Method for regenerating a vehicle's fuel cell

Abstract

The invention relates to a method for regenerating a fuel cell of a vehicle, wherein the vehicle comprises at least one fuel cell system comprising a fuel cell, a fuel cell cooling circuit associated with the fuel cell, and a fuel cell controller, wherein the vehicle has an electrical energy storage device that can be electrically charged by the fuel cell, wherein the vehicle has an electric drive that can be supplied with electrical energy solely by the fuel cell, solely by the energy storage device, and in hybrid operation by the fuel cell and the energy storage device, and wherein the vehicle comprises a vehicle controller.

Description

[0001] The invention relates to a method for regenerating a fuel cell of a vehicle.

[0002] The use of fuel cells is well-known in vehicles. Such vehicles usually comprise a fuel cell and an electrical energy storage system.

[0003] When using fuel cells, degradation can never be completely avoided. The underlying physical mechanisms of this degradation are essentially the drying out of the fuel cell membrane and the adsorption of chemical compounds onto the surface of the fuel cell catalyst.

[0004] Such degradations are at least partially reversible and can be reversed through regeneration, for example by re-wetting the membrane and electrochemically removing the catalyst poisoning, thereby improving the efficiency of the fuel cell.

[0005] In known systems, the operating states of a fuel cell in a vehicle can depend on the driver's load demand. This results in dynamic operation of the fuel cell. Controlling specific operating states of the fuel cell would restrict the driver's vehicle use. Therefore, protocols or operating modes of the fuel cell that need to be regulated for regenerating the reduced fuel cell power resulting from reversible degradation can only be set to a limited extent, or possibly not at all.

[0006] One object of an embodiment of the invention is to propose a method for regenerating a fuel cell of a vehicle in which the vehicle can be used without restriction during the regeneration of the fuel cell.

[0007] This problem is solved by a method for regenerating a fuel cell of a vehicle, wherein the vehicle has at least one fuel cell system comprising a fuel cell, a fuel cell cooling circuit associated with the fuel cell, and a fuel cell controller, wherein the vehicle has an electrical energy storage device that can be electrically charged by the fuel cell, wherein the vehicle has an electric drive that can be supplied with electrical energy solely by the fuel cell, solely by the energy storage device, and in hybrid operation by the fuel cell and the energy storage device, and wherein the vehicle comprises a vehicle controller, comprising the steps: a. 100: Receipt of a request from the fuel cell control by the vehicle control to perform a regeneration operation for a regeneration period in which the relative humidity at the fuel cell is at its maximum and in which the fuel cell reaches or falls below a cooling temperature; b. 102: Recording the heat input into the fuel cell system, at least through the fuel cell in an actual operating state; recording a maximum possible heat output from the fuel cell system, at least through the fuel cell cooling circuit; and calculating a minimum temperature adjustable at the fuel cell. c. 103: Performing the regeneration operation when the calculated adjustable minimum temperature is less than or equal to the cooling temperature and when, over the regeneration duration of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and from the actual power provided by the energy storage from the actual energy content of the electrical energy storage is greater than the actual electrical power requirement of the vehicle; or d. 104: Rejection of the request by the vehicle control if the calculated adjustable minimum temperature is greater than the cooling temperature or if, over the regeneration period of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and from the actual power of the energy storage provided from the actual energy content of the electrical energy storage is less than the electrical actual power requirement of the vehicle.

[0008] Because the process allows the fuel cell controller to send and receive a request to initiate a regeneration cycle from the vehicle control unit, and because the vehicle control unit checks whether a regeneration cycle is possible in step 103 and whether the vehicle's actual power requirement is simultaneously met, a fuel cell regeneration cycle is only performed if the conditions are right. This ensures that the vehicle user does not experience any noticeable driving effects, for example, if the electric drive's actual power requirement is high due to a user demand, but this power cannot be provided because of a regeneration cycle.

[0009] Furthermore, this ensures that the fuel cell system can be adapted to the required thermal state at the time of the request.

