A hydrogen injection control method for a fuel cell system

Abstract

The present invention provides a hydrogen injection control method for a fuel cell system, which belongs to the technical field of fuel cell systems. The method first controls and adjusts the main hydrogen injection duty cycle according to the pressure difference between the target hydrogen intake pressure P1 and the actual hydrogen intake pressure P2, so that P2 is close to P1; then, the actual hydrogen pressure control accuracy ΔP2 of the fuel cell system at the current moment is compared with the target hydrogen pressure control accuracy ΔP1, and the hydrogen injection frequency of the main hydrogen injection is adjusted accordingly according to the comparison result, so that |ΔP2‑ΔP1|≤the first set value. When the tail valve is in a closed state, the present invention controls the auxiliary hydrogen injection to be closed, and only provides the hydrogen intake pressure required for the fuel cell reaction by controlling the main hydrogen injection, and the control process of the main hydrogen injection is divided into two steps. The first step is a preliminary adjustment to make P2 close to P1. On this basis, a second step of fine adjustment is performed to make |ΔP2‑ΔP1|≤the first set value. This control method can maximize the hydrogen injection life while improving the hydrogen intake pressure control accuracy.

Description

Technical Field

[0001] The invention relates to a hydrogen injection control method for a fuel cell system, belonging to the technical field of fuel cell systems. Background Art

[0002] A fuel cell system primarily consists of a hydrogen supply system, air supply system, cooling system, and fuel cell stack. The hydrogen supply system provides the hydrogen required for the reaction, while the air supply system provides the air required for the reaction. The hydrogen and air react within the fuel cell stack to generate electricity. The fuel cell reaction requires a certain hydrogen flow rate and pressure, so the hydrogen supply system must be able to regulate the hydrogen flow and pressure. Hydrogen sprayers are widely used as hydrogen supply components in fuel cell systems due to their fast response and stable flow rate.

[0003] When a fuel cell reacts, the hydrogen pressure needs to be maintained within a certain range. At the same time, the pressure difference between hydrogen and air also needs to be maintained within a certain range. Large fluctuations in the reaction gas pressure or excessive hydrogen-air pressure difference will cause mechanical damage to the fuel cell membrane electrode and affect the life of the fuel cell stack.

[0004] The Chinese invention patent application document with publication number CN110957508A discloses a fuel cell hydrogen supply control system and control method. The hydrogen supply control system includes a parallel compensation valve and N hydrogen injection valves (N≥2). The compensation valve serves as an auxiliary valve for balancing the hydrogen pressure (i.e., auxiliary hydrogen injection), and the hydrogen injection valve serves as the main solenoid valve for hydrogen injection (i.e., main hydrogen injection). When the tail exhaust valve is not open, the system hydrogen pressure requirement is met by adjusting the N hydrogen injection valves. When the tail exhaust valve is open, the compensation valve is started to maintain hydrogen pressure stability. However, this method has the following disadvantages: (1) When the tail exhaust valve is closed, the working parameters of the N hydrogen injection valves are adjusted only by comparing the actual hydrogen pressure value entering the stack with the target hydrogen pressure value, and the hydrogen pressure control accuracy is not high; (2) When the tail exhaust valve is opened, the working cycle and opening time of the compensation valve are calculated based on the driving cycle and duty cycle of the tail exhaust valve. That is to say, this patent calculates the hydrogen flow rate lost when the tail exhaust valve is opened based on the driving cycle and duty cycle of the tail exhaust valve, and then determines the feedforward compensation flow rate provided by the compensation valve. However, this method does not take into account the tail exhaust valve action delay and is only effective when the tail exhaust valve is fully opened. The calculation accuracy during the opening or closing process of the tail exhaust valve is poor, which will lead to inaccurate feedforward compensation flow rate and poor hydrogen pressure control accuracy.

