Method for fuel cell system load reduction operation and fuel cell power system

Abstract

The application provides a method for load reduction operation of a fuel cell system, comprising: in the case that it is determined that the fuel cell system (1) needs load reduction operation based on an initial operation power and a target operation power of a stack (11), controlling the fuel cell system to operate in a first heat dissipation operation mode and an intermediate operation power, operating a motor (3) and charging a storage battery (2) by using the energy generated by the fuel cell system until the fuel cell system reaches a desired temperature condition corresponding to the intermediate operation power, when the fuel cell system operates in the intermediate operation power, the liquid water flow at the anode outlet of the stack is greater than the total amount of water vapor change at the cathode / anode outlet of the stack; controlling the fuel cell system to operate in a maximum heat dissipation operation mode and the target operation power, and after the fuel cell system reaches a desired temperature condition corresponding to the target operation power, controlling the fuel cell system to operate in a normal operation mode corresponding to the target operation power.

Description

Technical Field

[0001] This application relates to the field of fuel cells, and more particularly to a method for unloaded operation of a fuel cell system, a fuel cell power system, and a computer program product for at least assisting in implementing the steps of the method described according to this application. Background Technology

[0002] In the actual operation of vehicles that use fuel cell systems as the main power source, there may be some extreme driving conditions. For example, when a vehicle traveling at high speed suddenly encounters an obstacle in front, it needs to perform an emergency stop or deceleration operation. At this time, the power demand of the motor on the fuel cell system will be greatly reduced, thereby triggering the fuel cell system to operate under reduced load.

[0003] However, according to the existing control methods for de-load operation of fuel cell systems, directly and significantly reducing the operating power of the fuel cell system will cause drastic changes in the dryness of the proton exchange membrane of the stack, causing the proton exchange membrane to be repeatedly subjected to large-scale dry-wet cycles, which in turn causes mechanical stress in the proton exchange membrane, increases the possibility of mechanical degradation, and reduces the performance output and durability of the stack.

[0004] Therefore, in response to this problem, this application proposes an improved method for unloaded operation of fuel cell systems. Summary of the Invention

[0005] The purpose of this application is to provide a method for unloaded operation of a fuel cell system, a fuel cell power system, and a computer program product to at least partially solve the problems in the prior art.

[0006] According to a first aspect of this application, a method for de-load operation of a fuel cell system is provided, the method comprising:

[0007] -Based on the initial operating power P0 and target operating power P of the fuel cell stack w If it is determined that the fuel cell system needs to operate at reduced load, the fuel cell system can be controlled to operate under the first heat dissipation condition and the intermediate operating power P. m The system operates by using the energy generated by the fuel cell system to power the motor and charge the battery until the fuel cell system reaches its designated intermediate operating power P. m The desired temperature conditions, wherein the intermediate operating power P is determined in the following manner. m : When the fuel cell system operates at intermediate power P m During operation, the liquid water flow rate M at the anode outlet of the fuel cell stack f The total change in water vapor at the cathode / anode outlet of the fuel cell stack is greater than M. t ;

[0008] as well as

[0009] - The fuel cell system can be controlled to operate under the first heat dissipation condition and the target operating power P. w Run until the fuel cell system reaches its assigned target operating power P. w After achieving the desired temperature conditions, control the fuel cell system to match the target operating power P. w It operates under normal operating conditions.

[0010] The core concept of this application includes at least the following: when the fuel cell system needs to operate under a significant load reduction condition, maintaining the fuel cell system in an operating condition with high heat dissipation power, and controlling the operating power of the stack to decrease from the initial operating power P0 to an intermediate operating power P m Only after reaching the desired temperature regulation will the power be gradually reduced to the final target operating power P. w This ensures that the liquid water flow rate at the anode outlet of the fuel cell stack is always greater than the total change in water vapor at the cathode / anode outlets. This minimizes the fluctuations in the dryness of the proton exchange membrane during the de-load operation of the fuel cell system, effectively eliminates repeated wet-dry cycles of the proton exchange membrane, avoids mechanical stress on the proton exchange membrane, reduces the possibility of mechanical degradation, and effectively improves the performance output and durability of the fuel cell stack.

