JP2006318808A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve reduction of size and high efficiency without varying a supply voltage to a low voltage load. <P>SOLUTION: A current collection plate 4 is inserted between fuel cell stacks 2, and part of generated power of the fuel cell stack 2 generated between a current collection plate 3a arranged at the end of the fuel cell stack 2 and the current collection plate 4 is taken out therefrom. The power taken out is supplied to a load V2 operating with low voltage. By the above, a transformer for converting the power taken out from a whole of the fuel cell stacks into low voltage is disused, and system efficiency can be heightened. Further, when the load V2 is in need of a certain voltage, the voltage supplied to the load V2 can be stabilized by stabilizing the output current of the fuel cell 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system having a fuel cell stack.

2. Description of the Related Art Conventionally, a fuel cell system having a fuel cell stack configured by stacking a plurality of fuel cells that generate electricity by receiving fuel gas and oxidant gas supplied to an anode and a cathode, respectively (for example, Patent Document 1). See).
JP 2003-87988 A

  However, the conventional fuel cell system is configured to extract power from the entire fuel cell stack rather than selectively extracting power from the plurality of fuel cells constituting the fuel cell stack. There is a possibility that the fuel cell is deteriorated by taking out electric power from the fuel cell to which the reaction gas flow rate is not supplied.

  Also, when supplying power to a low voltage load that operates at a voltage lower than the output voltage of the fuel cell stack, a transformer such as a DC / DC converter for transforming the high voltage output into a low voltage output that matches the low voltage load Therefore, it is difficult to reduce the size of the system by the amount of the transformer, and the efficiency of the entire system is lowered because the transformer is operated.

  In order to solve such a problem, as disclosed in Patent Document 1, an electric double layer capacitor cell (hereinafter abbreviated as a capacitor cell) that stores power generated by the fuel cell is used as a fuel cell. A system is considered in which the number of capacitor cells connected to the low voltage load is set according to the voltage required by the low voltage load and power is supplied from the capacitor cell to the low voltage load.

  However, in such a system, if the voltage of the capacitor cell is increased to the upper limit of the allowable voltage of the low voltage load, the fuel cell cannot supply power to the corresponding capacitor cell. Power can be supplied to the capacitor cell only when the voltage of the cell has dropped below the upper limit of the allowable voltage. For this reason, according to the system as described above, the voltage of the electric power supplied to the low voltage load constantly fluctuates, and as a result, problems such as sensor detection errors and output fluctuations occur on the low voltage load side.

  The present invention has been made to solve the above-described problems, and an object thereof is a fuel cell system capable of realizing miniaturization and high efficiency without changing the supply voltage to the low voltage load. Is to provide.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a pair of end current collector plates that sandwich both ends of a fuel cell stack, and a plurality of additional current collector plates interposed between the fuel cell stacks. The first load that operates using the power generated by the fuel cell sandwiched by the plurality of additional current collector plates operates using the power generated by the fuel cell sandwiched by the end current collector plates Operating at a lower voltage than the second load.

  According to the fuel cell system of the present invention, low voltage power can be directly supplied from the fuel cell to the low voltage load, so that it is not necessary to use a transformer, and the system can be reduced in size and increased in efficiency. Can do. According to the fuel cell system of the present invention, since the low voltage power is directly supplied from the fuel cell to the low voltage load, the voltage of the power supplied to the low voltage load varies depending on the output current of the fuel cell. However, when the low voltage load requires a constant voltage, the supply voltage to the low voltage load can be stabilized by stabilizing the output current of the fuel cell.

  Hereinafter, the configuration and operation of a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings.

[Configuration of fuel cell system]
As shown in FIG. 1A, a fuel cell system according to a first embodiment of the present invention is a fuel cell that generates electricity by receiving supply of hydrogen and air as fuel gas and oxidant gas to an anode and a cathode, respectively. 1 includes a fuel cell stack 2 in which a plurality of 1 are stacked. The electrochemical reaction at the anode and the cathode and the electrochemical reaction as a whole of the fuel cell stack 2 are based on the following formulas (1) to (3).

[Anode] H ₂ → 2H ⁺ + 2e ⁻ (1)
[Cathode] 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
[Overall] H ₂ +1/2 O ₂ → H ₂ O (3)
As shown in FIG. 1A, the fuel cell stack 1 is sandwiched between a current collector plate 3a on a low voltage side and a current collector plate 3b on a high voltage side, and a voltage (Vs) taken out between the current collector plates 3a and 3b. × N: Vs is an output voltage of the fuel cell 1 (hereinafter referred to as a cell voltage), and N is the number of stacked fuel cells 1) is supplied to the load V1. In addition, a current collecting plate 4 is inserted in the fuel cell stack 2, and a voltage taken out between the current collecting plate 3a and the current collecting plate 4 is supplied to the load V2.

