System and method for operating a fuel cell system

Abstract

The invention relates to a system and a method for operating a fuel cell system, and particularly provides a system and a method for controlling operation of a fuel cell system of a vehicle, the fuel cell system including a fuel cell stack and a coolant system. The control system is configured to pre-determine that a fuel cell system power drop event will occur when power of the fuel cell system needs to be reduced as the vehicle approaches a portion of the route associated with a low power demand of the fuel cell system. A fuel cell system is controlled by: reducing a target inlet coolant temperature; and applying a first response strategy that involves continuously reducing the flow rate of the coolant flow and / or a second response strategy that may involve continuously and progressively increasing the flow rate of the coolant flow, and then, in some cases, continuously and progressively reducing the flow rate of the coolant flow.

Description

Technical Field

[0001] The present disclosure generally relates to operating a fuel cell system when a requested power output from the fuel cell system is reduced.

[0002] The present disclosure may be applicable to heavy-duty vehicles such as trucks, buses, and construction equipment, as well as generator sets. Background Art

[0003] A fuel cell is an electrochemical device that includes an electrolyte sandwiched between two electrodes such as an anode and a cathode. A solid polymer electrolyte fuel cell employing a proton exchange membrane (PEM) generates electric power or energy via an electrochemical reaction between a fuel such as hydrogen received at the anode or anode side and an oxidant such as oxygen or air received at the cathode or cathode side. PEM fuel cells are considered well-suited for vehicle applications as well as stationary applications employing fuel cell systems. Two or more fuel cells are arranged together as a fuel cell stack to provide a higher output voltage. One or more fuel cell stacks may form a fuel cell unit, and a fuel cell system may include one or more fuel cell units.

[0004] In a fuel cell, metals such as palladium and platinum are used as catalysts to facilitate the electrochemical reaction between hydrogen and an oxidizing gas, where the reaction occurs on a membrane or electrolyte. A support structure made of a catalyst support material such as carbon is configured to support the membrane, and the metal catalyst is typically used on the catalyst support material. The condition of the catalyst and the support material defines the durability, life, and performance of the fuel cell system. The catalyst needs to operate under certain conditions to produce an effective reaction rate. Thus, an excessive increase in the single cell voltage, which may be defined as the cell voltage or potential of each fuel cell of each fuel cell stack in a fuel cell system, may cause deterioration of the catalyst and the support material. Therefore, during operation of a fuel cell system, it is desirable to maintain the single cell voltage below a certain voltage level.

[0005] In fuel cell systems, such as higher power fuel cell systems that are increasingly of interest in automotive and other fields, problems arise as the load on the fuel cell system decreases. Specifically, in the case of a fuel cell system with a relatively high power, the single cell potential can reach a safety threshold. Thus, when the power of the fuel cell system decreases at a certain rate of decrease, the single cell voltage can increase to a value that has a negative impact on the condition of the catalyst and the carbon support material. Therefore, it can be challenging to control a fuel cell system operating at a lower load in a manner that takes into account the potential degradation of the catalyst and the support material. Additionally, in many cases, it may be desirable to relatively rapidly decrease (i.e., decrease at a rapid rate of decrease) the power of the fuel cell system. However, it can be a challenge to allow the power of the fuel cell system to decrease rapidly while avoiding degradation of the PEM due to dehydration, allowing the fuel cell stack temperature to increase excessively, and allowing the single cell voltage to increase above a safe level, which can lead to degradation of the catalyst and the support material.

[0006] Various methods have been proposed to control fuel cell systems. However, there is still a need for improved methods for controlling the operation of a fuel cell system as the power demand of the fuel cell system decreases. SUMMARY OF THE INVENTION

[0007] Aspects of the present disclosure relate to a control strategy for controlling a fuel cell system in a manner that limits the single cell voltage or potential to a value below 0.8 V as the power demand of the fuel cell system decreases. This allows avoidance of degradation of the catalyst and the support material of the fuel cell stack of the fuel cell system, avoidance of degradation of the PEM, and avoidance of excessive increase in the fuel cell stack temperature. The control strategy allows for a higher or faster rate of decrease, and thus a relatively rapid decrease in the power of the fuel cell system can occur, for example, in some cases, between about 75 kW / s and about 100 kW / s. For example, when a vehicle including the fuel cell system is braking, the power generated by the fuel cell system can be reduced sufficiently rapidly without causing an adverse impact on the fuel cell system.

[0008] In one aspect, a fuel cell system for a vehicle is provided. The fuel cell system includes a fuel cell unit that includes a fuel cell stack, a coolant system, and a control system. The fuel cell stack includes a cathode and an anode, and the cathode is configured to receive an air flow via a cathode inlet line. The coolant system is configured to circulate coolant through the fuel cell stack, and the coolant system includes: a coolant inlet line configured to direct a coolant flow to the fuel cell stack; and a coolant outlet line configured to carry the coolant flow away from the fuel cell stack after the coolant has passed through the fuel cell stack. The control system includes a processing circuit configured to pre-determine a required reduction in the power of the fuel cell system based on a required braking power needed for the vehicle to travel along a route on a portion of the route associated with a low power demand of the fuel cell system; and to control the fuel cell system to reduce the power of the fuel cell system based on the required braking power in preparation for a braking event. The processing circuit is configured to control the fuel cell system to reduce the power of the fuel cell system based on the required braking power to prepare for a braking event by: reducing a target inlet coolant temperature of the coolant flow to a first temperature threshold such that when the vehicle begins to travel on a portion of the route associated with a low power demand of the fuel cell system, the inlet temperature of the coolant flow drops below a threshold coolant flow inlet temperature; applying a first response strategy in response to determining that a magnitude of the required reduction in the power of the fuel cell system is equal to or less than a first threshold power level and is associated with a first rate of decrease requirement, the first response strategy including continuously reducing a flow rate of the coolant flow to a value corresponding to the required reduction in the power of the fuel cell system; and applying a second response strategy in response to determining that the magnitude of the required reduction in the power of the fuel cell system is greater than the first threshold power level and is associated with a second rate of decrease requirement. The second response strategy includes: in a first stage of the second response strategy, continuously and gradually increasing the flow rate of the coolant flow; and in a second stage of the second response strategy, continuously and gradually reducing the flow rate of the coolant flow as the power of the fuel cell system decreases and in response to determining that an outlet temperature of the coolant flow drops below a threshold coolant flow outlet temperature.

[0009] Technical benefits include controlling the fuel cell system in a manner that allows the power demand or load on the fuel cell system to be reduced at a desired rate of decrease while avoiding the risk of the single cell voltage rising to a value higher than the 0.8 V safety threshold. Thus, the systems and methods of the present disclosure provide improved control of a fuel cell system in a low power demand state in a manner that avoids degradation of the catalyst and support materials of the fuel cell stack of the fuel cell system. As another advantage, if the fuel cell system power is reduced more quickly, this allows for more regenerative braking to occur. Thus, the overall efficiency of the vehicle is improved.

[0010] In some examples, the processing circuitry can be configured to monitor the single cell voltage of a fuel cell stack such that the single cell voltage does not exceed 0.79 V.

[0011] In some examples, the processing circuitry can also be configured to control the fuel cell system to reduce the power of the fuel cell system based on a required braking power in order to prepare for a braking event by continuously monitoring the outlet temperature of the coolant flow to avoid increasing the temperature of the fuel cell stack of the fuel cell unit; and maintaining the cathode stoichiometry constant.

[0012] In some examples, the cathode stoichiometry can be maintained constant by adjusting the power of an air compressor configured to pressurize the air flow supplied to the cathode of the fuel cell stack such that the flow rate of the air flow maintains a constant relationship with the current output from the fuel cell system.

[0013] In some examples, the processing circuitry can be configured to obtain a prediction or predictive information that a vehicle traveling on a route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to occur after a portion associated with a low power demand of the fuel cell system where a braking event is expected to occur.

[0014] In some examples, the prediction can include a prediction of an upcoming top of a downhill along the route.

[0015] In some examples, the fuel cell unit includes one fuel cell unit. Thus, the fuel cell system includes a single fuel cell unit.

