Hydrogen purity measurement method for fuel cell system, and control method for fuel cell system

Abstract

Disclosed in the present invention are a hydrogen purity measurement method for a fuel cell system, and a control method for a fuel cell system. An anode subsystem comprised in a fuel cell system feeds, by means of a flow supply device, a hydrogen-containing mixed gas into a stack for reaction to generate a current. The method comprises, in a state where the fuel cell system is operating and a drain valve is closed: calculating a pure hydrogen consumption Mpure hydrogen on the basis of the current of the stack; on the basis of a pressure change of an anode loop and Mpure hydrogen, calculating a mixed gas supply amount Mmixed gas of the anode loop; and substituting Mmixed gas calculated above into a gas flow formula of the flow supply device, to calculate a hydrogen purity of the mixed gas, wherein the gas flow formula of the flow supply device is: Mmixed gas=M0*(Pin / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x))), wherein M0 is the hydrogen flow of the flow supply device under standard conditions, P0 and T0 are the pressure and temperature at an inlet of the flow supply device under the standard conditions, Pin and T are the pressure and temperature at the inlet of the current supply device under current conditions, m is the average molecular weight of impurity gases in the mixed gas, and x is the purity of hydrogen.

Description

Hydrogen purity detection method of fuel cell system and control method of fuel cell system Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a method for detecting hydrogen purity in a fuel cell system and a method for controlling the fuel cell system. Background Art

[0002] Fuel cells convert the chemical energy of hydrogen into electrical energy, with water as the reaction product. They offer advantages such as zero emissions, low noise, and high conversion efficiency. Current on-board fuel cell systems typically use high-purity hydrogen with a purity exceeding 99.97%.

[0003] If the hydrogen refilled into a fuel cell hydrogen cylinder is not rigorously tested, the gas inside the cylinder will contain a high concentration of impurities, such as N2, O2, H2O, CO, and nitrogen oxides. Excessive impurities in the hydrogen supply gas can directly lead to a decrease in hydrogen concentration in the anode of the vehicle's hydrogen fuel cell, and even catalyst poisoning, resulting in severe performance degradation and significantly shortening the fuel cell's service life. Therefore, timely purity testing of the hydrogen in the fuel cell vehicle's gas supply system is necessary to ensure that the hydrogen quality supplied to the fuel cell system meets usage requirements. If the purity is insufficient, targeted control measures can be implemented.

[0004] The traditional gas purity detection method mainly involves collecting the target gas and then placing the gas sample on a specific mass spectrometer device for analysis and detection to determine the content of each gas component. Although this method can accurately determine the specific content of each gas, the complex collection and detection process requires a lot of time and manpower. Another existing technology uses the anode model of the fuel cell system to detect the component content in the anode subsystem, and then calculates the component content of the hydrogen supply through the components of the anode subsystem, such as the patent document with application number CN201810634256.6. However, this method requires a sufficiently accurate fuel cell anode component estimation model. From the perspective of engineering application, this method is relatively complex. The model involves multi-physical field calculation processes such as fuel cells, and requires a large amount of system and stack test data to accurately verify the model estimation.

[0005] Based on this, it is necessary to propose a technical solution to overcome the shortcomings of the existing technology.

[0006] Summary of the Invention

[0007] In order to overcome the defects of the prior art, the present invention proposes a hydrogen purity detection method for a fuel cell system and a fuel cell system control method, which can realize online detection of hydrogen purity by utilizing existing components of the fuel cell without adding additional components.