[0011] According to a second aspect of this application, a fuel cell power system is provided, which may include a fuel cell system, a battery, a motor, and a control unit, wherein the control unit is configured to perform the method according to this application.

[0012] According to a third aspect of this application, a computer program product, such as a computer-readable program carrier, is provided, comprising computer program instructions that, when executed by a processor, at least partially implement the steps of the method described in this application. Attached Figure Description

[0013] The principles, features, and advantages of this application will be better understood below with reference to the accompanying drawings. The drawings include:

[0014] Figure 1 A schematic block diagram of a fuel cell power system according to an exemplary embodiment of this application is shown;

[0015] Figure 2 A flowchart illustrating a method for unloaded operation of a fuel cell system according to an exemplary embodiment of this application is shown.

[0016] Figure 3A schematic diagram showing the flow direction of fluid within a fuel cell stack according to an exemplary embodiment of this application is shown; and

[0017] Figure 4 The total water vapor variation M at the cathode / anode outlet of the fuel cell stack according to an exemplary embodiment of this application is shown. t The liquid water flow rate M at the anode outlet of the fuel cell stack f A schematic diagram of the curves showing the variation of the stack current I. Detailed Implementation

[0018] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit the scope of protection of this application.

[0019] Figure 1 A schematic block diagram of a fuel cell power system 10 according to an exemplary embodiment of this application is shown. Figure 1 As shown, the fuel cell power system 10 may include a fuel cell system 1, a battery 2, a motor 3, and a control unit configured to execute a method for unloading operation of the fuel cell system 1. According to an exemplary vehicle architecture, the control unit may include a fuel cell control unit 41 for controlling the fuel cell system, a battery management system 42 for controlling the battery 2, and a vehicle control unit 43 for controlling the vehicle. The vehicle control unit 43 may allocate energy to the fuel cell control unit 41 and the battery management system 42 according to the vehicle's operating conditions (the direction of information flow is marked by dashed arrows). The fuel cell control unit 41 and the battery management system 42 respectively control the fuel cell system 1 and the battery 2 to supply the allocated energy to the motor 3 (the direction of energy flow is marked by solid arrows), enabling the vehicle to operate normally.

[0020] However, when a vehicle traveling at high speed suddenly encounters an obstacle in front, it needs to perform an emergency stop or deceleration operation. At this time, the actual power demand of the motor 3 will be greatly reduced. The initial operating power P0 generated by the fuel cell system 1 under the current operating conditions may be greater than the actual power demand of the motor, thereby triggering the control units 41, 42, and 43 to jointly execute the method for unloading operation of the fuel cell system 1 according to this application.

[0021] Figure 2 A flowchart illustrating a method for de-load operation of a fuel cell system according to an exemplary embodiment of this application is shown. The following exemplary embodiments describe the method according to this application in more detail.

[0022] like Figure 2 As shown, the method may include steps S1 and S2. In step S1, based on the initial operating power P0 and the target operating power P of the fuel cell stack... w When it is determined that fuel cell system 1 needs to operate under reduced load, especially under significantly reduced load, fuel cell system 1 can be controlled to operate under the first heat dissipation condition and the intermediate operating power P. m The system operates by using the energy generated by the fuel cell system 1 to power the motor 3 and charge the battery 2 until the fuel cell system 1 reaches its intermediate operating power P. m The desired temperature conditions. Here, the target operating power P of the fuel cell stack can be set based on the vehicle's operating conditions. w For example, when encountering vehicle operating conditions such as parking and deceleration, the actual power demand of motor 3 will be significantly reduced, thus allowing for a lower target operating power P to be set for fuel cell system 1. w If the initial operating power P0 of the fuel cell stack—for example, 80 kW—is greater than a first preset power threshold and the target operating power P of the fuel cell stack is... w —For example, 11kW—is less than the second preset power threshold, meaning the fuel cell stack is currently operating at a high power level, and the deviation between the target operating power and the current operating power of the fuel cell stack is too large. Therefore, it is determined that the fuel cell system 1 needs to operate at a reduced load to reduce the operating power of the fuel cell stack.

