storage battery Based on the converter, the second current sensor for detecting the charging current Ib, the second voltage sensor for detecting the battery voltage Eb of the lead storage battery, and the battery voltage Eb, the DC charging current Ib of the lead storage battery is adjusted. The present invention relates to a fuel cell system including a charge control unit that sets a transformation ratio PS of a DC converter.

  Here, the charging control unit sets the transformation ratio PS so as to keep the charging current Ib constant while the battery voltage Eb is lower than the first reference voltage, and obtains the maximum output power of the fuel cell. When the output current If increases to the upper limit current value UI or the output voltage Ef decreases to the lower limit voltage value DE, the output current If is set to the upper limit current value UI or lower, or the output voltage Ef is set to the upper limit voltage value DE or higher. As such, the transformation ratio PS is set. Further, when the battery voltage Eb reaches the first reference voltage, the charge control unit sets the transformation ratio PS so as to decrease the charging current Ib stepwise.

  Here, the upper limit current value UI is set with reference to the optimum output current MFI at which the maximum output of the fuel cell can be obtained. Further, the lower limit voltage value DE is set based on the optimum output voltage MFE that provides the maximum output of the fuel cell. At this time, as shown in FIG. 4, since the graph is sufficiently gentle around the point Pmax (MFI, MFE) at which the output power P of the fuel cell is maximized, the upper limit current value UI is the optimum output current. The current value can be set in a range where the difference from the MFI is 0 to 3000 mA. Similarly, the lower limit voltage DE can be set to a voltage value in a range where the difference from the optimum output voltage MFE is 0 to 0.1 V / cell. The “cell” refers to a cell when the fuel cell includes a fuel cell stack in which a plurality of cells each having one MEA are stacked.

  As the fuel cell, a fuel cell using methanol as a fuel, for example, a direct methanol fuel cell can be used. At this time, air can be used as the oxidizing agent.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
As shown in FIG. 1, a direct oxidation fuel cell system 20 according to this embodiment includes a direct oxidation fuel cell (fuel cell stack) 22 including a cathode and an anode, an air pump 24 that supplies air to the cathode, A fuel pump 26 for supplying a fuel aqueous solution to the anode, an anode fluid discharged from the anode and a cathode 28 for recovering the cathode fluid discharged from the cathode, a lead storage battery 30 for storing the electric power generated by the fuel cell 22, And a control unit 44. Control unit 44 includes a charge control unit. As the lead storage battery 30, a control valve type lead storage battery or a so-called deep cycle battery can be used.

  An information processing device such as a microcomputer can be used for the control unit 44. The information processing apparatus includes a calculation unit, a storage unit, various interfaces, and the like. The calculation unit performs calculations necessary for power generation of the fuel cell in accordance with a program stored in the storage unit. Commands necessary to control the output of each component are output. Further, a storage unit (auxiliary storage device such as a flash memory) of the control unit 44 includes a first current If (1) to an nth current If (n), a first voltage Ef (1) to an nth voltage Ef, which will be described later. (N), first oxidant supply amount AQ (1) to nth oxidant supply amount AQ (n), first fuel supply amount FQ (1) to nth fuel supply amount FQ (n), upper limit current The value UI and the lower limit voltage value DE can be stored. The calculation unit of the control unit 44 can read the above data from the storage unit as necessary when executing the charging process of the present embodiment.

  FIG. 2 shows a structure of a cell constituting the fuel cell (fuel cell stack) 22. The cell 1 has a membrane electrode assembly (MEA) 5 including an anode 2, a cathode 3, and an electrolyte membrane 4 interposed between the anode 2 and the cathode 3. A gasket 14 is disposed on one side surface of the MEA 5 so as to seal the anode 2, and a gasket 15 is disposed on the other side surface so as to seal the cathode 3.

