A method for controlling hydrogen pressure in a hydrogen fuel cell

Abstract

The present invention relates to the field of fuel cells, and specifically to a method for controlling hydrogen pressure in a hydrogen fuel cell. It comprises the following steps: step one, calculating the difference D2 between the actual value P1 of the air entering the stack pressure measured by sensor 1 and the actual value P2 of the hydrogen entering the stack pressure measured by sensor 2, D2=P2-P1; step two, calculating the target hydrogen inlet pressure P6 according to the hydrogen-air pressure difference maintenance algorithm; step three, calculating the difference between P6 and the actual pressure value P2 of the hydrogen entering the stack, and using the difference to perform PI adjustment on the opening of the proportional valve on the hydrogen circuit; step four, adding the proportional valve opening feedforward value on the basis of PI adjustment of the proportional valve opening; step five, adding the PI processing result of step three and the opening feedforward value obtained in step four to obtain the final proportional valve target opening. The present invention solves the problem that the proportional valve has hysteresis for hydrogen inlet pressure control and reduces the dependence on the pressure sensor.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a method for controlling hydrogen pressure in a hydrogen fuel cell. Background Art

[0002] When a hydrogen fuel cell engine is operating, hydrogen and oxygen are transported into the fuel cell stack from different subsystems for reaction. The hydrogen fuel cell control system adjusts the pressure of hydrogen entering the fuel cell stack at different fuel cell stack operating points to ensure that the pressure requirement of the current fuel cell stack operating point is met, and the hydrogen pressure promptly follows the changes in air pressure to avoid an imbalance in the flow ratio of hydrogen and air, which in turn affects the output power and efficiency of the fuel cell system. Hydrogen is flammable and explosive, so it is crucial to control the hydrogen inlet pressure. Increasing the hydrogen inlet pressure can improve the reaction efficiency of the fuel cell stack to a certain extent, but the safety of the hydrogen pipeline needs to be ensured. At the same time, the pressure difference between the hydrogen inlet pressure and the air inlet pressure needs to be limited to a reasonable range to prevent damage to the fuel cell stack structure and economic losses.

[0003] Currently, hydrogen pressure is often regulated by adjusting the valve opening in the hydrogen supply circuit. Existing technical solutions often install various pressure detection sensors in the hydrogen supply circuit to achieve the purpose of real-time monitoring of the pressure of hydrogen entering the fuel cell stack and adjust the proportional valve based on the detected pressure.

[0004] like Figure 1 As shown, sensor 1 measures the air pressure entering the fuel cell stack, sensor 2 measures the pressure of the hydrogen entering the stack, sensor 3 measures the pressure of the coolant entering the stack, and sensor 4 is a medium-pressure sensor that measures the pressure of the hydrogen after entering the system but before passing through the proportional valve (valve 1). Sensor 5 measures the temperature of the hydrogen entering the fuel cell stack. Valve 1 is a proportional valve installed in the hydrogen circuit. Adjusting the opening of the proportional valve controls the pressure of the hydrogen entering the system. Valve 2 is a shutoff valve that controls the opening and closing of the hydrogen supply.

[0005] The hydrogen delivered into the loop will be mixed with some gases after passing through valves 2 and 1, and then delivered to the fuel cell stack together. This part of the added gas is the remaining unreacted hydrogen extracted from the gas discharged from the fuel cell stack (because in most current hydrogen fuel cell engines, in order to improve the utilization rate of hydrogen, hydrogen will be recycled. The main method of extracting unreacted hydrogen is: the reacted gas at the outlet of the fuel cell stack is discharged from the system through a hydrophobic nitrogen exhaust device to remove water vapor and other non-reactive gases, thereby obtaining hydrogen that does not participate in the redox reaction) using a hydrogen pump and an ejector device to mix the unreacted hydrogen with the hydrogen newly delivered to the engine and deliver it to the fuel cell stack again. According to the installation position of the proportional valve (valve 1), it can be seen that the proportional valve mainly controls the hydrogen newly entering the system.

