Patent Application
20240234759
The invention relates to a method for controlling a drying process of a fuel cell system, in particular during shutdown of the fuel cell system, preferably in preparation for a start, in particular a cold start, of the fuel cell system according to the disclosure. In addition, the invention relates to a corresponding control unit and a corresponding computer program product.
In vehicles, so-called fuel cell vehicles, in which the drive energy is supplied by one or more fuel cell systems, among other things, the oxidizing agent oxygen from the ambient air and hydrogen as the reducing agent or fuel are generally used to react in the fuel cell to form water (or water vapor) and thus to supply electrical power by electrochemical conversion. The fuel cell systems mostly comprise multiple fuel cells assembled into a stack. The challenge for mobile fuel cell systems is to start the system under all globally relevant conditions and when the vehicles are stationary for different lengths of time:
In so-called cold starts, also known as freeze starts, the focus, among other things, is on bringing the stack out of the freezing zone (temperature >0° C.) as quickly as possible, so that water produced does not freeze at critical locations in the stack. In the event of an incorrect freeze start, both the stack can suffer massively irreversible damage and the system cannot be started, i.e. the vehicle must be brought into a “warm” environment as quickly as possible during a freeze start. Mostly, it is important how much water the stack contains before the start or at the beginning of the start. This level of water should advantageously be within a tolerance range, so that the stack, on the one hand, can still store the water produced at the start in its storage components (such as e.g. membrane, gas diffusion layer, etc.), without getting blockages due to freezing water. On the other hand, the stack should also not be completely dried so that no proton conductivity of the membrane is possible and the membrane is damaged due to excessively dry conditions. Thus, upstream states and operating modes are essential to already ensure preparatory measures for the restart, such as e.g.:
The drying of the cathode path can be performed, for example, by means of an air compression system (for “blowing out” the stack) for a defined time.
The present invention provides: a method for controlling a drying process of a fuel cell system, in particular during shutdown of the fuel cell system, preferably in preparation for a start, in particular a cold start or a freeze start, of the fuel cell system having the features of the disclosure. In addition, the invention provides a corresponding control unit and a corresponding computer program. Of course, features and details described in connection with the different embodiments and/or aspects of the invention also apply in connection with the other embodiments and/or aspects of the invention, and respectively vice versa, so that with respect to the disclosure, mutual reference to the individual embodiments and/or aspects of the invention is or can always be made.
According to the first aspect, the present invention provides: a method for controlling a drying process of a fuel cell system, in particular during shutdown of the fuel cell system, preferably in preparation for a start, in particular a cold start of the fuel cell system.
The method comprises the following steps:
The steps of the method according to the invention can be performed in the specified order or in an amended order. The steps of the method according to the invention can be carried out simultaneously, at least in part concurrently, and/or sequentially.
The fuel cell system within the meaning of the invention can preferably be used for mobile applications, for example in vehicles, in particular fuel-powered vehicles. The fuel cell system within the meaning of the invention can serve as the main energy supplier for a vehicle. At the same time, however, it is also conceivable that the fuel cell system within the meaning of the invention can be a slave drive and/or auxiliary drive of a vehicle, for example a hybrid vehicle. The fuel cell system within the meaning of the invention can also be used for stationary applications, for example in generators.
The fuel cell system within the meaning of the invention can have one or more stacks each having multiple stacked fuel cells and the associated functional systems comprising: Media systems (air or cathode system, fuel or anode system, cooling system), as well as an electrical system. Preferably, the fuel cell system within the meaning of the invention can comprise multiple modules in the form of individual stacks having multiple stacked fuel cells.
The at least one functional system within the meaning of the invention can comprise a media system (containing: an air or cathode system, a fuel or anode system and a cooling system), as well as an electrical system.
The invention proposes to optimally control the drying process of the fuel cell system and, in particular, to end it in a suitable window of time so that the following advantages can be achieved, preferably such that:
The invention idea is to control the duration of the drying process based on temperature(s) in the anode path, in particular at the stack output, and/or temperature(s) in the cathode path, in particular at the stack output.
Preferably, the invention can provide for the setting of constant stack operating conditions in the functional systems of the fuel cell system, comprising:
Monitoring can in particular comprise:
The temperature(s), meaning in particular the output temperature(s), in the cathode path and/or in the anode path, can be sensed over time and can be used as function(s) or trajectory/trajectories depending on the time.
