AT527712A1 - Control procedure for controlling a short-term load reduction of a fuel cell system - Google Patents

Abstract

The present invention relates to a control method for controlling a short-term load reduction of a fuel cell system (100) with at least one fuel cell stack (110), wherein the following steps are provided: - detecting a short-term, reduced load requirement (LA) for the fuel cell system (100), - at least partially opening a cathode bypass valve (142) in a cathode bypass section (140) between a cathode feed section (132) and a cathode discharge section (134) of the fuel cell system (100) to generate a cathode bypass mass flow (KBM) of cathode feed gas (KZG) past the at least one fuel cell stack (100).

Description

Control procedure for controlling a short-term load reduction of a fuel cell system

The present invention relates to a control method for controlling a short-term load reduction of a fuel cell system, a computer program product for carrying out such a control method, a control device for carrying out such a control method and a fuel cell system with such a control device.

It is well known that fuel cell systems are used in mobile applications to provide electrical power, for example to power vehicles. In such mobile applications, short-term load reductions can occur, as the respective consumer adapts the required load very dynamically to the environment. If a fuel cell system is used, for example, to supply the electric motor of a motor vehicle, this vehicle can and must react to the environmental situation. If, for example, wheel slip occurs, which leads to the wheels spinning, the drive power must be reduced quickly. Driving downhill, sudden braking maneuvers, or similar events also lead to a short-term, reduced load requirement from the consumer in the form of the vehicle's electric drive. In addition to motor vehicles, ships, trains, airplanes, and similar vehicles should also be mentioned here.

A disadvantage of existing fuel cell systems is that their dynamic response to short-term load reductions is limited by various design parameters. If the load requirement is reduced briefly, i.e., gradually or even abruptly, the fuel cell system can only partially follow this dynamic change in the load requirement. A fuel cell system is a significantly slower system compared to the control requirements of a vehicle. Thus, in the case of a short-term, reduced load reduction, existing fuel cell systems react in two steps. First, the fuel cell system is regulated down in order to generate less electrical energy in line with the reduced load requirement. However, due to the inertia of the fuel cell system, this reduction in the produced electrical power can only occur relatively slowly along a reduction ramp. To nevertheless enable a rapid load reduction and, in particular, to avoid power peaks,

The object of the present invention is to at least partially remedy the disadvantages described above. In particular, the object of the present invention is to improve the dynamics for short-term load reductions in fuel cell systems in a cost-effective and simple manner.

The above object is achieved by a control method having the features of claim 1, a computer program product having the features of claim 12, a control device having the features of claim 13, and a fuel cell system having the features of claim 14. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the control method according to the invention naturally also apply in connection with the computer program product according to the invention, the control device according to the invention, and the fuel cell system according to the invention, and vice versa, so that reciprocal reference is or can always be made to the individual aspects of the invention with regard to the disclosure.

According to the invention, a control method is used to control a short-term load reduction of a fuel cell system with at least one fuel cell stack. Such a control method is characterized by the following steps:

- Detection of a short-term, reduced load requirement for the fuel cell system,

- at least partially opening a cathode bypass valve in a cathode bypass section between a cathode feed section and a

If the load requirement is reduced for a short time, the fuel cell system must react in various ways. To ensure a reduction in electrical power, the fuel supply, usually hydrogen-containing gas, must be throttled. This can be done very easily and cost-effectively because the fuel gas is usually stored in a high-pressure tank and a corresponding throttle valve can be opened and closed highly dynamically. On the air side of the fuel cell stack, which is provided by the cathode section, the corresponding throttling can be less dynamic, since the air is usually drawn in from the environment via a compressor device. Compared to throttle valves that can be controlled highly dynamically, a compressor device can be controlled significantly less dynamically. The speed and the resulting mass flow of cathode feed gas are correspondingly slower to control and cannot be quickly and dynamically adapted to short-term reduced load requirements.

According to the invention, a short-term, reduced load requirement is no longer responded to, or at least not exclusively, by reducing the compressor speed. Instead, a cathode bypass valve is at least partially opened, so that a cathode bypass section is opened or opened further, and a cathode bypass flow is generated and/or increased accordingly. Because the compressor device continues to operate, in particular at a constant compressor speed, the remaining residual flow can now be reduced as a stack mass flow to the fuel cell stack by the amount of the cathode bypass mass flow by diverting the cathode bypass mass flow. The larger the cathode bypass mass flow that is diverted from the generated mass flow of the compressor device, the lower the stack mass flow will be.

