Anode pressure control method for fuel cell system

Abstract

The present invention discloses a method for controlling the anode pressure of a fuel cell system, comprising the following steps: after the fuel cell system enters a low-power anode operation range, setting the anode pressure of the stack 1 to a target pressure P2, and simultaneously setting the target speed of the hydrogen circulation pump 5 to R1, thereby increasing the actual anode pressure; when it is detected that the actual anode pressure is greater than or equal to the target pressure P2, then setting the target pressure to P1, and simultaneously setting the target speed of the hydrogen circulation pump 5 to R2, thereby gradually decreasing the actual anode pressure; when it is detected that the actual anode pressure is less than or equal to the anode pressure P1, then setting the target pressure to P2, and setting the target speed of the hydrogen circulation pump 5 to R1; repeating the above process, wherein P2>P1, R2>R1. The present invention avoids the unstable region of the proportional valve by controlling the opening of the proportional valve and the speed of the hydrogen circulation pump, thereby avoiding high-frequency fluctuations in the proportional valve opening and the anode pressure, thereby improving the stability of the operation of the fuel cell system.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to an anode pressure control method for a fuel cell system. Background Art

[0002] Fuel cell systems require an appropriate anode hydrogen pressure for electrochemical reactions. The fuel cell anode subsystem regulates the flow of hydrogen into the stack through a control valve (proportional valve or hydrogen injection valve), thereby controlling the anode pressure. The pressure differential across the control valve is high (usually over 10 bar), and the valve's adjustable ratio is limited. Therefore, when the fuel cell system is operating at low power and with low hydrogen consumption, the valve opening is extremely small, making stable control difficult. Fluctuations in the valve opening can also easily cause high-frequency fluctuations in the anode pressure, such as Figure 4 、 Figure 5 As shown, this makes the operation of the fuel cell system unstable, which will affect the life of the valve and stack in the long run.

[0003] Current solutions for fuel cell anode subsystem pressure control include using multiple parallel high-precision hydrogen injection valves or multiple parallel proportional valves to increase the adjustable ratio and improve the pressure control accuracy under low power. However, this also increases the system volume and reduces economic efficiency. In addition, the use of multiple hydrogen injection valves also makes their switching noise more obvious, affecting the user experience. Summary of the Invention

[0004] In order to solve one of the above technical problems, the present invention provides an anode pressure control method for a fuel cell system. By controlling the opening of the proportional valve and the speed of the hydrogen circulation pump, the unstable area of ​​the proportional valve is avoided, and high-frequency fluctuations in the proportional valve opening and the anode pressure are avoided, thereby improving the stability of the fuel cell system operation.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for controlling an anode pressure of a fuel cell system is provided, wherein the method is operated on a fuel cell system, wherein the fuel cell system includes a fuel cell stack, a hydrogen supply unit, a proportional valve, a gas-water separator, a hydrogen circulation pump, and a drain and exhaust valve. The fuel cell stack includes a hydrogen inlet and a hydrogen outlet. The hydrogen supply unit, the proportional valve, and the hydrogen inlet of the fuel cell stack are connected in sequence. The hydrogen outlet of the fuel cell stack, the gas-water separator, and the drain and exhaust valve are connected in sequence. The gas-water separator, the hydrogen circulation pump, and the hydrogen inlet of the fuel cell stack are connected in sequence. The method is characterized in that the method comprises the following steps:

[0007] After the fuel cell system enters the low-power anode operation range, the actual anode pressure drops to P1, the anode target pressure of the fuel cell stack 1 is set to P2, and the target speed of the hydrogen circulation pump 5 is set to R1, and the actual anode pressure increases; when the actual anode pressure is monitored to be greater than or equal to P2, the target pressure is set to P1 again, and the target speed of the hydrogen circulation pump 5 is set to R2, and the actual anode pressure gradually decreases; when the actual anode pressure is monitored to be less than or equal to P1, the target pressure is set to P2 again, the target speed of the hydrogen circulation pump 5 is set to R1, and the actual anode pressure is increased;

[0008] Repeat the above process, where P2>P1, R2>R1.

[0009] Furthermore, in the anode pressure control method of a fuel cell system, when the fuel cell system is running, the proportional valve and the hydrogen circulation pump are opened, the proportional valve opening is changed through closed-loop control to control the anode pressure of the stack, the hydrogen recirculation flow is changed by adjusting the speed of the hydrogen circulation pump, and the drain and exhaust valve is periodically opened to discharge water and nitrogen accumulated on the anode; the stack current is monitored in real time, and when the stack current is less than the current threshold, it is determined that the fuel cell system has entered a low-power operation range.

[0010] The closed-loop control refers to a common closed-loop control method such as PID.

[0011] Furthermore, the current threshold is 10% of the maximum stack current.

