Method for judging on-line activation of hydrogen fuel cell system

Abstract

The invention discloses a method for judging online activation of a hydrogen fuel cell system, and relates to the technical field of fuel cells. When the system runs, the running time of the low current density and the running time of the non-low current density are recorded respectively, and when the running time of the low current density reaches a certain value, the running time of the non-low current density is calculated by judging the ratio of the running time of the low current density to the total running time. And judging whether to enter the activation process or not according to the proportion of the electric energy generated by the hydrogen fuel cell system in the primary activation process to the SOC capacity value of the lithium battery. According to the method, the internal humidity of the galvanic pile is effectively adjusted, the galvanic pile runs under ideal conditions, and the performance of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a method for determining whether a hydrogen fuel cell system enters online activation. Background Art

[0002] In the field of new energy vehicles, hydrogen fuel cell systems are regarded as one of the important development directions of future transportation power systems due to their high efficiency, cleanliness and renewable characteristics. However, in practical applications, the operating conditions of hydrogen fuel cell vehicles are complex and changeable, which are not only affected by the driving habits of the driver, but also highly dependent on the vehicle's usage scenarios, such as urban road congestion, highway cruising, and driving under extreme weather conditions. These diverse operating conditions pose severe challenges to the performance and durability of hydrogen fuel cell systems, especially under the conditions of long-term low-electricity operation (i.e., low current density operation), the problem of system performance degradation is particularly prominent.

[0003] With the continuous development of hydrogen fuel cell technology, domestic and foreign researchers and automakers have invested a lot of resources to improve the durability and efficiency of fuel cell systems. In order to solve the performance degradation problem caused by long-term low-voltage operation, the existing technology has mainly explored the following aspects:

[0004] Water management optimization: Water management is a key link in the hydrogen fuel cell system, which is directly related to the wetness state and overall performance of the membrane inside the stack. The literature (Zhang, J. et al., 'Enhanced Water Management Strategies for Prolonging Lifetime of PEMFCs under Low Current Density Conditions', Journal of Power Sources, 2020.) proposes that by optimizing the design of the gas diffusion layer and enhancing the water transmission efficiency inside the stack, the problem of membrane drying during low current density operation can be effectively alleviated. In addition, some patents (such as publication number CN109638200A) also disclose that by adjusting the gas flow channel structure to achieve a more uniform water distribution, the performance stability of the fuel cell under low load can be improved.

[0005] Adjustment of operation strategy: To reduce the low-power operation time, some advanced control strategies have been developed. For example, the output power of the fuel cell is dynamically adjusted according to the actual driving needs of the vehicle to avoid long-term operation in the low-power range. At the same time, the energy distribution strategy is optimized in combination with the battery management system (BMS) and the energy recovery system (such as brake energy recovery) to reduce dependence on the fuel cell, thereby extending its service life.

[0006] Materials and technology innovation: Researchers are constantly seeking breakthroughs in key fuel cell materials, such as proton exchange membranes (PEMs), catalyst layers, and gas diffusion layers. The development of new membrane materials (such as membranes with higher water retention and mechanical strength) and the improvement of catalyst activity can alleviate the risk of membrane cracking under low electrical density to a certain extent. In addition, adaptive heating / cooling systems are also widely used in fuel cell systems to maintain the balance of temperature and moisture inside the stack, further improving system durability.

[0007] Fault diagnosis and early warning: Build an intelligent fault diagnosis and early warning system to monitor the operating status of the fuel cell system in real time. Once it is found that the low-electrical density operation time is too long or the membrane humidity is abnormal, an alarm will be immediately issued and corresponding measures will be taken, such as adjusting the operation strategy or performing maintenance, so as to avoid further deterioration of performance degradation.

[0008] In summary, the existing technology has effectively dealt with the performance degradation problem of hydrogen fuel cell systems under long-term low-power operation in various ways. However, with the continuous expansion of the new energy vehicle market and the increasing requirements of users for vehicle performance, continuous technological innovation and optimization are still necessary. It is urgent to further reduce the performance degradation of hydrogen fuel cell systems under complex working conditions to meet the commercialization process of hydrogen fuel cell technology. Summary of the invention

[0009] Based on the deficiencies in the prior art, the present invention introduces an online activation judgment strategy, that is, a method for judging whether a hydrogen fuel cell system enters online activation, which can effectively adjust the humidity inside the fuel cell stack, allow the fuel cell stack to operate under relatively ideal conditions, and improve the performance of the system.

[0010] When the system is running, the operating time of low current density and non-low current density are recorded respectively. When the low current density operating time reaches a certain value, the ratio of the low current density operating time to the total operating time is judged, and combined with the vehicle's lithium battery SOC value to determine whether to enter the activation process.

