Method for detecting hydrogen purity of fuel cell system and control method for fuel cell system

Abstract

The application discloses a hydrogen purity detection method of a fuel cell system and a control method of the fuel cell system. The fuel cell system comprises an anode subsystem which inputs hydrogen-containing mixed gas into an electric pile through a flow supply device to generate electric current. The method comprises the following steps: when the fuel cell system is running and the exhaust valve is closed, calculating the pure hydrogen consumption M 纯氢气 of the electric pile according to the electric current of the electric pile; 纯氢气 calculating the mixed gas supply amount M 混合气 of the anode loop according to the pressure change of the anode loop and M 混合气 ; and substituting M 混合气 obtained by the above calculation into the gas flow formula of the flow supply device to obtain the hydrogen purity of the mixed gas; the gas flow formula of the flow supply device is M 混合气 =M0*(P in / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1‑x))); M0 is the hydrogen flow 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, P in and T are the inlet pressure and temperature of the flow supply device under current conditions, m is the average molecular weight of impurity gas in the mixed gas, and x is the purity of hydrogen.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for detecting hydrogen purity in a fuel cell system and a control method for a fuel cell system. Background Technology

[0002] A fuel cell is a device that converts the chemical energy of hydrogen into electrical energy. Its reaction product is water, and it boasts advantages such as zero emissions, low noise, and high conversion efficiency. Currently, the fuel used in on-board fuel cell systems is generally high-purity hydrogen with a purity of over 99.97%.

[0003] When the hydrogen supplied to a fuel cell hydrogen tank is not rigorously tested, the gas inside the tank will contain a significant amount of impurities, such as N2, O2, H2O, CO, and nitrogen oxides. Excessive impurities in the supplied hydrogen will directly lead to a decrease in the hydrogen concentration at the anode of the vehicle's hydrogen fuel cell, and may even cause catalyst poisoning, resulting in severe performance degradation and significantly reducing the lifespan of the fuel cell. Therefore, it is necessary to conduct timely purity testing of the hydrogen supplied to the fuel cell system in fuel cell vehicles to ensure that the quality of the hydrogen supplied to the fuel cell system meets the usage requirements, or to take targeted control measures when the purity is insufficient.

[0004] Traditional methods for gas purity detection primarily involve collecting the target gas and then analyzing the sample using a specialized mass spectrometer to determine the content of each component. While this method accurately identifies the specific content of each gas, the complex collection and analysis process consumes significant time and manpower. Another existing technology uses a fuel cell system anode model to detect the component content within the anode subsystem, and then uses the components of the anode subsystem to calculate the hydrogen supply component content, as illustrated in patent application CN201810634256.6. However, this method requires a sufficiently accurate fuel cell anode component estimation model. From an engineering application perspective, this method is quite complex, involving multi-physics calculations related to the fuel cell and requiring extensive system and stack test data to accurately validate the model estimation.

[0005] Therefore, it is necessary to propose a technical solution to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, this invention proposes a method for detecting hydrogen purity in a fuel cell system and a control method for the fuel cell system, which can realize online detection of hydrogen purity using existing fuel cell components without the need for additional components.

[0007] This invention is achieved through the following technical solution: a method for detecting hydrogen purity in a fuel cell system, suitable for detecting hydrogen purity during the operation of the fuel cell system, wherein the anode subsystem of the fuel cell system inputs a hydrogen-containing mixture into the stack via a supply device to react and generate current; the method includes the following steps when the fuel cell system is running and the exhaust valve is closed:

[0008] S1. Calculate the pure hydrogen consumption M based on the current of the fuel cell stack. 纯氢气 ;

[0009] S2. Based on the pressure change in the anode circuit and the aforementioned pure hydrogen consumption M... 纯氢气 Calculate the mixed gas supply M in the anode circuit. 混合气 ;as well as

[0010] S3. The calculated mixed gas supply quantity M is... 混合气 Substituting the gas flow rate formula of the supply device, the hydrogen purity of the mixed gas can be obtained by solving the problem.

[0011] The gas flow rate formula of the supply device is used to calculate the amount of gas flowing through the supply device. The gas flow rate 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 supply device under standard conditions, P0 and T0 are the inlet pressure and temperature of the supply device under standard conditions, P in T represents the inlet pressure and temperature of the supply device under the current conditions, m represents the average molecular weight of the impurity gases in the mixture, and x represents the purity of hydrogen.

[0012] As a further improved technical solution, the average molecular weight m of the impurity gases in the mixture is between 16 and 32.

[0013] As a further improved technical solution, the average molecular weight m of the impurity gases in the mixture is 28.

