Fuel cell stack performance self-recovery control method and system and vehicle

Abstract

The invention provides a fuel cell stack performance self-recovery control method and system and a vehicle, and relates to the technical field of fuel cells, and the method comprises the steps: obtaining the membrane resistance of each single cell in a fuel cell; and judging the proportion of the number of the single cells of which the membrane resistance is greater than the resistance threshold in the total number, judging whether the fuel cell is in a normal operation state according to the proportion, and executing preset operation on the fuel cell according to a judgment result. The normal operation state of the fuel cell can be ensured.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell technology, and in particular to a fuel cell stack performance self-recovery control method, system and vehicle. Background Art

[0002] A fuel cell is a chemical device that converts the chemical energy of a fuel directly into electrical energy, among which hydrogen fuel cells are the most widely used fuel cells. Due to the high cost of hydrogen, lack of hydrogen sources, and few hydrogen refueling stations, existing fuel cell vehicles are not in a hydrogen-electric operation state for a long time, which will cause the membrane electrode (MEA), a core component in the fuel cell system, to lose water. However, MEA uses water molecules as a carrier to conduct protons, and the membrane will become dry after the water is lost. When membrane drying occurs, the proton conductivity will drop significantly, affecting the normal operation of the battery; at the same time, the membrane resistance increases, and the heat generated when the current passes through the membrane increases. In severe cases, it will cause local overheating and burn the proton exchange membrane. If the membrane is in a dry state for a long time, the dry area will continue to expand, eventually causing the entire membrane to dry and rupture, causing irreversible damage. Therefore, how to reduce or avoid the damage caused by membrane drying to fuel cells is a problem that the prior art needs to solve. Summary of the invention

[0003] In order to address the deficiencies of the prior art, an object of the present invention is to provide a fuel cell stack performance self-recovery control method, system and vehicle to proactively resolve the fuel cell membrane dry problem and ensure the normal operation of the fuel cell.

[0004] In order to achieve the above objectives, according to some embodiments, a first aspect of the present invention provides a fuel cell stack performance self-recovery control method, comprising:

[0005] Obtaining the membrane resistance of each single cell in the fuel cell;

[0006] The ratio of the number of battery cells whose membrane resistance is greater than the resistance threshold to the total number of cells is determined, whether the fuel cell is in a normal operating state is determined based on the ratio, and a preset operation is performed on the fuel cell based on the determination result.

[0007] Preferably, if the ratio is greater than a first ratio threshold, a first alarm action is executed; if the ratio is greater than a second ratio threshold, a second alarm action is executed; the second ratio threshold is greater than the first ratio threshold; the second alarm action includes prompting the driver to manually confirm whether to switch the vehicle operation mode to the hydrogen-electric mode.

[0008] Preferably, when the second alarm action is executed and no switching instruction to switch to the hydrogen-electric operation mode is received from the driver within a set power-on cycle, the vehicle is controlled to autonomously switch to the hydrogen-electric mode at the start of the next power-on cycle.

[0009] Preferably, in the hydrogen-electric mode, the mean square error of the membrane resistance of each single cell in the fuel cell is calculated. If the obtained mean square error is greater than the mean square error set threshold and the vehicle state meets the activation conditions, the vehicle is controlled to enter the hydrogen-electric activation mode to activate the fuel cell.

[0010] Preferably, activating the fuel cell comprises:

[0011] Control the load current to start from the current corresponding to the idle power and increase it upwards with the set step length;

[0012] According to the response activation power corresponding to each current value in the current pull-up process, the preset volt-ampere characteristic curve is compared with the corresponding power point in the actual volt-ampere characteristic curve to obtain the voltage compensation value of each power point;

[0013] Determining activation time according to the voltage compensation value;

[0014] The fuel cell is activated according to the determined activation time.

[0015] Preferably, when the error of the voltage compensation value at each power point is smaller than the set error, and the mean square deviation of the membrane resistance at each power point is smaller than the mean square deviation set threshold, the activation process is completed.

