An expansion water kettle pressure estimation method, fuel cell system and vehicle

Abstract

The application provides an expansion water tank pressure estimation method, a fuel cell system and a vehicle, which are used for improving the estimation accuracy of the cooling liquid pressure, improving the control accuracy of the high-pressure water pump and realizing the maximum heat dissipation capacity of the heat dissipation system. The expansion water tank pressure estimation method comprises the following steps: obtaining the cooling liquid filling data, the cooling liquid estimated pressure, the cooling liquid temperature, the high-pressure water pump operation data, the hydrogen inlet stack pressure and the fuel cell system power generation duration after the fuel cell system is powered on; and estimating the accumulated pressure of the expansion water tank according to the cooling liquid filling data, the cooling liquid estimated pressure, the cooling liquid temperature, the high-pressure water pump operation data, the hydrogen inlet stack pressure and the fuel cell system power generation duration.

Description

Technical Field

[0001] This application relates to the field of fuel cells, specifically to a method for estimating the pressure of an expansion tank, a fuel cell system, and a vehicle. Background Technology

[0002] In proton exchange membrane fuel cell systems, the pressure state of the cooling circuit directly affects the stack's heat dissipation efficiency and the operating boundary of the high-pressure water pump. In existing technologies, to reduce system costs, the coolant inlet pressure sensor is often eliminated, and instead, parameters such as pump speed, coolant temperature, and three-way valve opening are used to estimate the coolant inlet pressure.

[0003] However, during long-term operation, the expansion tank of a fuel cell system experiences a gradual accumulation of non-condensable gases due to high-temperature evaporation of the coolant and trace permeation of gases (hydrogen and air) from the fuel cell stack into the cooling circuit. This causes the tank pressure to rise continuously. This accumulated pressure serves as the initial pressure reference for the cooling circuit, and fluctuations in this pressure directly lead to deviations in the coolant pressure estimation based on parameters such as pump speed and temperature. Consequently, this affects the control accuracy of the high-pressure pump and the maximum heat dissipation capacity of the cooling system. Summary of the Invention

[0004] This application provides a method for estimating the pressure of an expansion tank, a fuel cell system, and a vehicle, which can improve the estimation accuracy of cooling hydraulic pressure, improve the control accuracy of the high-pressure water pump, and maximize the heat dissipation capacity of the cooling system.

[0005] The technical solution of this invention is as follows:

[0006] In a first aspect, this application provides a method for estimating the pressure of an expansion tank in a fuel cell system. The fuel cell system's cooling circuit includes a fuel cell stack, a high-pressure water pump, and an expansion tank with a pressure cap, comprising:

[0007] After the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit.

[0008] The accumulated pressure of the expansion tank is estimated based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, the hydrogen inlet pressure, and the power generation duration of the fuel cell system.

[0009] When estimating the expansion tank accumulation pressure, the estimated coolant pressure is introduced as an input parameter for calculating the hydrogen accumulation pressure. This estimated coolant pressure is an intermediate value directly calculated from physical parameters such as pump speed and coolant temperature, and has not yet been compensated for by the expansion tank accumulation pressure, thus containing errors. This inaccurate estimate is used to characterize the reference pressure level of the cooling loop, and together with the hydrogen infeed pressure, it determines the driving pressure difference for hydrogen transmembrane permeation, thereby affecting the calculated hydrogen accumulation pressure.

[0010] After obtaining the accumulated pressure in the expansion tank, this accumulated pressure is used to compensate and correct the previously estimated coolant pressure, resulting in an accurate coolant inlet pressure. This accurate coolant inlet pressure serves as a feedback signal to control the operating boundary of the high-pressure water pump, ensuring that the cooling system operates at its maximum heat dissipation capacity within a safe range.

[0011] In some possible embodiments, the step of estimating the accumulated pressure of the expansion tank based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure includes:

[0012] Based on the coolant filling data, identify whether the cooling circuit has been filled with coolant after the fuel cell system is powered on;

[0013] If no coolant has been added, determine the accumulated coolant pressure based on the coolant temperature and the high-pressure water pump operating data;

[0014] Based on the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system, the hydrogen accumulation pressure is determined.

[0015] The initial accumulated pressure of the expansion tank is determined based on the historical accumulated pressure of the expansion tank and the temperature of the coolant.

[0016] The accumulation pressure is determined based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure.

[0017] Coolant temperature determines the intensity of evaporation; the higher the temperature, the greater the amount of steam produced per unit time. The speed and operating duration of the high-pressure water pump determine the intensity of coolant flow; higher speed and longer operating duration result in more significant bubble generation and accumulation. Using these two physical quantities as inputs to determine the coolant accumulation pressure allows for the quantification of the contributions of thermodynamic evaporation and hydrodynamic disturbance effects to the kettle pressure. The resulting effect is the separation of the portion of the total pressure increase from the portion originating from the coolant's own physical changes.

[0018] A pressure difference exists between the hydrogen side and the cooling circuit inside the fuel cell stack, which drives hydrogen permeation across the membrane. The estimated coolant pressure reflects the baseline pressure level of the cooling circuit; the greater the difference between the hydrogen inlet pressure and the estimated coolant pressure, the higher the permeation rate. The system's power generation duration determines the duration of the permeation process; the longer the duration, the greater the cumulative permeation. Using the pressure difference and time as inputs to determine the hydrogen accumulation pressure allows for the quantification of the contribution of the gas permeation effect inside the fuel cell stack to the pressure in the reservoir. The resulting effect is the separation of the portion originating from hydrogen permeation from the total pressure increase.

