SE545066C2

SE545066C2 - Fuel cell stack assembly and method for controlling a temperature of a fuel cell stack assembly

Info

Publication number: SE545066C2
Application number: SE2051437A
Authority: SE
Inventors: Thomas Tingelöf
Original assignee: Powercell Sweden Ab
Priority date: 2020-12-09
Filing date: 2020-12-09
Publication date: 2023-03-21
Also published as: WO2022124959A1; SE2051437A1

Abstract

:A fuel cell stack assembly (1) is provided which comprises at least a fuel cell stack (2) with a plurality of fuel cells (4), first and second endplates (20, 22} between which the fuel cell stack is arranged, and which are provided with at least a cooling fluid inlet (11, 18), which is configured to provide a cooling fluid to the fuel cell stack for regulating a temperature within the fuel cell stack, and a cooling fluid outlet (13, 19); a heating unit (38) arranged between at least one of the end plates (20, 22) and the fuel cell stack (2); and a control unit (40) for controlling the heating unit (38); wherein a first temperature sensor (44) is provided, which is configured to measure a first temperature value and to provide the measured first temperature value as an output value of the first temperature sensor (44) to the control unit (40), wherein the control unit (40) is configured to control the heating unit (38) based on the output value of the first temperature sensor (44), wherein the first temperature sensor (44) is arranged at and/or in the cooling fluid outlet (13, 19) of the first endplate (20).

Description

Description: The present lnvention relates to a fuel cell stack assembly. Further, the present in- vention relates to method for controlling a temperature of a fuel cell stack assembly.

Usually, a fuel cell stack cornprises a plurality of membrane electrode assemblies (MEAs), which are separated by so called bipolar plates (BPP). The loipolar plates themselves usually comprise at least two electrically conducting metal plates, so called flow field plates, which are placed on top of each other and have a flow field for the reactants at one side and a flow field for a Cooling fluid on the other side. Thereby, the cooling fluid flow fields are facing each other, wherein the reactant fluid flow fields face the MEAs. The electric current produced by the MEAs during operation of the fuel cell stack results in a voltage potential difference between the bipolar plate assemblies. Consequentiy, the individual bipolar plates must be kept electrically separated from each other under all circumstances in order to avoid a short circuit.

During the production of electrical energy by means of a fuel cell, however, also thermal energy is produced, which results in a temperature increase of the fuel cell or the fuel cell stack, respectively. The temperature increase is not evenly distrib~ uted over the fuel cells in a fuel cell stack due to heat losses at the edges of a sin- gle fuel cell. An uneven temperature distribution within a fuel cell stack, however, results in an uneven power output provided by the fuel cell stack. Partlcularly the end cells of the fuel cell stack constitute elements with a low power output, for ex~ ample compared to a fuel cell in a center area of the fuel cell stack. lvloreover, the described temperature gradients may end up in undesired degradation rates and reduced fuel cell lifetime. i lt is therefore an object of the present invention to provide a fuel cell stack assem~ bly as well as a method for controlling a temperature of a fuel cell stack assembly which allows to keep the thermal conditions within a fuel cell stack assembly sub- stantially stable.

This object is achieved by a fuel cell stack assembly according to claim i and by a method for controiling a temperature of a fuel cell stack assembly according to ciaim ln the following a fuel cell stack assembly is provided which comprises a fuel cell stack with a pturality of fuel cells. The fuel cell stack assembly comprises first and second endplates between which the fuel cell stack is arranged, and which are provided with at least a cooling fluid inlet, which is configured to provide a cooling fluid to the fuel cell stack for regulating a temperature within the fuel cell stack, and a coollng fluid outlet. At least one heating unit is arranged between at least one of the end plates and the fuel cell stack and a control unit is provided for controlling the heating unit.

As mentioned above, the operation of the fuel cell stack assembly does not only generate etectrical energy but also thermal energy. That is, an individual fuel cell may heat up and/or may be heated up by an adjacent fuel cell. ln order to meas- ure the thermal conditions within the fuel cell stack assembly, a first temperature sensor is provided, which is configured to measure a first temperature value and to provide the measured first temperature value as an output value of the first tem- perature sensor to the control unlt, wherein the control unit is further configured to control the heating unit based on the output value of the first temperature sensor.

