COMPUTER-IMPLEMENTED METHOD FOR CONTROLLING OPERATION OF AT LEAST TWO FUEL CELL SYSTEMS

Abstract

A method and apparatus for controlling operation of at least two fuel cell systems, wherein each fuel cell system is adapted to be operated with adjustable operating dynamics and/or in an adjustable operating window defining operating constraints for the fuel cell system, wherein increasing the operating dynamics and/or the operating window is associated with an increased expected degradation of the fuel cell system and wherein reducing the operating dynamics and/or the operating window is associated with a reduced expected degradation of the fuel cell system.

Claims

1. A computer-implemented method for controlling operation of at least two fuel cell systems, wherein each fuel cell system is adapted to be operated with adjustable operating dynamics and in an adjustable operating window defining operating constraints for the fuel cell system, wherein increasing the operating dynamics and the operating window is associated with an increased expected degradation of the fuel cell system and wherein reducing the operating dynamics and the operating window is associated with a reduced expected degradation of the fuel cell system, the method comprising: obtaining an estimated actual state of health of each fuel cell system; comparing the actual states of health of the fuel cell systems; and when the comparison is indicative of a predefined difference between the actual states of health of the fuel cell systems: identifying a first fuel cell system of the at least two fuel cell systems having a lowest actual state of health of the at least two fuel cell systems; comparing the actual state of health of the first fuel cell system with a determined expected state of health of the first fuel cell system, wherein the expected state of health is based on historical use conditions of the first fuel cell system; and when the actual state of health of the first fuel cell system is worse than its expected state of health, reducing the operating dynamics and the operating window of the first fuel cell system and increasing the operating dynamics and the operating window of the other fuel cell system.

2. The method of claim 1, wherein, when the comparison of the actual states of health of the fuel cell systems is indicative of no difference between the actual states of health of the fuel cell systems, the method comprises operating the fuel cell systems with the same operating dynamics and in the same operating window.

3. The method of claim 1, wherein the result of the comparison between the actual states of health of the fuel cell systems is indicative of the predefined difference when a difference therebetween exceeds a predefined difference threshold.

4. The method of claim 1, further comprising: when the actual state of health of the first fuel cell system is better than its expected state of health, operating the fuel cell systems with the same operating dynamics and in the same operating window.

5. The method of claim 1, wherein the reducing of the operating dynamics and the operating window of the first fuel cell system and the increasing of the operating dynamics and the operating window of the other fuel cell system are done so that combined operating dynamics and a combined operating window of the at least two fuel cell systems is/are kept unchanged.

6. The method of claim 1, wherein the method is initiated in response to obtaining a request to activate all of the at least two fuel cell systems.

7. The method of claim 1, wherein the historical use conditions of the first fuel cell system comprise at least one of the following: power output of the fuel cell system during operation; operating dynamics of the fuel cell system during operation; power cycling frequency of the fuel cell system during operation; ambient temperature conditions during operation; ambient air conditions during operation, such as level of pollution; ambient weather conditions during operation; start/stop history; history of coolant temperature in the fuel cell system; operating time.

8. The method of claim 1, wherein, during operation of the fuel cell systems, the method is updated with a predetermined update frequency, such as an update frequency corresponding to a predetermined number of operating hours of at least one of the fuel cell systems.

9. The method of claim 8, wherein the predetermined update frequency is variable, such as variable with respect to at least one of ambient temperature conditions and ambient weather conditions.

10. The method of claim 8, wherein the predetermined update frequency is modified during operation based on a magnitude of the difference in the actual state of health between the fuel cell systems.

11. A control unit for controlling operation of at least two fuel cell systems, wherein the control unit is configured to perform the steps of the method of claim 1.

12. A propulsion system for a vehicle comprising at least two fuel cell systems, and further comprising the control unit of claim 11.

13. A vehicle comprising the propulsion system of claim 12.

14. A computer program comprising program code means for performing the steps of claim 1 when the program is run on a computer.

