Fuel cell system

Abstract

Fuel cell system comprising a fuel cell unit (100) for generating electrical energy, an electrical storage device (107, 109) for storing or supplying electrical energy, and an electrical consumer (103, 110, 101) for consuming electrical energy, in particular an electric drive motor (103) designed as a consumer for driving a vehicle, wherein a control unit (113) is provided for determining the functionality of at least the fuel cell unit (100) during a diagnostic phase, characterized in that the control unit (113) is provided for determining the electrical power (PBZ) generated by the fuel cell unit (100) at least during the diagnostic phase, which is decoupled from any electrical power consumed during the diagnostic phase.

Description

[0001] The invention relates to a fuel cell system according to the preamble of claim 1. State of the art:

[0002] When using fuel cell systems, e.g., as APUs (Auxiliary Power Units) and / or in the propulsion systems of vehicles and stationary systems, the electrical energy management system should be aware of the status of the fuel cell or fuel cell stack in terms of dynamics, performance, degradation, and / or minimum voltage. Especially in reformer systems, additional information on the degradation and dynamics of the gas generation unit is required. This is the only way to ensure the availability and reliability of the system.

[0003] Previously known systems only inadequately meet these requirements. For example, US Pat. No. 5,945,229 A describes a fuel cell system in which the behavior of the stack's current-voltage characteristic is determined using additional fuel cells at the stack inlet and stack outlet. This determines the CO concentration in the hydrogen-rich anode gas. In the event of a deviation from a reference behavior, i.e., a target-actual comparison is performed, protective measures are automatically triggered to prevent CO poisoning of the stack.

[0004] Furthermore, from document US 6,322,917 B1, a diagnostic method and a method for controlling the preferential oxidation of CO in a reformed fuel gas stream are known, wherein the periodic modulation of the amount of air supplied to a preferential oxidation reactor at a specific operating characteristic of the fuel cell is used to determine the amount of air necessary to reduce the CO content to an acceptable level. Object and advantages of the invention:

[0005] The object of the invention is to propose a fuel cell system which has improved availability and reliability of the system compared to the prior art.

[0006] This object is achieved, starting from a fuel cell system of the type mentioned in the introduction, by the characterizing features of claim 1. Advantageous embodiments and further developments of the invention are possible by the measures mentioned in the subclaims.

[0007] Accordingly, a fuel cell system according to the invention is characterized in that a control unit is provided for determining the electrical power generated by the fuel cell unit, at least during the diagnostic phase. This measure allows for the generation of an advantageous diagnostic profile of the electrical power of the fuel cell unit. For example, a wide variety of current densities of the fuel cell unit can be generated and used to diagnose the functionality of the fuel cell unit.

[0008] The electrical power generated by the fuel cell unit is decoupled from the electrical power consumed at that time or during the diagnostic phase. This is particularly advantageous because it allows the operation of the fuel cell unit and the power it generates to be largely independent of current consumption. This allows the electrical power generated by the fuel cell unit to depend essentially on the diagnosis and its requirements. This enables optimization of the diagnosis and leads to a significant improvement in diagnostics compared to the state of the art.

[0009] Through the advantageous integration of the electrical storage device, which is designed to both store and release electrical energy, the independence of the fuel cell unit's electrical energy generation from current or instantaneous energy consumption is advantageously realized. For example, if required, the electrical storage device can, on the one hand, release electrical energy and, on the other hand, store excess electrical energy generated by the fuel cell unit. This means that the electrical storage device advantageously compensates for any difference that may exist between the electrical power generated by the fuel cell unit and the electrical power consumed by the electrical consumer(s). This advantageously ensures the operational reliability and usability of the entire fuel cell system, especially during the diagnostic phase.

[0010] In general, according to the invention, a reproducible diagnosis or measurement of the fuel cell unit, in particular of the polarization characteristic or the like, can be carried out in an advantageous manner. This significantly increases the accuracy of the diagnosis compared to the prior art. The invention opens up completely new possibilities for diagnosing the fuel cell unit or the entire fuel cell system. For example, in vehicle applications, the lower load range of the fuel cell unit is generally passed through relatively quickly, so that in a fuel cell system according to the prior art, findings that can only be obtained from the lower load range cannot be obtained, or can hardly be obtained. According to the invention, for example, the fuel cell unit can deliberately be operated in the lower load range and its functionality or condition can be diagnosed accordingly.

[0011] It is conceivable to operate the fuel cell unit in such a way that it generates a largely constant, varying electrical output during the diagnostic phase. For example, the electrical output of the fuel cell unit could exhibit a sinusoidal or similar curve during the diagnostic phase. It is also conceivable that this variant of the invention could be used to determine, for example, the inertia of the fuel cell unit or individual components and compare it with a target state. This could provide information regarding, for example, the functionality or condition of the fuel cell unit.