[0014] As a further improved technical solution, the pure hydrogen consumption M 纯氢气 M is obtained by calculating using the following formula: 纯氢气 =I*N / 2F; where I is the current in the fuel cell stack, N is the number of fuel cell stack plates, and F is the Faraday constant.

[0015] As a further improved technical solution, if the pressure of the anode circuit remains stable, the mixed gas supply M 混合气 The pure hydrogen consumption M 纯氢气 Satisfy: M 混合气 =M 纯氢气 .

[0016] As a further improved technical solution, if the pressure in the anode circuit is unstable, the mixed gas supply M... 混合气 The pure hydrogen consumption M 纯氢气 All are obtained by integration over the time interval t0 to t1, and satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ;

[0017] Where, 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 The anode circuit pressures at times t1 and t0 are respectively, T 阳极t1 T 阳极t0 The anode circuit temperatures at times t1 and t0 are V, respectively. 阳极 Let R be the volume of the anode circuit, and R be the ideal gas constant.

[0018] As a further improved technical solution, P 阳极t1 P 阳极t0 The average value of the anode inlet and anode outlet pressures of the fuel cell stack is used.

[0019] As a further improved technical solution, T 阳极t1 T 阳极t0 The average values ​​of the inlet and outlet temperatures of the fuel cell stack coolant are used.

[0020] As a further improved technical solution, the flow supply device is one of an ejector, a hydrogen supply valve, and a hydrogen supply nozzle.

[0021] The present invention also provides a control method for a fuel cell system, which includes the hydrogen purity detection method described above, 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 drainage, accelerating nitrogen discharge, and increasing anode pressure.

[0022] The hydrogen purity detection method for fuel cell systems provided by this invention can realize online detection of hydrogen purity by utilizing existing components of the fuel cell without adding any 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 improve the service life of the fuel cell. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the anode subsystem of the fuel cell system of the present invention.

[0024] The attached diagram is labeled as follows: 1-hydrogen source; 2-pressure reducing valve; 3-flow supply device; 4-water distributor; 5-discharge valve; 6-fuel stack. Detailed Implementation

[0025] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1 As shown, this invention provides a method for detecting hydrogen purity in a fuel cell system. This method is suitable for detecting hydrogen purity during the operation of the fuel cell system. Specifically, the method performs online hydrogen purity detection, enabling real-time monitoring of the purity of the hydrogen used in the operating fuel cell system. This facilitates timely detection of changes in hydrogen purity and allows for rapid adjustment and control. The fuel cell system includes a cathode subsystem (not shown) and an anode subsystem. The cathode subsystem supplies air to the fuel cell stack 6, and the anode subsystem supplies hydrogen to the fuel cell stack 6. Hydrogen and oxygen react chemically in the fuel cell stack 6 to generate an electric current. The hydrogen supplied to the fuel cell stack 6 by the anode subsystem must be of high purity. Low-purity hydrogen will significantly degrade the performance of the fuel cell and severely impact its lifespan. Therefore, timely detection of the purity of the hydrogen supplied by the anode subsystem is extremely important. Because some impurity gases are inevitably present in the hydrogen produced and stored, the hydrogen supplied by the anode subsystem is usually not 100% pure hydrogen, but a mixture of gases containing impurities, such as N2, O2, H2O, and CO. In this embodiment of the invention, the hydrogen containing impurity gases supplied by the anode subsystem is referred to as a mixed gas. Figure 1As shown, 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 installed at the inlet and outlet of the flow supply device 3, and a temperature sensor is installed at the outlet of the fuel cell stack 6. The hydrogen supply source 1 provides a hydrogen-containing mixture and can be, for example, a hydrogen cylinder or other hydrogen storage device. The pressure reducing valve 2 changes the pressure of the high-pressure hydrogen. The flow supply device 3 changes the gas flow state, for example, by injecting gas into the fuel cell stack 6. The water separator 4 separates liquid from the gas flow discharged from the fuel cell stack 6, facilitating hydrogen recycling. The discharge valve 5 discharges exhaust gas. The hydrogen-containing mixture is fed into the fuel cell stack 6 via the flow supply device 3 to react and generate current. The gas flow rate through the flow supply device 3 can be calculated based on its operating parameters. 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.