15. A computer readable medium carrying a computer program comprising program code means for performing the steps of claim 1 when the program is run on a computer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0052] In the drawings:

[0053] FIG. 1 is a side view of a vehicle according to an example embodiment of the present invention,

[0054] FIG. 2 is a flowchart of a method according to an example embodiment of the present invention,

[0055] FIG. 3 is a flowchart of a method according to another example embodiment of the present invention,

[0056] FIG. 4 is a schematic illustration of a propulsion system according to an example embodiment of the present invention, and

[0057] FIG. 5 is a graph showing an expected and actual state of health over time.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0058] FIG. 1 depicts a vehicle 100 in the form of a heavy-duty truck. In this case, the heavy-duty truck 100 is a so-called towing vehicle which is configured to tow one or more trailers (not shown). The present invention is however not only applicable to this type of vehicle but may also be used in many other types of vehicles and vessels, such as other trucks, buses, passenger cars, construction equipment, including but not limited to wheel loaders, dump trucks, excavators etc.

[0059] In the shown embodiment, the vehicle 100 comprises a propulsion system 1. The propulsion system 1 may for example be a propulsion system 1 as shown in FIG. 4 which will be described further in the below. The vehicle 100 further comprises a control unit 110 according to an example embodiment of the second aspect of the invention.

[0060] In particular, the propulsion system 1 comprises a fuel cell system, FCS1, and another fuel cell system, FCS2. The propulsion system 1 may, as further shown in FIG. 4, comprise an electrical energy storage system EES. For example, the electrical energy storage system EES may be an electric battery, such as a lithium-ion battery, and/or a capacitor.

[0061] Typically, such a propulsion system 1 for the vehicle 1 is adapted so that, during operation, the fuel cell systems FCS1, FCS2 contribute the most to the propulsion of the vehicle 1, whereas the EES is used to compensate for situations when the fuel cell systems FCS1, FCS2 can't provide, or are not suitable for providing, all of the required propulsion force.

[0062] FIG. 2 depicts a flowchart of a computer-implemented method according to an example embodiment of the present invention. The method controls operation of at least two fuel cell systems FCS1, FCS2.

[0063] Each fuel cell system FCS1, FCS2 is adapted to be operated with adjustable operating dynamics and/or in an adjustable operating window defining operating constraints for the fuel cell system FCS1, FCS2. Increasing the operating dynamics and/or the operating window is associated with an increased expected degradation of the fuel cell system FCS1, FCS2 and reducing the operating dynamics and/or the operating window is associated with a reduced expected degradation of the fuel cell system FCS1, FCS2.

[0064] The method comprises: [0065] S1: obtaining an estimated actual state of health of each fuel cell system FCS1, FCS2, [0066] S2: comparing the actual states of health of the fuel cell systems FCS1, FCS2, and when the comparison is indicative of a predefined difference between the actual states of health of the fuel cell systems FCS1, FCS2: [0067] S3: identifying a first fuel cell system of the at least two fuel cell systems FCS1, FCS2 having a lowest actual state of health of the at least two fuel cell systems FCS1, FCS2, [0068] S4: comparing the actual state of health of the first fuel cell system with a determined expected state of health of the first fuel cell system, wherein the expected state of health is based on historical use conditions of the first fuel cell system, and [0069] S5: when the actual state of health of the first fuel cell system is worse than its expected state of health, reducing the operating dynamics and/or the operating window of the first fuel cell system and increasing the operating dynamics and/or the operating window of the other fuel cell system.

[0070] The first fuel cell system may be any one of the fuel cell systems FCS1, FCS2. For example, an actual state of health for the fuel cell systems FCS1, FCS2 may be estimated by the so-called electrochemical impedance spectroscopy method which is well-known. There are also other methods for estimating an actual state of health, such as polarization curve comparison between a used fuel cell system and a new, or fresh, fuel cell system. Still further, by way of example, an actual state of health may be estimated as disclosed in any one of US8907675B2 and US10345389B2.

[0071] An expected state of health based on historical use conditions may for example be determined by comparing a current usage with a maximum usage. For example, the first fuel cell system may in a certain application be supposed to last for a specific amount of operating hours, such as 1000 hours. During this time it may be assumed that the degradation characteristics is known, such as linear. As such, if for example the first fuel cell system has been operated for 500 hours, then, with a linear logic, the expected state of health should be 50%. This is a rather simple and thereby efficient approach of estimating the expected state of health. However, more advanced approaches are also feasible. For example, by taking at least one of the other below mentioned historical use conditions into account, any event that is related to degradation of the first fuel cell system, such as ambient temperature, start/stop history etc, can be considered to thereby obtain a value of the expected state of health which may be closer to the actual state of health. For example, an expected state of health based on historical use conditions may be determined by use of tests. By way of example, an empirical model may be created which is based on tests performed under different use conditions, e.g. based on one or more use conditions which correspond to the herein mentioned historical use conditions. Thereby, an improved value of the expected state of health may be obtained.