For providing a precise control, internal temperature values are required. The tem- perature values may be achieved by provided a plurality of sensors within the stack which is very costly. For avoiding this, the inventors have proposed to ar- range the first temperature sensor at and/or in the cooling fluid outlet of the end- plate. Thereby the internal temperature may be indirectly deterrnined, but the sen- sor still gives precisa information on the beat accumulation. Also, more than one first temperature sensor may be provided. By measuring the temperature at and/orin the cooling fluid Outlet of the endplate a more accurate temperature control over the fuel cell stack assembly can be achieved.

The control unit in turn is configured to control the heating unit in such a way that the thermal conditions within an individual fuel cell or in the fuel cell stack can be kept substantially similar and an uneven power output provided by the individual fuel cells in the fuel cell stack and undesired degradation rates and reduced fuel cell lifetime can be avoided or at least minimized. By measuring the temperature at and/or in the cooling fluid outlet of the endplate has the advantage that the number of sensors can be reduced.

Furthermore, the at least one heating unit may be configured to provide sections of the fuel cell stack or portions of individual fuel cells with thermal energy in order to compensate for a heat loss occurring during the operation of the fuel cell stack or for heating up the fuel cell stack during start up. Said heat loss may occur at an edge of the fuel cell and/or at a peripheral zone of the stack of the plurality of fuel cells. Moreover, the heat loss may also occur in the middle of the fuel cell stack.

The at least one heating unit may be of any kind that is suitable for the implernen» tatlon ln a fuel cell stack. lt is conceivable to make use of an electric heating means. Further, an advantageous design of the heating unit may be a planar de- sign. ln this way, an easy interposition of the at least one heating unit between at least one of the end plates and the fuel cell stack is enabled.

The preferred electric heating unit may include a thin-filrn structure and/or it may comprise a resistance heating element. One example of this electric heating unit is a resistance heater produced by means of metallic thin film coating. Alternatively, the use of a PTC (Positive Temperature Coefficient) heating element may be con- sidered. The aforementioned PTC heating element is configured for a self-regu- lated temperature control and for a selﬂsufficient prevention of overheating. With such an element a thermal regulation towards a predetermined temperature value representing a usual temperature level of an interior of an individual fuel cell or of a tfuel cell arranged in a central area of the fuel cell stack is feasible.

According to a preferred embodlment, the control unit is configured to control the heating un it such that the output value of the first temperature sensor is within a predefined range. Preferably, the control unit is configured to control the heating unit such that a difference between the output value of the first temperature sen~ sors and a reference value is minimal. This allows to keep the temperature within the fuel cell stack assembly as constant as possible. For example, the reference value may be predetermined, for example experimentally, and stored in a table, for example in a memory of the control unit. The table can be accessed and/or read by the control unit.

Preferably, the control unit is configured to use a control algorithm including a feedback loop. Feedback loops provide an effective way to regulate the tempera- ture at and/or in the cooling fluid outlet of the endplate and/or at and/or in the cool~ ing fluid outlet manífold of the cooling structure. For example, the feedback loop may be configured such that if the measured temperature is higher than a refer- ence value, theheatlng unit is turned off, and if the measured temperature is tower than the reference value, the heating unit is turned on. lvlore particularly, depend- lng on the used heating unit it may be also possible that the heating unit is capable of cooling. This may be the case if a Peltier element is used as the heating unit.

According to a further preferred embodíment, at least one of the endplates is made form en eleotrically insulating material. This allows for a simplified design of the fuel cell stack as addltionally eiements for insulting the fuel cell stack to the envi- ronment may be omitted.

Alternativeiy or addtionally, a first insulatlon plate is arranged between the first end plate and the fuel cell stack, particularly between the endplate and a current col~ lector plate, and a second insulation plate is arranged between the second end plate and the fuel cell stack, particularly between the endplate and a current cci» lector plate. The first and second insulation plates advantageously provide an electrical insulation between the fuel cell stack and the endplate.

Furthermore, the first end plate and the first insulatíon plate may be formed as an integral part and/or the second end plate and the second insulation plate are formed as an integral part. This allows for a more compact design of the fuel cell stack assembly. ln this case, the first and/or the second end plate may be made from or may comprise a non~conducting materiai, so that provision of a separate insulation plate is not necessary.