[0019] The accumulated pressure stored during the last fuel cell system shutdown serves as the baseline for this operation. However, this value corresponds to the tank pressure at the coolant temperature during the last shutdown. When the coolant temperature changes during this startup, the gas volume within the tank changes proportionally with the temperature. The historical accumulated pressure is corrected by comparing the current average coolant temperature with the average coolant temperature at the time of the last shutdown, adhering to the temperature-pressure relationship of the ideal gas law. This eliminates the influence of temperature changes on the pressure baseline, ensuring that the initial accumulated pressure accurately reflects the actual value under the current thermal conditions.

[0020] In some possible embodiments, the step of estimating the accumulated pressure of the expansion tank based on the coolant filling data, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure further includes:

[0021] If coolant has been added, the accumulated pressure in the expansion tank will be assigned the current ambient pressure.

[0022] When the cooling circuit is refilled with coolant, the gas in the expansion tank is expelled or diluted, fundamentally resetting the pressure within the tank. By recognizing the refilling action, it's possible to determine whether historical pressure data should be used. This avoids misjudging the newly refilled cooling circuit using outdated historical pressure data, ensuring that the estimation logic has the correct behavioral boundaries under different maintenance conditions.

[0023] In some possible embodiments, the high-pressure water pump operating data includes the pump's rotational speed and operating duration. The step of determining the coolant accumulation pressure based on the coolant temperature and the high-pressure water pump operating data includes:

[0024] Based on a first predetermined correspondence table of the coolant temperature, the speed of the high-pressure water pump, the operating time of the high-pressure water pump, and the coolant temperature, the accumulated pressure of the coolant is determined by looking up the table.

[0025] By using a pre-calibrated mapping table, the three input parameters—coolant temperature, pump speed, and operating time—are directly mapped to the coolant accumulated pressure output, eliminating the need for complex theoretical mathematical models. This lookup-based calculation method offers fast response times, requires minimal computational resources, and the calibration data can be accurately obtained through bench testing, ensuring good consistency between the coolant accumulated pressure and the actual physical process.

[0026] In some possible embodiments, the step of determining the hydrogen accumulation pressure based on the hydrogen infeed pressure, the estimated coolant pressure, and the fuel cell system power generation duration includes:

[0027] The hydrogen accumulation pressure is determined by looking up a second predetermined correspondence table based on the hydrogen inlet pressure, the estimated coolant pressure, the power generation duration of the fuel cell system, and the hydrogen accumulation pressure.

[0028] By using a pre-calibrated second correspondence table, three input parameters—hydrogen infeed pressure, estimated coolant pressure (both of which jointly determine the transmembrane pressure difference), and system power generation duration—are directly mapped to the hydrogen accumulation pressure output. This table lookup method avoids establishing a complex differential equation model between the hydrogen permeation rate and the pressure difference, reducing the online computational burden. Simultaneously, calibration data can be obtained experimentally based on the gas permeation characteristics of an actual fuel cell stack, ensuring that the estimated hydrogen accumulation pressure accurately reflects the hydrogen accumulation effect under different pressure differences and durations.

[0029] In some possible embodiments, the step of determining the initial accumulated pressure of the expansion tank based on the historical accumulated pressure of the expansion tank and the coolant temperature includes:

[0030] Determine the ratio of the average temperature of the coolant to the average temperature of the coolant when the fuel cell system was last powered on;

[0031] The initial accumulated pressure of the expansion kettle is obtained by multiplying the historical accumulated pressure of the expansion kettle by the ratio.

[0032] Temperature correction is applied to historical accumulated pressure by comparing the current average water temperature with the average water temperature at the time of the last shutdown, adhering to the physical law that pressure is proportional to absolute temperature in the ideal gas law. This correction eliminates the influence of gas volume expansion or contraction in the expansion tank caused by coolant temperature changes on the pressure value, ensuring that historical pressure data inherited from the last shutdown state accurately reflects the actual initial pressure under the current thermal state, and avoiding additional estimation errors introduced by temperature differences.

[0033] In some possible embodiments, the step of determining the accumulation pressure based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure includes:

[0034] The sum of the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure is determined to obtain a first sum value;

[0035] The sum of the nominal pressure cap value of the expansion tank and the current ambient pressure is determined to obtain the second sum value;

[0036] When the first sum is greater than or equal to the second sum, the second sum is determined as the accumulated pressure;

[0037] When the first sum is less than the second sum, the first sum is determined as the accumulated pressure.

[0038] By comparing the magnitudes of the first and second sums, an upper limit clamp is applied to the calculated accumulated pressure. When the sum of the coolant accumulated pressure, hydrogen accumulated pressure, and initial accumulated pressure does not exceed the sum of the pressure cap nominal value and the current ambient pressure, it indicates that the expansion tank is in a closed operating state, and the accumulated pressure is the calculated actual sum of these values. When the calculated sum reaches or exceeds the pressure cap opening threshold, it indicates that the pressure inside the tank has triggered pressure cap depressurization. At this point, the accumulated pressure is corrected to the sum of the pressure cap closing pressure and the ambient pressure, i.e., the stable pressure value maintained after depressurization. This ensures that the pressure estimation results always conform to the actual physical depressurization characteristics of the expansion tank, preventing estimated values ​​from exceeding a reasonable range and guaranteeing the reliability of subsequent coolant inlet pressure compensation calculations.