Because now, solely or at least partially through a highly dynamically switchable bypass valve via the direct control of the cathode bypass mass flow, a control of the stack mass flow is also possible in an indirect way, a highly dynamic reaction can also be achieved on the cathode side of the

As can be seen from the above explanation, a control method according to the invention can provide a highly dynamic response option by changing valve positions on both the cathode and anode sides. This means that, despite the relatively continuous and less dynamic operation of the compressor device, the electrical power output of the fuel cell system can also be dynamically adjusted, in particular reduced, in accordance with the dynamic valve change. This dynamic and thus rapid reduction in electrical power output allows even the otherwise sluggish fuel cell system to respond dynamically to the short-term, reduced load demand. This leads, on the one hand, to a stronger and faster response of the fuel cell system than with known solutions. On the other hand, the remaining excess electrical power of the fuel cell system is lower compared to known solutions, so that this reduced surplus also only needs to be stored in a battery device with less effort. In terms of control capability, this means that even with relatively fully charged battery devices, i.e., a low remaining storage capacity, a dynamic response to a reduced load demand is still possible. Furthermore, the control dynamics now available for the fuel cell system eliminate the need for high storage capacities in the battery device. This leads to a smaller, lighter, and more cost-effective design of the battery device and the entire fuel cell system.

It should be noted that a short-term, reduced load requirement is understood to mean a gradual, step-by-step, or even sudden reduction in the load requirement. As will be explained later,

This sudden reduction in load requirements, especially from a ram-

to distinguish between a slow and intermittent reduction of a load requirement.

It can be advantageous if, in a control method according to the invention, a compressor speed of a compressor device in the cathode supply section is kept constant or essentially constant. As already explained, in the case of a short-term, reduced load demand, the desired dynamic response to this load demand can be generated simply by at least partially opening the cathode bypass valve. Adjusting the compressor speed is not necessary for this dynamic response. Particularly when it is taken into account that short-term, reduced load demands are often very temporary, i.e., only present over a short period of time, for example, wheel spin, the compressor speed can be kept constant or essentially constant for this period. Thus, there is no need to readjust or adjust the compressor speed. As soon as the short-term and temporary reduction in load demand is over, i.e., the load demand rises back to the normal value, the compressor speed does not have to be increased again; instead, the desired amount of stack mass flow can be made available quickly and dynamically by simply returning the cathode bypass valve to a changed closed position. Not only the reaction to the short-term reduction of the load requirement, but also the reaction to the elimination of this short-term, reduced load requirement is now possible in a highly dynamic manner according to the invention.

Further advantages can be achieved if, in a control method according to the invention, a compressor speed of a compressor device in the cathode feed section is reduced immediately and/or after a waiting period. Reducing the compressor speed results in the compressor speed also being adjusted to reduce the power demand. In particular, this only occurs after a waiting period in order to distinguish whether it is a temporary, short-term load demand reduction, for example, a short-term, temporary spinning of drive wheels, or a continuous reduction, such as when driving down an incline. It is therefore possible to readjust the compressor speed without affecting the dynamics in the response to the load demand.

to influence the situation.

Further advantages can also be achieved if, in a control method according to the invention, at least one backpressure valve is additionally partially closed on a cathode side of the at least one fuel cell stack in response to the detected short-term, reduced load requirement. The moment a larger amount of cathode bypass mass flow is diverted, the pressure situation in the fuel cell stack may change. This is particularly true if the anode supply gas is also throttled on the anode side. For example, closing the backpressure valve on the cathode side can increase the pressure on the cathode side. If, in contrast, a reduced pressure is expected on the anode side, opening the backpressure valve in the opposite direction can also relieve the pressure on the cathode side, so that pressure equalization on the cathode side and the anode side of the fuel cell stack can be ensured, in particular by controlling the backpressure valve.

A further advantage is achieved if, according to the preceding paragraph, at least one backpressure valve downstream of the fuel cell stack is partially closed. The same applies to a corresponding partial opening of such a backpressure valve. By arranging and controlling the backpressure valve

Further advantages can be achieved if, in a control method according to the invention, the pressure in the cathode section is kept constant or essentially constant. This means that a constant pressure in the cathode section should be achieved and maintained regardless of the actual control situation, i.e., even during a detected short-term, reduced load demand. Quantitative control of the cathode bypass valve and/or a backpressure valve, as previously described, is particularly advantageous for this purpose.