The evaluation can in particular comprise:
The temperature(s), in particular the function(s) or trajectory/trajectories of the temperature(s), in the cathode path and/or in the anode path can be evaluated with respect to the first derivative or the gradient, wherein in particular the evaluation can be outsourced at least in part or entirely to an external computing unit, e.g. a cloud.
Determining the termination time can include, in particular:
In addition, the method can be refined and/or plausibilized by a combination with further criteria, such as an evaluation (of the trajectory/trajectories of an impedance and/or a voltage.
It can further be provided in a method that when setting the at least one operating parameter, at least one of the following parameters is set to a constant level or a constant value:
In this way, conditions on and/or in the stack can be set as constant as possible, so that the output temperature(s) in the cathode path and/or in the anode path, in particular their derivatives or gradients, can be indicative of the progress of the drying process or of the residual moisture in the system. During the drying process or when blowing out the cathode system and/or anode system, moisture or water droplets are discharged in the cathode path and also in the anode path and thus also reach the temperature sensors downstream of the stack. Evaporation of this moisture results in a cooling effect (vaporization enthalpy of water is in the relevant range at 41 to 45 KJ/mol), whereby the sensors indicate a drop in temperature. The temperatures at the stack input are thereby above the temperatures at the stack output. In turn, the coolant can be at a higher temperature than the temperatures at the stack outlet, which the temperatures at the stack outlet would also approach, provided that the input conditions do not change or do not change significantly, and provided that little fuel or only pre-tempered fuel is added to the anode circuit. At the beginning of the drying process, the membrane, the gas diffusion layer, the channels or the complete surfaces of the bipolar plates are well supplied with moisture or wetted with water. After progressive drying, the unbound and thus easily transportable water decreases more and more. The gas mass flows in the cathode path and anode path remove fewer and fewer water droplets from the stack and the humidity downstream of the stack decreases. This also reduces the evaporation and, as a result, the temperature gradients at the stack output also decrease. If the gradients at the stack outlet drop below the applicable threshold values or if the output temperatures rise again, then the drying process has been sufficiently carried out. Further drying would dry out the membrane too much, possibly leading to increased degradation, undesirable fuel transport from anode to cathode, unnecessary fuel consumption, an unnecessary time requirement and unnecessary vibrations during shutdown of the system.
Advantageously, when setting the at least one operating parameter, at least one parameter of different functional systems can be set simultaneously, at least partially at the same time, or sequentially. In this way, control of the drying process can be facilitated in a flexible manner.
Preferably, prior to initiating the drying process, at least one preparation step can be performed to, in particular, set or at least bring the at least one operating parameter to a desired level in at least one functional system of the fuel cell system. In this way, constant conditions in the system can be set relatively quickly after the initiation of the drying process and the method can be performed in a time-saving manner.
Furthermore, it is conceivable that different parameter sets of the at least one operating parameter are used when performing the method, and/or that different values of the at least one operating parameter are used when performing the method, in particular sequentially, preferably with a transient transition without evaluation. In this way, the drying process can be carried out in stages, which is gentle on the stack.
As already mentioned above, when monitoring the at least one outlet temperature:
Advantageously, when evaluating the at least one outlet temperature, at least one gradient of a temperature function and/or a temperature difference can be evaluated between at least two points of a temperature function. The gradients that drop and approach zero with the time of the drying process can be indicative of sufficient progress of the drying process, and thus for an appropriate termination time of the drying process. By monitoring the temperature difference, the results of the method can be refined.
Preferably, when evaluating the at least one outlet temperature, at least one threshold value, in particular for the gradient of a temperature function, can be monitored for undershooting. This can be a computationally simple and reliable method for determining sufficient progress of the drying process and thus an appropriate termination time of the drying process.
Furthermore, it can be contemplated that when monitoring the at least one outlet temperature, an outlet temperature in a cathode system and an outlet temperature in an anode system of the fuel cell system (or both outlet temperatures of the reactant paths at the stack output) are sensed,
The drying process can thus be carried out variably, providing refined results, and being appropriately ended or ended in a timely manner.