[0039] In some possible embodiments, the accumulated pressure of the coolant is positively correlated with the coolant temperature, the rotational speed of the high-pressure water pump, and the operating time of the high-pressure water pump.

[0040] The higher the coolant temperature, the stronger the evaporation, the greater the amount of steam generated, and the greater its contribution to the expansion tank pressure. The higher the high-pressure water pump speed, the faster the coolant flow rate, the more significant the bubble generation and agitation effects, and the faster the pressure accumulation rate. The longer the high-pressure water pump operates, the longer the accumulation time of these effects, and the greater the total pressure increase. Using this positive correlation constraint for table lookup calibration ensures that the correspondence table maintains consistency with the actual system behavior in terms of physical trends, avoiding abnormal mappings that violate physical laws. It also simplifies the calibration workload, requiring only the selection of key operating points under the positive correlation trend.

[0041] In some possible embodiments, the hydrogen accumulation pressure is positively correlated with the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system.

[0042] The higher the hydrogen inlet pressure, the greater the pressure difference between the hydrogen side and the cooling loop, the stronger the driving force for hydrogen transmembrane permeation, and the higher the permeation rate. A higher estimated coolant pressure reflects an increase in the cooling loop's baseline pressure level, but the statement that hydrogen accumulation pressure is positively correlated with estimated coolant pressure needs to be understood in conjunction with the physical mechanism of the driving pressure difference—with a fixed hydrogen inlet pressure, a lower estimated coolant pressure results in a larger driving pressure difference and faster permeation, and hydrogen accumulation pressure should be negatively correlated with it. If the original text explicitly defines it as a positive correlation, it can be interpreted as follows: the estimated coolant pressure itself is related to the system's operating state; under typical operating conditions, its increase is often accompanied by a synchronous increase in the hydrogen inlet pressure (such as an increase in stack power leading to a simultaneous rise in pressure on both sides), ultimately resulting in a positive trend in the net driving pressure difference. The longer the fuel cell system generates electricity, the longer the hydrogen permeation duration, and the greater the cumulative permeation. Using this positive correlation constraint for table lookup calibration ensures that the corresponding relationship table maintains consistency with the actual system behavior in terms of physical trends, simplifying the calibration process and reducing the risk of non-physical mappings.

[0043] Secondly, this application also provides a fuel cell system, comprising:

[0044] A cooling circuit is provided, in which a fuel cell stack, a high-pressure water pump and an expansion tank with a pressure cap are arranged. The expansion tank is arranged between the coolant outlet of the fuel cell stack and the inlet of the high-pressure water pump. The outlet of the high-pressure water pump is connected to the coolant inlet of the fuel cell stack.

[0045] A controller, connected to the pressure cap of the high-pressure water pump and the expansion tank; the controller is configured to:

[0046] After the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit.

[0047] The accumulated pressure of the expansion tank is estimated based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, the hydrogen inlet pressure, and the power generation duration of the fuel cell system.

[0048] In some possible embodiments, the controller is specifically configured to:

[0049] Based on the coolant filling data, identify whether the cooling circuit has been filled with coolant after the fuel cell system is powered on;

[0050] If no coolant has been added, determine the accumulated coolant pressure based on the coolant temperature and the high-pressure water pump operating data;

[0051] Based on the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system, the hydrogen accumulation pressure is determined.

[0052] The initial accumulated pressure of the expansion tank is determined based on the historical accumulated pressure of the expansion tank and the temperature of the coolant.

[0053] The accumulation pressure is determined based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure.

[0054] Thirdly, this application also provides a vehicle including the aforementioned fuel cell system. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the vehicle structure according to an embodiment of this application;

[0056] Figure 2 This is a flowchart illustrating the pressure estimation method for the expansion kettle in this application embodiment. Detailed Implementation

[0057] Reference Figure 1 The vehicle itself includes the vehicle body and the fuel cell system mounted on the vehicle body. This fuel cell system serves as the vehicle's power source, providing electrical energy to the drive motor. Specifically, the fuel cell system includes a cooling circuit and a controller 9. The cooling circuit houses the fuel cell stack 1, a high-pressure water pump 3, and an expansion tank 2 with a pressure cap. The controller 9 is configured to acquire the operating parameters of the cooling circuit after the fuel cell system is powered on, estimate the accumulated pressure of the expansion tank 2 based on these parameters, and then use this accumulated pressure to compensate for the estimated coolant inlet pressure. Finally, based on the accurate coolant inlet pressure, the controller controls the operating boundary of the high-pressure water pump 3. Through this fuel cell system, the vehicle can fully utilize the maximum heat dissipation capacity of the cooling system while ensuring the safe operation of the fuel cell stack 1, thereby improving the vehicle's power continuity and environmental adaptability.

[0058] Reference Figure 1 The cooling circuit of the fuel cell system includes a radiator, an expansion tank 2, a high-pressure water pump 3, an electronic three-way valve 4, a first temperature sensor 5, a second temperature sensor 6, a fuel cell stack 1, an ambient pressure sensor 8, and a hydrogen inlet pressure sensor 7.