[0023] according to Figure 3 The diagram shown illustrates the flow direction of fluid within a fuel cell stack 11 according to an exemplary embodiment of this application. The fluid inside the stack 11 of the fuel cell system 1 primarily comprises hydrogen A flowing through the anode 111, air B flowing through the cathode 112, and coolant C flowing between the anode 111 and the cathode 112. The hydrogen A supplied by the anode 111 and the air B supplied by the cathode 112 undergo an electrochemical reaction in the catalyst layer of the fuel cell system to generate electrical and thermal energy, and water is produced at the cathode 112. To improve the discharge capacity of the generated water from the stack 11, as indicated by the arrow, the flow directions of air B and coolant C are set to be substantially the same, i.e., the inlet of the cathode 112 is adjacent to the inlet of the coolant, and the outlet of the cathode 112 is adjacent to the outlet of the coolant. Since the heat capacity of the coolant is much greater than that of the gas, the outlet temperature of the coolant can be considered approximately equal to the outlet gas temperature of the cathode 112. The water produced by the cathode 112 diffuses through the proton exchange membrane of the fuel cell stack 11 to the anode 111. In order to enhance the fluid management inside the fuel cell stack, the flow direction of hydrogen gas A flowing through the anode 111 is set to be opposite to the flow direction of coolant C. That is, the inlet of the anode 111 is close to the outlet of the coolant, and the outlet of the anode 111 is close to the inlet of the coolant. Therefore, the inlet temperature of the coolant can be considered to be approximately equal to the outlet gas temperature of the anode 111.

[0024] According to the working principle of the fuel cell system, the stack 11 generates more water and heat under high power and high current conditions, resulting in a higher water content in the proton exchange membrane (PEM). Conversely, the stack 11 generates less water and heat under low power and low current conditions, leading to a lower PEM. A significant reduction in the operating power of the stack 11 results in a decrease in the water and heat generated, causing the PEM to transition from a wet to a dry state. However, due to the limited heat dissipation capacity of the thermal management device in the fuel cell system 1, it takes time to lower the temperature of the stack 11 to the temperature required for normal operation. Excessively high stack temperatures exacerbate the drying of the PEM, while increasing the stack power causes the PEM to re-wet. This repeated, large-scale wet-dry cycle easily generates mechanical stress in the PEM, increasing the likelihood of mechanical degradation and reducing the stack's performance output and durability. The method according to this application aims to minimize or avoid this repeated, large-scale wet-dry cycle of the PEM.

[0025] Here, the first heat dissipation operating condition, especially the maximum heat dissipation operating condition of the fuel cell system 1, can control the thermal management devices of the fuel cell system 1—including water pumps and / or fans, etc.—to operate at maximum speed, so that the fuel cell system 1 enters the maximum heat dissipation operating condition. It is understood that the first heat dissipation operating condition can also be an operating condition with a relatively high heat dissipation power, or an operating condition with a heat dissipation power close to the maximum heat dissipation power. Simultaneously, the fuel cell system 1 is controlled to operate at an intermediate power P. m Running, the intermediate operating power P m At the initial operating power P0 and the target operating power P w Between, because the fuel cell system operates at an intermediate power P m The energy generated during operation will exceed the actual power requirement of motor 3. While utilizing the energy generated by fuel cell system 1 to operate motor 3, it can also simultaneously charge battery 2—such as… Figure 1 The solid arrows in the diagram indicate the direction of energy flow, thereby improving energy efficiency through energy recovery. Based on the intermediate operating power P... m The selection principle is based on the fact that fuel cell system 1 operates at an intermediate power P. m During operation, the liquid water flow rate M at the anode outlet of the fuel cell stack f The total water vapor variation M at the cathode / anode outlet of the fuel cell stack should be maintained greater than that of the fuel cell stack. t .

