TECHNICAL FIELD

The disclosure relates to a computer-implemented method for controlling a plurality of fuel cell systems for a vehicle. The disclosure further relates to a control unit, a propulsion system, a vehicle, a computer program and a computer-readable medium.

The disclosure can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the disclosure will be described with respect to a truck, the disclosure is not restricted to this particular vehicle, but may also be used in other vehicles such as passenger cars and marine vessels.

BACKGROUND

A fuel cell is an electrochemical cell which converts chemical energy into electricity. The fuel cell converts the chemical energy of a fuel, typically hydrogen, and an oxidizing agent, typically oxygen, into electricity. Accordingly, a fuel cell can be used as an alternative or as a complement to electric batteries. In recent years fuel cells have been considered for powering electric vehicles, such as pure electric vehicles and hybrid electric vehicles.

Typically, a fuel cell system for a vehicle comprises a fuel cell stack comprising one or more fuel cells. In addition, the fuel cell system may comprise a turbo and a humidifier. The turbo comprises a turbine and a compressor which are drivingly connected. During use of the fuel cell system, an inlet airflow to the fuel cell stack flows via the compressor and the humidifier. The inlet airflow delivers the above-mentioned oxidizing agent to the fuel cell(s). An outlet airflow from the fuel cell stack flows via the humidifier and the turbine until it exits into an external environment. Some or all of the outlet airflow may bypass the humidifier at certain occasions. During use, the humidifier transfers water, or water and heat, from the outlet airflow to the inlet airflow. There are also examples of fuel cell systems which do not use a humidifier and/or a turbo. For example, water injectors and water separators may be used to humidify the inlet airflow and to dehumidify the outlet airflow. A vehicle may be equipped with a plurality of fuel cell systems to be able to provide sufficient power for driving the vehicle. In addition, the plurality of fuel cell systems is often used in combination with an electrical energy storage system, such as a battery pack comprising lithium-ion cells. The requested power for the vehicle can be delivered in combination by the plurality of fuel cell systems and the electrical energy storage system or by less than all of the systems. For example, the power distribution between the systems may be optimized in dependence on energy efficiency.

The plurality of fuel cell systems needs to be cooled during driving. Hence, at least one cooling system is required for the plurality of fuel cell systems. More particularly, in addition to electric power, thermal load is generated by the fuel cell systems during use and cooling is required to maintain a sufficient performance and/or to ensure that the fuel cell system degradation is not too high.

Even though it is known to use a plurality of fuel cell systems for powering a vehicle, e.g. as mentioned in the above, there is still a strive to develop further improved fuel cell system technology.

SUMMARY

An object of the disclosure is to provide a computer-implemented method for controlling a plurality of fuel cell systems for a vehicle, which alleviates at least one of the drawbacks of the prior art, or which at least provides a suitable alternative. Other objects of the disclosure are to provide a control unit, a propulsion system, a vehicle, a computer program and a computer-readable medium, which alleviate(s) at least one drawback of the prior art, or which at least provide(s) a suitable alternative.

According to a first aspect of the disclosure, the object is achieved by a method according to claim 1.

Hence, there is provided a computer-implemented method for controlling a plurality of fuel cell systems for a vehicle, comprising:

- estimating required power needs from the plurality of fuel cell systems for a planned trip of the vehicle, and - in response to determining that a fuel cell system combination including less than all of the plurality of fuel cell systems is sufficient to deliver the required power needs for the planned trip:

- estimating a thermal load of the fuel cell system combination for the planned trip and comparing the estimated thermal load with cooling capabilities allocated for the fuel cell system combination, and

- based on the comparison, activating all of the plurality of fuel cell systems for the planned trip when the comparison fulfils a first criterion and activating the fuel cell system combination for the planned trip when the comparison fulfils a second criterion.