[0012] Preferably, the electrical power generated by the fuel cell unit is essentially constant, at least during a period of the diagnostic phase. An advantageously constant, generated electrical power or a correspondingly steady state of the fuel cell unit is of particular importance, or in some cases, an absolute prerequisite, for determining the functionality of the fuel cell unit or for obtaining specific information about the condition or functionality of the fuel cell unit. This significantly expands the diagnosability of the fuel cell unit compared to the prior art, and further improves the accuracy of the diagnosis.

[0013] For example, during the diagnostic phase, the electrical power generated by the fuel cell unit is in an upper range and / or a lower range of the achievable or maximum power. This allows insights into the upper or lower power range of the fuel cell unit to be advantageously obtained and used to diagnose the functionality or condition of the fuel cell unit. Operating the fuel cell unit in both the upper and lower range of the achievable or maximum power ensures a particularly broad examination or diagnostic range of the fuel cell unit. This leads to a further improvement in the diagnosability of the fuel cell unit. This allows particularly advantageous insights into the functionality or condition of the fuel cell unit to be obtained with the help of the control unit or the diagnostic unit.

[0014] In a particular development of the invention, the upper range is the top two-fifths and / or the lower range is the bottom two-fifths of the generable or maximum power of the fuel cell unit. Advantageously, the upper range is the top third and / or the lower range is the bottom third of the generable or maximum power of the fuel cell unit. It has been demonstrated that determining the functionality or condition of the fuel cell unit in these areas in particular enables special insights. Furthermore, these measures allow a particularly broad power or load range of the fuel cell unit to be examined.

[0015] Preferably, a first time period with substantially constant, generated electrical power is provided in the upper range, and / or a second time period with substantially constant, producible, or maximum power of the fuel cell unit is provided in the lower range. This enables a steady state of the fuel cell unit in the upper and / or lower power range, thereby further improving the diagnosability of the fuel cell unit or fuel cell system.

[0016] For example, the electrical energy or power consumed during the diagnostic phase can be modified by switching off and / or on less relevant consumers, and / or by slightly modifying their consumption in a beneficial manner. For example, particularly in vehicle applications, the power of electric window drives, a heating and / or air conditioning system, etc., can be switched on or off, and / or their power can be reduced or slightly increased, without, for example, significantly impairing comfort in a vehicle.

[0017] The control unit is preferably designed to change at least the efficiency of the electrical consumer. With the aid of this measure, for example, more and / or less electrical power, in particular electrical power generated by the fuel cell unit, is consumed when the functionality of the consumer remains almost the same, e.g. with the same drive power of the drive motor. With the aid of this measure, an increase in the electrical power generated by the fuel cell unit is possible, especially when the electrical storage device is almost full. For example, with a wide variety of electric motor types, in particular with permanent magnet synchronous machines or the like, the operating point of the electric motor or the like can be changed by field weakening and / or by changing the duty cycle of the power electronics, in particular when using DC / DC and / or DC / AC converters or the like.The efficiency of an electric drive can be changed or reduced in such a way that more or less power is drawn from the consumer in a torque-neutral manner. This effectively changes or preferably reduces the efficiency of the consumer in a beneficial way, so that, for example, more electrical power is consumed for the same drive power. This can also be applied accordingly to other electrical machines, such as asynchronous machines, SR motors, etc. For example, by changing the control angle and / or duty cycle, the input power can be increased, while at the same time the output torque of the electric motor remains essentially constant.

[0018] In a preferred variant of the invention, the control unit is designed to change the efficiency of the fuel cell unit. For example, the efficiency of the fuel cell unit is achieved by varying an operating pressure, the lambda value, or the like. This also allows the functionality, in particular the current-voltage behavior of the fuel cell unit, to be diagnosed using corresponding operating states or these parameter specifications. This, in turn, realizes an advantageous expansion of the diagnosability of the fuel cell unit according to the invention compared to the prior art.

[0019] It is generally advantageous to perform the diagnostic phase during an operating phase, especially in vehicle applications while the vehicle is moving. It is particularly advantageous not to perform the diagnostic phase before and / or after the fuel cell system has been shut down or during a break in the driving process. This advantageously prevents, for example, individual components of the fuel cell system or the vehicle from emitting noises that could confuse or disturb the user. Furthermore, it is sometimes extremely difficult to generate sufficient electrical energy for the diagnostic phase during breaks in driving or when the vehicle is at a standstill.

[0020] Advantageously, at least one detection unit is provided for detecting at least one actual value of a first parameter of the fuel cell unit at a first time T1. This allows for particularly simple diagnosis of the fuel cell unit.

[0021] Furthermore, according to the invention, the diagnosis can be initiated, or the diagnosis phase can be initiated, using the control unit or the like, for example, if the detected actual value deviates from a predetermined target value of the corresponding parameter. This is particularly advantageous in the event of malfunctions in the fuel cell system. For example, if a reduction in the efficiency of the fuel cell unit is detected, the diagnosis can be initiated and carried out accordingly.