[0026] Next, the intermediate operating power P will be explained in detail. m The method for determining this is as follows: First, it can be based on the stack current I and the actual output voltage U of the stack. r The theoretical output voltage U of the fuel cell stack sThe formula for calculating the heat generation Q of the fuel cell stack is as follows:

[0027] Q = I × (U s -U r ).

[0028] It is understandable that hydrogen and air undergo an electrochemical reaction in the catalyst layer of the fuel cell system within the fuel cell stack. Since the electrochemical conversion rate is limited, a certain amount of heat Q is generated along with electrical energy. This heat Q is the difference between the theoretical output power of the fuel cell stack and the actual output power of the fuel cell stack.

[0029] Then, based on the calculated heat generation Q, the coolant flow rate L through the stack under the first heat dissipation operating condition of fuel cell system 1, and the coolant temperature T at the stack inlet at the initial operating power P0, the calculation can be performed. hi Determine the coolant temperature T at the stack outlet under the initial operating power P0. ho Specifically, the thermal management device of the fuel cell system 1—including a water pump and / or a fan—can be controlled to operate at maximum speed, causing the fuel cell system 1 to enter, for example, a maximum heat dissipation operating condition. The flow rate L of the coolant flowing through the stack 11 under this maximum heat dissipation operating condition can be measured. Based on the heat generated Q and the coolant flow rate L through the stack, the theoretical temperature difference ΔT between the coolant at the stack outlet and the coolant at the stack inlet at the initial operating power P0 can be determined. Simultaneously, the coolant temperature T at the stack inlet at the initial operating power P0 can be measured. hi Adding this to the determined theoretical temperature difference ΔT gives the coolant temperature T at the stack outlet under the initial operating power P0. ho .

[0030] Then, the coolant temperature T at the stack outlet of fuel cell system 1 under normal operating conditions with stack current I can be obtained. so —It is approximately equal to the outlet gas temperature of the fuel cell cathode, and is calculated in relation to the coolant temperature T at the fuel cell outlet. ho The corresponding saturated vapor pressure W ho This refers to the saturated vapor pressure of the gas exiting the cathode of the fuel cell stack. The cathode gas supply parameters of the fuel cell stack can also be obtained under normal operating conditions of the fuel cell system 1 with the stack current I, including, for example, the gas pressure W at the cathode outlet of the fuel cell stack. ca The stoichiometric ratio λ of the cathode inlet of the fuel cell stack ca Therefore, the coolant temperature T at the stack outlet can be used as a basis for calculation. ho The corresponding saturated vapor pressure W ho Under normal operating conditions of fuel cell system 1 with stack current I, the cathode gas supply parameters of the stack and the coolant temperature T at the stack outlet are as follows: so The corresponding saturated vapor pressure Wso Calculate the change in water vapor concentration M at the cathode outlet of the fuel cell stack. ca The formula is, for example:

[0031]

[0032] Where, λ ca W represents the stoichiometric ratio at the cathode inlet of the fuel cell stack. ca The value represents the gas pressure at the cathode outlet of the fuel cell stack, N represents the number of individual cells in the fuel cell stack, F represents the Faraday constant with a value of 96485 C / mol, and mv represents the molar mass of water vapor with a value of 18 g / mol.

[0033] Simultaneously, the coolant temperature T at the stack inlet can be collected at the initial operating power P0. hi —It is approximately equal to the outlet gas temperature of the fuel cell anode, and is calculated in relation to the coolant temperature T at the fuel cell inlet. hi The corresponding saturated vapor pressure W hi —That is, the saturated vapor pressure of the outlet gas at the anode of the fuel cell stack. The coolant temperature T at the stack inlet can also be obtained under normal operating conditions of the fuel cell system 1 with stack current I. si Calculate the coolant temperature T at the fuel cell inlet. si The corresponding saturated vapor pressure W si And obtain the anode gas supply parameters of the fuel cell system 1 under normal operating conditions with stack current I, which include, for example, the gas pressure W at the stack anode outlet. an The stoichiometric ratio λ of the anode inlet of the fuel cell stack an Therefore, the coolant temperature T at the stack inlet can be used as a basis for calculations. hi The corresponding saturated vapor pressure W hi Under normal operating conditions of fuel cell system 1 with stack current I, the anode gas supply parameters of the stack and the coolant temperature T at the stack inlet are as follows: si The corresponding saturated vapor pressure W si Calculate the change in water vapor concentration M at the anode outlet of the fuel cell stack. an The formula is, for example:

[0034]

[0035] Where, λ an W represents the stoichiometry at the anode inlet of the fuel cell stack. an The pressure at the anode outlet of the fuel cell stack is represented by N, the number of individual cells in the stack is represented by F, and the F-value is 96485 C / mol. v This represents the molar mass of water vapor, with a value of 18 g / mol.

[0036] Here, the change in water vapor at the anode outlet, Man and the change in water vapor at the cathode outlet M ca The sum is the total change in water vapor at the cathode / anode outlet of the fuel cell stack, M. t And the change in water vapor at the anode outlet, M an and the change in water vapor at the cathode outlet M ca Both are functions of the stack current I, and thus can be used to determine the change in water vapor at the anode outlet, M. an and the change in water vapor at the cathode outlet M ca Determine the total change in water vapor M at the cathode / anode outlet of the fuel cell stack. t The first mathematical relationship between the changes in the stack current I and the current is... Figure 4 In the schematic diagram, the first curve, represented by the first mathematical relationship, is marked with a dashed line. The horizontal axis I represents the stack current, and the vertical axis M represents the change in water vapor or liquid water flow rate. When the initial operating power P0 of the stack 11 is high, the operating temperature of the stack 11 is also high. Due to the lag in heat dissipation from the thermal management system of the fuel cell system 1, a decrease in the operating power of the stack 11 may cause overheating, leading to evaporation of moisture from the proton exchange membrane and exacerbating the drying process. Figure 4 It can be seen that the greater the power change of fuel cell stack 11 from its initial operating power P0—that is, the smaller the operating condition from which the stack current I decreases—the greater the total change in water vapor M at the cathode / anode outlets of fuel cell stack 11. t The larger the current, the more liquid water evaporates from the fuel cell stack 11, and the more severe the drying of the proton exchange membrane; the smaller the power change of the fuel cell stack 11 from the initial operating power P0—that is, the smaller the power change to the operating condition with a higher fuel cell current I—the greater the total change in water vapor M at the cathode / anode outlet of the fuel cell stack 11. t The smaller the size, the less liquid water evaporates from the stack 11, and the less dry the proton exchange membrane becomes. However, the energy generated by the fuel cell system 1 will deviate more from the energy required for the motor 3 to operate, requiring more energy to be charged to the battery 2. This also places higher charging requirements on the battery 2, especially since the battery 2 cannot fully consume the excess energy generated by the fuel cell system 1 when it is fully charged.

[0037] Furthermore, the liquid water flow rate M at the anode outlet of the fuel cell stack can be determined based on measurement data under normal operating conditions with stack current I in fuel cell system 1. f The second mathematical relationship between the stack current I and the fuel cell system 1 is as follows: Specifically, the stack current I can be gradually adjusted under normal operating conditions, and the liquid water flow rate M at the anode outlet of the stack can be measured and recorded as the stack current I changes. f Therefore, based on the measurement data, the second mathematical relationship is determined. Figure 4 In the curve diagram, the second curve, represented by the second mathematical relationship, is marked with a solid line. For example... Figure 4 As shown, when the stack current I is small, the water production of the stack is small, and almost no liquid water flows out of the anode outlet. As the stack current gradually increases, liquid water gradually appears at the anode outlet, and the liquid water flow rate increases with the increase of the stack current I. It can be understood that the greater the liquid water flow rate, the greater the water content of the proton exchange membrane, and the lower the dryness of the proton exchange membrane.

