A method and system for multi-stage ejector and water management control of a fuel cell

Abstract

The application provides a fuel cell multi-stage ejector and water management control method and system. The method comprises obtaining the current operating power of a fuel cell stack; determining the target working mode of a multi-stage ejector according to the power level of the current operating power, the multi-stage ejector comprising at least a first nozzle and a second nozzle, the first nozzle and the second nozzle having different diameters; and controlling the multi-stage ejector to switch between the first nozzle and the second nozzle according to the target working mode to adjust the ejector flow of a hydrogen loop, so that the water content in the stack is maintained within a preset range. The method can make the multi-stage ejector present different ejector characteristics at different power levels through a hierarchical control strategy, accurately match the water production law of the stack, maintain the water content in the stack in a dynamic balance within the full operating condition range, improve the single cell voltage consistency and system net power, reduce the dependence on the performance of auxiliary humidification equipment and gas-water separators, and optimize the system cost and control complexity.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and specifically to a method and system for controlling multi-stage ejection and water management in fuel cells. Background Technology

[0002] Fuel cells (such as proton exchange membrane fuel cells) produce water during operation, and the presence of water has a significant impact on fuel cell performance. Specifically, because the proton exchange membrane in a fuel cell needs to be fully wetted to maintain high proton conductivity, insufficient water leads to a decrease in ionic conductivity and a decline in cell performance. On the other hand, excessive liquid water can clog the gas diffusion layer and flow channels, hindering the transport of reactant gases, causing flooding, and resulting in a sharp drop in cell voltage. Therefore, water management is one of the core technologies of fuel cells, directly affecting their power output, durability, and other performance characteristics.

[0003] Currently, water management in fuel cells mainly involves two aspects: air path humidity regulation and hydrogen path water management. Regarding the air path, existing technologies typically control the water content inside the fuel cell stack by adjusting the air path humidity. A common approach is to use a membrane humidifier to humidify the air entering the stack and regulate the humidity of the air entering the stack by setting up a humidification bypass (drying throttle).

[0004] In terms of hydrogen circulation, existing technologies mainly employ two methods for water management: hydrogen recirculation pumps and ejectors. Hydrogen recirculation pumps actively circulate unreacted, moistened hydrogen from the anode outlet back to the anode inlet, thereby improving hydrogen utilization efficiency and optimizing battery hydrothermal management. However, these pumps require additional electricity to operate, resulting in higher costs. Ejectors, on the other hand, require no additional power supply, are simple in structure, reliable in operation, and have a long lifespan, thus attracting increasing attention. However, as passive circulation devices, traditional ejectors have essentially fixed ejection performance once their mechanical structure is determined. Their recirculation capability is only effective within a certain output power range, failing to adapt to the variable operating conditions of fuel cells across a wide power range. Especially during initial startup or at low power, when the stack output power is low and the unreacted hydrogen flow rate is small, the ejector diameter is typically designed for maximum power, leading to a decrease in flow rate and ejection capacity. This results in ineffective water drainage from the anode, causing flooding of the stack.

[0005] To address the issue of the narrow operating range of ejectors, existing technologies have proposed multi-stage or multi-nozzle ejector solutions. By using nozzles of different diameters, different nozzles can be switched at different power levels to expand the ejector's operating range. For example, a small nozzle can be used at low power levels, and a large nozzle can be switched at high power levels. However, in existing water management schemes using multi-stage ejectors, ejector switching control typically only focuses on matching the hydrogen circulation volume, failing to systematically coordinate ejector switching with the retention and removal requirements of moisture within the fuel cell stack.

[0006] In summary, existing fuel cell water management technologies suffer from the following problems: high energy consumption and cost of hydrogen circulation pumps; narrow operating range of traditional ejectors, unable to adapt to the full power range; insufficient integration of multi-stage ejector switching control with water management requirements; and lack of coordinated control between air path humidification regulation and hydrogen path water management. These problems make it difficult for fuel cell systems to maintain suitable water content at different power levels, affecting stack performance and lifespan, while also increasing system cost and control complexity. Summary of the Invention

[0007] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a multi-stage ejector and water management control method and system for fuel cells, which aims to solve the technical problems in the related technology to a certain extent.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for controlling multi-stage ejection and water management in a fuel cell is provided, comprising the following steps:

[0010] Obtain the current operating power of the fuel cell stack;

[0011] Based on the power level of the current operating power, the target operating mode of the multi-stage ejector is determined. The multi-stage ejector includes at least a first nozzle and a second nozzle, wherein the first nozzle and the second nozzle have different diameters.

[0012] According to the target working mode, the multi-stage ejector is controlled to switch between the first nozzle and the second nozzle to adjust the ejection flow rate of the hydrogen circuit and keep the moisture inside the fuel cell stack within a preset range.

[0013] In particular, at low power levels, the multi-stage ejector is controlled to operate with the first nozzle to reduce the ejection flow rate or even eliminate ejection, so as to retain moisture inside the fuel cell stack.

[0014] At medium power levels, the multi-stage ejector is controlled to operate with the second nozzle to increase the ejection flow rate, thereby enhancing fuel cell drainage and preventing flooding.

[0015] At high power levels, the multi-stage ejector is controlled to operate with the first nozzle or with the first nozzle and the second nozzle operating simultaneously to meet the hydrogen flow requirements at high power levels.

[0016] Preferably, the multi-stage ejector is a variable nozzle ejector, wherein the first nozzle is a large nozzle and the second nozzle is a small nozzle.

[0017] Preferably, the multi-stage ejector is a series ejector or a parallel ejector.

