Fuel cell device

Details Fuel cell device Fuel cell device

1999-12-09

2001-04-10

Wong, Peter S. (Department: 2838)

Electricity: battery or capacitor charging or discharging

One cell or battery charges another

Vehicle battery charging

C320S103000

Reexamination Certificate

active

06215272

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell device. More particularly, it relates to a fuel cell device suitable for a fuel cell such as a solid polymer electrolyte fuel cell in which hydrogen is used as the fuel and the air is employed as the oxidant.
Stacking unit cells, in each of which an electrolyte layer is held by being sandwiched between a fuel flow field and an air flow field, forms the main body of the fuel cell. The fuel flow field and the air flow field are supplied with fuel gas and air, respectively. Then, an electrical chemical reaction is caused to occur, thereby generating the electric power. Moreover, the main body of the fuel cell has a characteristic that, if a load current density is increased, activated polarization of an electrode catalyst, the ohmic loss and the concentration polarization bring about a drop in an output voltage from the fuel cell. On account of this, when power output is performed to an external load that consumes the power with the fuel cell as the power supply, the main body of the fuel cell is used as the following system: The use of a DC-DC converter or a DC-AC converter makes it possible to output, as a constant voltage, a direct current power outputted from the fuel cell. Also, the main body of the fuel cell is slow in the response of the output voltage to a variation in the load current density. Because of this, when a sudden change occurs in the external load, the output voltage is temporarily lowered exceedingly, becoming an output voltage smaller than the minimum operation voltage that the external load side requires. This has resulted in a fear that the system itself may come to a halt.
In order to solve this problem, in publications such as JP-A-50-116925, the following system has been proposed: A secondary battery is located in parallel to the fuel cell and, at the time of the sudden change of the external load, the power is supplied from the secondary battery to the external load so that the external load variation on the fuel cell side is reduced.
However, in the system where, as illustrated in
FIG.2
, the power is supplied from the secondary battery to the external load at the time of the sudden change of the external load, a voltage needed for charging the secondary battery differs from a voltage needed for the load. This has required that the DC-DC converter or the DC-AC converter be equipped with
2
lines of outputs, i.e., an output for the load and an output for charging the secondary battery, thereby bringing about complexities and cost-up of the appliances.
Also, as illustrated in
FIG. 3
, in the case of a system where the output for charging the secondary battery is branched from the output line for the load, it turns out that the output line for the secondary battery is inputted into the DC-DC converter or the DC-AC converter. At that time, the power to be supplied from the secondary battery to the load is outputted to the load by way of the DC-DC converter or the DC-AC converter. As the result, the power from the secondary battery is multiplied by conversion efficiency of the DC-DC converter or that of the DC-AC converter. This has caused the power loss to occur.
SUMMARY OF THE INVENTION
In order to solve the above-described problems, it is an object of the present invention to effectively supply the fuel cell device with the power from the secondary battery at the time of the sudden change of the external load, and to simplify the system and to provide the fuel cell device that is inexpensive.
In order to solve the above-described problems, the fuel cell device according to the present invention includes a main body of the fuel cell, a DC-DC converter or a DC-AC converter for converting a direct current power into a direct current of a predetermined voltage V
1
or an alternating current thereof, the direct current power being outputted from the main body of the fuel cell, an output terminal to an external load, an auxiliary device necessary for driving the fuel cell device, a secondary battery that, when the output from the main body of the fuel cell is lacking, outputs an output voltage V
2
for driving the auxiliary device, the auxiliary device being necessary for driving the fuel cell device, a charge controlling unit for controlling charge of the secondary battery, and a circuit-switching controlling unit for controlling supply of the output current from the DC-DC converter or the DC-AC converter to the output terminal to the external load, the auxiliary device and the charge controlling unit, and for controlling supply of the output power from the secondary battery, the auxiliary device being necessary for driving the fuel cell device, wherein, when the output voltage V from the main body of the fuel cell becomes lower than a predetermined voltage V
3
at the time of a sudden change of the external load, the output to the charge controlling unit is stopped, and in addition, when the output voltage V from the main body of the fuel cell becomes lower than a predetermined voltage V
4
, the output to the auxiliary device is switched from the output from the DC-DC converter or the DC-AC converter to the output from the secondary battery, the auxiliary device being necessary for driving the fuel cell device, the relation between the output voltage V
1
from the DC-DC converter or the DC-AC converter and the output voltage V
2
from the secondary battery being so set as to satisfy V
1
>V
2
.
The configuration of another fuel cell device related to the present invention is as follows: When the output voltage V from the main body of the fuel cell becomes higher than a predetermined recovering voltage V
6
after the sudden change of the external load of the fuel cell device, the output to the charge controlling unit is restarted, and when the output voltage V from the main body of the fuel cell becomes higher than a recoverying voltage V
7
, the output to the auxiliary device is restarted, the auxiliary device being necessary for driving the fuel cell device.
The employment of the configuration as described above permits a stable load output to be obtained even at the time of the sudden change of the external load, thus making it possible to provide the fuel cell device that is simple, inexpensive and highly effective.


REFERENCES:
patent: 5212431 (1993-05-01), Origuchi et al.
patent: 5389825 (1995-02-01), Ishikawa et al.
patent: 5686766 (1997-11-01), Tamechika
patent: 50-116925 (1975-09-01), None

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