[0016] Preferably, it also includes:

[0017] Get the maximum continuous operation time of the fuel cell during the last operation;

[0018] If the maximum continuous operation time is greater than a first set time threshold, a reversible self-repair process is performed on the fuel cell.

[0019] Preferably, the reversible self-repairing process includes controlling the oxygen and air flow difference between the cathode and anode of the fuel cell so that the hydrogen evolution at the cathode reacts with the oxygen-containing energy group, and the reversible self-repairing process is completed after a second set time threshold.

[0020] A second aspect of the present invention provides a fuel cell stack performance self-recovery control system, comprising:

[0021] A membrane resistance monitoring module is used to obtain the membrane resistance of each single cell in the fuel cell;

[0022] The control module is used to determine the ratio of the number of battery cells with membrane resistance greater than the resistance threshold to the total number of cells, determine whether the fuel cell is in a normal operating state based on the ratio, and perform a preset operation on the fuel cell based on the determination result.

[0023] A third aspect of the present invention provides a vehicle comprising a fuel cell, wherein the vehicle is controlled by a fuel cell stack performance self-recovery control method provided in the first aspect, or the vehicle comprises a fuel cell stack performance self-recovery control system provided in the second aspect.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a fuel cell stack performance self-recovery control method, system and vehicle. Based on the monitoring of the membrane resistance of each single cell in the fuel cell, the membrane dry state of the fuel cell can be accurately and quickly determined, so that the fuel cell stack performance can be self-recovered according to the judgment result. When it is judged that the risk of membrane dryness is high and irreversible damage to the fuel cell may be caused, it is automatically switched to the hydrogen-electric mode to activate the fuel cell. During the activation process, a personalized activation strategy is implemented according to the actual state of the battery, and the activation time is determined according to the preset volt-ampere characteristic curve and the actual volt-ampere characteristic curve, so as to continuously correct the polarization curve until the activation is completed, and the battery can be targetedly activated, thereby improving the activation efficiency and ensuring the activation effect, thereby ensuring that the fuel cell is in a normal operating state. In addition, considering the risk of catalyst poisoning when the fuel cell is continuously running for a long time, the present invention also performs reversible self-recovery on the fuel cell according to the maximum continuous operation time of the last operation.

[0026] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 A schematic diagram of the overall process of a fuel cell stack performance self-recovery control method provided in Embodiment 1 of the present invention;

[0029] Figure 2 A schematic diagram of a reversible self-repair process in a fuel cell stack performance self-recovery control method provided in Embodiment 1 of the present invention;

[0030] Figure 3 A schematic diagram of a fuel cell activation process in a fuel cell stack performance self-recovery control method provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] Embodiment 1

[0033] Embodiment 1 of the present invention provides a fuel cell stack performance self-recovery control method, such as Figure 1-Figure 3 As shown, including:

[0034] Obtaining the membrane resistance of each single cell in the fuel cell;

[0035] The ratio of the number of battery cells whose membrane resistance is greater than the resistance threshold to the total number of cells is determined, whether the fuel cell is in a normal operating state is determined based on the ratio, and a preset operation is performed on the fuel cell based on the determination result.

[0036] This embodiment monitors the state of the fuel cell from the vehicle level, and determines the proportion of abnormal cell units by monitoring the membrane resistance of each single cell in the fuel cell, thereby determining whether the entire fuel cell is in a normal operating state. When the vehicle is under normal high voltage, the impedance monitor monitors and collects the membrane resistance Rs of all single cells, and determines the proportion of the number of cells greater than the preset resistance threshold Rs1. If the proportion of the number of cells satisfying Rs>Rs1 to the total number of cells is greater than the first proportion threshold a, the first alarm action is executed, and at the beginning of each power-on cycle, a first-level fault warning is issued through the vehicle instrument for a period of t0 to warn the driver; if the proportion of the number of cells satisfying Rs>Rs1 to the total number of cells is greater than the second proportion threshold b, b>a, the second alarm action is executed, and at the beginning of each power-on cycle, a second-level fault warning is issued through the vehicle instrument, a flashing light alarm is added, and a manual confirmation option for the driver is added to prompt the driver to switch the vehicle operation mode to the hydrogen-electric mode and activate it. The second-level fault warning lasts for t1 time, t1>t0.