[0010] By ensuring maximum relative humidity at the fuel cell during regeneration and maintaining a cooling temperature throughout the regeneration process, humid operating conditions can be maintained. This reduces reversible degradation at the fuel cell, particularly the humidification of the fuel cell membrane and the adsorption of chemical compounds onto the surface of the fuel cell catalyst (catalyst poisoning). These compounds can be reduced through chemical reduction reactions due to the controlled cooling temperature and high humidity, or washed off the outside of the fuel cell membrane by the moisture.

[0011] Physically, both the energy storage device and the fuel cell provide electrical power in watts (or kilowatts). This power is measured in terms of the instant it is being delivered. In this case, an electric current flows at a given voltage, the product of which is the electrical power. In contrast to the fuel cell, the energy storage device stores electrical energy. The energy storage device can include a battery. The fuel cell is a power converter and cannot store electrical energy. The fuel cell electrochemically converts, for example, hydrogen and oxygen into electricity, water, and heat.

[0012] If the vehicle control unit cannot grant the request from the fuel cell control unit, it can be checked whether conditions suitable for carrying out the regeneration operation can be created. In one embodiment of the method, this can involve determining a target energy content of the electrical energy storage system, where, over the duration of the regeneration operation, the sum of the power supplied from the actual power of the fuel cell and the actual power provided by the energy storage system from its actual energy content is greater than the vehicle's actual electrical power requirement when determining a target power of the fuel cell where the minimum temperature is less than or equal to the cooling temperature.

[0013] By determining the target energy content of the electrical energy storage system, it is possible to determine whether the electrical energy storage system can be prepared accordingly to meet the actual power requirements of the vehicle during regeneration operation, either alone or with significant contributions, over the regeneration period.

[0014] If the target energy content is higher than the actual energy content, regeneration can be ensured by raising the actual energy content of the electrical energy storage system to the target energy content. However, if the determined target energy content of the electrical energy storage system exceeds its maximum possible energy content, this measure alone will not create the necessary conditions for regeneration.

[0015] If the minimum temperature adjustable on the fuel cell is higher than the cooling temperature, it can be checked whether the fuel cell can be operated in a different mode where the actual power output is reduced by determining a target power output of a fuel cell where the minimum temperature is less than or equal to the cooling temperature.

[0016] In further developing the latter two measures, it proves advantageous if the method includes operating the fuel cell in a charging mode in which the fuel cell is operated with high electrical power, in which the actual power of the fuel cell is greater than the actual power requirement of the vehicle, and in which the excess electrical power of the fuel cell is stored in the electrical energy storage system.

[0017] If the target energy content of the electrical energy storage system, where the regeneration duration of the regeneration operation is the sum of the power provision from the actual power of the fuel cell and from the actual power provided by the energy storage system from its actual energy content, is greater than the electrical actual power requirement of the vehicle, is lower than the current actual energy content, the electrical energy storage system can be charged by operating the fuel cell in charging mode.

[0018] If the energy storage system, particularly a high-voltage battery, is unable to meet the vehicle's expected energy demand, the described hybrid strategy aims to increase the energy stored in the energy storage system, for example, the battery's state of charge (SoC), when the vehicle's average energy demand falls below a defined threshold. This serves to build up an energy reserve, specifically a SoC reserve, to enable extended regeneration operation in the near future. Therefore, the hybrid strategy increases the power demand on the fuel cell to boost the energy stored in the energy storage system, the battery's SoC, by charging the energy storage system with a higher power output from the fuel cell.

[0019] In this case, the fuel cell can be driven in high-load operation during charging.

[0020] The fuel cell can be operated in charging mode until at least the actual energy content of the electrical storage is equal to or greater than the determined target energy content of the electrical storage for carrying out the regeneration operation.

[0021] Furthermore, a further development of the procedure can include calculating the reduced target power of the fuel cell with respect to the actual power of the fuel cell, where the calculated adjustable minimum temperature is less than or equal to the target temperature, and reducing the actual electrical power of the fuel cell to the target power of the fuel cell if, over the regeneration period of the cooling operation, the sum of the power supply from the target power of the fuel cell and the actual energy content of the electrical energy storage is greater than the actual electrical power requirement of the vehicle.

[0022] This allows testing to determine whether the fuel cell can be operated at a lower power output, thereby reducing the heat to be dissipated in the fuel cell system and enabling a lower minimum temperature to be set at the fuel cell.