It is further advantageous if, in a control method according to the invention, a reduced load request is detected as short-term if the requested reduction rate of the reduced load request exceeds a limit value. This makes it possible to distinguish between a normal, reduced load request and a short-term, reduced load request. In particular, the reduction rate is taken into account, for example, the negative gradient with which the load request is reduced is checked. In the case of flat gradients, i.e. a slow reduction in the load request, it may be that a normal, ramp-like control of the compressor speed is sufficient to compensate for the reduced load request. Only in the case of a particularly rapid and therefore short-term, reduced load request is the drop sufficiently steep to exceed this limit value, which can also be referred to as the gradient limit value, and accordingly trigger the at least partial opening of the cathode bypass valve.

It is also advantageous if, in a control method according to the invention, a reduced load requirement is recorded as short-term if the requested reduced absolute load requirement falls below an absolute limit. Here, the speed of the requested reduction in the load requirement is less important than the step depth, i.e., how far the load requirement drops. In particular, this correlates with various stable and unstable operating modes of the fuel cell system to ensure that it is not operated below a minimum stability limit. Of course, such an absolute limit

value also with a relative gradient limit according to the preceding

set can be combined.

Furthermore, it is further advantageous if, in a control method according to the invention, the absorption capacity of a battery device connected to the fuel cell system is additionally taken into account. Absorption capacity can be understood as the storage capacity as well as the remaining absorption capacity, i.e., a state of charge (SoC). In particular, the absorption capacity can provide the primary absorption of the excess electrical power, and the control method according to the invention can dynamically buffer only the portion that exceeds the absorption capacity of the connected battery device at the respective time.

Furthermore, it is also advantageous if, in a control method according to the invention according to the preceding paragraph, the cathode bypass valve is at least partially closed depending on the electrical charge level and/or the electrical storage capacity. This preferably results in maximum utilization of the battery device in order to largely exclude the loss of electrical power.

The present invention also provides a computer program product comprising instructions which, when executed by a computer, cause the computer to perform the steps of a control method according to the invention. Thus, a computer program product according to the invention also provides the same advantages as those explained in detail with reference to a control method according to the invention.

The present invention also relates to a control device for controlling a short-term load reduction of a fuel cell system having at least one fuel cell stack. Such a control device is characterized in that a detection module is provided for detecting a short-term, reduced load requirement for the fuel cell system. With the aid of an opening module, a cathode bypass valve is at least partially opened in a cathode bypass section between a cathode feed section and a cathode discharge section of the fuel cell system to generate a cathode bypass mass flow of cathode feed gas past the at least one fuel cell stack. The detection module and/or the opening module

are particularly suitable for the execution of a control device according to the invention.

Thus, a control device according to the invention also

the same advantages as those described in detail with reference to an inventive

Res control procedures have been explained.

Furthermore, the present invention relates to a fuel cell system for generating electrical power. Such a fuel cell system has at least one fuel cell stack with an anode section and a cathode section. The anode section is equipped with an anode feed section for supplying anode feed gas and with an anode discharge section for discharging anode exhaust gas. The cathode section is equipped with a cathode feed section for supplying cathode feed gas and with a cathode discharge section for discharging cathode exhaust gas. Furthermore, the cathode feed section and the cathode discharge section are fluidly connected to one another via a cathode bypass section. A cathode bypass valve is located in this cathode bypass section. A fuel cell system according to the invention is characterized in that a control device according to the invention is provided for controlling the at least one cathode bypass valve. Thus, a fuel cell system according to the invention also brings with it the same advantages as have been explained in detail with reference to a control method according to the invention.

Further advantages, features and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. They show schematically

table:

Fig. 1 shows an embodiment of a fuel cell system according to the invention,

Fig. 2 shows an embodiment of a control device according to the invention,

Fig. 3 a possible course of a load request,

Fig. 4 another possible course of the load requirement,

Fig. 5 another possible course of the load requirement,

10 Fig. 6 shows a further possible course of the load requirement, Fig. 7 shows a further possible course of the load requirement, Fig. 8 shows a further embodiment of a fuel cell system according to the invention, Fig. 9 shows a formation of a limit value and Fig. 10 shows a further formation of a limit value.

Figure 1 schematically shows a fuel cell system 100 according to the invention. This system is equipped with a single fuel cell stack 110, which has a cathode section 130 and an anode section 120. Of course, two, three, four, or more fuel cell stacks 110 can also be provided. During power generation, anode feed gas AZG, for example, as a hydrogen-containing gas, is supplied via the anode feed section 122 and chemically converted in the fuel cell stack 110 to generate electrical energy. The resulting anode exhaust gas AAG is discharged from the anode section 120 via the anode discharge section 124. Residual heat utilization and water discharge are not shown in detail here.

