Patent Application
20120237841
This application claims the benefit of priority under 35 U.S.C. ยง119 of German Patent Application 10 2011 005 693.9 filed Mar. 17, 2011, the entire contents of which are incorporated herein by reference.
The present invention pertains to a fuel cell system, especially of a motor vehicle. The present invention pertains, in addition, to a process for operating such a fuel cell system.
Fuel cells are galvanic cells, which convert a chemical energy generated during a chemical reaction into electric energy and make this available within a fuel cell system especially for electric users. A fuel cell therefore comprises two electrodes, the anode and the cathode, which are separated from one another by an electrolyte. The educts considered for use are specially hydrogen and hydrocarbons as anode gas and especially oxygen or an oxygen-containing gas, especially air, as a cathode gas. Water is formed as the principal waste product during the chemical reaction of the educts in the fuel cell, and fuel cells are therefore considered to be a clean form of energy production. Fuel cells may be combined in a fuel cell system, which can be scaled over a broad range and has therefore numerous applications, both in the area of stationary applications and in that of mobile applications, especially in a motor vehicle. The fuel cell system may have especially gas feed means for supplying the electrodes with the respective educts. If hydrocarbons are used to supply the anode gas, these can be pretreated by a reformer within the fuel cell system. The fuel cell system may also have a recirculation of the anode waste gas especially to increase the efficiency of the fuel cell system.
An object of the present invention is to provide an improved or at least alternative embodiment for a fuel cell system of the type mentioned in the introduction, which is characterized especially by a simplified handling.
The present invention is based on the general idea of providing a voltage-measuring device for measuring an electric voltage at the electrodes and of using a control such that it controls the feed of at least one educt to the fuel cell as a function of the measured voltage in a fuel cell system, especially of a motor vehicle, with at least one fuel cell, which has at least two electrodes for connecting at least one electrode user. In particular, the control can consequently actuate an anode gas feed means for supplying the fuel cell with anode gas as a function of the measured voltage. The voltage-measuring device may be placed both upstream and downstream of at least one user or in parallel thereto.
The control of the educt supply of the fuel cell has direct consequences for the electrical power that can be obtained from the fuel cell. A variation of the measured fuel cell voltage stems, for example, from a change in the electric power drain of the users connected thereto. Thus, a voltage drop over the electrodes results from an increase in the power drain of the users, whereas an increase in the voltage on the electrodes results from a reduction of the power drain of the users. Controlling the educt supply as a function of the measured voltage therefore represents an especially simple variation and adaptation of the fuel cell capacity, because it depends on one measured variable only.
In one possible embodiment, the control is connected to the voltage-measuring device by a polling connection for polling the measured voltage and is connected by a control connection to the anode gas supply means for controlling the anode gas supply means.
Especially the capacity of the anode gas supply means and hence a generated anode gas volume flow are varied depending on the measured voltage. This can be achieved especially by varying the delivery capacity of a delivery means, for example, of a pump.
In another embodiment of the fuel cell system, the anode gas feed means has at least one reformer. The reformer is used here especially to generate the anode gas or anode gas volume flow. The control is connected by a control connection to the reformer and changes the capacity of the reformer or hence especially the anode gas volume flow as a function of the measured voltage. The anode gas feed means, especially the reformer, may optionally have an oxidant gas feed means. The control can be connected in this case by the afore-mentioned control connection or by another control connection to the oxidant gas feed means and change the quantity of oxidant gas being delivered as a function of the measured voltage in order to vary especially the anode gas volume flow. This can be achieved especially by actuating a delivery means, especially a pump. In addition or as an alternative, the anode gas feed means may, moreover, have a fuel feed means, especially to the reformer, where especially hydrocarbons can be mentioned as the fuel. The control can be connected in this case to the fuel feed means by one of the aforementioned control connections or another control connection and change the quantity of fuel being delivered as a function of the measured voltage especially in order to vary the anode gas volume flow. The control can vary the capacity of the pump in this case. If the fuel is stored in a pressurized container, especially a gas cylinder, the quantity of gas being delivered can be regulated by a controllable passage, especially by a valve or pressure regulating valve. The control varies in this case the quantity of fuel let through the passage. These embodiments as well as combinations thereof also represent an especially simple control of the fuel cell system, because these depend on one measured variable only. In addition, they also make it possible, in particular, to affect the processes taking place within the reformer in a simple manner.
Corresponding to another advantageous embodiment, the anode gas feed means comprises a partial or complete recirculation of anode waste gas, especially to the reformer. The control now has, in addition, a control connection to a recirculating means in order to change the recirculation of anode waste gas as a function of the measured voltage in order to vary especially the anode gas volume flow. It should be noted that both an increase and a reduction of recirculation of the anode waste gas increase or reduce the anode gas volume flow depending on operating parameters of the fuel cell. This shall be taken into account correspondingly in the changes to be achieved in the anode gas volume flow. The changes in the recirculation of the anode waste gas can be embodied by a delivery means, especially a pump, the control varying the capacity of the delivery means here. The recirculating means may have, besides, a heat exchanger for regulating the thermal parameters, for example, in order to heat the oxidant gas fed to the reformer and/or the cathode gas fed to the fuel cell and/or to cool the anode waste gas.