[0016] In one aspect, a fuel cell vehicle is provided that includes a fuel cell system according to an example of the present disclosure. The fuel cell vehicle can include a vehicle controller that can be configured to determine a required braking power required by the vehicle on a portion of the route associated with a low power demand of the fuel cell system; and provide the determined required braking power to a control system of the fuel cell system. In some examples, the vehicle controller can generate a prediction that a vehicle traveling on a route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to occur after a portion associated with a low power demand of the fuel cell system where a braking event is expected to occur. The vehicle controller can provide the generated prediction to a control system of the fuel cell system, such as a fuel cell control unit (FCCU).

[0017] In one aspect, a method of controlling the operation of a fuel cell unit of a fuel cell system of a vehicle is provided. The method includes: predetermining a required reduction in the power of the fuel cell system based on a required braking power for the vehicle to travel along a route on a portion of the route associated with a low power demand; and controlling the fuel cell system to reduce the power of the fuel cell system based on the required braking power in preparation for a braking event. The control includes: reducing a target inlet coolant temperature of a coolant flow to a first temperature threshold such that when the vehicle begins to travel on a portion associated with a low power demand of the fuel cell system, an inlet temperature of the coolant flow of the coolant system flowing through the fuel cell system drops below a threshold coolant flow inlet temperature; applying a first response strategy in response to determining that a magnitude of the required reduction in the power of the fuel cell system is equal to or less than a first threshold power level and is associated with a first rate of descent requirement, the first response strategy including continuously reducing a flow rate of the coolant flow to a value corresponding to the required reduction in the power of the fuel cell system; and applying a second response strategy in response to determining that the magnitude of the required reduction in the power of the fuel cell system is greater than the first threshold power level and is associated with a second rate of descent requirement. The second response strategy includes: in a first stage of the second response strategy, continuously and gradually increasing the flow rate of the coolant flow; and in a second stage of the second response strategy, continuously and gradually reducing the flow rate of the coolant flow as the power of the fuel cell system decreases and in response to determining that an outlet temperature of the coolant flow drops below a threshold coolant flow outlet temperature.

[0018] Technical benefits of the method include benefits similar to the technical benefits described above in connection with the fuel cell system. Accordingly, the method of the present disclosure provides improved control of a fuel cell system that reduces power at a desired rate of descent in a manner that avoids degradation of the catalyst and support materials of the fuel cell stack of the fuel cell system.

[0019] In some examples, the method may include monitoring a single cell voltage of the fuel cell stack such that the single cell voltage does not exceed 0.79 V.

[0020] In some examples, controlling the fuel cell system to reduce the power of the fuel cell system based on the required braking power in preparation for a braking event may include: continuously monitoring an outlet temperature of the coolant flow to avoid increasing the temperature of the fuel cell stack of the fuel cell unit; and maintaining cathode stoichiometry constant.

[0021] In some examples of the method, cathode stoichiometry may be maintained constant by adjusting the power of an air compressor configured to pressurize an air flow supplied to the cathode of the fuel cell stack such that a flow rate of the air flow maintains a constant relationship with a current output from the fuel cell system.

[0022] In some examples, the method can include obtaining a prediction that a vehicle traveling on a route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to occur after a portion associated with a low power demand of the fuel cell system where a braking event is expected to occur.

[0023] In some examples, the prediction can include a prediction of an upcoming top of a downhill along the route. In some examples, the prediction can be obtained or received from a vehicle controller of the vehicle.

[0024] In one aspect, a control system for controlling a fuel cell system of a fuel cell vehicle is provided. The control system includes processing circuitry configured to execute a method according to an example of the present disclosure.

[0025] In one aspect, a fuel cell vehicle is provided, the fuel cell vehicle including a control system according to an example of the present disclosure. The fuel cell vehicle can include a vehicle controller communicatively coupled to the control system of the fuel cell system. In some examples, the control system of the fuel cell system is part of the vehicle controller.

[0026] In one aspect, a computer program product is provided, the computer program product including computer-executable instructions that, when executed by processing circuitry, cause the processing circuitry to execute a method according to any aspect and example of the present disclosure. The processing circuitry can be, for example, the processing circuitry of a control system of a fuel cell system.

[0027] In one aspect, a computer-readable storage medium is provided, having stored thereon a computer program product, the computer program product including computer-executable instructions that, when executed by processing circuitry, cause the processing circuitry to execute a method according to any aspect and example of the present disclosure. The processing circuitry can be, for example, the processing circuitry of a control system of a fuel cell system.

[0028] Additional features and advantages are disclosed in the following specification, claims, and drawings. Additionally, additional advantages will be apparent to those skilled in the art from the present disclosure or will be recognized by practicing the disclosure as described herein. Control units, computer program products, and computer-readable media associated with the technical effects and corresponding advantages discussed above are also disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Aspects of the present disclosure, cited as examples, will be described in more detail below with reference to the drawings.

[0030] Figure 1A side view showing an example of a vehicle including a fuel cell system in which a method according to an example of the present disclosure may be implemented.

[0031] Figure 2 is a block diagram showing a fuel cell system and a control system of a vehicle according to an example. Figure 1

[0032] Figure 3 is a flowchart showing a method for operating a fuel cell system according to an example.

[0033] Figure 4A and Figure 4B is a schematic block diagram showing a control system according to an example. DETAILED DESCRIPTION

[0034] In a fuel cell system, for example, in a fuel cell system capable of generating high power or higher power, as the power demand or load on the fuel cell system decreases, the single cell voltage may reach a safety threshold at a higher power level, for example, in some cases has reached 50 kW or higher. The fuel cell system may include two or more fuel cells, or in some cases includes one fuel cell, and each fuel cell includes one or more fuel cell stacks. A single fuel cell unit may be used in some applications, such as in a fuel cell vehicle, and the benefits include space savings considerations, more direct maintenance, and simplified control strategies. This makes it challenging to operate the fuel cell system correctly at reduced power and / or low power without the risk of damaging the catalyst and support materials of the fuel cell stack. In addition, in some cases, excess power may be wasted, for example when the ESS is fully charged.

[0035] Therefore, in a fuel cell system that can operate at higher power, there are limitations on how fast the power of the fuel cell system can be reduced. Too rapid a reduction in the fuel cell system power may cause the fuel cell stack temperature to increase, the membrane (e.g., PEM) to dehydrate, and the single cell voltage to soar above 0.8 V. Dehydration of the membrane results in increased ohmic losses and increased heat generation, and the change in moisture content as the membrane expands and contracts causes mechanical stress. In addition, if the single cell voltage (also interchangeably referred to as the single cell potential) increases to a value of 0.8 V or above, platinum dissolution begins to occur, thereby reducing the electrochemically active surface area (ECSA), which in turn leads to a reduction in the durability, performance, efficiency, and lifespan of the fuel cell system. Therefore, if the maximum value that the single cell voltage is allowed to reach is set to 0.8 V or just below 0.8 V (e.g., 0.79 V), the risk of catalyst and support material degradation can be reduced or avoided.

[0036] In some applications, such as in fuel cell electric vehicles, when a high propulsion power period is suddenly interrupted by a high power braking event, it may be necessary to rapidly reduce the power of the fuel cell system. For example, the vehicle may be at the top of a downhill where braking is required. In some cases, the ability of the battery to absorb braking power may be limited, and thus some form of braking assistance, such as a retarder, a braking resistor, etc., may be needed. During a braking event, the braking power may be affected because the fuel cell system generates electricity, and the generated fuel cell electricity must be directed to the ESS (such as a battery) or dissipated to the surrounding environment as it decreases or drops. Additionally, the longer it takes for the fuel cell system to drop from a high power level to a low or minimum power level, the more pronounced the harmful effects may be, such as wasting the electricity generated by the fuel cell system. Moreover, the fuel cell system dissipates heat while still operating at a high or higher power, which may limit the ability of the cooling system to handle the rapidly increasing demand of the auxiliary brake, thereby limiting the actual braking performance of the vehicle.

[0037] As another example, in a stationary application, when it is necessary to quickly disconnect from the grid or suddenly reduce power, the longer it takes for the fuel cell system to reduce its power, the more energy is wasted, and thus the lower the efficiency of the fuel cell system in the application.

