DE102005000611A1 - Fuel cell system for automobiles has a diagnostic facility with a controller to maintain electrical power during diagnosis phase - Google Patents

Abstract

Fuel cell (100) operates with electrical batteries for energy storage (107,109) and supplies energy to an electric motor (103) driving the road wheels (105) and other load devices (101,110). Coupled to the fuel cell is a control unit (113) that ensures that constant electrical power is provided during the diagnostic phase.

Description

The The invention relates to a fuel cell system according to the preamble of claim 1.

At the Use of fuel cell systems, e.g. as so-called APU (Auxiliary Power Unit) and / or in the drive system of vehicles and in stationary systems, should the electrical energy management the state of the fuel cell or of the fuel cell stack with respect Dynamics, performance, Degradation and / or minimum voltage know. Especially with reformer systems are additionally information about the degradation and dynamics of the gas generating unit needed. Just so can the availability and reliability of Systems are ensured.

Previously known systems meet these requirements only insufficient. For example, the document describes US 5,945,229 a fuel cell system in which the behavior of the current-voltage characteristic of the stack is determined via additional fuel cells at the stack input and stack output. From this it is concluded that the CO concentration in the hydrogen-rich anode gas. If there is a deviation from a reference behavior, ie a target / actual comparison is carried out, protective actions are automatically triggered to avoid CO poisoning of the stack.

task and advantages of the invention: In contrast, the object of the invention is a To propose fuel cell plant, the one compared to Prior art improved availability and reliability of the system.

These Task is, starting from a fuel cell system of the introductory mentioned type, by the characterizing features of the claim 1 solved. By the mentioned in the dependent claims activities are advantageous embodiments and further developments of the invention possible.

Accordingly is a fuel cell system according to the invention in that a control unit for setting the at least while the diagnostic phase generated by the fuel cell unit electrical Performance is provided. With the help of this measure can be an advantageous Diagnostic profile of the electric power of the fuel cell unit be generated. For example, you can generates different current densities of the fuel cell unit and for the diagnosis of functioning the fuel cell unit can be used.

Preferably is a decoupling generated by the fuel cell unit electric power of the at this time or during the Diagnostic phase consumed electrical power provided. This is therefore of particular advantage, since thereby the operation of Fuel cell unit or their power generated as far as possible independently can be from the current consumption. Hereby, that of the fuel cell unit generated electrical power substantially from the diagnosis or depend on their requirements. this makes possible An optimization of the diagnosis leads to a decisive one Improvement of the diagnosis compared to the prior art.

By an advantageous integration of the electrical storage, both designed for storage and for the delivery of electrical energy is, independence becomes the generation of electrical energy of the fuel cell unit from the current or current energy consumption in an advantageous Realized way. For example, if necessary, the electric Memory on the one hand give off electrical energy and on the other hand generated excessively by the fuel cell unit store electrical energy. This means that the electric Memory advantageously the possibly existing difference between the generated electric power of the fuel cell unit and the consumed electrical power of the or the electrical Balances consumers in an advantageous manner. This will be the Operational safety or the operational capability of the entire fuel cell system, especially in the diagnostic phase, advantageously guaranteed.

As a general rule can according to the invention a reproducible diagnosis or measurement of the fuel cell unit, in particular the polarization characteristic or the like, in an advantageous manner Manner performed become. This increases the accuracy of the diagnosis Way increased compared to the prior art. According to the invention open up completely new possibilities the diagnosis of the fuel cell unit or the entire fuel cell system. For example, in vehicle applications, the lower load range of Fuel cell unit usually go through relatively quickly, so that in a fuel cell system according to the prior art knowledge, which are only recoverable from the lower load range, not or can hardly be won. According to the invention For example, the fuel cell unit can be aware of the lower Operated load range and the functionality or condition accordingly be diagnosed.

It is conceivable to operate the fuel cell unit in such a way that it has a substantially ste current, changing electrical power generated during the diagnostic phase. For example, the electrical power of the fuel cell unit could have a sinusoidal or similar course during the diagnostic phase. It is also conceivable that with this variant of the invention, for example, the inertia of the fuel cell unit or individual components can be determined and compared with a desired state. From this, it is possible, for example, to obtain statements regarding the functionality or the state of the fuel cell unit.

Preferably is at least during a period of the diagnostic phase that of the fuel cell unit generated electrical power substantially constant. An advantageous constant, generated electrical power or a corresponding stationary state the fuel cell unit is for determining the functionality the fuel cell unit or for the production of certain knowledge about the Condition or functionality the fuel cell unit of particular importance or in part unconditional requirement. This is the diagnosability the fuel cell unit on the one hand compared to the prior art significantly expanded and secondly the accuracy of the diagnosis further improved.

