Idling standby operation voltage control method of fuel cell system

Abstract

The invention relates to an idling standby operation voltage control method for a fuel cell system, which comprises the following steps of: receiving a shutdown standby instruction by the fuel cell system, controlling a pile entering stop valve and a back pressure valve in an air path so as to cut off air from entering a fuel cell pile, and keeping hydrogen and circulation in a hydrogen path, so that the pile voltage is reduced to a reasonable value; and entering a voltage maintaining stage. A small amount of external air is introduced into an electric pile by adjusting switches of an inlet pile stop valve and a back pressure valve, the voltage of the electric pile is maintained in a reasonable interval in combination with self-discharge of the electric pile, and then a starting command is received to enable a fuel cell system to enter a starting program. Compared with the prior art, the fuel cell can be prevented from outputting power outwards in the standby process, meanwhile, due to the fact that the fuel cell only naturally discharges to consume trace hydrogen, the wet state is kept, and restart preparation is made. In addition, the problems that the fuel cell is frequently started and swept and the power cell is too small and cannot receive electric quantity when the vehicle is idled and parked can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell systems, and in particular to a method for controlling the idle standby operation voltage of a fuel cell system. Background Art

[0002] During the operation of fuel cell vehicles, there are idling situations such as waiting for traffic lights or parking on the roadside. During this period, the vehicle is not running and the required fuel cell power supply is very little.

[0003] Generally, fuel cell vehicles are equipped with power batteries to supplement the power demand when the vehicle is loaded and to buffer the output power of the fuel cell when the load is reduced. However, when the power battery capacity of the fuel cell vehicle is small and cannot withstand high-power charging, it is necessary to reduce the idle output power of the fuel cell or stop the output power of the fuel cell system when the vehicle is idling.

[0004] However, when the fuel cell operates at low power, the current is small and the voltage is high, resulting in a high potential situation, which is not good for the fuel cell catalyst and carbon carrier. Before high-potential and corrosion-resistant materials are widely used, it is still necessary to avoid the influence of high potential as much as possible.

[0005] If the fuel cell chooses to shut down normally, shutdown purging may occur, which requires hydrogen and air purging of the anode and cathode to remove liquid water from the stack for the next normal start. Shutting down and purging the fuel cell system simply for idling will lead to frequent starts and stops, which is an important reason for the degradation of fuel cell performance. At the same time, when the vehicle is driving again, the fuel cell system needs time to start and then respond to the vehicle's power demand, which causes a certain delay.

[0006] Therefore, it is urgent to study a control method for the idle standby operating voltage of a fuel cell system, so that when the vehicle is in a parked idling state, the fuel cell system can be put into standby mode in a targeted manner, and can quickly respond to the required power and generate electricity, thereby meeting the parking idling of the fuel cell vehicle, avoiding frequent starting and stopping of the fuel cell system, and extending its life. Summary of the invention

[0007] The purpose of the present invention is to provide a method for controlling the idle standby voltage of a fuel cell system in order to overcome the defects of the above-mentioned prior art. The amount of external air entering the stack is controlled by intermittently opening and closing the stack inlet shut-off valve and the back pressure valve. At the same time, the lower hydrogen pressure and circulation volume on the hydrogen side are controlled, and combined with the self-discharge of the stack, the average voltage of the stack is maintained at about 0.76V and basically no power is output to the outside.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The present invention provides a method for controlling the idle standby voltage of a fuel cell system, the control method comprising:

[0010] The fuel cell system receives the shutdown standby command, controls the stack shutoff valve and back pressure valve in the air path to cut off the air from entering the fuel cell stack, and maintains the hydrogen circulation in the hydrogen path, so that the stack voltage drops to a reasonable value and enters the voltage maintenance stage;

[0011] Adjust the switches of the stack entry shut-off valve and the back-pressure valve to introduce a small amount of external air into the fuel cell stack, and combine the self-discharge of the fuel cell stack to maintain the stack voltage within a reasonable range. Then receive the start command to allow the fuel cell system to enter the start-up procedure.

[0012] Furthermore, the hydrogen circuit includes a hydrogen supply module and a circulation pump, and the hydrogen circuit is used to maintain the pressure and flow rate on the hydrogen side of the fuel cell stack during the voltage maintenance stage to meet the trace amount of hydrogen consumed during the self-discharge process of the fuel cell stack.

[0013] Furthermore, the process of reducing the stack voltage to a reasonable value includes: adjusting the load current to 10A, the stack hydrogen pressure to 6kPa, maintaining the idle speed of the circulating pump at 600rpm, stopping the air compressor, closing the stack shut-off valve and the back pressure valve, so that the stack voltage drops to a reasonable value.