[0037] The vehicle's fuel cell control unit FCU obtains the membrane resistance of all single cells in real time through an impedance monitor, and feeds back the monitoring results to the VCU in real time through interaction with the vehicle controller VCU. The vehicle controller VCU monitors and stores the membrane resistance of all single cells of the current fuel cell, screens the membrane resistance and calculates the abnormal proportion of membrane resistance in real time, and always keeps the maximum proportion for storage. Since the membrane resistance of the fuel cell is closely related to factors such as the stack environment and whether it is running or not, the membrane resistance parameter data of the single cell changes all the time. The membrane resistance is continuously monitored, the proportion of membrane resistance abnormality at each moment is recorded, and the proportion of the largest abnormality is stored, thereby recording the degree to which the fuel cell is in the worst state. For example, if the proportion of monomers that meet Rs>Rs1 at the previous moment accounts for 2% of the total number of pieces. The current proportion is 3%, and the 3% value is stored after comparison.

[0038] When a level 2 fault warning is issued and the driver does not confirm the current power-on cycle, that is, the vehicle's operating mode is not switched, the VCU determines the number of unconfirmed power-on cycles and automatically switches the vehicle's operating mode to the hydrogen-electric mode at the beginning of N power-on cycles to activate the fuel cell.

[0039] After switching to the hydrogen-electric mode, the VCU determines whether the fuel cell meets the startup state. When the SOC of the power battery is less than the set threshold a1%, the hydrogen HSOC of the hydrogen system is greater than the set threshold b1%, and the power battery allows charging and there are no serious faults in the vehicle systems, the VCU outputs the fuel cell startup command and sends the starting activation current I0 and the set step length △I of each activation current increase during the activation process to the FCU. Before the fuel cell is started, the mean square deviation σ of the membrane resistance of each single cell in the fuel cell is monitored and calculated, and whether the fuel cell needs to be activated is determined based on σ.

[0040] The fuel cell control strategy built into the VCU has two modes. One is the normal operating mode of the fuel cell, where the mean square error σ is less than the mean square error setting threshold σ1. At this time, power requests are made according to different power battery SOC interval modes. The other is the hydrogen-electric activation mode, where the mean square error σ is greater than or equal to the mean square error setting threshold σ1. At this time, the fuel cell needs to be activated.

[0041] If the activation conditions are met, the fuel cell is activated in the hydrogen-electric activation mode. The load current is pulled up from the initial activation current I0, that is, the current corresponding to the idle power, with a step size of ΔI0. At the same time, the mean square error of the membrane resistance in each power range is continuously corrected through the deviation-compensation curve fitting algorithm until the voltage and current values ​​meet the polarization curve. Finally, when the load reaches the rated current, the rated power is stably output and then the fuel cell is shut down to complete an activation.

