Method, inspection device, and fuel cell system for preventing vibration excitations produced by an exhaust gas recirculation device

Abstract

The invention relates to a method (100) for preventing vibration excitations produced by a recirculation device (400) of a fuel cell system (200). The target speed (SG) for the operational speed of the recirculation device (400) is determined, and the actual operational speed (IG) of the recirculation device (400) is detected. The determined target speed (SG) is compared with at least one operational-speed speed corridor (GK) in which a vibration excitation of the fuel cell system (200) due to the recirculation device (400) is to be expected. A corrected target speed (kSG) is then determined as an operational speed outside of the at least one speed corridor (GK) on the basis of the actual operational speed (IG) and the determined target speed (SG). The corrected target speed (kSG) is output as the target speed (SG). The invention additionally relates to a computer program product for the computer-supported execution of the aforementioned method (100) and to an inspection device (300) and a recirculation device (400), each of which comprises a respective configuration corresponding to the execution of the method (100). The invention additionally relates to a fuel cell system (200) comprising the aforementioned inspection device (300) and / or the aforementioned recirculation device (400).

Description

[0001] Method, control device and fuel cell system for preventing vibration excitation by an exhaust gas recirculation device

[0002] The present invention relates to a method, a control device, and a recirculation device for preventing vibration excitations in a fuel cell system that are attributable to a recirculation device provided in the fuel cell system. The invention further relates to a computer program product for the computer-assisted execution of the method and to a fuel cell system with the control device and / or recirculation device according to the invention.

[0003] Fuel cell systems are widely used and are also used in mobile applications. For example, PEM fuel cells are used in vehicle propulsion. The efficiency and resource consumption of fuel cells are particularly important for mobile applications.

[0004] It is known from the prior art to divert a portion of the exhaust gas generated at the anode and mix it with the fresh fuel intended for the anode before it is fed to the anode. This makes it possible to combine and utilize any unused fuel in the exhaust gas with the fresh fuel. This type of recirculation and reintroduction of exhaust gas into the fuel cycle can reduce fuel consumption and increase the efficiency of the fuel cell stack. This is primarily due to the fact that recirculation only replaces the amount of fuel actually consumed in the fuel cell stack, and furthermore, the fuel cell can be operated at a higher stoichiometry.

[0005] Mechanical components such as pumps, compressors, or recirculation fans are used for recirculation, which return the exhaust gas to the fuel cell stack at a set supply pressure. Since the risk of a fuel undersupply can be reduced by adjusting the supply pressure, the service life of the fuel cell can be extended. A frequently observed disadvantage of such recirculation implementations is that the mechanical components excite other components in the fuel cell system to vibrate. The vibration excitation can be mechanically induced, for example, by excitation by rotating components such as the rotor and compressor wheel. These components perform oscillatory movements at high speeds during operation. The resulting vibrations are transmitted to other components by mechanical coupling of the mechanical component.Bearings or housing components can provide a coupling for vibration propagation. Furthermore, vibration excitation can be flow-induced. For example, turbulence, cavitation, and pressure pulsations can occur in the line during exhaust gas circulation, leading to vibration excitation of downstream components. In addition to mechanical vibrations, noise can also occur, which is particularly noticeable at high speeds.

[0006] The consequences of vibrational excitation of components in a fuel cell system can become particularly evident when components or assemblies are excited at frequencies identical to or close to their resonant frequencies. Within such a resonance range, the components' oscillations become significantly more intense, which can lead to damage. Due to the oscillating movement of the rotor or compressor wheel, high-frequency excitation accelerations are generated even at low speeds, so that the fuel cell system is excited by the mechanical component not only at the fundamental frequency but also by harmonics. Accordingly, there is a relatively high risk that at least some of the resonant frequencies occurring in the fuel cell system will be exceeded when the mechanical component is ramped up to operating speed.However, due to the vibration problem described above, it is important to avoid passing or even operating the mechanical components at speeds in the range of resonance frequencies.

[0007] The problem of vibration excitation by mechanical components is known in the state of the art, but has so far been either not addressed or inadequately addressed. For example, the mechanical components' operating ranges are not restricted, allowing any desired speed to be set. Typically, a setpoint is specified and compared with an actual speed value. However, these solutions accept the risk of damage to the fuel cell system when resonance frequencies occur. This results in the fuel cell system not operating at its full potential.

[0008] Alternatively, the prior art includes proposals for adapting the mechanical structure of the fuel cell system. For example, vibration dampers are provided between components, or the weight and / or stiffness of components are adjusted to adapt their vibration characteristics and, in particular, resonance frequencies.

