DE102022211778A1 - Control device for a fuel cell system, fuel cell system and method for controlling a fuel cell system - Google Patents

Abstract

The invention relates to the control of air compressor units in a fuel cell system which has several air compressor units arranged in series in a cathode path. For this purpose, it is provided to determine the control variables for the air compressor units on the basis of a multi-objective optimization, whereby a total power consumption for the air compressor units can be minimized.

Description

Technical area

The present invention relates to a control device for a fuel cell system, a fuel cell system with such a control device and a method for controlling a fuel cell system.

State of the art

Fuel cell systems, such as purely hydrogen-based systems, can comprise one or more fuel cell stacks that are supplied with an anode gas, for example hydrogen, and a cathode gas, for example air. A reaction in the fuel cell stacks can, for example, oxidize the hydrogen with the oxygen in the air, whereby electrical energy can be generated. The power density can be increased if the reactions in the fuel cell stacks are operated under pressure.

The publication EN 1 0 2011 087 912 A1 describes, for example, a fuel cell system in which cooled air can be supplied to the fuel cell stacks via a compressor.

To increase the efficiency and/or the inlet pressure at the fuel cell stacks, several air compressors can be arranged in series in the cathode path of such a fuel cell system.

Disclosure of the invention

The present invention provides a control device for a fuel cell system, a fuel cell system of such a control device and a method for controlling a fuel cell system with the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

Accordingly, it is envisaged:

A control device for a fuel cell system with at least two electrically driven air compressor units. The control device is designed to
to determine an individual control variable for each of the at least two air compressor units. The individual control variables for the at least two air compressor units are determined using several setpoint specifications by means of a multi-objective optimization to minimize a total electrical power requirement of the air compressor units using at least one further optimization objective.

Furthermore, it is planned:

A fuel cell system with a fuel cell unit, a cathode path, an anode path and a control device according to the invention. The fuel cell unit comprises at least one fuel cell stack. The cathode path is designed to provide a cathode gas, for example air, in particular oxygen, in the fuel cell unit. The cathode path comprises at least two electrically driven air compressor units. The anode path is designed to provide an anode gas, for example hydrogen, in the fuel cell unit.

Finally, it is planned:

A method for controlling at least two electrically driven air compressor units in a cathode path of a fuel cell system.

The method includes a step for receiving a plurality of setpoint specifications for the fuel cell system. The method also includes a step for determining individual control variables for each of the at least two air compressor units in the cathode path. The individual control variables for the at least two air compressor units are determined using a plurality of setpoint specifications by means of a multi-objective optimization to minimize a total electrical power requirement of the plurality of air compressor units, taking into account at least one further optimization objective.

Advantages of the invention

The efficient control of the air compressor units in fuel cell systems, in which several such air compressor units are provided in the cathode path, currently represents a major control engineering challenge due to the large number of parameters that have to be taken into account. In addition to the primary goal of providing the cathode gas, for example air, at the cathode inlets of the fuel cell stacks with a desired inlet pressure and with a desired mass flow, it is desirable or even necessary to take numerous other parameters into account and to optimize them.

It is therefore an idea of the present invention to provide a control for the air compressor units in a fuel cell system, which che enables efficient, reliable, stable and as easy as possible to implement control of the air compressor units in a cathode path with several air compressor units arranged in series. For this purpose, a multi-objective optimization is provided, which provides for minimizing the total energy requirement of the air compressor units as one of the primary optimization goals and also takes at least one other goal into account.

Due to the high complexity and the large number of parameters to be taken into account, multi-objective optimization is very well suited to controlling the multiple air compressor units in a cathode path of a fuel cell system. The primary goal of minimizing the total energy requirement for the air compressor units can also reduce the energy requirement of the fuel cell system and thus increase the efficiency of the fuel cell system.