By the provision of a method according to the first aspect of the disclosure, improved control of the plurality of fuel cell systems is achieved. For example, the present disclosure is based on a realization that on some occasions it may be desirable to use all of the plurality of fuel cell systems even though a combination including less than all of the fuel cell systems may be able to deliver the required power needs for a planned trip. In addition, on some occasions it may be desirable to use less than all of the fuel cell systems even though the thermal load therefrom will be higher than if all of the plurality of fuel cell systems delivered the required power needs for the planned trip. As such, by determining if the comparison fulfils the first or the second criterion, the control can be improved so that for example the combined service life of the plurality of fuel cell systems is increased and/or so that fuel cell system efficiency is improved. Hence, even though the disclosure is based on a realization that it is advantageous to use all of the fuel cell systems to reduce the thermal load from each fuel cell system, implying increased efficiency, the disclosure is further based on a realization that on some occasions it may be desirable to not activate all of the fuel cell systems to thereby save on fuel cell system degradation.

A fuel cell system combination including less than all of the plurality of fuel cell systems means herein that the fuel cell system combination does not include each fuel cell system of the plurality of fuel cell systems, but instead a lower number of fuel cell systems. As such, by way of example, if the plurality of fuel cell systems is defined by a number n of fuel cell systems, the fuel cell system combination will include n-1 , or fewer, fuel cell systems, wherein n is a positive integer and n > 2. A fuel cell system may herein be at least defined by a fuel cell stack comprising a plurality of fuel cells. A fuel cell system may further comprise the above-mentioned turbo and/or humidifier, and/or water injector and/or water separator. It may further comprise a cooling system for the fuel cell stack. However, according to some embodiments, the plurality of fuel cell systems may share some components, such as the turbo, the humidifier, the water injector, the water separator, and/or the cooling system.

Optionally, the first criterion is indicative of that the cooling of the thermal load, i.e. the thermal load of the fuel cell system combination, is below a first threshold and the second criterion is indicative of that the cooling of the thermal load is above the first threshold. Still optionally, being below the first threshold is indicative of that the estimated thermal load is exceeding the cooling capabilities allocated for the fuel cell system combination. Still optionally, being above the first threshold is indicative of that the estimated thermal load is lower than the cooling capabilities allocated for the fuel cell system combination. The cooling being below the first threshold may imply that the cooling is insufficient and the cooling being above the first threshold may imply that the cooling is sufficient.

Sufficient cooling for the fuel cell system combination may be indicative of a condition when it is advantageous to not use all of the plurality of fuel cell systems. This implies that degradation can be saved for the non-used fuel cell system(s). Still further, insufficient cooling for the fuel cell system combination may be indicative of a condition when it is advantageous to use all of the plurality of fuel cell systems to thereby improve fuel cell system efficiency. Fuel cell system efficiency may correspond to a ratio of delivered power and generated thermal load. It may be assumed that a higher power output from a fuel cell system result in a lower efficiency, and vice versa, i.e. the ratio of power delivered and generated thermal load may be reduced for higher power outputs.

Optionally, the thermal load of the fuel cell system combination for the planned trip is estimated in dependence on a state of health, SoH, of the fuel cell system combination. Estimating the thermal load in dependence on SoH of the fuel cell system combination implies a more reliable and accurate thermal load estimation. In particular, thermal load may typically increase when SoH is deteriorating.

Optionally, the SoH is continuously updated in dependence on a usage of the fuel cell system combination. Thereby, a more accurate thermal load estimation can be achieved. This in turn implies that the decision whether to activate the fuel cell system combination or all of the fuel cell systems for the planned trip will be improved.

Optionally, the cooling capabilities allocated for the fuel cell system combination are estimated for the planned trip. For example, the cooling capabilities may vary in dependence on different factors associated with the vehicle and/or the planned trip. This implies that a more accurate and reliable decision whether to activate the fuel cell system combination or all of the fuel cell systems for the planned trip may be provided.