[0009] It is therefore an object of the present invention to at least partially remedy the disadvantages described above. In particular, it is an object of the present invention to provide a method and devices by means of which critical rotational speeds of a mechanical component intended for recirculation are avoided during operation or are passed in such a way that the fuel cell system is not excited to oscillate while, at the same time, still ensuring that the fuel cells are supplied by the component.

[0010] The above object is achieved by a method having the features of claim 1, a computer program product having the features of claim 11, a control device having the features of claim 12, a recirculation device having the features of claim 13 and a fuel cell system having the features of claim 15.

[0011] Further advantages and features of the invention emerge from the dependent claims, the description and the drawings. Features and details described in connection with the 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, the recirculation device according to the invention and the fuel cell system according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is and can always be made to each other. A first aspect of the present invention relates to a method for avoiding vibration excitation by a recirculation device of a fuel cell system. The method comprises determining a target speed for an operating speed of the recirculation device.The method further comprises detecting an actual operating speed of the recirculation device. The determined target speed is compared, in particular by a comparison module, with at least one speed corridor for the operating speed, in which vibration excitation of the fuel cell system by the recirculation device is to be expected. The method further comprises determining a corrected target speed as an operating speed outside the at least one speed corridor as a function of the actual operating speed and the determined target speed. The corrected target speed is output as the target speed, and the recirculation device is operated at the corrected target speed as the target speed, for which purpose the corrected target speed is transmitted, in particular, to the recirculation device.This can preferably be done via data lines or wirelessly, for example.

[0012] The target speed for the operating speed of the recirculation device is advantageously a known physical value that depends on the recirculation device and / or the fuel cell system and / or a specific load operation of the fuel cell system. In any case, this value is advantageously predetermined.

[0013] The inventive step of detecting an actual operating speed of the recirculation device is carried out in particular via physical sensors, which are preferably designed for speed measurement. In principle, the actual operating speed can also be advantageously determined using an indirect measurement method.

[0014] Determining a corrected target speed as an operating speed outside the at least one speed corridor as a function of the actual operating speed and the determined target speed is understood to mean, in particular, calculating the same. The inventive step of outputting a corrected target speed comprises, in particular, displaying and storing the corrected target speed, in particular as physical data, in an output module. The stored data are preferably forwarded from the output module to the recirculation device, wherein the recirculation device is operated at the corrected target speed. In other words, the invention provides a method that makes it possible to avoid the excitation of a fuel cell system to oscillations by a recirculation device.In this context, "avoiding vibration excitation" can be understood in particular as preventing the attainment of conditions necessary for the excitation of vibrations. For example, the duration, frequency, and intensity of excitation forces are conditions on which the oscillation of vibrating components may depend.

[0015] A “recirculation device” in the context of the invention can be understood in particular as a conveying device which is in particular designed to convey at least a portion of a process medium from the process outlet to the process inlet using mechanical work, i.e. to return it or, in other words, to recirculate it. In the context of the invention, the process medium can preferably be a fluid or, in particular, a gas. The recirculation device is preferably operated at an operating speed. Furthermore, the recirculation device can preferably be, in particular, an anode recirculation blower. Particularly preferably, the recirculation device can be provided in the exhaust gas path of an electrode of the fuel cell system, preferably in the exhaust gas path of an anode of a fuel cell of the fuel cell system.

[0016] In the method, a target speed for the operating speed of the recirculation device is determined. In the context of the invention, “determining” can be understood in particular as setting or specifying. For example, the target speed can be determined by means of a calculation, read from a table, or directly specified by a user. The target speed can in particular be a target value for the operating speed to be assumed by the recirculation device. In the context of the invention, the “operating speed” can in particular be a speed of a component oscillating or preferably rotating in the recirculation device. For example, the operating speed can be the rotational speed, rpm, or rotational frequency of a rotor or compressor wheel provided in the recirculation device.

[0017] The method also involves detecting the actual operating speed of the recirculation device. Within the scope of the invention, "detecting" can be understood in particular as measuring and / or tapping a current actual value.

[0018] In the method, the determined target speed is further compared with at least one speed corridor of the operating speed in which vibration excitation of the fuel cell system by the recirculation device is to be expected. In the context of the invention, a "speed corridor" can be understood in particular as an interval of values ​​for the operating speed enclosed between a lower and upper limit. The interval can preferably be a closed interval, so that the interval boundaries are also included. As part of the comparison, the upper limit and / or the lower limit of the speed corridor can be compared with the target speed. The fuel cell system can preferably have a plurality of speed corridors. A speed corridor can preferably have one or more resonant frequencies occurring in the fuel cell system.Furthermore, a speed corridor can preferably alternatively or additionally have at least one frequency corresponding to a harmonic. The lower and upper limits can preferably be defined as a range with an offset around a resonant frequency occurring in the fuel cell system or another critical frequency. The upper limit can be defined as the maximum value of the speed corridor and the lower limit as the minimum value of the speed corridor. Resonant frequencies of the fuel cell system can be identified, for example, in experiments by mechanical impulse excitation (e.g., an impact hammer) of the assembled and fully mounted fuel cell system. Alternatively or additionally, only critical individual components of the fuel cell system can be investigated in this way. It is also possible to quickly scan through a speed range to identify resonant frequencies.