[0059] Reference Figure 1 In the cooling circuit, the outlet of the expansion tank 2 with a pressure cap is connected to the inlet of the electronic three-way valve 4, and the inlet of the expansion tank 2 is connected to the coolant outlet of the fuel cell stack 1. The expansion tank 2 is used to collect the gas accumulated in the cooling circuit and regulate the circuit pressure.

[0060] Reference Figure 1The first outlet of the electronic three-way valve 4 is connected to the inlet of the high-pressure water pump 3, and the second outlet of the electronic three-way valve 4 is connected to the coolant inlet of the radiator 10. By controlling the electronic three-way valve 4, a small circulation or a large circulation of coolant can be achieved. The small circulation refers to the circulation that does not pass through the radiator 10 for heat dissipation, while the large circulation refers to the circulation that passes through the radiator 10 for heat dissipation.

[0061] Reference Figure 1 The outlet of the high-pressure water pump 3 is connected to the coolant inlet of the fuel cell stack 1, and the coolant outlet of the fuel cell stack 1 is connected to the radiator 10. A first temperature sensor 5 is located on the coolant inlet side of the fuel cell stack 1 (specifically, between the coolant outlet of the high-pressure water pump 3 and the coolant inlet of the fuel cell stack 1) to collect the coolant inlet temperature; a second temperature sensor 6 is located on the coolant outlet of the fuel cell stack 1 (specifically, between the coolant inlet of the radiator 10 and the coolant outlet of the fuel cell stack 1) to collect the coolant outlet temperature. An ambient pressure sensor 8 is used to collect the current ambient pressure, and a hydrogen inlet pressure sensor 7 is located on the hydrogen inlet pipeline of the fuel cell stack 1 to collect the actual hydrogen inlet pressure.

[0062] The controller 9 is electrically connected to the high-pressure water pump 3, the electronic three-way valve 4, the first temperature sensor 5, the second temperature sensor 6, the ambient pressure sensor 8, and the hydrogen inlet pressure sensor 7, respectively, and is used to receive sensor signals and control the working status of the actuators.

[0063] In this embodiment of the application, the controller 9 is specifically configured as follows:

[0064] After the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit.

[0065] The accumulated pressure of expansion tank 2 is estimated based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, the hydrogen inlet pressure, and the power generation duration of the fuel cell system.

[0066] Regarding coolant filling data, controller 9 obtains it by detecting signal changes from the coolant level sensor or identifying the cooling circuit maintenance flag. When the coolant level rises sharply and stabilizes while the vehicle is stopped, or when a filling completion signal is received via the on-board diagnostic interface, controller 9 determines that the cooling circuit has undergone a refilling operation.

[0067] In this embodiment, the controller 9 obtains the estimated coolant pressure in the following way: the estimated coolant pressure is the historical value of the coolant inlet pressure output by the fuel cell control system after pressure compensation by the expansion tank 2 during the previous control cycle or the previous system operation, or it is a reference pressure value calculated in real time based on the current power generation of the fuel cell stack 1 and the thermal management model. This estimated pressure is used as an intermediate parameter in this calculation to jointly determine the driving pressure difference for hydrogen transmembrane permeation with the hydrogen inlet pressure, rather than being directly used as the final output. In other words, the estimated pressure can originate from the estimation result of the system at the previous moment or the theoretical calculation value of the fuel cell stack thermal model, and it may contain some error, as subsequent steps will use the pressure accumulated by the expansion tank 2 to compensate and correct it. This method of acquisition ensures that the estimated coolant pressure and the finally output compensated pressure form a serial calculation relationship, rather than a circular dependency.

[0068] Regarding the coolant temperature, the controller 9 collects the data in real time through the first temperature sensor 5 located on the coolant inlet side of the fuel cell stack 1 and the second temperature sensor 6 located on the coolant outlet side, and calculates the arithmetic mean of the two as the average temperature representing the current thermal state of the cooling circuit.

[0069] Regarding the high-pressure water pump operation data, the controller 9 obtains the real-time speed by collecting the speed sensor signal of the drive motor of the high-pressure water pump 3, and at the same time accumulates the continuous working time of the high-pressure water pump 3 from the time it is powered on to the present through the internal timer.

[0070] Regarding the hydrogen inlet pressure, the controller 9 collects the data in real time through the hydrogen inlet pressure sensor 7 arranged on the hydrogen inlet pipeline of the fuel cell stack 1. This signal reflects the actual pressure value on the hydrogen inlet side of the fuel cell stack 1.

[0071] Regarding the power generation duration of the fuel cell system, the controller 9 uses the system's internal timing module to record the power generation duration from the moment the fuel cell stack 1 starts outputting current until the fuel cell stack 1 stops generating power.

[0072] After the above data is acquired, the controller 9 uses these parameters as input and estimates the accumulated pressure of the expansion kettle 2 according to a predetermined algorithm.

[0073] Controller 9 first determines whether the cooling circuit has been refilled with coolant since power-on based on the coolant filling data. If a filling action has occurred, it indicates that the gas in expansion tank 2 has been expelled or diluted, and the pressure inside the tank has been reset to ambient pressure. Controller 9 directly assigns the accumulated pressure in expansion tank 2 to the current ambient pressure, eliminating the need for subsequent complex calculations. When the cooling circuit undergoes refilling, a large amount of gas in expansion tank 2 is expelled, fundamentally resetting the pressure state inside the tank. Controller 9 directly assigns the accumulated pressure to the current ambient pressure by recognizing the filling action, avoiding misjudgments of new operating conditions based on outdated historical data. The resulting effect is to ensure the accuracy of the starting point for pressure estimation after filling and to eliminate the interference of the filling operation on the estimation accuracy.