Optionally, the cooling capabilities allocated for the fuel cell system combination are estimated based on at least one of a vehicle ambient temperature, a predicted vehicle speed during the planned trip and a predicted performance of a vehicle cooling equipment during the planned trip. Anyone of vehicle ambient temperature, vehicle speed and/or vehicle cooling equipment performance may vary. As such, by estimating the cooling capabilities allocated for the fuel cell system combination based on at least one of these parameters, a further improved decision whether to activate the fuel cell system combination or all of the fuel cell systems for the planned trip may be provided.

Optionally, the required power needs of the plurality of fuel cell systems for the planned trip are estimated based on any one of traffic information, terrain information, available state of charge level and/or power capacity of an electrical energy storage system of the vehicle, vehicle weight and speed limits along the planned trip. By estimating the required power needs based on anyone of these parameters, a more accurate estimation of the required power needs may be provided. Thereby, a further improved decision whether to activate the fuel cell system combination or all of the fuel cell systems for the planned trip may be provided.

According to a second aspect of the disclosure, the object is achieved by a control unit according to claim 10.

Hence, there is provided a control unit for controlling a plurality of fuel cell systems for a vehicle. The control unit is configured to:

- estimate required power needs from the plurality of fuel cell systems for a planned trip of the vehicle, and - in response to determining that a fuel cell system combination including less than all of the plurality of fuel cell systems is sufficient to deliver the required power needs for the planned trip:

- estimate a thermal load of the fuel cell system combination for the planned trip and compare the estimated thermal load with cooling capabilities allocated for the fuel cell system combination, and

- based on the comparison, activate all of the plurality of fuel cell systems for the planned trip when the comparison fulfils a first criterion and activate the fuel cell system combination for the planned trip when the comparison fulfils a second criterion.

Advantages of the second aspect of the disclosure are analogous to the advantages of the first aspect of the disclosure. It shall also be noted that all embodiments of the first aspect of the disclosure are combinable with all embodiments of the second aspect of the disclosure.

According to a third aspect of the disclosure, the object is achieved by a propulsion system according to claim 11.

Hence, there is provided a propulsion system for a vehicle comprising a plurality of fuel cell systems, and further comprising a control unit according to any one of the embodiments of the second aspect of the disclosure.

According to a fourth aspect of the disclosure, the object is achieved by a vehicle according to claim 12.

Hence, there is provided a vehicle comprising a propulsion system according to any one of the embodiments of the third aspect of the disclosure.

According to a fifth aspect of the disclosure, the object is achieved by a computer program according to claim 13.

Hence, there is provided a computer program comprising program code means for performing the steps of any of the embodiments of the first aspect of the disclosure when said program is run on a computer. According to a sixth aspect of the disclosure, the object is achieved by a computer readable medium according to claim 14.

Hence, there is provided a computer readable medium carrying a computer program comprising program code means for performing the steps of any of the embodiments of the first aspect of the disclosure when said program product is run on a computer

Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the disclosure cited as examples.

In the drawings:

Fig. 1 is a side view of a vehicle according to an example embodiment of the disclosure,

Fig. 2 is a schematic view of a propulsion system for a vehicle according to an example embodiment of the disclosure,

Fig. 3 is a flowchart of a method according to example embodiments of the first aspect of the disclosure,

Fig. 4 is a graph representing thermal load and power output of a fuel cell system, and

Fig. 5 is a flowchart of a method according to example embodiments of the first aspect of the disclosure.

Like reference numbers in the drawings refer to the same or similar element unless expressed otherwise.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE Fig. 1 depicts a vehicle in the form of a truck 100 according to an example embodiment of the fourth aspect of the disclosure. The truck 100 is herein a towing truck for towing one or more trailers (not shown). It shall however be noted that the vehicle may be any other kind of vehicle, such as a bus, a construction equipment, e.g. a wheel loader, an excavator etc., or a passenger car. The vehicle may in some embodiments also be in the form of a marine vessel. The vehicle may be an autonomous vehicle, i.e. a self-driving vehicle, and/or the vehicle may be arranged to be operated by a driver. The driver may be an on-board driver and/or an off-board driver which controls the vehicle from a remote location.