Preferably, the first end plate and/or the second end plate and/orthe first insula- tion plate and/or the second insulation plate comprises a recess that is configured to accommodate the heating unit. Thus, the first and/or second and plate and/or the first and/or second insulation plate also serves as a support for the heating unit. This allows for a more compact design of the fuel cell stack assembly. Also, the recess of the first and/or second end plate and/or the first insulation plate and/or the second insulation plate may be designed in such a way that it cannot only accornmodate the heating unit but also the current collector plate. Also, the recess may be dimensioned in such a way that the inserted heating unit and/or current collector plate are flush with the surface of the insulation plate and/or the surface of the end plate.

According to another preferred embodiment, a second temperature sensor is ar~ ranged at and/or within the heating unit, wherein the second temperature sensor is conflgured to measure a second temperature value and provide the second tem- perature value as an output value of the second temperature sensor to the control unit. Preferably, the control unit is configured to control the heating unit such that the measured second temperature value is close to the measured first tempera- ture value. By measuring the temperature at and/or within the heating unit and providing the measured second temperature value to the control unit, the ternpera~ ture control in the fuel cell stack assembly can be improved. The temperature of the heating unit may be controlled directly. Furthermore, keeping the measured second temperature value close to the measured first temperature value allows to keep a temperature gradient between the plurality of fuel cells of the fuel cell stack minimal. ln other words, if the temperature at and/or in the cooling fluid outlet of the endplate, namely the position of the first temperature sensor, and the tempera~ ture at the heating unit, namely the position of the second temperature sensor, areapproximately the same it can be assumed that a temperature gradient between these two position is minimal.

A further aspect, of the present invention relates to a method for controlling a tem- perature of a fuel cell stack assembly, wherein the fuel cell stack assembly is the above mentioned a fuel cell assembly, vvherein the method comprising the follow~ ing steps: measuring a first temperature value at and/or in the cooling fluid outiet of the end~ plate, and controlling the heating unit based on the first temperature value.

The embodiments and features that have been described in connection with the fuel cell stack assembly correspondingly apply to the proposed method.

An even further aspect of the present invention reiates to a computer program product comprising a computer program code which is adapted to prompt a control unit, eg. a computer, and/or a computer of the above discussed manufacturing ar- rangement to perform the above discussed steps.

The computer program product may be a provided as memory device, such as a memory card, USB stick, CD-Rom, DVD and/or may be a file which may be down- loaded from a server, particularly a remote server, in a network. The network may be a wireless communication network for transterring the file with the computer program product.

Further preferred embodiments are defined in the dependent ciaims as well as in the description and the figures. Thereby, elements described or shown in combi~ nation with other elements may be present alone or in combination with other ele~ merlts without departing from the scope of protection. ln the following, preferred embodiments of the invention are described in relation to the drawings, wherein the drawings are exemplarily only, and are not intended to limit the scope of protection. T he scope of protection is defined by the accompa» nied ciaims, only. in the figures: Flg. 1: shows a schematic diagram of a fuel cell stack assembly according an em- bodiment in a cross-sectional view, Flg. 2: shows schematically a distribution structure of a fuel cell of the fuel cell stack according to Fig. l in a top view, Fig. 3: shows a perspective view of an lnsulation plate of the fuel cell stack as- sembly of Fig. l, and Fig. 4: shows a perspective view of an insulation plate of the fuel cell stack as- sembly according to a second embodiment. ln the following same or similar elements are indicated with the same reference signs.

A fuel cell stack assembly l is described with reference to Fig. 1 to 3. ln Fig. l, the fuel cell stack assembly l is only partly shown under omlssion of some elements. The fuel cell stack assembly 1 comprises a fuel cell stack 2 consisting of a plurality of fuel cells 4 which are arranged in alignment with each other and stacked on top of each other and thereby form a fuel cell stack 2. ln the fuel cell stack 2, bipolar plates 6 and a membraneelectrode assembly (MEA) 8 are alternately stackecl.

The lVlEA 8 may be a soacalled 3~layer MEA comprising a membrane sandwiched by anode and cathode. Further, the lVlEA can also comprise a gas diffusion layer arranged at the eieotrodes (S-layer) or even comprise a subgasket framing the MEA and GDL (T-layer).

