A method for on-line diagnosis of a fuel cell system heat dissipation capacity reduction

Abstract

The application discloses a kind of fuel cell system heat dissipation capacity decline online diagnosis method, comprising: when judging fuel cell stack enters steady state, enter diagnostic window;Based on heat neutral voltage, calculate the heat production of electric pile, calculate heat dissipation value, the heat dissipation value includes: shell heat dissipation value and exhaust gas heat carrying value;The heat dissipation value is obtained by subtracting the heat production of electric pile from heat dissipation value and obtains radiator heat load;Logarithmic mean temperature difference is calculated, and the actual heat transfer capacity of radiator is obtained by dividing radiator heat load by logarithmic mean temperature difference;Calculate reference heat transfer capacity, and the fouling factor is obtained by dividing the actual heat transfer capacity of radiator by reference heat transfer capacity, and the capacity loss is obtained by subtracting the fouling factor from 1, when the fouling factor is less than the first value or the capacity loss is greater than the second value and the duration is greater than the third value, simultaneously judge fan reference residual is greater than the fourth value, judge heat dissipation capacity decline.The application solves the problems of poor environmental adaptability of fuel cell system, false alarm, lack of physical modeling of radiator obstruction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell system heat dissipation capacity decline diagnosis, in particular to a fuel cell system heat dissipation capacity decline online diagnosis method. BACKGROUND

[0002] The heat generated by the vehicle-mounted fuel cell stack in operation needs to be dissipated into the environment through the cooling circuit and the radiator (in cooperation with the fan and the driving wind). When the windward surface of the radiator is blocked by willow catkins, leaves, plastic bags or dust, the equivalent convective heat transfer coefficient decreases. In order to maintain the temperature of the stack, the system often increases the fan speed, resulting in the increase of energy consumption / hydrogen consumption; in severe cases, it may trigger the over-temperature power reduction or protection shutdown.

[0003] The existing method for diagnosing the decline of the heat dissipation capacity of the fuel cell system is through fixed threshold and machine learning diagnosis, but after adopting the temperature / speed fixed threshold rule, the fuel cell system has poor environmental adaptability, false positives are many, the data-based machine learning diagnosis has high dependence on training set and computing power, and lacks physical modeling of "radiator obstruction". SUMMARY

[0004] The purpose of the present application is to provide a fuel cell system heat dissipation capacity decline online diagnosis method, which aims to solve the problem that after adopting the temperature / speed fixed threshold rule in the fuel cell online diagnosis process, the fuel cell system has poor environmental adaptability, false positives are many, the data-based machine learning diagnosis has high dependence on training set and computing power, and lacks physical modeling of "radiator obstruction".

[0005] The present application provides a fuel cell system heat dissipation capacity decline online diagnosis method, comprising:

[0006] When the fuel cell stack enters a steady state, enter the diagnosis window;

[0007] Calculate the heat generation of the stack based on the heat-neutral voltage, calculate the heat dissipation value, the heat dissipation value includes: the shell heat dissipation value and the heat carried by the exhaust gas value;

[0008] Subtract the heat dissipation value from the heat generation of the stack to obtain the heat load of the radiator;

[0009] Calculate the logarithmic mean temperature difference, divide the heat load of the radiator by the logarithmic mean temperature difference to obtain the actual heat transfer capacity of the radiator;

[0010] Calculate the reference heat transfer capacity, divide the actual heat transfer capacity of the radiator by the reference heat transfer capacity to obtain the fouling factor, subtract 1 from the fouling factor to obtain the capacity loss, when the fouling factor is less than the first value or the capacity loss is greater than the second value and the duration is greater than the third value, and the fan reference residual is greater than the fourth value, judge the heat dissipation capacity decline.

[0011] The technical scheme of the present application establishes energy closure in a steady state window, calculates the actual heat transfer capacity of the radiator, obtains a reference capacity, constructs a fouling factor / residual by comparison, and solves the problems of poor environmental adaptability, frequent false alarms, and lack of physical modeling of radiator obstruction of the fuel cell system.

[0012] The above description is only a summary of the technical scheme of the present application, in order to more clearly understand the technical means of the present application, and to implement the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the specific embodiments of the present application or the technical scheme in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings without creative labor on the basis of these drawings.