For example is during the diagnostic phase, the electrical generated by the fuel cell unit Power in an upper area and / or in a lower area the producible or maximum power. This can provide insights the upper and lower power range of the fuel cell unit obtained in an advantageous manner and to diagnose the functionality or the state of the fuel cell unit can be used. Especially the operation of the fuel cell unit both in the upper as well as in the lower range of the producible and maximum power guaranteed a particularly wide dimensioned examination or diagnostic area the fuel cell unit. This leads to a further improvement the diagnosability of the fuel cell unit. This can be special advantageous findings regarding the functionality or the state of the fuel cell unit by means of the control unit or the diagnostic unit are obtained.

In a particular embodiment of the invention is the upper area the top two-fifths and / or the lower area the lower two-fifths of the producible or maximum power of the fuel cell unit. advantageously, the upper area is the upper third and / or the lower area the lowest third of the producible or maximum power of the Fuel cell unit. It could be proven that straight in these areas, the determination of the functionality or the state of the fuel cell unit special findings allows. In addition, with the help of these measures a particularly wide power or load range of the fuel cell unit examinable.

Preferably is at the top of a first period of time with substantially constant, generated electrical power and / or at the bottom a second period of time with substantially constant, producible or maximum power of the fuel cell unit. This allows one hand a stationary one State of the fuel cell unit in the upper and / or lower power range, whereby the diagnosability of the fuel cell unit or the fuel cell system is further improved.

For example can the during the diagnostic phase consumed electrical energy or power thereby changed that, where appropriate, less relevant consumers are shut down and / or switched on and / or their consumption in an advantageous way something changed becomes. For example, in particular in vehicle applications the Power of electric window drives, a heating and / or Air conditioning, etc. switched on or off and / or in their performance throttled or slightly increased without, for example, the comfort in a vehicle in significant extent becomes.

Preferably, the control unit is designed to change at least the efficiency of the electrical load. With the help of this measure, for example, with almost constant functionality of the consumer, for example, with the same drive power of the drive motor, more and / or less electric power, in particular from the fuel cell unit generated electrical power consumed. With the help of this measure, an increase in the electrical power generated by the fuel cell unit is possible, especially in a nearly full electrical storage. For example, in a variety of types of electric motors, in particular permanent magnetically excited synchronous machines or the like, via a field weakening and / or by means of a change in the duty cycle of the power electronics, in particular when using DC / DC and / or DC / AC converters or the like Operating point of the electric motor or electric drive are changed or deteriorated in such a way that advantageously more torque-neutral more or less power is absorbed by the consumer. Hereby effectively the efficiency of the consumer is advantageously changed or preferably reduced, so that, for example, with the same drive power more electrical noise is consumed. Accordingly, this can also be applied to other electric machines, such as asynchronous machines, SR motors, etc. For example, with the aid of a change in the control angle and / or duty cycle, the recording power can be increased, while at the same time the output torque of the electric motor remains substantially constant.

In A preferred variant of the invention is the control unit to change formed the efficiency of the fuel cell unit. For example The efficiency of the fuel cell unit is changed by a variation an operating pressure, the lambda value or the like realized. hereby can also with corresponding operating states or with these parameter specifications the functionality, in particular the current-voltage behavior the fuel cell unit to be diagnosed. Hereby becomes again an advantageous extension of the diagnosability the fuel cell unit according to the invention realized in comparison to the prior art.

As a general rule is advantageous, the diagnostic phase during an operating phase, especially in vehicle applications while driving the vehicle, perform. It is of particular advantage that the fuel cell system not be performed before and / or after parking or during a driving break. This advantageously prevents, for example individual components of the fuel cell system or the vehicle Sounds which could confuse or disturb the user. In addition, it is in driving breaks or stoppages of the vehicle sometimes extremely difficult, a relevant electrical energy consumption for to produce the diagnosis.

In an advantageous manner, 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 T ₁ . Hereby, the diagnosis of the fuel cell unit can be implemented particularly easily.

Furthermore can the diagnosis according to the invention For example, in case of a deviation of the detected actual value of a predetermined desired value of the corresponding parameter with the aid of Control unit or the like causes or the diagnostic phase to be started. This is especially in case of disturbances of the fuel cell system of particular advantage. For example, with a detected reduction the efficiency of the fuel cell unit may be the diagnosis be initiated and carried out accordingly.

Basically due to the diagnosis or the knowledge gained the diagnosis is an optimization of the control behavior of the fuel cell system or the vehicle can be realized.