[0022] In principle, the control behavior of the fuel cell system or the vehicle can be optimized through the diagnosis or the knowledge gained from the diagnosis.

[0023] In general, the diagnosis or the insights gained from the diagnosis regarding the functionality of the fuel cell system can be used to initiate and implement advantageous control of one and / or more components of the fuel cell system. This is particularly advantageous in the event of an acute deterioration or malfunction of the fuel cell system.

[0024] Preferably, at least one control unit is provided for checking at least one target value of a second parameter, which is dependent on the first actual value of the first parameter, at a second time T2 later by a time difference ΔT. Accordingly, T2 = T1 + ΔT, where, in the sense of the invention, ΔT is greater than the pure computing time of the control unit. This means that ΔT for current or future processors, etc., is not in the range of fractions of a second, but that ΔT is equal to the computing time of the control unit, in particular the processor, plus a definable or measurable delay time. According to the invention, ΔT is several seconds, minutes, hours, days, and / or even months.

[0025] According to this variant of the invention, a statement or comparison with a reference behavior at a future point in time T2 is possible. In principle, this prediction regarding the fuel cell system or individual components thereof can be determined independently of any impairments or damage already present at point in time T1 or the time the actual value of the first parameter is recorded. This means that at point in time T1, there may be no or no impairment of the system, but according to the invention, in the future, for example, under unchanged conditions and / or possible or expected changes to one or more parameters of the fuel cell system, impairment of or damage to the system or individual components of the system could be possible or are to be expected.This advantageously saves time for any countermeasures and / or protective measures or the like that may be required to prevent or reduce corresponding impairments or damage. This leads to the advantageous avoidance of expected impairments such as inadequate supply, poisoning, or degradation of the fuel cell unit and / or other components of the system, or at least to a significant extent, of occurring in the first place, according to the invention.

[0026] In contrast to the present invention, in the prior art, an already occurring impairment or malfunction of the system or individual components, in particular a degeneration of the fuel cell unit, is detected as early as possible or at its inception in order to immediately initiate appropriate countermeasures. This means that the impairment has already occurred. According to the invention, countermeasures or protective measures are advantageously initiated with the help of the control unit before the impairment or damage to the system or individual components occurs, so that these damages are prevented from occurring in the first place. This significantly increases the reliability and availability of the system.

[0027] Preferably, a temporal profile, in particular a temporal change, of the actual value of the first parameter is recorded. This allows, among other things, a trend to be determined or a temporal extrapolation of the first parameter to be calculated, preferably up to time T2 or during the time difference ΔT. According to the invention, this allows a comparison of the actual value of the first parameter at time T2 with the target value of the second parameter at time T2 to be performed.

[0028] The second parameter is preferably an aggregated or highly aggregated parameter of the fuel cell system or individual components thereof, which is formed using at least one relatively easy-to-determine first parameter. In particular, an aggregated parameter of the fuel cell unit is provided as the second parameter.

[0029] Advantageously, the target value of the second parameter is at least a lifetime and / or a power and / or a minimum electrical voltage of the fuel cell unit.

[0030] In practice, it has been shown that these parameters of the fuel cell unit are particularly relevant for describing the condition of the fuel cell unit or the fuel cell system.

[0031] In a particular variant of the invention, the control unit is designed to change an actual value of a third parameter, in particular during the time difference ΔT, depending on the target value of the second parameter, in particular at time T2. In principle, the control unit is designed to compare a value of the second parameter with the target value (reference value of the second parameter at any time T x), in particular at time T2. Advantageously, in the event that the value of the second parameter at time T2 does not reach the predetermined target value of the second parameter taking into account an advantageous tolerance, i.e. exceeds or falls below it, a third parameter or a counter / protective measure or the like is changed or initiated with the aid of the control unit according to the invention. The change to the third parameter is advantageously designed or carried out in such a way that the target value of the second parameter can be reached, in particular at time T2. This means, for example, that according to the invention, a potentially foreseeable impairment (a possible or expected exceeding or falling below the target value of the second parameter at time T2) can be avoided or prevented due to a previously initiated advantageous measure, in particular during the time difference ΔT.can be prevented before it even occurs.

[0032] In an advantageous embodiment of the invention, the third parameter is at least one parameter of a component of the fuel cell system and / or a vehicle, e.g. a passenger / commercial vehicle, ship, etc.

[0033] For example, the third parameter is an on / off parameter or a state parameter of an electrical consumer of the system. For example, depending on the target / actual comparison according to the invention, an air conditioning system of a fuel cell vehicle can be switched off or throttled during the time difference ΔT, in particular to ensure that the fuel cell unit does not fall below a minimum electrical voltage and / or electrical power at a later time T2.