[0014] Figure 1 is a flow chart of a fuel cell system heat dissipation capacity reduction online diagnosis method according to an embodiment of the present application;

[0015] Figure 2 is a corresponding device schematic diagram of a fuel cell system heat dissipation capacity reduction online diagnosis method according to an embodiment of the present application;

[0016] MARKED FOR EXPLANATION:

[0017] 1. Stack module; 2. Air supply system; 3. Hydrogen supply system; 4. Power module; 5. Water pump; 6. Thermostat; 7. Radiator module; 8. Water tank; 9. Stack coolant inlet thermometer; 10. Stack coolant outlet thermometer; 11. Radiator coolant outlet thermometer; 12. Ambient temperature meter; 13. Ambient pressure meter; 14. Stack air inlet thermometer; 15. Stack air outlet thermometer; 16. Radiator fan outlet thermometer; 17. Signal collector; 18. Controller. DETAILED DESCRIPTION

[0018] The technical scheme of the present application will be described below in conjunction with the embodiments, obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0019] Method embodiment

[0020] According to the embodiment of the present application, a fuel cell system heat dissipation capacity decline online diagnosis method is provided, Figure 1 is a flow chart of a fuel cell system heat dissipation capacity decline online diagnosis method according to the embodiment of the present application, as shown in the figure, specifically comprising: Figure 1

[0021] When the fuel cell stack enters a steady state, enter a diagnosis window;

[0022] Calculate the heat generation of the stack based on the heat neutral voltage, and calculate the heat dissipation value, the heat dissipation value including: the shell heat dissipation value and the exhaust gas heat carrying value;

[0023] Subtract the heat dissipation value from the heat generation of the stack to obtain the heat load of the radiator;

[0024] Calculate the logarithmic mean temperature difference, and divide the heat load of the radiator by the logarithmic mean temperature difference to obtain the actual heat transfer capacity of the radiator;

[0025] Calculate the reference heat transfer capacity, and divide the actual heat transfer capacity of the radiator by the reference heat transfer capacity to obtain the fouling factor, and subtract 1 from the fouling factor to obtain the capacity loss;

[0026] When the fouling factor is less than the first value or the capacity loss is greater than the second value and the duration is greater than the third value, and the fan reference residual is greater than the fourth value, it is judged that the heat dissipation capacity is reduced.

[0027] The specific implementation method is as follows:

[0028] In the embodiment of the present application, the heat generation of the stack based on the heat neutral voltage is calculated using the following formula:

[0029] ;

[0030] Wherein, Q_stack represents the heat generation of the stack, U_cell represents the voltage of each stack piece, U_cell=U / N_stack, the calibration coefficient κ∈[0.98, 1.02], I represents the current of the fuel cell system, U represents the voltage of the fuel cell system, N_stack represents the number of stack pieces, and E_th=1.48 V.

[0031] In the embodiment of the present application, the heat dissipation value is calculated using the following formula:

[0032] Shell heat dissipation value: ;

[0033] Wherein, Q_shell represents the shell heat dissipation, k_shell represents the shell thermal conductivity coefficient, the value range is 50-100 W / K, T_out represents the temperature of the cooling liquid leaving the stack, and T_amb represents the ambient temperature, the value range is -30℃ to 45℃;

[0034] ​Tail gas heat value: ;

[0035] Wherein, Q_exh represents tail gas heat, c_p represents specific heat capacity of dry air, c_p=1005 J / (kg·K), m_air represents air mass flow, the value range is 0.02-0.15, T_air_out represents stack air outlet temperature, and T_air_in represents stack air inlet temperature.

[0036] In the embodiment of the application, the heat dissipation value further includes other heat dissipation values, and the calculation formula is as follows:

[0037] ;

[0038] Wherein, Q_other represents other heat dissipation values, k0 takes the value range of ±500 W, k1 takes the value range of 5 W / K-20 W / K, k2 takes the value range of 0-2000, and k0, k1 and k2 represent coefficients.