[0018] Preferably, at the low power level, the multi-stage ejector cycles between the first nozzle and the second nozzle according to a preset period;

[0019] The preset cycle includes a first nozzle running time and a second nozzle running time, wherein the first nozzle running time is much longer than the second nozzle running time.

[0020] Preferably, as the current operating power increases within the low power level, the operating time of the first nozzle gradually decreases, while the operating time of the second nozzle gradually increases.

[0021] Preferred options also include:

[0022] During the switching process of the multi-stage ejector, the opening and closing of the tail exhaust valve are controlled to assist in the drainage and venting of the fuel cell stack.

[0023] Preferably, the opening cycle of the tail valve is related to the switching cycle of the multi-stage ejector, with different power levels corresponding to different switching cycles and tail valve cycles.

[0024] Preferably, the fuel cell system further includes an air humidification bypass, which is provided with a humidification throttle valve and a drying throttle valve;

[0025] The method further includes:

[0026] Based on the current operating power level, control the opening of the humidifying throttle valve and / or the drying throttle valve to adjust the humidity of the air path;

[0027] At low power levels, the dry throttle valve is closed, and air enters the fuel cell stack via a humidifier;

[0028] At medium power level, the humidifying throttle valve is closed and the drying throttle valve is opened;

[0029] At high power levels, both the humidifying throttle valve and the drying throttle valve are opened simultaneously.

[0030] Preferably, the ejector flow rate regulation of the hydrogen circuit and the humidity regulation of the air circuit are arranged and combined according to the actual operating state of the fuel cell stack to jointly regulate the water management of the fuel cell stack system.

[0031] A multi-stage ejector and water management system for fuel cells is also provided, including:

[0032] Fuel cell stack;

[0033] A multi-stage ejector is disposed on the hydrogen circuit of the fuel cell stack, and includes at least a first nozzle and a second nozzle, wherein the first nozzle and the second nozzle have different diameters.

[0034] A tailpipe valve is installed on the hydrogen outlet pipeline of the fuel cell stack;

[0035] The controller, which is signal-connected to the multi-stage ejector and the tailpipe valve, is configured to perform the method provided in the embodiments of this application.

[0036] Based on the above technical solution, the advantages of the present invention compared with the prior art are as follows:

[0037] The fuel cell multi-stage ejector and water management control method provided in this application includes acquiring the current operating power of the fuel cell stack, determining the target operating mode of the multi-stage ejector based on the power level of the current operating power, and controlling the multi-stage ejector to switch between the first nozzle and the second nozzle according to the target operating mode to adjust the ejection flow rate of the hydrogen circuit, so that the moisture inside the stack is maintained within a preset range. Therefore, through this method, the multi-stage ejector can exhibit differentiated ejection characteristics at different power levels through a hierarchical control strategy, which can accurately match the water production pattern of the stack, so that the moisture inside the stack is in dynamic balance across the entire operating range, improving the consistency of single-cell voltage and the net power of the system, reducing the performance dependence on auxiliary humidification equipment and gas-water separator, and optimizing system cost and control complexity. Attached Figure Description

[0038] Figure 1 A schematic diagram of the specific structure of a fuel cell multi-stage ejector and water management system provided in an embodiment of this application;

[0039] Figure 2 This is a schematic flowchart illustrating the multi-stage ejector and water management control method for a fuel cell, provided as an embodiment of this application. Detailed Implementation

[0040] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0042] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0043] In view of the problems of the prior art mentioned in the background section, this application proposes a multi-stage ejector and water management control method and system for fuel cells, such as... Figure 1 The diagram shows the specific structure of the fuel cell multistage ejector and water management system (hereinafter referred to as the system). The system includes: fuel cell stack 1, multistage ejector 2, tail valve 3, controller 4, and air supply passage 5.

[0044] The fuel cell stack 1 of this application can be a stack in a proton exchange membrane fuel cell. The stack is a power generation device composed of multiple individual cells stacked in series. Specifically, the air supply passage 5 and the hydrogen supply passage inject air and hydrogen into the fuel cell stack 1, respectively, so as to generate electricity using the fuel cell stack 1.

[0045] The multi-stage ejector 2 is disposed on the hydrogen circuit in the hydrogen supply passage of the fuel cell stack 1. Structurally, the multi-stage ejector 2 includes at least a first nozzle and a second nozzle, and the first nozzle and the second nozzle have different diameters. Specifically, the diameter of the first nozzle is larger than that of the second nozzle. In the embodiments of this application, the multi-stage ejector can be a variable nozzle ejector, in which case the first nozzle is in a large nozzle state formed by mechanical adjustment, and the second nozzle is in a small nozzle state; of course, the multi-stage ejector can also be a series ejector or a parallel ejector, with fixed nozzles of different diameters provided in each ejection branch, and the activation of different nozzles is achieved by switching valves.

[0046] In this application, the variable nozzle ejector 2 is configured as a fluid control device with dynamic flow channel adjustment function. It changes the effective flow cross-sectional area of ​​the nozzle throat through the movement of internal mechanical components, achieving switching between different equivalent diameters on a single physical entity. The specific structure includes a control execution unit, a nozzle displacement component, and a fluid flow channel. The control execution unit, in response to received control commands, drives the nozzle displacement component to change the geometric boundary of the fluid flow channel, enabling the flow channel to switch between a large nozzle state and a small nozzle state. The large nozzle state has a larger equivalent flow diameter, a relatively lower jet velocity, and weaker entrainment capacity, providing a lower ejection ratio, which is beneficial for achieving water retention within the fuel cell stack. The small nozzle state has a smaller equivalent flow diameter, a significantly increased fluid velocity, and generates a strong negative pressure entrainment effect based on the Bernoulli effect, greatly increasing the ejection flow rate to enhance fluid circulation in the hydrogen circuit and promote the discharge of liquid water from inside the fuel cell stack.