[0005] The Chinese invention patent application document with publication number CN110797558A discloses a transient feedforward control method for hydrogen injection valves for fuel cell stacks. This method compensates for the flow loss when the tail valve is opened by adding a feedforward compensation flow to the injection flow when the tail valve is actuated, thereby maintaining hydrogen pressure. The feedforward compensation flow of this method is simulated by a trapezoidal curve after a period of delay. In other words, the patent uses the trapezoidal curve after a period of delay as the hydrogen flow curve lost when the tail valve is opened. Although the tail valve action delay is taken into account, it is obviously inaccurate to determine the hydrogen flow lost when the tail valve is opened based solely on the tail valve action delay. This will also lead to inaccurate feedforward compensation flow, resulting in poor hydrogen pressure control accuracy. In addition, when the tail valve is actuated, all hydrogen injections are following the action, which has a certain impact on the life of the hydrogen injection.

[0006] In summary, the current fuel cell system has poor hydrogen pressure control accuracy, which is mainly reflected in the following aspects: (1) when the tail valve is not in operation, the control accuracy of the main hydrogen injection is poor, resulting in poor hydrogen pressure control accuracy; (2) when the tail valve is in operation, the hydrogen flow rate lost when the tail valve is opened is inaccurately calculated, resulting in inaccurate feedforward compensation flow rate, which in turn leads to poor hydrogen pressure control accuracy. Summary of the Invention

[0007] The object of the present invention is to provide a hydrogen injection control method for a fuel cell system, which can improve the control accuracy of the main hydrogen injection when the tail valve is not actuated, thereby improving the hydrogen pressure control accuracy.

[0008] In order to achieve the above object, the present invention provides a method for controlling hydrogen injection of a fuel cell system, the method comprising the following steps:

[0009] Detect the status of the tail valve of the fuel cell system. When the tail valve is closed, the auxiliary hydrogen injection is controlled to be closed. The control process of the main hydrogen injection is as follows:

[0010] (1) Real-time acquisition of the current density, actual hydrogen inlet pressure P2, and hydrogen pressure target control accuracy ΔP1 of the fuel cell system at the current moment;

[0011] (2) Determine the hydrogen inlet pressure required for the fuel cell reaction based on the current density of the fuel cell system at the current moment, and use it as the target hydrogen inlet pressure P1. Based on the pressure difference between P1 and P2, control and adjust the main hydrogen injection duty cycle so that P2 is close to P1;

[0012] (3) Calculate the actual control accuracy of the hydrogen pressure at the current moment ΔP2 = |P2-P1|, compare ΔP2 with ΔP1, and adjust the hydrogen injection frequency of the main hydrogen injection accordingly according to the comparison result so that |ΔP2-ΔP1| ≤ the first set value.

[0013] The beneficial effects of the present invention are as follows: when the tail valve is closed, the auxiliary hydrogen injection is turned off, and only the main hydrogen injection is controlled to provide the hydrogen intake pressure required for the fuel cell reaction. The main hydrogen injection control process is divided into two steps. The first step is preliminary adjustment, that is, adjusting the main hydrogen injection duty cycle based on the pressure difference between the target hydrogen intake pressure and the actual hydrogen intake pressure to bring the actual hydrogen intake pressure close to the target hydrogen intake pressure. On this basis, the second step is fine adjustment, that is, adjusting the main hydrogen injection frequency to make the absolute value of the difference between the actual hydrogen pressure control accuracy and the target hydrogen pressure control accuracy less than a first set value. This control method can improve the control accuracy of the hydrogen intake pressure while maximizing the life of the hydrogen injection.

[0014] Furthermore, in the above method, the process of adjusting the hydrogen injection frequency of the main hydrogen injection according to the comparison result includes:

[0015] If ΔP2>ΔP1, then when |ΔP2-ΔP1|>the second set value, the main hydrogen injection frequency is increased until |ΔP2-ΔP1|≤the first set value; when |ΔP2-ΔP1|≤the second set value, the current state of the main hydrogen injection is maintained unchanged; wherein the second set value is greater than the first set value;

[0016] If ΔP2≤ΔP1, then when |ΔP1-ΔP2|>the second set value, the main hydrogen injection frequency is reduced until |ΔP2-ΔP1|≤the first set value; when |ΔP1-ΔP2|≤the second set value, the current state of the main hydrogen injection is maintained unchanged.