[0014] Furthermore, in the voltage maintenance stage, the average voltage of the battery stack is 0.76V, the load current is 0A, and no power is output to the outside.

[0015] Furthermore, in the voltage maintenance stage, when the average voltage of the stack is less than 0.72V, the stack inlet shut-off valve and the back-pressure valve are opened by 30% to allow air to flow in, thereby increasing the stack voltage.

[0016] Furthermore, in the voltage maintenance stage, when the average voltage of the fuel cell stack is greater than 0.8V, the stack entry shutoff valve and the back pressure valve are closed to prevent air from entering the fuel cell stack, so that the fuel cell stack consumes oxygen in the air and reduces the self-discharge voltage.

[0017] Furthermore, when the stack shut-off valve and the back pressure valve are opened to 30% and the average voltage of the fuel cell stack is less than 0.7V, the air compressor and the air bypass valve are turned on to deliver air into the fuel cell stack, thereby increasing the voltage of the fuel cell stack.

[0018] Furthermore, when the air compressor and the air bypass valve are turned on, the average voltage of the fuel cell stack is greater than 0.8V, then the air bypass valve, the air compressor, the stack shut-off valve and the back pressure valve are closed.

[0019] Furthermore, when the fuel cell system receives an idle standby command, the fuel cell system does not perform purging, but quickly reduces the operating voltage of the stack by discharging a load current of 10A and stopping the air supply, so that the humidity state in the stack remains consistent with that before standby.

[0020] Furthermore, the air circuit also includes an air compressor and an air bypass valve, and the air compressor and the air bypass valve are used to transport a small amount of air in the atmosphere to the fuel cell stack.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] The present invention enters the standby program by receiving an external shutdown standby demand, during which the amount of external air entering the stack is controlled by intermittent opening and closing of the stack entry cutoff valve and the back pressure valve. At the same time, the lower hydrogen pressure and circulation volume on the hydrogen side are controlled, and combined with the self-discharge of the stack, the average voltage of the stack is maintained at about 0.76V and basically no power is output to the outside. The present invention can quickly respond to external start commands and output power to meet the parking idling of fuel cell vehicles, and the fuel cell system avoids frequent start and stop, thereby extending the life. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the fuel cell system architecture in Example 1;

[0024] Figure 2 This is a process diagram of normal shutdown and restart of the fuel cell system in Example 1;

[0025] Figure 3 This is a logic diagram of the idle standby operation voltage control method of the fuel cell system in Example 1;

[0026] Figure 4 This is a diagram showing the effect of the fuel cell system being shut down and restarted after using the idle standby operation voltage control method in Example 1.

[0027] Figure 1 Description of the mark in:

[0028] 1-air filter, 2-air flow meter, 3-air compressor, 4-intercooler, 5-air bypass valve, 6-humidifier, 7-inlet temperature and pressure integrated sensor, 8-inlet stop valve, 9-outlet temperature and pressure integrated sensor, 10-back pressure valve, 11-hydrogen inlet solenoid valve, 12-hydrogen supply module, 13-hydrogen pressure sensor, 14-water separator, 15-hydrogen circulation pump, 16-drain valve, 17-exhaust valve, 18-fuel cell module, 19-current and voltage sensor, 20-mixing silencer. DETAILED DESCRIPTION

[0029] The specific implementation methods of the present invention are described in detail below through examples. These examples are implemented on the premise of the scheme described in the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0030] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Any features such as component models, material names, connection structures, preparation methods, materials, structures or composition ratios not clearly described in this technical solution are deemed to be common technical features disclosed in the prior art.

[0031] Figure 1 It is a schematic diagram of the fuel cell system architecture. When the fuel cell system is working normally, the air compressor inhales external air, the air filter filters impurities in the air, and the air flow meter 2 measures the amount of air entering the fuel cell system. The intercooler 4 cools the air at the rear end of the air compressor, and the humidifier 6 is used to humidify the air entering the stack module 18. The inlet temperature and pressure integrated sensor 7 and the outlet temperature and pressure integrated sensor 9 measure the air temperature and pressure entering and leaving the stack respectively. The shut-off valve 8 is used to close after shutdown to prevent air from entering the stack inlet. The back pressure valve 10 is used to adjust the air pressure and close after shutdown to prevent air from entering from the stack outlet.

