WO2013079148A1

WO2013079148A1 - Method for operating a fuel cell system, and fuel cell system

Info

Publication number: WO2013079148A1
Application number: PCT/EP2012/004616
Authority: WO
Inventors: Andreas Knoop
Original assignee: Daimler Ag
Priority date: 2011-11-29
Filing date: 2012-11-06
Publication date: 2013-06-06
Also published as: DE102011119666A1

Abstract

The invention relates to a method for operating a fuel cell system (1), comprising at least one fuel cell (3), an electrical machine (13), and an air conveying device (9) for supplying air to the fuel cell (3), wherein the electrical machine (13) stores electrical power in order to drive the air conveying device (9). The invention is characterized in that in a normal operating state of the fuel cell system (1), the air conveying device (9) is powered in a normal rotational direction, and in a warm-up state of operation of the fuel cell system (1), the air conveying device (9) is powered in the reverse rotational direction.

Description

Method for operating a fuel cell system and fuel cell system

The invention relates to a method for operating a fuel cell system according to the further defined in the preamble of claim 1. The invention also relates to the use of such a method and a fuel cell system.

Fuel cell systems are known from the general state of the art. In fuel cells are hydrogen and oxygen or hydrogen and

oxygen-containing gases with relatively high efficiency converted into electrical energy. Such fuel cell systems are suitable under certain

Requirements as a primary source of energy for vehicles. It can do that

Fuel cell system depending on the location of the vehicle in the course of the season subject to strong temperature fluctuations. In cold outdoor temperatures, especially at temperatures below freezing, this cools

Fuel cell system and must be brought back to operating temperature after a long break before a normal normal operation during a warm-up during a freeze start or cold start again.

As a result, immediately after the start of the fuel cell system, the full power of the fuel cell system is not available to the vehicle and may not be sufficient for moving the vehicle. Thus, the driver can either only move the vehicle after a certain waiting time or must expect a significantly reduced driving performance within the waiting time.

During the warm-up operation, the fuel cell system initially gives only a relatively small amount of power due to the low efficiency associated with the low fuel cell temperature. At temperatures below freezing it can In addition, it happens that the surfaces within the fuel cell system are covered with ice, which can further reduce the removal performance.

However, due to the reduced efficiency of the fuel cells in the warm-up mode, a significant thermal power loss occurs, which contributes significantly to the self-heating of the fuel cell system. One way to shorten the Aufwärmbetriebsphase is now to provide as high a power loss for the fuel cell system during this phase, as long as the output power is not sufficient for the supply of the drive motor.

The number of potential users is limited in the warm-up phase. In addition to, for example, the heating of the cab are usually only power users available whose power consumption is deliberately limited either for energy efficiency reasons and their power consumption can not or only slightly increased.

It is known from WO 2009010113 A1 to arrange a flow resistance element in a fuel cell system in the supply line between a compressor and the cathode space of the fuel cell and a second

To arrange flow resistance element in a bypass line which connects a leading away from the cathode compartment of the fuel cell discharge line with the supply line. Through this cathode arrangement and design, while the

Warm-up phase of the fuel cell can be reduced during cold start. However, this flow resistance element requires not inconsiderable structural interventions and additional components.

It is an object of the invention to provide a method of operating a

Specify fuel cell system and a fuel cell system, in which the warm-up operation phase can be shortened and can be implemented easily and inexpensively.

According to the invention, this object is solved by the features of claim 1.

Further advantageous embodiments of the method will become apparent from the dependent therefrom dependent claims. The object is also achieved by a fuel cell system according to claim 5. Corresponding advantageous embodiments are specified in the dependent claims. In claim 3 is a preferred Use for the method according to the invention, specified in claim 10, a vehicle with a fuel cell system according to the invention.

The method according to the invention serves to operate a fuel cell system. The fuel cell system comprises at least one fuel cell and an electric machine and an air conveyor for supplying air from the

Fuel cell. The electric machine receives electrical power to drive the air conveyor. The inventive method is characterized in that in a normal operating state of the fuel cell system, the air conveying device in a normal direction of rotation and in a

Warm-up operating state of the fuel cell system, the air conveyor is driven in the reverse direction.