[0047] A series ejector consists of several ejector units connected sequentially. Each ejector unit has an independent nozzle and mixing chamber. High-pressure hydrogen gas expands and accelerates step by step through each nozzle, using the mixed fluid from the previous stage as the ejected fluid for the next stage, thus achieving a higher overall ejection ratio under conditions where the inlet pressure is limited. A parallel ejector contains two or more ejector branches connected in parallel. Each ejector branch is equipped with fixed nozzles of different diameters. The branches converge at the inlet and outlet through a gas collecting pipeline. By controlling the on / off state of the control valves (such as solenoid valves or pneumatic valves) installed on each branch, nozzle branches of different diameters can be selectively activated, or multiple branches can be opened simultaneously to superimpose the flow area.

[0048] The tail valve 3 is installed on the hydrogen outlet pipe in the hydrogen supply passage of the fuel cell stack 1. Specifically, it can be installed at the end of the hydrogen circulation loop or at the drain outlet of the gas-water separator. It is used to discharge liquid water and impurity gases such as nitrogen that have accumulated on the anode side of the stack at specific times (such as each emission cycle).

[0049] Air supply passage 5 includes an air compressor, an intercooler, and a humidification bypass. The air compressor is responsible for drawing in ambient air and compressing it to establish the back pressure required for the fuel cell stack's chemical reactions and ensure a sufficient oxygen supply. The intercooler is located downstream of the air compressor and is used for heat exchange cooling of the high-temperature, high-humidity air generated after compression. The humidification bypass includes a humidification throttle valve and a drying throttle valve. The humidification throttle valve regulates the airflow through the humidifier, while the drying throttle valve regulates the airflow through the drying bypass. By differentially adjusting the flow cross-sectional area of ​​these two throttle valves, the relative humidity of the air entering the fuel cell stack can be precisely controlled.

[0050] The controller 4 is signal-connected to the multi-stage ejector 2 and the tail valve 3, thereby enabling the controller 4 to actively control the multi-stage ejector 2 and the tail valve 3 and execute the method provided in the embodiments of this application.

[0051] like Figure 2 The diagram shown is a schematic flowchart of a fuel cell multi-stage ejector and water management control method provided in an embodiment of this application. This method can be applied to the fuel cell multi-stage ejector and water management system provided in this embodiment of the application and is executed by the controller 4 in the system. The method includes the following steps:

[0052] Step S601: Obtain the current operating power of the fuel cell stack.

[0053] Specifically, the current operating power can be determined by acquiring real-time voltage and current values ​​and calculating their product through voltage and current sensors connected to the fuel cell stack output, or by directly reading power command or feedback values ​​from the communication bus of the vehicle control unit (VCU) or fuel cell stack controller (FCU). Clearly, this current operating power reflects the system's real-time load status and can therefore serve as a basis for adjusting subsequent water management strategies.

[0054] Step S602: Determine the target operating mode of the multi-stage ejector based on the current power level.

[0055] Specifically, the rated power range of the fuel cell stack can be pre-divided into three power levels: low, medium, and high. For example, 0% to 30% is the low power level, 30% to 70% is the medium power level, and above 70% is the high power level. Corresponding operating modes are assigned to each power level. These operating modes include activating only the first nozzle, activating only the second nozzle, or activating both the first and second nozzles simultaneously. This aims to adapt the ejector's operating state to the water production and gas supply characteristics under the current power demand. Thus, in step S602, the current operating power level can be determined, for example, by comparing the current operating power with preset thresholds for each power level. Based on this power level, the target operating mode of the multi-stage ejector is then determined. The multi-stage ejector integrates a first nozzle and a second nozzle with different diameters. The first nozzle has a larger diameter than the second nozzle, resulting in different ejection coefficients (i.e., the ratio of ejection flow rate to driving flow rate) due to the difference in their flow cross-sectional areas.

[0056] In one embodiment of this application, the multi-stage ejector is a variable nozzle ejector, with the first nozzle being a large nozzle and the second nozzle a small nozzle. In this case, the variable nozzle ejector is configured as a fluid control device with dynamic flow channel adjustment capabilities. It is not a fixed-aperture throttling element, but rather a precision fluid dynamics unit integrating an actuator and a flow channel deformation mechanism. This device changes the effective flow cross-sectional area of ​​the nozzle throat through the movement of internal mechanical components, achieving switching between different equivalent orifices on a single physical entity. The specific structure includes a control execution unit, a nozzle displacement assembly, and a fluid flow channel. The control execution unit, in response to received control commands, drives the nozzle displacement assembly to change the geometric boundaries of the fluid flow channel, enabling the flow channel to switch between a large nozzle state and a small nozzle state. This design allows the system to adapt to different flow and pressure conditions without hardware replacement, simply by adjusting the nozzle opening.

[0057] The first nozzle corresponds to the large nozzle state, possessing a large equivalent flow diameter. When the execution unit output flow channel is fully open or at a large opening, the throat of the variable nozzle ejector maintains a large opening, forming the large nozzle operating condition. In this state, the jet velocity is relatively low, and the entrainment capacity of the ejected fluid is weak, thus providing a lower ejection ratio. This operating condition keeps the circulating flow rate in the hydrogen circuit at a low level, thereby reducing the power required to carry liquid water out of the fuel cell stack, which is beneficial for achieving water retention within the fuel cell stack.