The MEA 5 is sandwiched between the anode side separator 10 and the cathode side separator 11. The anode side separator 10 is in contact with the anode 2, and the cathode side separator 11 is in contact with the cathode 3. The anode separator 10 has a fuel flow path 12 that supplies fuel to the anode 2. The fuel flow path 12 has an anode inlet through which fuel flows and an anode outlet through which CO ₂ produced by the reaction, unused fuel, and the like are discharged. The cathode-side separator 11 has an oxidant channel 13 that supplies an oxidant to the cathode 3. The oxidant flow path 13 has a cathode inlet into which the oxidant flows and a cathode outlet through which water generated by the reaction, unused oxidant, and the like are discharged.

  A stack is formed by providing a plurality of cells as shown in FIG. 2 and electrically stacking the cells in series. In this case, the anode-side separator 10 and the cathode-side separator 11 are usually formed as a single unit. That is, one side of one separator is an anode side separator and the other side is a cathode side separator. The anode inlet of each cell is usually combined into one, such as by using a manifold. Similarly, the anode outlet, the cathode inlet, and the cathode outlet are aggregated.

  The anode side space in the fuel cell system, that is, the space from the fuel pump 26 through the anode to the liquid in the recovery unit is a sealed space so that oxygen does not enter the anode 2 while the fuel cell is stopped. It has become. The anode 2 of the MEA 5 is sealed with a gasket 14 so that only the anode inlet and the anode outlet are communicated with the outside. By disposing the conductor plates 16 and 17 so as to be in contact with the anode side separator 10 and the cathode side separator 11, respectively, the cells 1 can be stacked so as to be electrically connected in series. By arranging the end plates 18 so as to be in contact with the conductor plates 16 and 17, respectively, a plurality of stacked cells 1 can be fastened.

  Further, in FIG. 1, air is supplied to the cathode 3 of the fuel cell by an air pump 24, and fuel (methanol) is supplied to the anode 2 of the fuel cell by a fuel pump 26. The liquid discharged from the anode side is recovered by the recovery unit 28. The liquid in the recovery unit 28 is mixed with fuel and supplied to the anode 2 as an aqueous fuel solution. Further, at least a part of the cathode fluid from the cathode 3 flows into the recovery unit 28. The high-concentration methanol from the fuel tank 32 is mixed with the liquid (thin aqueous methanol solution) from the recovery unit 28 and sent to the anode 2 of each cell of the fuel cell 22 by the fuel pump 26.

  1 further includes a first voltage sensor (FVS) 34 that detects the output voltage Ef of the fuel cell 22, and a first current sensor (FIS) that detects the output current If of the fuel cell 22. 36, a DC / DC converter 38 that outputs the power generated by the fuel cell to the lead storage battery 30 by transforming the output voltage Ef with a transformation ratio PS, and a battery voltage Eb (charging voltage, DC / DC converter) of the lead storage battery 30 A second voltage sensor (BVS) 40 for detecting the charging current Ib of the lead storage battery 30 (output current of the DC / DC converter). Detection signals from the first voltage sensor 34, the first current sensor 36, the second voltage sensor 40, and the second current sensor 42 are input to the control unit 44. The control unit 44 controls the transformation ratio PS of the air pump 24, the fuel pump 26, and the DC / DC converter 38 based on the input detection signals.

  Next, the charging method of this embodiment will be described. In this method, a step of supplying an oxidant at a first predetermined flow rate AQ to the fuel cell, a step of supplying a fuel at a second predetermined flow rate FQ to the fuel cell, a lead storage battery, and a charging current Ib from the generated power of the fuel cell In order to obtain the maximum output power of the fuel cell, the process of charging at a constant level, the output current If of the fuel cell is increased and the output voltage Ef of the fuel cell is decreased as the battery voltage Eb of the lead storage battery increases. When the output current If increases to the upper limit current value UI or the output voltage Ef decreases to the lower limit voltage value DE, the output current If is set to the upper limit current value UI or less, or the output voltage Ef is The step of gradually decreasing the charging current Ib according to the increase of the battery voltage Eb so as to be equal to or higher than the lower limit voltage value DE, and every time the battery voltage Eb reaches the first reference voltage ER1, A step of reducing the current Ib in a stepwise manner (n−1) times from the first current Ib (1) to the nth current Ib (n), where n is an integer of 2 or more and Ib (1 )> Ib (2)>, and when the charging current Ib is reduced to the nth current Ib (n), the battery voltage Eb is the second reference voltage ERmax, where ERmax> ER1. The process of charging the lead-acid battery with the nth current Ib (n) is executed until the value reaches. Even if the battery voltage Eb does not reach the second reference voltage ERmax, the battery is charged with the nth current (n) for a predetermined time (for example, 0.25 to 5.0 hours, preferably 1.5 to 2.5 hours). Then, charging can be terminated.

