Fuel cell system capable of reducing electric power loss

Details Fuel cell system capable of reducing electric power loss Fuel cell system capable of reducing electric power loss

1999-07-14

2001-07-03

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having diverse cells or diverse removable cells in a support...

C429S006000, C180S065310

Reexamination Certificate

active

06255008

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-219648 filed on Jul. 16, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell system capable of reducing electric power loss in a power conducting passage for supplying power from a fuel cell to a load.
2. Description of the Related Art
A conventional fuel cell system installable in an electric vehicle is constructed as illustrated in
FIG. 5. A
fuel
124
, such as water and methanol and the like, is supplied into a reformer
128
. The reformer
128
produces a fuel gas, such as hydrogen gas, from the fuel
124
through steam reforming reaction with methanol. The fuel gas produced by the reformer
128
and air
130
are supplied into a fuel cell
136
. The fuel cell
136
generates an electromotive force through electrochemical reactions. The generated electric power is supplied from the fuel cell
136
to an inverter
144
via a DC/DC converter
138
and a diode
139
. The inverter
144
also receives electric power from a battery
140
that is connected in parallel to the DC/DC converter
138
. Using the power supplied thereto, the inverter
144
drives a motor
146
to provide driving force for the electric vehicle. The DC/DC converter
138
regulates the voltage output from the fuel cell
136
, and applies the regulated voltage to the inverter
144
and the battery
140
in parallel.
A control unit
120
calculates a required output of the inverter
144
(i.e., required electric power) from the amount of depression of an accelerator pedal of the electric vehicle detected by an accelerator pedal position sensor
122
. Based on the calculated required output, the control unit
120
controls the inverter
144
so that an electric power corresponding to the required output is supplied to the motor
146
via the inverter
144
.
Normally, the fuel cell
136
outputs an amount of power that provides the required output of the inverter
144
. However, if the power from the fuel cell
136
alone is not sufficient for the required output of the inverter
144
, the control unit
120
sets the output voltage of the battery
140
to a desired value such that a supplement power for the required output is outputted (discharged) from the battery
140
to the inverter
144
, by controlling the DC/DC converter
138
to adjust the output voltage of the DC/DC converter
138
in accordance with a state of charge (SOC) of the battery
140
detected by an SOC sensor
142
.
If the power from the fuel cell
136
has a surplus after providing the required output of the inverter
144
, the control unit
120
controls the DC/DC converter
138
to set the output voltage of the battery
140
to a desired value such that the surplus power is stored (charged) into the battery
140
.
That is, the related-art fuel cell system adjusts the output voltage of the DC/DC converter
138
provided between the fuel cell
136
and the parallel circuit of the battery
140
and the inverter
144
, so as to set the output voltage of the battery
140
to various desired values, whereby a desired amount of power is outputted (discharged) from or stored (charged) into the battery
140
.
Therefore, power from the fuel cell
136
is supplied to the inverter
144
, always via the DC/DC converter
138
.
However, the power converting efficiency of the DC/DC converter
138
is normally as low as 70-80%. Since power from the fuel cell
136
is supplied via the DC/DC converter
138
, the related-art fuel cell system has a problem of a considerable power loss caused by the DC/DC converter
138
.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a fuel cell system capable of minimizing the power loss that occurs in a power conducting passage during supply of power from a fuel cell to a load.
To achieve at least a portion of the aforementioned and other objects of the invention, the fuel cell system of the invention includes a fuel cell that is supplied with a fuel and generates a power, a secondary battery capable of storing the power generated by the fuel cell and of supplying a power stored therein to a load, a voltage adjusting device for adjusting a voltage generated by the fuel cell, a bypass device for supplying the power generated by the fuel cell to the load, bypassing the voltage adjusting device, and a switch device for selectively changing the path for the supply of the power generated by the fuel cell to the load between a path via the voltage adjusting device and a path via the bypass device.
In the invention, if the switch device is switched so that the power generated by the fuel cell is supplied to the load via the bypass device, the power supply from the fuel cell to the load bypasses the voltage adjusting device, so that substantially no power loss occurs in the conduction passage.
In a case where it is unnecessary to store power into the secondary battery or output power from the secondary battery, the electric connection between the secondary battery and the bypass device and the electric connection between the secondary battery and the load may be discontinued by using a shutting device in such a manner that the secondary battery is completely electrically disconnected from the load, the fuel cell and the like. The electrical disconnection of the secondary battery in this manner does not cause any substantial problem. When the secondary battery is thus disconnected, it becomes unnecessary to set the output voltage of the second battery to a desired value, so that the voltage adjusting device becomes unnecessary in this case. Therefore, the power generated by the fuel cell can be supplied to the load via the bypass device by using the switch device, without causing any problem. Hence, substantially no power loss occurs in the conduction passage.
The aforementioned case where it is unnecessary to store power into the secondary battery or output power from the secondary battery may include a case where an amount of charge of the secondary battery is substantially 100% and a case where a difference between a required power of the load and an expected output power of the fuel cell is substantially zero and where the amount of charge of the secondary battery is greater than a predetermined reference amount.
In the case where the amount of charge of the secondary battery is substantially 100%, no more power can be stored into the secondary battery. Therefore, this case can be regarded as a case where storage of power into the secondary battery is unnecessary. In the case where the difference between the required power of the load and the expected output power of the fuel cell is substantially zero, there is no need to supply power from the secondary battery to the load. In the case where the amount of charge of the secondary battery is greater than the predetermined reference amount, there is not a considerable need to store power into the secondary battery. Therefore, these cases can be regarded as a case where it is unnecessary to output power from the secondary battery or store power into the secondary battery.
In the fuel cell system of the invention, the voltage adjusting device may be formed by a DC/DC converter that is suitable to adjust, that is, increase or decrease, the voltage outputted from the fuel cell, to a desired value.


REFERENCES:
patent: 5156928 (1992-10-01), Takabayashi
patent: 5334463 (1994-08-01), Tajima et al.
patent: 5519312 (1996-05-01), Wang et al.
patent: 5677073 (1997-10-01), Kawatsu
patent: 5780981 (1998-07-01), Sonntag et al.
patent: 3-276573 (1991-12-01), None
patent: 8-213032 (1996-08-01), None

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