[0019] The method further comprises determining a corrected target speed as an operating speed outside the at least one speed corridor as a function of the actual operating speed and the determined target speed. Within the scope of the invention, "determining" can be understood in particular as specifying or specifying.

[0020] The corrected target speed is output as the target speed. "Output" can be understood in particular as the provision or transmission of the corresponding output value via signaling.

[0021] The aforementioned configuration thus makes it possible to identify, avoid, or at least appropriately overcome setpoint requirements for the operating speed that lie within the operating ranges of the recirculation device relevant for the excitation of the fuel cell system. This makes it possible to prevent the conditions necessary for vibration excitation and thus prevent the occurrence of noise, vibration, or damage to the fuel cell system equipped with a recirculation device. For example, a speed corridor can be traversed so quickly that the excitation duration required for the excitation of the otherwise oscillating component of the fuel cell system is too short to excite it to oscillate.Furthermore, taking the actual operating speed into account when determining the corrected target operating speed allows safety mechanisms to be provided in the method by means of which, for example, an undersupply of fuel to the anode to be supplied by the recirculation device can be prevented.

[0022] According to a preferred embodiment, the determined target speed can be determined as the corrected target speed if the at least one speed corridor does not have the determined target speed. Thus, if the speed specifications are acceptable, the vehicle can continue to operate at the originally desired speed. This can increase the efficiency of the fuel cell system, since the recirculation device can be operated primarily depending on the operating point to be reached.

[0023] According to a further preferred embodiment, the determination of the corrected target speed in the event that the determined target speed is exhibited by a size-relevant speed corridor of the at least one speed corridor can comprise a comparison of the actual operating speed with the determined target speed, and the determination of the corrected target speed can furthermore be carried out as a function of the comparison.

[0024] In the context of the invention, a size-relevant speed corridor can be understood, in particular, as a speed corridor within which the determined target speed lies. Thus, such a speed corridor can be considered the size-relevant speed corridor from a set of speed corridors.

[0025] This makes it possible to distinguish between a reduction or increase in operating speed, which would result from the requested target speed. This is particularly important because a reduction in operating speed results in less exhaust gas and thus less unconsumed fuel being transported to the corresponding electrode. If the operating speed is reduced too much, this can lead to an undersupply of fuel at the electrode. By comparing the actual operating speed with the target speed, it is possible to incorporate appropriate safety measures into the process to prevent such shortages.

[0026] According to a preferred embodiment, if the actual operating speed is lower than the determined target speed, the corrected target speed can be determined to be greater than the maximum speed of the size-relevant speed corridor. Preferably, the corrected target speed can be the maximum speed of the size-relevant speed corridor plus a definable upper offset value. The definable upper offset value can, for example, be an offset value freely selectable by a user. Preferably, the offset value can be selected depending on a lower limit of an adjacent and preferably higher speed corridor and / or depending on the operating speed.

[0027] In this way, it can be achieved that the speed corridor is passed within a short time in order to prevent vibration excitation of the fuel cell system long enough for oscillation to occur.

[0028] According to a further preferred embodiment, if the actual operating speed is greater than the determined target speed, the corrected target speed can be determined as a speed less than the minimum speed of the size-relevant speed corridor. Alternatively, the corrected target speed can be determined as a speed with the minimum speed of the size-relevant speed corridor minus a definable sub-offset value.

[0029] The definable sub-offset value can, for example, be an offset value freely selectable by a user. Preferably, the offset value can be selected depending on an upper limit of a neighboring, preferably lower, speed corridor and / or depending on the operating speed.

[0030] In this way, it can be achieved that the speed corridor is passed within a short time in order to prevent vibration excitation of the fuel cell system long enough for oscillation to occur.

[0031] According to a preferred embodiment, the corrected target speed can also be determined as a function of at least one freely definable parameter. Preferably, the parameter can be measurable and / or derivable from measurable variables.

[0032] This makes it possible to consider additional factors influencing the vibration behavior of the fuel cell system in the method. Measurement uncertainties or fluctuations in recorded signals used, for example, for operating point control can also be taken into account. This increases the stability of the method according to the invention when determining the corrected target speed.