[0023] In a further development of the latter embodiment of the method, it proves advantageous if the reduction of the actual electrical power of the fuel cell to the target power of the fuel cell is carried out continuously and abruptly, or if the reduction of the actual electrical power of the fuel cell to the target power of the fuel cell is carried out in stages.

[0024] Furthermore, it may prove advantageous if the request to the fuel cell control is event-related, periodic or continuous and / or if the regeneration period includes at least 1 minute, in particular at least 5 minutes, and in particular at least 10 minutes.

[0025] If the regeneration period is at least 1 minute, in particular at least 5 minutes, and especially at least 10 minutes, the fuel cell can be operated in regeneration mode for a sufficient length of time to reduce reversible degradation sufficiently.

[0026] If the regeneration period is at least 1 minute, it is conceivable, for example, to achieve a complete cleaning of the fuel cell in several regeneration cycles staggered over time. If the regeneration period is at least 10 minutes, all reversible degradation that can be removed during low-load operation of the fuel cell can be eliminated.

[0027] Furthermore, embodiments of the method are conceivable in which the electrical actual power requirement of the vehicle includes at least the electrical actual power requirement of the electric drive and the fuel cell cooling circuit in the fuel cell system and / or in which the detection of the heat input includes at least the heat generated by the fuel cell, a heat exchanger in the fuel cell circuit and a heat transfer medium.

[0028] The vehicle's actual electrical power requirement can also include the actual power requirement of other electrical consumers in the vehicle. These can include, for example, an air conditioning unit, navigation system, entertainment system, or additional cooling measures in the fuel cell system, such as heating elements, cooling elements, fans, and the like.

[0029] During normal vehicle operation, the fuel cell can be operated dynamically. This means that the actual power output of the fuel cell is determined by the actual power demand of the electric drive; accordingly, it operates at high power output when the actual power demand of the electric drive is high, and at lower power output when the actual power demand of the electric drive is low.

[0030] In principle, it is conceivable that the fuel cell can also be operated dynamically during regeneration. It proves advantageous if the regeneration process of the fuel cell includes a constant, steady-state operating condition and / or if the regeneration process of the fuel cell includes a low-load operating condition in which the fuel cell is operated with, in particular, the lowest possible electrical power, low electrical currents, low heat dissipation, and high electrical cell voltage.

[0031] If the fuel cell is operated constantly and stationary in regeneration mode, the conditions at the fuel cell, namely cool and humid conditions, can be kept at the same level, thereby improving the reduction of degradation effects.

[0032] In the low-load operating state of the fuel cell, there is a lower actual power output of the fuel cell, low currents, a high electrical voltage and at the same time little heat to be dissipated, which offers improved conditions for electrochemical oxidation or reduction.

[0033] Furthermore, embodiments of the method are conceivable in which, during the charging operation of the fuel cell, the electric drive is supplied exclusively with electrical energy by the fuel cell and excess electrical energy can be supplied to the energy storage device, whereby the energy storage device is used exclusively for charging, and / or in which the electrical energy generated by the fuel cell during regeneration operation can be supplied to the energy storage device and, if necessary, to an electrical consumer other than the drive, whereby the drive is supplied exclusively with electrical energy by the energy storage device.

[0034] If, during the charging operation of the fuel cell, the electric drive is supplied exclusively with electrical energy by the fuel cell, an unwanted discharge of the electrical energy storage can be avoided.

[0035] If, during regeneration mode, the electrical charge generated by the fuel cell can be supplied exclusively to the energy storage and, if necessary, to another electrical consumer besides the drive, operating the fuel cell in a stationary, constant mode is simplified.

[0036] The process can be further improved if capturing the maximum possible heat dissipation from the fuel cell system includes additional heat dissipation through at least one cooling element and / or if performing the regeneration operation of the fuel cell includes the supply of additional moisture through a humidifying agent.

[0037] Further features, details and advantages of the invention will become apparent from the attached patent claims, the graphic representation and the following description of a preferred embodiment of the method.

[0038] The drawing shows: Fig. 1 A schematic flowchart of an embodiment of the method.