[0032] When the fuel cell system is operating normally, the hydrogen inlet solenoid valve 11 is opened to allow external hydrogen to enter the system, the hydrogen supply module 12 replenishes hydrogen to the system according to the hydrogen pressure sensor 13, the water separator 14 separates the liquid water at the outlet of the stack module 18, and the gaseous water circulates to the inlet of the stack module 18 through the hydrogen circulation pump 15. The drain valve 16 and the exhaust valve 17 are opened at intervals to discharge liquid water, hydrogen and nitrogen permeated from the air side.

[0033] Figure 2 This is a process diagram for the normal shutdown and restart of the fuel cell system. When the fuel cell is shut down normally, it is necessary to first reduce the load to a smaller current for shutdown purge, so as to blow out the liquid water in the stack and reduce the humidity in the stack. During this process, the air compressor 3 maintains a certain speed, the back pressure valve 10 provides a certain opening, and the excess air flows through the stack module 18. The inlet temperature and pressure integrated sensor 7 and the outlet temperature and pressure integrated sensor 9 measure the temperature and pressure parameters of the stack module 18. The hydrogen supply module 12 on the hydrogen side controls a certain hydrogen pressure according to the hydrogen pressure sensor 13, and the hydrogen circulation pump 15 rotates, combined with the water separator 14, the drain valve 16 and the exhaust valve 17, to discharge the liquid water on the hydrogen side from the stack and reduce the humidity on the hydrogen side at the same time. The mixed gas is mixed in the mixing silencer 20 and then discharged from the system. This time period is from T1 to T2.

[0034] Combination Figure 1 and Figure 2 After the shutdown purge is completed, the discharge phase begins, which is from T2 to T3. By closing the air compressor 3, the stack shut-off valve 8 and the back pressure valve 10, the air is stopped from entering the stack. At the same time, the hydrogen side continues to maintain a certain hydrogen pressure. A small current is used for discharge until the current and voltage sensor 19 detects that the stack voltage is lower than a certain value and then stops.

[0035] After the discharge is stopped, the hydrogen consumption phase begins. The hydrogen pressure is maintained for a period of time on the hydrogen side, and the remaining oxygen in the stack is consumed by the natural discharge of the fuel cell. This period is from T3 to T4.

[0036] During the period from T4 to T5, the system is shut down. When receiving an external start signal, the system starts, and the time period is from T5 to T6. The air compressor 3 needs to rotate to establish air pressure, the hydrogen supply module 12 needs to establish hydrogen pressure, and the voltage of the fuel cell module 18 needs to rise before loading.

[0037] Example 1

[0038] Based on the above principle, this embodiment provides a fuel cell system idle standby operation voltage control method, such as Figure 3 As shown in the figure, after receiving the shutdown standby command, the system does not perform the purge process, but directly discharges and maintains the battery stack voltage in a suitable range until it receives the restart command and enters the startup and normal operation. Specifically, the following steps are included:

[0039] S1: The fuel cell system receives a shutdown standby command.

[0040] S2: Control the load end discharge current to 10A, the hydrogen supply module 12 controls the inlet hydrogen pressure to 6kPa, the rotation speed of the circulating pump 15 to 600rpm, the air compressor 3 stops rotating, and the inlet stop valve 8 and the back pressure valve 10 are closed.

[0041] S3: Wait for the average voltage of the battery stack module 18 to drop below 0.72V; if the average voltage is above 0.72V, repeat S2 until the average voltage of the battery stack module drops below 0.72V.

[0042] S4: After reaching the lower limit of the stack voltage, adjust the load current to 0A.

[0043] S5: The stack entry stop valve 8 and the back pressure valve 10 are opened to 30%.

[0044] S6: Determine whether the average voltage of the battery stack module 18 exceeds 0.8V. If it is greater than 0.8V, execute S7; if the average voltage of the battery stack module 18 continues to drop even if the stack shut-off valve 8 and the back pressure valve 10 are opened to 30%, when the average voltage of the battery stack module 18 is lower than 0.7V, the air compressor bypass valve 5 is fully opened, and the air compressor 3 is turned on and runs at the lowest speed to compress a small amount of fresh air into the battery stack module 18, and again determine whether the average voltage of the battery stack module 18 is greater than 0.8V. If it is greater than 0.8V, the air compressor 3 stops rotating, closes the air compressor bypass valve 5, and executes S7.

[0045] S7: Close the stack entry stop valve 8 and the back pressure valve 10.

[0046] S8: Determine whether the average voltage of the stack module 18 is lower than 0.72 V. If the average voltage of the stack module 18 is lower than 0.72 V, execute S5, adjust the stack cut-off valve 8 and the back pressure valve 10 to 30% opening, and repeat this process until an external start command is received, and execute S9.