[0008] The present invention is implemented through the following technical solution: a method for detecting hydrogen purity in a fuel cell system, suitable for detecting hydrogen purity during operation of the fuel cell system, wherein the fuel cell system includes an anode subsystem that inputs a hydrogen-containing mixed gas into a fuel cell stack via a flow supply device for reaction to generate current; the method comprises: when the fuel cell system is operating and the exhaust valve is closed:

[0009] S1. Calculate the pure hydrogen consumption M based on the current of the fuel cell stack 纯氢气 ;

[0010] S2, according to the pressure change of the anode circuit and the above pure hydrogen consumption M 纯氢气 Calculate the mixed gas supply volume M of the anode circuit 混合气 ;as well as

[0011] S3, the mixed gas supply amount M obtained by the above calculation 混合气 Substituting the gas flow rate formula of the flow supply device into the formula, the hydrogen purity of the mixed gas is obtained;

[0012] The gas flow formula of the flow supply device is used to calculate the amount of gas flowing through the flow supply device. The gas flow formula is: M 混合气 =M0*(P in / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x))); where M0 is the hydrogen flow rate of the flow supply device under standard conditions, P0 and T0 are the inlet pressure and temperature of the flow supply device under standard conditions, and P in and T are the inlet pressure and temperature of the flow supply device under the current conditions, m is the average molecular weight of the impurity gas in the mixed gas, and x is the purity of hydrogen.

[0013] As a further improved technical solution, the average molecular weight m of the impurity gas in the mixed gas is between 16 and 32.

[0014] As a further improved technical solution, the average molecular weight m of the impurity gas in the mixed gas is 28.

[0015] As a further improved technical solution, the pure hydrogen consumption M 纯氢气 It is calculated by the following formula: M 纯氢 气 =I*N / 2F; where I is the current of the battery stack, N is the number of cells in the stack, and F is the Faraday constant.

[0016] As a further improved technical solution, if the pressure of the anode circuit remains stable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 Satisfied: M 混合气 =M纯氢气 .

[0017] As a further improved technical solution, if the pressure of the anode circuit is unstable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 All are obtained by integral calculation during the time period t0 to t1 and satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ;

[0018] Among them, ΔM 阳极 =(P 阳极t1 / T 阳极t1 -P 阳极t0 / T 阳极t0 )*V 阳极 / R; where P 阳极t1 、P 阳极t0 are the anode circuit pressure at time t1 and time t0, T 阳极t1 、T 阳极t0 are the anode circuit temperatures at time t1 and time t0, respectively, V 阳极 is the volume of the anode circuit, and R is the ideal gas constant.

[0019] As a further improved technical solution, P 阳极t1 、P 阳极t0 The average value of the stack anode inlet and anode outlet pressure is used.

[0020] As a further improved technical solution, T 阳极t1 、T 阳极t0 The average value of the stack coolant inlet and outlet temperatures is used.

[0021] As a further improved technical solution, the flow supply device is one of an ejector, a hydrogen supply valve, and a hydrogen supply nozzle.

[0022] The present invention also provides a control method for a fuel cell system, which includes the hydrogen purity detection method as described above, wherein, when the detected hydrogen purity is lower than the purity threshold, the fuel cell system is controlled to perform one or more operations of accelerating water discharge, accelerating nitrogen discharge, and increasing anode pressure.

[0023] The hydrogen purity detection method for a fuel cell system provided by the present invention utilizes existing fuel cell components and can achieve online detection of hydrogen purity without the need for additional components. The detection is simple, and when the detected hydrogen purity does not meet the requirements, targeted control measures can be taken in a timely manner to extend the service life of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1 is a schematic diagram of an anode subsystem of a fuel cell system according to the present invention.

[0025] The figures are marked as follows: 1-hydrogen source; 2-pressure reducing valve; 3-flow supply device; 4-water separator; 5-discharge valve; 6-fuel cell stack. DETAILED DESCRIPTION