[0039] Fig. Figure 1 shows a schematic flowchart of a process for regenerating a vehicle fuel cell. The vehicle comprises at least one fuel cell system, which includes a fuel cell, a fuel cell cooling circuit associated with the fuel cell, and a fuel cell controller. Furthermore, the vehicle includes an electrical energy storage device that can be electrically charged by the fuel cell.

[0040] The vehicle also includes an electric drive that can be powered solely by the fuel cell, solely by the energy storage system, and in hybrid mode by the fuel cell and energy storage system.

[0041] In a first step, the fuel cell controller sends a request to the vehicle control unit, which then receives it. This request requests that a regeneration cycle be initiated, during which the relative humidity at the fuel cell is at its maximum and the fuel cell temperature remains at or below a certain level for a specified period.

[0042] In step 102, the vehicle control unit detects the heat input into the fuel cell system. This includes at least the heat input from the fuel cell itself in its current operating state. Furthermore, the heat input from other heat sources within the fuel system can be determined, such as the heat input from a heat exchanger and / or a heating element.

[0043] Furthermore, in step 102, the vehicle control system detects the maximum possible heat dissipation from the fuel cell system. This includes, in particular, the heat that can be dissipated via the fuel cell cooling circuit.

[0044] Furthermore, in step 102, a minimum temperature adjustable at the fuel cell is calculated based on the heat input and heat output.

[0045] In step 103, the regeneration operation is carried out if the calculated adjustable minimum temperature is less than or equal to the cooling temperature and if, over the regeneration duration of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and from the actual power of the energy storage provided from the actual energy content of the electrical energy storage is greater than the electrical actual power requirement of the vehicle.

[0046] Alternatively, in step 104, the request can be rejected by the vehicle control system if the calculated adjustable minimum temperature is greater than the cooling temperature, or if, over the regeneration period of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and from the actual power of the energy storage provided from the actual energy content of the electrical energy storage is less than the electrical actual power requirement of the vehicle.

[0047] Fig. Figure 1 shows an embodiment of the method in which, in the event of a rejection of the request in step 104, a step 101 can be placed before step 102, or as a loop.

[0048] In step 101, a target energy content of the electrical energy storage is determined, in which the regeneration duration of the regeneration operation is greater than the sum of the power provision from the actual power of the fuel cell and the target energy content of the electrical energy storage.

[0049] Furthermore, in step 101, a target power output for the fuel cell is determined, at which the minimum temperature is less than or equal to the cooling temperature. In step 105, the fuel cell can then be operated in charging mode.

[0050] During fuel cell charging, the fuel cell operates at high electrical power. The actual power output of the fuel cell is greater than the actual power requirement of the vehicle. The excess electrical power generated by the fuel cell is fed into the energy storage system, thereby charging it. This allows the electrical energy storage system to increase its actual energy content to the target energy content, ensuring that after charging is complete, the electrical energy storage system has an actual energy content sufficient to initiate regeneration.

[0051] Alternatively or additionally, step 106 can be performed in step 101, which includes calculating a target power of the fuel cell reduced with respect to the actual power of the fuel cell.

[0052] At the target power of the fuel cell, an adjustable minimum temperature subsequently calculated in step 102 is less than or equal to the target temperature. Simultaneously, in step 106, the actual electrical power of the fuel cell is reduced to the target power of the fuel cell if, over the regeneration period of the cooling operation, the sum of the power supplied from the actual power of the fuel cell and from the actual power supplied by the energy storage system is greater than the actual electrical power requirement of the vehicle.

[0053] Step 102 is then performed again, and steps 103 and 104 determine whether the conditions for carrying out the regeneration operation are met (step 103) or whether the request from the fuel cell control must be rejected again (step 104).