[0042] Deviation type - compensation curve fitting algorithm, based on the preset UI* (volt-ampere characteristic curve) curve and the actual UI (volt-ampere characteristic curve), by calculating the voltage compensation value ΔU at each power point to determine the activation time T act During the activation process, the activation current is pulled up from I0 to I1, I2, ..., I n , FCU outputs the response activation power P1, P2, ..., P according to the load activation current and the preset polarization curve of the fuel cell. n VCU compares the preset UI* (volt-ampere characteristic curve) two-dimensional MAP with the actual UI (volt-ampere characteristic curve) two-dimensional MAP according to the bias-compensation curve fitting algorithm to obtain the voltage compensation values ​​ΔU1, ΔU2, ..., ΔU at each power point. n , and determine the activation time T required for this power segment based on the compensation value act, until the actual UI of each power point is infinitely close to the preset UI*, that is, the voltage compensation value error ratio is less than %, and the mean square error of membrane resistance at all power points σ<σ1, the activation process is completed. Among them, the preset UI* is the polarization curve measured when the fuel cell leaves the factory, which represents the performance of the fuel cell stack; the actual UI is the current volt-ampere characteristic curve of the fuel cell. Due to the attenuation of the fuel cell, under the same load activation current, the difference between the current actual voltage of the fuel cell and the corresponding theoretical voltage in the polarization curve measured at the factory is the voltage compensation value. Different activation times are determined according to the different voltage compensation values ​​at different power points.

[0043] The activation time is proportional to the voltage compensation value and is calculated using the following formula:

[0044] T act =k×ΔU, k≥1;

[0045] Among them, T act represents the activation time, k represents the proportional coefficient, k=U* / U, U* is the theoretical voltage under the current load activation current, U is the actual voltage under the load activation current, and ΔU represents the voltage compensation value.

[0046] After activation is completed, the VCU strategy enters the normal operation mode of the fuel cell. The FCU responds to VCU instructions and power requests corresponding to the SOC interval and continues to operate until the conditions are not met or it is manually shut down.

[0047] Simply relying on a single set time may not meet the activation requirements under different currents. Therefore, this embodiment dynamically adjusts the activation time and determines the activation time according to the voltage deviation value, which can comprehensively and efficiently improve the performance of the fuel cell and restore it to the optimal state. The algorithm has strong adaptability, fast response speed, and small error, and can restore the fuel cell state to the optimal state to a great extent. It plays a key role in protecting the life of the stack and improving its performance.

[0048] After a fuel cell has been running for a long time, for example, under normal circumstances, the fuel cell continues to work for a long time, or after the fuel cell is activated or the user receives an alarm, the user allows the fuel cell to work continuously for a long time to ensure the activity of the fuel cell. At this time, the fuel cell may also have the problem of catalyst poisoning and deactivation. Based on this, in some embodiments, the maximum continuous operation time of the fuel cell is further monitored. The VCU stores and records the most recent maximum continuous operation time T of the fuel cell. rmax , if T rmax Greater than or equal to the first set time threshold T r0When the next stack is started, the VCU requests the fuel cell to enter the reversible self-repair mode, and the instrument displays the fuel cell mode as starting. The reversible self-repair mode is the cathode hydrogen absorption effect produced by the fuel cell by controlling the oxygen and air flow difference. When the fuel cell enters the reversible self-repair mode, the time T run Reaching the second set time threshold T r1 After the reversible self-repair process of the fuel cell is completed, the fuel cell begins to respond to normal power requests and outputs power, and the operation mode changes from starting to running.

[0049] The following describes in detail the control process in the three states, taking the case where the driver and passengers manually confirm the switch to the hydrogen-electric mode, the VCU automatically switches to the hydrogen-electric mode, and the VCU controls the entry into the reversible self-repair mode as examples.