  The load V2 operates at a voltage lower than the load V1. The loads V1 and V2 operate at voltages of 200 to 300 [V] and 10 to 13.5 [V], respectively, and each cell voltage is 0.9 to 0.6 [V] depending on the current density. , The total number of cells N in the fuel cell stack 2 is 333 (∵200 ÷ 0.6≈333, 300 ÷ 0.9≈333) [sheets], the current collector plate 3a and the current collector plate 4 The number of cells in between is set to 15 (∵9 ÷ 0.6≈15, 13.5 ÷ 0.9≈15).

  The loads V1 and V2 independently extract power from the fuel cell stack 2 according to the load request. For this reason, when the load V1 and the load V2 simultaneously extract power from the fuel cell stack 2, the power generation amount of the cell group C2 (see FIG. 1A) between the current collector plate 3a and the current collector plate 4 is other than that. Compared with the power generation amount of the cell group C1 in the stack region, the amount of power supplied to the load V2 is increased, and the current value and current density of each fuel cell constituting the cell group C2 are also each fuel cell constituting the cell group C1. Becomes larger than the current value and current density.

Specifically, the active area (power generation effective area) of each fuel cell is 200 [cm ² ], and the loads V1 and V2 require current amounts of 100 [A] and 20 [A], respectively. The fuel cells constituting the cell group C1 and the cell group C2 are 0.5 (= 100 [A] / 200 [cm ² ]) [A / cm ² ] and 0.6 (= 100 [A] / 200 [, respectively]. cm ² ] +20 [A] ÷ 200 [cm ² ]) [A / cm ² ] is generated at a current density.

  As shown in FIG. 1B, the supply port and the discharge port for air and hydrogen supplied to the fuel cell 1 are provided at one and the other ends of the fuel cell stack 2, respectively. Are provided with a gas supply channel 5 and a gas discharge channel 6 for supplying air and hydrogen to each fuel cell 1 and supplying a reaction gas to each fuel cell 1 individually.

  According to such a configuration, the static pressure of air and hydrogen in the gas supply channel 5 on the side close to the current collector plate 3a is equal to the static pressure of air and hydrogen in the gas supply channel 5 on the side close to the current collector plate 3b. On the contrary, the static pressure of air and hydrogen in the gas discharge channel 6 on the side close to the current collector plate 3a is higher than the pressure, and the static pressure of air and hydrogen in the gas discharge channel 6 on the side close to the current collector plate 3b. Lower than pressure.

  Therefore, the static pressure difference between the gas supply channel 5 and the gas discharge channel 6 in the fuel cell 1 on the side close to the current collector plate 3a is the same as that in the fuel cell 1 on the side near the current collector plate 3b. The flow rate of hydrogen and air flowing in the fuel cell 1 closer to the current collector plate 3a becomes larger than the difference in static pressure between the flow paths 6, and the flow rate of hydrogen and air flowing in the fuel cell 1 closer to the current collector plate 3b is larger. Become.

  The cooling water for cooling the fuel cell stack 2 is cooled by a heat radiating device (not shown) and then supplied from the current collecting plate 3a side to the current collecting plate 3b side as shown in FIG. 1 (c). According to such a configuration, the cooling water temperature on the side closer to the current collector plate 3a is lower than the cooling water temperature on the side closer to the current collector plate 3b, so that the amount of power generation is larger than that of the cell group C1. It is possible to prevent the cell group C1 from being overheated.

  As is apparent from the above description, in the fuel cell system according to the first embodiment of the present invention, the current collector plate 4 is inserted into the fuel cell stack 2 and the current collector provided at the end of the fuel cell stack 2. A part of the generated power of the fuel cell stack 2 is taken out between the plate 3a and the current collector plate 4, and the extracted power is supplied to the load V2 that operates at a low voltage. A transformer for converting to a low voltage is not necessary, and the system can be reduced in size and efficiency.

  Further, in the fuel cell system according to the first embodiment of the present invention, the output is taken out directly from the fuel cell 1 instead of taking out the output from the fuel cell via the capacitor cell as in the conventional fuel cell system, Since the extracted electric power is supplied to the load V2, the supply voltage to the load V2 varies with respect to the output current of the fuel cell 1. For this reason, when the load V2 requires a constant voltage, for example, to suppress fluctuations in the rotational speed of the pump, the supply voltage to the load V2 can be stabilized by stabilizing the output current of the fuel cell 1. .