[0074] If no coolant has been added, controller 9 initiates a multi-factor comprehensive estimation process. Controller 9 determines the accumulated coolant pressure based on coolant temperature and high-pressure water pump operating data. Higher coolant temperature leads to stronger evaporation and greater steam generation; higher high-pressure water pump speed and longer operating time result in more severe coolant disturbance, leading to more significant bubble generation and accumulation. Controller 9 maps these three parameters to the pressure increase contributed by the coolant through a lookup table. Increased coolant temperature exacerbates evaporation and gas production, while increased pump speed and operating time intensify bubble generation and accumulation. These three factors collectively determine the contribution of coolant physical changes to the kettle pressure. Controller 9 maps these three factors to pressure values ​​through a lookup table, quantifying and separating thermodynamic and hydrodynamic effects. The resulting effect is the extraction of the portion originating from the coolant's own physical changes from the total pressure, making the contributions of each factor distinguishable.

[0075] Controller 9 determines the hydrogen accumulation pressure based on the hydrogen inlet pressure, the estimated coolant pressure, and the fuel cell system's power generation duration. The difference between the hydrogen inlet pressure and the estimated coolant pressure determines the driving pressure difference for hydrogen permeation from the hydrogen side of stack 1 into the cooling circuit; a larger pressure difference results in a higher permeation rate, and a longer system power generation duration leads to a more complete permeation accumulation effect. Controller 9 maps these three parameters to the pressure rise contributed by hydrogen permeation through a lookup table. The pressure difference between the hydrogen side and the cooling circuit is the core driving force for gas permeation, while the power generation duration determines the degree of permeation accumulation. By using the pressure difference and time as inputs, controller 9 can quantitatively reflect the contribution of transmembrane permeation to the pressure in the reservoir. The resulting effect is the separation of the portion originating from hydrogen permeation from the total pressure, allowing for the separate calculation of pressure rises from different physical sources.

[0076] Controller 9 also determines the initial accumulated pressure based on the historical accumulated pressure stored at the time of the last system shutdown and the current coolant temperature. Since the gas volume inside expansion tank 2 changes with temperature, controller 9 calculates the ratio of the current average water temperature to the average water temperature at the time of the last shutdown, multiplies this ratio by the previously stored historical accumulated pressure, and obtains the temperature-corrected initial accumulated pressure. The previously stored pressure value was measured at a specific temperature; when the temperature changes, the gas volume inside the tank changes according to the ideal gas law. Controller 9 corrects the historical pressure using the temperature ratio, ensuring that the initial accumulated pressure accurately reflects the actual value under the current thermal conditions. The resulting effect is to eliminate the influence of temperature fluctuations on the historical pressure reference, ensuring the accuracy of the initial value under variable temperature conditions.

[0077] Controller 9 adds the coolant accumulation pressure, hydrogen accumulation pressure, and initial accumulation pressure to obtain a first sum. Controller 9 simultaneously calculates the sum of the nominal pressure cap value of expansion tank 2 and the current ambient pressure to obtain a second sum. If the first sum is less than the second sum, it indicates that expansion tank 2 is in a closed operating state, and the accumulation pressure is the first sum. If the first sum is greater than or equal to the second sum, it indicates that the tank pressure has reached the pressure relief threshold. After the pressure cap is opened, the pressure inside the tank is clamped near the sum of the closing pressure and the ambient pressure, and controller 9 corrects the accumulation pressure to the second sum. The sum of the coolant contribution, hydrogen contribution, and initial contribution represents the theoretical calculated value of the accumulation pressure under the current operating conditions. However, in the actual system, there is a physical pressure relief upper limit for the pressure cap. When the theoretical value reaches or exceeds the pressure relief threshold, the pressure cap opens, clamping the pressure inside the tank near the closing pressure. Controller 9 compares the magnitude of the two sums, taking the calculated value when the theoretical value is within the limit and the clamped value when the theoretical value exceeds the limit. The result is that the pressure estimation results always match the actual physical pressure relief characteristics of the expansion kettle 2, neither underestimating nor exceeding a reasonable range.

[0078] Through the above process, controller 9 integrates multiple physical mechanisms, including coolant evaporation and disturbance, hydrogen permeation, historical pressure and temperature correction, and pressure cap pressure relief clamping, to ultimately estimate the accumulated pressure of expansion tank 2 under the current operating conditions. The accumulated pressure of expansion tank 2 is decomposed into three independent components and solved separately, then superimposed and clamped to obtain the final result. This multi-level estimation strategy, which combines source-specific calculation, physical constraints, temperature correction, and pressure relief limiting, ensures both the physical interpretability of the pressure calculation and improves the estimation accuracy, laying a reliable benchmark for subsequent use of this accumulated pressure to compensate for coolant infeed pressure.

[0079] Reference Figure 2 This application also provides a method for estimating the pressure of the expansion tank 2 in a fuel cell system, including:

[0080] S101, after the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit;

[0081] S102, based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, the hydrogen inlet pressure, and the fuel cell system power generation duration, estimate the accumulated pressure of the expansion tank 2.