[0038] In existing fuel cell system solutions, to avoid the above problems associated with reducing the power of the fuel cell system at a high rate of descent, a limit can be set on the rate of descent. In systems where durability and performance are less important, a rapid rate of descent can still be applied, but at the cost of sacrificing the durability and performance of the fuel cell system.

[0039] The methods and systems of the present disclosure employ a control strategy that allows for a rapid rate of descent at which the power of the fuel cell system can be reduced when needed. In a fuel cell system according to an example of the present disclosure, the cathode stoichiometry or cathode stoichiometric ratio can be monitored and actively controlled during normal operation and a descent event. Cathode stoichiometry can be defined as the ratio of the amount of air supplied to the fuel cell to the amount of air required by the electrochemical reaction to provide a given output current. The cathode stoichiometry during normal operation of the fuel cell system is typically maintained at a relatively high value, with the cathode stoichiometry being higher at lower loads than at higher loads to minimize the risk of oxygen deficiency. In some examples, during a descent event, the cathode stoichiometry can be maintained at a cathode stoichiometry of about 1.5 instead of increasing to a higher stoichiometry for normal operation at lower power.

[0040] The target inlet coolant temperature can be actively controlled while monitoring the actual inlet coolant temperature and the outlet coolant temperature. Additionally, the coolant flow rate can be actively controlled during normal operation and during a depressurization event. The fuel cell control unit or system can be configured to change one or more of the following parameters, such as for example: the flow rate of the coolant, the cathode stoichiometry, the target inlet coolant temperature, etc., while monitoring these parameters and the single cell voltage. In a vehicle application, predictions can be applied to predict battery power capabilities, braking requirements, fuel cell power requirements, etc.

[0041] The control system can obtain information or determine that a vehicle traveling on a route is approaching a portion of the route where a high power demand associated with the fuel cell system is expected to occur after a portion where a braking event is expected associated with a low power demand of the fuel cell system. When the vehicle is located at or near a portion of the route associated with a low power demand of the fuel cell system, the ability of the vehicle's ESS to absorb power may be limited. The control system can pre-determine a required reduction in the power of the fuel cell system based on the required braking power of the vehicle on the portion of the route associated with the low power demand of the fuel cell system. The control system can control the fuel cell system to reduce the power of the fuel cell system based on the required braking power in order to prepare for the braking event by: reducing the target inlet coolant temperature of the coolant flow to a first temperature threshold such that when the vehicle begins to travel on the portion of the route associated with the low power demand of the fuel cell system, the inlet temperature of the coolant flow of the coolant system flowing through the fuel cell unit drops below the threshold coolant flow inlet temperature. Additionally, depending on the magnitude of the required reduction in the power of the fuel cell system (which reduction is associated with a corresponding required rate of decrease), the control system can apply a first response strategy or a second response strategy, thereby allowing a rapid decrease in the power of the fuel cell system. Monitor and control the single cell voltage not to exceed 0.79 V.

[0042] Thus, in the method and system according to an example of the present disclosure, a lower power level of the fuel cell system can be achieved more quickly, that is, a higher rate of decrease can be applied, without the risk of the single cell potential rising above the 0.8 V safety threshold and without negatively affecting the durability and performance of the fuel cell stack membrane. Therefore, the overall life of the fuel cell system can be increased. As a further advantage, less power is wasted and, since the fuel cell system may generate less power when the rate of decrease increases, the regenerative braking ability can also be improved.

[0043] Thus, the system and method of the present disclosure advantageously provide improved control of a fuel cell system in a low power demand situation in a manner that avoids degradation of the catalyst and support materials.

[0044] Figure 1Depicts a side view of a vehicle 10 according to an example of the present disclosure. The vehicle 10 is shown as a truck, such as a heavy-duty truck for towing one or more trailers (not shown). The vehicle 10 can be a fuel cell electric vehicle (FCEV) or a hybrid vehicle. It should be understood that the present disclosure is not limited to any other particular type of vehicle, but can be used for any other type of vehicle, such as buses, construction equipment, e.g., wheel loaders or excavators, passenger vehicles, aircraft, and marine vessels. The present disclosure also applies to other applications unrelated to vehicles, including stationary applications.

[0045] As Figure 1 Schematically shown, the vehicle 10 includes a fuel cell system 20, the fuel cell system including a fuel cell unit 21, the fuel cell unit including one or more fuel cell stacks 22. The fuel cell system 20 can be used to power one or more electric drive motors (not shown) for generating driving force for the vehicle 10. The fuel cell system 20 can additionally or alternatively be used to power other power-consuming devices (not shown) of the vehicle 10 (such as an electric motor for a crane, an electric motor for a refrigerator system, an electric motor for an air conditioning system, or any other power-consuming function of the vehicle 10). Thus, the fuel cell system 20 can additionally or alternatively be used to power a power take-off (PTO) device, which is a device that transfers the power of an electric motor to another piece of equipment. The vehicle 10 can include or be coupled to one or more PTO devices or be associated with the one or more PTO devices.

[0046] The fuel cell unit 21 of the fuel cell system 20 includes one or more fuel cell stacks 22, each fuel cell stack including two or more (usually multiple) fuel cells. In the examples herein, the fuel cell unit 21 can include multiple fuel cell stacks 22, and any reference to a fuel cell stack 22 applies to two or more fuel cell stacks. The fuel cell unit 21 is arranged to provide the necessary fuel supply, such as hydrogen, an oxidant (such as air or oxygen), cooling, heating, etc. for the fuel cells. The fuel cell system 20 can include Figure 1 Various components not shown. In some examples, the fuel cell system 20 can include more than one fuel cell unit 21, and each fuel cell unit can include its own controller system, which can be communicatively connected to a controller or control unit configured to control the operation of the fuel cell system 20.

[0047] The fuel cell system 20 may include a single fuel cell system, two fuel cell systems, or more than two fuel cell systems, such as three or more fuel cell systems. When a number of fuel cell units or systems are provided, the fuel cell systems may be controlled independently or jointly. When controllable independently, each fuel cell system may be controlled to an on state or an off state regardless of the state of other fuel cell systems. When two or more of the fuel cell systems are controllable jointly, these fuel cell systems may be jointly controlled to an on state or an off state, i.e., all fuel cell systems are jointly controlled to the same state.

[0048] According to an example of the present disclosure, the vehicle 10 further includes a control device or control system 30. The control system 30 is configured or adapted to control the operation of the fuel cell system 20 according to an example of the present disclosure. The system 30 may be referred to as a fuel cell control unit (FCCU). The control system 30 may be part of the fuel cell system 20 or it may be a separate component. The control system 30 may be communicatively coupled to Figure 1 the vehicle control system or controller 50 shown. The vehicle control system 50 may be, for example, a main vehicle controller. In some embodiments, the control system 30 may be part of the vehicle controller 50. Additionally, although an on-vehicle control system 30 is shown, it should be understood that the control system 30 may also be a combination of one or more on-vehicle control systems and one or more non-on-vehicle control systems.

[0049] The control system 30 may be configured to control the fuel cell system 20 and one or more fuel cell units 21 by issuing control signals and by receiving status information related to the fuel cell system 20. The control system 30 may be configured to receive information from various sensors, which may include a temperature sensor, a humidity sensor, a voltage sensor, and one or more of other sensors included in or associated with the fuel cell system 20 and / or the vehicle 10. For example, one or more temperature sensors may be positioned such that they can obtain measurements of the temperature of the coolant and other media in the fuel cell system 20. In some examples, temperature sensors may be used to measure the inlet coolant temperature and the outlet coolant temperature of the coolant flow through the fuel cell stack 22. One or more voltage sensors may be included in the fuel cell unit to monitor the voltage of the fuel cell stack. Various other sensors may obtain measurements regarding the operation of components of the fuel cell system 20.