[0017] The beneficial effects of this are: by setting the first set value to ensure the control accuracy of the hydrogen inlet pressure, by setting the second set value to control when to adjust the main hydrogen injection frequency, and making the second set value greater than the first set value, it can also reduce the frequency of adjusting the main hydrogen injection frequency and reduce the main hydrogen injection working intensity.

[0018] Furthermore, in the above method, the method further comprises the following steps:

[0019] When the tail drain valve is actuated, the main hydrogen injection is controlled to maintain the current state unchanged, and the auxiliary hydrogen injection is controlled to open, and the auxiliary hydrogen injection is used to provide a feedforward compensation flow to make up for the hydrogen flow lost when the tail drain valve is actuated, thereby maintaining a stable hydrogen inlet pressure; the tail drain valve action includes opening action, full opening and closing action, the opening action being the process from opening to completion of the tail drain valve, and the closing action being the process from closing to completion of the tail drain valve;

[0020] Among them, the current lost hydrogen flow is determined by combining the current density of the fuel cell system at the current moment, the current tail valve opening time, the current tail valve front end pressure, and the predetermined correspondence between the fuel cell system current density, tail valve opening time, tail valve front end pressure and the lost hydrogen flow. By adjusting the auxiliary hydrogen injection opening so that the feedforward compensation flow provided by it is equal to the current lost hydrogen flow, the hydrogen inlet pressure is maintained stable.

[0021] The beneficial effect of this approach is that, when the tailpipe valve is actuated, a feedforward control method is used to adjust the auxiliary hydrogen injection opening in real time, providing a feedforward compensation flow rate equal to the lost hydrogen flow rate. Because the lost hydrogen flow rate in this method is determined based on the fuel cell system current density, the tailpipe valve opening time, and the pressure at the tailpipe valve front end, compared to the prior art method of determining the lost hydrogen flow rate based on a trapezoidal curve after a time delay, this method calculates the lost hydrogen flow rate with higher accuracy, and thus determines the feedforward compensation flow rate with higher accuracy, thereby improving the accuracy of hydrogen pressure control and extending the service life of the hydrogen injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a fuel cell system in an embodiment of the method of the present invention;

[0023] Figure 2 Flowchart of a method for controlling hydrogen injection of a fuel cell system when the tail exhaust valve is in a closed state in an embodiment of the method of the present invention;

[0024] Figure 3 This is a flow chart of a method for controlling hydrogen injection of a fuel cell system when the tail exhaust valve is actuated in an embodiment of the method of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Method Example:

[0027] The fuel cell system to which the fuel cell system hydrogen injection control method of this embodiment is applicable is as follows: Figure 1 As shown, the fuel cell system includes a hydrogen supply system, an air supply system, a cooling system, a fuel cell stack and other parts. The hydrogen supply system provides the hydrogen required for the reaction, and the air supply system provides the air required for the reaction. The hydrogen and air react inside the fuel cell stack to generate electricity.

[0028] Among them, the hydrogen supply system is as follows Figure 1As shown, a hydrogen source (not shown) connected in series, a solenoid valve, and a hydrogen supply assembly consisting of multiple hydrogen injectors connected in parallel are connected to the stack hydrogen inlet. The stack hydrogen outlet is connected to the stack hydrogen inlet via a tail valve (including a hydrogen discharge valve and a water discharge valve), a hydrogen circulation pump, and a one-way valve. In this embodiment, the hydrogen supply assembly includes auxiliary hydrogen injectors and N main hydrogen injectors arranged in parallel (N ≥ 2, with N = 3 used as an example in this embodiment).