[0033] According to a further preferred embodiment, the parameter can have a threshold value for a rate of change of the determined target speed. The corrected target speed can only be determined when a deviation between two consecutive determined target speeds exceeds this threshold value. The threshold value can preferably correspond to a short-term variation from a temporal profile of the determined target speed, wherein the short-term variation can be determined as an average deviation from consecutive determined target speeds within a time interval.

[0034] This ensures that the target speed for the recirculation device is only passed on and / or corrected when a newly specified target speed differs sufficiently from its previous value. The threshold can serve as a fulfillment criterion or as an entry threshold for assessing sufficient difference. In this way, target value adjustments made due to fluctuations in measured signals can be filtered out. This allows the recirculation device to operate stably and consistently, improving the operation of the fuel cell system. Furthermore, a fuel shortage is avoided, as higher operating speeds are maintained in case of doubt.

[0035] According to a preferred embodiment, the parameter can have a time delay value. The corrected target speed can be determined only after the time delay value has elapsed. Preferably, the time delay value can correspond inversely to a frequency at which the determined target speed changes over a time interval. The frequency can, for example, be different from or higher than the update rate of the target speed.

[0036] This also ensures that the target speed for the recirculation device is only transmitted and / or corrected when a new target speed is specified sufficiently late after the last specification. The time delay value can serve as a fulfillment criterion or as an entry threshold for assessing the sufficient length of the time interval between the two specifications. This allows setpoint adjustments made due to fluctuations in measured signals to be filtered out. Consequently, the recirculation device can be operated stably and with continuity, which can improve the operation of the fuel cell system. Furthermore, a fuel undersupply is avoided because higher operating speeds are maintained in case of doubt.

[0037] According to a further development of the aforementioned preferred embodiment, the determination of the corrected target speed can preferably be carried out as a function of the time delay value if the determined target speed is lower than the actual operating speed and this is preferably also lower than the minimum speed of the at least one speed corridor which is to be passed last when reducing the operating speed to the determined target speed.

[0038] This makes it possible to delay a reduction in operating speed, and thus a reduction in the exhaust gas flow rate. This is particularly advantageous in cases where a speed reduction to an operating speed outside the speed range is specified, as it ensures that no undersupply occurs at the electrode supplied with recirculated exhaust gas, especially during large speed adjustments. Furthermore, a fuel undersupply is avoided, as higher operating speeds are maintained in case of doubt.

[0039] According to a preferred embodiment, the target speed can be determined in the method by specifying a target operating point for the operation of a fuel cell stack provided in the fuel cell system. Preferably, a target pressure difference occurring in the fuel cell stack can be determined based on this. Furthermore, the target pressure difference can preferably be a pressure difference between an inlet-side and outlet-side pressure of the fuel cell stack. The target speed can be determined accordingly based on the target operating point and / or, if present, based on the target pressure difference. Thus, the target speed can be determined as a function of an operating point of the fuel cell system.

[0040] According to a further preferred embodiment, in the output step, the corrected target speed can be provided as an input variable to a control device of the recirculation device.

[0041] This allows direct control and monitoring of the recirculation device.

[0042] A further aspect of the invention relates to a computer program product which has instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the aforementioned method.

[0043] The computer program product allows the same effects and advantages to be achieved that have already been described for the method according to the invention. In particular, a computer-implemented implementation of the method can be provided.

[0044] A further aspect of the present invention relates to a control device for preventing vibration excitation by a recirculation device of a fuel cell system. The control device comprises a target speed determination module for determining a target speed for an operating speed of the recirculation device. Furthermore, the control device comprises an operating speed detection module for detecting an actual operating speed of the recirculation device. A comparison module is also provided for comparing the determined target speed with at least one speed corridor for the operating speed, within which vibration excitation of the fuel cell system by the recirculation device is to be expected.The control device further comprises a determination module for determining a corrected target speed as an operating speed outside the at least one speed corridor as a function of the actual operating speed and the determined target speed. In addition, the control device comprises an output module for outputting the corrected target speed as the target speed, wherein the recirculation device is operated with the corrected target speed as the target speed. Within the scope of the invention, the term "control" can be understood in particular to mean controlling, regulating and / or influencing. The control device can preferably be configured to carry out the steps of the method according to the invention. The control device can preferably comprise a control unit of the fuel cell system, or vice versa.

[0045] The control device allows the same effects and advantages to be achieved that have already been described for the method according to the invention. In particular, a physical control unit can be provided by means of which the method according to the invention can be implemented.

[0046] A further aspect of the present invention relates to a recirculation device comprising a control device for implementing the method according to the invention. Alternatively, the recirculation device according to the invention may comprise the aforementioned control device according to the invention.