For example, a cost function can be created for multi-objective optimization to determine the control variables for the air compressor units while simultaneously optimizing several target variables. This cost function is defined as a function of the objectives to be optimized. The different objectives can be individually weighted or prioritized. The weighting can also be adaptive. For example, the weighting can depend on energy costs, individual applications, aging of the units or other factors.
For example, a cost function can be formulated in this way for multi-objective optimization, which describes the energy requirements of the air compressor units over a predetermined period of time.

• - einen Gasmassenstrom an einen Stackeingang der Kathode eines Brenstoffzellenstacks,
• - einen Druck oder eine Druckdifferenz an einen Stackeingang der Kathode eines Brenstoffzellenstacks,
• - ein Wassergehalt des Gases an einen Stackeingang der Kathode eines Brenstoffzellenstacks,
• - einen Gasmassenstrom an einer Einleitestelle eines Purge-Gase in dem Kathodenpfad des Brennstoffzellensystems.

According to one embodiment, the plurality of setpoint specifications comprise two or more of the following setpoint specifications:

• - a gas mass flow to a stack inlet of the cathode of a fuel cell stack,
• - a pressure or a pressure difference at a stack inlet of the cathode of a fuel cell stack,
• - a water content of the gas at a stack inlet of the cathode of a fuel cell stack,
• - a gas mass flow at an inlet point of a purge gas in the cathode path of the fuel cell system.

In particular, an individual value can be specified for each fuel cell stack of the fuel cell system for the first three parameters. For the last-mentioned gas quantity at the purge gas inlet point, however, depending on the topology, just one parameter may be sufficient for the entire fuel cell system. As an alternative to the parameters mentioned, values derived from them can also be used.

• - Genauigkeit für die jeweiligen Sollwertvorgaben,
• - Dynamik für das Regelverhalten des Brennstoffzellensystems,
• - Belastungsunterschiede zwischen den Luftverdichtereinheiten, und/oder
• - einer Anzahl von Start/Stopp-Vorgängen der Luftverdichtereinheiten.

According to one embodiment, the control device is designed to determine the control variables for the at least two air compressor units further using at least one of the following optimization objectives???:

• - Accuracy for the respective setpoint specifications,
• - Dynamics for the control behaviour of the fuel cell system,
• - Load differences between the air compressor units, and/or
• - a number of start/stop operations of the air compressor units.

For the accuracy of the setpoint specifications, it can be taken into account, for example, that the mass flow of the cathode gas, in particular the oxygen provided in the cathodes of the fuel cell stacks, is of high relevance and should therefore be provided with great precision. Other parameters such as water content, on the other hand, can be set with a large tolerance if necessary. When taking the dynamics into account, specifications or operating conditions of a system supplied with electrical energy by the fuel cell system can be taken into account. If, for example, an electric vehicle is supplied with electrical energy via the fuel cell system, current requirements or specifications of the vehicle can be taken into account when determining the control variables for the air compressor units. With regard to the load differences, it can be taken into account, for example, that the several air compressor units should be loaded as evenly as possible over a longer period of time. An imbalance in which one air compressor unit is loaded relatively lightly over a longer period of time and another air compressor unit is loaded heavily over a longer period of time can be avoided in this way. Since the start and stop processes in particular represent a heavy load for the air compressor units and thus lead to increased aging, this can also be taken into account when determining the control variables for controlling the air compressor units, and an operating strategy can be provided in which such start and stop processes are minimized and balanced.

According to one embodiment, the multi-objective optimization includes a prioritization of the multiple target value specifications. Additionally or alternatively, a prioritization or weighting of the optimization objectives can also be provided.

Such prioritization allows particularly relevant target values to be given a higher weighting. In particular, if multi-objective optimization does not make it possible to fully meet all target values, appropriate prioritization can at least meet the target values considered important. The cost function of multi-objective optimization can take several objectives into account, which enables adaptive weighting of the individual objectives. The weighting of the objectives can be adjusted accordingly during operation, for example depending on energy costs, use cases, aging of the units or other factors, so that the operating strategy also adapts accordingly.