[0039] In the embodiment of the application, the calculation of the logarithmic mean temperature difference specifically includes: calculating the first difference ΔT1 by subtracting the stack air inlet temperature from the cooling liquid leaving the stack temperature, calculating the second difference ΔT2 by subtracting the stack air outlet temperature from the radiator cooling liquid outlet temperature, wherein the stack air inlet temperature takes the ambient temperature, the stack air outlet temperature takes the fan outlet temperature, and the logarithmic mean temperature difference ΔT_lm is calculated by using the following formula:

[0040] ,

[0041] The numerical guardrail is set according to the first difference ΔT1 and the second difference ΔT2, and the following formula is used: when |ΔT1-ΔT2|<1K, ΔT_lm=(ΔT1+ΔT2) / 2; if ΔT1≤0 or ΔT2≤0, the diagnosis is suspended.

[0042] In the embodiment of the application, the calculation of the reference heat transfer capacity is calculated by using the following formula:

[0043]

[0044] Wherein, UA_ref(n_f,v) represents a reference heat transfer capacity, the value range is 500-2500, n_f represents a heat dissipation fan rotating speed, UA_NTP(n_f) represents a pressure value corresponding to n_f in the calibration table, the reference air density is p_NTP=1.18 kg / m³, a=0.75, k_v takes the value range of 0.003-0.006 (km / h)^−1, v represents the vehicle speed, the value range is 80-110, the air density is p_air = (p_amb×1000) / (287·(T_amb+273.15)), p_amb represents the ambient pressure, the value range is 80-110.

[0045] In the embodiment of the present application, the calibration table is shown in Table 1:

[0046] Table 1

[0047] n_f (rpm) UA_NTP (W / K) 1000 446 1500 643 2000 833 2500 1018 3000 1200 3500 1379 4000 1555 4500 1728 5000 1900

[0048] In the embodiment of the present application, the fan reference residual is calculated by the following formula:

[0049] ;

[0050] Wherein, n_ref is the fan rotating speed reaching the actual heat transfer capacity of the radiator, the air density is calculated according to the ambient pressure and the ambient temperature , the density and vehicle speed are corrected to obtain , and let , the calibration table / interpolation or numerical solution is obtained by inversion . In the embodiment of the present application, the first value takes the value range of 0.75-0.85, the second value takes the value of 0.2, the third value takes the value range of 0.1-0.2, and the fourth value takes the value range of 30-120.

[0051] In the embodiment of the present application, a working condition is used for numerical demonstration.

[0052]

[0053] Working condition: T_amb=30 ℃, p_amb=101 kPa, v=20 km / h, n_f=3000 rpm; U=360 V, I=200A, N_stack=400; T_in=70 ℃, T_out=75 ℃, radiator coolant outlet temperature T_rad_out=60 ℃; T_air_in=35 ℃, T_air_out=65 ℃; m_air=0.08 kg / s; k_shell=80 W / K; κ=1.00.​​

[0054] Calculation: U_cell = 0.9 V; Q_stack = 1.00 · 200 · 400 · (1.48 - 0.9) = 46400 W.

[0055] Q_shell = 80 · (75 - 30) = 3600 W; Q_exh = 1005 · 0.08 · (65 - 35) = 2414 W; take Q_other = 300 W.

[0056] Q_rad = 46400 - 3600 - 2414 - 300 = 40086 W.

[0057] ΔT1 = T_out - T_amb = 75 - 30 = 45 K; if there is a fan port outlet temperature T_fan_out = 36℃, then ΔT2 = T_rad_out - T_fan_out = 60 - 36 = 24 K; ΔT_lm = (45 - 24) / ln(45 / 24) ≈ 33.0 K.

[0058] UA_act = 40086 / 33.0 ≈ 1215 W / K.

[0059] ρair / ρ_NTP ≈ 1.00;

[0060] UA_NTP(3000) = 1200 W / K; UA_ref = 1200 · (1 + 0.004 · 20) = 1296 W / K (according to k_v = 0.004).

[0061] K_foul = 1215 / 1296 ≈ 0.94 (normal, no fault). If the UA_act decreases to 950 W / K after shielding, then K_foul ≈ 0.73 < 0.75, triggering an alarm.