[0012] Furthermore, the target pressure P1 has a value range of 1.2 bara to 1.4 bara, the target pressure P2 has a value range of 1.6 bara to 1.8 bara, the target speed R1 has a value range of 1000 rpm to 2000 rpm, and the target speed R2 has a value range of 3000 rpm to 4000 rpm.

[0013] After adopting the above technical solution, the present invention has at least the following beneficial effects: when the fuel cell system enters the low-power anode operating range, the present invention avoids the unstable area of ​​the proportional valve by controlling the proportional valve opening and the speed of the hydrogen circulation pump, avoids high-frequency fluctuations in the proportional valve opening and the anode pressure, and improves the operating stability and life of the fuel cell system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the structure of the fuel cell system of the present invention.

[0015] Figure 2 This is a step framework diagram of the anode pressure control method of the present invention.

[0016] Figure 3Schematic diagram of changes in proportional valve opening, anode pressure and hydrogen circulation pump speed during the anode pressure control method of the present invention.

[0017] Figure 4 Schematic diagram of the changes of a proportional valve or a hydrogen injection valve in the background art during the operation of a fuel cell system.

[0018] Figure 5 Schematic diagram of the change of anode pressure during the operation of a fuel cell system in the background art. DETAILED DESCRIPTION

[0019] It should be noted that, unless there is a conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The application is further described in detail below with reference to the drawings and specific embodiments.

[0020] Example 1: This example discloses a method for controlling the anode pressure of a fuel cell system, which is operated on the fuel cell system. Figure 1 As shown, the fuel cell system includes a fuel cell stack 1, a hydrogen supply unit 2, a proportional valve 3, a gas-water separator 4, a hydrogen circulation pump 5, a drain and exhaust valve 6, a pressure sensor 7, a current sensor 8 and an FCU control module 9. The fuel cell stack 1 includes a hydrogen inlet and a hydrogen outlet. The hydrogen supply unit 2, the proportional valve 3 and the hydrogen inlet of the fuel cell stack 1 are connected in sequence. The hydrogen outlet of the fuel cell stack 1, the gas-water separator 4 and the drain and exhaust valve 6 are connected in sequence. The gas-water separator 4, the hydrogen circulation pump 5 and the hydrogen inlet of the fuel cell stack 1 are connected in sequence. The pressure sensor 7 is connected to the hydrogen inlet of the fuel cell stack 1 or is built into the hydrogen inlet of the fuel cell stack 1.

[0021] The current sensor 8 is connected to the battery stack 1 and is used to detect the current of the battery stack 1;

[0022] The FCU control module connects to and controls the proportional valve 3 , the hydrogen circulation pump 5 , the drain and exhaust valve 6 , the pressure sensor 7 and the current sensor 8 .

[0023] Specifically, the anode pressure control method of a fuel cell system is as follows: Figure 2 As shown, the following steps are included:

[0024] During fuel cell system operation, proportional valve 3 and hydrogen circulation pump 5 are opened. Closed-loop control varies the opening of proportional valve 3 to control the anode pressure of stack 1. The hydrogen recirculation flow rate is varied by adjusting the speed of the hydrogen circulation pump. The drain and exhaust valve 6 is periodically opened to drain water and nitrogen accumulated on the anode. During fuel cell system operation, the anode pressure generally operates in the range of 1.2 bara to 2.7 bara, and the hydrogen circulation pump speed ranges from 1000 rpm to 8000 rpm.

[0025] The closed-loop control refers to a common closed-loop control method such as PID.

[0026] The current sensor 8 monitors the current of the fuel cell stack 1 in real time. When the current of the fuel cell stack 1 is less than the current threshold, it is determined that the fuel cell system enters the low-power operation range, where the current threshold is 10% of the maximum fuel cell stack current. The maximum fuel cell stack current is not a fixed value. Since the specifications of each fuel cell stack 1 are different, the maximum fuel cell stack current of each fuel cell stack 1 can be determined through testing when the fuel cell stack leaves the factory.

[0027] After the fuel cell system enters the low-power anode operation range, the original target pressure is P1, and the actual pressure has reached P1. First, the anode pressure of the fuel cell stack 1 is set to the target pressure P2, then the opening of the proportional valve 3 is increased, so that the hydrogen flow entering the fuel cell stack 1 is increased, and the target speed of the hydrogen circulation pump 5 is set to R1. The actual anode pressure increases rapidly. When the actual anode pressure is monitored to be greater than or equal to P2, the target pressure is set to P1 again, and the opening of the proportional valve 3 is reduced until it is closed. At the same time, the target speed of the hydrogen circulation pump 5 is set to R2. The fuel cell stack continuously consumes hydrogen, and the actual anode pressure gradually decreases. When the actual anode pressure is monitored to be less than or equal to P1, the target pressure is set to P2, and the target speed of the hydrogen circulation pump 5 is set to R1, then the proportional valve 3 is opened again to increase the anode pressure; and this process is repeated. In the above, P2>P1 (the value range of P1 is 1.2bara~1.4bara, the value range of P2 is 1.6bara~1.8bara), R2>R1 (the value range of R1 is 1000rpm~2000rpm, the value range of R2 is 3000rpm~4000rpm).