[0050] The control system 30 can be communicatively coupled to an internal database, an external database, or a combination thereof, for example, to receive data related to a route on which the vehicle is traveling or will travel. The data related to the route can include a starting point, an ending point, and a path along which the vehicle 10 travels between the starting point and the ending point. The control system 30 can store and / or can access data related to the route, the data including terrain information, speed limits, obstacles, etc. The control system 30 can also receive real-time or near-real-time information about the route, the information including traffic congestion, accident reports, road closures, construction, etc. The control system 30 can also store and / or can access historical data related to a driver's driving pattern, historical data about vehicle operation (e.g., the location where the vehicle travels, the frequency and location of stops), historical data about environmental conditions at the location where the vehicle travels, etc. The control system 30 can also receive data from a weather service, the data which can include data about actual and predicted weather conditions and other types of data. The control system 30 can have data about the vehicle's current location and a predicted location (e.g., along the route) where the vehicle is expected to travel.

[0051] The control system 30 can be configured as an electronic control unit and can include processing circuitry adapted to execute a computer program (such as computer-executable instructions) to perform methods in accordance with aspects of the present disclosure. The control system 30 can include hardware and / or software for performing methods in accordance with aspects of the present disclosure. The control system 30 can be represented as a computer. The control system 30 can be composed of one or more separate subunits, and the control system 30 can communicate by using wired and / or wireless communication technologies.

[0052] As Figure 1 shown, the vehicle 10 includes an energy storage system (ESS) 40, such as one or more batteries and / or one or more supercapacitors, for storing electrical energy, including excess electrical energy generated by the fuel cell system 20. The ESS 40 can store energy regenerated during braking (such as regenerative braking), and / or it can be configured to be charged by a charger (such as from an external power grid). The ESS 40 is configured to assist the fuel cell system 20 in supplying energy to the drive motor to meet the power / energy requirements of the vehicle 10. The ESS 40 can be configured to provide additional power in cases where the fuel cell system 20 cannot provide all of the required power or the fuel cell system 20 is not suitable for providing all of the required power. In various examples, the ESS 40 provides electrical energy storage for the electrical energy generated by the fuel cell system at low loads, assists the fuel cell system 20 in generating power at higher loads, or can act as the primary energy supplier in some situations. The fuel cell system 20 and the ESS 40 can supply power to one or more auxiliary systems of the vehicle 10.

[0053] Vehicle 10 may also include Figure 1 various other components not shown in

[0054] Although the present disclosure is described with respect to a vehicle, such as a truck, aspects of the present disclosure are not limited to that particular vehicle, but may also be used in other vehicles, such as passenger vehicles, off-road vehicles, aircraft, and marine vessels. The present disclosure may also be applied to ships and stationary applications, such as grid-connected auxiliary generators or generators independent of the grid.

[0055] Figure 2 An example of a fuel cell system 20 that may be deployed in a fuel cell vehicle, such as vehicle 10, is further shown. As shown, the fuel cell system 20 includes a fuel cell unit 21, which in turn includes a fuel cell stack 22. The fuel cell unit 21 may include more than one fuel cell stack, and the fuel cell stack 22 is shown only by way of example. The operation of the fuel cell system 20 is controlled by a control system 30 also shown in Figure 2 as well.

[0056] The fuel cell stack 22 includes an anode side or anode 24, a cathode side or cathode 26, and an electrolyte 28 (not shown), such as, for example, a proton exchange membrane (PEM) sandwiched between the anode 24 and the cathode 26. The fuel cell stack 22 is configured to generate electricity through an electrochemical reaction between hydrogen and an oxidant. The anode 24 is configured to receive a fuel such as hydrogen, which may be supplied from a hydrogen storage device 33 (e.g., a refillable and / or replaceable hydrogen container or tank). Any other suitable hydrogen source may be used. The anode 24 is configured to receive hydrogen via an anode inlet line 34, and an anode outlet line 36 may be configured to receive and carry away the by-products of the operation of the anode 24 from the anode 24.

[0057] The cathode 26 is configured to receive air or oxygen (referred to herein as an air stream) from the surrounding environment, for example, via a cathode inlet line 38, at a cathode inlet 42 of the fuel cell stack 22. The air may be pressurized by an air compressor 39 including a motor 41. In some examples, the air compressor 39 may be an electric turbocharger (ETC) including a turbine and a compressor. In some examples, the power of the air compressor 39 may be controlled or adjusted, for example, by adjusting the rotational speed of the motor 41, to control the flow rate of the air stream in the cathode inlet line 38, thereby controlling the cathode stoichiometry. In some examples, the power of the air compressor 39 may be controlled or adjusted to maintain a constant relationship between the flow rate of the air stream and the current output from the fuel cell system, thereby maintaining a constant cathode stoichiometry. This may be performed as a reduction event when the power of the fuel cell system is reduced.

[0058] In addition, in some examples, the cathode air pressure (also referred to as the air pressure in the cathode 26) can be controlled to prevent the membrane 28 of the fuel cell stack 22 from drying out. For example, the pneumatic pressure control valve 43 can be fluidly coupled to the cathode inlet line 38, and the pressure control valve 43 can be controlled to regulate the air pressure in the cathode 26. In some embodiments, additionally or alternatively, the air compressor 39 can be controlled to regulate the air pressure in the cathode 26.

[0059] The air compressor 39 can be fluidly coupled to Figure 2 a charge air cooler (CAC) not shown in, which is configured to cool the pressurized air flow or air stream in the cathode inlet line 38. The air stream can also be humidified by a humidifier (not shown). The cathode 26 can be configured to discharge a cathode exhaust stream via the cathode outlet line 44.

[0060] As Figure 2 shown, the fuel cell unit 21 includes a coolant circuit or system 46, which is configured to circulate coolant through the fuel cell stack 22. As Figure 2 shown in the example of, the coolant system 46 shown using a dashed line can be configured to circulate coolant through the fuel cell stack 22 such that the coolant flows to the coolant inlet 52 of the fuel cell stack 22 via the coolant inlet line 48 and flows out of the coolant outlet 54 of the fuel cell stack 22 via the coolant outlet line 56. The coolant system 46 can include a coolant circulation pump 45, which is configured to circulate coolant through the fuel cell stack 22. The coolant circulation pump 45 is configured to be controlled to control the flow rate of the coolant flowing into the fuel cell stack 22 at the coolant inlet 52 of the fuel cell stack 22. Other components can be used additionally or alternatively to control the flow rate of the coolant in the fuel cell stack 22.

[0061] In addition, it should be understood that the specific location of the pump 45 is shown only as an example for illustrative purposes. The coolant system 46 can include Figure 2 other components not shown in, such as for example a radiator, a coolant tank for storing coolant, etc. Although Figure 2 not shown in, the coolant circulates through the coolant system 46 such that the coolant outlet line 54 can be in fluid communication with the coolant inlet line 48, and the coolant is recycled back to the coolant inlet 52 after passing through the fuel cell stack 22.

[0062] The coolant system 46 (e.g., circuit) is configured to regulate the temperature of the fuel cell stack 22, including dissipating the heat generated due to the operation of the fuel cell stack 22. The temperature of the coolant at the coolant inlet 52 and the coolant outlet 54 can be adjusted and / or controlled according to, for example, the power demand of the fuel cell system 20 and other factors.Figure 2 Schematically shown, the coolant system 46 may include a coolant inlet temperature sensor 60 and a coolant outlet temperature sensor 62, which are configured to monitor the temperatures of the coolant at the coolant inlet 62 and the coolant outlet 54, respectively. In various embodiments, more than two temperature sensors may be deployed.

[0063] In an example according to the present disclosure, the target coolant inlet temperature of the coolant at the coolant inlet 52 can be controlled. The flow rate of the coolant flow can also be controlled, for example, by controlling the operation of the pump 45. In this way, the single-cell voltage of the fuel cell stack 22 is maintained at below 0.79 V. The target coolant inlet temperature can be defined as a set point, that is, set to the value of the coolant temperature to be achieved at the coolant inlet 52. The actual temperature of the coolant entering the fuel cell stack 22 at the coolant inlet 52 in the coolant inlet line 48 can be adjusted by setting the target coolant inlet temperature, and the actual coolant inlet temperature can be measured using, for example, the coolant inlet temperature sensor 60. The actual coolant outlet temperature at the coolant outlet 54 will also depend on the target coolant inlet temperature, but it will also vary according to the heat dissipation properties of the fuel cell stack 22, the ability of the coolant system 46 to adjust the temperature of the fuel cell stack, and other factors.