[0006] The above technical solution has the following problems:

[0007] In the case of hydrogen recycling, the hydrogen inlet pressure measured by sensor 2 is affected by the recycled hydrogen. Using the hydrogen inlet pressure measured by sensor 2 as the only reference standard for controlling the proportional valve, on the one hand, is highly dependent on the real-time measurement accuracy and sensitivity of the pressure sensor. On the other hand, the hysteresis of the hydrogen pressure control is not taken into account, and the hydrogen inlet pressure cannot be changed in time according to the needs of the fuel cell stack. Summary of the Invention

[0008] The purpose of the present invention is to address the problems existing in the background technology and propose a hydrogen pressure control method in a hydrogen fuel cell, which solves the problem of hysteresis of the proportional valve in controlling the hydrogen inlet pressure and reduces the dependence on the pressure sensor.

[0009] The technical solution of the present invention is a method for controlling hydrogen pressure in a hydrogen fuel cell, comprising the following steps:

[0010] Step 1: Calculate the difference D2 between the actual pressure value P1 of the air entering the fuel cell stack measured by sensor 1 and the actual pressure value P2 of the hydrogen entering the fuel cell stack measured by sensor 2, D2 = P2 - P1;

[0011] Step 2: Calculate the target hydrogen inlet pressure P6 according to the hydrogen-air pressure difference maintenance algorithm;

[0012] Step 3: Calculate the difference between P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack, and use this difference to perform PI adjustment on the opening of the proportional valve in the hydrogen circuit;

[0013] Step 4: Add the proportional valve opening feedforward value based on the PI adjustment of the proportional valve opening;

[0014] Step 5: Add the PI processing result of step 3 and the opening feedforward value obtained in step 4 to obtain the final proportional valve target opening.

[0015] Preferably, the hydrogen-air pressure difference maintenance algorithm includes the following steps:

[0016] S1. Determine whether D2 is in the interval [a, b]. The values ​​of a and b in the difference interval [a, b] are calibrated according to the stack performance.

[0017] S2. If D2∈[a, b], calculate the target pressure of hydrogen entering the fuel cell stack: P6=P4+D1, where P4 is the target pressure of air entering the fuel cell stack, and D1 is the ideal difference between the hydrogen and air pressures determined based on the fuel cell stack performance.

[0018] S3. If D2 is not within the interval [a, b], calculate the target pressure value of hydrogen entering the fuel cell stack, P6 = P1 + D1.

[0019] Preferably, PI regulation comprises the following steps:

[0020] Step 1. Calculation error: The error refers to the difference between the target hydrogen inlet pressure P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack;

[0021] Step 2, proportional control: multiply the error obtained in Step 1 by the proportional gain coefficient Kp to obtain the proportional control term;

[0022] Step 3, Integral control: Multiply the error obtained in Step 1 by the integral gain Ki, and add the result to the previous integral accumulated value to obtain the integral control term;

[0023] Step 4. Calculate the PI controller output: Add the proportional control term obtained in Step 2 and the integral control term obtained in Step 3 to obtain the final result of PI regulation.

[0024] Preferably, the proportional valve opening feedforward value calculation process includes the following steps A1-A4:

[0025] A1. Determine the reference value of the proportional valve opening feedforward value based on the target current I1 that the stack needs to output under the current operating conditions;

[0026] A2, determining the correction value 1 of the proportional valve feedforward value according to the target current I1 and the temperature at the proportional valve;

[0027] A3. Determine the correction value 2 of the proportional valve feedforward value based on the hydrogen medium pressure P3;

[0028] A4, the proportional valve opening feedforward value reference value, correction value 1 and correction value 2 are multiplied together to obtain the final proportional valve opening feedforward value.