[0054] The features of the invention disclosed in the foregoing description, in the claims and in the drawing can be essential, both individually and in any combination, in the realization of the invention in its various embodiments within the scope of protection of the following claims. Reference symbol list 100-106 process steps

Claims

[1] A method for regenerating a fuel cell of a vehicle, wherein the vehicle comprises at least one fuel cell system comprising a fuel cell, a fuel cell cooling circuit associated with the fuel cell, and a fuel cell controller, wherein the vehicle has an electrical energy storage device that can be electrically charged by the fuel cell, wherein the vehicle has an electric drive that can be supplied with electrical energy solely by the fuel cell, solely by the energy storage device, and in hybrid operation by the fuel cell and the energy storage device, and wherein the vehicle comprises a vehicle controller, comprising the steps: a. 100: Receipt of a request from the fuel cell control by the vehicle control to perform a regeneration operation for a regeneration period in which the relative humidity at the fuel cell is at its maximum and in which the fuel cell reaches or falls below a cooling temperature; b. 102: Recording the heat input into the fuel cell system, at least through the fuel cell in an actual operating state; recording a maximum possible heat output from the fuel cell system, at least through the fuel cell cooling circuit; and calculating a minimum temperature adjustable at the fuel cell. c. 103: Performing the regeneration operation when the calculated adjustable minimum temperature is less than or equal to the cooling temperature and when, considered over the regeneration duration of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and the actual power provided by the energy storage from the actual energy content of the electrical energy storage is greater than the actual electrical power requirement of the vehicle; or d. 104: Rejection of the request by the vehicle control if the calculated adjustable minimum temperature is greater than the cooling temperature or if, over the regeneration period of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and from the actual power of the energy storage provided from the actual energy content of the electrical energy storage is less than the electrical actual power requirement of the vehicle. [2] Method according to claim 1, characterized byDetermining a target energy content of the electrical energy storage system, where, over the regeneration period of the regeneration operation, the sum of the power provision from the actual power of the fuel cell and the target energy content of the electrical energy storage system is greater than the actual electrical power requirement of the vehicle and / or by determining a target power of the fuel cell where the minimum temperature is less than or equal to the cooling temperature. [3] Method according to claim 2, characterized by Operating the fuel cell in a charging mode where the fuel cell is operated with high electrical power, where the actual power of the fuel cell is greater than the actual power requirement of the vehicle, and where the excess electrical power of the fuel cell is stored in the electrical energy storage system. [4] Method according to any one of the preceding claims, characterized bya calculation of a reduced target power of the fuel cell with respect to the actual power of the fuel cell, where the calculated adjustable minimum temperature is less than or equal to the target temperature, and a reduction of the actual electrical power of the fuel cell to the target power of the fuel cell if, over the regeneration period of the cooling operation, the sum of the power supply from the target power of the fuel cell and the actual energy content of the electrical energy storage is greater than the actual electrical power requirement of the vehicle. [5] Method according to claim 4, characterized by , that the reduction of the actual electrical power of the fuel cell to the target power of the fuel cell occurs continuously and abruptly, or that the reduction of the actual electrical power of the fuel cell to the target power of the fuel cell occurs in stages. [6] Method according to any one of the preceding claims, characterized bythat the request to the fuel cell control is event-related, periodic or continuous and / or that the regeneration period comprises at least one minute, in particular at least 5 minutes, in particular at least ten minutes. [7] Method according to any one of the preceding claims, characterized by that the electrical actual power requirement of the vehicle includes at least the electrical actual power requirement of the electric drive and the fuel cell cooling circuit in the fuel cell system and / or that the measurement of the heat input includes at least the heat generated by the fuel cell, a heat exchanger in the fuel cell circuit and a heat transfer medium. [8] Method according to any one of the preceding claims, characterized bythat the regeneration operation of the fuel cell includes a constant, steady-state operating condition and / or that the regeneration operation of the fuel cell includes a low-load operating condition in which the fuel cell is operated with, in particular, the lowest possible electrical power, low electrical currents, low heat to be dissipated and high electrical cell voltage. [9] Method according to any one of the preceding claims, characterized by, that during the charging operation of the fuel cell the electric drive is supplied exclusively with electrical energy by the fuel cell and excess electrical energy can be supplied to the energy storage, whereby the energy storage is used exclusively for charging, and / or that the electrical energy generated in the regeneration operation of the fuel cell can be supplied to the energy storage and possibly to another electrical consumer besides the drive, whereby the drive is supplied exclusively with electrical energy by the energy storage. [10] Method according to any one of the preceding claims, characterized by , that capturing the maximum possible heat dissipation from the fuel cell system includes additional heat dissipation through at least one cooling element and / or that carrying out the regeneration operation of the fuel cell includes the supply of additional moisture through a humidifying agent.

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