The vehicle 100 as shown in fig. 1 comprises a propulsion system 1 for providing propulsion force to ground engaging members 50 of the vehicle 100. The ground engaging members 50 are herein a pair of wheels. However, in other embodiments, crawler members may be used in addition or as an alternative.

The vehicle 100 further comprises a control unit 110 which will be further described in the below.

Fig. 2 depicts an example embodiment of a propulsion system 1 , such as the propulsion system 1 depicted in fig. 1 , which comprises a plurality of fuel cell systems FCS1 , FCS2. In this embodiment, the plurality of fuel cell systems is in the form of two fuel cell systems FCS1, FCS2. It shall be noted that the propulsion system 1 may comprise more than two fuel cell systems, such as three, four or five fuel cell systems.

As shown, the propulsion system 1 may further comprise an electrical energy storage system ESS. 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 wheel 50 of the vehicle 100. As such, the solid lines between the parts in the fig. 2 represent electrical connections, except for the line between the electrical machine 40 and the at least one 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 ESS is controlled by a control unit 110, such as the control unit 110 shown in fig. 1. 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 wheel 50. Accordingly, the electrical energy storage system ESS is preferably adapted to provide additional propulsive power in situations when the complete required power cannot be provided by the fuel cell systems FCS1, FCS2, or when it is not suitable to provide the complete required power by the fuel cell systems FCS1, FCS2.

The fuel cell system FCS1 may comprise a cooling system (not shown) and the fuel cell system FCS2 may comprise a cooling system (not shown) for cooling a fuel cell stack (not shown) of the respective fuel cell system FCS1, FCS2 during use. The cooling systems may be at least partly separate cooling systems which are arranged to be at least partly individually controlled. The cooling systems may be at least partly integrated, sharing at least some cooling equipment, such as sharing one or more cooling fans.

The control unit 110 is herein an electronic control unit. It may comprise processing circuitry which is adapted to run a computer program 112 as disclosed herein. The control unit 110 may comprise hardware and/or software for performing the method according to the first aspect of the disclosure. 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. 2. 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.

Turning to fig. 3, a flowchart of a method according to embodiments of the first aspect of the disclosure is depicted. The method is computer-implemented and used for controlling a plurality of fuel cell systems FCS1 , FCS2 for a vehicle 100, such as shown in figs. 1 and 2, respectively.

The method comprises:

S1: estimating required power needs from the plurality of fuel cell systems FCS1, FCS2 for a planned trip of the vehicle 100, and - in response to determining that a fuel cell system combination including less than all of the plurality of fuel cell systems FCS1 , FCS2 is sufficient to deliver the required power needs for the planned trip:

S2: estimating a thermal load of the fuel cell system combination for the planned trip, and S3: comparing the estimated thermal load with cooling capabilities allocated for the fuel cell system combination, and

- based on the comparison,

S4: activating all of the plurality of fuel cell systems FCS1, FCS2 for the planned trip when the comparison fulfils a first criterion, and

S5: activating the fuel cell system combination for the planned trip when the comparison fulfils a second criterion.

In a similar vein, the control unit 110 as e.g. shown in fig. 2 is configured to:

- estimate required power needs from the plurality of fuel cell systems FCS1 , FCS2 for a planned trip of the vehicle 100, and

- in response to determining that a fuel cell system combination including less than all of the plurality of fuel cell systems FCS1 , FCS2 is sufficient to deliver the required power needs for the planned trip:

- estimate a thermal load of the fuel cell system combination for the planned trip and compare the estimated thermal load with cooling capabilities allocated for the fuel cell system combination, and

- based on the comparison, activate all of the plurality of fuel cell systems FCS1 , FCS2 for the planned trip when the comparison fulfils a first criterion and activate the fuel cell system combination for the planned trip when the comparison fulfils a second criterion.

In the example shown in fig. 2, activating less than all of the plurality of fuel cell systems FCS1, FCS2 means that only one of the fuel cell systems is activated, i.e. FCS1 or FCS2. According to an example embodiment, the fuel cell system combination is selected as one or more fuel cell systems with a highest state of health, SoH, i.e. the fuel cell system(s) which is/are in a better health condition. Thereby, the combined service life may be extended.