[0038] Here, the total water vapor variation M at the cathode / anode outlet of the fuel cell stack is used as the basis. t The first mathematical relationship between the change of the stack current I and the liquid water flow rate M at the anode outlet of the stack. f The second mathematical relationship between the stack current I and the power of fuel cell system 1, P, can be used to determine the intermediate operating power. m This allows fuel cell system 1 to operate at an intermediate power P. m —that is, intermediate operating power P m Must be in Figure 4 The stack current value I is determined based on the intersection of the two curves. c Within the operating power range above the corresponding operating power—during operation, the liquid water flow rate M at the anode outlet of the fuel cell stack. f The total change in water vapor at the cathode / anode outlet of the fuel cell stack is greater than M. t This means that the amount of water generated at the cathode that passes through the proton exchange membrane and flows out of the anode outlet exceeds the amount of water that evaporates from inside the stack, thereby minimizing the drying process of the proton exchange membrane during the unloaded operation of the fuel cell system 1 and effectively eliminating repeated wet-dry cycles of the proton exchange membrane.

[0039] Here, the intersection point of the first curve represented by the first mathematical relationship and the second curve represented by the second mathematical relationship can be determined, and the stack current value I corresponding to the intersection point can be set. c (e.g., 146A) plus a pre-defined current threshold I r (e.g., 4A) to obtain the first intermediate operating current value I1 of the fuel cell stack (e.g., 150A), and determine the first intermediate operating power P of the fuel cell system 1 based on the first intermediate operating current value I1. m1 (e.g., 30kW) is used as the intermediate operating power P m The fuel cell system 1 is controlled to operate under a first heat dissipation condition and a first intermediate operating power P. m1 During operation, the energy generated by the fuel cell system 1 can be used to power the motor 3, and the excess energy can be used to charge the battery 2 until the fuel cell system 1 reaches the first intermediate operating power P. m1 The desired temperature conditions. Here, this can be based on the fuel cell system 1 operating at a first intermediate power P. mThe coolant temperature setting at the fuel cell stack inlet during operation is assigned to the first intermediate operating power P. m The desired temperature conditions are based on the fact that the coolant temperature at the fuel cell inlet is approximately equal to the temperature of motor 3. These desired temperature conditions must ensure that the temperature operation requirements of motor 3 are met.

[0040] The intermediate operating power P m It may also include at least one second intermediate operating power P m2 Wherein, the second intermediate operating power P m2 Less than the first intermediate operating power P m1 And greater than the target operating power P w The second intermediate operating power P m2 For example, it is determined to be the first intermediate operating power P. m1 and target operating power P w The average value (e.g., 20.5 kW). When fuel cell system 1 reaches the first intermediate operating power P... m1 After achieving the desired temperature conditions, the fuel cell system 1 can be controlled to operate under the first heat dissipation condition and the second intermediate operating power P. m2 The system operates by using the energy generated by the fuel cell system 1 to power the motor 3, and uses excess energy to charge the battery 2 until the fuel cell system 1 reaches the second intermediate operating power P. m2 By applying the desired temperature conditions, and so on, the fuel cell system 1 can achieve de-load operation from one second intermediate operating power to the next second intermediate operating power, thereby gradually reducing the operating power of the stack 11. Here, the second intermediate operating power P... m2 The desired temperature conditions can also be based on the fuel cell system 1 operating at a second intermediate power P. m2 The coolant temperature setting at the fuel cell inlet during operation.

[0041] In step S2, the fuel cell system 1 can be controlled to operate under a first heat dissipation condition and the target operating power P. w Run until fuel cell system 1 reaches the target operating power P. w The desired temperature conditions. Here, this can be based on the target operating power P of fuel cell system 1. w The coolant temperature setting at the fuel cell stack inlet during operation is assigned to the target operating power P. w The desired temperature conditions. As the operating power of the fuel cell stack 11 further decreases, the fuel cell system 1 still needs further cooling under the first heat dissipation operating condition, especially the maximum heat dissipation operating condition, in order to achieve the target operating power P. w The desired temperature conditions. When fuel cell system 1 reaches the target operating power P. wAfter achieving the desired temperature conditions, the fuel cell system 1 can be controlled to match the target operating power P. w The system operates under normal operating conditions, especially controlling the fuel cell system 1 to switch from maximum heat dissipation operation to the target operating power P. w The normal heat dissipation operation condition is thus achieved, thereby completing the entire process of unloading operation of fuel cell system 1.