[0064] Also as Figure 2 Schematically shown, a voltage sensor 55 can be deployed to monitor the voltage of the fuel cell stack 22. One or more suitable voltage sensors can be used. The measurement results obtained by the voltage sensor can be used to determine the single-cell voltage of the fuel cell stack 22. In some examples, the single-cell voltage of the fuel cell stack 22 can be determined as the measured voltage of the fuel cell stack 22 divided by the number of fuel cells in the fuel cell stack 22. Therefore, the single-cell voltage can be determined as the average single-cell voltage and it represents the voltage of each fuel cell in each fuel cell stack, and the value of this voltage shall not exceed the safety threshold. In some examples, the single-cell voltage can be determined from the measured voltage of the entire fuel cell unit. In this case, the measured voltage is divided by the number of fuel cell stacks and the number of cells in each fuel cell stack. In some examples, the voltage of each fuel cell is measured, and the average value of these measured voltages can be used as the single-cell voltage of the fuel cell stack. As in some examples of the present disclosure, regardless of the method used to measure the single-cell voltage of the fuel cell stack, the fuel cell system will be controlled such that the single-cell voltage does not exceed 0.8 V or 0.79 V.

[0065] The operation of the fuel cell unit 21 is controlled by the control system 30. In some examples, the control system 30 can be Figure 1 a part of the vehicle controller 50 shown. In the examples herein, asFigure 2 As shown, control system 30 includes processing circuitry 32 configured to execute computer-executable instructions that, when executed by processing circuitry 32, can perform the methods according to examples of the present disclosure. Control system 30 also includes a memory 31 configured to store computer-executable instructions and various data. In some embodiments, the computer-executable instructions can be stored at least partially remotely, such as in a remote memory. Memory 31 can obtain data from various sources, including from one or more remote storage devices.

[0066] The processing circuitry 32 of control system 30 can be configured to obtain the power of the fuel cell system (also referred to as the power output value) requested from fuel cell system 20. Processing circuitry 32 is configured to monitor the voltage of fuel cell stack 22, and processing circuitry 32 is configured to control the target coolant inlet temperature of the coolant flow and the flow rate of the coolant flow to maintain the single cell voltage of fuel cell stack 22 at below 0.79 V. In this way, the risk of damaging the catalyst and support materials of the fuel cell stack can be reduced or eliminated, thereby improving durability and extending the life of the fuel cell stack and the entire fuel cell system.

[0067] In some examples, fuel cell unit 21 includes one fuel cell unit. Thus, fuel cell system 20 can include a single fuel cell unit. Such fuel cell systems may be more efficient, but this may be associated with an increase in the single cell voltage at lower loads.

[0068] It should be understood that Figure 2 the configuration of fuel cell system 20 shown in Figure 2 is merely illustrative. Additionally, fuel cell system 20 can include

[0069] In a fuel cell electric vehicle (e.g., vehicle 10), in certain situations, a high propulsion power period (where the ESS and cooling system operate at high power) may be suddenly interrupted by a high power braking event (at which time the auxiliary brake is also operating at high power). The power generated by the fuel cell system reduces the braking power. For example, each kilowatt of fuel cell power generated during a braking event may reduce the braking power by one kilowatt. This is because the fuel cell power generated must be directed to the ESS (such as a battery) for neutralization and / or must be dissipated to the surrounding environment through the auxiliary brake and cooling system as it decreases.

[0070] As an example, the vehicle may be approaching the top of an uphill grade where maximum power from the fuel cell system is required until the brakes are applied. In this case, the fuel cell stack will operate at a high temperature and the cooling system will be almost entirely dedicated to managing the heat load of the fuel cell stack. As another example, if an ESS (such as a battery) has been providing power to climb a hill under specific driving conditions, the ESS may overheat or may have a high state of charge (SOC) when the vehicle approaches the top of the hill. In both cases, the ability of the ESS to absorb braking power will be limited.

[0071] In some examples, a controller (e.g., a vehicle control system and / or a fuel cell system controller) can predict an upcoming downhill grade or the apex of an upcoming downhill grade along a route. Another scenario that can be predicted is that the vehicle will need to decelerate and may decelerate quickly. This prediction, along with information regarding the power capabilities of the ESS, the output power of the fuel cell system, the heat dissipation from the fuel cell to the coolant, the target inlet coolant temperature, the target outlet coolant temperature, the actual coolant inlet and outlet temperatures, the fuel cell coolant flow rate, the single cell voltage, and the cathode stoichiometry, can be used to estimate the required braking power.

[0072] If, for example, in the case of a vehicle descending, the ESS power capabilities are limited or non - existent, an auxiliary braking system may be required and thus the coolant system will need to be able to manage its demands. Therefore, it will be necessary and / or desirable for the fuel cell system control system and / or the vehicle control system to attempt to reduce the fuel cell system power and cooling demands as quickly as possible without compromising the durability and performance of the fuel cell system.

[0073] Accordingly, examples in accordance with the present disclosure provide a method that allows for a rapid decrease in the power of a fuel cell system in a manner that does not negatively impact the durability, performance, and lifespan of the fuel cell system.

[0074] Figure 3An example of a process or method for operating a fuel cell system is shown, the fuel cell system including a fuel cell unit, the fuel cell unit including a fuel cell stack, the fuel cell stack including a cathode and an anode. The cathode is configured to receive an air stream via a cathode inlet line and provide a cathode exhaust stream via a cathode outlet line. The air stream is received at a cathode inlet in fluid communication with the cathode inlet line, and the cathode exhaust stream exits from a cathode outlet in fluid communication with the cathode outlet line. The fuel cell unit further includes a coolant system configured to circulate coolant through the fuel cell unit, the coolant system including: a coolant inlet line configured to direct coolant from a coolant source to the fuel cell stack; and a coolant outlet line configured to carry the coolant away from the fuel cell stack after the coolant has passed through the fuel cell stack.

[0075] The fuel cell system can be Figure 1 and Figure 2 the fuel cell system 20 of Figure 2 or a fuel cell system having another configuration. The method 300 is described below in connection with

[0076] for illustrative purposes only, and it should be understood that another fuel cell system can be used.

[0076] The method 300 can be executed by a controller or control system 30 (such as, for example, Figure 1 and Figure 2 the control system shown in

[0077] . The processing circuit 32 of the control system 30 can execute computer-executable instructions stored in, for example, the memory of the control system 30, where the computer-executable instructions, when executed, cause the processing circuit 32 to execute the method 300.

[0077] The process 300 can start at any suitable time. For example, it can be executed when a vehicle (e.g., vehicle 10 including the fuel cell system 20) is traveling on a route and the load on the fuel cell system 20 changes. When the vehicle 10 is traveling downhill, when it decelerates due to traffic conditions, etc., and in various other situations, the power demand of the fuel cell system 20 may decrease. The vehicle can be traveling on a route, for example, as part of a task or job, which can include traveling from a starting point to an ending point. The vehicle can be part of a fleet of vehicles.

[0078] At block 302, the control system can obtain or acquire a prediction that a vehicle traveling on a route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to occur after a portion where a braking event is expected associated with a low power demand of the fuel cell system. A vehicle braking event will require a ramp down or ramp down event of the fuel cell system, where the power output requested from the fuel cell system is reduced. In some cases, the ramp down event requires a higher ramp down rate, such as approximately 75 kilowatts per second (kW / s). Higher ramp down rates may include other values. The prediction can be obtained from a vehicle controller (e.g., Figure 1 the vehicle controller 50 shown).

[0079] For example, the vehicle may be traveling uphill and it can be predicted that the vehicle is approaching a downhill portion, i.e., the top of the downhill, where vehicle brakes will need to be applied, i.e., a braking event is expected to occur. As another example, the vehicle may be traveling at a high speed on a portion of the route and the control system may predict that the vehicle will slow down due to various factors (e.g., one or more of the characteristics of the road, an expected stop, traffic conditions, etc.). Thus, in some examples, the prediction made at block 302 can be a prediction of the upcoming top of a downhill along the route.