The planned trip may be a trip from one point in an area to another point in the area, such as when the vehicle is conducting a driving mission, such as for transporting or picking up a load. The planned trip may also be a portion of a longer planned trip, such as a portion of the longer planned trip comprising one or more uphill climbs, a portion of the longer planned trip comprising a substantially horizontally extending road stretch, and/or a portion of the longer planned trip comprising one or more downhill segments.

The planned trip may be predetermined. Additionally, or alternatively, the planned trip may be provided by a user, such as by a driver providing the planned trip via a human machine interface (not shown) of the vehicle 100. Additionally, or alternatively, the planned trip may be provided as an instruction to the vehicle 100 from a remote server, such as via a wireless communication system. Additionally, or alternatively, the planned trip may be provided from an electronic memory (not shown) of e.g. the vehicle 100.

The first criterion may be indicative of that the cooling of the thermal load is below a first threshold and the second criterion may be indicative of that the cooling of the thermal load is above the first threshold. For example, being below the first threshold may be indicative of that the estimated thermal load is exceeding the cooling capabilities allocated for the fuel cell system combination. Still further, being above the first threshold may be indicative of that the estimated thermal load is lower than the cooling capabilities allocated for the fuel cell system combination.

According to example embodiments, the first threshold may be set in dependence on a maximum allowed operating temperature during use of the fuel cell stack(s) of the fuel cell system combination. For example, the first threshold may be set so that the maximum allowed operating temperature of the fuel cell stack(s) of the fuel cell system combination is not exceeded during use. By way of example, the maximum allowed operating temperature may vary over time, such as vary in dependence on the SoH of the fuel cell system combination. However, it shall be noted that even though the operating temperatures are kept the same throughout the lifetime of the fuel cell system(s), the thermal load is expected to increase with decreasing state of health of the fuel cell system(s).

The cooling capabilities allocated for the fuel cell system combination may be estimated for the planned trip. For example, the cooling capabilities allocated for the fuel cell system combination may be estimated based on at least one of a vehicle ambient temperature, a predicted vehicle speed during the planned trip and a predicted performance of a vehicle cooling equipment during the planned trip. For example, if the vehicle 100 is operating in a hot climate condition, it may be assumed that more cooling will be required than if the vehicle 100 is operating in colder conditions. As another example, it may be assumed that cooling capabilities increase in dependence on increased vehicle speed. As yet another example, it may be assumed that a higher performance, such as a higher fan speed, of the vehicle cooling equipment results in a higher, or improved, cooling capability.

The required power needs of the plurality of fuel cell systems FCS1, FCS2 for the planned trip may be estimated based on any one of traffic information, terrain information, available state of charge level and/or power capacity of an electrical energy storage system ESS of the vehicle 100, vehicle weight and speed limits along the planned trip.

For example, traffic information may indicate that the vehicle 100 will only be able to drive at lower speeds, or even stop and stand still during periods of the planned trip. It may for example be assumed that a denser traffic situation results in lower power needs for the planned trip. As another example, terrain information may indicate that the propulsion system 1 of the vehicle 100 will need to operate at higher power levels due to e.g. one or more uphill climbs during driving along the planned trip.

Fig. 4 depicts a graph where thermal load TL of a fuel cell system is represented on a y- axis and power output, or net power, NP is represented on an x-axis. The dashed line 1 :1 represents the situation when the power output NP is the same as the generated thermal load, or heat rejection, TL, i.e. a ratio of 1 :1.

The solid line curve C1 represents the ratio of power output NP and generated thermal load TL for a fuel cell system. As shown, when the fuel cell system is operating at lower power levels, power output NP is expected to be higher than thermal load TL, i.e. NP > TL. On the other hand, when the fuel cell system is operating at higher power levels, power output is expected to be lower than thermal load TL, i.e. NP < TL.