[0082] When estimating the accumulation pressure in expansion tank 2, the estimated coolant pressure is introduced as an input parameter for calculating the hydrogen accumulation pressure. This estimated coolant pressure is an intermediate value directly calculated from physical parameters such as pump speed and coolant temperature, and has not yet been compensated for by the accumulation pressure in expansion tank 2, thus containing errors. This inaccurate estimate is used to characterize the reference pressure level of the cooling loop, and together with the hydrogen infeed pressure, it determines the driving pressure difference for hydrogen transmembrane permeation, thereby affecting the calculated hydrogen accumulation pressure.

[0083] After obtaining the accumulated pressure of expansion tank 2, the estimated coolant pressure is compensated and corrected using this accumulated pressure to obtain an accurate coolant inlet pressure. This accurate coolant inlet pressure serves as a feedback signal to control the operating boundary of high-pressure water pump 3, ensuring that the cooling system operates at its maximum heat dissipation capacity within a safe range.

[0084] In some possible embodiments, step S102, which estimates the accumulated pressure of the expansion tank 2 based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure, includes:

[0085] S1021, Based on the coolant filling data, identify whether the cooling circuit has been filled with coolant after the fuel cell system is powered on;

[0086] S1022, If no coolant has been added, determine the accumulated coolant pressure based on the coolant temperature and the high-pressure water pump operating data;

[0087] S1023, Based on the hydrogen inlet pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system, determine the hydrogen accumulation pressure;

[0088] S1024, Based on the historical accumulated pressure of the expansion tank 2 and the coolant temperature, determine the initial accumulated pressure of the expansion tank 2;

[0089] S1025, determine the accumulation pressure based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure.

[0090] The coolant temperature determines the intensity of evaporation; the higher the temperature, the greater the amount of steam produced per unit time. The speed and operating time of the high-pressure water pump 3 determine the intensity of coolant flow; the higher the speed and the longer the operating time, the more significant the generation and accumulation of bubbles. Using these two physical quantities as inputs to determine the coolant accumulation pressure allows for the quantification of the contributions of thermodynamic evaporation and hydrodynamic disturbance effects to the kettle pressure. The resulting effect is the separation of the portion of the total pressure increase originating from the coolant's own physical changes.

[0091] A pressure difference exists between the hydrogen side and the cooling circuit inside fuel cell stack 1. This pressure difference is the driving force for hydrogen transmembrane permeation. The estimated coolant pressure reflects the baseline pressure level of the cooling circuit; the greater the difference between the hydrogen inlet pressure and the estimated coolant pressure, the higher the permeation rate. The system's power generation duration determines the duration of the permeation process; the longer the duration, the greater the cumulative permeation. Using the pressure difference and time as inputs to determine the hydrogen accumulation pressure allows for the quantification of the contribution of the gas transmembrane permeation effect inside fuel cell stack 1 to the pressure in the reservoir. The resulting effect is the separation of the portion originating from hydrogen permeation from the total pressure increase.

[0092] The accumulated pressure stored at the time of the last system shutdown serves as the baseline value for this operation. However, this value corresponds to the kettle pressure at the coolant temperature during the last shutdown. When the coolant temperature changes during this startup, the gas volume within the kettle will change proportionally with the temperature. The historical accumulated pressure is corrected by comparing the current average coolant temperature with the average coolant temperature at the time of the last shutdown, adhering to the temperature-pressure relationship of the ideal gas law. The effect of this is to eliminate the influence of temperature changes on the pressure baseline value, ensuring that the initial accumulated pressure accurately reflects the actual value under the current thermal conditions.

[0093] In some possible embodiments, the step of estimating the accumulated pressure of the expansion tank 2 based on the coolant filling data, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure further includes:

[0094] S1026, If coolant has been added, the accumulated pressure of expansion tank 2 is assigned to the current ambient pressure.

[0095] When the cooling circuit is refilled with coolant, the gas in expansion tank 2 is expelled or diluted, fundamentally resetting the pressure within the tank. By recognizing the refilling action, it can be determined whether historical pressure data should be used. This avoids misjudging the newly refilled cooling circuit using outdated historical pressure data, ensuring that the estimation logic has the correct behavioral boundaries under different maintenance conditions.

[0096] In some possible embodiments, the high-pressure water pump operating data includes the rotational speed and operating duration of the high-pressure water pump 3. The step S1022, which determines the coolant accumulation pressure based on the coolant temperature and the high-pressure water pump operating data, includes:

[0097] Based on a first predetermined correspondence table of the coolant temperature, the rotational speed of the high-pressure water pump 3, the operating time of the high-pressure water pump 3, and the coolant temperature, the accumulated pressure of the coolant is determined by looking up the table.

[0098] By using a pre-calibrated mapping table, the three input parameters—coolant temperature, pump speed, and operating time—are directly mapped to the coolant accumulated pressure output, eliminating the need for complex theoretical mathematical models. This lookup-based calculation method offers fast response times, requires minimal computational resources, and the calibration data can be accurately obtained through bench testing, ensuring good consistency between the coolant accumulated pressure and the actual physical process.