In addition, it is contemplated that when determining the termination time for ending the drying process, a theoretically determined time is used depending on the evaluation, wherein preferably:
In the former case, a quick implementation of the method can be enabled. In the latter case, any uncertainties from the evaluation and/or three-dimensional distribution of the thermodynamic variables in the stack can still be compensated for.
In addition, it is contemplated that after the end of the drying process, at least one further shutdown process will be performed, for example comprising:
In this way, the shutdown process of the fuel cell system can be combined with further advantageous actions in addition to the optimized drying process.
To further refine the method, it can be contemplated that in addition to monitoring and evaluating the at least one outlet temperature, at least one further operating parameter of the fuel cell system is monitored and evaluated, comprising:
The method can thus be combined with further triggers or diagnostics or monitoring functions. By combining several criteria, the duration of the drying process can be adapted even more robustly.
Furthermore, it is contemplated that when multiple operating parameters of the fuel cell system are monitored and evaluated,
In the former case, a refined and at the same time relatively fast implementation of the method can be enabled. In the latter case, the method can provide particularly robust and reliable results.
Advantageously, the method, which can proceed as described above, can at least in part, in particular in part, be performed for: evaluation and/or determination, using an external computing unit, in particular a cloud.
The method can further be performed at least in part, comprising initiating, setting, and/or monitoring, by a control unit of the fuel cell system.
A corresponding control unit provides a further aspect of the invention. A computer program can be stored in a memory unit of the control unit in the form of a code, which, when the code is executed by a computing unit of the control unit, carries out a method that can proceed as described above. Using the control unit according to the invention, the same advantages can be achieved as described above in connection with the method according to the invention. In the present case, reference to these advantages is made in full.
The control unit can be in a communication link with temperature sensors at the stack output of the cathode system and/or the anode system to interrogate and/or obtain, for example, the output temperatures. The control unit can control the actuators in the functional systems of the fuel cell system accordingly to perform the method accordingly.
In addition, the control unit can be in a communication link with an external computing unit in order to outsource some method steps and/or calculations, in whole or part, to the external computing unit.
According to a further aspect, the invention provides a computer program product comprising instructions that, when the computer program is executed by a computer, such as e.g. the computing unit of the control unit, causes the computer to perform the method which can proceed as described above. Using the computer program product, the same advantages can be achieved as described above in connection with the method according to the invention and/or the control unit according to the invention. In the present case, reference to these advantages is made in full.
The invention and its further developments, as well as its advantages, are explained in further detail below with reference to the drawings. The drawings schematically show:
In the various figures, like parts of the invention are always given the same reference numbers, for which reason they are typically only described once.
The fuel cell system 100 comprises a cathode system 1 having a supply line 11 to the stack 101 and an exhaust line 12 from the stack 101. An air filter AF is usually arranged at the inlet of the supply line 11 in order to filter harmful chemical substances and particles or to prevent their entry into the system 100.
The gas conveying machine V in the cathode system 1 can be embodied in the form of a compressor to draw air from the environment U and provide it to the stack 101 in the form of incoming air. After passing through the stack 101, exhaust air from the system 100 is released back to the environment U.
As
Shut-off valves SV1, SV2 can be provided upstream and downstream of the fuel cell stack or stack 101. In addition, a CVexh valve can be provided as a pressure regulator in the exhaust line 12.
Multiple sensors can also be provided in the supply line 11 and/or in the exhaust line 12, such as e.g. moisture sensors, temperature sensors, pressure sensors, mass and/or volume sensors, etc. All sensors are not shown in
A bypass line 13 with a bypass valve ByCath can be provided between the supply line 11 and the exhaust line 12. For example, the bypass line 13 can be used for mass flow control in the cathode system 1 and/or for diluting the exhaust air, which can contain hydrogen, from the fuel cell stack or stack 101.
The anode system 3 comprises multiple components. The components used in order to supply fuel include a fuel tank 31 and at least a pressure regulator 32. The pressure regulator 32 can also have a shut-off function. If the pressure regulator 32 does not have a shut-off function, a separate shut-off valve can be provided at the input to the anode space or anode path A.
Further components in the anode system 3 are a jet pump 33 and a recirculation pump 34. In addition, a purge and/or drain valve 35 can be provided in the anode system 3.
Using
The method comprises the following steps:
The invention thus enables the optimal control of the drying process of the fuel cell system 100 and, in particular, to end it at an appropriate termination time tdryEnd.