[0072] An example of an actual SoH.sub.A and an expected SoH.sub.E state of health over time of one of the fuel cell systems, in this case the fuel cell system FCS1, is shown in FIG. 5. FIG. 5 represents a graph where state of health is represented on the y-axis and where time, or age, is represented on the x-axis. The dotted curve represents the actual state of health SoH.sub.A and the solid curve represents the expected state of health SoH.sub.E. In the example shown, the expected state of health SoH.sub.E forms an almost straight line which is based on historical use conditions of the fuel cell system FCS1. A straight line may for example imply that the use conditions are substantially static during operation. For example, a power cycling frequency, ambient temperature conditions during operation etc., may not substantially vary over time. Of course, the historical use conditions may additionally, or alternatively, vary over time, resulting in a varying degradation rate over time. Thereby, the expected state of health may evidently not only be represented by a straight line. Historical use conditions as used herein may refer to any previous use conditions of the fuel cell system FCS1, FCS2.

[0073] An example when the actual state of health SoH.sub.A of the first fuel cell system FCS1 is worse than its expected state of health SoH.sub.E is indicated by FCS1 in FIG. 5. As such, when this situation is identified by the comparison performed in S5, the operating dynamics and/or the operating window of the first fuel cell system FCS1 is reduced and the operating dynamics and/or the operating window of the other fuel cell system FCS2 is increased.

[0074] For example, the result of the comparison between the actual states of health of the fuel cell systems FCS1, FCS2 may be indicative of the predefined difference when a difference therebetween exceeds a predefined difference threshold. Thereby, unnecessary adjustments which only would have a slight effect on the combined service life, or even no effect at all, can be avoided. The predefined difference threshold may for example correspond to a difference of 1-5% in actual state of health.

[0075] Additionally, or alternatively, the reducing of the operating dynamics and/or the operating window of the first fuel cell system FCS1 and the increasing of the operating dynamics and/or the operating window of the other fuel cell system FCS2 may be done so that combined operating dynamics and/or a combined operating window of the at least two fuel cell systems FCS1, FCS2 is/are kept unchanged.

[0076] The historical use conditions of the first fuel cell system FCS1 may comprise at least one of the following: [0077] power output of the fuel cell system during operation, [0078] operating dynamics of the fuel cell system during operation, [0079] power cycling frequency of the fuel cell system during operation, [0080] ambient temperature conditions during operation, [0081] ambient air conditions during operation, such as level of pollution, [0082] ambient weather conditions during operation, [0083] start/stop history, [0084] history of coolant temperature in the fuel cell system, [0085] operating time.

[0086] During operation of the fuel cell systems FCS1, FCS2, the method may be updated with a predetermined update frequency, such as an update frequency corresponding to a predetermined number of operating hours of at least one of the fuel cell systems FCS1, FCS2.

[0087] The predetermined update frequency may further be variable, such as variable with respect to at least one of ambient temperature conditions and ambient weather conditions.

[0088] The predetermined update frequency may additionally or alternatively be modified during operation based on a magnitude of the difference in the actual state of health between the fuel cell systems FCS1, FCS2.

[0089] FIG. 3 depicts another embodiment of a method according to the invention.

[0090] The box 200 represents when the vehicle 100 is started, i.e. turned on or activated.

[0091] The method may be initiated in response to obtaining a request to activate all of the at least two fuel cell systems FCS1, FCS2. This is herein represented by activating both fuel cell systems FCS1, FCS2.

[0092] The method may accordingly comprise an initial step 210 of determining a need to activate all of the at least two fuel cell systems FCS1, FCS2. If the answer is yes, the method may be continued to 220 as shown in FIG. 3.

[0093] In 220, information about an estimated actual state of health of each fuel cell system FCS1, FCS2 is obtained. This is represented by the arrows from each fuel cell system FCS1, FCS2 to the box 220.

[0094] In 220, the actual states of health of the fuel cell systems FCS1, FCS2 are compared, and when the comparison is indicative of a predefined difference between the actual states of health of the fuel cell systems FCS1, FCS2, the method is either continued to 240 or 250.

[0095] However, when the comparison of the actual states of health of the fuel cell systems FCS1, FCS2 is indicative of no difference between the actual states of health of the fuel cell systems FCS1, FCS2, the method is instead continued to 230. In 230, the fuel cell systems FCS, FCS2 are operated with the same operating dynamics and/or in the same operating window.