As a general rule may be due to the diagnosis or due to the diagnosis obtained Findings about the functionality the fuel cell system advantageous regulation of and / or several components of the fuel cell system in an advantageous Induced and executed become. This is especially true of acute deterioration or a fault that has occurred the fuel cell system of particular advantage.

Preferably, at least one control unit is provided for testing at least one desired value of a second parameter dependent on the first actual value of the first parameter for a second time T2 later by a time difference ΔT. Accordingly, T ₂ = T ₁ + ΔT, wherein in the sense of the invention ΔT is greater than a pure computing time of the control unit. That is, ΔT in 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, particularly the processor, plus a definable or measurable delay time. ΔT according to the invention is a few seconds, minutes, hours, days and / or even months.

According to this variant of the invention, a statement or a comparison with a reference behavior at a future time T _{2 is} possible. In principle, this prediction or so-called prediction with respect to the fuel cell system or individual components thereof can be determined independently of any impairment or damage already present at time T ₁ or the time of detection of the actual value of the first parameter. This means that at the time T ₁ no or no impairment of the system may be present, but according to the invention in the future, for example, under unchanged conditions and / or possible or expected changes of one or more parameters of the fuel cell system, an impairment or damage of the system or individual components of the system could be possible or expected. As a result, an advantage in time for any counter and / or protective measures or the like which may be necessary to avoid or reduce corresponding impairments or damage can be realized in an advantageous manner. As a result, for example, expected impairments, such as, for example, a shortage supply, a poisoning, a degradation of the fuel cell unit and / or others, can advantageously be achieved according to the invention Components of the system are avoidable or can not even arise, at least to a significant extent.

in the Contrary to the present invention, the prior art on the other hand an already occurred impairment or disturbance of the Systems or individual components, in particular a degeneration the fuel cell unit, if possible early or recognized in the approach to immediate countermeasures initiate. This means, that impairment already occurred. According to the invention become countermeasures or protective measures advantageously already before the onset of impairment or damage to the System or individual components using the control unit initiated so that this possible not even arise. This significantly increases the reliability or availability of the system.

Preferably, a time course, in particular a temporal change, of the actual value of the first parameter is detected. As a result, among other things, a tendency can be determined or a temporal extrapolation of the first parameter can preferably be calculated up to the time T ₂ or during the time difference ΔT. Hereby, according to the invention, a comparison of the actual value of the first parameter at time T ₂ with the desired value of the second parameter at time T ₂ can be performed.

At the the second parameter is preferably an aggregated one or highly aggregated parameters of the fuel cell system or individual Components of this, with the help of at least one comparatively easy to be determined first parameter is formed. Especially is an aggregated parameter of the fuel cell unit as a second parameter intended.

advantageously, the target value of the second parameter is at least one lifetime and / or a power and / or a minimum electrical voltage of the fuel cell unit.

In In practice, it has been shown that precisely these parameters of the fuel cell unit particular relevance regarding a description of the state of the fuel cell unit or represent the fuel cell system.

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, as a function of the setpoint value of the second parameter, in particular at the time T ₂ . In principle, the control unit is designed to compare a value of the second parameter with the desired value (reference value of the second parameter at an arbitrary time T _X ), in particular at time T ₂ . Advantageously, in the case that the value of the second parameter at the time T _2, the predetermined target value of the second parameter, taking into account an advantageous tolerance is not reached, ie exceeded or below, according to the invention, a third parameter or Counter- / protective measure or the like with the help of the control unit changed or initiated. The change of the third parameter is advantageously designed or carried out in such a way that the desired value of the second parameter, in particular at time T ₂ , can be reached. This means, for example, that according to the invention, for example, a potential foreseeable impairment (a possible or expected overshoot or undershoot of the setpoint value of the second parameter at time T ₂ ) due to a previously introduced advantageous measure, in particular during the time difference .DELTA.T avoided or can be prevented even before the potential emergence.

In an advantageous embodiment According to the invention, the third parameter is at least one parameter a component of the fuel cell system and / or a vehicle, e.g. a passenger / utility motor vehicle, ship, etc ..

For example, the third parameter is an on / off parameter or a state parameter of an electrical load 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 order not to fall below a minimum electrical voltage and / or electrical power of the fuel cell unit at a later time T ₂ .

On the other hand, for example, can be increased by a reformer unit mass flow of a hydrogen-containing fuel. Advantageously, a case can be realized, wherein in particular the generated mass flow is greater than the mass flow required at this time and the excess mass flow in an advantageous hydrogen storage or the like is cacheable. As a result, for example, at later time T ₂ hydrogen-containing fuel stream from the buffer and the reformer of the fuel cell system available, so that a shortage of hydrogen-containing fuel should not occur.