[0058] Additionally, the second nozzle corresponds to the small nozzle state, with a smaller equivalent flow diameter. When the unit output flow channel contracts or a small opening command is executed, the throat opening of the variable nozzle ejector contracts, forming the small nozzle condition. The fluid velocity increases significantly as it flows through the contracted throat. Based on the Bernoulli effect, the static pressure at the nozzle outlet decreases, generating a strong negative pressure entrainment effect, which greatly increases the ejection flow rate of moisture from the fuel cell stack outlet. This condition is used to enhance fluid circulation in the hydrogen circuit, promote the discharge of liquid water inside the fuel cell stack, and prevent flooding.

[0059] It is important to note that by defining the first nozzle as a large nozzle and the second nozzle as a small nozzle, a mapping relationship is established between nozzle diameter and ejector flow capacity. Low and high ejector flow requirements can be met by switching the state of the same variable nozzle ejector, thus adapting to the differentiated water management needs of fuel cells at different power levels.

[0060] In another implementation of this application, the multi-stage ejector is either a series ejector or a parallel ejector. In this embodiment, the multi-stage ejector serves as the core actuator for hydrogen circulation and flow regulation, and its physical configuration encompasses engineering implementation architectures such as series and parallel ejectors. When the multi-stage ejector is configured as a series ejector, the cascading effect of the multi-stage ejection gradually enhances the suction capacity for moisture at the fuel cell stack outlet. The series ejector consists of several ejection units connected sequentially, each with an independent nozzle and mixing chamber. High-pressure hydrogen expands and accelerates through each nozzle, using the mixed fluid from the previous stage as the ejected fluid for the next stage, thereby achieving a higher overall ejection ratio under conditions of limited inlet pressure. This structure is particularly suitable for applications requiring high hydrogen reflux ratios or experiencing large system back pressure fluctuations.

[0061] Furthermore, by configuring the multi-stage ejector as a parallel ejector, flexible adjustment and redundancy of the ejector flow rate can be achieved through a multi-branch combination. The parallel ejector comprises two or more ejector branches connected in parallel, each branch equipped with fixed nozzles of different diameters (corresponding to the first and second nozzles in the above embodiment). The branches converge at the inlet and outlet via a gas collection pipeline. During actual operation, by controlling the on / off state of control valves (such as solenoid valves or pneumatic valves) on each branch, nozzle branches of different diameters can be selectively activated, or multiple branches can be opened simultaneously to superimpose the flow area. This structural form avoids the complex motion mechanisms inside the variable mechanical nozzle, reduces manufacturing precision requirements and failure rate, and offers the advantages of modular replacement and maintenance.

[0062] Regardless of the structural form adopted, both series and parallel ejectors are integrated into the hydrogen circuit and controlled by the method provided in this application. The controller sends corresponding control commands (such as valve opening commands or branch switching commands) to the series or parallel ejectors based on the current power level of the fuel cell stack, thereby switching between the first and second nozzles or adjusting the operating state of each ejector unit. This structural diversity allows the multi-stage ejector and water management control method proposed in this application to adapt to the design requirements of fuel cell systems with different power levels (such as 40kW low-power systems or 100kW high-power systems). While meeting the water management objective of maintaining the internal moisture of the stack within a preset range, it also provides system integrators with flexible hardware selection options.

[0063] Step S603: Control the multi-stage ejector to switch between the first nozzle and the second nozzle according to the target working mode, so as to adjust the ejection flow rate of the hydrogen circuit and keep the moisture inside the fuel cell stack within the preset range.

[0064] Specifically, the controller outputs control signals to drive the actuators (such as solenoid valves or servo motors) inside the multi-stage ejector, switching the physical paths of the first and second nozzles, thereby changing the nozzle flow area to adjust the ejection flow rate. The large-diameter first nozzle drives a large flow rate but has a lower ejection velocity under the same pressure differential, resulting in a smaller ejection ratio; the small-diameter second nozzle generates a higher jet velocity, stronger entrainment capacity, and a larger ejection ratio. By adjusting the ejection flow rate, the amount of liquid water carried out from the stack outlet is controlled, dynamically balancing the produced and discharged water within the stack, maintaining the proton exchange membrane humidity within a preset optimal range that is neither dehydrated nor flooded. This preset range can be calibrated based on the stack impedance characteristics, single-chip voltage consistency, or empirical data, thus avoiding performance degradation caused by moisture imbalance.

[0065] In this way, at low power levels, the multi-stage ejector is controlled to operate with the first nozzle, reducing or even eliminating the ejection flow rate to retain moisture inside the fuel cell stack. Specifically, at low power levels, the fuel cell stack's chemical reaction rate is low and water production is minimal, making the membrane electrode assembly (MEA) prone to drying. By controlling the multi-stage ejector to switch to the first nozzle, its large-diameter characteristic generates a weak entrainment capacity at low drive flow rates, significantly reducing the ejection flow rate or approaching a near-zero ejection state. This weak ejection state reduces the amount of liquid water carried by the hydrogen circulation loop inside the fuel cell stack, causing the water generated by the reaction to remain in the flow channels and gas diffusion layer to wet the proton exchange membrane, effectively solving the membrane dehydration problem under low power conditions and improving proton conductivity and fuel cell stack operating efficiency.

[0066] At medium power levels, the multi-stage ejector is controlled to operate with the second nozzle, increasing the ejection flow rate to enhance fuel cell stack drainage and prevent flooding. Specifically, at medium power levels, the fuel cell stack produces significantly more water, posing a risk of accumulation and flooding. In this case, the multi-stage ejector is switched to operate with the second nozzle, utilizing its small-diameter characteristic to significantly increase the hydrogen flow rate and create a strong negative pressure zone under the same hydrogen supply pressure, thereby greatly increasing the ejection flow rate. The high-flow-rate circulating hydrogen rapidly carries the liquid water generated inside the fuel cell stack to the gas-liquid separator, enhancing drainage capacity, preventing liquid water blockage in the flow channels, ensuring a smooth supply of reactant gases, and avoiding voltage drops caused by localized flooding.