[0034] On the other hand, for example, the mass flow of a hydrogen-containing fuel generated by a reformer unit can be increased. Advantageously, a case can be realized in which, in particular, the generated mass flow is greater than the mass flow required at that time, and the excess mass flow can be temporarily stored in a suitable hydrogen storage device or the like. This makes hydrogen-containing fuel flow available from the intermediate storage device and the reformer of the fuel cell system, for example, at a later time T2, so that an undersupply of hydrogen-containing fuel should not occur.

[0035] The same can also be achieved for the oxidizing agent, e.g. air, whereby, for example, a precautionary pressure increase can be carried out and / or a compressed air reservoir can be filled accordingly on the basis of the test according to the invention in order to avoid, for example, an insufficient supply of the fuel cell unit with oxidizing agent at the later time T2.

[0036] In a particular development of the invention, the fuel cell system has an electrical energy storage device, in particular a so-called high-performance battery and / or a so-called supercapacitor or the like. Advantageously, the third parameter is a parameter of the electrical energy storage device. This makes it possible, for example, to charge and / or discharge the energy storage device depending on the test according to the invention. This can, in particular, prevent the expected or sufficient amount of electrical energy from being available at a time T2. In this case, electrical energy is made available to the system by the fuel cell unit and / or the electrical energy storage device at time T2.

[0037] Advantageously, the first parameter is at least one model parameter of a mathematical model of the fuel cell unit or fuel cell system. It is precisely with the help of such a model description of the fuel cell unit and / or fuel cell system that a simplification of the operation of the fuel cell system and a simplification of the control or regulation of the system becomes possible.

[0038] Furthermore, the second parameter is at least one model parameter of a mathematical model of the fuel cell unit or fuel cell system. For example, the service life, power, and / or minimum electrical voltage of the fuel cell unit are determined using the mathematical model of the fuel cell unit as a function of the first parameter.

[0039] In a particular embodiment of this variant of the invention, both the second parameter and the first parameter are model parameters. This significantly simplifies the sometimes very complex relationships in a fuel cell system, thus significantly simplifying the regulation or control of the fuel cell unit and / or the fuel cell system.

[0040] Preferably, the first parameter configured as a model parameter is at least one of a Nernst voltage and / or an activation energy and / or an internal resistance and / or a mass transfer parameter, in particular a parameter relating to the gas diffusion process, of the fuel cell unit. In practice, it has been found that these model parameters enable a sufficiently accurate description of the behavior of the fuel cell unit or fuel cell stack.

[0041] Preferably, a device is provided for forming the model parameter(s) as a function of at least one actual value of a base parameter. For example, a mass flow and / or a temperature and / or an electric current and / or a pressure of the fuel cell unit or fuel cell system and / or a vehicle is embodied as a base parameter. Accordingly, advantageous base parameters are advantageously particularly easy to acquire or are already acquired in current fuel cell systems, so that no or only very little additional effort is required to acquire corresponding parameters according to the invention.

[0042] Preferably, the base parameter is at least one parameter of the fuel cell unit and / or a supply unit for supplying the fuel cell unit with a fuel. The supply unit comprises, for example, a reformer or the like.

[0043] In a specific variant of the invention, the first parameter is formed from one or more base parameters using the mathematical model of the fuel cell unit, and the second parameter is formed from this first model parameter using the and / or another mathematical model of the fuel cell unit. This means, for example, that the Nernst voltage, activation energy, internal resistance, and / or the gas diffusion process are described from at least one mass flow, temperature, electric current, and / or pressure using the mathematical model, and from this, the service life, performance, and / or minimum electrical voltage of the fuel cell unit are determined.

[0044] Advantageously, the first parameter is a base parameter. This measure simplifies the generation of the second parameter according to the invention.

[0045] In principle, a single or multiple second parameters can be formed from a single first parameter or from a set of multiple first parameters and / or base parameters.

[0046] In an advantageous variant of the invention, the control unit is designed to check the target value of the second parameter as a function of a fourth parameter. With the help of the fourth parameter, in particular, a more precise description of the expected or potential second parameter can be achieved at a later time T2 or at a future time after the time difference ΔT. This advantageously allows the control unit to perform a better comparison of the expected or potential value with the target value of the second parameter.

[0047] In general, a change in the fourth parameter that is already determined at time T1 can be provided. With this variant of the invention, a particularly precise description or calculation of the expected or potential value of the second parameter at the future time T2 is achievable.

[0048] Alternatively, or in combination with the aforementioned variant, at least one potential change in the fourth parameter is provided during the time difference ΔT. For example, the potential change in the fourth parameter represents a suspected or probable change in the fourth parameter. Past experience can advantageously be taken into account here. In particular, recorded temporal changes in one of the parameters of the fuel cell system must be taken into account. Based on these temporal changes, the potential change in the fourth parameter can be determined or calculated using the control unit according to the invention, for example by means of extrapolation.

[0049] Advantageously, the fourth parameter is configured as a base parameter and / or as a first and / or second and / or third parameter. Preferably, the fourth parameter is configured as a load or a so-called load profile, i.e., the dependence of the electrical power on time. Such load profiles, in particular, have a particular influence on the dynamics of the system.