According to one embodiment, the control device is further designed to determine control variables for one or more valves in the cathode path of the fuel cell system by means of multi-objective optimization. By appropriately controlling the valves and any throttle valves present in the cathode path of the fuel cell system, further control parameters are available for adjusting the gas flow in the cathode path. In this way, the required setpoint specifications and optimizations can be better achieved.

According to one embodiment, the control device is designed to determine the control variables for the at least two air compressor units using exhaust air flows available on turbo units of the air compressor units. By using such turbo units on the air compressor units, an additional or alternative option for driving the air compressor units is available. This allows kinetic energy of the gas flow in the exhaust air path of the cathode path to be used to drive the air compressor units. This can also be taken into account when optimizing the control variables for the air compressor units and, if applicable, the valves in the cathode path.

According to one embodiment, the multi-objective optimization includes minimizing a cost function for the parameters to be optimized. As already explained at the beginning, by setting up a suitable cost function and minimizing it in a suitable manner, an optimization of preferably several objectives can be achieved and at the same time the determination of requested control variables for the air compressor units in the cathode path of a fuel cell system can be achieved.

According to one embodiment, the multi-objective optimization includes a model predictive control (MPC), a moving horizon estimation (MHE) method or a reinforcement learning (RL) method. These methods are well suited to implementing multi-variable control while simultaneously optimizing one or more objectives.

The above embodiments and developments can be combined with one another as desired, provided this makes sense. Further embodiments, developments and implementations of the invention also include combinations of features of the invention described above or below with regard to the exemplary embodiments that are not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

Short description of the drawings

• 1: eine schematische Darstellung eines Blockschaubilder Brennstoffzellensystems gemäß einer Ausführungsform;
• 2: eine schematische Darstellung eines Blockschaubilder Brennstoffzellensystems gemäß einer weiteren Ausführungsform; und
• 3: ein Ablaufdiagramm, wie es einem Verfahren zur Steuerung eines Brennstoffzellensystems gemäß einer Ausführungsform zugrunde liegt.

Further features and advantages of the invention are explained below with reference to the figures.

• 1 : a schematic representation of a block diagram fuel cell system according to an embodiment;
• 2 : a schematic representation of a block diagram fuel cell system according to another embodiment; and
• 3 : a flow chart underlying a method for controlling a fuel cell system according to an embodiment.

Description of embodiments

1 shows a schematic representation of a block diagram of a fuel cell system 1 according to an embodiment. The fuel cell system 1 comprises a fuel cell unit 30, an anode path 20 with a supply line 21 and a discharge line 22 for an anode gas, for example hydrogen. Furthermore, the fuel cell system 1 comprises a cathode path 10 with a supply line 11 and a discharge line 12 for a cathode gas, in particular air. The fuel cell unit 30 can comprise several fuel cell stacks 31, 32. The number of two fuel cell stacks 31, 32 shown here are merely a schematic example and do not represent a restriction of the present invention. If several fuel cell stacks 31, 32 are provided, they can be individually supplied with anode gas and cathode gas. Accordingly, individual setpoints are also possible for the individual fuel cell stacks 31, 32, for example for inlet pressure, pressure difference between inlet and outlet, moisture content of the cathode gas, etc.

At the cathode inlet of the fuel cell unit 30 or the fuel cell stacks 31, 32, the cathode gas, for example ambient air, can be provided via the supply line 11 of the cathode path 10. The cathode gas can be compressed via several air compressor units 101, 102 provided in the cathode path 10. In this way, the cathode gas can be provided at the inlets of the fuel cell stacks 31, 32 according to predetermined target values such as pressure, mass flow, moisture content, etc.

The air compressor units 101, 102 can each be driven by an electric machine. For example, electric drive systems with an electric machine and an upstream power converter are possible for this purpose. The control of the several air compressor units 101, 102 connected in series takes place, for example, via a control device 15. The control device 15 can control the individual air compressor units 101, 102 in such a way that the cathode gas is provided at the inputs of the fuel cell stacks 31, 32 according to predetermined target values.