[0067] At high power levels, the multi-stage ejector is controlled to operate with only the first nozzle or with both the first and second nozzles operating simultaneously to meet the high hydrogen flow rate requirements. Specifically, at high power levels, the hydrogen consumption of the fuel cell stack is enormous. In this case, the multi-stage ejector is controlled to operate with only the first nozzle, utilizing its large-diameter characteristic to meet the high hydrogen flow rate requirement and reduce flow resistance; or the first and second nozzles are controlled to operate simultaneously, maximizing the hydrogen flux through parallel or series connection to ensure sufficient gas supply under high load. Given the extremely high water production of the fuel cell stack itself under high power, even with a high-flow ejector, the internal relative humidity of the fuel cell stack can still be maintained, eliminating concerns about excessive dryness. This strategy meets the high-power hydrogen flow rate requirements while also taking into account water management, ensuring the stability of the system's power output under high load.

[0068] In another embodiment of this application, the method may further include: at a low power level, the multi-stage ejector cyclically switches between the first nozzle and the second nozzle according to a preset cycle; wherein the preset cycle includes the running time of the first nozzle and the running time of the second nozzle, wherein the running time of the first nozzle is much greater than (10 times or more) the running time of the second nozzle.

[0069] Specifically, under low-power conditions, the multi-stage ejector performs a cyclic switching action between the first and second nozzles according to a preset cycle. This preset cycle serves as a time reference for controlling the nozzle switching rhythm, and its parameter configuration is determined based on engineering analysis of the fuel cell stack water distribution characteristics. During system initialization or operating condition calibration, data on the accumulation rate of liquid water inside the fuel cell stack and the flow channel pressure fluctuation characteristics are collected under low-power operating conditions. Based on the water accumulation rate, the interval time window for discharging accumulated water is determined, thereby establishing the reference value for the first nozzle's operating time. Simultaneously, combined with flow channel fluid dynamics analysis, the shortest jet time required to effectively disturb the flow field and carry away accumulated liquid is determined, thereby establishing the reference value for the second nozzle's operating time. The above two reference values ​​are combined to form the initial configuration parameters of the preset cycle. This preset cycle is not fixed and can be dynamically fine-tuned according to real-time conditions such as ambient temperature, fuel cell stack aging degree, or actual single-cell voltage consistency. By introducing the preset cycle, time-domain control of the ejection state in the low-power segment is achieved, breaking the static flow field equilibrium caused by the continuous operation of a single nozzle.

[0070] The preset cycle specifically encompasses two core time periods: the first nozzle runtime and the second nozzle runtime. The first nozzle runtime refers to the duration during which the multi-stage ejector operates with the first nozzle within the preset cycle, and this duration constitutes the dominant proportion of the cycle. Its value is prioritized to meet the water retention requirements of the fuel cell stack under low-power conditions; for example, it can be set to 30 to 120 seconds, with the specific value depending on the humidity of the produced water and the intake air. The second nozzle runtime refers to the duration during which the multi-stage ejector switches to operating with the second nozzle within the preset cycle, and this duration constitutes only a very small proportion of the cycle. Its value is based on the physical time required to generate a transient high-speed airflow sufficient to flush out accumulated liquid in the flow channels; for example, it can be set to 1 to 5 seconds. The coordination of the first and second nozzle runtimes constitutes a complete water retention-drainage micro-cycle, ensuring a high humidity environment inside the fuel cell stack for most of the time, and activating a powerful drainage mechanism only during very short time windows.

[0071] Furthermore, based on the configuration that the first nozzle's operating time is much longer than the second nozzle's operating time, the control logic is driven by a preset cycle to perform cyclic switching. During the first nozzle's operating time, the multi-stage ejector remains in the first nozzle's operating state. At this time, the ejection flow rate is extremely low or even non-extracting, allowing a large amount of moisture inside the fuel cell stack to be retained, fully meeting the wetting requirements of the proton exchange membrane. When the first nozzle's operating time ends, it immediately switches to the second nozzle's operating state and starts the second nozzle's operating time timing. At this time, the ejection flow rate increases instantaneously, and the hydrogen circulation velocity increases significantly, creating a mechanical flushing and carrying effect on the liquid water in the fuel cell stack's flow channels. This rapidly discharges liquid water that may accumulate in the flow channel bends or diffusion layer pores, preventing excessively low single-cell voltage due to localized flooding. When the second nozzle's operating time ends, it immediately switches back to the first nozzle's operating state, re-entering the water retention phase, and this cycle repeats continuously. This cyclical control strategy, which prioritizes long-term water retention and supplements it with short-term drainage, can retain the moisture generated by the fuel cell reaction to the greatest extent possible while ensuring that the entire fuel cell stack does not suffer severe flooding. This reduces the dependence on the separation efficiency of the gas-water separator and the need for an external humidification system.

[0072] In an optional implementation, the method further includes: as the current operating power increases within the low power range, the operating time of the first nozzle gradually decreases, while the operating time of the second nozzle gradually increases. Specifically, within the low power operating range, the water production rate and water demand characteristics of the fuel cell stack will shift with slight changes in load. If a fixed-cycle switching parameter is used, it is easy to cause lag or imbalance in water management. Therefore, this embodiment introduces a dynamic timing adjustment strategy to respond to the trend of increased stack reaction activity and increased internal water generation. By shortening the single continuous opening time of the first nozzle (such as a large nozzle or a low ejector flow nozzle) and simultaneously extending the single continuous opening time of the second nozzle (such as a small nozzle or a high ejector flow nozzle), the risk of local flooding caused by maintaining the original long-term water retention strategy can be effectively avoided.