It shall be pointed out that the polling and control connections of the control do not necessarily consist of an electric conductor. In particular, wireless transmission of the corresponding signals is conceivable as well. It shall be mentioned, furthermore, that the individual connections of the control may also have a return channel, especially for polling the values of the individual controlled elements of the fuel cell system.
It is apparent that the variation of the anode gas volume flow can be correspondingly and analogously applied to a cathode gas volume for supplying the fuel cell with cathode gas. This can be achieved, for example, by varying a delivery means of a cathode gas feed means. The change in the cathode gas volume flow serves especially the purpose of operating the cathode at the corresponding operating points of the fuel cell with a high percentage of oxygen.
It is apparent that the above-mentioned features, which will also be explained below, can be applied not only in the particular combination indicated, but also in other combinations or alone, without going beyond the scope of the present invention.
Preferred exemplary embodiments of the present invention are shown in the drawings and will be explained in more detail in the following description, where identical reference numbers designate identical or similar or functionally identical components. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
Referring to the drawings in particular, according to
In the embodiment shown in
Control 15 is programmed and equipped such that it can vary, depending on the voltage measured by voltage-measuring device 5, an anode gas volume flow by varying the delivery capacities of the individual deliver means 13 of the fuel feed means 9, of the oxidant gas feed means 11 and of recirculating means 12, each individually or together or in any desired combination. The respective delivery means 13 may be actuated independently from each other or together or in any desired combination or in a coupled manner.
Corresponding to an advantageous use of the fuel cell system 1 presented and of the embodiment shown as an example, control 15 may be programmed such that it can embody the operating process described below.
If, however, the measured voltage is higher in comparison section 18 than the minimum voltage, the process follows a path 22 and the measured voltage is compared with a preset maximum voltage in another comparison section 23. If the measured voltage is higher than the maximum voltage, the process follows a path 24 and the anode gas volume flow is reduced in an operation step 25. The process then returns to path 22 via a path 26 or to the starting point via a path 28. The reduction of the anode gas volume flow is carried out continuously or in a stepped manner and operation 25 is repeated as long as the measured voltage is above the maximum voltage. If the measured voltage is below the maximum voltage, the process returns to the starting point 17 via a path 27 and the process is repeated.
The process can also be described as follows in connection with
If the measured voltage in comparison step 18 is higher than the minimum voltage, the measured voltage is compared in comparison section 23 with a preset maximum voltage. The maximum voltage may be characterized especially in that it reflects a dropping power drain of the connected users 4. If a measured voltage that is higher than the maximum voltage is detected, the anode gas volume flow is reduced in an operation step 25. This reduction of the anode gas volume flow serves especially the purpose of reducing the capacity of fuel cell 2. A reduction of the anode gas volume flow can be achieved especially by reducing the capacity of reformer 8, which can be achieved especially by reducing the delivery capacity of the fuel feed means 9 and/or of the oxidant gas feed means 11 and/or by varying the delivery capacity of recirculating means 12, especially of the corresponding delivery means 13. The control actions mentioned within operation step 25 may be carried out both simultaneously and independently from one another. In addition, they may be combined as desired. The reduction of the anode gas volume flow may take place in a preset change step, especially of the capacity of the individual delivery means 13. The process returns to comparison step 23 after the corresponding change step within operation step 25, and the above-mentioned steps are repeated until the measured voltage becomes lower than the maximum voltage. The change steps used in the individual passages, especially of the capacities of the individual delivery means 13, and hence the change steps of the anode gas volume flow, may vary. The individual change steps may depend in this case especially on the difference between the measured voltage and the maximum voltage. In addition, a continuous change of the anode gas volume flow until the measured voltage drops below the maximum voltage is conceivable as well.
To avoid an oscillating behavior or hysteresis, it is possible, in particular, to set in the process a minimum desired voltage above the minimum voltage and below the maximum voltage and/or a maximum desired voltage below the maximum voltage and above the minimum voltage. If both a minimum desired voltage and a maximum desired voltage are provided, the minimum desired voltage should preferably be selected to be lower than the maximum desired voltage. As an alternative, the minimum desired voltage and the maximum desired voltage may also be equal or coincide. The control can now be programmed such that the operation steps 20 and/or 25 take placed continuously or in a stepped manner until the minimum desired voltage or correspondingly the maximum desired voltage is reached.
The above-mentioned minimum voltage and/or maximum voltage and/or minimum desired voltage and/or maximum desired voltage may have a dependence on external parameters, especially the temperature. These dependences may be integrated, especially in the form of characteristics and/or characteristic diagrams, in control 15, and affect this. However, they may also be changed as desired.
It is pointed out that a transposition of the comparison steps 18 and 23 and the operation steps associated therewith lead to the same result and do not therefore differ from the process described above as an example.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 005 693.9 | Mar 2011 | DE | national |