[0042] According to embodiments of this application, when the fuel cell system needs to operate under significantly reduced load, the fuel cell system is kept in an operating condition with high heat dissipation power, and the operating power of the fuel cell stack is controlled to decrease from the initial operating power P0 to an intermediate operating power P. m Only after reaching the desired temperature regulation will the power be gradually reduced to the final target operating power P. w This ensures that during the deload operation of the fuel cell system, the liquid water flow rate at the anode outlet of the stack is always greater than the total change in water vapor at the cathode / anode outlets. This minimizes the significant fluctuations in the dryness of the proton exchange membrane during the deload operation of the fuel cell system, effectively eliminates repeated large-scale wet-dry cycles of the proton exchange membrane, avoids mechanical stress on the proton exchange membrane, reduces the possibility of mechanical degradation, and effectively improves the performance output and durability of the fuel cell stack.

[0043] In addition, it should be noted that the step numbers described herein do not necessarily represent the order of steps, but are merely a reference numeral. The order may be changed depending on the specific circumstances, as long as the technical objective of this application can be achieved.

[0044] It should be understood that in this document, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance, nor should they be construed as implicitly indicating the number of technical features indicated.

[0045] If an embodiment includes an "and / or" association between a first feature and a second feature, it should be interpreted as follows: according to one implementation, the embodiment has not only the first feature but also the second feature; according to another implementation, the embodiment has either only the first feature or only the second feature.

[0046] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of this application, even when only a single embodiment is described with respect to a particular feature. The feature examples provided in this application are intended for illustrative purposes and not for limitation, unless otherwise stated. In practice, multiple features may be combined with each other as needed and where technically feasible. Various substitutions, modifications, and alterations are also conceived without departing from the spirit and scope of this application.

Claims

1. A method for unloaded operation of a fuel cell system (1), the method comprising: Based on the initial operating power P0 and target operating power P of the fuel cell stack (11) w If it is determined that the fuel cell system (1) needs to operate under reduced load, the fuel cell system (1) is controlled to operate under the first heat dissipation condition and the intermediate operating power P. m The fuel cell system (1) operates by using the energy generated to power the motor (3) and charge the battery (2) until the fuel cell system (1) reaches the intermediate operating power P. m The desired temperature conditions, wherein the intermediate operating power P is determined in the following manner. m The fuel cell system (1) operates at the intermediate power P. m During operation, the liquid water flow rate M at the anode outlet of the fuel cell stack (11) is... f The total change in water vapor at the cathode / anode outlet of the fuel cell stack (11) is greater than M. t ;as well as Control the fuel cell system (1) to operate under the first heat dissipation condition and the target operating power P. w Run until the fuel cell system (1) reaches the target operating power P. w After achieving the desired temperature conditions, the fuel cell system (1) is controlled to operate at the target power P. w It operates under normal operating conditions.

2. The method according to claim 1, wherein, Based on the fuel cell current I and the actual output voltage U of the fuel cell. r The theoretical output voltage U of the fuel cell stack s Calculate the heat generation Q of the fuel cell stack, and based on the calculated heat generation Q, the coolant flow rate L through the fuel cell stack (11) under the first heat dissipation operation condition of the fuel cell system (1), and the coolant temperature T at the stack inlet under the initial operating power P0. hi Determine the coolant temperature T at the stack outlet under the initial operating power P0. ho ; Based on the coolant temperature T at the stack outlet at the initial operating power P0. ho The corresponding saturated vapor pressure W ho The cathode gas supply parameters and the coolant temperature T at the stack outlet of the fuel cell system (1) when the stack current I is running are as follows: so The corresponding saturated vapor pressure W so Calculate the change in water vapor at the cathode outlet of the fuel cell stack (11) M. ca ; Based on the coolant temperature T at the stack inlet at the initial operating power P0. hi The corresponding saturated vapor pressure W hi When the fuel cell system (1) is running at stack current I, the anode gas supply parameters of the stack and the coolant temperature T at the stack inlet are as follows: si The corresponding saturated vapor pressure W si Calculate the change in water vapor at the anode outlet of the fuel cell stack (11) M. an .