On the side of the cathode section 130, air, in particular, is supplied to the cathode section 130 as cathode supply gas KZG for this chemical reaction with the anode supply gas AZG. The resulting cathode exhaust gas KAG is accordingly discharged via a cathode discharge section 134. While the anode supply gas AZG is supplied, for example, from a pressurized gas tank via a corresponding throttle valve (not shown), the cathode supply gas KZG can be drawn in in the form of air from the environment via the compressor device 136.

According to the invention, a cathode bypass section 140 is provided, which allows a cathode bypass mass flow KBM to be guided directly from the cathode feed section 132 via the cathode bypass section 140 into the cathode discharge section 134 and thus past the cathode section 130 of the fuel cell stack 110. The amount and the basic control of the cathode bypass mass flow KBM is carried out via the open position and/or the closed position of the cathode bypass valve 142. This cathode bypass valve 142 can be

fe of a control device 10, as shown in more detail in Figure 2, for example, con-

This control device 10 is particularly connected to a consumer

300 are coupled to transmit information in order to generate a load requirement LA

to get from there.

Figure 2 shows a control device 10. It has a detection module 20 capable of detecting a load demand LA from consumer 300. This detected load demand LA is forwarded to the opening module 30, where it is used to at least partially open the cathode bypass valve 142. This increases the cathode bypass mass flow KBM and correspondingly reduces the remaining stack mass flow SBM.

Figure 3 schematically illustrates a possible progression of this situation. Starting from the left along the time axis, the load demand LA runs within a defined range. At time T1, the load demand drops significantly, for example, triggered by the spinning of drive wheels. This sharp drop in power in the load demand LA cannot be dynamically replicated directly by the fuel cell system 100. In particular, the compressor device 136 cannot follow this reduced load demand LA with the same dynamics. Therefore, in accordance with the invention, the cathode bypass valve 142 is now opened, either qualitatively and/or quantitatively, so that a significant and, above all, dynamic increase in the cathode bypass mass flow KBM can be seen in Figure 3. At the same time, the supply of anode feed gas AZG is also reduced on the anode section 120 side, for example, by partially closing a throttle valve (not explained in more detail).

Figure 4 shows that this increase in cathode bypass mass flow KBM allows the compressor speed KD to be maintained. Thus, the compressor speed KD remains constant or essentially constant even after time T1, as shown in Figure 4.

Figure 5 shows a more extensive control option. The compressor speed KD remains essentially constant while the load demand LA remains within the normal range. At time T1, similar to Figures 3 and 4, the desired cathode bypass mass flow KBM is generated and increased by opening the cathode bypass valve 142. By reducing the

Compressor speed KD, also from time T1, can now be adjusted step by step.

se or continuously over the further course of time the cathode bypass valve 142

be closed again, so that accordingly in Figure 5 over time

the cathode bypass mass flow KBM decreases again.

Figure 6 further develops the variant of Figure 5. Starting at time T1, a waiting period WT is used to determine whether the reduction in load demand LA is temporary or permanent. Since the load demand LA remains longer here, after the waiting period WT, at time T2, the compressor speed KD is reduced similarly to Figure 5, so that the cathode bypass mass flow KBM can be reduced again by closing the cathode bypass valve 142 accordingly.

Figure 7 shows a variant of the temporary formation of the short-term, reduced load requirement LA. Here, similar to Figures 3 to 6, the reduction in the load requirement LA is again briefly detected at time T1, and the cathode bypass mass flow KBM is generated by opening the cathode bypass valve 142. At time T2, the increased load requirement LA is detected again, so that this temporary reduction can thus be considered to have ended. At this time T2, the cathode bypass valve 142 is at least partially closed again, so that the cathode bypass mass flow KBM also drops back to its previous value. In this operating mode, in particular the compressor speed KD is kept constant or essentially constant (not shown).

In Figure 8, the fuel cell system 100 is further supplemented by a battery device 200. This battery device 200 can serve as an electrical buffer storage device to ensure charging and discharging in the event of fluctuations in the load demand LA. In particular, the control device 10 can now take into account the state of charge, as well as the maximum storage capacity, over a period of time in order to accordingly include the battery device 200 in the response to a short-term, reduced load demand LA.

Figure 9 illustrates one way to distinguish a short-term, reduced load demand LA from a non-short-term, reduced load demand LA. Here, the limit value GW is a gradient limit value, which sets the steepness of the reduction in the load demand LA as a parameter.