[0029] Preferably, the hydrogen temperature at the proportional valve takes the coolant inlet temperature T1 as a reference value.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] This invention utilizes a PI control algorithm based on feedforward compensation. This algorithm comprehensively considers the air pressure entering the fuel cell stack and the real-time temperature and pressure of the hydrogen at the proportional valve to control the opening of the proportional valve. This solves the hysteresis problem of the proportional valve in controlling the hydrogen inlet pressure and reduces dependence on pressure sensors. Furthermore, by using the coolant inlet temperature T1 as a reference value for the hydrogen temperature at the proportional valve, it eliminates the need for an additional temperature sensor at the proportional valve, reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a simplified diagram of the hydrogen supply system for an existing hydrogen fuel cell engine;

[0033] Figure 2 It is the flow chart of proportional valve opening control;

[0034] Figure 3 This is a schematic diagram of the hydrogen-air pressure difference maintenance algorithm;

[0035] Figure 4 This is a schematic diagram of the hydrogen inlet pressure PI regulation process;

[0036] Figure 5 This is a schematic diagram of the proportional valve opening feedforward calculation process. DETAILED DESCRIPTION

[0037] like Figure 1-Figure 5 As shown, the present embodiment provides a method for controlling hydrogen pressure in a hydrogen fuel cell, comprising the following steps:

[0038] Step 1: Calculate the difference D2 between the actual pressure value P1 of the air entering the fuel cell stack measured by sensor 1 and the actual pressure value P2 of the hydrogen entering the fuel cell stack measured by sensor 2, D2 = P2 - P1;

[0039] Step 2: Calculate the target hydrogen inlet pressure P6 according to the hydrogen-air pressure difference maintenance algorithm. The hydrogen-air pressure difference maintenance algorithm includes the following steps S1-S3:

[0040] S1. Determine whether D2 is in the interval [a, b]. The values ​​of a and b in the difference interval [a, b] are calibrated according to the stack performance.

[0041] S2. If D2∈[a, b], calculate the target pressure of hydrogen entering the fuel cell stack, P6=P4+D1, where P4 refers to the target pressure of air entering the fuel cell stack. P4 is calibrated through experiments at different fuel cell stack output currents. For example, the system requires the fuel cell stack to output a continuous current of 24A. In order to generate such electrical energy, the pressure of the air supply system must reach a certain threshold. For example, it was found through experiments that when the pressure of the air entering the fuel cell stack reaches 100kpa, the current output by the fuel cell stack can reach 24A. The target air pressure entering the fuel cell stack at the 24A operating point is P4=100kpa. Therefore, through experimental calibration, the air pressure entering the fuel cell stack that needs to be met at different output currents can be obtained. This is related to the model of the fuel cell stack, so different fuel cells need to be calibrated separately. D1 is generally data provided by the supplier. It is the difference between the ideal hydrogen and air pressures entering the fuel cell stack determined based on the comprehensive performance of the fuel cell stack. It is usually a constant for fuel cells of fixed models.

[0042] S3. If D2 is not within the interval [a, b], calculate the target pressure of hydrogen entering the fuel cell stack, P6 = P1 + D1, where P1 refers to the actual air pressure entering the fuel cell stack measured by sensor 1;

[0043] Step 3: Calculate the difference between P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack, and use this difference to perform PI adjustment on the opening of the proportional valve in the hydrogen circuit. PI adjustment includes the following steps:

[0044] Step 1. Calculate the error: The error refers to the difference between the target hydrogen inlet pressure P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack. In this control method, it refers to the difference between the target hydrogen inlet pressure P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack.

[0045] Step 2, Proportional Control: Multiply the error obtained in Step 1 by the proportional gain coefficient Kp (Kp is determined through experimental calibration) to obtain the proportional control term Kp*e(t). Proportional control makes the controller output proportional to the error. The larger the error, the greater the controller output, which means that the controller will adjust the system more actively.

[0046] Step 3, integral control: multiply the error obtained in Step 1 by the integral gain Ki (Ki is determined by experimental calibration), and add the result to the previous integral cumulative value to obtain the integral control term Integral control can eliminate steady-state errors and enable the system to achieve the desired output in steady state;

[0047] Step 4. Calculate the PI controller output: Add the proportional control term obtained in Step 2 and the integral control term obtained in Step 3 to obtain the final result of PI regulation.