[0028] Taking the aforementioned fuel cell system as an example, the hydrogen purity detection method includes the following steps performed while the fuel cell system is running and the discharge valve is closed:

[0029] S1. Calculate the pure hydrogen consumption M based on the current of fuel cell stack 6. 纯氢气 ;

[0030] S2. Based on the pressure change in the anode circuit and the aforementioned pure hydrogen consumption M... 纯氢气 Calculate the mixed gas supply M in the anode circuit. 混合气 ;as well as

[0031] S3. The calculated mixed gas supply quantity M is... 混合气 Substituting the gas flow rate formula of the supply device 3, the hydrogen purity of the mixed gas can be obtained by solving the problem.

[0032] The gas flow rate formula of the supply device 3 is used to calculate the amount of gas flowing through the supply device 3. The gas flow rate 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 supply device 3 under standard conditions, P0 and T0 are the inlet pressure and temperature of the supply device 3 under standard conditions, P in T represents the inlet pressure and temperature of the supply device 3 under the current conditions, m represents the average molecular weight of the impurity gases in the mixture, and x represents the purity of hydrogen. In this embodiment, the supply device 3 is an ejector, and M0 is the hydrogen molar flow rate of the ejector nozzle under standard conditions (pressure P0, temperature T0, and nozzle outlet pressure less than P0 / 2).

[0033] In the above formula, sqrt is the square root operation, and M 混合气 Calculated in step S2, M0, P0, and T0 are the inherent performance parameters of the power supply device 3, where P... in T is obtained from the pressure and temperature sensors in the fuel cell system, and m is determined by the type of impurity gas itself; therefore, the only unknown in the above formula is the purity of hydrogen, x, which can be solved to obtain the purity of hydrogen.

[0034] This invention innovatively proposes that, under the condition of fuel cell system operation and exhaust valve closed, the relationship between consumption and supply is determined based on the current of stack 6 and the pressure change of the anode circuit, according to the ideal gas law; then, the amount of gas flowing through supply device 3 is calculated through the flow characteristics of supply device 3 itself; according to the law of conservation of mass, the supply amount calculated based on the ideal gas law should be equal to the amount of gas flowing through supply device 3 calculated based on the flow characteristics of supply device 3 itself, and the purity of hydrogen can be obtained by solving them together.

[0035] Furthermore, since the impurity gases are mainly N2, CO, O2, and NO, the average molecular weight m of the impurity gases in the mixture is between 16 and 32. Preferably, the average molecular weight m of the impurity gases in the mixture is 28. Of course, in other embodiments, the average molecular weight m of the impurity gases is not limited to the above range and specific value. 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.

[0036] In this embodiment, the pure hydrogen consumption M 纯氢气 and the supply of mixed gas M 混合气 The flow rate is expressed as molar flow rate, in mol / s. In step S1, the pure hydrogen consumption M... 纯氢气 M is obtained by calculation using the following formula: 纯氢气 =I*N / 2F; where I is the current in the fuel cell stack, N is the number of fuel cell stack plates, and F is the Faraday constant 96485.

[0037] If the pressure in the anode circuit remains stable, according to the ideal gas law, the total number of moles of gas in the anode circuit remains constant. Therefore, the mixed gas supply rate M... 混合气 The pure hydrogen consumption M 纯氢气 Satisfy: M 混合气 =M 纯氢气 .

[0038] If the pressure in the anode circuit is unstable, the mixed gas supply M 混合气 The pure hydrogen consumption M 纯氢气 It is obtained by integration over the time interval t0 to t1, that is:

[0039] M 混合气 =∫{M0*(Pin / P0)*sqrt(T0 / T)*sqrt(2 / (2*x+m*(1-x)))};

[0040] M 纯氢气 =∫I*N / 2F;

[0041] And both satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ; where ΔM 阳极 Let ΔM be the change in moles in the anode circuit during the time interval from t0 to t1. 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 The anode circuit pressures at times t1 and t0 are respectively, T 阳极t1 T 阳极t0 The anode circuit temperatures at times t1 and t0 are V, respectively. 阳极 Let P be the volume of the anode circuit, ρ be the sum of the volumes through which hydrogen flows in the anode circuit, and R be the ideal gas constant. Further, the pressure P... 阳极t1 P 阳极t0 The average value of the anode inlet and anode outlet pressures of the fuel cell stack can be used, along with the temperature T. 阳极t1 T 阳极t0 The average value of the inlet and outlet temperatures of the fuel cell stack coolant can be used.

[0042] The hydrogen purity detection method for fuel cell systems provided by this invention utilizes existing components of the fuel cell, such as pressure sensors, temperature sensors, and ejectors, to achieve online hydrogen purity detection without the need for additional components, making the detection process simple. When the detected hydrogen purity does not meet requirements, targeted control measures can be taken in a timely manner to improve the performance and lifespan of the fuel cell.