During use of the fuel cell system, i.e. during degradation of the fuel cell system, the curve C1 is expected to change so that a range where NP > TL will decrease, i.e. the vertical separation line L1 is expected to move to the left in the graph during use. As such, according to example embodiments of the disclosure, the thermal load of the fuel cell system combination for the planned trip may be estimated in dependence on a state of health, SoH, of the fuel cell system combination.

Accordingly, by state of health, SoH, is herein meant a level of degradation of the fuel cell system which affects the remaining lifetime of the fuel cell system. For example, 100 % state of health implies that the system is new and not used, whereas 50 % state of health implies that the remaining lifetime is 50 % of the total lifetime of the system.

For example, state of health, SoH, for a fuel cell system may be estimated by electrochemical impedance spectroscopy. Additionally, or alternatively, state of health may be estimated by use of polarization curve comparison between a used fuel cell system and a new, or fresh, fuel cell system.

The SoH may be continuously updated in dependence on a usage of the fuel cell system combination. Thereby an improved thermal load estimation may be provided. In particular, it is assumed that the thermal load will increase in dependence on the degradation of the fuel cell system, as explained in the above with respect to fig. 4.

T urning to fig. 5, another flowchart of a method according example embodiments of the disclosure is shown.

S10 represents when the vehicle 100 starts, such as when starting the propulsion system 1.

In S20, required power needs from the plurality of fuel cell systems FCS1 , FCS2 are estimated for a planned trip of the vehicle 100.

The estimation in S20 may be based on any one of traffic information, terrain information, available state of charge level and/or power capacity of an electrical energy storage system ESS of the vehicle 100, vehicle weight and speed limits along the planned trip, as e.g. mentioned in the above. This is received from B1 , which may be an electronic memory, such as a database, and/or a human machine interface. The method may comprise an intermediate step S30 in which a complete power estimation for the planned trip is performed. Accordingly, the required power needs from the plurality of fuel cell systems FCS1 , FCS2 may be lower than the complete power needs for the planned trip since e.g. the ESS, or any other power provider, may be used in addition to the plurality of fuel cell systems FCS1 , FCS2 for providing the power for the planned trip.

In S40 it may be determined if a fuel cell system combination including less than all of the plurality of fuel cell systems FCS1, FCS2 is sufficient to deliver the required power needs for the planned trip.

If the answer is no, the method is continuing to S50 where all of the plurality of fuel cell systems FCS1, FCS2 are activated.

However, if the answer is yes, the method is continuing to S60. In S60, a thermal load of the fuel cell system combination for the planned trip is estimated. This may be performed by using a SoH of the fuel cell system combination. The SoH is in this example received from B2, which may be an electronic memory, such as a database. Additionally, or alternatively, the SoH may be estimated during use of the method, e.g. by use of electrochemical impedance spectroscopy and/or by use of polarization curves as mentioned in the above.

In S70, the estimated thermal load is compared with cooling capabilities allocated for the fuel cell system combination.

When the comparison fulfils a first criterion, the method is continuing to S80 where all of the plurality of fuel cell systems FCS1, FCS2 are activated for the planned trip. For example, the first criterion may be fulfilled when cooling of the thermal load is below a first threshold, wherein being below the first threshold is indicative of that the estimated thermal load is exceeding the cooling capabilities allocated for the fuel cell system combination.

However, when the comparison fulfils a second criterion, the method is continuing to S90 where the fuel cell system combination for the planned trip is activated. For example, the second criterion may be fulfilled when cooling of the thermal load is above the first threshold, wherein being above the first threshold is indicative of that the estimated thermal load is lower than the cooling capabilities allocated for the fuel cell system combination. The cooling capabilities used in the comparison in S70 may be estimated in S100. For example, the cooling capabilities may be estimated by information from B3, which may be an electronic memory, such as a database, and/or a human machine interface. The information for estimating the cooling capabilities may be at least one of a vehicle ambient temperature, a predicted vehicle speed during the planned trip and a predicted performance of a vehicle cooling equipment during the planned trip.

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.