The concept of the invention now consists in that the air conveying device, the

for example, may be a rotary compressor, is driven in the normal operating state of the fuel cell system in a so-called normal direction of rotation. In this normal direction of rotation of the air conveyor this works with codes that are particularly adapted for the normal operating condition. During the

On the other hand, in the warm-up mode, the air conveyor is driven in the reverse direction, i. E. in the opposite direction to the normal direction of rotation. With this reverse direction, other ratios of the result

Air conveying device, which result from the optimized for the normal direction of rotation impeller geometry. This results, for example, in significantly increased losses of the air conveyor, which manifests itself in particular in increased heating of the air conveyed by the air conveyor. It will thus be during the

Warm-up phase allows operation of the air conveyor with significantly increased power dissipation, which additionally heats the conveyed air and thus shortens the warm-up.

An advantageous embodiment of the invention provides that the

Fuel cell system having an electric turbocharger with a turbine, wherein the turbine is operated with an exhaust gas flow of the fuel cell. The turbine, the electric machine and the air conveyor of the electric turbocharger may advantageously be arranged on a common shaft. The turbine is typically mechanically coupled to and drives the air conveyor. If the power of the turbine for driving the air conveyor is not sufficient, which is almost always the case in the usual operating conditions, in addition electric power can be provided via the electric machine to drive the air conveyor with sufficient power.

An alternative embodiment of the invention provides that the air conveyor is a turbocompressor.

According to an embodiment of the invention drives in the

In the warm-up operation state, the electric machine drives the air-conveying device in the reverse direction of rotation. Thus, in addition to the advantageous heating of the conveyed air through deliberately generated thermal power loss also an electrical consumer can be provided, due to intentionally

deteriorated efficiency of the driven in the reverse direction of rotation air conveyor with maximum power consumption can be controlled and thus additionally generates electrical power loss.

According to a particularly preferred embodiment of the invention, it is provided that the air conveying device is a radial compressor. A centrifugal compressor has the advantage that the conveyed air is conveyed in the same direction as in the normal direction of rotation despite a reversal of the direction of rotation. The compression process takes place in this case at a much lower efficiency. Thus increase the electrical power consumption of the electric machine and the

Compressor outlet temperature on. Both effects have a positive effect with regard to a rapid heating of the fuel cell system.

The fuel cell system according to the invention has at least one fuel cell and an electric machine and an air conveying device for supplying air to the fuel cell. The electric machine receives electrical power to drive the air conveyor. According to the invention, the air conveying device is characterized in that it is in a normal operating state of the fuel cell system in a normal direction of rotation and in a warm-up operating state of

Fuel cell system is driven in the reverse direction. In one embodiment of the invention it is provided that an electric turbocharger is provided with a turbine, wherein the turbine is operated with an exhaust gas flow of the fuel cell. Alternatively, a turbo compressor can be provided.

According to a preferred embodiment, the air conveying device is characterized in that it is a radial compressor. In this particularly preferred embodiment, a reversal of the direction of rotation has no influence on the general direction of the air promotion.

In a further preferred embodiment, it is provided that the blading of the radial compressor is designed so that in the normal direction of rotation

Compression with a first efficiency and in the reverse direction of a compression with a second efficiency is carried out, in particular, it may be provided that the first efficiency is higher than the second efficiency. According to this particularly preferred embodiment, the efficiency of the air conveying device, in particular of the

Radial compressors, reduced and thus the power loss can be achieved. On the one hand, this leads to increased heating of the conveyed air and, on the other hand, it makes it possible to operate the compressor with high electrical power. This allows rapid and efficient heating of the fuel cell system.

Further advantageous embodiments of the method according to the invention and the fuel cell system according to the invention will become apparent from the further dependent claims and will be apparent from the embodiment, which is described below with reference to the figures.

Showing:

1 shows a schematically indicated first fuel cell system, which is for

Implementation of the method according to the invention is suitable; and

2 shows a schematically indicated second fuel cell system, which is used for

Implementation of the method according to the invention is suitable; and

3 shows a flow chart for carrying out the method according to the invention. FIG. 1 shows a first fuel cell system 1. The fuel cell system 1 is shown in a highly simplified and schematized manner. Only the relevant components for carrying out the invention are shown. The fuel cell system 1 can

Of course, have more components and components, as is known and customary in fuel cell systems.