[0026] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Please refer to Figure 1. The present invention provides a method for detecting the purity of hydrogen in a fuel cell system, which is suitable for detecting the purity of hydrogen during the operation of the fuel cell system, that is, the detection method performs online detection of the purity of hydrogen, and is used to monitor the purity of the hydrogen used in the operating fuel cell system in real time, so as to facilitate timely detection of changes in the purity of hydrogen and to quickly perform corresponding adjustment controls. The fuel cell system includes a cathode subsystem (not shown) and an anode subsystem, the cathode subsystem is used to transport air to the stack 6, and the anode subsystem is used to transport hydrogen to the stack 6, and hydrogen and oxygen react chemically in the stack 6 to generate current. The hydrogen input to the stack 6 by the anode subsystem must be high-purity hydrogen. Low-purity hydrogen will cause the performance of the fuel cell to drop significantly, and will have a serious impact on the service life of the fuel cell. Therefore, it is extremely important to detect the purity of the hydrogen supplied by the anode subsystem in a timely manner. Since the production and storage of hydrogen inevitably results in the presence of some impurity gases, the hydrogen supplied by the anode subsystem is typically not 100% pure hydrogen. Instead, it is a mixed gas containing some impurity gases, such as N₂, O₂, H₂O, CO, etc. In the present embodiment, the hydrogen supplied by the anode subsystem containing impurity gases is referred to as a mixed gas. As shown in Figure 1, in this embodiment, the anode subsystem includes a hydrogen supply source 1, a pressure reducing valve 2, a flow supply device 3, a water separator 4, a discharge valve 5, and a fuel cell stack 6. Pressure sensors are provided at the inlet and outlet of the flow supply device 3, and a temperature sensor is provided at the outlet of the fuel cell stack 6. Among them, the hydrogen supply source 1 is used to provide a hydrogen-containing mixed gas, and the hydrogen supply source 1 can be, for example, a hydrogen bottle or other hydrogen storage device; the pressure reducing valve 2 is used to change the pressure of the high-pressure hydrogen; the flow supply device 3 is used to change the state of the airflow, for example, to realize the injection of airflow into the fuel cell 6; the water separator 4 is used to separate the liquid in the airflow discharged from the fuel cell 6, so as to facilitate the recycling of hydrogen; the exhaust valve 5 is used to discharge the tail gas. The hydrogen-containing mixed gas is input into the fuel cell 6 through the flow supply device 3 to react and generate electric current. The gas flow rate flowing through the flow supply device 3 can be calculated based on some operating parameters of the flow supply device 3 itself. In this embodiment, the flow supply device 3 is an ejector. In other embodiments, the flow supply device 3 can also be a hydrogen supply valve, a hydrogen supply nozzle, etc.

[0029] Taking the above-mentioned fuel cell system as an example, the hydrogen purity detection method includes performing the following steps when the fuel cell system is running and the exhaust valve is closed:

[0030] S1. Calculate the pure hydrogen consumption M based on the current of the fuel cell stack 6 纯氢气 ;

[0031] S2, according to the pressure change of the anode circuit and the above pure hydrogen consumption M 纯氢气Calculate the mixed gas supply volume M of the anode circuit 混合气 ;as well as

[0032] S3, the mixed gas supply amount M obtained by the above calculation 混合气 Substitute the gas flow rate formula of the flow supply device 3 into the equation to obtain the hydrogen purity of the mixed gas;

[0033] The gas flow formula of the flow supply device 3 is used to calculate the amount of gas flowing through the flow supply device 3. The gas flow formula is: M 混合气 =M0*(P in / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x))); where 2 is the molecular weight of hydrogen, M0 is the hydrogen flow rate of the flow supply device 3 under standard conditions, P0 and T0 are the inlet pressure and temperature of the flow supply device 3 under standard conditions, and P in and T are the inlet pressure and temperature of flow supply device 3 under current conditions, m is the average molecular weight of the impurity gases in the mixed gas, and x is the purity of the hydrogen. In this embodiment, flow supply device 3 is an ejector, and M0 is the molar flow rate of hydrogen at the ejector nozzle under standard conditions (pressure P0, temperature T0, and nozzle outlet pressure less than P0 / 2).

[0034] In the above formula, sqrt is the square root operation, M 混合气 Calculated in step S2, M0, P0 and T0 are the inherent performance parameters of the flow supply device 3, P in and T are detected by the pressure sensor and temperature sensor in the fuel cell system, and m is determined by the type of impurity gas itself; therefore, the only unknown number in the above formula is the purity x of hydrogen, which can be solved to obtain the purity of hydrogen.