[0073] This dynamic adjustment process updates the runtime of the first and second nozzles in real time within a preset period based on power change trends. In practice, the specific runtime values ​​can be determined by consulting a pre-calibrated power-time mapping table, which records the optimal nozzle opening time ratio for different power points within the low-power range. For example, when the current operating power is 5kW, the runtime of the first nozzle is set to 60 seconds, and the runtime of the second nozzle is set to 2 seconds; when the power increases to 15kW, the runtime of the first nozzle is automatically adjusted to 45 seconds, and the runtime of the second nozzle is correspondingly adjusted to 5 seconds.

[0074] Furthermore, as the power continues to climb to the upper limit of the low-power level, the operating time of the first nozzle is further reduced until it approaches or reaches the critical point for switching from the medium-power level to the independent operation of the second nozzle. This continuously and gradually changing duration adjustment mechanism allows the ejection intensity of the multi-stage ejector to exhibit a smooth climbing curve as the power increases, avoiding the sudden flow changes caused by the fixed switching mode, thereby achieving a smooth transition from a pure water-holding state to an active drainage state.

[0075] In an optional embodiment of this application, the method may further include: coordinating the opening and closing of the tailpipe valve during the multi-stage ejector switching process to assist in the drainage and venting of the fuel cell stack. Specifically, the tailpipe valve, as a key actuator in the fuel cell hydrogen circuit, is typically located at the end of the hydrogen circulation circuit or at the drain outlet of the gas-liquid separator, and is used to discharge liquid water and impurity gases such as nitrogen accumulated on the anode side of the fuel cell stack at specific times. During the dynamic process of nozzle switching of the multi-stage ejector, by coordinating the opening and closing state of the tailpipe valve, the liquid water and high-concentration nitrogen accumulated in the dead zone of the flow channel or the gas diffusion layer are forcibly discharged by utilizing the fluid disturbance effect generated at the moment of switching. The control logic is configured to send a trigger command to the tailpipe valve at the critical moment when the multi-stage ejector switches from a large-diameter nozzle to a small-diameter nozzle, or from a small-diameter nozzle to a large-diameter nozzle. When the ejector flow rate changes abruptly, the instantaneous change in hydrogen flow rate can carry some accumulated water and impurities to the tail outlet. If the tail outlet valve is open at this time, the impurities can be discharged from the fuel cell stack, preventing insufficient supply of reaction gas and voltage fluctuations caused by local flooding or nitrogen accumulation.

[0076] In practice, the opening of the tail valve and the switching action of the multi-stage ejector are closely coordinated in timing. When the multi-stage ejector switches from the first nozzle to the second nozzle, the ejection flow rate increases instantaneously, and the gas velocity in the flow channel accelerates. At this time, the tail valve is opened for a certain period of time (e.g., 0.5 to 2 seconds, this is just an example) to flush out the accumulated liquid water using the high-speed airflow. Subsequently, the tail valve is closed to avoid excessive hydrogen consumption. When the multi-stage ejector switches back from the second nozzle to the first nozzle, the ejection flow rate decreases. At this time, the tail valve can also be opened to use pressure fluctuations to discharge excess water that may have accumulated due to the previous high-flow operation. Through the above coordinated control, the opening of the tail valve is no longer limited to periodic venting based on fixed time, but is linked in real time with the state changes of the multi-stage ejector. This significantly improves the efficiency and accuracy of fuel cell stack drainage and venting without increasing additional energy consumption, helping the fuel cell stack maintain a stable hydrothermal balance.

[0077] In one optional implementation, the opening cycle of the tailpipe valve is correlated with the switching cycle of the multi-stage ejector, with different power levels corresponding to different switching cycles and tailpipe cycles. Specifically, in the water management control strategy of the fuel cell system, the opening and closing of the tailpipe valve is not only a necessary means to discharge nitrogen and liquid water accumulated in the hydrogen path, but its opening frequency and timing are also directly related to the hydrogen utilization efficiency and the humidity stability inside the fuel cell stack. If the opening cycle of the tailpipe valve is independent of the nozzle switching cycle of the multi-stage ejector, the tailpipe valve may open when the ejector has just established a high-flow ejection (i.e., high drainage capacity), resulting in the ineffective discharge of a large amount of hydrogen, or the tailpipe valve may not open in time when the ejector is in a low-flow water-holding mode, leading to the risk of liquid water accumulation and flooding. Therefore, the method provided in this application configures the opening cycle of the tailpipe valve to have a definite correlation with the switching cycle of the multi-stage ejector to achieve timing coordination between the two.

[0078] This correlation is specifically reflected in the corresponding switching cycle and tail-out cycle configured in the system at different power levels. The switching cycle refers to the time interval during which the multi-stage ejector cycles between the first and second nozzles, while the tail-out cycle refers to the time interval during which the tail-out valve performs one opening action. The design principle for this correlation is usually based on the dynamic balance of gas-liquid transmission: for example, when the switching cycle is short (meaning frequent ejector drainage actions), the tail-out cycle can be set accordingly shorter to facilitate rapid drainage; when the switching cycle is long (meaning it is mainly in a water-retaining state), the tail-out cycle is also extended accordingly to reduce hydrogen loss.