[0047] Preferably, the recirculation device may comprise a recirculation section comprising an anode recirculation fan, a mechanical pump, or a mechanical compressor. The mechanical pump may preferably be a scroll pump, a claw pump, a Roots pump, a centrifugal pump, or a regenerative pump.

[0048] The recirculation device allows the same effects and advantages to be achieved that have already been described for the method according to the invention. In particular, the recirculation device itself can now provide implementation and control according to the method according to the invention, thus simplifying the control of the recirculation device in the fuel cell system.

[0049] A further aspect of the present invention relates to a fuel cell system. The fuel cell system can preferably be a PEM fuel cell system. The fuel cell system comprises a fuel cell stack with an anode section and a cathode section. A plurality of fuel cells are arranged in a stack in the fuel cell stack. The cathode section has a cathode supply section for supplying cathode supply gas and a cathode discharge section for discharging cathode exhaust gas. The anode section accordingly has an anode supply section for supplying anode supply gas and an anode discharge section for discharging anode exhaust gas. The anode section further comprises an anode exhaust gas recirculation section with a recirculation device for recirculating at least a portion of the anode exhaust gas to the anode supply section.The recirculation device is the recirculation device according to the invention. Alternatively or additionally, the fuel cell system comprises the control device according to the invention, which is connected to a control device of the recirculation device in order to provide the corrected target speed to the control device as an input variable.

[0050] The fuel cell system allows the same effects and advantages to be achieved that have already been described for the method according to the invention. In particular, vibrations and noise generation in the fuel cell system can be reduced because operation of the recirculation device at operating speeds corresponding to the resonant frequencies occurring in the fuel cell system is avoided.

[0051] 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:

[0052] Fig. 1 shows an embodiment of a method according to the invention,

[0053] Fig. 2 is a detailed view of embodiments of two steps of the method according to the invention from Figure 1,

[0054] Fig. 3 is a detailed view of an embodiment of a further step of the method according to the invention from Fig. 1,

[0055] Fig. 4 shows an embodiment of a control device according to the invention,

[0056] Fig. 5 shows embodiments of a recirculation device according to the invention and of a fuel cell system according to the invention, and Fig. 6 shows a diagram with time courses of the target speed, the corrected target speed and the resulting actual operating speed.

[0057] The figures show different views and aspects of the invention.

[0058] In the following, the basic structure and operation of a fuel cell system and a recirculation device are first explained with reference to Figure 5. Figure 5 also shows the fuel cell system 200 according to the invention and the recirculation device 400 according to the invention.

[0059] The fuel cell system 200 in Figure 5 comprises a fuel cell stack 201 with an anode section 210 and a cathode section 220. Several fuel cells are arranged in a stack within the fuel cell stack 201. A cathode supply gas (CSG), such as air or oxygen, is supplied to a cathode supply section 221. Cathode exhaust gas (CAG) generated in the cathode section 220, for example, moist air or water vapor, is discharged via a cathode discharge section 222. The anode section 210 also comprises an anode supply section 211 for supplying an anode supply gas (AZG), which can be composed of a fuel (BS), such as hydrogen or methane. The anode section 210 further comprises an anode discharge section 212 for discharging anode exhaust gas AAG, which may, for example, contain, in addition to unused hydrogen, water vapor, nitrogen, carbon monoxide and / or other components of air.The fuel BS can be provided, for example, from an anode feed gas reservoir 215.

[0060] Furthermore, an anode exhaust gas recirculation section 213 is provided on the anode section 210 and in particular on the anode discharge section 212, via which at least a portion of the anode exhaust gas AAG is returned to the anode supply section 211. The recirculated portion of the anode exhaust gas AAG is identified in Figure 5 as recirculated anode exhaust gas rAAG.

[0061] A recirculation device 400 is provided in the return path for the recirculated anode exhaust gas rAAG, by means of which the branched portion of the anode exhaust gas AAG is conveyed to the connecting line with the fuel line BS under a supply pressure. The recirculation device 400 can be operated at an operating speed.

[0062] For this purpose, the recirculation device 400 can have a recirculation section 402, which can be configured, for example, as an anode recirculation fan, a compressor, or a pump. The supply pressure can be determined, for example, by a pressure gauge 202 as the pressure difference Δp between an inlet-side and outlet-side pressure of the fuel cell stack 201.

[0063] Furthermore, the recirculation device 400 can have a control device 401, which is configured, for example, to carry out the method 100 according to the invention explained below.

[0064] Figure 1 shows the basic structure of a method 100 according to the invention, by means of which vibration excitations of the fuel cell system 200 by the recirculation device 400 are avoided.

[0065] The method 100 includes a step 101 in which a target speed SG for the operating speed of the recirculation device 400 is determined. For example, an operating point of the fuel cell system 200 can be set using the aforementioned pressure difference Ap, and the target speed SG can be determined based thereon.