The same is also true for the oxidizing agent, such as air, feasible, for example, carried out a precautionary pressure increase and / or a compressed air reservoir can be filled according to the test according to the invention, for example, to avoid a shortage supply of the fuel cell unit with oxidizing agent at the later time T ₂ .

In a particular development of the invention, the fuel cell system has an electrical energy store, in particular a so-called high-performance battery and / or a so-called supercap or the like. Advantageously, the third parameter is a parameter of the electrical energy store. This makes it possible that, for example, a loading and / or unloading of the energy storage in dependence of the test according to the invention is feasible. This can be avoided in particular that at a time T _{2 is} not available in expected or sufficient amount of electrical energy available. In this case, electrical energy is made available to the system at the time T ₂ by the fuel cell unit and / or the electrical energy store.

advantageously, the first parameter is at least one model parameter of a mathematical one Model of the fuel cell unit or fuel cell system. Especially with the help of such a model description of the fuel cell unit and / or fuel cell plant will simplify the operation the fuel cell system or a simplification of the control or regulation of the system possible.

Furthermore the second parameter is at least one model parameter of a mathematical model the fuel cell unit or fuel cell system. For example is the life, power and / or minimum electrical voltage of Fuel cell unit using the mathematical model of Fuel cell unit depending formed of the first parameter.

In a particular embodiment this variant of the invention is both the second parameter as also the first parameter is a model parameter. Here is a particularly strong simplification of the sometimes very complex relationships in one Fuel cell system, so that in an advantageous manner the Control of the fuel cell unit and / or the Fuel cell system decisively simplified.

Preferably is the first parameter formed as a model parameter at least a Nernst voltage and / or an activation energy and / or a Internal resistance and / or a mass transfer parameter, in particular a parameter regarding the gas diffusion process, the fuel cell unit. In practice was found to be just using these model parameters a sufficiently accurate description of the behavior of the fuel cell unit or the fuel cell stack is possible.

Preferably is a device for forming the model parameter (s) in dependence provided at least one actual value of a base parameter. When Basic parameter is for example a mass flow and / or a Temperature and / or an electric current and / or pressure of Fuel cell unit or the fuel cell system and / or a vehicle formed. Correspondingly advantageous basic parameters are advantageously particularly easy to capture or be at existing fuel cell systems already recorded, so no or only a very small additional effort to capture corresponding parameter according to the invention necessary is.

Preferably the basic 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 includes, for example a reformer or the like.

at a special variant of the invention becomes the first parameter with the help of the mathematical model of the fuel cell unit from one or more base parameters and from this first model parameter the second parameter in turn with the help of and / or another mathematical model of the fuel cell unit formed. This means, for example, that from at least one mass flow, a temperature, an electric current and / or a pressure using the mathematical model, the Nernst voltage, activation energy, Internal resistance and / or the gas diffusion process will be described and in turn the life, power and / or electrical Minimum voltage of the fuel cell unit.

advantageously, the first parameter is a base parameter. This measure is simplified the generation of the second parameter according to the invention.

Basically one or more second parameters from a single first one Parameter or from a set of several first parameters and / or Basis parameters are formed.

In an advantageous variant of the invention, the control unit is designed to check the setpoint value of the second parameter as a function of a fourth parameter. With the help of the fourth parameter, in particular a more detailed description of the expected or potential second parameter at the later time T ₂ or at a future time after the time difference .DELTA.T be achieved. In this way, the control unit can advantageously carry out a better comparison of the expected or potential value with the desired value of the second parameter.

In general, a change of the fourth parameter, which is already fixed at time T _1, can be provided. In this variant of the invention, a particularly accurate description or calculation of the expected or potential value of the second parameter at the future time T ₂ can be achieved.

alternative or in combination with the aforementioned variant is during the Time difference ΔT at least a potential change of the fourth parameter. For example, the potential change represents of the fourth parameter a presumed or probable change of the fourth parameter. Here can advantageously from the past experiences are taken into account. in this connection In particular, recorded changes over time are one of the parameters to consider the fuel cell system. Based on these temporal changes For example, with the help of extrapolation, the potential change of the fourth parameter by means of the control unit according to the invention calculated or calculated.

advantageously, is the fourth parameter as base parameter and / or first and / or second and / or third parameters formed. Prefers is the fourth parameter as load or so-called load profile formed, i. the dependence the electrical power of the time. Just the right load profiles have a special influence on the dynamics of the system on.

in the Meaning of the invention means the numbering or designation chosen the parameter is not a compulsive succession but merely serves the distinctness of possibly to use parameters. Thus, e.g. the third parameter is not needed However, the fourth parameter to the formation of the second is quite considered become.