  Hereinafter, the nominal voltage of the lead storage battery 30 is 12V, and as shown in FIG. 3, the charging current Ib is switched at the maximum of three stages (n = 4) as an example with reference to FIGS. 4 and 5. The charging method of this embodiment will be described.

  First, the battery voltage EOb before starting charging is detected (ST1). Charging start or stop is determined according to the battery voltage EOb at this time. If the detected voltage is equal to or lower than a predetermined value (for example, 12.3 V), charging is started with the first current Ib (1) (8A in the example of FIG. 3) (ST2). At this time, the fuel cell starts power generation with the oxidant supply amount AQ (1) and the fuel supply amount FQ (1) that are larger by a predetermined amount than the flow rate corresponding to the rated output, respectively. If the battery voltage EOb exceeds the predetermined value, the process is terminated without charging the lead storage battery 30 as being fully charged.

  Next, in order to monitor the battery voltage Eb during charging, the battery voltage Eb is detected (ST3). The procedure of ST3 is executed every minute predetermined time Δt. Next, it is determined whether the variable k is a value “n” (here, n = 4 and k = 1 at first) (ST4). If so (Yes in ST4), the lead-acid battery 30 is charged with a constant current at the smallest nth current Ib (n) (here, the fourth current Ib (4)). Go to step. The procedure after ST9 will be described later.

  If the variable k is not “n” (No in ST4), the variable k is one of 1, 2,..., (N−1) (here, (n−1) = 3), and ST5 Then, it is determined whether the battery voltage Eb is smaller than the first reference voltage ER1. If the battery voltage Eb has reached the first reference voltage ER1 (No in ST5), the variable k is increased by the value “1” (ST6), and the process returns to ST3. In ST3, the battery voltage Eb is detected when the predetermined time Δt has elapsed since the previous voltage detection (the same applies hereinafter). The charging current Ib is reduced from Ib (k) to Ib (k + 1) by the procedure of ST6. At first, since k = 1, the charging current Ib is switched from the first current Ib (1) to the second current Ib (2). Thus, every time it is determined No in ST5, the charging current Ib is reduced stepwise from the first current Ib (1) to the nth current Ib (n) a total of (n−1) times. At this time, the oxidant supply amount AQ (k) and the fuel supply amount FQ (k) are also switched to the oxidant supply amount AQ (k + 1) and the fuel supply amount FQ (k + 1) in accordance with the switching of the charging current Ib. be able to. However, AQ (k + 1) <AQ (k) and FQ (k + 1) <FQ (k). For example, if Ib (k) / Ib (k + 1) = α × (FQ (k) / FQ (k + 1)) = β × (AQ (k) / AQ (k + 1)), α = 0.9-2 0.0, β = 0.9 to 2.0. As described above, in response to switching of the charging current Ib, the oxidant supply amount AQ (k) is changed from the first oxidant supply amount AQ (1) to the nth oxidant supply amount AQ (n) (n -1) It is possible to switch between times. Similarly, the fuel supply amount FQ (1) can be switched (n−1) times from the first fuel supply amount FQ (1) to the nth fuel supply amount FQ (n).