[0080] In some cases, when the vehicle is located at or near a portion of the route associated with a low power demand of the fuel cell system, the ability of the vehicle's ESS to absorb power may be limited. Thus, during a ramp down event, the ESS will not be able to absorb the power generated by the fuel cell system or may only be able to absorb a limited amount of electrical power. At the same time, according to examples of the present disclosure, allowing the fuel cell system power to rapidly ramp down can improve the vehicle's regenerative braking ability because during a rapid ramp down, the fuel cell system remains at a high level or a higher level for a shorter duration. In any case, the present disclosure does not discuss in detail the management of the ESS and regenerative braking.

[0081] As used herein, a low power demand can be defined as a power requirement of the fuel cell system where, for example, the fuel cell is in an idle condition or at a power level less than half of the full power capacity of the fuel cell system. A high power demand can be defined as a condition where the fuel cell system is operating at its full power capacity or at a power level greater than half of the full power capacity of the fuel cell system.

[0082] The prediction may relate to a certain time period or time range. The duration of the time range can be selected according to specific circumstances, for example, according to the nature of the vehicle driving route, according to the frequency of expected braking events along the route, according to the known driving patterns and driver behavior of the vehicle driver, etc. In some examples, the duration of the time range can be a dynamic parameter such that it can be adjusted based on the current and predicted route nature, which can include the topological nature of the route (including the degree of each descent), road type (including speed limits), traffic conditions, weather conditions, etc. The duration of the time range can be selected such that there is sufficient time to determine or detect that the vehicle is traveling on the route section where a braking event is expected to occur, so that the fuel cell system will need to be prepared for the braking event and the corresponding rapid power drop. A rapid response of the fuel cell system is required. For example, in some cases, the rapid response of the fuel cell system can be such that a power drop rate from about 30 kW / s to about 100 kW / s can be achieved. As used herein, the term "about" indicates within 10% of the specified value. The power drop rate can depend on the magnitude of the required power drop, such that for example, the greater the power drop, the higher the power drop rate may be required, that is, the faster the response of the fuel cell system, so that its power output is reduced.

[0083] Non-limiting examples of the duration of the time range can be 30 minutes, one hour, two hours, three hours, etc. Any other suitable duration of the time range can be used additionally or alternatively.

[0084] The control system can obtain the prediction from, for example, a vehicle control system (such as Figure 1 the vehicle controller 50 shown). The vehicle control system can include, for example, a task management system configured to monitor and control the vehicle's completion of a task or job (such as a driving route and performing other tasks). In an embodiment where the control system is part of the vehicle control system, the control system can generate a prediction that the vehicle is approaching a section of the route where a high power demand associated with the fuel cell system is expected to occur after a section associated with a low power demand of the fuel cell system.

[0085] At block 303, the control system can monitor the single-cell voltage of the fuel cell unit such that the single-cell voltage does not exceed 0.79 V. It should be understood that the monitoring of the single-cell voltage can be continuously performed during process 300, and block 303 is shown after block 302 only for illustrative purposes. Thus, when a rapid reduction in fuel cell power is required, the single-cell voltage is monitored while performing other processes.

[0086] At block 304, the control system may pre-determine (i.e., in advance) a required reduction in the power of the fuel cell system based on the required braking power of the vehicle for a route segment associated with a low power demand. For example, when the vehicle is decelerating, vehicle braking may be required and the amount of electrical power drawn from the fuel cell system (also referred to as the load on the fuel cell system) will need to be reduced accordingly. In some instances, the control system may obtain the required braking power, which may be determined by the vehicle master controller. The power of the fuel cell system includes the current generated by the fuel cell system, such as the current generated by each fuel cell stack of the fuel cell units of the fuel cell system.

[0087] The required braking power may be determined by, for example, a vehicle controller (e.g., Figure 1 the vehicle controller 50 as shown), and it may be communicated to the control system. Thus, in some examples, the control system may receive information about the determined required braking power from the vehicle controller (e.g., Figure 1 the vehicle controller 50 as shown).

[0088] Pre-determining the required reduction in the power of the fuel cell system may allow the fuel cell system to prepare for a braking event. For example, as discussed in more detail below, when the vehicle begins to travel on a segment associated with a low power demand of the fuel cell system, the coolant temperature will need to be reduced in advance. A vehicle braking event may occur when the vehicle begins to travel on the low power demand segment or with some delay during the vehicle's travel on a route segment associated with a low power demand of the fuel cell system.

[0089] At block 306, the control system controls the fuel cell system to reduce the power of the fuel cell system based on the required braking power to prepare for a braking event. The control at block 306 may include several processes as shown at blocks 308, 310, 312, 314, 316, 318, and 320.

[0090] At block 308, process 300 includes reducing the target inlet coolant temperature of the coolant flow to a first temperature threshold such that when the vehicle begins to travel on a segment associated with a low power demand of the fuel cell system, the inlet coolant temperature of the coolant flow of the coolant system flowing through the fuel cell units drops below the threshold coolant flow inlet temperature. Since process 300 is performed in a scenario where the fuel cell system is initially operating at a high power output, it will be necessary to reduce the temperature of the fuel cell stack and thus the temperature of the coolant flow in order to allow for a rapid reduction in fuel cell power during a braking event.

[0091] The target coolant inlet temperature can be defined as a setpoint, i.e., the value of the coolant temperature to be achieved in the coolant inlet line when the coolant enters the fuel cell stack. As the target inlet coolant temperature decreases, the actual temperature of the coolant at the coolant inlet line decreases, and the progress of the actual temperature drop of the coolant flow at the coolant inlet line can be monitored.

[0092] In some examples, the first temperature threshold can be 60 °C, such that the target inlet coolant temperature can be reduced to 60 °C. The first temperature threshold (which can have other values) can depend on the estimated time required for the target inlet coolant temperature to reach the first temperature threshold when the vehicle starts braking (e.g., at the start of a downhill slope) given the characteristics of the known coolant system. Thus, when it is expected that the target inlet coolant temperature will take longer to drop to the first temperature threshold, the first temperature threshold can be set to a lower value.

[0093] At decision block 310, the control system determines whether the required amount of reduction in the power of the fuel cell system is equal to or less than a first threshold power level and is associated with a first rate-of-descent requirement. In some examples, the first threshold power level can be a value such as approximately 250 kW, but other values can also be used. The required amount of reduction in the power of the fuel cell system (i.e., the power output from the fuel cell system) can define how quickly the power needs to be reduced. Thus, a particular first rate-of-descent requirement is associated with the required reduction in the power of the fuel cell system being equal to or less than the first threshold power level.

[0094] At block 312, in response to determining that the required amount of reduction in the power of the fuel cell system is equal to or less than the first threshold power level and is associated with the first rate-of-descent requirement, the control system can apply a first response strategy. The first response strategy includes continuously reducing the flow rate of the coolant flow to a value corresponding to the required power reduction of the fuel cell system. The flow rate of the coolant flow can be reduced from the current flow rate value to a lower flow rate value corresponding to the continuously decreasing power of the fuel cell system. The current flow rate value can be associated with the fuel cell output power at the start of the descent event, and the value corresponding to the required power reduction of the fuel cell system is the power required at the end of the descent event.

[0095] The continuous reduction in the flow rate of the coolant flow is required after the power reduction of the fuel cell system, such that the rate of reduction of the coolant flow rate depends on the first rate-of-descent requirement and the rate of actual power reduction of the fuel cell system.

[0096] When the control system applies the first response strategy, the control system can continuously monitor the outlet temperature of the coolant flow to avoid increasing the temperature of the fuel cell stack of the fuel cell unit. The control system also maintains the cathode stoichiometry constant. In some examples, the cathode stoichiometry can be maintained constant by adjusting the power of an air compressor configured to pressurize the air flow supplied to the cathode of the fuel cell stack such that the flow rate of the air flow maintains a constant relationship with the current output from the fuel cell system. In some examples, during a descent event, the cathode stoichiometry can be maintained at a cathode stoichiometry of about 1.5.

[0097] In some examples, the control system controls the fuel cell system to start a descent targeting the power required at the end of the descent event based on the required reduction in the power of the fuel cell system. During the descent event, the coolant flow rate and coolant temperature are controlled, and the cathode stoichiometry is maintained constant during this descent event. As the descent event progresses, the coolant flow rate is continuously reduced while monitoring the fuel cell outlet temperature to slowly reduce it during the process.