[0047] S9: Receive external start command.

[0048] S10: Enter the system startup procedure. At this time, because there is a certain voltage in the fuel cell stack, the air compressor 3, the hydrogen supply module 12, etc. can be quickly controlled to enter the operating state and the fuel cell stack power can be quickly output.

[0049] like Figure 4 As shown, T1-T2 is the idle standby acceptance stage, T2 to T3 is the idle standby operation voltage maintenance stage, and T3 to T4 is the fast recovery to operation stage.

[0050] The system idle standby operation voltage control method in this embodiment quickly enters the standby program after receiving the external shutdown standby demand, and uses the intermittent opening and closing of the stack entry shut-off valve and the back pressure valve to control the amount of external air entering the stack. At the same time, the lower hydrogen pressure and circulation volume on the hydrogen side are controlled, and the average voltage of the stack is maintained at about 0.76V through the self-discharge of the stack, and basically no power is output to the outside. At the same time, it can quickly respond to external start commands and output power. In this way, the parking idling of fuel cell vehicles can be met, and the fuel cell system can avoid frequent start and stop, thereby extending its life.

[0051] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for controlling the idle standby voltage of a fuel cell system, characterized in that: The control method comprises: The fuel cell system receives the shutdown standby command, controls the stack shutoff valve and back pressure valve in the air path to cut off the air from entering the fuel cell stack, and maintains the hydrogen circulation in the hydrogen path, so that the stack voltage drops to a reasonable value and enters the voltage maintenance stage; Adjust the switches of the stack shut-off valve and the back-pressure valve to introduce a small amount of external air into the fuel cell stack, and combine the self-discharge of the fuel cell stack to maintain the stack voltage within a reasonable range. Then receive the start command to allow the fuel cell system to enter the start-up procedure.

2. A fuel cell system idle standby operation voltage control method according to claim 1, characterized in that: The hydrogen circuit includes a hydrogen supply module and a circulation pump, and the hydrogen circuit is used to maintain the pressure and flow rate on the hydrogen side of the fuel cell stack during the voltage maintenance stage to meet the trace amount of hydrogen consumed during the self-discharge process of the fuel cell stack.

3. A fuel cell system idle standby operation voltage control method according to claim 2, characterized in that: The process of reducing the voltage of the fuel cell stack to a reasonable value includes: adjusting the load current to 10A, the hydrogen pressure of the stack to 6kpa, maintaining the idle speed of the circulating pump at 600rpm, stopping the air compressor, and closing the stack shut-off valve and the back pressure valve.

4. A fuel cell system idle standby operation voltage control method according to claim 1, characterized in that: During the voltage maintenance stage, the average voltage of the battery stack is 0.76V, the load current is 0A, and no power is output to the outside.

5. A fuel cell system idle standby operation voltage control method according to claim 1, characterized in that: In the voltage maintenance stage, when the average voltage of the fuel cell stack is less than 0.72V, the stack inlet shut-off valve and the back-pressure valve are opened by 30% to allow air to flow in, thereby increasing the voltage of the fuel cell stack.

6. A fuel cell system idle standby operation voltage control method according to claim 1, characterized in that: In the voltage maintenance stage, when the average voltage of the fuel cell stack is greater than 0.8V, close the stack entry shut-off valve and the back-pressure valve to prevent air from entering the fuel cell stack, allowing the fuel cell stack to consume oxygen in the air and reduce the self-discharge voltage.

7. A fuel cell system idle standby operation voltage control method according to claim 5, characterized in that: When the stack shut-off valve and the back-pressure valve are opened to 30% and the average voltage of the fuel cell stack is less than 0.7V, the air compressor and the air bypass valve are turned on to deliver air into the fuel cell stack, thereby increasing the stack voltage.

8. A fuel cell system idle standby operation voltage control method according to claim 7, characterized in that: When the air compressor and the air bypass valve are turned on, if the average voltage of the fuel cell stack is greater than 0.8V, the air bypass valve, the air compressor, the stack shut-off valve and the back pressure valve are closed.

9. A fuel cell system idle standby operation voltage control method according to claim 1, characterized in that: When the fuel cell system receives the idle standby command, the fuel cell system does not perform purging. Instead, it quickly reduces the operating voltage of the stack by discharging a load current of 10A and stopping the air supply, so that the humidity state inside the stack remains the same as before standby.

10. The method for controlling the idle standby voltage of a fuel cell system according to claim 1, characterized in that: The air circuit also includes an air compressor and an air bypass valve, which are used to transport a small amount of air from the atmosphere to the fuel cell stack.

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