Each BPP 6 is formed by two flow field plates Ba, Bb. One of the flow field plates is shown in Fig. 2. Each flow field plate 6a, 6b has on a front side facing the elec~ trode and a backside which is in contact with the other flow field plate of the BPP 6. Each flow field plate further has a flow field for distrlbuting reactants on the front side and a flow field for distributing a Cooling fluid on the back side, wherein each of the flow fields is formed by a series of Channels on each side of the flow field plates. ln particular, the channels may be arrahged parallel to each other. Thus, the Cooling fluid flows in between the BPP 6 and thereby effectively regulates the temperature of the fuel cell As can be seen in Fig. 2, each flow field plate Ga, Eib has at least a cooling fluid in~ let rnanifold 10 and a cooling fluid outlet manifold 12, which are adapted to provide cooling fluid to a Cooling fluid flow field (not shown) of the flow field plate. Further, each flow field plate has reactant lniet manifolds 14, 15 and reactant outlet mani- folds 16, 17, wherein the reactants are hydrogen and oxygen or air. When the fuel cells 4 are stacked upon each other (see Fig. 1), the cooling fluid inlet manifolds 10 of each fuel cell form a cooling fluid inlet supply structure 11 and the cooling fluld outlet manifold 12 of each fuel cell form a cooling fluid outlet supply structure 13. Sirnilarly, the reactant inlet manifolds 14, 16 for each reactant form respective reactant intet supply structures (not shown in Pig. 1) and the reactant outlet mani- foids 15, 1? for each reactant form respective reactant outlet supply structures (not shown in the cross-section of Fig. 1). For the sake of simplicity, in the cross sec- tion of Fig. 1 only the cooling fluid inlet supply structure 11, and the cooling fluid outlet supply structure 13 are shown and indicated.

The coollng fluid is supplied to the cooling fluid inlet structure 11 by means of a Cooling fluid inlet port 18 and exit the Cooling fluid outlet structure 13 through the cooling fluid outlet port The fuel cell stack 2 is sandwiched, by first and second end plates 20, 22. The first end plate 20 of the fuel cell stack assembly 1 is indicated on the bottom of the il- lustration in Fig. 1. At the top (according to the orientation shown in Fig. 1), the fuel cell stack 1 assembly is provided with the second end plate 22. The entire fuel cell stack assembly 1 may be housed in a housing.

The fuel cell stack assembly 1 also includes current collector plates (CCP) 24, 26 for tapping current from the fuel cell stack 2 and particularly from so called end cells, 4a, 4b. Further, each current Collector plate 24, 26 comprises a terminal or conneotor 28, 30 that is configurecl to guide the collected current to the outside of the fuel ce i stack assembly 1. ln the illustrated embodiment, the CCP 24, 26 have connectors 28, 30 which may pass through the end plates 20, 22. The currentcollector plates 24, 26 are adapted to contact the first and last fuel cells 4a, 4b of the fuel cell stack.