[0011] The specific technical solutions of the present invention are as follows:

[0012] The present invention provides a method for determining whether a hydrogen fuel cell system enters online activation, wherein the hydrogen fuel cell system is used in a vehicle power system, and the vehicle power system further includes a lithium battery, and the method is characterized in that the method comprises the following steps:

[0013] (1) Obtaining the ratio ΔS of the electric energy generated by the hydrogen fuel cell system to the SOC capacity value of the lithium battery in a primary activation process;

[0014] (2) Start the hydrogen fuel cell system, begin the timing cycle, record the cumulative duration of operation at low current density and the cumulative duration of operation at non-low current density. When the cumulative duration of operation at low current density reaches the set duration of one cycle, one timing cycle ends. Record the cumulative duration of operation at low current density at this time as T1, the duration of operation at non-low current density as T2, and the SOC capacity value of the lithium battery at this time as S0;

[0015] (3) If T1 / (T1 + T2) ≥ a and S0 + ΔS < b, where 60% < a < 80% and 75% < b < 80%, then the hydrogen fuel cell system enters the activation process; otherwise, it does not enter the activation process and starts a new timing cycle.

[0016] During the activation process of the fuel cell system, a certain amount of electrical energy is generated and used to charge the lithium battery through a DC charger. Therefore, it is necessary to determine whether the SOC of the lithium battery meets the activation process before activation. If the lithium battery S0 + ΔS is between 80% and 100%, the activation process cannot be carried out, which may damage the system.

[0017] Specifically, in step (1), when obtaining ΔS, first detect the amount of electricity Q1 generated when the hydrogen fuel cell system enters the activation process; the capacity of the lithium battery is Q2, and calculate ΔS = Q1 / Q2.

[0018] Preferably, in step (2), the standard for operation at low current density is that the current density is less than 0.8 - 0.9 A / cm 2 .

[0019] Tests have found that in the low current density range, the long-term steady-state operation performance of the system decreases relatively quickly, and in the high current density range, the long-term steady-state operation performance of the system decreases relatively slowly. Therefore, a current density of 0.8 - 0.9 A / cm2 is taken as the dividing line for judging high and low current densities in the activation strategy and is also the intermediate current density point of the system operation.

[0020] In addition, taking the high-speed working condition of a hydrogen energy heavy truck as an example, the general maintenance cycle is 5000 km, and the average speed is taken as 80 - 100 km / h, that is, running for 50 - 62.5 h, which can be appropriately adjusted according to the actual vehicle operation conditions. In the embodiment of the present invention, the set cycle duration of operation at low current density is taken as 50 h as an example.

[0021] Preferably, in step (2), a = 70%. b = 80%.

[0022] Specifically, the process of the activation process is as follows: The hydrogen fuel cell system starts to the idle running state, is loaded to 1.2 A / cm 2 , and runs for 2 min; then it is loaded to 1.6 A / cm 2, run for 3 minutes, then stop, which is regarded as a single cycle; after an interval of 5 minutes, start the next cycle. When the performance improvement (average single-cell voltage) between two cycles is less than 3%, stop the cycle, and the activation ends.

[0023] If the stack module is installed in a fuel cell system, when it is stored for a long time or its performance decays, the above cycle condition is used to activate the stack module. Increasing the current density helps to accelerate the performance recovery of the stack module. It is recommended to stop the cycle when the performance improvement between two cycles is less than 3%.

[0024] The present invention also provides a determination device for a hydrogen fuel cell system to enter online activation. The hydrogen fuel cell system is used for a vehicle power system, and the vehicle power system further includes a lithium battery. The determination device includes:

[0025] An acquisition unit, configured to acquire the electric quantity Q1 generated when detecting that the hydrogen fuel cell system enters the activation process, and the capacity Q2 of the lithium battery;

[0026] A recording unit, which starts the hydrogen fuel cell system and is configured to record the cumulative duration of low current density operation and the cumulative duration of non-low current density operation; when the cumulative duration of low current density operation reaches a set cycle duration, one timing cycle ends, and record the cumulative duration of low current density operation at this time as T1, the duration of non-low current density operation as T2, and the SOC capacity value of the lithium battery at this time as S0;

[0027] A processing unit, configured to process the data of the acquisition unit and the recording unit to obtain the result of whether to enter the activation process;

[0028] A result output unit, configured to output the result obtained by the processing unit;

[0029] When processing the data of the acquisition unit and the recording unit, if T1 / (T1 + T2) ≥ a and S0 + ΔS < b, where 60% < a < 80% and 75% < b < 80%, then the hydrogen fuel cell system enters the activation process; otherwise, it does not enter the activation process and starts a new timing cycle.