[0062] In the embodiments of the present application, a device for implementing the above method is provided, as shown in Figure 2 .

[0063] It comprises: a stack module, an air supply system, a hydrogen supply system, a power module, a water pump, a thermostat, a heat dissipation module, a water tank, a stack coolant inlet thermometer, a stack coolant outlet thermometer, a radiator coolant outlet thermometer, an environment thermometer, an environment pressure gauge, a stack air inlet thermometer, a stack air outlet thermometer, a radiator fan outlet thermometer, a signal collector and a controller.

[0064] The stack module 1 is the core of electrochemical reaction, and the signal collector can obtain the number of stack sheets in the stack module.

[0065] Air supply system 2, providing oxidant and regulating flow and pressure, signal collector acquires air inlet temperature of stack T_air_in, air outlet temperature of stack T_air_out, air mass flow m_air (kg / s);

[0066] Hydrogen supply system 3, providing fuel;

[0067] Power module 4, measuring point electric power, including: current, voltage of fuel cell system.

[0068] Water pump 5, driving cooling liquid circulation;

[0069] Thermostat 6, controlling cooling liquid flow to radiator or bypass;

[0070] Radiator module 7, including fan and radiator;

[0071] Water tank 8, cooling liquid compensation and storage;

[0072] Stack cooling liquid inlet thermometer 9, monitoring cooling liquid entering stack temperature T_in (℃);

[0073] Stack cooling liquid outlet thermometer 10, monitoring cooling liquid leaving stack temperature T_out (℃);

[0074] Radiator cooling liquid outlet thermometer 11, monitoring cooling liquid temperature after radiator T_rad_out (℃);

[0075] Ambient thermometer 12, measuring ambient temperature T_amb (℃);

[0076] Ambient pressure gauge 13, measuring ambient pressure p_amb (Pa / Bar), p_amb (Pa / Bar) is used for air density correction;

[0077] Stack air inlet thermometer 14, monitoring stack air inlet temperature T_air_in (℃);

[0078] Stack air outlet thermometer 15, monitoring cathode exhaust gas temperature after reaction T_air_out (℃);

[0079] Radiator fan outlet thermometer 16, monitoring fan outlet air outlet temperature T_fan_out (℃);

[0080] A signal collector 17 is configured to collect the number of cell pieces in the cell module, obtain the air inlet temperature T_air_in of the cell, the air outlet temperature T_air_out of the cell, the air mass flow m_air, the current and voltage of the fuel cell system, the monitoring cooling liquid inlet temperature T_in of the cell, the monitoring cooling liquid outlet temperature T_out of the cell, the monitoring post-reaction cathode tail gas temperature T_air_out, and the monitoring fan outlet air temperature T_fan_out.

[0081] A controller 18 is configured to receive the data collected by the signal collector and execute the above method.

[0082] The present application has the following advantages: energy closure is established within a steady state window, the actual heat transfer capacity UA_act of the radiator is calculated, the reference capacity UA_ref is obtained according to the fan speed, air density and vehicle speed, the "dirt blocking factor / residual" is constructed by comparison of the two, and the steady state filtering, threshold hysteresis and duration joint strategy are used for robust determination.

[0083] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the above embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements of the technical solutions of the embodiments of the present application do not make the essence of the corresponding technical solutions deviate from the scope of the present application.