  On the other hand, if the battery voltage Eb is smaller than the first reference voltage ER1 in ST5 (Yes in ST5), the charging is continued with the charging current Ib (k) set in ST2, and the output current If of the fuel cell 22 is further increased. Is larger than the upper limit current value UI (ST7). The upper limit current value UI can be set based on a value (MFI) that can obtain the maximum power generation efficiency when the fuel cell 22 is generating power at the rated output. For example, the difference from MFI can be set to a value that is 0 to 3000 mA.

  If the output current If is equal to or lower than the upper limit current value UI (No in ST7), it is further determined whether the output voltage Ef of the fuel cell 22 is smaller than the lower limit voltage value DE (ST8). The lower limit voltage value DE can be set based on a value (MFE) that can obtain the maximum power generation efficiency when the fuel cell 22 is generating power at the rated output. For example, the difference from MFE can be set to a value of 0 to 0.1 V / cell.

  Here, if the output voltage Ef is equal to or higher than the lower limit voltage value DE (No in ST8), in order to continue charging with a constant charging current Ib (k), so as to obtain the maximum or near-maximum power generation efficiency, The output current If is increased by a minute predetermined amount, and the process returns to ST3. At this time, the output voltage Ef is decreased by a minute predetermined amount. Note that the determination procedure of ST7 and ST8 is actually a problem only when k = 1 (see FIG. 3), so the procedure of determining whether k = 1 is executed before ST7, Only when k = 1, the determination procedure of ST7 and ST8 may be executed.

  If the variable k is the value “n (= 4)” in ST4 (Yes in ST4), it is determined whether the battery voltage Eb is smaller than the second reference voltage ERmax (for example, 18.0 V) (ST9). If the battery voltage Eb has reached the second reference voltage ERmax (No in ST9), charging is immediately terminated. If the battery voltage Eb has not reached the second reference voltage ERmax (Yes in ST9), whether or not a predetermined time TI (for example, 2.5 hours) has elapsed since the variable k becomes the value “n (= 4)”. Determine (ST10). If the predetermined time TI has elapsed (Yes in ST10), the charging is terminated. If the predetermined time TI has not elapsed (No in ST10), the process returns to ST3, and charging is continued with the n-th current Ib (n) (n = 4) until No in ST9 or Yes in ST10.

  If the output current If is larger than the upper limit current UI in ST7 (Yes in ST7) or the output voltage Ef is smaller than the lower limit voltage DE in ST8 (Yes in ST8), it is the maximum or near the maximum. In order to maintain the power generation efficiency, the charging current Ib is decreased by a predetermined amount of minute current value ΔIb so as to decrease the charging current Ib according to the increase in the battery voltage Eb, and the process returns to ST3.

  As described above, by adjusting the output current If and the output voltage Ef, the fuel cell can generate power at a point that always exhibits the maximum power generation efficiency, and the fuel cell exceeds, for example, the rated output. Since power generation is prevented, power generation efficiency can be improved.

  Then, by reducing the charging current Ib stepwise, constant current charging can be executed immediately before the lead storage battery is fully charged or until the point where the lead storage battery is fully charged. Therefore, the charging time can be shortened.

  Furthermore, as the charging current Ib is reduced stepwise from the first current Ib (1) to the nth current Ib (n), the oxidant supply amount AQ (k) and the fuel supply amount FQ (k) are reduced. By gradual reduction from AQ (1) and FQ (1) to AQ (n) and FQ (n), unnecessary fuel circulation can be prevented. Thereby, the power consumption of auxiliary machines, such as a fuel pump and an oxidant pump (air pump), can be reduced. As a result, the efficiency of the entire system can be improved.

  Next, each component of the direct oxidation fuel cell system will be described with reference to FIG. However, each component is not limited to the following.

  The cathode 3 includes a cathode catalyst layer 8 in contact with the electrolyte membrane 4 and a cathode diffusion layer 9 in contact with the cathode-side separator 11. The cathode diffusion layer 9 includes, for example, a conductive water repellent layer in contact with the cathode catalyst layer 8 and a base material layer in contact with the cathode side separator 11.