[0050] In the spirit of the invention, the chosen numbering or designation of the parameters does not imply a mandatory sequence, but merely serves to distinguish between the parameters that may be used. For example, the third parameter may not be required, but the fourth parameter may be considered to form the second.

[0051] In general, the control unit according to the invention can have an advantageous electronic storage unit which comprises or stores the aforementioned dependencies and / or model relationships and / or target values ​​of the different parameters.

[0052] In an advantageous embodiment of the invention, the control unit is designed to adjust or adapt, primarily, the target parameters. This measure can be used to take into account, for example, aging or degeneration of the fuel cell unit and / or the supply unit, etc. Preferably, the degeneration or aging is taken into account for the mathematical model and / or determined based on the model.

[0053] In general, the invention allows for prediction or prevention of critical system states. For example, it is possible to predict how the voltage will change and whether the voltage will drop below a critical value, depending, for example, on the operation or activation of an air conditioning system, a full-throttle overtaking maneuver in a fuel cell vehicle, etc.

[0054] Advantageously, a plurality of second parameters is provided to describe a plurality of potential operating states of individual components and / or the overall system. Here, all conceivable or imaginable operating states are to be taken into account, so that the availability and reliability of the system according to the invention are maximized. Preferably, an optimization of the system is provided with regard to the dynamics, efficiency, and / or durability of individual components and / or the overall system. Example:

[0055] An embodiment of the invention is shown in the drawing and is explained in more detail below with reference to the figures.

[0056] In detail: Fig. 1 a block diagram of a section of a fuel cell system according to the invention, Fig. 2 a schematic characteristic curve of a current-voltage characteristic for a model of a fuel cell unit, Fig. 3 a schematic characteristic curve of a dynamic behavior of a gas supply of a fuel cell system according to the invention, Fig. 4 schematic characteristics of a gas generation system with degradation phenomena, Fig. 5 schematic characteristic curves of various components of the fuel cell system according to the invention and Fig. 6 a schematic block diagram of an on-board network structure in a fuel cell drive according to the invention.

[0057] In Fig. 1 schematically shows a part of a fuel cell system according to the invention as a block diagram. A fuel cell unit 1 or a fuel cell stack 1 has one or more input parameters X1 and one or more output parameters X2. The input parameters X1 are, for example, parameters of mass flows, temperatures, electrical currents and / or pressures of the fuel cell system. An output parameter X2 of the fuel cell 1 is, for example, a voltage. In the sense of the invention, the input / output parameters X1, X2 can be designed as so-called basic parameters. Furthermore, the output parameter X2 can be designed as a so-called second parameter according to the invention. In the latter case, the actual voltage X 2Istat a current time T1 and / or a potential voltage X to be expected at a time T2 later by a time difference ΔT 2pot with a given setpoint voltage X 2Soll or with the minimum electrical voltage X 2min the fuel cell unit 1 to one.

[0058] Fig. 1 further shows that the parameter(s) X1 are made available to a model block 2. The model block 2 comprises a particularly stored or stored model 21, a feedback unit 22, and a parameter adaptation unit 23. Primarily with the aid of the units 22 and 23, an adaptation to, for example, aging or degeneration of individual or multiple components of the fuel cell system, such as the fuel cell unit 1, can be carried out, so that the model 21 can be adapted accordingly. This makes it possible to realize a dynamically changing model 21. If necessary, a quasi-self-learning model 21 can be realized using already known adaptation routines.

[0059] In Fig. Figure 2 shows schematically the model current-voltage characteristic as well as the corresponding mathematical description of an example of model 21. Here, the parameters P iwith i = 1 to 6, depending on the mass flow, pressure, and temperature. The first term of the formula describes the Nernst voltage, the second term the activation energy, the third term the internal resistance, and the fourth term the gas diffusion process of fuel cell unit 1.

[0060] In Fig. 1 further illustrates how, with the help of one or more model parameters X M of the model block 2 and one or more load parameters X3 of an expected or potential load 3 predictors X P a predictor block 4.

[0061] Using the predictors X P If necessary, measures are initiated to achieve, for example, a target value of the parameter X2.

[0062] In Fig. Figure 3 schematically illustrates the dynamics of the gas supply, in particular of an air path and / or a reformer or the like. Mass flows i are plotted as a function of time t for different cases. Fig. 3 additionally includes the mathematical description of the corresponding functional dependencies, where the variable a is defined as a function of pressure, temperature and a mass flow m to be achieved. End is.

[0063] For example, at time T1 a mass flow m 01 At a time T2 after a time period ΔT, a potential increase in the electrical power X3 of the fuel cell unit 1 should be available (see in particular Fig. 1, Block 3). It is assumed, for example, that the load change occurs at time t0 within the time period ΔT. Furthermore, it is assumed that to provide the potential electrical power X 3Endat time T2 a mass flow m End is necessary. According to Fig. 3 it becomes clear that in the case where at time t0 the mass flow m 01 would be available, this to achieve m End would require a time period Δt3. Fig. 3 now shows that in this case at time T2 m End would not be achieved.