[0066] In a further step 102, an actual operating speed IG of the recirculation device 400 is detected. For example, a value currently occurring in the recirculation device 400 can be read from a speed sensor provided in the recirculation section 402 (see Figure 5). In principle, this value can also be a model value or simulation value.

[0067] In a step 103, the determined target speed SG is compared with at least one speed corridor GK for the operating speed, in which vibration excitation of the fuel cell system 200 by the recirculation device 400 is to be expected. Figure 1 shows that the fuel cell system 200 can, for example, also have n multiple speed corridors GK1 to GKn, with respect to which the comparison can be performed. The result of step 103 can be output as the comparison result VE.

[0068] In a further step 104, a corrected target speed kSG is determined as a function of the actual operating speed IG and the determined target speed SG. The corrected target speed is further determined such that it is an operating speed outside the speed corridors GK1 to GKn. The comparison result VE can also be used to determine the corrected target speed kSG.

[0069] Finally, in a step 105, the corrected target speed kSG is output as the target speed SG.

[0070] Figure 2 shows a detailed sequence of an exemplary implementation of steps 103 and 104 of the inventive method 100 from Figure 1.

[0071] For example, in step 103, a comparison of the determined target speed SG with the speed corridors GK1 to GKn is performed. For this purpose, an upper limit OG and a lower limit UG can be compared with the determined target speed SG. The result, whether the determined target speed SG lies within one of the speed corridors GK1 to GKn or not, can then be output as the comparison result VE.

[0072] Figure 2 shows that, for example, in the case where the determined target speed SG is not located in any of the speed corridors GK1 to GKn, the determined target speed SG can be determined as the corrected target speed kSG.

[0073] However, if the determined target speed SG lies within one of the speed corridors GK1 to GKn, the determination of the corrected target speed kSG is carried out differently. In Figure 2, the determined target speed SG lies within the size-relevant speed corridor GKx.

[0074] Subsequently, in Figure 2 it is determined whether the determined target speed SG is less than the actual operating speed IG.

[0075] If the determined target speed SG is at least equal to the actual operating speed IG, the corrected target speed kSG is determined as the upper limit OG of the size-relevant speed corridor GKx or as the maximum speed MaxG plus an upper offset value OVW. The upper offset value OVW can be freely specified by the user.

[0076] For the alternative case that the determined target speed SG is lower than the actual operating speed IG, the corrected target speed kSG can, for example, be determined as the lower limit UG of the size-relevant speed corridor GKx or as the minimum speed MinG less a sub-offset value UVW.

[0077] To allow speed reductions only for specific situations, two additional conditions must be met in advance in the method 100 shown in Figure 2. These can be performed either in parallel or in series.

[0078] A first condition can be specified by requiring that a deviation DSG between two temporally consecutive specified target speeds SG_t1, SG_t2 exceed a threshold value SW for a rate of change of the specified target speed SG. If the condition is not met, the routine can be exited from step 103.

[0079] A further condition can be specified by specifying that the corrected target speed kSG is only applied after a specified time delay value ZVW has elapsed. For this purpose, a start time of the deceleration TO can first be compared with a current measurement time Tx, thus determining an elapsed time DT. The time delay value ZVW can, for example, be an inversely correlated number of changes in the determined target speed SG within a time interval [T1, T2].

[0080] In addition, after the time delay value ZVW has elapsed, it can still be checked whether a reduction in the operating speed should still be carried out at the current time based on the current value of the target speed SG.

[0081] Figure 3 illustrates by way of example how the target speed SG can be determined in step 101 of Figure 2. Thus, in a preferred step 111, a target operating point SBP of the fuel cell stack 201 can be specified. In a further step 112, a target pressure difference SDD resulting from the target operating point SBP can be determined. Based on this, the target speed SG can then be determined in a further step 113.

[0082] Figure 6 shows example curves of the target speed SG, the corrected target speed kSG, and the actual operating speed IG resulting from the corrected target speed kSG. Furthermore, two speed corridors GK1 and GK2 are shown, in each of which resonance frequencies occur between the respective upper limits OG1, OG2 and lower limits UG1, UG2. Figure 6 shows that at time t101, the associated target speed SG101 lies within the speed corridor GK1, i.e., the size-relevant speed corridor GKx is below the speed corridors GK1 and GK2. The corrected target speed kSG101 is maintained at the value of the upper limit OG1 before the corrected target speed kSG is subsequently reduced below the lower limit UG1 minus a sub-offset value UVW1. A corresponding curve can be observed for the time t102 for the speed corridor GK2.At time t103, a speed increase is carried out.