Using the invention, the following advantages can be achieved so that:
Advantageously, the duration of the drying process is controlled based on temperature(s) in the anode system 3, in particular at the stack output TAnodOut, and/or temperature(s) in the cathode system 1, in particular at the stack output TCathOut.
As schematically indicated in
The method can provide that when setting at least one operating parameter is set i, ii, iii, at least one of the following parameters is set to a constant level or a constant value:
In this way, conditions as constant as possible can be set on and/or in the stack 101 in order to monitor and evaluate the output temperature(s) TCathOut, TAnodOut in the cathode path K and/or in the anode path A, in particular their derivations dT(t)/dt and/or gradients.
Consequently, the output temperature(s) TCathOut, TAnodOut in the cathode path K and/or in the anode path A, in particular their derivatives dT(t)/dt or gradients, can be indicative factors for the progress of the drying process or for the residual moisture in the system 101.
During the drying process or when blowing out the cathode system 1 and/or anode system 3, moisture or water droplets are discharged from the cathode path K and also from the anode path A and thus also reach the temperature sensors S1, S3 downstream of the stack 101. Evaporation of this moisture results in a cooling effect on the sensors S1, S3, whereby the sensor values indicate a decrease (dT(t)/dt<0) of the temperature T. The temperatures at the stack input are above the temperatures TCathOut, TAnodOut at the stack output. The coolant, in turn, can have a higher temperature TCoolIn than the temperatures TCathOut, TAnodOut at the stack output, as
At the beginning of the drying process, the membrane, the gas diffusion layer, the channels or the complete surfaces of the bipolar plates are well supplied with moisture or wetted with water. As the drying process progresses, the unbound and thus easily transportable water decreases more and more. The gas mass flows in the cathode path K and anode path A remove fewer and fewer water droplets from the stack 101 and the humidity downstream of the stack 101 decreases. This also reduces the evaporation and the temperature gradients dTCathOut(t)/dt, dTAnodOut(t)/dt at the stack output also decrease along with this, as
If the temperature gradients dTCathOut(t)/dt, dTAnodOut(t)/dt at the stack output drop, e.g. below applicable thresholds values tdryEndEvalAnod, tdryEndEvalCath, or if the temperatures TCathOut, TAnodOut rise again, then the drying process has been performed sufficiently.
Further drying would dry out the membrane too much, possibly leading to increased degradation, fuel transport from anode space A to cathode space K, unnecessary fuel consumption, unnecessary time required and unnecessary vibrations during shutdown of the system 100.
The parameters of different functional systems 1, 2, 3, 4 can be set simultaneously, at least partially at the same time, or sequentially.
As further schematically indicated in
It is further contemplated that different parameter sets P1-A, P1-B of the at least one operating parameter i, ii, iii and different values P1-A, P1-B of the at least one operating parameter i, ii, iii are used when performing the method. In this case, the different values P1-A, P1-B can advantageously be initiated sequentially, preferably with a transient transition, in particular without evaluation. Thus, it can be possible to perform the drying process in stages.
As further indicated schematically in
As further indicated schematically in
As indicated in
As also indicated in
As further shown schematically in
In addition,
In addition,
In addition,
When multiple operational parameters TCathOut, TAnodOut, Z1, Z2, Z3 of the fuel cell system 100 are monitored and evaluated, the method can provide that:
An example of the quality function G can be depicted as follows:
For a quality function G, the criteria K1, K2, K3, K4, K5 (i.e., the operating parameters TCathOut, TAnodOut, Z1, Z2, Z3) can be used as continuous variables or converted as normalized variables (e.g., degree of performance k, %). In addition, the criteria K1, K2, K3, K4, K5 can be weighted (g). Parameter b can stand for a plausible determination (and availability) (b=0 or b=1), so that only the criteria that are available and plausible during the current evaluation are applied. For example, a sensor could freeze and become implausible. In this case, the parameter would be b=0.
If the quality function is G>Glim, the drying process is then ended directly or after another time dtadditional.
The above description of the figures describes the present invention solely in the context of examples. Of course, individual features of the embodiments can be freely combined with one another, insofar as technically sensible, without leaving the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 204 910.9 | May 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/059480 | 4/8/2022 | WO |