[0079] Furthermore, for low-power levels, due to the low water production of the fuel cell stack and the primary objective of water retention, both the switching cycle and the tail-out cycle are configured with longer values. In this case, the tail-out valve only opens once after a long period of accumulation, typically during a short window coinciding with the operation of the second nozzle, primarily for small-scale drainage. At medium-power levels, as the fuel cell stack's water production increases, the switching cycle and tail-out cycle are configured with medium values, and the tail-out valve opening frequency is appropriately increased to meet normal drainage needs. At high-power levels, if rapid nozzle switching or high-flow ejection is involved, the switching cycle and tail-out cycle are matched and set according to specific flow regulation requirements to ensure timely removal of impurity gases and excess water under high-flow transmission conditions, while maintaining stable system pressure.

[0080] In another embodiment, the method further includes: controlling the opening of the humidifying throttle and / or the drying throttle according to the power level of the current operating power to adjust the humidity of the air path.

[0081] Specifically, this application embodiment introduces an air path humidification bypass control mechanism to actively regulate the humidity of the air entering the fuel cell stack. This air path humidification bypass consists of a humidification branch and a drying branch connected in parallel to the main air path. The humidification branch is equipped with a humidification throttle valve, and the drying branch is equipped with a drying throttle valve. The humidification branch uses a membrane humidifier to humidify the intake air with wet exhaust gas, while the drying branch guides the dry air after the intercooler directly into the main flow. Based on the current operating power level determined in the aforementioned steps, the control device outputs a corresponding pulse width modulation (PWM) signal or voltage signal to the drive motors of the humidification and drying throttle valves. By adjusting the valve opening, the airflow ratio through the humidification and drying branches is changed, thereby regulating the humidity of the mixed air entering the fuel cell stack. This process coordinates with the multi-stage ejector control on the hydrogen side to form a dual-loop collaborative water management mechanism on both the hydrogen and air sides.

[0082] The method provided in this application embodiment may further include, at low power levels, closing the drying throttle valve and allowing air to enter the fuel cell stack via a humidifier. Specifically, at low power levels, the amount of water produced inside the fuel cell stack is relatively small. The primary goal is to prevent the proton exchange membrane from dehydrating due to lack of water, ensuring that the membrane has good proton conductivity. The controller sends a closing command to the drying throttle valve, reducing its opening to zero to completely block the drying branch; simultaneously, it controls the humidification throttle valve to remain fully open or at a preset opening, guiding all air to flow through the humidifier. After being compressed by the air compressor and cooled by the intercooler, all the air enters the humidifier, using the high-temperature, high-humidity exhaust gas from the fuel cell to humidify the intake air, achieving a high relative humidity for the air entering the fuel cell stack. Through this full humidification mode, the moisture in the exhaust gas is utilized to the maximum extent to replenish the internal humidity of the fuel cell stack, solving the membrane drying problem caused by insufficient water production at low power levels, and avoiding a decrease in ionic conductivity and battery performance degradation. At this point, the high humidity environment of the air path and the strategy of using multi-stage ejectors to retain moisture in the hydrogen path complement each other, jointly maintaining the water and heat balance inside the fuel cell stack.

[0083] The method provided in this application embodiment may further include closing the humidification throttle and opening the drying throttle at medium power levels. Specifically, as the stack operating current increases to the medium power level, the internal electrochemical reaction produces a large amount of liquid water. If the humidity of the incoming air is too high, it can easily lead to water flooding of the gas diffusion layer, hindering the diffusion of reactant gases. The controller switches the throttle state, closing the humidification throttle to cut off the path of air through the humidifier, while simultaneously opening the drying throttle, allowing the dry air cooled by the intercooler to directly or mostly directly enter the stack. Through this dehumidification regulation, the relative humidity of the air entering the stack is reduced, and the large flow of dry air carries away the liquid water accumulated in the stack, preventing local flooding and abnormal voltage drops. In addition, closing the humidification throttle reduces the impact of high-temperature and high-humidity exhaust gas on the humidification membrane, helping to extend the service life of the membrane humidifier. At this stage, the operation of reducing humidity in the air path and the action of increasing the ejector flow rate of the hydrogen path through small nozzles to drain water work together to meet the drainage needs during the peak water production period of the stack.

[0084] The method provided in this application embodiment can further include simultaneously opening the humidification throttle and the drying throttle at high power levels. Specifically, at high power levels, the airflow of the fuel cell stack is enormous, and the air itself has a strong ability to carry away moisture. Excessive drying can lead to insufficient membrane humidity, while excessive humidification may cause localized liquid water accumulation. The controller simultaneously opens the humidification throttle and the drying throttle, and adjusts their opening ratio according to actual operating conditions. This allows some air to be humidified by the humidifier, while some air bypasses through the drying branch. The two mix and enter the fuel cell stack with appropriate humidity. This mixed adjustment mode avoids both the excessive dryness of the membrane caused by purely drying intake and the risk of excessive humidifier load or excessive humidity under specific operating conditions caused by fully humidified intake. At this time, the coordinated opening control of the humidification throttle and the drying throttle in the air path, combined with the high-flow ejection or dual-nozzle operation of the multi-stage ejector in the hydrogen path, adapts to the complex and variable hydrothermal management requirements under high power conditions, ensuring that the fuel cell stack maintains a highly efficient and stable operating state across the entire power range.

[0085] The method provided in this application embodiment may further include arranging and combining the ejector flow regulation of the hydrogen circuit and the humidity regulation of the air circuit according to the actual operating state of the fuel cell stack, so as to jointly regulate the water management of the fuel cell stack system. Specifically, by establishing a coordinated regulation mechanism between the hydrogen circuit and the air circuit, independent humidity control measures are integrated into a unified water management strategy. During actual operation, the actual operating state of the fuel cell stack is monitored and evaluated in real time. This actual operating state does not only reflect a single power point, but is a comprehensive characterization of multi-dimensional information including the internal temperature distribution of the fuel cell stack, the humidity difference between the inlet and outlet, the current density distribution, and the voltage consistency.