[0096] The method is continued from 220 to 240 when the actual state of health of the fuel cell system FCS1 is worse than the actual state of health of the fuel cell system FCS2, and from 220 to 250 when the actual state of health of the fuel cell system FCS2 is worse than the actual state of health of the fuel cell system FCS1.

[0097] In 240, the actual state of health of the fuel cell system FCS1 is compared with a determined expected state of health of the fuel cell system FCS1, wherein the expected state of health is based on historical use conditions of the fuel cell system FCS1.

[0098] The expected state of health of the fuel cell system FCS1 is determined in box 242. The historical use conditions may for example be obtained from a database or memory, represented by box 244.

[0099] When the actual state of health of the fuel cell system FCS1 is worse than its expected state of health, the operating dynamics and/or the operating window of the fuel cell system FCS1 is/are reduced and the operating dynamics and/or the operating window of the other fuel cell system FCS2 is/are increased. This is represented by box 248 in FIG. 3.

[0100] On the other hand, when the actual state of health of the fuel cell system FCS1 is better than its expected state of health, the fuel cell systems FCS1, FCS2 are operated with the same operating dynamics and/or in the same operating window. This is represented by box 246 in FIG. 3.

[0101] In 250, the actual state of health of the fuel cell system FCS2 is compared with a determined expected state of health of the fuel cell system FCS2, wherein the expected state of health is based on historical use conditions of the fuel cell system FCS2.

[0102] The expected state of health of the fuel cell system FCS2 is determined in box 252. The historical use conditions may for example be obtained from a database or memory, represented by box 254.

[0103] When the actual state of health of the fuel cell system FCS2 is worse than its expected state of health, the operating dynamics and/or the operating window of the fuel cell system FCS2 is/are reduced and the operating dynamics and/or the operating window of the other fuel cell system FCS1 is/are increased. This is represented by box 258 in FIG. 3.

[0104] On the other hand, when the actual state of health of the fuel cell system FCS2 is better than its expected state of health, the fuel cell systems FCS1, FCS2 are operated with the same operating dynamics and/or in the same operating window. This is represented by box 256 in FIG. 3.

[0105] FIG. 4 depicts schematically a propulsion system 1 for a vehicle according to an example embodiment of the invention. The propulsion system 1 comprises a fuel cell system FCS1 and another fuel cell system FCS2. As shown, the propulsion system 1 may further comprise an electrical energy storage system EES. The propulsion system 1 may for example be part of the vehicle 100 as shown in FIG. 1. In the shown embodiment, the propulsion system 1 further comprises a respective DC/DC converter 20, 22 for the respective fuel cell systems FCS1, FCS2. It further comprises a junction box 30 and an electrical machine 40 which is drivingly connected to at least one traction wheel 50 of the vehicle 100. As such, the solid lines between the parts in the figure represent electrical connections, except for the line between the electrical machine 40 and the at least one traction wheel 50 which instead represents a mechanical driving connection. The operation of the fuel cell systems FCS1, FCS2, and of the electrical energy storage system EES is controlled by a control unit 110. The control unit 110 may further be used for controlling operation of the propulsion system 1, i.e. also for controlling e.g. the electrical machine 40. The fuel cell systems FCS1, FCS2 are preferably adapted to be the main contributors for providing propulsive power to the at least one traction wheel 50. Accordingly, the electrical energy storage system EES is preferably adapted to provide additional propulsive power in situations when the complete requested power cannot be provided by the fuel cell systems FCS1, FCS2, or when it is not suitable to provide the complete requested power by the fuel cell systems FCS1, FCS2.

[0106] The control unit 110 is herein an electronic control unit. It may comprise processing circuitry which is adapted to run a computer program as disclosed herein. The control unit 110 may comprise hardware and/or software for performing the method according to the invention. In an embodiment the control unit 110 may be denoted a computer. The control unit 110 may be constituted by one or more separate sub-control units. In addition, the control unit 110 may communicate with the propulsion system 1 by use of wired and/or wireless communication means. This is indicated by dashed lines in FIG. 4. The control unit 110 may be part of the vehicle 100 as shown in FIG. 1. Still further, even though the control unit 110 preferably is a vehicle on-board control unit, it shall be noted that the control unit 110 may additionally or alternatively be a vehicle off-board control unit, such as a control unit being part of a computer cloud system.

[0107] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.