[0050] like Figure 1 As shown, when the vehicle has no serious level (level 4) faults and meets the high voltage conditions for the whole vehicle, the instrument will display the READY signal after the whole vehicle is high voltage. After the whole vehicle is high voltage, the impedance monitor monitors and collects the membrane resistance Rs of all single cells; when the ratio of the number of single cells with the monitored membrane resistance Rs>Rs1 to the total number of cells reaches a%, the instrument will issue a level 1 fault content warning at the beginning of each power-on cycle, and the alarm duration is t0; when the ratio of the number of single cells with the membrane resistance Rs>Rs1 to the total number of cells reaches b%, the instrument will issue a level 2 fault content warning at the beginning of each power-on cycle, use flashing lights to warn, and the driver needs to manually touch the screen to confirm, the alarm duration is t1, and t0 is less than t1. If the driver or passenger manually touches the screen to confirm and switch to the hydrogen-electric mode, the VCU receives the command and makes a judgment. If the power battery SOC is less than a1%, the hydrogen system hydrogen HSOC is greater than b1%, the power battery is allowed to be charged, and there are no serious faults in the vehicle systems, the VCU outputs the fuel cell stack control command, the initial activation current I0, and the command to increase the current by ΔI. The FCU enters the hydrogen-electric activation mode and responds to the load activation current according to its own conditions. The current is increased from I0 by ΔI. The FCU outputs the response activation power according to the load activation current. The VCU calculates the voltage compensation value of each power point, and determines the activation time T required for the power segment according to the voltage compensation value. act , until the actual UI at each power point is infinitely close to the preset UI*, that is, the voltage compensation value error ratio is less than %, and the mean square error of membrane resistance at all power points σ<σ1, the activation process is completed. After the activation is completed, the fuel cell enters the normal operation mode, and the FCU responds to the VCU command and the power request of the corresponding SOC interval and continues to operate until the conditions are not met or it is manually shut down.

[0051] If no manual touch screen confirmation operation is received from the driver when a secondary fault content warning is issued, and no manual touch screen confirmation operation is received from the driver for N consecutive power-on cycles, the VCU automatically confirms entry into the hydrogen-electric mode at the beginning of the next power-on cycle and determines whether the conditions for entering the hydrogen-electric activation mode are met.

[0052] After the vehicle is high-voltage, if the fuel cell is switched to hydrogen-electric mode and the fuel cell is started, the VCU will first detect the most recent maximum continuous operation time T of the stored fuel cell. rmax , when T rmax Greater than or equal to the set threshold T r0 (For example, it can be set to 15 hours), before the fuel cell system starts, it first enters the reversible self-repair mode, and the instrument shows that the fuel cell mode is starting, with no actual power output. At this time, the FCU controls the oxygen and air flow difference to produce a cathode hydrogen absorption effect, so that hydrogen fully reacts with the oxygen-containing energy groups on the proton exchange membrane, improves the activity of the catalyst, and activates and rewet the membrane electrode, thereby improving the performance and efficiency of the fuel cell. When entering the reversible self-repair mode time T run More than T r1 When the reversible self-repair process is completed (for example, 10 minutes), the fuel cell enters normal operating mode, and the FCU responds to VCU instructions and power requests corresponding to the SOC interval and continues to operate until the conditions are not met or it is manually shut down.

[0053] In order to prevent the fuel cell from being in an abnormal state such as membrane drying or poisoning for a long time, which would affect the battery performance, this embodiment proposes to execute a corresponding control strategy at the vehicle level to realize active judgment and intervention on the dry state of the fuel cell membrane, thereby automatically solving the problems of fuel cell catalyst poisoning and deactivation and membrane drying, so that the fuel cell is always in an ideal normal operating state, reducing the failure rate and improving the life of the fuel cell system and the reliability of the vehicle operation.

[0054] Embodiment 2

[0055] This embodiment provides a fuel cell stack performance self-recovery control system, including:

[0056] A membrane resistance monitoring module is used to obtain the membrane resistance of each single cell in the fuel cell;

[0057] The control module is used to determine the ratio of the number of battery cells with membrane resistance greater than the resistance threshold to the total number of cells, determine whether the fuel cell is in a normal operating state based on the ratio, and perform a preset operation on the fuel cell based on the determination result.

[0058] In some embodiments, the membrane resistance monitoring module uses an impedance monitor to monitor and collect membrane resistance data of all single cells in the fuel cell stack; the control module includes a vehicle controller (VCU) and a fuel cell control unit (FCU), which cooperate to realize the monitoring of the fuel cell status and the switching of the vehicle operation mode.