3. The method according to claim 2, wherein, Based on the change in water vapor at the anode outlet of the fuel cell stack (11) M an The change in water vapor at the cathode outlet of the fuel cell stack (11) M ca Determine the total change M of water vapor at the cathode / anode outlet of the fuel cell stack (11). t The first mathematical relationship between the fuel cell current I and the fuel cell current; and / or The liquid water flow rate M at the anode outlet of the fuel cell stack was determined based on measurement data obtained during operation of the fuel cell system (1) at stack current I. f The second mathematical relationship between the stack current I and the change in the fuel cell current; and / or The intermediate operating power P of the fuel cell system (1) is determined based on the first mathematical relationship and the second mathematical relationship. m This allows the fuel cell system (1) to operate at an intermediate power P. m The liquid water flow rate M at the anode outlet of the fuel cell stack during operation f The total change in water vapor at the cathode / anode outlet of the fuel cell stack is greater than M. t .

4. The method according to claim 3, wherein, The intermediate operating power P m Including the first intermediate operating power P m1 Wherein, the intersection point of the first curve represented by the first mathematical relationship and the second curve represented by the second mathematical relationship is determined, and the stack current value I corresponding to the intersection point is... c Add a pre-defined current threshold I r The first intermediate operating current value I1 of the fuel cell stack is obtained, and the first intermediate operating power P of the fuel cell system (1) is determined based on the first intermediate operating current value I1. m1 .

5. The method according to claim 4, wherein, The intermediate operating power P m Including at least one second intermediate operating power P m2 Wherein, the second intermediate operating power P m2 Less than the first intermediate operating power P m1 And greater than the target operating power P w Wherein, the second intermediate operating power P m2 For example, it is determined to be the first intermediate operating power P. m1 and target operating power P w The average value.

6. The method according to any one of claims 1 to 5, wherein, The first heat dissipation operation condition is the maximum heat dissipation operation condition of the fuel cell system (1), wherein the thermal management device of the fuel cell system (1) is controlled to operate at the maximum speed, so that the fuel cell system (1) enters the maximum heat dissipation operation condition, wherein the thermal management device includes a water pump and / or a fan.

7. The method according to any one of claims 1 to 5, wherein, Based on the fuel cell system (1) operating at intermediate power P m The coolant temperature setting at the fuel cell stack inlet during operation is assigned to the intermediate operating power P. m The desired temperature conditions; and / or Based on the target operating power P of the fuel cell system (1) w The coolant temperature setting at the fuel cell stack inlet during operation is assigned to the target operating power P. w The desired temperature conditions.

8. The method according to any one of claims 1 to 5, wherein, The target operating power P of the fuel cell stack is set based on the vehicle's operating conditions. w When the initial operating power P0 of the fuel cell stack is greater than the first preset power threshold and the target operating power P of the fuel cell stack is... w If the power is less than the second preset power threshold, it is determined that the fuel cell system (1) needs to operate with reduced load, wherein the vehicle operating conditions include parking operation conditions and / or vehicle deceleration operation conditions.

9. A fuel cell power system (10), the fuel cell power system (10) comprising a fuel cell system (1), a battery (2), a motor (3), and a control unit (41, 42, 43), wherein, The control unit (41, 42, 43) is configured to perform the method according to any one of claims 1 to 8.

10. A computer program product, such as a computer-readable program carrier, comprising computer program instructions that, when executed by a processor, at least partially implement the steps of the method according to any one of claims 1 to 8.

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