[0029] The hydrogen injection control method of the fuel cell system of this embodiment is as follows: Figure 2 and Figure 3 As shown, the control method detects the state of the tail valve of the fuel cell system, and has different control processes when the tail valve is in different states, mainly including: (1) the control process when the tail valve is in the closed state, and (2) the control process when the tail valve is in operation, which are introduced in detail below.

[0030] The fuel cell system starts, the solenoid valve is opened, the main hydrogen injection is turned on, and the corresponding control process is determined according to the tail valve status:

[0031] 1. Control process when the tail valve is in closed state, see Figure 2 .

[0032] At this time, the auxiliary hydrogen injection is closed and the main hydrogen injection is working. The control process of the main hydrogen injection is:

[0033] (1) Real-time acquisition of the current density, actual hydrogen inlet pressure P2, and hydrogen pressure target control accuracy ΔP1 of the fuel cell system at the current moment;

[0034] The values of the target control accuracy of the hydrogen pressure at different times are fixed values determined during design based on product requirements. In practical applications, the actual accuracy of the selected pressure sensor must also be taken into account when determining the target control accuracy of the hydrogen pressure. The target control accuracy of the hydrogen pressure is set to a smaller value (the smaller the better, provided the accuracy allows). In addition, the target control accuracy of the hydrogen pressure at different times can be set to the same value, or the target control accuracy of the hydrogen pressure at different times can be set to different values. In this embodiment, the target control accuracy of the hydrogen pressure at different times is set to the same value.

[0035] (2) Determine the hydrogen inlet pressure required for the fuel cell reaction based on the current density of the fuel cell system at the current moment, and use it as the target hydrogen inlet pressure P1. Based on the pressure difference between the target hydrogen inlet pressure P1 and the actual hydrogen inlet pressure P2, control and adjust the main hydrogen injection duty cycle so that P2 is close to P1;

[0036] Specifically, the hydrogen intake pressure required for the fuel cell reaction corresponding to the fuel cell current density at the current moment, that is, the target hydrogen intake pressure P1, is obtained by looking up the table. P1 is compared with P2, and according to the pressure difference between P1 and P2, the PID control adjusts the main hydrogen injection duty cycle to make P2 close to P1.

[0037] (3) Calculate the actual control accuracy of hydrogen pressure at the current moment ΔP2 = |P2-P1|, compare the actual control accuracy of hydrogen pressure at the current moment ΔP2 with the target control accuracy of hydrogen pressure at the current moment ΔP1, and adjust the hydrogen injection frequency of the main hydrogen injection accordingly based on the comparison result so that |ΔP2-ΔP1| ≤ 0.1 kPa (i.e., the first set value);

[0038] That is, the hydrogen intake pressure control target of this embodiment is to make |ΔP2-ΔP1|≤0.1 kPa. As long as |ΔP2-ΔP1|≤0.1 kPa, it is considered that ΔP2=ΔP1.

[0039] The specific process of adjusting the hydrogen injection frequencies of the three main hydrogen injections according to the comparison results of ΔP2 and ΔP1 is as follows:

[0040] If ΔP2>ΔP1, then when |ΔP2-ΔP1|>0.5kPa (i.e., the second set value), the main hydrogen injection frequency is increased until |ΔP2-ΔP1|≤0.1kPa (i.e., the first set value); when |ΔP2-ΔP1|≤0.5kPa, the current state of the main hydrogen injection is maintained unchanged;

[0041] If ΔP2≤ΔP1, then when |ΔP1-ΔP2|>0.5kPa, the main hydrogen injection frequency is reduced until |ΔP2-ΔP1|≤0.1kPa; when |ΔP1-ΔP2|≤0.5kPa, the current state of the main hydrogen injection is maintained unchanged.