Due to the high complexity of such a fuel cell system 1, the control device 15 must take a large number of setpoints into account when controlling the air compressor units 101, 102. For example, individual specifications for the gas mass flow at the individual cathode inlets of the fuel cell stacks 31, 32 can be specified as setpoints. Alternatively, corresponding variables such as volume flow, molar flow, or the like can also be specified. Furthermore, a pressure for the individual inlets of the cathodes of the fuel cell stacks 31, 32 can be specified as a setpoint. Alternatively, pressure differences or other specifications for pressure ratios can also be specified. Furthermore, a setpoint for a humidity at the inlets of the cathode of the fuel cell stacks 31, 32 can also be specified, for example. Alternatively, information such as the water content of the cathode gas, specifications for an activity of the cathode gas, or the like can also be specified. The aforementioned information can be specified individually for each fuel cell stack 31, 32 of the fuel cell unit 30. Furthermore, for example, a gas mass flow can also be specified for the fuel cell unit 30 at an inlet point of a purge gas. Alternatively, a volume flow, molar flow or similar can also be specified at this inlet point.

When determining the control variables for the air compressor units 101, 102, in particular for the electric drives of these air compressor units 101, 102, the energy requirement of the air compressor units 101, 102 can also be taken into account. In particular, optimization can be carried out in order to minimize the total energy requirement of the drives for the air compressor units 101, 102 and, if necessary, to optimize other goals.

To determine the suitable control variables for controlling the air compressor units 101, 102, in particular the electric drives of these air compressor units 101, 102, a so-called multi-objective optimization can be used. For this purpose, for example, a cost function can be defined which includes as a target the energy requirement of the two air compressor units for the fuel cell system 1, in particular with respect to the cathode path 10. This cost function provides the energy requirement of the individual air compressor units 101, 102 in the cathode path 10. To minimize the total energy requirement, such a cost function can then be minimized. For example, the cost function can be integrated over a predetermined time interval and an optimal operating strategy for minimizing this integration of the cost function can be sought.

If it is not possible to fully meet all setpoint specifications when determining the control variables for the air compressor units 101, 102, individual setpoint specifications can be prioritized, for example. In this way, it can be ensured that particularly important parameters, such as the oxygen provided in the fuel cell stacks 31, 32, are provided with sufficient precision, even if, for example, other parameters, such as moisture content or similar, cannot be fully met in accordance with the setpoint specifications.

2 shows a schematic representation of a block diagram of a fuel cell system 1 according to a further embodiment. The fuel cell system 1 according to 2 differs from the previously described embodiment in that components designated as turbo units 111, 112 are provided on the air compressor units 101, 102. These turbo units 111, 112 are components which are generated by using the output gas flow in the discharge path 12 of the cathode the path 10 of the fuel cell unit 30 can drive the air compressor units 101, 102 or can at least support the electrical drive of the air compressor units 101, 102. However, the basic principle of a turbocharger or similar is assumed to be known here and therefore will not be explained further.

Furthermore, several valves 121 to 124 can be provided in the fuel cell system 1, in particular in the cathode path 10 of the fuel cell system 1. The four valves shown here are to be understood as examples only. In principle, any other number of valves can also be provided. The position of the valves is also not limited to the illustration according to 2 limited. By appropriately controlling such valves 121 to 124, the gas flow in the cathode path 10 can be adjusted. For example, the amount of gas provided to the turbo units 111, 112 can be adjusted and thus the drive energy provided by the turbo units 111, 112 to drive the air compressor units 101, 102 can be adjusted. These parameters for controlling the valves 121 to 124 and the resulting gas flows can also be taken into account and adjusted by the control device 15. In particular, this parameterization can also be included in the multi-objective optimization for determining the manipulated variables for the air compressor units 101, 102. For example, a model predictive control (MPC), a moving horizon estimation (MHE) or a reinforcement learning (RL) method can be used as a method for multi-objective optimization.