[0035] The present invention innovatively proposes that when the fuel cell system is running and the exhaust valve is closed, the relationship between consumption and supply is judged based on the current of the fuel cell stack 6 and the pressure change of the anode circuit according to the ideal gas state equation; then the amount of gas flowing through the flow supply device 3 is calculated based on the flow characteristics of the flow supply device 3 itself; according to the law of conservation of matter, it can be seen that the supply amount calculated based on the ideal gas state equation should be equal to the amount of gas flowing through the flow supply device 3 calculated based on the flow characteristics of the flow supply device 3 itself, and the purity of the hydrogen can be obtained by jointly solving it.

[0036] Furthermore, since the impurity gases are mainly N2, CO, O2, and NO, the average molecular weight m of the impurity gases in the mixed gas is between 16 and 32. Preferably, the average molecular weight m of the impurity gases in the mixed gas is 28. Of course, in other embodiments, the average molecular weight m of the impurity gases is not limited to the above ranges and specific values. Those skilled in the art can reasonably select the value of the average molecular weight m based on the main components of the impurity gases.

[0037] In this embodiment, the pure hydrogen consumption M 纯氢气 and the mixture supply amount M 混合气 is the molar flow rate, in mol / s. In step S1, the pure hydrogen consumption M 纯氢气 It is calculated by the following formula: M 纯氢气 =I*N / 2F; where I is the current of the battery stack, N is the number of cells in the stack, and F is the Faraday constant of 96485.

[0038] If the pressure of the anode circuit remains stable, according to the ideal gas state equation, the total gas mole number in the anode circuit remains unchanged, then the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 Satisfied: M 混合 气 =M 纯氢气 .

[0039] If the pressure of the anode circuit is unstable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯 氢气 Obtained by integrating the time period from t0 to t1, namely: M 混合气 =∫{M0*(Pin / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x)))}; M 纯氢气 =∫I*N / 2F;

[0040] And both satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ; where ΔM 阳极 is the molar change in the anode circuit from t0 to t1, ΔM 阳极 =(P 阳极t1 / T 阳极t1 -P 阳极t0 / T 阳极t0 )*V 阳极 / R; where P 阳极t1 、P 阳极t0 are the anode circuit pressure at time t1 and time t0, T 阳极t1 、T 阳极t0are the anode circuit temperatures at time t1 and time t0, respectively, V 阳极 is the volume of the anode circuit, is the sum of all the volumes through which hydrogen flows in the anode circuit, and R is the ideal gas constant. 阳极t1 、P 阳极t0 The average value of the anode inlet and anode outlet pressure of the stack can be used, and the temperature T 阳极t1 、T 阳极t0 The average value of the stack coolant inlet and outlet temperatures can be used.

[0041] The hydrogen purity detection method for a fuel cell system provided by this invention utilizes existing fuel cell components, such as pressure sensors, temperature sensors, and ejectors, to achieve online hydrogen purity detection without requiring additional components. This simplifies detection. If the detected hydrogen purity does not meet requirements, targeted control measures can be implemented promptly to improve the performance and service life of the fuel cell.

[0042] The present invention also provides a control method for a fuel cell system, which includes the hydrogen purity detection method as described above, wherein when the detected hydrogen purity is lower than the purity threshold, the fuel cell system is controlled to perform one or more operations of accelerating water drainage, accelerating nitrogen drainage, and increasing anode pressure. In one embodiment, the purity threshold is set to 99.8%. The purity threshold is set to the above value. On the one hand, it can avoid the fuel cell system from easily over-protecting due to the purity threshold being set too high, thereby affecting the normal operation of the fuel cell system. On the other hand, it also avoids the excessively high detection accuracy requirements due to the purity threshold being set too high, thereby increasing the difficulty of detection and calculation. Moreover, the inventors have found through research that when the hydrogen purity is above 99.8%, it will hardly cause a significant negative impact on the fuel cell stack. The hydrogen purity detected by the above method is combined with the anode component model to control the hydrogen partial pressure at the anode to avoid problems such as system performance degradation and fuel cell stack failure caused by low anode hydrogen concentration due to impure hydrogen. This ensures that the system can still operate reliably and stably when the hydrogen purity is insufficient, and issues reminders and shutdown protection when the purity further decreases and cannot meet the system operation requirements.