[0042] The three main hydrogen nozzles are controlled by opening simultaneously, alternating, and coordinating for coordinated regulation. The three main hydrogen nozzles regulate gas flow by transmitting three control signals to each nozzle, controlling its opening, opening duration, and closing. The control signals are pulsed signals; when the pulse is at a high level of 1, the nozzle opens; when the pulse is at a low level of 0, the nozzle closes. The duty cycle of the control signal represents the length of time the nozzle remains open, while the frequency of the control signal represents the number of times the nozzle remains open. A greater duty cycle and frequency increase the nozzle opening time and the greater the hydrogen flow rate. Conversely, a smaller duty cycle and frequency decrease the hydrogen flow rate.

[0043] In this embodiment, the first set value is set to ensure the control accuracy of the hydrogen inlet pressure, and the second set value is set to control when to adjust the main hydrogen injection frequency. By making the second set value greater than the first set value, the frequency of adjusting the main hydrogen injection frequency can be reduced, thereby reducing the intensity of the main hydrogen injection. It should be noted that in actual applications, the specific values of the first and second set values should be determined based on actual conditions and the accuracy of the selected sensor, and are not limited to the values given in this embodiment.

[0044] In summary, when the tailpipe valve is closed, the auxiliary hydrogen injection is turned off, and only the main hydrogen injection is controlled to provide the hydrogen intake pressure required for the fuel cell reaction. The main hydrogen injection control process is divided into two steps. The first step is preliminary adjustment, that is, adjusting the main hydrogen injection duty cycle based on the pressure difference between the target hydrogen intake pressure and the actual intake pressure to make the actual hydrogen intake pressure close to the target intake pressure. On this basis, the second step is fine adjustment, that is, adjusting the hydrogen injection frequency of the main hydrogen injection to make the absolute value of the difference between the actual hydrogen pressure control accuracy and the target hydrogen pressure control accuracy less than the first set value. This control method can maximize the life of the hydrogen injection while improving the hydrogen pressure control accuracy.

[0045] In addition, when a main hydrogen injection fails, the auxiliary hydrogen injection can be used to fill the gap in time, reducing the impact of damage to the main hydrogen injection on the fuel cell system and minimizing the loss.

[0046] 2. Control process of tail valve operation, see Figure 3 .

[0047] In this embodiment, the tailpipe valve's actions include opening, fully opening, and closing. Opening refers to the process from opening to completion of the tailpipe valve's opening, while closing refers to the process from closing to completion of the closing. Because the tailpipe valve's transition from opening to fully opening to closing is continuous, and the duration of the opening is typically less than 0.5 seconds, feedforward compensation flow is also required when the tailpipe valve is fully open.

[0048] When the tail valve is actuated, the three main hydrogen injections maintain their current state, and the auxiliary hydrogen injection is turned on. The auxiliary hydrogen injection is used to provide feedforward compensation flow to make up for the hydrogen flow lost when the tail valve is actuated, thereby maintaining the hydrogen inlet pressure stable.

[0049] Among them, the current lost hydrogen flow is determined by combining the current density of the fuel cell system at the current moment, the current tail valve opening time, the current tail valve front end pressure, and the predetermined correspondence between the fuel cell system current density, tail valve opening time, tail valve front end pressure and the lost hydrogen flow. By adjusting the auxiliary hydrogen injection opening so that the feedforward compensation flow provided by it is equal to the current lost hydrogen flow, the hydrogen inlet pressure is maintained stable.

[0050] Specifically, the tail valve opening time and the tail valve front-end pressure corresponding to the hydrogen flow rate lost under different fuel cell system current densities can be repeatedly tested through bench tests to determine the correspondence between the fuel cell system current density, tail valve opening time, tail valve front-end pressure and the lost hydrogen flow rate when the tail valve is actuated (this correspondence can be saved in the form of a curve, i.e., the hydrogen flow rate lost when the tail valve is actuated). In this way, when the tail valve is actuated, the current current density of the fuel cell system at the current moment, the current tail valve opening time, the current tail valve front-end pressure and the above correspondence can be combined to determine the current lost hydrogen flow rate, and the auxiliary hydrogen injection opening degree can be adjusted in real time through PID control so that the feedforward compensation flow rate it provides is equal to the current lost hydrogen flow rate, thereby maintaining the stability of the hydrogen inlet pressure; when the tail valve is completely closed, the auxiliary hydrogen injection is turned off.