Claims

1. An online diagnostic method for reduced heat dissipation capacity of a fuel cell system, characterized in that, include: When the fuel cell stack is determined to have entered a steady state, the diagnostic window is activated. The heat generation of the fuel cell stack is calculated based on the thermal neutral voltage, and the heat dissipation value is calculated. The heat dissipation value includes: the heat dissipation value of the shell and the heat carried by the exhaust gas. The calculation of stack heat generation based on thermal neutral voltage uses the following formula: Where Q_stack represents the heat generated by the fuel cell stack in W, U_cell = U / N_stack, U_cell represents the voltage of a single fuel cell stack in V, the calibration coefficient κ∈[0.98, 1.02], I represents the current of the fuel cell system, U represents the voltage of the fuel cell system, N_stack represents the number of fuel cell stacks, and the thermal neutral voltage E_th = 1.48 V; The heat dissipation value is calculated using the following formula: Where Q_shell represents heat dissipation from the casing in W, k_shell represents the thermal conductivity coefficient of the casing, ranging from 50 W / K to 100 W / K, T_out represents the temperature at which the coolant leaves the fuel cell stack in K, and T_amb represents the ambient temperature in K. Where Q_exh represents the heat carried by the exhaust gas in W, c_p represents the specific heat capacity of dry air at normal pressure, c_p=1005 J / (kg·K), m_air represents the air mass flow rate in kg / s, T_air_out represents the fuel cell stack air outlet temperature in K, and T_air_in represents the fuel cell stack air inlet temperature in K. The heat dissipation value also includes other heat dissipation values, calculated using the following formula: Where Q_other represents other heat dissipation values ​​in W, k0 ranges from ±500 W, k1 ranges from 5W / K to 20W / K, and k2 ranges from 0 to 2000 in W·s / kg. k0, k1 and k2 represent coefficients. The heat load of the radiator is obtained by subtracting the heat dissipation value from the heat generated by the fuel cell stack. Calculate the logarithmic mean temperature difference, and divide the radiator heat load by the logarithmic mean temperature difference to obtain the radiator's actual heat transfer capacity. The calculation of the logarithmic mean temperature difference specifically includes: calculating the difference between the temperature of the coolant leaving the fuel cell stack and the temperature of the air inlet of the fuel cell stack to obtain a first difference value ΔT1, and calculating the difference between the coolant outlet temperature of the radiator and the air outlet temperature of the fuel cell stack to obtain a second difference value ΔT2, wherein the air inlet temperature of the fuel cell stack is taken as the ambient temperature, and the air outlet temperature of the fuel cell stack is taken as the fan outlet temperature. The logarithmic mean temperature difference ΔT_lm is calculated using the following formula: The unit of the logarithmic mean temperature difference is K, and the units of ΔT1 and ΔT2 are K. Calculate the baseline heat transfer capacity, divide the actual heat transfer capacity of the radiator by the baseline heat transfer capacity to obtain the fouling factor, and subtract the fouling factor from 1 to obtain the capacity loss. The baseline heat transfer capacity is calculated using the following formula: UA_ref(n_f,v) = UA_NTP(n_f)·(ρ_air / ρ_NTP)^α·(1 + k_v·v); Wherein, UA_ref(n_f,v) represents the reference heat transfer capacity in W / K, n_f represents the cooling fan speed in rpm, and UA_NTP(n_f) represents the ambient pressure value corresponding to n_f in the calibration table in W / K. The calibration table includes ambient pressure values ​​corresponding to different cooling fan speeds. In the calibration table, the cooling fan speeds are 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, and 5000, respectively, and the corresponding ambient pressure values ​​are 446, 643, 833, 1018, 1200, 1379, 1555, 1728, and 1900, respectively. The reference air density ρ_NTP = 1.18 kg / m³, and α = 0.

75. v represents the car's speed in km / h, air density ρ_air = (p_amb×1000) / (287·(T_amb+273.15)) in kg / m³, p_amb represents ambient pressure in kPa, and T_amb represents ambient temperature; When the clogging factor is less than the first value and the fan reference residual is greater than the fourth value, the heat dissipation capacity is judged to have decreased; or when the capacity loss is greater than the second value and the duration is greater than the third value, and the fan reference residual is also judged to be greater than the fourth value, the heat dissipation capacity is judged to have decreased; wherein, the first value ranges from 0.75 to 0.85, the second value ranges from 0.2, the third value ranges from 0.1 to 0.2, and the fourth value ranges from 30 to 120.

2. The method according to claim 1, characterized in that, The fan reference residual is calculated using the following formula: Where n_ref is the fan speed at which the heatsink achieves its actual heat transfer capacity, r_n represents the fan reference residual, and n_f represents the cooling fan speed.

3. The method according to claim 1, characterized in that, The numerical guardrail is set based on the first difference ΔT1 and the second difference ΔT2, using the following formula: When ΔT_lm = (ΔT1 + ΔT2) / 2; if ΔT1 ≤ 0 or ΔT2 ≤ 0, the diagnosis is paused.

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