[0098] At block 314, in response to determining that the magnitude of the required reduction in the power of the fuel cell system is greater than a first threshold power level and is associated with a second descent rate requirement, the control system can apply a second response strategy. The second response strategy can be applied when the power of the fuel cell system needs to be reduced to a larger value (e.g., reduced to 300 kW in an example). The second descent rate requirement (i.e., the desired rate at which the power of the fuel cell system is to be reduced) is higher than the first descent rate requirement. The higher the required power reduction, the faster the power of the fuel cell is desired to be reduced according to the required reduction.

[0099] The second response strategy can include two phases, which are referred to herein as the first phase and the second phase. In the first phase, the flow rate of the coolant flow can be increased. In the second phase, if the outlet temperature of the coolant flow drops below a predetermined threshold temperature or a threshold coolant flow outlet temperature, the flow rate of the coolant flow can be reduced. The process at block 314 is shown to include blocks or sub - blocks 316, 318, and 320.

[0100] At block 316, in the first phase of the second response strategy, process 300 includes continuously and gradually (i.e., in an incremental manner rather than a sudden manner) increasing the flow rate of the coolant flow. The flow rate of the coolant flow can be increased from the current flow rate value to a higher flow rate value that can correspond to a certain drop in the outlet temperature of the coolant flow. The current flow rate value may be associated with the fuel cell output power at the start of the descent event.

[0101] At block 317, the outlet temperature of the coolant flow can be monitored. However, it should be understood that the outlet temperature of the coolant flow is continuously monitored throughout process 300, and the process at block 317 is shown separately only for illustrative purposes.

[0102] As the flow rate of the coolant increases, the outlet temperature of the coolant flow decreases, and it may be undesirable to decrease below a certain predetermined threshold temperature.

[0103] The outlet temperature of the coolant flow can also be continuously monitored to avoid an increase in the temperature of the fuel cell stack. It is desirable to avoid an increase in the fuel cell stack temperature because if the fuel cell stack temperature increases, membrane dehydration will occur faster.

[0104] The cathode stoichiometry can be maintained constant. The single cell voltage is also monitored to ensure that it does not exceed 0.79 V.

[0105] At decision block 318, the control system can determine whether the outlet temperature of the coolant flow has dropped below a threshold coolant flow outlet temperature. In some examples, the threshold coolant flow outlet temperature can be a temperature that is about 3°C, or about 4°C, or about 5°C lower than the expected known coolant outlet temperature at a given power of the fuel cell system. When the outlet temperature of the coolant flow drops below the threshold coolant flow outlet temperature of the coolant flow, it may indicate that the fuel cell temperature is too low, which is undesirable.

[0106] As Figure 3 shown, if it is determined at block 318 that the outlet temperature of the coolant flow is not below the predetermined threshold temperature, process 300 can return to block 317, where the outlet temperature of the coolant flow continues to be monitored.

[0107] If it is determined at block 318 that the outlet temperature of the coolant flow is equal to the threshold coolant flow outlet temperature or has dropped below the threshold coolant flow outlet temperature, process 300 proceeds to block 320.

[0108] At block 320, in the second stage of the second response strategy, process 300 includes: continuously and gradually (e.g., without sudden changes) decreasing the flow rate of the coolant flow as the fuel cell power decreases and in response to detecting that the outlet temperature of the coolant flow has dropped below the threshold coolant flow outlet temperature. The outlet temperature of the coolant flow can be continuously monitored to avoid an increase in the temperature of the fuel cell stack. The cathode stoichiometry is maintained constant, and the single cell voltage is monitored not to exceed 0.79 V.

[0109] In addition, continuously monitoring the outlet temperature of the coolant flow is used to ensure that the temperature of the fuel cell stack is maintained within a certain range. For example, if the outlet temperature of the coolant flow drops to the target inlet coolant temperature or below, the fuel cell stack will be overcooled, resulting in a single cell voltage exceeding 0.79 V. When the coolant flow increases, this may increase the risk of membrane flooding.

[0110] As described above, the method according to an example of the present disclosure can be implemented in a power generation unit. In some examples, the method according to an example of the present disclosure can be implemented in a stationary system including a fuel cell system.

[0111] To perform the method steps described herein, the control system 30 can be configured to perform processing in combination with Figure 4A and Figure 4B and / or as described in any other example of the present disclosure. The control system 30 can include, for example, an arrangement as depicted in Figure 4A and Figure 4B . The control system 30 can be located in any suitable location of the vehicle 10 or in another system implementing the method according to aspects of the present disclosure. In some examples, the control system 30 can be part of a vehicle controller (e.g., the vehicle controller 50 as shown in Figure 1 ).

[0112] As shown in Figure 4A , the control system 30 includes a processing circuit 32, a memory 31, and an input and output interface 400, which is configured to communicate with any necessary components and / or entities of the examples herein. The input and output interface 400 can include wireless and / or wired receivers and wireless and / or wired transmitters. In some examples, the input and output interface 400 can include wireless and / or wired transceivers. The control system 30 can use the input and output interface 400 to control and communicate with various sensors, actuators, subsystems, and / or interfaces in the fuel cell system and the vehicle 10 by using any one or more of the following: a controller area network (CAN) bus, an Ethernet cable, Wi-Fi, Bluetooth, and / or other network interfaces.

[0113] The methods described herein can be implemented using a processing circuit (e.g., one or more processors such as the processing circuit 32 of the control system 30) together with computer program code stored in a computer-readable storage medium for performing the functions and actions of the examples herein.

[0114] The memory 31 may include one or more memory cells. The memory 31 includes computer-executable instructions executable by the processing circuit 32 of the control system 30. The memory 31 is configured to store, for example, information, data, etc., as well as computer-executable instructions that, when executed by the processing circuit 32, perform the methods according to the examples herein. The control system 30 may additionally obtain information from an external memory.

[0115] The method according to aspects of the present disclosure may be implemented by, for example, a computer program product 410 or a computer program including computer-executable instructions (i.e., software code portions) that, when executed on at least one processor (e.g., the processing circuit 32), cause the at least one processor to perform the actions described herein as performed by the control system 30.

[0116] In some examples, the computer program product 410 is stored on a computer-readable storage medium 420. The computer-readable storage medium 420 may be, for example, a magnetic disk, a universal serial bus (USB) stick, or a similar device. The computer-readable storage medium 420 storing the computer program product thereon may include computer-executable instructions that, when executed by the processing circuit 32, cause the processing circuit 32 to perform the actions of the method as performed by the control system 30 according to the examples of the present disclosure described herein.

[0117] As Figure 4B shown, the control system 30 may include an obtaining unit 402. The control unit system 30, the processing circuit 32, and / or the obtaining unit 402 may be configured to obtain or acquire a prediction that a vehicle including a fuel cell system traveling on a route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to occur after a portion associated with a low power demand of the fuel cell system where a braking event is expected to occur.

[0118] The control system 30 may include a monitoring unit 404. The control unit system 30, the processing circuit 32, and / or the monitoring unit 404 may be configured to monitor the single-cell voltage of the fuel cell unit such that the single-cell voltage does not exceed 0.79 V.

[0119] Similarly, as Figure 4B shown, the control system 30 may include a determining unit 406. The control system 30, the processing circuit 32, and / or the determining unit 406 are configured to pre-determine (i.e., in advance) the required reduction in the power of the fuel cell system based on the required braking power required by the vehicle on a portion of the route associated with a low power demand.

[0120] The control system 30 may include a control unit 408. The control system 30, the processing circuit 32, and / or the control unit 408 are configured to control the fuel cell system to reduce the power of the fuel cell system based on the required braking power in preparation for a braking event. The control may be performed by or using the control unit 408 as part of the processing shown in blocks 306, 308, 310, 312, 314, 316, 318, and 320 as Figure 3 shown.

[0121] Those skilled in the art should understand that the units in the control system 30 described above may refer to a combination of analog and digital circuits and / or one or more processors configured with software and / or firmware stored, for example, in the control system 30, and the software and / or firmware, when executed by the corresponding one or more processors, may execute the methods according to the embodiments of the present disclosure. One or more of these processors and other digital hardware may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed over several separate components, whether individually packaged or assembled into a system-on-chip.