[0043] The present invention is described by means of several specific embodiments. It should be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the present invention without departing from the scope of the present invention. In addition, various modifications may be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but is intended to include all embodiments falling within the scope of the claims of the present invention.

Claims

1. A method for detecting the purity of hydrogen in a fuel cell system, suitable for detecting the purity of hydrogen in the operation of the fuel cell system, wherein: The fuel cell system includes an anode subsystem that inputs a hydrogen-containing mixed gas into the fuel cell stack through a flow supply device for reaction to generate current; the method is characterized in that, when the fuel cell system is running and the exhaust valve is closed: S1. Calculate the pure hydrogen consumption M based on the current of the fuel cell stack 纯氢气 ; S2, according to the pressure change of the anode circuit and the above pure hydrogen consumption M 纯氢气 Calculate the mixed gas supply volume M of the anode circuit 混合气 ;as well as S3, the mixed gas supply amount M obtained by the above calculation 混合气 Substituting the gas flow rate formula of the flow supply device into the formula, the hydrogen purity of the mixed gas is obtained; The gas flow formula of the flow supply device is used to calculate the amount of gas flowing through the flow supply device. The gas flow formula is: M 混合气 =M0*(P in / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x))); where M0 is the hydrogen flow rate of the flow supply device under standard conditions, P0 and T0 are the inlet pressure and temperature of the flow supply device under standard conditions, and P in and T are the inlet pressure and temperature of the flow supply device under the current conditions, m is the average molecular weight of the impurity gas in the mixed gas, and x is the purity of hydrogen.

2. The method for detecting hydrogen purity of a fuel cell system according to claim 1, wherein: The average molecular weight m of the impurity gas in the mixed gas is between 16 and 32.

3. The method for detecting hydrogen purity of a fuel cell system according to claim 2, wherein: The average molecular weight m of the impurity gas in the mixed gas is 28.

4. The method for detecting hydrogen purity of a fuel cell system according to claim 1, wherein: The pure hydrogen consumption M 纯氢气 It is calculated by the following formula: M 纯氢气 =I*N / 2F; where I is the current of the battery stack, N is the number of cells in the stack, and F is the Faraday constant.

5. The method for detecting hydrogen purity of a fuel cell system according to claim 1 or 4, wherein: If the pressure of the anode circuit remains stable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 Satisfied: M 混合气 =M 纯氢气 .

6. The method for detecting hydrogen purity of a fuel cell system according to claim 1 or 4, wherein: If the pressure of the anode circuit is unstable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 All are obtained by integral calculation during the time period t0 to t1 and satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ; Among them, ΔM 阳极 =(P 阳极t1 / T 阳极t1 -P 阳极t0 / T 阳极t0 )*V 阳极 / R; where P 阳极t1 、P 阳极t0 are the anode circuit pressure at time t1 and time t0, T 阳极t1 、T 阳极t0 are the anode circuit temperatures at time t1 and time t0, respectively, V 阳极 is the volume of the anode circuit, and R is the ideal gas constant.

7. The method for detecting hydrogen purity of a fuel cell system according to claim 6, wherein: P 阳极t1 、P 阳极 t0 The average value of the stack anode inlet and anode outlet pressure is used.

8. The method for detecting hydrogen purity of a fuel cell system according to claim 7, wherein: T 阳极t1 、T 阳极 t0 The average value of the stack coolant inlet and outlet temperatures is used.

9. The method for detecting hydrogen purity of a fuel cell system according to any one of claims 1 to 4, wherein: The flow supply device is one of an ejector, a hydrogen supply valve, and a hydrogen supply nozzle.

10. A method for controlling a fuel cell system, characterized in that: The method comprises the hydrogen purity detection method as claimed in any one of claims 1 to 9, wherein when the detected hydrogen purity is lower than a purity threshold, the fuel cell system is controlled to perform one or more operations of accelerating water discharge, accelerating nitrogen discharge and increasing anode pressure.

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