[0043] This invention also provides a control method for a fuel cell system, including the hydrogen purity detection method described above. When the detected hydrogen purity is lower than a purity threshold, the fuel cell system is controlled to perform one or more operations: accelerated drainage, accelerated nitrogen removal, and increased anode pressure. In one embodiment, the purity threshold is set to 99.8%. Setting the purity threshold to this value avoids the fuel cell system easily over-protecting due to an excessively high purity threshold, thus affecting the normal operation of the fuel cell system. It also avoids the excessively high requirements for detection accuracy caused by an excessively high purity threshold, which would increase the difficulty of detection and calculation. Moreover, the inventors have found that when the hydrogen purity is above 99.8%, it has almost no significant negative impact on the fuel cell stack. By combining the hydrogen purity detected by the above method with the anode component model, the hydrogen partial pressure at the anode is controlled to avoid problems such as system performance degradation and stack failure caused by excessively low anode hydrogen concentration due to impurities. This ensures that the system can maintain reliable and stable operation even when hydrogen purity is insufficient, and issues warnings and performs shutdown protection when the purity further decreases and cannot meet the system's operating requirements.

[0044] This invention has been illustrated through several specific embodiments. Those skilled in the art will understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A method for detecting hydrogen purity in a fuel cell system, suitable for detecting hydrogen purity during the operation of the fuel cell system, wherein, The fuel cell system includes an anode subsystem that feeds a hydrogen-containing mixture into the stack via a supply device to generate an electric current; characterized in that the method includes the following steps while 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 The pure hydrogen consumption M 纯氢气 M is obtained by calculating using the following formula: 纯氢气 =I*N / 2F; where I is the current in the fuel cell stack, N is the number of fuel cell stack plates, F is the Faraday constant, and M is the current in the fuel cell stack. 纯氢气 The unit is mol / s; S2. Based on the pressure change in the anode circuit and the aforementioned pure hydrogen consumption M... 纯氢气 Calculate the mixed gas supply M in the anode circuit. 混合气 Wherein, if the pressure in the anode circuit remains stable, the mixed gas supply amount M 混合气 The pure hydrogen consumption M 纯氢气 Satisfy: M 混合气 =M 纯氢气 If the pressure in the anode circuit is unstable, the mixed gas supply M... 混合气 The pure hydrogen consumption M 纯氢气 All are obtained by integration over the time interval t0 to t1, and satisfy: M 混合气 =M 纯氢气 +ΔM 阳极 ;where 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 The anode circuit pressures at times t1 and t0 are respectively, T 阳极t1 T 阳极t0 The anode circuit temperatures at times t1 and t0 are V, respectively. 阳极 Let M be the volume of the anode circuit, R be the ideal gas constant, and M be the volume of the anode circuit. 混合气 The unit is mol / s; and S3. The calculated mixed gas supply quantity M is... 混合气 Substituting the gas flow rate formula of the supply device, the hydrogen purity of the mixed gas can be obtained by solving the problem. The gas flow rate formula of the supply device is used to calculate the amount of gas flowing through the supply device. The gas flow rate 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 supply device under standard conditions, P0 and T0 are the inlet pressure and temperature of the supply device under standard conditions, P in T represents the inlet pressure and temperature of the supply device under the current conditions, m represents the average molecular weight of the impurity gases in the mixture, and x represents the purity of hydrogen.

2. The hydrogen purity detection method for a fuel cell system as described in claim 1, characterized in that, The average molecular weight m of the impurity gases in the mixture is between 16 and 32.

3. The hydrogen purity detection method for a fuel cell system as described in claim 2, characterized in that, The average molecular weight m of the impurity gases in the mixture is 28.

4. The hydrogen purity detection method for a fuel cell system as described in claim 1, characterized in that, P 阳极t1 P 阳极t0 The average value of the anode inlet and anode outlet pressures of the fuel cell stack is used.

5. The hydrogen purity detection method for a fuel cell system as described in claim 4, characterized in that, T 阳极t1 T 阳极t0 The average values ​​of the inlet and outlet temperatures of the fuel cell stack coolant are used.

6. The method for detecting hydrogen purity in a fuel cell system as described in any one of claims 1 to 4, characterized in that, The flow supply device is one of an ejector, a hydrogen supply valve, or a hydrogen supply nozzle.

7. A control method for a fuel cell system, characterized in that, The method includes the hydrogen purity detection method as described in any one of claims 1 to 6, wherein when the detected hydrogen purity is lower than a purity threshold, the fuel cell system is controlled to perform one or more of the following operations: accelerating water drainage, accelerating nitrogen discharge, and increasing anode pressure.

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