As a general rule may be the control unit according to the invention have an advantageous electronic storage unit, the aforementioned dependencies and / or model relationships and / or Setpoint values of the different parameters are included or stored Has.

In an advantageous embodiment the invention is the control unit for adaptation or adaptation especially the desired parameters formed. With the help of this measure can For example, aging or degeneration of the fuel cell unit and / or the supply unit, etc. are taken into account. Preferably becomes the degeneration or aging for the mathematical model considered and / or based on the model.

As a general rule can according to the invention realizes a prediction or provision with regard to critical system states become. For example, it can be predicted how the voltage and whether the voltage drops below a critical value, depending on for example, from the operation or switching on an air conditioner, from an overtaking maneuver with Full load on a fuel cell vehicle, etc.

advantageously, is a variety of second parameters for describing a variety potential operating conditions individual components and / or the overall system provided. Here are possible all conceivable or imaginable operating conditions to be considered, so that the availability or reliability of the system according to the invention is maximized. Preferably, an optimization of the system in Reference to the dynamics, the efficiency and / or the durability of individual Components and / or the entire system provided.

Embodiment:

One embodiment The invention is illustrated in the drawing and is based on the Figures in more detail below explained.

in the Individual shows:

1 1 is a block diagram of a section of a fuel cell system according to the invention,

2 a schematic characteristic of a current-voltage characteristic for a model of a fuel cell unit,

3 a schematic characteristic of a dynamic behavior of a gas supply of a fuel cell system according to the invention,

4 schematic characteristics of a behavior of a gas generating system with degradation phenomena,

5 schematic characteristics of various components of the fuel cell system according to the invention and

6 a schematic block diagram ei ner wiring system in a fuel cell propulsion drive according to the invention.

In 1 is schematically shown 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 X ₁ and one or more output parameters X ₂ . The input parameters X ₁ are, for example, parameters of mass flows, temperatures, electrical currents and / or pressures of the fuel cell system. An output parameter X _{2 of} the fuel cell 1 is a voltage, for example. In the sense of the invention, the input / output parameters X ₁ , X _{2 can be designed} as so-called basic parameters. In addition, the output parameter X _{2 can be designed} as a so-called second parameter according to the invention. In the last-mentioned case, the actual voltage X ₂ can be expected at a current _instant T ₁ and / or a potential voltage X _2pot to be expected at a later _instant T ₂ at a time difference ΔT with a predetermined desired value of the voltage X _2soll or with the minimum electrical _voltage X _{2min of} the fuel cell unit 1 compared to one.

1 It can also be seen that the parameter X ₁ / a model block 2 to provide. The model block 2 includes a particular stored or deposited model 21 , a feedback unit 22 and a parameter adaptation 23 , Especially with the help of the units 22 and 23 can adapt to, for example, aging or degeneration of individual or several components of the fuel cell system such as the fuel cell unit 1 done so that the model 21 according to this is customizable. This becomes a dynamically changing model 21 realizable. Optionally, by means of already known matching routines a quasi-self-learning model 21 will be realized.

In 2 schematically is the model current voltage characteristic as well as the corresponding mathematical description of an example of the model 21 shown. Here, the parameters P _i with 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 the fuel cell unit 1 ,

In 1 is further clarified, as with the help of one or more model parameters X _{M of} the model block 2 and one or more load parameters X _{3 of} an expected or potential load 3 Predictors X _{P of} a predictor block 4 be formed.

If necessary, measures are initiated with the help of the predictors X _{P in} order, for example, to achieve a desired value of the parameter X ₂ .

In 3 is exemplified a dynamics of the gas supply, in particular an air path and / or a reformer or the like shown schematically. In this case, mass flows i are listed as a function of the time t for different cases. 3 additionally includes the mathematical description of the corresponding functional dependencies, where the variable a is a function of pressure, temperature and a mass flow m _end to be reached.

For example, a mass flow m _{01 is} present at time T ₁ . At a point in time T ₂ after a period of time ΔT, a potential increase in the electrical power X _{3 of} the fuel cell unit should take place 1 available (see in particular 1 , Block 3 ). It is assumed by way of example that the load change occurs at time t ₀ within the period ΔT. Furthermore, it is assumed that in order to provide the potential electrical power X _3End at time T _2, a mass flow m _{End is} necessary. According to 3 It is clear that in the case in which the mass flow mol would be present at the time t ₀ , this would require a period Δt ₃ to reach m _end . 3 illustrates now that in this case at time T ₂ m _{end would} not be achieved.

On the other hand, a mass flow m ₀₂ m _end increasing from time t ₀ would almost reach _end time T ₂ . A mass flow m ₀₃ increasing from time t ₀ would reach m _end already before time T ₂ .