[0051] In summary, when the tailpipe valve is actuated, the three main hydrogen injectors maintain their current states, while the auxiliary hydrogen injector is activated. A feedforward control method is used to adjust the auxiliary hydrogen injector opening in real time to provide a feedforward compensation flow rate equal to the lost hydrogen flow rate. Because the lost hydrogen flow rate in this embodiment is determined based on the fuel cell system current density, the tailpipe valve opening time, and the pressure at the tailpipe valve front end, compared to the prior art method of determining the lost hydrogen flow rate based on a trapezoidal curve after a time delay, the lost hydrogen flow rate calculation in this embodiment is more accurate, and the feedforward compensation flow rate determined is therefore more accurate, thereby improving the accuracy of hydrogen pressure control and extending the service life of the hydrogen injector.

Claims

1. A method for controlling hydrogen injection of a fuel cell system, characterized in that: The method comprises the following steps: Detect the status of the tail valve of the fuel cell system. When the tail valve is in the closed state, the auxiliary hydrogen injection is controlled to be closed. The control process of the main hydrogen injection is as follows: (1) Real-time acquisition of the current density, actual hydrogen inlet pressure P2, and hydrogen pressure target control accuracy ΔP1 of the fuel cell system at the current moment; (2) Determine the hydrogen inlet pressure required for the fuel cell reaction based on the current density of the fuel cell system at the current moment, and use it as the target hydrogen inlet pressure P1. Based on the pressure difference between P1 and P2, control and adjust the main hydrogen injection duty cycle so that P2 is close to P1; (3) Calculate the actual control accuracy of the hydrogen pressure after duty cycle adjustment ΔP2 = |P2-P1|, compare ΔP2 with ΔP1, and adjust the hydrogen injection frequency of the main hydrogen injection accordingly according to the comparison result so that |ΔP2-ΔP1| ≤ the first set value.

2. The hydrogen injection control method for a fuel cell system according to claim 1, characterized in that: The process of adjusting the hydrogen injection frequency of the main hydrogen injection according to the comparison result includes: If ΔP2>ΔP1, then when |ΔP2-ΔP1|>the second set value, the main hydrogen injection frequency is increased until |ΔP2-ΔP1|≤the first set value; when |ΔP2-ΔP1|≤the second set value, the current state of the main hydrogen injection is maintained unchanged; wherein the second set value is greater than the first set value; If ΔP2≤ΔP1, then when |ΔP1-ΔP2|>the second set value, the main hydrogen injection frequency is reduced until |ΔP2-ΔP1|≤the first set value; when |ΔP1-ΔP2|≤the second set value, the current state of the main hydrogen injection is maintained unchanged.

3. The hydrogen injection control method for a fuel cell system according to claim 1 or 2, characterized in that: The method further comprises the following steps: When the tail drain valve is actuated, the main hydrogen injection is controlled to maintain the current state unchanged, and the auxiliary hydrogen injection is controlled to open, and the auxiliary hydrogen injection is used to provide a feedforward compensation flow to make up for the hydrogen flow lost when the tail drain valve is actuated, thereby maintaining a stable hydrogen inlet pressure; the tail drain valve action includes opening action, full opening and closing action, the opening action being the process from opening to completion of the tail drain valve, and the closing action being the process from closing to completion of the tail drain valve; Among them, the current lost hydrogen flow is determined by combining the current density of the fuel cell system at the current moment, the current tail valve opening time, the current tail valve front end pressure, and the predetermined correspondence between the fuel cell system current density, tail valve opening time, tail valve front end pressure and the lost hydrogen flow. By adjusting the auxiliary hydrogen injection opening so that the feedforward compensation flow provided by it is equal to the current lost hydrogen flow, the hydrogen inlet pressure is maintained stable.

Images