[0122] The operating steps described in any of the exemplary aspects herein are described to provide examples and discussions. These steps may be performed by hardware components, embodied in machine-executable instructions to cause a processor to perform these steps, or performed by a combination of hardware and software. Although a specific order of method steps may be shown or described, the order of the steps may vary. Additionally, two or more steps may be performed simultaneously or partially simultaneously.

[0123] The terms used herein are for the purpose of describing particular aspects only and are not intended to limit the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and / or" includes any and all combinations of the associated listed items. It should also be understood that the terms "comprises" and / or "comprising," when used herein, specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0124] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0125] In this document, relative terms such as "below" or "above", or "upper" or "lower", or "horizontal" or "vertical" may be used to describe the relationship of one element to another element, as shown in the figures. It should be understood that these terms, as well as those discussed above, are intended to cover different device orientations in addition to the orientation depicted in the figures. It should be understood that when an element is referred to as "connected to" or "coupled to" another element, the element can be directly connected or coupled to the other element or there may be intervening elements. In contrast, when an element is referred to as "directly connected to" or "directly coupled to" another element, there are no intervening elements.

[0126] Unless otherwise defined, all terms used in this document (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that, unless explicitly defined herein, the terms used in this document should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art, and should not be interpreted in an idealized or overly formal sense.

[0127] It should be understood that this disclosure is not limited to the aspects described above and shown in the figures; rather, those skilled in the art will recognize that many changes and modifications can be made within the scope of this disclosure and the appended claims. In the figures and the specification, various aspects have been disclosed for illustrative purposes only and not for purposes of limitation, and the scope of the inventive concept is set forth in the claims above.

Claims

1. A fuel cell system (20) for a vehicle (10), the fuel cell system (20) comprising: A fuel cell unit (21) comprising a fuel cell stack (22), the fuel cell stack comprising a cathode and an anode, the cathode being configured to receive an air flow via a cathode inlet line (38); a coolant system (46) configured to circulate a coolant through the fuel cell stack (22), the coolant system comprising: a coolant inlet line (48) configured to direct a flow of coolant to the fuel cell stack; and a coolant outlet line (56) configured to direct a flow of coolant away from the fuel cell stack after the coolant has passed through the fuel cell stack (22); A control system (30), the control system comprising a processing circuit (32), the processing circuit being configured to: predetermining a required reduction in power of the fuel cell system based on a required braking power required for the vehicle to travel along a route on a portion of the route associated with a low power demand of the fuel cell system; and Controlling the fuel cell system to prepare for a braking event by reducing the power of the fuel cell system based on the required braking power by: reducing a target inlet coolant temperature of the coolant flow to a first temperature threshold such that when the vehicle begins traveling on the portion associated with the low power demand of the fuel cell system, the inlet temperature of the coolant flow drops below a threshold coolant flow inlet temperature; in response to determining that the magnitude of the desired reduction in the power of the fuel cell system is equal to or less than a first threshold power level and is associated with a first ramp down rate requirement, applying a first response strategy, the first response strategy comprising continuously reducing the flow rate of the coolant flow to a value corresponding to the desired reduction in the power of the fuel cell system; and In response to determining that the magnitude of the required reduction in the power of the fuel cell system is greater than the first threshold power level and is associated with a second ramp down rate requirement, applying a second response strategy, the second response strategy comprising: In a first stage of the second response strategy, continuously and stepwise increasing the flow rate of the coolant flow; and In a second phase of the second response strategy, the flow rate of the coolant flow is continuously and gradually reduced as the power of the fuel cell system decreases and in response to determining that the outlet temperature of the coolant flow drops below a threshold coolant flow outlet temperature. 2 . The fuel cell system of claim 1 , wherein the processing circuit is configured to monitor a single cell voltage of the fuel cell stack so that the single cell voltage does not exceed 0.79 V. 3 .

3. The fuel cell system of claim 1 or 2, wherein the processing circuit is further configured to control the fuel cell system to prepare for the braking event by reducing the power of the fuel cell system based on the required braking power in the following manner: continuously monitoring the outlet temperature of the coolant flow so as to avoid increasing the temperature of the fuel cell stack of the fuel cell unit; and The cathode stoichiometry was maintained constant.

4. A fuel cell system as described in any one of claims 1 to 3, wherein the cathode stoichiometry is maintained constant by adjusting the power of an air compressor configured to pressurize the air flow provided to the cathode of the fuel cell stack so that the flow rate of the air flow maintains a constant relationship with the current output from the fuel cell system.

5. A fuel cell system as described in any one of claims 1 to 4, wherein the processing circuit is configured to obtain a prediction that the vehicle traveling on the route is approaching a portion of the route where the portion associated with a high power demand of the fuel cell system is expected to be after the portion associated with a low power demand of the fuel cell system where the braking event is expected to occur.

6. The fuel cell system of claim 5, wherein the prediction includes a prediction of an upcoming crest of a downhill grade along the route.

7. A fuel cell vehicle comprising the fuel cell system according to any one of claims 1 to 6.

8. A method for controlling operation of a fuel cell system for a vehicle, the fuel cell system comprising a fuel cell unit, the fuel cell unit comprising a fuel cell stack, the method comprising: predetermining (304) a required reduction in power of the fuel cell system based on a required braking power required for the vehicle to travel along a route on a portion of the route associated with a low power demand; as well as Controlling (306) the fuel cell system to prepare for a braking event by reducing the power of the fuel cell system based on the required braking power by: reducing (308) a target inlet coolant temperature of a coolant flow to a first temperature threshold such that an inlet temperature of the coolant flow flowing through a coolant system of the fuel cell system drops below a threshold coolant flow inlet temperature when the vehicle begins traveling on the portion associated with the low power demand of the fuel cell system; In response to determining (310) that the magnitude of the desired reduction in the power of the fuel cell system is equal to or less than a first threshold power level and is associated with a first ramp down rate requirement, applying (312) a first response strategy, the first response strategy comprising continuously reducing the flow rate of the coolant flow to a value corresponding to the desired reduction in the power of the fuel cell system; as well as In response to determining (310) that the magnitude of the desired reduction in power of the fuel cell system is greater than the first threshold power level and is associated with a second ramp down rate requirement, applying (314) a second response strategy, the second response strategy comprising: In a first stage of the second response strategy, continuously and stepwise increasing (316) the flow rate of the coolant flow; as well as In a second stage of the second response strategy, the flow rate of the coolant flow is continuously and gradually (320) reduced as the power of the fuel cell system decreases and in response to determining that the outlet temperature of the coolant flow drops below a threshold coolant flow outlet temperature.

9. The method of claim 8, comprising monitoring (303) a single cell voltage of the fuel cell stack so that the single cell voltage does not exceed 0.79 V.

10. The method of claim 8 or 9, wherein the controlling the fuel cell system to reduce the power of the fuel cell system based on the required braking power in preparation for the braking event comprises: continuously monitoring the outlet temperature of the coolant stream to avoid increasing the temperature of the fuel cell stack of the fuel cell unit; as well as The cathode stoichiometry was maintained constant.

11. A method as described in any one of claims 8 to 10, wherein the cathode stoichiometry is maintained constant by adjusting the power of an air compressor configured to pressurize an air flow supplied to the cathode of the fuel cell stack so that the flow rate of the air flow maintains a constant relationship with the current output from the fuel cell system.

12. A method as described in any one of claims 8 to 11, comprising obtaining a prediction that the vehicle traveling on the route is approaching a portion of the route where a portion associated with a high power demand of the fuel cell system is expected to follow the portion associated with a low power demand of the fuel cell system where the braking event is expected to occur.

13. A control system (30) for controlling a fuel cell system (20) of a fuel cell vehicle (10), the control system (30) comprising a processing circuit (32) configured to perform the method according to any one of claims 8 to 12.

14. A fuel cell vehicle (10) comprising the control system (30) according to claim 13.

15. A computer program product comprising computer executable instructions which, when executed by a processing circuit, cause the processing circuit to perform the method of any one of claims 8 to 12.

16. A computer-readable storage medium having a computer program product stored thereon, the computer program product comprising computer-executable instructions, which when executed by a processing circuit cause the processing circuit to perform the method according to any one of claims 8 to 12.

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