According to the invention, the control unit, not shown, is designed to test corresponding relationships. In the situation described above at the time T _1, for example, this would initiate a change in the mass flow m ₀₁ already before the time t ₀ at which the change or increase in the required electrical power should take place, so that at the time T ₂ m _{end is} safely reached can be. Preferably, the excess electrical energy generated in this case before the time T ₂ is temporarily stored with an advantageous energy store, for example in a high-performance battery and / or a supercap.

It could possibly be with the help of the cached energy that in the above situation according to 3 it would be sufficient to have realized only a mass flow m ₀₂ at time t ₀ . In this case, the small difference at time T ₂ between the mass flow m _IstT2 and m _End and the difference between the outputs P _elT2 and P _{elEnd would} be the power of the energy store P _{elBa t be} bridged or compensated. To initiate appropriate measures or tests and / or calculations, the control unit is designed according to the invention.

4 Here is a mass flow mg of a fuel to be reformed such as gasoline or the like to a hydrogen-containing fuel in response to an electric power P _el and one along an arrow 5 or an increasing degradation 5 shown.

In general, according to the invention, the number of model parameters is advantageously kept as low as possible in order to allow a good convergence or approximation of corresponding adaptation routines for the enabled parameters. Examples of input variables are measured values or values derived from the measured values, such as current, system pressure, stoichiometry of the anode and / or cathode gases and / or temperature of the stack 1 or the response times of the system.

Using the mathematical model, model output quantities for the voltage are calculated from this and compared with the measured quantities accordingly. From the differences that may be present, improved or changed model parameters are derived, reused and tracked in time or stored in a control unit. With these current descriptions of the model state variables or model parameters and their temporal progressions, predictors X _P are subsequently calculated in a second step.

These predictors X _P can predict whether a minimum _voltage would be _exceeded in the case of, for example, relatively large load jumps or whether a required power _could indeed be provided. With potential load profiles X ₃ , eg load jump, cold start, drive cycle, etc., the response of the system, in particular the voltage level X ₂ and the maximum available power P _{elIstmax, are} pre-calculated at a later time T ₂ . The reaction of the system is limited, for example, by the ramp-up time of a blower, a compressor, by heating of a catalyst, by climatic conditions such as outside temperature, etc., by delays in the fuel gas supply or the like. However, it is also possible for degradation (cf. 4 ) lead to reduced performance. According to the model 2 stored behavior or dynamic parameters is at any time T _X , for a potential load _{step .DELTA.P elpot} only a maximum available system power P _elmaxTx available. If this maximum available system power P _{elmaxTx lies} below the power P _{elpotmaxT2 that is} likely or potentially necessary at a later time T ₂ , correspondingly advantageous countermeasures can already be initiated or initiated at an earlier time T ₀ , in particular within the time span ΔT to be able to provide the desired system performance P _elpotmaxT2 . This means that P _elpotmaxT2 ≥ P _elSollmaxT2 , 50 that no critical situation for the system or impairment of the functioning of the system arises.

The parameter adaptation according to 1 and their time course advantageously allow a long-term prediction on the degradation of a catalyst, in particular the fuel cell 1 and / or the gas generating unit. For example, by extrapolation of the time profile and comparison with set limits for individual parameters, eg model parameters of the internal resistance of the membrane, conversion rate of the reformer, etc., statements can be made about the remaining service life of the critical components.

For example, with the aid of starting values, the parameters P ₁ to P _{6 can be determined} according to FIG 2 the voltages measured during a current draw are compared with the corresponding model value. In case of deviations, the parameters P ₁ to P ₆ are adapted in an advantageous manner. There are different, already known mathematical or so-called fit methods such as Kalman filters, etc.

In general, with the operating strategy according to the invention, a fuel cell system can advantageously be integrated into a modern vehicle electrical system of a vehicle. The electrical energy management of the fuel cell system realized thereby thus has the possibility of taking timely measures to ensure a minimum supply for important consumers or components, in particular already at a time T ₁ , which is before a potential requirement t ₀ . For example, additional energy stores such as high-performance batteries and / or supercaps can be charged early to provide a potential power P _{elpot to} the system at a later time T ₂ . For this purpose, inter alia, an advantageous charge control or charging strategy of the energy storage can be introduced in good time.

In addition, for example, a less relevant consumer such as an air conditioner, etc. throttled or shut down to a minimum supply of relevant components of the system, eg the drive motor, the electronic control or control, etc., to ensure th.

Furthermore, a Vorhalt in the fuel cell system can be realized. That is, for example, the air supply or the lambda value of the fuel cell supply is increased and / or a higher system pressure, in particular on the air side of the fuel cell unit 1 , realized and / or especially in reformer systems advantageous temporary store with reformate gas as a precaution. In this way, an advantageous dynamics of the overall system can be maintained in order to enable potential load jumps ΔP _elpot or load requirements for a later time T ₂ .