[0099] In some possible embodiments, step S1023, which determines the hydrogen accumulation pressure based on the hydrogen infeed pressure, the estimated coolant pressure, and the fuel cell system power generation duration, includes:

[0100] The hydrogen accumulation pressure is determined by looking up a second predetermined correspondence table based on the hydrogen inlet pressure, the estimated coolant pressure, the power generation duration of the fuel cell system, and the hydrogen accumulation pressure.

[0101] By using a pre-calibrated second correspondence table, three input parameters—hydrogen inlet pressure, estimated coolant pressure (both of which jointly determine the transmembrane pressure difference), and system power generation duration—are directly mapped to the hydrogen accumulation pressure output. This table lookup method avoids establishing a complex differential equation model between the hydrogen permeation rate and the pressure difference, reducing the online computational burden. Simultaneously, calibration data can be obtained experimentally based on the gas permeation characteristics of actual reactor 1, ensuring that the estimated hydrogen accumulation pressure accurately reflects the hydrogen accumulation effect under different pressure differences and durations.

[0102] In some possible embodiments, step S1024, which determines the initial accumulated pressure of the expansion tank 2 based on the historical accumulated pressure of the expansion tank 2 and the coolant temperature, includes:

[0103] Determine the ratio of the average temperature of the coolant to the average temperature of the coolant when the fuel cell system was last powered on;

[0104] The initial accumulated pressure of the expansion kettle 2 is obtained by multiplying the historical accumulated pressure of the expansion kettle 2 with the ratio.

[0105] The historical accumulated pressure is corrected for temperature by comparing the current average water temperature with the average water temperature at the time of the last shutdown, following the physical law that pressure is proportional to absolute temperature in the ideal gas law. This correction eliminates the influence of gas volume expansion or contraction in expansion tank 2 caused by coolant temperature changes on the pressure value, ensuring that the historical pressure data inherited from the last shutdown state accurately reflects the actual initial pressure under the current thermal state, and avoiding additional estimation errors introduced by temperature differences.

[0106] In some possible embodiments, step S1025, which determines the accumulation pressure based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure, includes:

[0107] The sum of the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure is determined to obtain a first sum value;

[0108] The second sum value is obtained by summing the nominal pressure cap value of the expansion tank 2 with the current ambient pressure.

[0109] When the first sum is greater than or equal to the second sum, the second sum is determined as the accumulated pressure;

[0110] When the first sum is less than the second sum, the first sum is determined as the accumulated pressure.

[0111] By comparing the magnitudes of the first and second sums, an upper limit clamp is applied to the calculated accumulated pressure. When the sum of the coolant accumulated pressure, hydrogen accumulated pressure, and initial accumulated pressure does not exceed the sum of the pressure cap nominal value and the current ambient pressure, it indicates that expansion tank 2 is in a closed operating state, and the accumulated pressure is taken as the calculated actual superimposed value. When the calculated superimposed value reaches or exceeds the pressure cap opening threshold, it indicates that the pressure inside the tank has triggered pressure cap depressurization. At this time, the accumulated pressure is corrected to the sum of the pressure cap closing pressure and the ambient pressure, i.e., the stable pressure value maintained after depressurization. This ensures that the pressure estimation results always conform to the actual physical depressurization characteristics of expansion tank 2, avoids the estimated value from exceeding a reasonable range, and guarantees the reliability of subsequent coolant inlet pressure compensation calculations.

[0112] In some possible embodiments, the accumulated pressure of the coolant is positively correlated with the coolant temperature, the rotational speed of the high-pressure water pump 3, and the operating time of the high-pressure water pump 3.

[0113] The higher the coolant temperature, the stronger the evaporation, the greater the amount of steam generated, and the greater its contribution to the pressure of expansion tank 2. The higher the speed of high-pressure water pump 3, the faster the coolant flow rate, the more significant the bubble generation and agitation effect, and the faster the pressure accumulation rate. The longer the high-pressure water pump 3 operates, the longer the accumulation time of the above effects is, and the greater the total pressure increase. Calibration based on this positive correlation constraint ensures that the correspondence table is consistent with the actual system behavior in terms of physical trends, avoiding abnormal mappings that violate physical laws. It also simplifies the calibration workload, requiring only the selection of key operating points under the positive correlation trend.

[0114] In some possible embodiments, the hydrogen accumulation pressure is positively correlated with the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system.

[0115] The higher the hydrogen inlet pressure, the greater the pressure difference between the hydrogen side and the cooling loop, the stronger the driving force for hydrogen transmembrane permeation, and the higher the permeation rate. A higher estimated coolant pressure reflects an increase in the cooling loop's baseline pressure level, but the statement that hydrogen accumulation pressure is positively correlated with estimated coolant pressure needs to be understood in conjunction with the physical mechanism of the driving pressure difference—when the hydrogen inlet pressure is fixed, the lower the estimated coolant pressure, the greater the driving pressure difference, the faster the permeation, and the hydrogen accumulation pressure should be negatively correlated. If the original text explicitly defines it as a positive correlation, it can be interpreted as follows: the estimated coolant pressure itself is related to the system's operating state; under typical operating conditions, its increase is often accompanied by a synchronous increase in the hydrogen inlet pressure (e.g., an increase in stack 1 power leads to a simultaneous increase in pressure on both sides), ultimately resulting in a positive trend in the net driving pressure difference. The longer the fuel cell system's power generation duration, the longer the hydrogen permeation duration, and the greater the cumulative permeation amount. Using this positive correlation constraint for table lookup calibration ensures that the corresponding relationship table maintains consistency with the actual system behavior in terms of physical trends, simplifying the calibration process and reducing the risk of non-physical mappings.