  Further, in the fuel cell system according to the first embodiment of the present invention, since the current density of the cell group C2 between the current collector plate 3a and the current collector plate 4 does not become too large, the voltage taken out from the cell group C2 is reduced. Even when it is larger than the upper limit of the operating voltage of the load V2 and it is necessary to use a transformer, the step-down rate of the transformer is smaller than the step-down rate when stepping down the output from the entire fuel cell stack 2, The transformer device can be made smaller and lighter.

  In general, the cell voltage increases as the reaction gas flow rate (in the case of FIG. 2, the air flow rate) increases as shown in FIG. 2, but in the fuel cell system according to the first embodiment of the present invention, as described above, Since the flow rate of air flowing to the fuel cell 1 on the side close to the current collector plate 3a is larger than the flow rate of air flowing to the fuel cell 1 on the side close to the current collector plate 3b, power is supplied only to the load V1. In this case, the cell voltage VC2 of the fuel cell 1 constituting the cell group C2 is larger than the cell voltage VC1 of the fuel cell 1 constituting the cell group C1, as shown in FIG.

  On the other hand, when power is supplied to both the load V1 and the load V2 at the same time, the cell group C2 outputs the current supplied to both the load V1 and the load V2, and thus the fuel cell 1 that constitutes the cell group C2. The current density of the fuel cell 1 changes from the curve L1 to the curve L2 shown in FIG. For this reason, when the flow rate of air supplied to the fuel cell 1 is the same, the cell voltage decreases from VC2 shown in FIG. 2 to VC2 '. However, as described above, since a large amount of air flow is originally supplied to the cell group C2, a voltage equivalent to the cell voltage VC1 of the fuel cell 1 constituting the cell group C1 is output even if the cell voltage decreases. The overall system performance can be maintained.

  Further, like the air flow rate, the hydrogen supply flow rate to the cell group C2 is also configured to be larger than the hydrogen supply flow rate to the cell group C1 as described above, so the output of the fuel cell 1 constituting the cell group C2 Even when the current is larger than the output current of the fuel cell 1 constituting the cell group C1, it is possible to prevent the hydrogen supply amount to the fuel cell 1 constituting the cell group C2 from being insufficient. It is possible to prevent the performance from deteriorating. The hydrogen supply flow rate to the cell groups C1 and C2 is set so that the hydrogen surplus rates in the cell groups C1 and C2 are substantially the same when the loads V1 and V2 are consuming the maximum power. Thereby, the cell voltage of the fuel cell 1 constituting the cell group C2 can be made equal to the cell voltage of the fuel cell 1 constituting the cell group C1.

[Configuration of fuel cell system]
As shown in FIG. 3, the fuel cell system according to the second embodiment of the present invention includes a current collecting plate 3b and a current collecting plate 4 in addition to the configuration of the fuel cell system according to the first embodiment. A current collecting plate 10 interposed therebetween is provided. The voltage taken out between the current collector plate 3a and the current collector plate 10 is supplied to a load V3 that operates at a voltage between the operating voltage of the load V1 and the operating voltage of the load V2. Note that the current collector plate 10 has a larger number of cells between the current collector plate 4 and the current collector plate 10 than the number of cells between the current collector plate 3 a and the current collector plate 4. Interpolated in position.

  According to such a configuration, voltage can be supplied to the three loads V1, V2, and V3 having different operating voltages without using a transformer, and therefore an appropriate load is selected according to the size of the required load. It becomes possible. Specifically, when the electric motor has a large current at a voltage of around 12 [V] and the efficiency decreases, the electric motor can be operated at a voltage of around 48 [V] by changing to an electric motor that operates at a voltage of around 48 [V]. The current value can be lowered, and the electric motor can be made smaller and more efficient. However, when trying to obtain 48 [V] voltage by transforming the voltage of the entire fuel cell stack as in the conventional fuel cell system, in addition to the transformer for 12 [V], the voltage for 48 [V] is used. A transformer is required and the system cannot be miniaturized. In contrast, according to the fuel cell system according to the second embodiment of the present invention, a voltage of 48 [V] can be supplied without using a transformer, so that the fuel cell system can be downsized. Can do.

[Configuration of fuel cell system]
In the fuel cell system according to the third embodiment of the present invention, as shown in FIG. 4, in addition to the configuration of the fuel cell system according to the first embodiment, a flow rate distribution plate for distributing the flow rates of air and hydrogen. Reference numerals 20 a and 20 b are provided in the gas supply channel 5 and the gas discharge channel 6 between the current collector plate 3 a and the current collector plate 4. According to such a configuration, air and hydrogen that are not insufficient for power generation can be supplied to the fuel cell between the current collector plate 3a and the current collector plate 4 regardless of the positions of the air and hydrogen supply ports and discharge ports. .