[0064] In contrast, an increasing mass flow m from time t0 would 02 m End at time T2. An increasing mass flow m 03 would m End reach before time T2.

[0065] According to the invention, the control unit (not shown in detail) is designed to check corresponding relationships. In the situation described above, this would, for example, detect a change in the mass flow m at time T1. 01initiate before the time t0 at which the change or increase in the required electrical power is to take place, so that at the time T2 m End can be safely achieved. Preferably, the excess electrical energy generated before time T2 is temporarily stored in a suitable energy storage device, e.g., in a high-performance battery and / or a supercapacitor.

[0066] It might be possible that with the help of the stored energy, in the above situation according to Fig. 3 it would be sufficient to have only a mass flow m 02 In this case, the small difference at time T2 between the mass flow m IstT2 and m End and the resulting difference between the services P elT2 and P elEnd by the performance of the energy storage P elBatbridged or compensated. The control unit according to the invention is designed to initiate appropriate measures, tests, and / or calculations.

[0067] Fig. Figure 4 schematically shows the behavior of a gas generation system or reformer (not shown in detail) with regard to degradation. Here, a mass flow m B of a fuel to be reformed, such as gasoline or the like, to a hydrogen-containing fuel depending on an electrical power P el and one along an arrow 5 or an increasing degradation 5.

[0068] In general, according to the invention, the number of model parameters is advantageously kept as low as possible to enable good convergence or approximation of corresponding adaptation routines for the released parameters. Input variables include, for example, measured variables or variables derived from the measured values, such as current, system pressure, stoichiometry of the anode and / or cathode gases, and / or temperature of stack 1, or the system's response times.

[0069] Using the mathematical model, model output variables for the voltage are calculated and compared with the measured variables. From any differences, improved or modified model parameters are derived, reused, and tracked over time or stored in a control unit. Using these current descriptions of the model state variables or model parameters and their temporal progression, predictors X are then derived in a second step. P calculated.

[0070] These predictors X P can predict whether a minimum voltage would be undercut in the case of relatively high load jumps, for example, or whether a required power P elEnd could actually be provided. With potential load profiles X3, e.g. load step, cold start, driving cycle, etc., the response of the system, in particular the voltage level X2 and the maximum available power P elIstmax, predicted at a later time T2. The reaction of the system is limited, for example, by the run-up time of a fan, a compressor, by the heating of a catalyst, by climatic conditions such as outside temperature, etc., by delays in the fuel gas supply, or the like. However, degradations (cf. in particular Fig. 4) lead to reduced performance. According to the behavioral or dynamic parameters stored in Model 2, at any given time T x , for a potential load step ΔP elpot , only a maximum available system power P elmaxTx available. If this maximum available system power P elmaxTx below the performance P that is likely or potentially necessary at a later time T2 elpotmaxT2, advantageous countermeasures can be initiated or initiated at an earlier time T0, in particular within the time period ΔT, in order to achieve the desired system performance P elpotmaxT2 This means that P elpotmaxT2 ≥ P elSollmaxT2 so that no critical situation arises for the system or any impairment of the functioning of the system.

[0071] The parameter adaptation according to Fig. 1 and its temporal progression advantageously allow for a long-term prediction of the degradation of a catalyst, in particular of the fuel cell 1 and / or the gas generation unit. For example, by extrapolating the temporal progression and comparing it with set limits for individual parameters, e.g., model parameters of the membrane's internal resistance, the reformer's conversion rate, etc., statements can be made about the remaining service life of the critical components.

[0072] For example, using initial values ​​of the parameters P1 to P6 according to Fig. 2 The voltages measured during a current draw are compared with the corresponding model value. If deviations occur, parameters P1 to P6 are adjusted accordingly. Various well-known mathematical or so-called fitting methods exist for this, such as Kalman filters, etc.

[0073] In general, the operating strategy according to the invention allows a fuel cell system to be advantageously integrated into a modern vehicle electrical system. The electrical energy management of the fuel cell system thus implemented has the ability to take timely measures to ensure a minimum supply for important consumers or components, in particular at a time T1 prior to a potential demand t0. For example, additional energy storage devices such as high-performance batteries and / or supercapacitors can be charged early in order to provide a potential power P at a later time T2. elpot to the system. This can be achieved by initiating, among other things, an advantageous charging control or charging strategy for the energy storage system in a timely manner.

[0074] In addition, a less relevant consumer such as an air conditioning system, etc. can be throttled or switched off in order to ensure a minimum supply to relevant components of the system, e.g. the drive motor, the electronic control or controller, etc.