  The cathode catalyst layer 8 includes a cathode catalyst and a polymer electrolyte. As the cathode catalyst, a noble metal such as Pt having high catalytic activity is preferable. The cathode catalyst may be used as it is or may be used in a form supported on a carrier. As the carrier, it is preferable to use a carbon material such as carbon black because of its high electron conductivity and acid resistance. As the polymer electrolyte, it is preferable to use a perfluorosulfonic acid polymer material or a hydrocarbon polymer material having proton conductivity. As a perfluorosulfonic acid polymer material, for example, Nafion (registered trademark) can be used.

  The anode 2 includes an anode catalyst layer 6 in contact with the electrolyte membrane 4 and an anode diffusion layer 7 in contact with the anode-side separator 10. The anode diffusion layer 7 includes, for example, a conductive water repellent layer in contact with the anode catalyst layer 6 and a base material layer in contact with the anode side separator 10.

  The anode catalyst layer 6 includes an anode catalyst and a polymer electrolyte. The anode catalyst is preferably an alloy catalyst of Pt and Ru from the viewpoint of reducing catalyst poisoning by carbon monoxide. The anode catalyst may be used as it is or may be used in a form supported on a support. As the carrier, the same carbon material as the carrier supporting the cathode catalyst can be used. As the polymer electrolyte contained in the anode catalyst layer 6, the same material as that used for the cathode catalyst layer 8 can be used.

  The conductive water repellent layer included in the anode diffusion layer 7 and the cathode diffusion layer 9 includes a conductive agent and a water repellent. As the conductive agent contained in the conductive water repellent layer, a material commonly used in the field of fuel cells such as carbon black can be used without any particular limitation. As the water repellent contained in the conductive water repellent layer, a material commonly used in the field of fuel cells such as polytetrafluoroethylene (PTFE) can be used without any particular limitation.

  As the base material layer, a conductive porous material is used. As the conductive porous material, a material commonly used in the field of fuel cells such as carbon paper can be used without any particular limitation. These porous materials may contain a water repellent in order to improve the diffusibility of the fuel and the discharge of generated water. As the water repellent, the same material as the water repellent contained in the conductive water repellent layer can be used.

  As the electrolyte membrane 4, for example, a conventionally used proton conductive polymer membrane can be used without any particular limitation. Specifically, perfluorosulfonic acid polymer membranes, hydrocarbon polymer membranes and the like can be preferably used. Examples of the perfluorosulfonic acid polymer membrane include Nafion (registered trademark).

  The direct oxidation fuel cell shown in FIG. 2 can be manufactured, for example, by the following method. MEA 5 is manufactured by bonding anode 2 to one surface of electrolyte membrane 4 and cathode 3 to the other surface using a hot press method or the like. Next, the MEA 5 is sandwiched between the anode side separator 10 and the cathode side separator 11. At this time, the anode 2 of the MEA 5 is sealed with the gasket 14 and the cathode 3 is sealed with the gasket 15. Thereafter, current collecting plates 16 and 17 and end plates 18 and 19 are laminated on the outside of the anode side separator 10 and the cathode side separator 11, respectively, and are fastened. Furthermore, a temperature adjusting heater may be laminated outside the end plates 18 and 19.

  According to the present invention, life characteristics and efficiency of a fuel cell system including a lead storage battery can be improved. Therefore, it is possible to provide a fuel cell system that can maintain excellent power generation characteristics over a long period of time and maintain stable performance. The direct oxidation fuel cell system of the present invention is very useful as a medium-sized power source used for outdoor activities.