As a general rule is according to the invention an operating strategy for, among other things, a fuel cell drive derivable from vehicles, with the minimum allowable for a desired dynamics can be determined. This minimum allowance could include, among others adapted driver profiles, seasons, etc. are adjusted. To the Example becomes a higher one Guess for a sporty driver and / or during the winter as for an economic Driver and / or during needed in the summer.

In addition, with the help of the advantageous predictors X _P could be triggered in the fuel cell system measures that serve the regeneration of the system, such as purges, recirculation, pressure and / or humidity variation of individual components or material flows.

Basically, the determination has, for example, the remaining service life of the fuel cell unit 1 As a predictor X _P crucial service advantages to prevent a possible complete failure of the system in good time.

5 comprises several, schematic characteristics to illustrate the invention. In 5a is a diagnosis beginning D _A a diagnostic phase and a diagnosis end D _E shown. In a first time period I, an operating point shift along the polarization characteristic of the fuel cell unit is shifted downward and in a time interval II upwards by means of the control unit according to the invention.

5b schematically shows the power P _{BZ of} the fuel cell unit as a function of time t. Here it is clear that from the time D _A due to the in 1a illustrated operating point shift in the time period I, the stack power P _{BZ is} for example reduced from 10 kW to 5 kW, the 5 kW are almost constant, especially during a predetermined period of time. The fuel cell unit is accordingly operated during this time phase in the stationary state in order to carry out an advantageous diagnosis according to the invention.

In 5c a plurality of characteristic curves are shown, which are assigned to the time periods, in particular the time periods I and II. In the characteristic curves, both a current-voltage characteristic BZ of the fuel cell unit or the fuel cell stack and a current-voltage characteristic Bat of a memory or of a battery or rechargeable battery are shown schematically. The points shown in the curves symbolize the respective operating point or the arrows illustrate the shift of the operating point from one to the other operating point along the corresponding characteristic curve. For example, the first characteristic field shows according to 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 time period before the time period I. The second characteristic field according to 5c shows the operating point shift along the arrows for the period I, so that a new operating point of the fuel cell with a reduced, in particular constant electric power P _{BZ is} realized.

Accordingly, in the third characteristic field according to 5c the operating point of the fuel cell unit shifted upward. In this case, the fuel cell unit generates a power P _BZ , in particular over a certain period of time constant power P _BZ of about 15 kW within the time interval II.

The fourth characteristic field according to 5c shows the working point shift in the initial state before the diagnosis phase or before the time D _A , so that the diagnosis phase is terminated.

5d clarifies that in the in 5 example, the drive motor should have a constant electric power P _M of about 10 kW. It is expressly emphasized that, for example, in a drive motor of a vehicle, this is a rather rare condition, at least over a longer period of time. However, this special case has been chosen to simplify the illustration of the invention.

5e shows the course of the electric power P _{Bat of} the memory or the battery or rechargeable batteries. It becomes clear that in order to guarantee the 10 kW of electric motor power P _M demanded by the drive motor, in the time period I the storage device contributes 5 kW and during the time period II the storage device can store or buffer 5 kW.

In 6 schematically shows a block diagram of a Bohrnetzstruktur with a fuel cell propulsion system according to the invention. One Fuel cell stack 100 with a fuel cell periphery 101 is on the one hand via a DC / AC converter 102 with an electric drive motor 103 connected. The electric motor 103 is for driving drive wheels 105 by means of a gearbox 104 intended.

In addition, the fuel cell 100 by means of a DC / DC converter 106 with a traction memory 107 electrically connected.

Furthermore, another DC / DC converter 108 provided in particular with a 12V battery 109 or vehicle battery 109 As well as low-voltage consumer, in particular with a voltage of about 14 V, is electrically connected.

In addition, eg other DC / AC converters 111 respectively. 112 be optionally provided for high voltage consumers.

In 6 is still a control unit 117 According to the invention, which in particular advantageously comprises an FCU or APU control as well as an ECU or EEM and is advantageously connected to various components for their control, in particular control or regulation. In 6 In particular, advantageous sensors and other details are not shown for reasons of clarity.

With the help of the invention can for recording an evaluable U / I characteristic, especially in mobile use of the fuel cell 100 As drive or as so-called APU the largest possible load range are examined. Advantageously, numerous, most different or possible current densities of the fuel cell 100 stationary driven. This is generally not always possible while driving, because the load behavior depends on the driving style of the driver. 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 prior art, the lowest load range is usually passed through relatively quickly, so that hardly stationary states are to be expected here, which, however, are required for a reproducible measurement of the polarization characteristic for certain insights or diagnoses.