[Configuration of fuel cell system]
In the fuel cell system according to the fourth embodiment of the present invention, as shown in FIG. 5, in the fuel cell system according to the first embodiment, the inside of the fuel cell between the current collector plate 3a and the current collector plate 4 is provided. The gas flow path width W2 is designed to be larger than the gas flow path width W1 inside the fuel cell between the current collecting plate 4 and the current collecting plate 3b. According to such a configuration, the flow path pressure loss inside the fuel cell between the current collecting plate 3a and the current collecting plate 4 increases the fuel flow between the current collecting plate 4 and the current collecting plate 3b by increasing the flow path cross-sectional area. Since it is smaller than the flow path pressure loss inside the battery, hydrogen and air are present in the fuel cell between the current collector plate 3a and the current collector plate 4 as compared with the fuel cell interior between the current collector plate 4 and the current collector plate 3b. Will flow more. Therefore, regardless of the positions of the supply and discharge ports of air and hydrogen, and without using the flow distribution plates 20a and 20b, the fuel cell between the current collector plate 3a and the current collector plate 4 has sufficient air for power generation. Hydrogen can be supplied.

  As mentioned above, although the embodiment to which the invention made by the present inventor is applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

1 is a schematic diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a figure which shows the change characteristic of the cell voltage accompanying the change of the air flow rate supplied to a fuel cell. It is a schematic diagram which shows the structure of the fuel cell system used as the 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the fuel cell system used as the 3rd Embodiment of this invention. It is a schematic diagram which shows the structure of the fuel cell system used as the 4th Embodiment of this invention.

Explanation of symbols

1: Fuel cell 2: Fuel cell stack 3a, 3b, 4, 10: Current collector plate 5: Gas supply channel 6: Gas discharge channel 20a, 20b: Flow distribution plate C1, C2: Cell groups V1, V2, V3 : Load W1, W2: Gas flow path width

Claims (9)

A fuel cell system comprising a fuel cell stack in which a plurality of fuel cells that generate power by receiving supply of fuel gas and oxidant gas to an anode and a cathode, respectively,
A pair of end current collector plates sandwiching both ends of the fuel cell stack;
A plurality of additional current collector plates inserted into the fuel cell stack,
The first load that operates using the power generated by the fuel cell sandwiched by the plurality of additional current collector plates operates using the power generated by the fuel cell that is sandwiched by the end current collector plates. A fuel cell system that operates at a voltage lower than a load of 2. The fuel cell system according to claim 1,
The fuel cell system, wherein a flow rate of the reaction gas supplied to the fuel cells sandwiched between the plurality of additional current collector plates is larger than a flow rate of the reaction gas supplied to the fuel cells in the other stack regions. The fuel cell system according to claim 2, wherein
A reactive gas supply port and a discharge port are provided at one and the other ends of the fuel cell stack, respectively, and the additional current collector plate is interposed between the fuel cell stack and the supply port. Fuel cell system. The fuel cell system according to claim 2 or 3, wherein
The gas flow path pressure loss inside the fuel cell sandwiched between the plurality of additional current collector plates is smaller than the gas flow path pressure loss when the same reaction gas is supplied at the same flow rate inside the fuel cell in the other stack region. A fuel cell system. The fuel cell system according to claim 4, wherein
A fuel cell system, wherein a cross-sectional area of a gas flow path inside the fuel cell sandwiched between the plurality of additional current collector plates is larger than a cross-sectional area of the gas flow path inside the fuel cell in another stack region. The fuel cell system according to any one of claims 2 to 5, wherein
A fuel cell system comprising a guide plate for guiding a reaction gas to the fuel cell sandwiched between the plurality of additional current collector plates. The fuel cell system according to any one of claims 1 to 6, wherein
The fuel cell system, wherein an additional current collecting plate on the lowest voltage side among the plurality of additional current collecting plates is a current collecting plate on a low voltage side of the pair of current collecting plates. The fuel cell system according to any one of claims 1 to 7,
A fuel cell system for supplying cooling water for cooling the fuel cell from a fuel cell stack end side close to the fuel cell for supplying generated power to the first load. The fuel cell system according to any one of claims 1 to 8, wherein
The number of fuel cells sandwiched by the plurality of additional current collector plates is such that when the power is supplied to both the first and second loads, the fuel cells sandwiched by the plurality of additional current collector plates generate power. The surplus rate of the reaction gas supply flow rate with respect to the gas flow rate required for the fuel cell is substantially the same as the surplus rate of the reaction gas supply flow rate with respect to the gas flow rate required for power generation by the fuel cells in the other stack regions. A fuel cell system characterized by being set.

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