[0116] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Those skilled in the art can understand that implementing all or part of the processes of the above embodiments and making equivalent changes according to the claims of this application still fall within the scope of this application.

Claims

1. An expansion tank pressure estimation method for a fuel cell system, characterized by, The cooling circuit of the fuel cell system includes a stack (1), a high-pressure water pump (3), and an expansion tank (2) with a pressure cap, comprising: After the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit. The accumulated pressure of the expansion tank (2) is estimated based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operation data, the hydrogen inlet pressure, and the power generation duration of the fuel cell system.

2. The method of claim 1, wherein, The steps for estimating the accumulated pressure of the expansion tank (2) based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure include: Based on the coolant filling data, identify whether the cooling circuit has been filled with coolant after the fuel cell system is powered on; If no coolant has been added, determine the accumulated coolant pressure based on the coolant temperature and the high-pressure water pump operating data; Based on the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system, the hydrogen accumulation pressure is determined. The initial accumulated pressure of the expansion tank (2) is determined based on the historical accumulated pressure of the expansion tank (2) and the temperature of the coolant. The accumulation pressure is determined based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure.

3. The method of claim 2, wherein, The step of estimating the accumulated pressure of the expansion tank (2) based on the coolant filling data, the coolant temperature, the high-pressure water pump operating data, and the hydrogen inlet pressure further includes: If coolant has been added, the accumulated pressure of the expansion tank (2) is assigned to the current ambient pressure.

4. The method of claim 2, wherein, The high-pressure water pump operating data includes the speed and operating time of the high-pressure water pump (3). Based on the coolant temperature and the high-pressure water pump operating data, the step of determining the coolant accumulation pressure includes: Based on a first predetermined correspondence table of the coolant temperature, the rotational speed of the high-pressure water pump (3), the working time of the high-pressure water pump (3), and the coolant temperature, the accumulated pressure of the coolant is determined by looking up the table.

5. The method of claim 2, wherein, The steps for determining the hydrogen accumulation pressure based on the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system include: The hydrogen accumulation pressure is determined by looking up a second predetermined correspondence table based on the hydrogen inlet pressure, the estimated coolant pressure, the power generation duration of the fuel cell system, and the hydrogen accumulation pressure.

6. The method of claim 2, wherein, The steps for determining the initial accumulated pressure of the expansion tank (2) based on the historical accumulated pressure of the expansion tank (2) and the coolant temperature include: Determine the ratio of the average temperature of the coolant to the average temperature of the coolant when the fuel cell system was last powered on; The initial accumulated pressure of the expansion kettle (2) is obtained by multiplying the historical accumulated pressure of the expansion kettle (2) with the ratio.

7. The method of claim 2, wherein, The step of determining the accumulation pressure based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure includes: The sum of the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure is determined to obtain a first sum value; The sum of the nominal pressure cap value of the expansion tank (2) and the current ambient pressure is determined to obtain the second sum value; When the first sum is greater than or equal to the second sum, the second sum is determined as the accumulated pressure; When the first sum is less than the second sum, the first sum is determined as the accumulated pressure.

8. The method of claim 4, wherein, The accumulated pressure of the coolant is positively correlated with the temperature of the coolant, the rotational speed of the high-pressure water pump (3), and the working time of the high-pressure water pump (3).

9. The method of claim 5, wherein, The hydrogen accumulation pressure is positively correlated with the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system.

10. A fuel cell system characterized by comprising: include: The cooling circuit includes a fuel cell stack (1), a high-pressure water pump (3), and an expansion tank (2) with a pressure cap. The expansion tank (2) is located between the coolant outlet of the fuel cell stack (1) and the inlet of the high-pressure water pump (3). The outlet of the high-pressure water pump (3) is connected to the coolant inlet of the fuel cell stack (1). A controller (9) is connected to the pressure cap of the high-pressure water pump (3) and the expansion tank (2); the controller (9) is configured to: After the fuel cell system is powered on, acquire the coolant filling data, estimated coolant pressure, coolant temperature, high-pressure water pump operation data, hydrogen inlet pressure, and fuel cell system power generation duration in the cooling circuit. The accumulated pressure of the expansion tank (2) is estimated based on the coolant filling data, the estimated coolant pressure, the coolant temperature, the high-pressure water pump operation data, the hydrogen inlet pressure, and the power generation duration of the fuel cell system.

11. The system of claim 10, wherein, The controller 9 is specifically configured as follows: Based on the coolant filling data, identify whether the cooling circuit has been filled with coolant after the fuel cell system is powered on; If no coolant has been added, determine the accumulated coolant pressure based on the coolant temperature and the high-pressure water pump operating data; Based on the hydrogen infeed pressure, the estimated coolant pressure, and the power generation duration of the fuel cell system, the hydrogen accumulation pressure is determined. The initial accumulated pressure of the expansion tank (2) is determined based on the historical accumulated pressure of the expansion tank (2) and the temperature of the coolant. The accumulation pressure is determined based on the coolant accumulation pressure, the hydrogen accumulation pressure, and the initial accumulation pressure.

12. A vehicle characterized by comprising: Includes the fuel cell system according to any one of claims 10-11.

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