Two plate-Shaped insuiation plates 32, 34 are included in the fuel cell stack as- sembly 1, one at each side of the fuel cell stack assembly 1. Each ineulation plate 32, 34 may have the same outer dlmensions as the fuel cell stack 2. F lg. 3 illus- trates a preferred embodiment of an lnsulation plate 32, 34. As illustrated, at least one of the insulation plates 32, 34 may include a recess 36 into which an electric heating unit 38 is integrated such that the heating unit 38 is flush with the surface of the insulatiolw plate 32, 34. Each insulation plate 32, 34 is arranged between the end plate 20, 22 and the respective CCP 24, 26. Alternatively, the first end plate 20 and the first insulation plate 32 and/or the second end plate 22 and the second insuiation plate 34 can be formed as an integral part. ln this case, the first and/or the second end plate 20, 22 are made from a non-conducting material. ln case the end plate 20, 22 and the insuiation plate 32, 34 is formed as integral part, the re~ cess 36 may be provided in the end plate 20, The heating unit 38 is configured to convert electrical energy into thermal energy and allows to provide homogeneous thermal conditions within the fuel cell stack assembly 1 resulting in an uniform power output all over the fuel cells 4 of the fuel cell stack 2. The insulation plates 32, 34 may be designed similar to the fuel cells with openings for the hydrogen, air and coolant Channels for enabling connection to the respective inlets 10, 14, 15 and outlets 12, 16, 17 at the fuel cells 4. lvloreo- ver, it is also possible to provide more than one heating unit 38. For example, each of the insulation plates 32, 34 may be provided with a heating unit As is further indicated in Fig. 1, the heating unit 38 is controlled by a control unit 40 having a CPU 42, which can include an algorithm for an accurate control. The op~ eration of leach heating unit 40 is regulated based on a measured temperature value that is measured and provided to the control unit 40 by a first temperature sensor 44. The first temperature sensor 44 is arranged at the Cooling fluid outlet port 19. However, it is also possible to arrenge the first temperature sensor 44 in the cooling fluid outlet structure 13 in the vicinity of the endplate 20 or at and/or in the cooling fluid outlet manifold 12 of the cooling fluid outlet structure 13. lt is also possible to provide more than one first temperature sensor Depending on the needed accuracy, the control of the heating unit 38 may be per» formed such that the output value of the first temperature sensor 44 is within a pre- defined range and/or that a difference between the output value of the first temper- ature sensor 44 and a reference value is minimal. For example, the reference value may šbe experimentally determined and stored in a memory 46 of the control unit 40 in form of a table that can be accessed and/or read by the control unit 40 particuiarly the cPu Additionally, or alternatively, the control unit 40 is configured to use a control algo- rithm including a feedback loop. For example, the feedback loop may be config- ured such that if the measured temperature Tas is higher than a reference value Tre, Tse > Tar, the heating unit 38 is turned off, and if the measured temperature Tse is lower than the reference value Tfsf, Tse < Tre, the heating unit 38 is turned on. More particularly, depending on the used heating unit 38 it may be also possi- ble that the heating unit is capable of Cooling. This may be the case if a Peltier ele- ment is used as the heating unit 38, Fig. 4 shows an insulation plate 32, 34 of a second emloodiment of the fuel cell stack assembly 1. ln this embodiment a second temperature sensor 48 which is arranged next to the heating unit 38 as indicated with the dotted line in Fig. 4. The control unit 40 then receives sensor information from both the first and the second temperature sensors 44, 48 and a routine of the control algorithm evaiuates the output values of the sensors signals and controls the temperature of the heating unit 38 by means of a feedback loop to be close to the temperature of the cooling fluid Outlet 12 which is measured by the first temperature sensor 44. By measuring the temperature at and/or within the heating unit 38 and providing the measured second temperature value to the control unit 40, the temperature control in the fuel cell stack assembly i can be improved. iviore particularly, keeping the measured second temperature value close to the measured first temperature value allows to keep a temperature gradient within the fuel cell stack 2 minimal. it is to be noted that although the present embodirnent oiscloses only one first and second temperature sensors 44, 48, an arrangement of a pluraiity of first tempera- ture sensors 44 and a plurality of second temperature Sensors 48 may increase the accuracy of control, so that other embodiments may include such multiple sen- sor arrangements.

Consequently, by controlling the heating unit 38 based on the first temperature sensor 44 that ts arranged close to the coolant Outlet 12 of the fuel cells stack 2, the thermal gradients between the end cells -fl-e, 4b adjacent to the end plates 20, 22 and the fuel cells 4 in the center of the fuel cell stack assembly t are reduced to a minimum. As a result, a more accurate heating element control is enabled, and tower degradation rates and longer fuel cell lifetime is reelized.Reference numerals ﬁßOï-ië-hJ-l- , '12 "ll 13 14, 16 15, 17 18 19 20, 22 24, 26 28, 30 32, 34 36 38 42 44, 48fuel cell stack assembly *Fuel cell stack fuel cells bipoiar plate assernblies rnembrane-electrode assemblies coolant inlet, coolant Outlet ;nlet supply structure outlet supply structure šwydrogen inlet, hydrogen outlet :air lnlet, air outlet änlet port outlet port first and second end plates fcurrent Collector plates terminals insulation plate vrecess heating unit control unit CPU first and second temperature Sensors memory 12

Claims

Fuel cell stack assembly and method for controlling a temperature of a fuel cell stack assembly Clairns:

1. Fuel cell stack assembly (1) comprising at least a fuel cell stack (2) with a plurality of fuel cells (4), first and second endplates (20, 22) between which the fuel cell stack is ar~ ranged, and which are provided with at least a coollng fluid inlet (11, 18), which is configured to provide a cooling tluid to the fuel cell stack for regulating a tempera- ture vvithin the fuel cell stack, and a cooling fluid outlet (13, 19); a heating unit (38) arranged between at least one of the end plates (20, 22) and the fuel cell stack (2); and a control unit (40) 'for controlling the heating unit (38), characterized in that a ﬁrst temperature sensor (44) is provided, which is configured to measure a first temperature value and to provide the measured first temperature value as an output value of the first temperature sensor (44) to the control unit (40), wherein the control unit (40) is configured to control the heating unit (38) based on the out~ put value of the first temperature sensor (44), wherein the first temperature sensor (44) is arrangecl at and/or in the cool- ing fluid outlet (13, 19) of the first endplate (20).

2. Fuel cell stack assembly (1) according to claim 1, wherein the control unit (40) is configured to control the heating unit (38) such that the output value of the first temperature sensor (44) is within a predefined range.

3. Fuel cell stack assembly (1) according to claim 1 or 2, wherein the control unit (40) is configured to control the heating unit (38) such that a difference be- tween the output value of the first temperature sensor (44) and a reference value is minimal.

4. Fuel cell stack assembly (1) according to one of the previous clairns, wherein the endplate is made from an electricaily lnsulating material or comprises an electricaily insulating material.

5. Fuel cell stack assembly (1) according to one of the previous claims, whereln a first insulation plate (32) is arranged between the first end plate (20) and the fuel cell stack (2) and a second insulation plate (34) is arranged between the second end plate (22) and the fuel cell stack (2).

6. Fuel cell stack assembly (t) according to olaim 5, wherein the first end plate (20) and the first insuiation plate (32) are formed as an integral part and/or the second end plate (22) and the second insulation plate (34) are formed as an inte- gral part.

7. Fuel cell stack assembly (t) according to any one of claims 4 to 6, vvherein the first end plate (20) and/or the second end plate (22) and/or the first insulation plate (20) and/or the second insulation plate (22) cornprises a reoess (36) that is configured to accommodate the heating unit (38).

8. Fuel cell stack assembly (1) according to any one of the previous clalms, wherein a second temperature sensor (48) is arranged at and/or within the heating unit (38), wherein the second temperature sensor (48) is configured to measure a second temperature value and provide the second temperature value as an output value of the second temperature sensor (48) to the control unit (40).

9. Fuel cell stack assembly (1) according to claim 8, wherein the control unit (40) is conflgured to control the heating unit (38) such that the measured second temperature value at and/orwithin the heating unit (38) is close to the measured first temperature value at and/or in the cooling fluid outlet (13, 19) of the endplate (20).

10. Fuel cell stack assembly (1) according to claim 9, whereln the control unit (40) is configured to control the heating unit (38) based on the output value of the first temperature sensor (44) and the output value of the second temperaturesensor (48) such that a temperature gradient between the plurality of fuel cells (4) of the fuel cell stack (2) is minimal.

11. Fuel cell stack assembly (1) according to any one of the previous clairns, wherein the control unit (40) is configured to use a control algorithm including a feedback loop.

12. Method for controlling a temperature of a fuel cell stack assembly (1 ), wherein the fuel cell stack assembly (1) is a fuel cell assembly (1) according to any one of the claims 1 to 11, wherein the method comprlsing the following steps: measuring a first temperature value at and/or in the cooiing fiuid outlet (13, 19) of the endplate (20), and controlling the heating unit (38) based on the first temperature value.

13. Method for controlling a temperature of a fuel celi stack assembly (1) ac- cording to claim 12, wherein controlling the heating unit (38) includes controlling the heating unit (38) such that the output value of the first temperature sensor (44) is within a predefined range. wherein preferably the heating unit (38) is controlled in such a way that a difference between the first temperature value and a refer- ence value is minimal.

14. Method for controlling a temperature of a fuel cell stack assembly (1) at» cording to claims 12 or 13, wherein the method further comprises measuring a second temperature value at and/or within the heating unit (38), and controlling the heating unit (38) such that the measured second temperature value at and/or within the heating unit (38) is close to the measured first temperature value at and/or in the cooling fluid outlet (13, 19) of the endplate (20).