[0075] Furthermore, a lead time can be implemented in the fuel cell system. This means, for example, that the air supply or the lambda value of the fuel cell supply is increased and / or a higher system pressure, particularly on the air side of the fuel cell unit 1, is achieved and / or, especially in reformer systems, advantageous intermediate storage devices are preemptively filled with reformate gas. This allows the advantageous dynamics of the overall system to be maintained in order to counteract potential load jumps ΔP elpot or to enable load requirements for a later time T2.

[0076] In general, according to the invention, an operating strategy can be derived, among other things, for a fuel cell drive system in vehicles, with which a minimum lead time for a desired dynamic can be determined. This minimum lead time could also be adapted to learned driver profiles, seasons, etc. For example, a higher lead time is required for a sporty driver and / or during the winter than for an economical driver and / or during the summer.

[0077] In addition, with the help of the advantageous predictors X P Measures can also be triggered in the fuel cell system to regenerate the system, such as purging, recirculation, pressure and / or humidity variation of individual components or material flows.

[0078] In principle, the determination of the remaining lifetime of the fuel cell unit 1 as predictor X Pcrucial service advantages to prevent a possible complete failure of the system in good time.

[0079] Fig. Figure 5 includes several schematic characteristic curves to illustrate the invention. Fig. 5a is a diagnostic start D A a diagnostic phase and a diagnostic end D E shown. In a first time period I, the control unit according to the invention shifts the operating point downwards along the polarization characteristic curve of the fuel cell unit, and in a time period II, shifts it upwards.

[0080] Fig. Figure 5b shows schematically the power P BZ of the fuel cell unit as a function of time t. It becomes clear that from time D A due to the Fig. 1a shown operating point shift in time period I, the stack power P BZFor example, the power is reduced from 10 kW to 5 kW, with the 5 kW remaining virtually constant, particularly during a predetermined period of time. The fuel cell unit is accordingly operated in a steady state during this time phase in order to be able to carry out an advantageous diagnosis according to the invention.

[0081] In Fig. 5c shows several characteristic curve fields that are assigned to the time periods, in particular time periods I and II. The characteristic curve fields schematically show both a current-voltage characteristic curve BZ of the fuel cell unit or fuel cell stack and a current-voltage characteristic curve Bat of a storage device or battery or accumulator. The points shown in the characteristic curves symbolize the respective operating point, and the arrows illustrate the operating point shift from one operating point to another along the corresponding characteristic curve. For example, the first characteristic curve field according to Fig. 5c the operating point of the polarization characteristic of the stack P BZ and the operating point of the power of the electric drive motor P M in the period before period I. The second characteristic field according to Fig. Figure 5c shows the operating point shift along the arrows for the time period I, so that a new operating point of the fuel cell with reduced, in particular constant, electrical power P BZ is realized.

[0082] Accordingly, in the third characteristic field according to Fig. 5c the operating point of the fuel cell unit is shifted upwards. The fuel cell unit generates a power P BZ , in particular constant power P over a certain period of time BZ of about 15 kW within period II.

[0083] The fourth characteristic field according to Fig. 5c shows the operating point shift to the initial state before the diagnostic phase or before time D A , so that the diagnostic phase is terminated.

[0084] Fig. 5d shows that in the Fig. In the example shown in Figure 5, the drive motor has a constant electrical power P M of approximately 10 kW. It is expressly emphasized that this is a rather rare condition, at least over a longer period of time, in the case of a vehicle's drive motor, for example. However, this special case was chosen to simplify the illustration of the invention.

[0085] Fig. 5e shows the curve of the electrical power P Bat of the storage or battery. This clearly shows that to ensure the 10 kW of electrical power P required by the drive motor Min time period I the storage contributes 5 kW and during time period II the storage can absorb or temporarily store 5 kW.

[0086] In Fig. Figure 6 shows a schematic block diagram of a drilling network structure with a fuel cell propulsion system according to the invention. A fuel cell stack 100 with a fuel cell periphery 101 is connected to an electric drive motor 103 via a DC / AC converter 102. The electric motor 103 is provided for driving drive wheels 105 via a transmission 104.

[0087] In addition, the fuel cell 100 is electrically connected to a traction storage device 107 by means of a DC / DC converter 106.

[0088] Furthermore, a further DC / DC converter 108 is provided, which is electrically connected in particular to a 12V battery 109 or vehicle battery 109 as well as low-voltage consumers, in particular with a voltage of approximately 14V.

[0089] In addition, for example, additional DC / AC converters 111 or 112 can be optionally provided for high-voltage consumers.

[0090] In Fig. 6, a control unit 117 according to the invention is further provided, which advantageously comprises, in particular, an FCU or APU control and an ECU or EEM and is advantageously connected to various components for their control, in particular control or regulation. Fig. 6, particularly advantageous sensors and other details are not shown for reasons of clarity.