Here the load requirement LA is provided with a steep drop, so that the

Limit value GW exceeded and accordingly this reduced load requirement LA

is defined as short-term.

An alternative is shown in Figure 10. Here, the limit value GW is defined as an absolute limit value GW, which is exceeded at time T1 in Figure 10 and thus defines the short-term, reduced load requirement.

The above explanation of the embodiments describes the present invention exclusively by way of examples.

List of reference symbols

10 Control device 20 Detection module 30 Opening module

100 fuel cell system 110 fuel cell stack 120 anode section

122 Anode feed section 124 Anode discharge section 130 Cathode section

132 Cathode supply section 134 Cathode discharge section 136 Compressor device 140 Cathode bypass section 142 Cathode bypass valve 150 Backpressure valve

200 battery device

300 consumers

AZG anode feed gas

AAG anode exhaust gas

KZG cathode feed gas

KAG cathode exhaust

KBM cathode bypass mass flow SBM stack mass flow

LA load requirement

KD compressor speed GW limit

WT waiting time

T1 Time 1

T2 Time 2

Claims (1)

Patent claims 1. A control method for controlling a short-term load reduction of a fuel cell system (100) having at least one fuel cell stack (110), characterized by the following steps: - Detection of a short-term, reduced load requirement (LA) for the fuel cell system (100), - At least partially opening a cathode bypass valve (142) in a cathode bypass section (140) between a cathode feed section (132) and a cathode discharge section (134) of the fuel cell system (100) to generate a cathode bypass mass flow (KBM) of cathode feed gas (KZG) past the at least one fuel cell stack (100). 2. Control method according to claim 1, characterized in that a compressor speed of a compressor device (136) in the cathode supply section (132) is kept constant or substantially constant. 3. Control method according to one of the preceding claims, characterized in that a compressor speed (KD) of a compressor device (136) in the cathode supply section (132) is reduced immediately and/or after a waiting time (WT). 4. Control method according to one of the preceding claims, characterized in that, starting from the short-term, reduced load requirement (LA), a again increased load requirement (LA) is detected and then the cathode bypass valve (142) is again at least partially closed. 5. Control method according to one of the preceding claims, characterized in that on a cathode side of the at least one fuel cell stack (110) in response to the detected short-term, reduced load requirement (LA), at least one backpressure valve (150) is additionally partially closed. 7. Control method according to one of the preceding claims, characterized in that the pressure in the cathode section (130) is kept constant or substantially constant. 8. Control method according to one of the preceding claims, characterized in that a reduced load requirement (LA) is detected as short-term if the requested reduction rate of the reduced load requirement (LA) exceeds a limit value (GW). 9. Control method according to one of the preceding claims, characterized in that a reduced load requirement (LA) is detected as short-term if the requested reduced absolute load requirement (LA) falls below an absolute limit value (GW). 10. Control method according to one of the preceding claims, characterized in that a storage capacity of a battery device (200) connected to the fuel cell system (100) is additionally taken into account. 11. Control method according to claim 10, characterized in that the cathode bypass valve (142) is opened at least partially as a function of the electrical charge state and/or the electrical storage capacity. 12. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the steps of a control method having the features of one of claims 1 to 11. 13. Control device (10) for controlling a short-term load reduction of a fuel cell system (100) with at least one fuel cell stack (110), characterized by a detection module (20) for detecting a short-term, reduced load requirement (LA) for the fuel cell system (100) and an opening module (30) for at least partially opening a cathode bypass valve (142) in a cathode bypass section (140) between a cathode supply section (132) and a cathode discharge section (132). guide section (134) of the fuel cell system (100) for generating a cathode bypass mass flow (KBM) of cathode feed gas (KZG) past the at least one fuel cell stack (110), wherein the detection module (20) and/or the opening module (30) are designed in particular for carrying out a control method having the features of one of claims 1 to 11. 14. A fuel cell system (100) for generating electrical power, comprising at least one fuel cell stack (110) with an anode section (120) and a cathode section (130), the anode section (120) comprising an anode feed section (122) for supplying anode feed gas (AZG) and an anode discharge section (124) for discharging anode exhaust gas (AAG), the cathode section (130) comprising a cathode feed section (132) for supplying cathode feed gas (KZG) and a cathode discharge section (134) for discharging cathode exhaust gas (KAG), wherein the cathode feed section (132) and the cathode discharge section (134) are connected to one another in fluid communication via a cathode bypass section (140), in which at least one cathode bypass valve (142), characterized in that a control device (10) with the features of claim 13 is provided for controlling the at least one cathode bypass valve (142).