METHOD FOR ASCERTAINING THE RELATIVE HUMIDITY AT A CATHODE INLET OF A FUEL CELL STACK OF A FUEL CELL SYSTEM

Abstract

The present method relates to a method for ascertaining the relative humidity (RH) at a cathode inlet (113) of a fuel cell stack (110) of a fuel cell system (100), having the following steps: detecting at least one physical supply air parameter (ZP) of a supply air (ZU) to the cathode inlet (113), detecting a supply air mass flow (ZM) of the supply air (ZU), determining a supply air water mass flow (ZWM) on the basis of the at least one supply air parameter (ZP) detected and of the supply air mass flow (ZM) detected, detecting at least one physical cathode inlet parameter (KP) at the cathode inlet (113), determining a humidifier water mass flow (BWM) on the basis of the at least one cathode inlet parameter (KP) detected using a humidifier characteristic map (BK), ascertaining the relative humidity (RH) at the cathode inlet (113) on the basis of the supply air water mass flow (ZWM) determined, the humidifier water mass flow (BWM) determined and the at least one cathode inlet parameter (KP) detected.

Claims

1. Method for ascertaining the relative humidity (RH) at a cathode inlet of a fuel cell stack of a fuel cell system, having the following steps: detecting at least one physical supply air parameter (ZP) of a supply air (ZU) to the cathode inlet, detecting a supply air mass flow (ZM) of the supply air (ZU), determining a supply air water mass flow (ZWM) on the basis of the at least one supply air parameter (ZP) detected and of the supply air mass flow (ZM) detected, detecting at least one physical cathode inlet parameter (KP) at the cathode inlet, determining a humidifier water mass flow (BWM) on the basis of the at least one cathode inlet parameter (KP) detected using a humidifier characteristic map (BK), ascertaining the relative humidity (RH) at the cathode inlet on the basis of the supply air water mass flow (ZWM) determined, the humidifier water mass flow (BWM) determined and the at least one cathode inlet parameter (KP) detected.

2. Method according to claim 1, wherein at least one of the following is used as supply air parameter (ZP): supply air temperature (ZPT) supply air pressure (ZPP) relative supply air humidity (ZPH)

3. Method according to claim 1, wherein at least one of the following is used as cathode inlet parameter (KP): current requirement (KPI) cathode inlet temperature (KPT) cathode inlet pressure (KPP)

4. Method according to claim 1, characterised in that an additional characteristic map (ZK) is used to determine the supply air water mass flow (ZWM) and/or to ascertain the relative humidity (RH) at the cathode inlet.

5. Method according to claim 1, wherein a humidifier characteristic map (BK) specific to the fuel cell stack and/or the fuel cell system is used.

6. Method according to claim 1, wherein the humidifier characteristic map (BK) is at least partially in the form of a weighted neural network.

7. Method according to claim 1, wherein the relative humidity (RH) ascertained is compared with at least one limit value, wherein a control signal is generated in the event that the at least one limit is exceeded.

8. Ascertaining device for ascertaining the relative humidity (RH) at a cathode inlet of a fuel cell stack of a fuel cell system, comprising a supply air module for detecting at least one physical supply air parameter (ZP) of a supply air (ZU) to the cathode inlet and detecting a supply air mass flow (ZM) of the supply air (ZU), further comprising a supply air determining module for determining a supply air water mass flow (ZWM) on the basis of the at least one supply air parameter (ZP) detected and the supply air mass flow (ZM) detected, further comprising a cathode inlet module for detecting at least one physical cathode inlet parameter (KP) at the cathode inlet, further comprising a cathode inlet determining module for determining a humidifier water mass flow (BWM) on the basis of the at least one cathode inlet parameter (KP) detected using a humidifier characteristic map (BK), further comprising an ascertaining module for ascertaining the relative humidity (RH) at the cathode inlet on the basis of the determined supply air water mass flow (ZWM), the humidifier water mass flow (BWM) determined and the at least one cathode inlet parameter (KP) detected.

9. Ascertaining device according to claim 8, wherein the supply air module, the supply air determining module, the cathode input module, the cathode inlet determining module and/or the ascertaining module are designed to carry out a method for ascertaining the relative humidity (RH) at a cathode inlet of a fuel cell stack of a fuel cell system, having the following steps: detecting the at least one physical supply air parameter (ZP), detecting the supply air mass flow (ZM), determining the supply air water mass flow (ZWM) on the basis of the at least one supply air parameter (ZP) detected and of the supply air mass flow (ZM) detected, detecting the at least one physical cathode inlet parameter (KP).

10. Ascertaining device according to claim 8, wherein a supply air sensor device is provided to detect the at least one physical supply air parameter (ZP) and/or the supply air mass flow (ZM).

11. Ascertaining device according to claim 8, wherein a cathode inlet sensor device is provided to detect the at least one cathode inlet parameter (KP).

12. A generation method for generating a humidifier characteristic map (BK) for use in a method having the features of claim 1, comprising the following steps: operating a fuel cell stack (110) on a test bench, detecting the at least one physical supply air parameter (ZP), detecting the supply air mass flow (ZM), detecting the at least one physical cathode inlet parameter (KP), detecting the relative humidity (RH) at the cathode inlet (113), storing the relationships between the relative humidity (RH) detected and the at least one physical supply air parameter (ZP) detected, the supply air mass flow (ZM) detected and the at least one physical cathode inlet parameter (KP) detected in a humidifier characteristic map (BK).