[0030] Advantages of the present invention:

[0031] By respectively recording the operation time of low current density and non-low current density during the system operation, when the operation time of low current density reaches a certain value, the present invention determines whether to enter the activation process by judging the ratio of the operation time of low current density to the total operation time and combining the proportion of the electric energy generated by the hydrogen fuel cell system in a single activation process to the SOC capacity value of the lithium battery. This method effectively adjusts the humidity inside the stack, enables the stack to operate under relatively ideal conditions, and improves the performance of the system. Description of the Drawings

[0032] Figure 1 It is the activation flow chart of the present invention.

[0033] Figure 2 0.5A / cm 2 Current density steady-state 1h operation performance diagram.

[0034] Figure 3 0.7A / cm 2 Current density steady-state 1h operation performance diagram.

[0035] Figure 4 0.9A / cm 2 Current density steady-state 1h operation performance diagram.

[0036] Figure 5 1.1A / cm 2 Current density steady-state 1h operation performance diagram.

[0037] Figure 6 The performance change diagram after running for 1h at different current densities. DETAILED DESCRIPTION

[0038] Example 1

[0039] The specific steps of 1h steady-state operation with different electrical densities are as follows:

[0040] The hydrogen fuel cell system was hot-started to idle speed and loaded to the target electric density point (0.5, 0.7, 0.9, 1.1A / cm 2 ), run at this voltage density point for 1 hour, and record the average single-chip voltage data during the process.

[0041] The result data is as Figure 2 to Figure 6 As shown in the figure, in the low current density range, the system's long-term 1h steady-state performance decreases rapidly, and in the high current density range, the system's long-term steady-state performance decreases slowly, so 0.8~0.9A / cm 2 The electric density is used as the dividing line between high and low electric density in the activation strategy.

[0042] Example 2

[0043] A method for determining whether a hydrogen fuel cell system enters online activation, the specific steps are as follows:

[0044] (1) First, the ratio of the power Q1 generated by the 130kW hydrogen fuel cell system entering the activation process to the total power of the lithium battery is 30%; the capacity Q2 of the lithium battery in the vehicle power system is 100%, and ΔS = Q1 / Q2 = 30% is calculated;

[0045] (2) Start the hydrogen fuel cell system, start the timing cycle, and record a value less than 0.8A / cm 2The cumulative time of low current density operation is greater than or equal to 0.8A / cm 2 The cumulative duration of non-low current density operation: when the cumulative duration of low current density operation reaches 50h, a timing cycle ends, and the cumulative low current density operation duration T1 is recorded as 50h, and the non-low current density operation duration T2 is 20h. At this time, the lithium battery SOC capacity value S0 is 30%;

[0046] (3) T1 / (T1+T2)=71.4%>60%, S0+ΔS=60%<75%, satisfying the conditions.

[0047] The hydrogen fuel cell system enters the activation process. The activation conditions are as follows: Figure 1 As shown, the specific steps of activation are as follows:

[0048] The hydrogen fuel cell system is started to idle state and the load is 1.2A / cm 2 , run for 2 minutes; then pull the load to 1.6A / cm 2 , run for 3 minutes, stop, as a single cycle; start the next cycle after an interval of 5 minutes. After 3 cycles, stop the cycle when the average single-chip voltage increases by less than 3% compared with the second cycle, and the activation is completed.

[0049] Example 3

[0050] A method for determining whether a hydrogen fuel cell system enters online activation, the specific steps are as follows:

[0051] (1) First, the ratio of the power Q1 generated by the 130kW hydrogen fuel cell system entering the activation process to the total power of the lithium battery is 30%; the capacity Q2 of the lithium battery in the vehicle power system is 100%, and ΔS = Q1 / Q2 = 30% is calculated;

[0052] (2) Start the hydrogen fuel cell system, start the timing cycle, and record a value less than 0.9A / cm 2 The cumulative duration of low current density operation and the cumulative duration of non-low current density operation greater than or equal to 0.9A / cm2. When the cumulative duration of low current density operation reaches 50h, a timing cycle ends, and the cumulative duration of low current density operation T1 is recorded as 50h, and the duration of non-low current density operation T2 is recorded as 20h. At this time, the lithium battery SOC capacity value S0 is 30%;

[0053] (3) T1 / (T1+T2)=71.4%>60%, S0+ΔS=60%<75%, satisfying the conditions.