[0086] Based on the aforementioned actual operating conditions, the multi-stage ejector mode of the hydrogen circuit and the opening degrees of the humidification and drying throttle valves of the air circuit are arranged and combined. Specifically, a multi-dimensional control matrix is ​​constructed, in which the control strategies on the hydrogen side (such as large nozzle operation, small nozzle operation, or dual nozzle switching) and the control strategies on the air side (such as full humidification, full drying, or mixed humidification) are not fixedly bound, but flexibly paired according to actual operating conditions.

[0087] Furthermore, this combination of control methods allows the system to select the optimal solution from a set of combined strategies for specific water management objectives (such as resolving localized flooding or preventing membrane drying), thereby achieving precise intervention in the water content within the fuel cell stack. For example, when the fuel cell stack is detected to be operating at high power but with a risk of localized flooding, a large-nozzle ejection mode combined with a moderately dry air path mode is selected. This increases the hydrogen flow rate to remove liquid water while maintaining a certain intake humidity on the air side to keep the membrane wetted. Through the combined action of the hydrogen and air paths, the limitations of single-loop regulation are overcome, ensuring that the fuel cell stack is in an optimal humidity balance state across the entire operating range, thereby improving the overall efficiency and operational stability of the system.

[0088] The fuel cell multi-stage ejector and water management control method provided in this application includes acquiring the current operating power of the fuel cell stack, determining the target operating mode of the multi-stage ejector based on the power level of the current operating power, and controlling the multi-stage ejector to switch between the first nozzle and the second nozzle according to the target operating mode to adjust the ejection flow rate of the hydrogen circuit, so that the moisture inside the stack is maintained within a preset range. Therefore, through this method, the multi-stage ejector can exhibit differentiated ejection characteristics at different power levels through a hierarchical control strategy, which can accurately match the water production pattern of the stack, so that the moisture inside the stack is in dynamic balance across the entire operating range, improving the consistency of single-cell voltage and the net power of the system, reducing the performance dependence on auxiliary humidification equipment and gas-water separator, and optimizing system cost and control complexity.

[0089] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for controlling multi-stage ejection and water management in a fuel cell, characterized in that, Includes the following steps: Obtain the current operating power of the fuel cell stack; Based on the power level of the current operating power, the target operating mode of the multi-stage ejector is determined. The multi-stage ejector includes at least a first nozzle and a second nozzle, wherein the first nozzle and the second nozzle have different diameters. According to the target working mode, the multi-stage ejector is controlled to switch between the first nozzle and the second nozzle to adjust the ejection flow rate of the hydrogen circuit and keep the moisture inside the fuel cell stack within a preset range. In particular, at low power levels, the multi-stage ejector is controlled to operate with the first nozzle to reduce the ejection flow rate or even eliminate ejection, so as to retain moisture inside the fuel cell stack. At medium power levels, the multi-stage ejector is controlled to operate with the second nozzle to increase the ejection flow rate, thereby enhancing fuel cell drainage and preventing flooding. At high power levels, the multi-stage ejector is controlled to operate with the first nozzle or with the first nozzle and the second nozzle operating simultaneously to meet the hydrogen flow requirements at high power levels.

2. The method according to claim 1, characterized in that, The multi-stage ejector is a variable nozzle ejector, with the first nozzle being a large nozzle and the second nozzle being a small nozzle.

3. The method according to claim 1, characterized in that, The multi-stage ejector is either a series ejector or a parallel ejector.

4. The method according to claim 1, characterized in that, At the low power level, the multi-stage ejector cycles between the first nozzle and the second nozzle according to a preset period. The preset cycle includes a first nozzle running time and a second nozzle running time, wherein the first nozzle running time is much longer than the second nozzle running time.

5. The method according to claim 4, characterized in that, As the current operating power increases within the low power level, the operating time of the first nozzle gradually decreases, while the operating time of the second nozzle gradually increases.

6. The method according to claim 1, characterized in that, Also includes: During the switching process of the multi-stage ejector, the opening and closing of the tail exhaust valve are controlled to assist in the drainage and venting of the fuel cell stack.

7. The method according to claim 6, characterized in that, The opening cycle of the tail valve is related to the switching cycle of the multi-stage ejector; different power levels correspond to different switching cycles and tail valve cycles.

8. The method according to claim 1, characterized in that, The fuel cell system also includes an air path humidification bypass, which is equipped with a humidification throttle valve and a drying throttle valve; The method further includes: Based on the current operating power level, control the opening of the humidifying throttle valve and / or the drying throttle valve to adjust the humidity of the air path; At low power levels, the dry throttle valve is closed, and air enters the fuel cell stack via a humidifier; At medium power level, the humidifying throttle valve is closed and the drying throttle valve is opened; At high power levels, both the humidifying throttle valve and the drying throttle valve are opened simultaneously.

9. The method according to claim 8, characterized in that, The ejector flow rate regulation of the hydrogen circuit and the humidity regulation of the air circuit are arranged and combined according to the actual operating status of the fuel cell stack to jointly regulate the water management of the fuel cell stack system.

10. A multi-stage ejector and water management system for a fuel cell, characterized in that, include: Fuel cell stack; A multi-stage ejector is disposed on the hydrogen circuit of the fuel cell stack, and includes at least a first nozzle and a second nozzle, wherein the first nozzle and the second nozzle have different diameters. A tailpipe valve is installed on the hydrogen outlet pipeline of the fuel cell stack; The controller, signal-connected to the multistage ejector and the tailpipe valve, is configured to perform the method as described in any one of claims 1 to 9.

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