[0083] Figure 4 further shows, by way of example, the control device 300 according to the invention, which has a target speed determination module 301, an operating speed detection module 302, a comparison module 303, a determination module 304, and an output module 305. The control device 300 is configured to carry out the method 100.

[0084] Figure 5 further illustrates that the fuel cell system 200 may include the control device 300 according to the invention. The recirculation device 400 may include the control device 300 or may be equipped with the control device 401 as a separate unit from the control device 300. The control device 300 and the control device 401 may be connected to each other via signaling.

[0085] The above explanation of the embodiments describes the present invention exclusively by way of examples. List of reference symbols

[0086] IG actual operating speed

[0087] SG Target speed kSG Corrected target speed

[0088] GK speed corridor

[0089] GK1, GK2, GKn Variety of speed corridors

[0090] GKx size-relevant speed corridor

[0091] UG, UG1 , UG2 Lower limit of a speed corridor

[0092] OG, OG1, OG2 Upper limit of a speed corridor

[0093] VE comparison result

[0094] MaxG maximum speed

[0095] OVW upper offset value

[0096] MinG minimum speed

[0097] UVW, UVW1 sub-offset value

[0098] SW threshold

[0099] DSG Deviation of temporally consecutive specified target

[0100] Speeds

[0101] ZVW time delay value

[0102] T1 , T2 start and end time of a defined time interval

[0103] TO start time

[0104] Tx current measurement time

[0105] DT elapsed time

[0106] SBP target operating point

[0107] SDD target pressure difference

[0108] Ap pressure difference t101, t102, t103 observation times

[0109] SG_t1, SG_t2 temporally successive determined target speeds

[0110] SG101 , SG102, SG103 Target speeds for the respective

[0111] Observation times kSG101, kSG102, kSG103Target speeds at the respective observation times

[0112] 100 procedures

[0113] 101 to 105 Process steps 111 Specifying a target operating point of the fuel cell stack

[0114] 112 Determining the target pressure difference

[0115] 113 Determining the target speed

[0116] 200 fuel cell system

[0117] 201 fuel cell stacks

[0118] 202 pressure gauge

[0119] 210 Anode section

[0120] 211 Anode feed section

[0121] 212 Anode discharge section

[0122] 213 Anode exhaust gas recirculation section

[0123] 215 Anode feed gas reservoir

[0124] 220 cathode section

[0125] 221 Cathode feed section

[0126] 222 Cathode discharge section

[0127] KAG cathode exhaust gas

[0128] KZG cathode feed gas

[0129] AAG anode exhaust gas

[0130] AZG anode feed gas rAAG recirculated anode exhaust gas

[0131] BS Fuel

[0132] 300 control device

[0133] 301 Target speed determination module

[0134] 302 Operating speed detection module

[0135] 303 Comparison module

[0136] 304 Determination module

[0137] 305 Output module

[0138] 400 Recirculation device

[0139] 401 Control device

[0140] 402 Recirculation section

Claims

Patent claims 1. Method (100) for avoiding vibration excitations by a recirculation device (400) of a fuel cell system (200), comprising the following steps: - determining a target speed (SG) for an operating speed of the recirculation device (400) with a target speed determination module (301), - detecting an actual operating speed (IG) of the recirculation device (400), characterized by the steps - comparing the determined target speed (SG) with at least one speed corridor (GK) for the operating speed in which a vibration excitation of the fuel cell system (200) by the recirculation device (400) is to be expected, - determining a corrected target speed (kSG) as an operating speed outside the at least one speed corridor (GK) as a function of the actual operating speed (IG) and the determined target speed (SG), and - Outputting the corrected target speed (kSG) as the target speed (SG) and operating the recirculation device (400) with the corrected target speed (kSG) as the target speed (SG).

2. Method (100) according to claim 1, characterized by Determining the determined target speed (SG) as the corrected target speed (kSG) if the at least one speed corridor (GK) does not have the determined target speed (SG).

3. Method (100) according to claim 1 or claim 2, characterized in that determining the corrected target speed (kSG) in the event that the determined target speed (SG) is exhibited by a size-relevant speed corridor (GKx) of the at least one speed corridor (GK), comprises the steps: - comparing the actual operating speed (IG) with the determined target speed (SG); and - Determining the corrected target speed (kSG) depending on the comparison.

4. Method (100) according to claim 3, characterized in that in the event that the actual operating speed (IG) is less than the determined target speed (SG), the corrected target speed (kSG) is determined as a speed greater than the maximum speed (MaxG) of the size-relevant speed corridor (GKx), or as a speed with the maximum speed (MaxG) of the size-relevant speed corridor (GKx) in addition to a definable upper offset value (OVW).