[0059] It should be noted here that the various modules in this embodiment correspond one-to-one to the steps of the method in Example 1, and the specific implementation process is the same, which will not be repeated here.

[0060] Embodiment 3

[0061] This embodiment provides a vehicle, which is a hydrogen fuel cell vehicle. The vehicle is controlled by a fuel cell stack performance self-recovery control method provided in Embodiment 1, or the vehicle includes a fuel cell stack performance self-recovery control system provided in Embodiment 2.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fuel cell stack performance self-recovery control method, characterized in that: include: Obtaining the membrane resistance of each single cell in the fuel cell; The ratio of the number of battery cells whose membrane resistance is greater than the resistance threshold to the total number of cells is determined, whether the fuel cell is in a normal operating state is determined based on the ratio, and a preset operation is performed on the fuel cell based on the determination result.

2. A fuel cell stack performance self-recovery control method according to claim 1, characterized in that: If the ratio is greater than a first ratio threshold, a first alarm action is executed; if the ratio is greater than a second ratio threshold, a second alarm action is executed; the second ratio threshold is greater than the first ratio threshold; the second alarm action includes prompting the driver to manually confirm whether to switch the vehicle operation mode to the hydrogen-electric mode.

3. A fuel cell stack performance self-recovery control method as claimed in claim 2, characterized in that: When the second alarm action is executed and no switching instruction from the driver to switch to the hydrogen-electric operation mode is received within a set power-on cycle, the vehicle is controlled to autonomously switch to the hydrogen-electric mode at the start of the next power-on cycle.

4. A fuel cell stack performance self-recovery control method as claimed in claim 2 or 3, characterized in that: In the hydrogen-electric mode, the mean square error of the membrane resistance of each single cell in the fuel cell is calculated. If the mean square error obtained is greater than the set mean square error threshold and the vehicle state meets the activation conditions, the vehicle is controlled to enter the hydrogen-electric activation mode to activate the fuel cell.

5. A fuel cell stack performance self-recovery control method as claimed in claim 4, characterized in that: Activate the fuel cell, including: Control the load current to start from the current corresponding to the idle power and increase it upwards with the set step length; According to the response activation power corresponding to each current value in the current pull-up process, the preset volt-ampere characteristic curve is compared with the corresponding power point in the actual volt-ampere characteristic curve to obtain the voltage compensation value of each power point; Determining activation time according to the voltage compensation value; The fuel cell is activated according to the determined activation time.

6. A fuel cell stack performance self-recovery control method as claimed in claim 5, characterized in that: When the error of the voltage compensation value at each power point is less than the set error, and the mean square deviation of the membrane resistance at each power point is less than the mean square deviation set threshold, the activation process is completed.

7. A fuel cell stack performance self-recovery control method according to claim 1, characterized in that: Also includes: Get the maximum continuous operation time of the fuel cell during the last operation; If the maximum continuous operation time is greater than a first set time threshold, a reversible self-repair process is performed on the fuel cell.

8. A fuel cell stack performance self-recovery control method as claimed in claim 7, characterized in that: The reversible self-repairing process includes controlling the oxygen and air flow difference between the cathode and anode of the fuel cell so that the cathode hydrogen release reacts with the oxygen-containing energy group, and the reversible self-repairing process is completed after the second set time threshold is continued.

9. A fuel cell stack performance self-recovery control system, characterized in that: include: A membrane resistance monitoring module is used to obtain the membrane resistance of each single cell in the fuel cell; The control module is used to determine the ratio of the number of battery cells with membrane resistance greater than the resistance threshold to the total number of cells, determine whether the fuel cell is in a normal operating state based on the ratio, and perform a preset operation on the fuel cell based on the determination result.

10. A vehicle comprising a fuel cell, characterized in that: The vehicle is controlled by a fuel cell stack performance self-recovery control method as described in any one of claims 1 to 8, or the vehicle includes a fuel cell stack performance self-recovery control system as described in claim 9.

Images