Description

[0045] Further advantages, features and details of the invention are explained in the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description may in each case be essential to the invention individually or in any combination. In each case schematically:

[0046] FIG. 1 shows an embodiment of an ascertaining device according to the invention,

[0047] FIG. 2 shows a detail of a method according to the invention,

[0048] FIG. 3 shows a detail section of a method according to the invention,

[0049] FIG. 4 shows a further detail section of a method according to the invention,

[0050] FIG. 5 shows a further detail section of a method according to the invention,

[0051] FIG. 6 shows a further detail section of a method according to the invention,

[0052] FIG. 7 shows a further detail section of a method according to the invention.

[0053] FIG. 1 shows, schematically, how a part of a fuel cell system 100 can be designed. Here, a fuel cell stack 110 is equipped with a plurality of individual fuel cells, not represented in detail, whereby the fuel cell stack 110 is divided into a cathode section 112 and an anode section 114. In order to perform the desired current-generating chemical reaction in a fuel cell stack 110, a supply and removal of the respective gases is provided. Decisive for the present invention is the cathode inlet 113 and the anode inlet 115. The key aspect here is the consideration of the cathode side, i.e. the cathode inlet 113. Here, supply air ZU is sucked in from the environment and loaded with additional moisture via a humidifier 120.

[0054] FIG. 1 shows, schematically, an ascertaining device 10 according to the invention. This is equipped with a supply air module 20, a supply air determining module 30, a cathode inlet module 40, a cathode inlet determining module 50 and an ascertaining module 60. The individual modules 20, 30, 40, 50, 60 will be explained in more detail later. A supply air sensor device 70 and a cathode inlet sensor device 80 are also provided here, which communicate in a signal-communicating manner with the ascertaining device 10 and record the desired parameters at the appropriate points.

[0055] FIG. 2 shows, schematically, the locations at which the required parameters can basically be recorded. Thus, the supply air parameter ZP and the supply air mass flow ZM are recorded in the region of the input for the supply air ZU, i.e., seen in the direction of flow, before the humidifier 120. At least one cathode inlet parameter KP is recorded downstream of the humidifier 120 in the direction of flow, in the region of the cathode inlet 113. It can already easily be seen here that no physical sensor needs to be arranged between the humidifier 120 and the cathode inlet 113 in order to ascertain the relative humidity.

[0056] According to the invention, in a first step the supply air water mass flow ZWM is determined in the supply air determining module 30, as shown in FIG. 3. At least one physical supply air parameter ZP and a supply air mass flow ZM are taken into account here in order to determine the supply air water mass flow ZWM, for example in an algorithmic relationship. In this embodiment, the supply air temperature ZPT, the supply air pressure ZPP and the relative supply air humidity ZPH are used as supply air parameters ZP.

[0057] As an alternative to the embodiment in FIG. 3, a variant is shown in FIG. 4 in which, in addition to or alternatively to an algorithmic relationship, an additional characteristic map ZK based on the input parameters leads to the determination of the supply air water mass flow ZWM.

[0058] FIG. 5 represents the second preparatory method step wherein, in the cathode inlet determining module 50, the cathode inlet parameters KP lead here to the determination of the humidifier water mass flow BWM. According to the invention, no algorithmic relationship is provided here, the humidifier characteristic map BK is used instead. In this case the cathode inlet temperature KPT, the cathode inlet pressure KPP and the current requirement KPI are used as cathode inlet parameters KPI.

[0059] FIG. 6 shows the combination of the determined values in the ascertaining module 60. The parameters supply air water mass flow ZWM and humidifier water mass flow BWM determined in the first two steps of the method are used here in addition to the already existing cathode inlet parameters KP, which have already been used once, in order to ascertain the relative humidity RH again by an algorithmic relationship or using an additional characteristic map ZK, not shown in detail. In this embodiment shown in FIG. 6, the cathode inlet temperature KPT and the cathode inlet pressure KPP are used by way of example as cathode inlet parameters KP.

[0060] Finally, FIG. 7 shows the combination of the preceding steps in an ascertaining device 10. Here again it can clearly be seen that the cathode inlet parameters KP, the supply air parameters ZP and the supply air mass flow ZM are received from outside of the ascertaining device 10. The relative humidity RH is output on the other side. Due to the two-stage nature of the method according to the invention, the supply air water mass flow ZWM and the humidifier water mass flow BWM are determined by the supply air determining module 30 and the cathode inlet determining module 50 within the ascertaining device, so to speak as intermediate results, which in the second stage of the method according to the invention are converted into the relative humidity RH via the ascertaining module 60.

[0061] The preceding explanation describes the present invention exclusively on the basis of examples. Naturally, individual features of the embodiments can, insofar as technically expedient, be combined freely with each other without departing from the scope of the present invention.

LIST OF REFERENCE SYMBOLS

[0062] 10 ascertaining device [0063] 20 supply air module [0064] 30 supply air determining module [0065] 40 cathode inlet module [0066] 50 cathode inlet determining module [0067] 60 ascertaining module [0068] 70 supply air sensor device [0069] 80 cathode inlet sensor device [0070] 100 fuel cell system [0071] 110 fuel cell stack [0072] 112 cathode section [0073] 113 cathode inlet [0074] 114 anode section [0075] 115 anode inlet [0076] 120 humidifier [0077] ZU supply air [0078] RH relative humidity [0079] ZP supply air parameter [0080] ZPT supply air temperature [0081] ZPP supply air pressure [0082] ZPH relative supply air humidity [0083] ZM supply air mass flow [0084] ZWM supply air water mass flow [0085] KP cathode inlet parameter [0086] KPI current requirement [0087] KPT cathode inlet temperature [0088] KPP cathode inlet pressure [0089] BK humidifier characteristic map [0090] BWM humidifier water mass flow [0091] ZK additional characteristic map