[0048] Step 4: Based on the PI adjustment of the proportional valve opening, the proportional valve opening feedforward value is increased to reduce the PI algorithm's overshoot of the hydrogen inlet pressure and improve the system's tracking of the hydrogen inlet pressure control. Considering that during the operation of valve 1 (proportional valve), its opening is closely related to the pressure before the hydrogen flows through valve 1, that is, the hydrogen intermediate pressure P3, and the temperature at valve 1, the proportional valve opening feedforward value calculation process includes the following steps A1-A4:

[0049] A1. Determine the reference value of the proportional valve opening feedforward value based on the target current I1 that the stack needs to output under the current operating conditions. The specific determination method is to conduct a calibration test in advance to determine the feedforward reference value under various stack currents. The calibration results are shown in Table 1. Finally, based on the real-time current, the proportional valve feedforward reference value is obtained by interpolation from the table.

[0050] Table 1. Example of the corresponding relationship between the reference value of the proportional valve opening feedforward value obtained from the calibration test and the target output current of the fuel cell stack

[0051]

[0052] A2. Determine the correction value 1 of the proportional valve feedforward value based on the target current I1 and the temperature at the proportional valve. The specific determination method is similar to step A1: perform a calibration test in advance to determine the correction value 1 of the feedforward value corresponding to the target current I1 and the temperature at the proportional valve (valve 1). The specific form of the calibration results is shown in Table 2. Finally, based on the real-time current I1 and the temperature at the proportional valve, interpolate the table to obtain the correction value 1 of the valve 1 feedforward value;

[0053] Table 2. Example of the relationship between the proportional valve opening feedforward correction value 1, the stack target output current, and the temperature at valve 1 obtained from the calibration test

[0054]

[0055] In addition, the hydrogen temperature at the proportional valve (valve 1) uses the coolant inlet temperature T1 as a reference value. This is because when the actual coolant circulates, it will flow through the hydrogen preheater at the same time to achieve the purpose of preheating the hydrogen. Figure 1 As shown in the figure, the temperature of the coolant entering the preheating device is almost the same as that of the hydrogen passing through the preheating device, and the coolant flow rate and hydrogen flow rate are both very fast. The difference between the coolant temperature at the preheater, the hydrogen temperature at valve 1, and the coolant temperature T1 when entering the stack can be ignored. The coolant temperature T1 entering the stack is used as the reference value of the hydrogen temperature at valve 1.

[0056] A3. Determine the correction value 2 of the proportional valve feedforward value based on the hydrogen medium pressure P3. The specific determination method is to conduct a calibration test in advance to determine the correction value 2 of the proportional valve opening feedforward value at various hydrogen medium pressures. The calibration results are shown in Table 3. Finally, based on the real-time hydrogen medium pressure P3, the correction value 2 of the proportional valve opening feedforward value is obtained by interpolation from the table.

[0057] Table 3. Example of the relationship between the proportional valve feedforward correction value 2 and the hydrogen medium pressure P3 obtained from the calibration test

[0058]

[0059] A4, the product of the proportional valve opening feedforward value reference value, correction value 1 and correction value 2 is the final proportional valve opening feedforward value;

[0060] Step 5: Add the PI processing result of step 3 and the opening feedforward value obtained in step 4 to obtain the final proportional valve target opening, reduce the overshoot of the PI algorithm on the hydrogen inlet pressure, and improve the system's tracking performance on the hydrogen inlet pressure control.

[0061] This embodiment utilizes a PI control algorithm based on feedforward compensation. This algorithm comprehensively considers the air pressure entering the fuel cell stack, the real-time hydrogen temperature, and the pressure at the proportional valve (Valve 1), to control the opening of the proportional valve (Valve 1). This solves the hysteresis problem of the proportional valve in controlling the hydrogen inlet pressure and reduces dependence on the pressure sensor. Furthermore, because the difference between the coolant temperature at the preheater, the hydrogen temperature at Valve 1, and the coolant inlet temperature T1 is negligible, the coolant inlet temperature T1 is used as the reference value for the hydrogen temperature at Valve 1, eliminating the need for an additional temperature sensor at Valve 1 and reducing costs.