[0091] With the aid of the invention, the largest possible load range can be examined in order to record an evaluable U / I characteristic curve, particularly in mobile use of the fuel cell 100 as a drive or as a so-called APU. Advantageously, numerous, very different or possible current densities of the fuel cell 100 are operated in a stationary manner. This is generally not always possible during driving, because the load behavior depends on the driver's driving style. For example, a somewhat "nervous" driver will not remain in a certain load range for too long, so that a stationary recording of the U / I behavior is comparatively difficult or incomplete. In fuel cell systems in vehicle applications according to the state of the art, the lowest load range is generally passed through relatively quickly, so that steady-state conditions are hardly to be expected here, which, however, lead to a reproducible measurement of the polarization characteristic curve for certain findings orDiagnoses are needed.

[0092] According to the invention, however, completely new possibilities arise, particularly in fuel systems with traction storage units or batteries 107 for supplementing or buffering the primary energy supplier 100 or the fuel cell stack 100.

[0093] For example, with a relatively discontinuous specification of the electrical load 103 or 110 by the electrical storage 107 or 109, the dynamically required portion of electrical energy can be supplied to the electric drive motor 103 or, in the case of APU systems, to the general electrical consumers, while the fuel cell 100 itself can be operated at a stationary operating point over a specific period of time, in particular in time period I or II. The load distribution is divided into a direct and an alternating component via a control system in the energy management system 113, and a contribution to the direct component is specified to the fuel cell system 100. The load distribution is permanently or only temporarily limited by the capacity of the traction storage 107 or storage 109 and its performance.

[0094] The main advantage here is that the driver does not notice any changes in drive torque. It is even possible to intentionally operate the fuel cell stack 100 at a low efficiency for a short time, particularly through pressure and / or lambda variations, in order to be able to diagnose the U / I behavior of the stack 100 with this parameter setting. This operating point shift enables, in particular, different current densities in the stack or in the fuel cell unit 100 to be approached during driving and without the driver noticing an undesirable torque jump or the like.

[0095] In addition, to shift the load point of the stack 100, a variation in the control of the electric motor 103 can also be achieved, thereby changing the efficiency of the electric drive 103. For example, in a permanent magnet synchronous machine, the operating point of the electric drive 103 can be degraded by field weakening, preferably in combination with a change in the duty cycle of the power electronics, such that more current is consumed in a torque-neutral manner. This effectively reduces the efficiency.

Claims

[1] Fuel cell system with a fuel cell unit (100) for generating electrical energy, with an electrical storage device (107, 109) for storing or releasing electrical energy and with an electrical consumer (103, 110, 101) for consuming electrical energy, in particular with an electric drive motor (103) designed as a consumer for driving a vehicle, wherein a control unit (113) is provided for determining the functionality of at least the fuel cell unit (100) during a diagnostic phase, characterized by that the control unit (113) is provided for determining the electrical power (PBZ) generated by the fuel cell unit (100) at least during the diagnostic phase, which is decoupled from a consumed electrical power during the diagnostic phase. [2] Fuel cell system according to claim 1, characterized bythat at least during a time period (I, II) of the diagnostic phase, the electrical power (PBZ) generated by the fuel cell unit (100) is substantially constant. [3] Fuel cell system according to one of the preceding claims, characterized by that during the diagnostic phase, the electrical power (PBZ) generated by the fuel cell unit (100) is at least in an upper range of the power that can be generated (PBZ) or in a lower range of the power that can be generated (PBZ), wherein the upper range is the uppermost third and the lower range is the lowest third of the power that can be generated (PBZ). [4] Fuel cell system according to claim 3, characterized by that a first time period (II) with constant, generated power (PBZ) is provided in the upper range and a second time period (I) with constant, generated power (PBZ) is provided in the lower range. [5] Fuel cell system according to one of the preceding claims, characterized bythat the control unit (113) is designed to change at least the efficiency of the electrical consumer (103, 110, 101). [6] Fuel cell system according to one of the preceding claims, characterized by that the control unit (113) is designed to change at least the efficiency of the fuel cell unit (100). [7] Fuel cell system according to one of the preceding claims, characterized by that at least one detection unit is provided for detecting at least one actual value of a first parameter of the fuel cell unit (100) at a first time T1. [8] Fuel cell system according to claim 7, characterized by that the control unit (113) is designed to check at least one target value of a second parameter, which is dependent on the first actual value of the first parameter, at a second time T2 (T2 = T1 + [Delta]T) later by a time difference [Delta]T. [9] Fuel cell system according to claim 8, characterized by that the control unit (113) is designed to change at least one actual value of a third parameter depending on the target value of the second parameter. [10] Fuel cell system according to claim 7, characterized by that the first parameter is at least one model parameter of a mathematical model of the fuel cell unit (100). [11] Fuel cell system according to claim 8, characterized by that the control unit (113) is designed to check the target value of the second parameter as a function of a fourth parameter. [12] Fuel cell system according to claim 11, characterized by that at least one potential change of the fourth parameter is provided for during the time difference [Delta]T. [13] Vehicle with a drive motor (103) and a fuel cell system according to one of the preceding claims.

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