20 ... Fuel cell system,
22 ... secondary battery,
22 ... Fuel cell,
24 ... Air pump,
26 ... Fuel pump,
30 ... lead-acid battery,
32 ... Fuel tank,
34. First voltage sensor,
36 ... the first current sensor,
38 ... DC converter,
40. Second voltage sensor,
42 ... second current sensor,
44 ... Control unit

Claims (11)

A fuel cell system including a fuel cell and a lead storage battery, wherein the lead storage battery is charged with generated power of the fuel cell,
Supplying an oxidant at a first predetermined flow rate AQ to the fuel cell;
Supplying fuel at a second predetermined flow rate FQ to the fuel cell;
Charging the lead storage battery with a constant charging current Ib by the power generated by the fuel cell;
A step of increasing the output current If of the fuel cell and decreasing the output voltage Ef of the fuel cell as the battery voltage Eb of the lead storage battery increases.
When the output current If increases to the upper limit current value UI or the output voltage Ef decreases to the lower limit voltage value DE, the output current If is set to be equal to or lower than the upper limit current value UI, or the output voltage Ef Step of decreasing the charging current Ib in response to an increase in the battery voltage Eb so that is equal to or higher than the lower limit voltage value DE, and
Each time the battery voltage Eb reaches the first reference voltage ER1, the charging current Ib of the lead storage battery is changed stepwise (n-1) times from the first current Ib (1) to the nth current Ib (n). Wherein n is an integer equal to or greater than 2, and Ib (1)> Ib (2)>.   As the charging current Ib is gradually reduced from the first current Ib (1) to the nth current Ib (n), the first predetermined flow rate AQ and the second predetermined flow rate FQ or the The method for charging a fuel cell system according to claim 1, wherein the concentration of the fuel supplied to the fuel cell is reduced stepwise.   When the charging current Ib is reduced to the nth current Ib (n), the battery voltage Eb reaches the second reference voltage ERmax, where ERmax> ER1, until the nth current Ib (n 3) The method for charging a fuel cell system according to claim 1 or 2, wherein the lead storage battery is charged by the above method. A fuel cell;
A first current sensor for detecting an output current If of the fuel cell;
A first voltage sensor for detecting an output voltage Ef of the fuel cell;
A lead-acid battery that is charged by the output power of the fuel cell and an output terminal of the fuel cell, and the output voltage Ef is transformed to set a charging current Ib that charges the lead-acid battery. A DC / DC converter that outputs generated power to the lead-acid battery;
A second current sensor for detecting the charging current Ib;
A second voltage sensor for detecting a battery voltage Eb of the lead acid battery;
A charge control unit that sets a transformation ratio PS of the DC / DC converter so as to adjust a charging current Ib of the lead storage battery according to the battery voltage Eb;
The charging control unit sets the transformation ratio PS so as to keep the charging current Ib constant while the battery voltage Eb is lower than the first reference voltage, and the output current If reaches the upper limit current value UI. When the output voltage Ef increases or decreases to the lower limit voltage value DE, the output current If is set to be equal to or lower than the upper limit current value UI, or the output voltage Ef is set to be equal to or higher than the lower limit voltage value DE. Set the transformation ratio PS,
Further, when the battery voltage Eb reaches the first reference voltage, the charge control unit sets the transformation ratio PS so as to reduce the charging current Ib stepwise.   The fuel cell system according to claim 4, wherein the upper limit current value UI is set based on an optimum output current MFI at which the maximum output of the fuel cell is obtained.   The fuel cell system according to claim 5, wherein a difference between the optimum output current MFI and the upper limit current value UI is 0 to 3000 mA.   The fuel cell system according to any one of claims 4 to 6, wherein the lower limit voltage value DE is set with reference to an optimum output voltage MFE that provides a maximum output of the fuel cell.   The fuel cell system according to claim 7, wherein a difference between the optimum output voltage MFE and the lower limit voltage DE is 0 to 0.1 V / cell. further,
A fuel pump for sending fuel to the fuel cell;
An oxidant pump for sending an oxidant to the fuel cell;
The charge control unit according to any one of claims 4 to 8, wherein when the charge current Ib is reduced stepwise, the discharge amount of at least one of the fuel pump and the oxidant pump is reduced stepwise accordingly. The fuel cell system according to any one of claims.   The fuel cell system according to any one of claims 4 to 9, wherein the fuel includes methanol.   The fuel cell system according to any one of claims 4 to 10, wherein the oxidant includes air.

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