[0028] like Figure 3 As shown, through the above operation process, the proportional valve 3 can be freed from frequent opening fluctuations. The proportional valve 3 is periodically opened and closed, and the actual anode pressure varies periodically between P1 and P2, and the fluctuation frequency is greatly reduced. In the low-power anode pressure control mode, the speed of the hydrogen circulation pump 5 follows the actual anode pressure and is inversely proportional to it. When the actual pressure is P1, the speed of the hydrogen circulation pump is R2, and when the actual pressure is P2, the speed of the hydrogen circulation pump is R1, thereby reducing the change in the hydrogen flow through the stack anode, maintaining the anode hydrogen excess ratio, and improving the stability of the system operation.

[0029] In this embodiment, when the fuel cell system enters the low-power anode operating range, the proportional valve opening and the hydrogen circulation pump speed are controlled to avoid the unstable area of ​​the proportional valve, avoid high-frequency fluctuations in the proportional valve opening and the anode pressure, maintain the anode hydrogen excess ratio, and improve the operating stability and life of the fuel cell system.

[0030] Example 2: Based on Example 1, this example discloses specific parameter values. A method for controlling the anode pressure of a fuel cell system includes the following steps:

[0031] Assume that the maximum stack current of stack 1 is 600A, P1 is 1.2 bara, P2 is 1.5 bara, R1 is 2000 rpm, and R2 is 3500 rpm.

[0032] When the current of stack 1 is less than 60A (current threshold), the fuel cell system is determined to have entered the low-power anode operating range. Once the fuel cell system enters the low-power anode operating range, the target anode pressure of stack 1 is set to P2, the opening of proportional valve 3 is increased, and the hydrogen flow rate entering stack 1 is increased. At the same time, the target speed of hydrogen circulation pump 5 is set to R1. The speed decreases as the anode pressure increases, and the actual anode pressure increases rapidly. When the actual anode pressure is monitored to be greater than or equal to P2, the opening of proportional valve 3 is reduced until it closes. At the same time, the target speed of hydrogen circulation pump 5 is set to R2. The speed increases as the anode pressure decreases. The stack continuously consumes hydrogen, and the actual anode pressure gradually decreases. When the actual anode pressure is monitored to be less than or equal to P1, the target pressure is set to P2, the target speed of hydrogen circulation pump 5 is set to R1, and proportional valve 3 is opened to increase the anode pressure. This process is repeated.

[0033] While embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various equivalent changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the anode pressure of a fuel cell system, which runs on a fuel cell system, wherein the fuel cell system includes a fuel cell stack, a hydrogen supply unit, a proportional valve, a gas-water separator, a hydrogen circulation pump, and a drain and exhaust valve. The fuel cell stack includes a hydrogen inlet and a hydrogen outlet. The hydrogen supply unit, the proportional valve, and the hydrogen inlet of the fuel cell stack are connected in sequence. The hydrogen outlet of the fuel cell stack, the gas-water separator, and the drain and exhaust valve are connected in sequence. The gas-water separator, the hydrogen circulation pump, and the hydrogen inlet of the fuel cell stack are connected in sequence. The method comprises the following steps: when the fuel cell system is in operation, opening a proportional valve and a hydrogen circulation pump, controlling the anode pressure of the stack by changing the opening of the proportional valve, changing the hydrogen recirculation flow by adjusting the rotation speed of the hydrogen circulation pump, and periodically opening a drain and exhaust valve to discharge water and nitrogen accumulated on the anode; monitoring the stack current in real time, and determining that the fuel cell system has entered a low-power operation range when the stack current is less than a current threshold; after the fuel cell system enters the low-power anode operation range, the actual anode pressure drops to P1, the anode target pressure of the stack is set to P2, and the target rotation speed of the hydrogen circulation pump is set to R1, and the actual anode pressure increases; when it is monitored that the actual anode pressure is greater than or equal to P2, the target pressure is set to P1 again, and the target rotation speed of the hydrogen circulation pump is set to R2, and the actual anode pressure gradually decreases; when it is monitored that the actual anode pressure is less than or equal to P1, the target pressure is set to P2 again, the target rotation speed of the hydrogen circulation pump is set to R1, and the actual anode pressure increases; and repeating the above process, wherein P2>P1 and R2>R1.

2. The anode pressure control method of a fuel cell system according to claim 1, characterized in that: The current threshold is 10% of the maximum stack current.

3. The anode pressure control method of a fuel cell system according to claim 1, characterized in that: The value range of P1 is 1.2 bara to 1.4 bara, the value range of P2 is 1.6 bara to 1.8 bara, the value range of the target speed R1 is 1000 rpm to 2000 rpm, and the value range of the target speed R2 is 3000 rpm to 4000 rpm.

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