[0054] The hydrogen fuel cell system enters the activation process. The activation conditions are as follows: Figure 1 As shown, the specific steps of activation are as follows:

[0055] The hydrogen fuel cell system is started to idle state and the load is 1.2A / cm 2 , run for 2 minutes; then pull the load to 1.6A / cm 2 , run for 3 minutes, stop, as a single cycle; start the next cycle after an interval of 5 minutes. After 3 cycles, stop the cycle when the average single-chip voltage increases by less than 3% compared with the second cycle, and the activation is completed.

[0056] Example 4

[0057] A method for determining whether a hydrogen fuel cell system enters online activation, the specific steps are as follows:

[0058] (1) First, the ratio of the power Q1 generated by the 130kW hydrogen fuel cell system entering the activation process to the total power of the lithium battery is 30%; the capacity Q2 of the lithium battery in the vehicle power system is 100%, and ΔS = Q1 / Q2 = 30% is calculated;

[0059] (2) Start the hydrogen fuel cell system, start the timing cycle, and record a value less than 0.8A / cm 2 The cumulative duration of low current density operation and the cumulative duration of non-low current density operation. When the cumulative duration of low current density operation reaches 50h, a timing cycle ends, and the cumulative duration of low current density operation T1 is recorded as 50h, and the duration of non-low current density operation T2 is recorded as 50h. At this time, the lithium battery SOC capacity value S0 is 60%;

[0060] (3) Calculate T1 / (T1+T2)=50%<60%, S0+ΔS=90%>80%, do not enter the activation process, and restart a timing cycle.

Claims

1. A method for determining whether a hydrogen fuel cell system enters online activation, wherein the hydrogen fuel cell system is used in a vehicle power system, and the vehicle power system also includes a lithium battery, characterized in that: It includes the following steps: (1) Obtain the proportion ΔS of the electric energy generated by the hydrogen fuel cell system in the one-time activation process to the SOC capacity value of the lithium battery; (2) Start the hydrogen fuel cell system, start the timing cycle, record the cumulative duration of low current density operation and the cumulative duration of non-low current density operation. When the cumulative duration of low current density operation reaches the set duration of one cycle, one timing cycle ends. Record the cumulative duration of low current density operation at this time as T1, the duration of non-low current density operation as T2, and the SOC capacity value of the lithium battery at this time as S0; (3) If T1 / (T1 + T2) ≥ a and S0 + ΔS < b, where 60% < a ≤ 80% and 75% < b < 80%, then the hydrogen fuel cell system enters the activation process; Otherwise, do not enter the activation process and start a new timing cycle.

2. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: In step (1), when obtaining ΔS, first detect the electric quantity Q1 generated when the hydrogen fuel cell system enters the activation process; the capacity of the lithium battery is Q2, and calculate ΔS = Q1 / Q2.

3. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: In step (2), the standard for low current density operation is that the current density is less than 0.8-0.9 A / cm 2 .

4. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: In step (2), the set duration of one cycle of low current density operation is 50h.

5. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: In step (2), a = 70%.

6. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: b＝80％。 7. The method for determining whether a hydrogen fuel cell system enters online activation according to claim 1, characterized in that: The activation process is as follows: the hydrogen fuel cell system is started to idle state, and the load is pulled to 1.2A / cm 2 , run for 2 minutes; Then pull the load to 1.6A / cm 2 , run for 3 minutes, then stop, as a single cycle; Start the next cycle after an interval of 5 minutes. Stop the cycle when the average single-cell voltage increase between two cycles is < 3%, and the activation ends.

8. A device for determining whether a hydrogen fuel cell system enters online activation, wherein the hydrogen fuel cell system is used in a vehicle power system, and the vehicle power system further includes a lithium battery, characterized in that: The determination device includes: An acquisition unit for acquiring the electric quantity Q1 generated when detecting that the hydrogen fuel cell system enters the activation process and the capacity Q2 of the lithium battery; A recording unit for starting the hydrogen fuel cell system and recording the cumulative duration of low current density operation and the cumulative duration of non-low current density operation; when the cumulative duration of low current density operation reaches the set duration of one cycle, one timing cycle ends. Record the cumulative duration of low current density operation at this time as T1, the duration of non-low current density operation as T2, and the SOC capacity value of the lithium battery at this time as S0; A processing unit for processing the data of the acquisition unit and the recording unit to obtain the result of whether to enter the activation process; A result output unit for outputting the result obtained by the processing unit; When processing the data of the acquisition unit and the recording unit, if T1 / (T1 + T2) ≥ a and S0 + ΔS < b, where 60% < a < 80% and 75% < b < 80%, then the hydrogen fuel cell system enters the activation process; otherwise, do not enter the activation process and start a new timing cycle.

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