In addition to the previously mentioned target values for controlling the air compressor units 101, 102, any other optimization goals can also be taken into account. For example, in addition to the previously mentioned optimization of the energy requirement for the air compressor units 101, 102, additional optimization goals can be pursued.

For example, the gas mass flow or the oxygen mass flow in the cathodes of the fuel cell stacks 31, 32 can be of very high relevance. Accordingly, in order to optimize the control and the resulting determination of the target values for such a parameter of the oxygen provided in the cathode gas, the goal can be to control this target value as precisely as possible.

Furthermore, for example, individual loads of the individual air compressor units 101, 102 and a possible imbalance in the load caused by the corresponding drives of the air compressor units 101, 102 can also be taken into account. For this purpose, the optimization goal can be to achieve the most uniform possible load of the air compressor units 101, 102 provided in the cathode path 10 - at least as long as this does not conflict with further optimization goals.

Since the start-up/starting and the running-down/stopping of the air compressor units 101, 102 represent a high load on the respective components due to their design and can therefore lead to increased aging, a possible reduction of such start-stop processes including balancing can also be considered as a further optimization goal.

Furthermore, properties relating to the dynamics of the fuel cell system 1 can also be taken into account during optimization. If, for example, the fuel cell system 1 is intended to supply energy to a system such as an electrically powered motor vehicle which is operated with an at least approximately constant energy requirement over a period of time to be considered, an operating strategy with low requirements in terms of dynamics can also be set when controlling the fuel cell system and in particular the air compressor units 101, 102 in the cathode path 10. For this purpose, the operating strategy can be adapted, for example, so that the target variables such as pressure and mass/volume flows only vary with a relatively small time constant. If, on the other hand, larger performance fluctuations are to be expected in the system supplied with energy by the fuel cell system 1, an operating strategy with greater dynamics in the variables of the fuel cell system, in particular the cathode path 10, can also be provided as an optimization goal. This can be the case, for example, when selecting a sporty driving mode of an electric vehicle.

In addition, any other optimization goals are of course possible when determining the control variables for the fuel cell system 1, in particular the cathode path 10 and the air compressor units 101, 102 provided therein.

The optimization goals described can each be given individual weighting factors or priorities. In particular, optimization goals that are temporarily irrelevant can be given a correspondingly low factor down to zero.

In order to determine optimal target values for the air compressor units 101, 102 and possibly other components such as valves or similar in the cathode path 10 of the fuel cell system 1, the respective optimization goals can be included in the cost function for multi-goal optimization. The individual optimization goals can be individually weighted according to the weighting factors already mentioned. By minimizing the cost function obtained in this way, it is possible to achieve the most efficient control possible of the air compressor units 101, 102 and possibly other components in the cathode path 10 of the fuel cell system 1, even with a large number of individual target value specifications and optimization goals. In addition, the adaptive cost function enables the operating strategy to be adapted to the respective system state (e.g. aging), the respective driving cycles and the system boundary conditions.

3 shows a flow chart as it is based on a method for controlling at least two electrically driven air compressor units 101, 102 in a cathode path 10 of a fuel cell system according to an embodiment. The method can basically comprise any steps that are required to implement the previously described fuel cell system 1 and the operating strategy for controlling the air compressor units 101, 102. Analogously, the previously described fuel cell system 1 can also comprise any components that are required to implement the method described below.

In a step S1, several setpoint specifications for the fuel cell system 1, in particular for the cathode path 10 in the fuel cell system 1, are received. Then, in step S2, individual control variables are determined for each of the at least two air compressor units 101, 102 in the cathode path 10 of the fuel cell system 1. The individual control variables for the at least two air compressor units 101, 102 are determined using several setpoint specifications by means of a multi-objective optimization to minimize a total electrical power requirement of the several air compressor units 101, 102.