5. Method (100) according to claim 3 or claim 4, characterized in that in the event that the actual operating speed (IG) is greater than the determined target speed (SG), the corrected target speed (kSG) is determined as a speed less than the minimum speed (MinG) of the size-relevant speed corridor (GK), or as a speed with the minimum speed (MinG) of the size-relevant speed corridor (GK) less a definable under-offset value (UVW).

6. Method (100) according to one of the preceding claims, characterized in that the determination of the corrected target speed (kSG) is further carried out as a function of at least one freely definable parameter, wherein the parameter is preferably measurable and / or derivable from measurable variables.

7. The method (100) according to claim 6, characterized in that the parameter has a threshold value (SW) for a rate of change of the determined target speed (SG), wherein the threshold value (SW) preferably corresponds to a short-term variation from a temporal profile of the determined target speed (SG), wherein the short-term variation is determined as an averaged deviation from successive determined target speeds (SG) within a time interval, and the corrected target speed (kSG) is determined when a deviation (DSG) of two successive determined target speeds (SG_t1, SG_t2) exceeds the threshold value (SW).

8. Method (100) according to claim 6 or claim 7, characterized in that the parameter has a time delay value (ZVW), wherein the time delay value (ZVW) preferably corresponds inversely to a frequency with which the determined target speed (SG) changes over a time interval (T1, T2), and the determination of the corrected target speed (kSG) only takes place after the time delay value (ZVW) has elapsed.

9. Method (100) according to claim 8, characterized in that the determination of the corrected target speed (kSG) is carried out as a function of the time delay value (ZVW) if the determined target speed (SG) is lower than the actual operating speed (IG) and preferably further is smaller than the minimum speed (MinG) of the at least one speed corridor (GK) which is to be passed last when reducing the operating speed to the determined target speed (SG).

10. Method (100) according to one of the preceding claims, characterized in that in the method (100) the target speed (SG) is determined by the following steps: - specifying a target operating point (SBP) for the operation of a fuel cell stack (201) provided in the fuel cell system (200), and - determining a target pressure difference (SDD) occurring in the fuel cell stack (201) based on the target operating point (SBP), wherein the target pressure difference (SDD) is preferably a pressure difference (Ap) between an inlet-side and outlet-side pressure of the fuel cell stack (201), and / or - Determining the target speed (SG) based on the target operating point (SBP) and / or based on the target pressure difference (SDD).

11. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method (100) according to any one of the preceding claims 1 to 10.

12. Control device (300) for preventing vibration excitation by a recirculation device (400) of a fuel cell system (200), comprising - a target speed determination module (301) for determining a target speed (SG) for an operating speed of the recirculation device (400), - an operating speed detection module (302) for detecting an actual operating speed (IG) of the recirculation device (400), characterized by - a comparison module (303) for comparing the determined target speed (SG) with at least one speed corridor (GK) for the operating speed, in which a vibration excitation of the fuel cell system (200) by the recirculation device (400) is to be expected, - a determination module (304) for determining a corrected target speed (kSG) as an operating speed outside the at least one speed corridor (GK) as a function of the actual operating speed (IG) and the determined target speed (SG), and - an output module (305) for outputting the corrected target speed (kSG) as the target speed (SG), wherein the recirculation device (400) is operated with the corrected target speed (kSG) as the target speed (SG).

13. Recirculation device (400), characterized by further comprising a control device (401) for carrying out the method (100) according to one of claims 1 to 10, or by a control device (300) according to claim 12.

14. Recirculation device (400) according to claim 13, characterized in that the recirculation device (400) has a recirculation section (402) which has an anode recirculation fan, a mechanical pump, preferably a scroll pump, a claw pump, a Roots pump, a centrifugal pump or a regenerative pump, or a mechanical compressor.

5. Fuel cell system (200), preferably PEM fuel cell system, comprising: - a fuel cell stack (201) with an anode section (210) and with a cathode section (220), wherein a plurality of fuel cells are arranged in a stack in the fuel cell stack (201), wherein the cathode section (220) has a cathode feed section (221) for feeding cathode feed gas (KZG) and a cathode discharge section (222) for discharging cathode exhaust gas (KAG), wherein the anode section (210) has an anode feed section (211) for feeding anode feed gas (AZG) and an anode discharge section (212) for discharging anode exhaust gas (AAG), and wherein the anode section (210) further has an anode exhaust gas recirculation section (213) with a recirculation device (400) in order to recirculate at least a portion of the anode exhaust gas (AAG) to the anode feed section (211), characterized in that - the recirculation device (400) is designed according to claim 13 or claim 14, and / or - the fuel cell system (200) comprises a control device (300) according to claim 12, which is connected to a control device (401) of the recirculation device (400) in order to provide the corrected target speed (kSG) of the control device (401) as an input variable.

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