Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-07-16
2001-01-30
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000
Reexamination Certificate
active
06180271
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for operating a PEM fuel cell plant, and a PEM fuel cell plant.
Fuel cells enable electrical energy to be generated directly from hydrogen (H
2
) and oxygen (O
2
) with considerably greater efficiency and significantly lower pollutant emission than conventional measures for generating energy. In addition they operate almost silently.
In addition to those basic advantages, the fuel cell with a solid electrolyte of synthetic material (Polymer Electrolyte Membrane or PEM) has further positive features such as a lower operating temperature below 80° C., favorable overload behavior, low voltage degradation, long service life, favorable load and temperature cycle characteristics and the absence of a liquid, corrosive electrolyte. Furthermore, it can be used for operation with air from the surroundings instead of with oxygen (O
2
).
As a result of all of those characteristics, the PEM fuel cell which is operable with air is an almost ideal generator of electrical power, e.g. for the operation of a power-driven vehicle emitting no exhaust gases.
PEM fuel cells cannot be operated in isolation. For that reason a PEM fuel cell block including many PEM fuel cells, an operating part and an associated electronic module are combined together to form a PEM fuel cell module. The operating part contains devices for supplying hydrogen (H
2
) and air, for leading away water which is produced, for dissipation of heat losses, for wetting the reactants and for the separation of gas impurities.
Important parameters which characterize the operation with air of a PEM fuel cell plant (with at least one PEM fuel cell module) are the air ratio &lgr; and the air volume flow rate V
L
. The air volume flow rate V
L
is a measure of the quantity of air flowing through the PEM fuel cell block per unit time. The air ratio &lgr; indicates the amount of air required by the reaction if air from the surroundings is used instead of pure oxygen (O
2
).
The control or regulation of the air volume flow rate V
L
for a PEM fuel cell plant is complicated. For example, an air supply device for an air-driven fuel cell plant with a compressor is known from German Published, Non-Prosecuted Patent Application DE 43 18 818 A1, corresponding to U.S. Pat. Nos. 5,432,020; 5,434,016; and 5,645,950. In order to adjust the compressor, the air volume flow rate V
L
and the electric current I of a PEM fuel cell block are recorded continuously with a flowmeter and an actual current sensor, respectively. Both the air volume flow rate V
L
and the electric current I of the PEM fuel cell block are continuously transmitted to a control device. Thus, several parameters are continuously recorded and processed in order to adjust the compressor and therewith the PEM fuel cell block.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for operating a PEM fuel cell plant with a PEM fuel cell block as well as such a PEM fuel cell plant, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which ensure a simple adjustment of an air volume flow rate V
L
for the PEM fuel cell block, with low apparatus requirements and thus at a more reasonable cost than the method known from the state of the art.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a PEM fuel cell plant having at least one PEM fuel cell block and a speed-controlled compressor disposed upstream of the at least one PEM fuel cell block for supplying air at a volume flow rate V
L
, which comprises controlling a speed n of the compressor to a desired value n
SN
for adjusting an electric current I of the at least one PEM fuel cell block to a given value I
SN
; deriving the desired value n
SN
from the given value I
SN
of the electric current I according to a characteristic curve n=f(I
SN
); and simultaneously adjusting the desired value n
SN
of the speed to a value according to the characteristic curve when the given value I
SN
changes.
This method ensures a control with a simple apparatus of the speed n of the speed-controlled compressor and thus of the air volume flow rate V
L
for the PEM fuel cell block. This control does not involve measurement, either of the air volume flow rate V
L
through the PEM fuel cell block or of the electric current of the PEM fuel cell block.
For a given value I
SN
of the electric current I of the PEM fuel cell block, the corresponding desired value n
SN
for the speed n of the speed-controlled compressor is derived from a predefined characteristic curve for the given air ratio &lgr;. The desired value n
SN
is then applied to the speed-controlled compressor. Thus a controller for the speed-controlled compressor is not needed. The method is therefore less costly than the method known from the state of the art. In addition, this method is also very dynamic during changes of load.
In accordance with another mode of the invention, the desired value n
SN
of the speed n for the speed-controlled compressor is determined by a control unit.
In particular, the given value I
SN
of the electric current I for a load can be determined by the control unit.
In accordance with a further mode of the invention, a valve downstream of the PEM fuel cell block is adjusted in such a way that at a maximum speed n
M
of the compressor, air is delivered at a volume flow rate V
L
which corresponds to the given air ratio &lgr;. This measure creates optimized operating conditions for the PEM fuel cell plant such as, for example, a suitable operating pressure of operating material in the PEM fuel cell block or maintenance of a constant air ratio &lgr; during changes in the electric current I of the PEM fuel cell block through control of the speed n of the compressor.
With the objects of the invention in view, there is also provided a PEM fuel cell plant, comprising at least one PEM fuel cell block; a speed-controlled compressor disposed upstream of the at least one PEM fuel cell block for supplying air at a volume flow rate V
L
; and a control unit for adjusting an electric current I of the at least one PEM fuel cell block to a given value I
SN
, the control unit connected to the compressor for controlling the speed n of the compressor to a desired value n
SN
derived from the given value I
SN
of the electric current I.
In accordance with another feature of the invention, there is provided a valve disposed downstream of the at least one PEM fuel cell block.
In accordance with a concomitant feature of the invention, the control unit includes a gas pedal for adjusting the electric current of the at least one PEM fuel cell block.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for operating a PEM fuel cell plant and a PEM fuel cell plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 5290641 (1994-03-01), Harashima
patent: 5432020 (1995-07-01), Fleck
patent: 5434016 (1995-07-01), Benz et al.
patent: 5645950 (1997-07-01), Benz et al.
patent: 5780981 (1998-07-01), Sonntag et al.
patent: 5877600 (1999-03-01), Sonntag
patent: 43 22 765 C1 (1994-06-01), None
patent: 43 18 818 A1 (1994-12-01), None
patent: 195 26 774 A1 (1997-01-01), None
patent: 195 40 829 A1 (1997-05-01), None
patent: 195 40 824 A1 (1997-05-01), None
patent: 195 41 575 A1 (1997-05-01), None
patent: 196 40 808 C1 (1997-11-01), None
p
Keim Martin
Stenger Herbert
St{umlaut over (u)}hler Walter
Greenberg Laurence A.
Kalafut Stephen
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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