The fuel cell system 1 is arranged in a vehicle 2. This is indicated schematically by the dot-dashed frame. The core of

Fuel cell system 1 is a fuel cell 3, which is exemplified here as a PEM fuel cell. The fuel cell 3 essentially has an anode chamber 4 and a cathode chamber 5. The fuel cell 3 is realized as a so-called fuel cell stack or fuel cell stack. Hydrogen is supplied to the anode chamber 4 of the fuel cell, in the present case indicated by the arrow 7. Hydrogen-containing exhaust gas 8 is discharged accordingly from the anode chamber 4.

The cathode compartment 5 of the fuel cell 3 is supplied with air via an air conveyor 9. This air conveyor 9 may be formed, for example, as a flow compressor, preferably as a radial compressor. It is part of an electric turbocharger 10. The air conveyor 9 is arranged together with a turbine 11 on a common shaft 12. On this shaft 12, an electric machine 13 is also arranged. About the air conveyor 9, a supply air stream is compressed and fed to the cathode compartment 5 of the fuel cell. Optionally can here

Intercooler, humidifier and the like may be arranged, which are not relevant to the invention and therefore not shown.

Exhaust air from the cathode compartment then returns to the environment together with product water via the turbine 11. The pressure energy contained therein and thermal energy is at least partially converted into mechanical power in the region of the turbine 11, which drives the air conveying device 9 via the common shaft 12. In the normal case, the mechanical power generated by the turbine 11 for driving the air conveyor 9 is not sufficient. Therefore, the electric machine 13 is arranged on the common shaft 12. This works in the normal operating state as an electric motor and provides the additional power required to drive the

Air conveyor 9 already. In special cases, it may also be that in the region of the turbine 11 more power is generated than is required by the air conveyor 9. In these cases, the electric machine 13 can also be operated as a generator in order to provide electrical power in turn. The described arrangement of air conveyor 9, electric motor 13 and turbine 11 will also

collectively referred to as ETC ("Electric Turbocharger", electric turbocharger).

In the region of the exhaust air flow from the cathode compartment 5 of the fuel cell 3, a burner 14 may optionally be arranged. This burner 14 is preferably designed as a catalytic burner. He is always aware of the exhaust air flow of the

Cathode space 5 of the fuel cell 3 flows through. It can also continuously or from time to time exhaust gas from the anode chamber 4 of the fuel cell 3 are supplied, so that the residual hydrogen contained in this exhaust gas burns and

Avoiding hydrogen emissions to the environment. This will be the

Exhaust gas stream heated in front of the turbine 11 and can deliver more power in the region of the turbine 11.

FIG. 2 shows, in comparison to FIG. 1, a schematically indicated second

Fuel cell system which is suitable for carrying out the method according to the invention. In the figure 2, like reference numerals designate the same or similar components. To avoid unnecessary repetition, the differences to the embodiment shown in FIG. 1 are briefly discussed here. Instead of an electrically driven turbine turbocharger, a turbocompressor or compressor 18 is provided in the present embodiment. In the further course, the same applies to both embodiments of FIGS. 1 and 2

received.

A control unit 17 via a bidirectional line 15 to the electric machine 13 in connection. For the method described here, a temperature measurement signal can be used to determine the current operating state, which, for example, the ambient temperature or the temperature of the

Fuel cell stack reproduces. But it is also possible, another

Determination size for the current operating state of the fuel cell system 1 use. For example, a predetermined by a control unit control variable, which takes into account, for example, control or characteristics of the fuel cell stack or system, conceivable. Even simple quantities, such as the time that has elapsed since the ignition time, may optionally be used alone or in addition. The inventive method for operating the fuel cell system 1 provides that the controller 17 a current operating state of

Fuel cell system 1 determined. This can, as already stated, take place as a function of a temperature and / or by other control or characteristic variables. This procedure is shown in the representation of FIG. In a first step A, the current operating state of the fuel cell system 1 is determined. In a selection step B, it is decided whether the current operating state is on

Warm-up mode is. In this case, for example, the measured temperature can be compared with a predetermined limit temperature. But it can too