According to the invention, however, arise especially in fuel systems with traction accumulators or batteries 107 to supplement or buffer the primary energy supplier 100 or the fuel cell stack 100 completely new possibilities.

For example, at relatively unsteady specification of the electrical load 103 respectively. 110 through the electrical storage 107 respectively. 109 the dynamically demanded proportion of electrical energy to the electric drive motor 103 or be supplied to the general electrical consumers in APU systems, while the fuel cell 100 even in a stationary operating point over a certain period of time, in particular in the period I or II, can be operated. The load distribution is controlled by an energy management system 113 divided into a DC and an AC component and a contribution to the DC component of the fuel cell system 100 specified. The load distribution is determined by the capacity of the traction storage 107 or memory 109 and its performance permanently or even limited in time.

The advantage here is essentially that the driver feels no changes in the drive torque. It is even possible to use the fuel cell stack 100 operate briefly as long as intentionally with a poor efficiency, in particular by pressure and / or lambda variations, in order to comply with this parameter specification, the U / I behavior of the stack 100 to be able to diagnose. This shift in the operating point in particular makes it possible to approach different current densities in the stack or in the fuel cell unit 100 during the driving operation and without the driver noticing an undesired torque jump or the like.

In addition, the load point shift of the stack can 100 also a variation of the control of the electric motor 103 be achieved, reducing the efficiency of the electric drive 103 is changed. For example, in a permanent-magnetically excited synchronous machine can preferably over field weakening in combination with a change in the duty cycle of the power electronics, the operating point of the electric drive 103 be degraded so that moment-neutral more power is absorbed. In this case, the efficiency is effectively reduced.

Claims (14)

Fuel cell system with a fuel cell unit ( 100 ) for generating electrical energy, with an electrical storage ( 107 . 109 ) for storage or delivery of electrical energy and with an electrical consumer ( 103 . 110 . 101 ) for consuming electrical energy, in particular with an electric drive motor designed as a consumer ( 103 ) for driving a vehicle, wherein a diagnostic unit ( 113 ) for determining the operability of at least the fuel cell unit ( 100 ) is provided during a diagnostic phase, characterized that a control unit ( 113 ) for fixing the at least during the diagnostic phase of the fuel cell unit ( 100 ) generated electric power (P _BZ ) is provided. Fuel cell system according to claim 1, characterized in that at least during a period of time (I, II) of the diagnostic phase that of the fuel cell unit ( 100 ) electrical power (P _BZ ) is substantially constant. Fuel cell system according to one of the preceding claims, characterized in that during the diagnostic phase that of the fuel cell unit ( 100 ) Generated electric power (P _BZ) is also in a lower portion of producible power (P _BZ) at least both in an upper region than. Fuel cell system according to one of the preceding claims, characterized in that the upper region is the upper third and the lower region is the lowest third of the power to be generated (P _BZ ). Fuel cell system according to one of the preceding claims, characterized in that in the upper region a first period (II) with constant, generated power (P _BZ ) and in the lower region a second period of time (I) with constant, generated power (P _BZ ) is provided , Fuel cell system according to one of the preceding claims, characterized in that the control unit ( 113 ) for changing at least the efficiency of the electrical load ( 103 . 110 . 101 ) is trained. Fuel cell system according to one of the preceding claims, characterized in that the control unit ( 113 ) for changing at least the efficiency of the fuel cell unit ( 100 ) is trained. Fuel cell system according to one of the preceding claims, characterized in that at least one detection unit ( 113 ) for detecting at least one actual value of a first parameter of the fuel cell unit ( 100 ) is provided at a first time T ₁ . Fuel cell system according to one of the preceding claims, characterized in that the control unit ( 113 ) to test at least one of the first actual value of the first parameter-dependent desired value of a second parameter to a second, by a time difference ΔT later time T ₂ (T ₂ = T ₁ + ΔT) is formed. Fuel cell system according to one of the preceding claims, characterized in that the control unit ( 113 ) is designed to change at least one actual value of a third parameter as a function of the desired value of the second parameter. Fuel cell system according to one of the preceding claims, characterized in that the first parameter at least one model parameter of a mathematical model of the fuel cell unit ( 100 ). Fuel cell system according to one of the preceding claims, characterized in that the control unit ( 113 ) is designed to test the desired value of the second parameter as a function of a fourth parameter. Fuel cell system according to one of the aforementioned Claims, characterized in that during the time difference ΔT at least one potential change of the fourth parameter is provided. Vehicle with a drive motor ( 103 ) and a fuel cell system according to one of the preceding claims.