The multi-objective optimization can be carried out, for example, using the cost function described above to minimize the total energy requirement and, if necessary, any other optimization goals. If necessary, control variables for other components in the cathode path 10 of the fuel cell system 1 can also be determined, in particular control variables that are suitable for achieving the specified optimization goals.

In summary, the present invention relates to the control of air compressor units in a fuel cell system which has several air compressor units arranged in series in a cathode path. For this purpose, it is provided to determine the control variables for the air compressor units on the basis of a multi-objective optimization, whereby a total power consumption for the air compressor units can be minimized.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102011087912 A1 [0003]

Claims (11)

Control device (15) for a fuel cell system (1) with at least two electrically driven air compressor units (101, 102), wherein the control device (15) is designed to determine an individual control variable for each of the at least two air compressor units (101, 102), and wherein the individual control variables for the at least two air compressor units (101, 102) are determined using a plurality of setpoint specifications by means of a multi-objective optimization to minimize a total electrical power requirement of the air compressor units (101, 102) using at least one further optimization objective. Control device (15) according to Claim 1 , wherein the plurality of setpoint specifications comprise at least two of the following setpoint specifications or a variable derived therefrom: a gas mass flow at a stack inlet of the cathode of a fuel cell stack, a pressure or a pressure difference at a stack inlet of the cathode of a fuel cell stack (31, 32), a water content of the fluid at a stack inlet of the cathode of a fuel cell stack (31, 32), a gas mass flow at an introduction point of a purge gas in the cathode path (10) of the fuel cell system (1). Control device (15) according to Claim 1 or 2 , wherein the control device (15) is designed to determine the manipulated variables for the at least two air compressor units (101, 102) further using at least one of the following optimization objectives: accuracy for the respective setpoint specifications, dynamics for the control behavior of the fuel cell system (1), load differences between the air compressor units (101, 102), and/or a number of start/stop processes of the air compressor units (101, 102). Control device (15) according to one of the Claims 1 until 3 , wherein the multi-objective optimization comprises a prioritization of the multiple setpoint specifications and/or a prioritization or weighting of the optimization objectives. Control device (15) according to one of the Claims 1 until 4 , wherein the control device (15) is further designed to determine control variables for one or more valves (121 - 124) in a cathode path (10) of the fuel cell system (1) by means of multi-objective optimization. Control device (15) according to one of the Claims 1 until 5 , wherein the control device (15) is designed to determine the control variables for the at least two air compressor units (101, 102) further using exhaust air flows available at turbo units (111, 112) of the air compressor units (101, 102). Control device (15) according to one of the Claims 1 until 6 , where multi-objective optimization involves minimizing a cost function for the parameters to be optimized. Fuel cell system (1), comprising: a fuel cell unit (30) with at least one fuel cell stack (31, 32); a cathode path (10) which is designed to provide a cathode gas in the fuel cell unit (30), wherein the cathode path comprises at least two electrically driven air compressor units (101, 102); an anode path (20) which is designed to provide an anode gas in the fuel cell unit (30); and a control device (15) according to one of the Claims 1 until 8th . Fuel cell system (1) according to Claim 8 , wherein the fuel cell unit (30) comprises a plurality of fuel cell stacks (31, 32), and the control device (15) is designed to determine the control variables for the air compressor units (101, 102) using individual setpoint values for the plurality of fuel cell stacks (31, 32). Method for controlling at least two electrically driven air compressor units (101, 102) in a cathode path (10) of a fuel cell system (1), comprising the steps of: Receiving (S1) a plurality of setpoint specifications for the fuel cell system (1); Determining (S2) individual control variables for each of the at least two air compressor units (101, 102) in the cathode path (10), wherein the individual control variables for the at least two air compressor units (101, 102) are determined using a plurality of setpoint specifications by means of a multi-objective optimization to minimize a total electrical power requirement of the plurality of air compressor units (101, 102) taking into account at least one further optimization objective. Procedure according to Claim 10 , whereby the determination of the manipulated variables is carried out using a model predictive control, a moving horizon estimation procedure or a reinforcement learning procedure.

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