For example alone or in addition the history recorded in the control unit can be used. If the current operating condition is a warm-up operating condition, then in a step C the compressor is operated in the reverse direction, i.

reversed to the direction with optimized efficiency for the

Normal operating state is provided. Thereafter, the process starts again with step A. If the compressor is already operated in the reverse direction, no activity takes place in step C and it jumps back directly into step A. Will be at

Interrogation step B determines that the warm-up operation state is completed or is to be terminated because, for example, the measured temperature is greater than the predetermined limit temperature or corresponding control signals of the controller present, in a step D, the direction of rotation of the compressor is reversed, i. it is operated in the normal direction of rotation. Again, with the appropriate query applies that the step is passed through even with the correct direction of rotation of the compressor, without causing an action.

This method can be stored, for example, in the control unit 17. The control device 17 may be a central control device. Optionally, the control unit 17 may also be designed as a locally arranged control unit.

With the method according to the invention it is achieved that in the

Aufwärmbetriebszustand without further additional design measures the fuel cell stack supplied air is heated in an advantageous manner. This is done by reversing the direction of rotation of the centrifugal compressor. This is accompanied by a significant reduction in the efficiency of the centrifugal compressor, since its

Blading is usually optimized for one direction of rotation. Nevertheless, the of The air conveyed by the centrifugal compressor is conveyed in the "right" direction, but is advantageously heated by the losses that occur to a large extent as heat in that, even if the direction of rotation is reversed, the air continues to move in the direction of

Fuel cell stack can be done. However, this is always the case with centrifugal compressors of conventional design.

At the same time, the strong reduction of the efficiency of the centrifugal compressor occurring during operation in the reverse direction of rotation allows a maximum power consumption of the centrifugal compressor. This therefore represents a maximum

Power sink for the fuel cell stack and allows a much improved self-heating of the fuel cell. Thus, the warm-up is significantly shortened in particular at a freeze start by a simple control without further structural adjustments of the entire system.

Claims

claims

Method for operating a fuel cell system (1), with at least one fuel cell (3) and an electric machine (13) and a

Air conveying device (9) for supplying air to the fuel cell (3), wherein the electric machine (13) receives electrical power to the

To drive air conveyor (9),

characterized in that

in a normal operating state of the fuel cell system (1) the

Air conveyor (9) in a normal direction of rotation and

in a warm-up operation state of the fuel cell system (1) the

Air conveyor (9) is driven in the reverse direction.

Method according to claim 1,

characterized in that

the fuel cell system (1) has an electric turbocharger (10) with a turbine (11), wherein the turbine (11) is operated with an exhaust gas stream of the fuel cell (3).

Method according to claim 1 or 2,

characterized in that

in the warm-up operation state, the electric machine (13)

Air conveyor (9) in the reverse direction of rotation drives, in particular, the air conveyor (9) is a centrifugal compressor.

4. Use of the method for operating a fuel cell system (1) according to one of claims 1 to 3, in a vehicle (2), wherein in particular the Fuel cell system (1) provides electrical drive power for the vehicle (2).

5. Fuel cell system (1), with at least one fuel cell (3) and an electric machine (13) and an air conveyor (9) for supplying air to the fuel cell (3), wherein the electric machine (13) receives electrical power to the air conveyor ( 9), the

Air conveyor

characterized in that

in a normal operating state of the fuel cell system (1) in a normal rotational direction and

in a warm-up operation state of the fuel cell system (1) is drivable in the reverse direction of rotation.

6. Fuel cell system according to claim 5,

characterized in that

an electric turbocharger (10) with a turbine (11) is provided, wherein the turbine (11) is operated with an exhaust gas stream of the fuel cell (3).

7. Fuel cell system according to claim 5 or 6,

characterized in that

the air conveyor is a radial compressor.

8. Fuel cell system according to claim 7

characterized in that

the blading of the radial compressor is designed so that in the normal direction of rotation compression with a first efficiency and in the reverse direction of a compression with a second efficiency takes place.

9. Fuel cell system according to claim 8,

characterized in that

the first efficiency is higher than the second efficiency.

10. Vehicle with a fuel cell system according to one of claims 5 to 9.