[0062] During system operation, opening the drain valve or nitrogen exhaust valve will cause the pressure in the hydrogen circuit to drop, thus affecting the normal operation of the fuel cell. To avoid this, a certain proportional valve opening compensation can be given when opening the drain valve or nitrogen exhaust valve.

[0063] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for controlling hydrogen pressure in a hydrogen fuel cell, characterized in that: The following steps are involved: Step 1: Calculate the difference D2 between the actual pressure value P1 of the air entering the fuel cell stack measured by sensor 1 and the actual pressure value P2 of the hydrogen entering the fuel cell stack measured by sensor 2, D2 = P2 - P1; Step 2: Calculate the target hydrogen inlet pressure P6 according to the hydrogen-air pressure difference maintenance algorithm. The hydrogen-air pressure difference maintenance algorithm includes the following steps: S1. Determine whether D2 is in the interval [a, b]. The values ​​of a and b in the difference interval [a, b] are calibrated according to the stack performance. S2. If D2∈[a, b], calculate the target pressure of hydrogen entering the fuel cell stack, P6=P4+D1, where P4 is the target pressure of air entering the fuel cell stack, and D1 is the ideal difference between the hydrogen and air inlet pressures determined based on the fuel cell stack performance. S3. If D2 is not within the interval [a, b], calculate the target pressure of hydrogen entering the fuel cell stack, P6 = P1 + D1; Step 3: Calculate the difference between P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack, and use this difference to perform PI adjustment on the opening of the proportional valve in the hydrogen circuit; Step 4: Based on the PI adjustment of the proportional valve opening, the proportional valve opening feedforward value is added. The proportional valve opening feedforward value calculation process includes the following steps A1-A4: A1. Determine the reference value of the proportional valve opening feedforward value based on the target current I1 that the stack needs to output under the current operating conditions. Specific determination method: Perform a calibration test in advance to determine the feedforward reference value under various stack currents. Obtain a calibration result reference table. Based on the real-time current, interpolate the table to obtain the proportional valve feedforward reference value. A2. Determine the correction value 1 of the proportional valve feedforward value based on the target current I1 and the temperature at the proportional valve. Specific determination method: Perform a calibration test in advance to determine the correction value 1 of the feedforward value corresponding to the target current I1 and the temperature at the proportional valve. Obtain a calibration result reference table. Based on the real-time current I1 and the temperature at the proportional valve, interpolate the table to obtain the correction value 1 of the proportional valve feedforward value. A3. Determine the correction value 2 of the proportional valve feedforward value based on the hydrogen medium pressure P3. Specific determination method: Conduct a calibration test in advance to determine the correction value 2 of the proportional valve opening feedforward value at various hydrogen medium pressures. Obtain a calibration result reference table. Based on the real-time hydrogen medium pressure P3, interpolate the table to obtain the correction value 2 of the proportional valve opening feedforward value. A4, the product of the proportional valve opening feedforward value reference value, correction value 1 and correction value 2 is the final proportional valve opening feedforward value; Step 5: Add the PI processing result of step 3 and the opening feedforward value obtained in step 4 to obtain the final proportional valve target opening.

2. The method for controlling hydrogen pressure in a hydrogen fuel cell according to claim 1, wherein: PI regulation includes the following steps: Step 1. Calculation error: The error refers to the difference between the target hydrogen inlet pressure P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack; Step 2, proportional control: multiply the error obtained in Step 1 by the proportional gain coefficient Kp to obtain the proportional control term; Step 3, Integral control: Multiply the error obtained in Step 1 by the integral gain Ki, and add the result to the previous integral accumulated value to obtain the integral control term; Step 4. Calculate the PI controller output: Add the proportional control term obtained in Step 2 and the integral control term obtained in Step 3 to obtain the final result of PI regulation.

3. The method for controlling hydrogen pressure in a hydrogen fuel cell according to claim 1, wherein: The hydrogen temperature at the proportional valve is based on the coolant inlet temperature T1 as a reference value.

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