Method for controlling pressure of hydrogen in hydrogen fuel cell

Abstract

The invention relates to the field of fuel cells, in particular to a hydrogen pressure control method in a hydrogen fuel cell. The method comprises the following steps: step 1, calculating a difference D2 between an actual value P1 of the pressure of air entering a galvanic pile measured by a sensor 1 and an actual value P2 of the pressure of hydrogen entering the galvanic pile measured by a sensor 2, wherein D2 = P2-P1; step 2, calculating target hydrogen in-pile pressure P6 according to a hydrogen-air pressure difference keeping algorithm; 3, calculating the difference value between the P6 and the actual pressure value P2 of hydrogen entering the electric pile, and performing PI adjustment on the opening degree of a proportional valve on a hydrogen loop by using the difference value; step 4, adding a proportional valve opening feed-forward value on the basis of performing PI adjustment on the proportional valve opening; and 5, adding the PI processing result obtained in the step 3 and the opening feed-forward value obtained in the step 4 to obtain the final proportional valve target opening. According to the invention, the problem that the proportional valve has hysteresis on hydrogen in-pile pressure control is solved, and the dependence on a pressure sensor is reduced.

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 the hydrogen fuel cell engine is working, hydrogen and oxygen are transported into the stack from different subsystems for reaction. The hydrogen fuel cell control system adjusts the pressure of hydrogen entering the stack at different stack operating points to ensure that the pressure requirement of the current stack operating point is met, and the hydrogen pressure follows the changes in air pressure in time 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 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 stack structure and economic losses.

[0003] At present, the regulation of hydrogen pressure is often achieved by adjusting the valve opening on the hydrogen circuit. In the existing technical solutions, various pressure detection sensors are often installed on 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 according to the detected pressure.

[0004] like Figure 1 As shown, sensor 1 measures the air pressure entering the stack, sensor 2 measures the pressure of 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 hydrogen after it enters the system but before passing through the proportional valve (valve 1). Sensor 5 measures the temperature of hydrogen when it enters the stack. Valve 1 is a proportional valve installed in the hydrogen circuit. Adjusting the opening of the proportional valve can control the pressure of hydrogen entering the system. Valve 2 is a shut-off valve that controls the opening and closing of the hydrogen supply.

[0005] The hydrogen delivered into the loop will be mixed with some gas after passing through valve 2 and valve 1, and delivered into the stack together. This part of the added gas is the remaining unreacted hydrogen extracted from the gas discharged from the stack (because in most hydrogen fuel cell engines now, 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 stack is discharged from the system through a hydrophobic nitrogen discharge device to discharge 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 then deliver it to the 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, it does not take into account the hysteresis of hydrogen pressure control and cannot change the hydrogen inlet pressure 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 method for controlling the hydrogen pressure in a hydrogen fuel cell, thereby solving the problem of hysteresis of the proportional valve in controlling the hydrogen inlet pressure and reducing the dependence on the pressure sensor.

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

[0010] Step 1: Calculate the difference D2 between the actual value P1 of the air pressure entering the fuel cell stack measured by sensor 1 and the actual value P2 of the hydrogen pressure 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 the difference to perform PI adjustment on the opening of the proportional valve in the hydrogen circuit;

[0013] Step 4: Based on the PI adjustment of the proportional valve opening, increase the proportional valve opening feedforward value;

[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 comprises the following steps:

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

[0017] 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, and D1 is the difference between the ideal hydrogen and air pressures entering the fuel cell stack determined based on the fuel cell stack performance;

[0018] S3. If D2 is not in the interval [a, b], calculate the target pressure 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 accumulation 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 as 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 according to the target current I1 that the stack needs to output under the current working condition;

[0026] A2, determining a 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 according to the hydrogen medium pressure P3;

[0028] 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.

[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] The present invention adopts a PI control algorithm based on feedforward compensation, comprehensively considers the air pressure entering the fuel cell stack, the real-time temperature and pressure of hydrogen at the proportional valve, controls the opening of the proportional valve, solves the problem of hysteresis of the proportional valve for hydrogen inlet pressure control, and reduces the dependence on the pressure sensor. In addition, the coolant inlet temperature T1 is used as the reference value of the hydrogen temperature at the proportional valve, and there is no need to install an additional temperature sensor at the proportional valve, which reduces the economic cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a simplified diagram of the hydrogen supply system of 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 PI regulation process of hydrogen inlet pressure;

[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, a method for controlling hydrogen pressure in a hydrogen fuel cell proposed in this embodiment includes the following steps:

[0038] Step 1: Calculate the difference D2 between the actual value P1 of the air pressure entering the fuel cell stack measured by sensor 1 and the actual value P2 of the hydrogen pressure 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], and the values ​​of a and b in the difference interval [a, b] are calibrated according to the performance of the battery stack;

[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 output currents. For example, the system requires the current output by the fuel cell stack to be a continuous 24A. In order to generate such electrical energy, the pressure of the air supply system needs to reach a certain threshold. For example, it is 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 stack at the 24A operating point is P4=100kpa. Therefore, through experimental calibration, the air pressure entering the 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 pressure entering the 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 in the interval [a, b], calculate the target pressure value 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 the difference to perform PI adjustment on the opening of the proportional valve on the hydrogen circuit. The 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 the 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 the 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 by experimental calibration) to obtain the proportional control term Kp*e(t). Proportional control makes the output of the controller proportional to the error. The larger the error, the larger the output of the controller, 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 as 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 overshoot of the PI algorithm on the hydrogen inlet pressure and improve the tracking of the system on 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 medium 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 according to the target current I1 that the stack needs to output under the current working condition. The specific determination method is to conduct a calibration test in advance to determine the feedforward reference value under each stack current. The calibration result is in the form of Table 1. Finally, according to the real-time current, the proportional valve feedforward reference value is obtained by table interpolation.

[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 stack

[0051]

[0052] A2. Determine the correction value 1 of the proportional valve feedforward value according to 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 result is shown in Table 2. Finally, according to the real-time current I1 and the temperature at the proportional valve, the correction value 1 of the valve 1 feedforward value is obtained by looking up the table and interpolating;

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

[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 flow rates of the coolant and the hydrogen are both very fast. The difference between the coolant temperature at the preheater, the hydrogen temperature at valve 1 and the temperature T1 when the coolant enters 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 according to 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 under each hydrogen medium pressure. The calibration result form is shown in Table 3. Finally, according to the real-time hydrogen medium pressure P3, the correction value 2 of the proportional valve opening feedforward value is obtained by looking up the table and interpolating;

[0057] Table 3. Example of the corresponding 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 reference value of proportional valve opening feedforward 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 adopts a PI control algorithm based on feedforward compensation, comprehensively considers the air pressure entering the fuel cell stack, the real-time temperature and pressure of the hydrogen at the proportional valve (valve 1), and controls the opening of the proportional valve (valve 1), thereby solving the problem of hysteresis of the proportional valve for the pressure control of hydrogen entering the stack and reducing the dependence on the pressure sensor. In addition, since the difference between the coolant temperature at the preheater, the hydrogen temperature at valve 1 and the temperature T1 when the coolant enters 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, and there is no need to install an additional temperature sensor at valve 1, thereby reducing the economic cost.

[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. In order 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, and various changes can be made within the knowledge scope of technicians in the relevant technical field without departing from the purpose 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 value P1 of the air pressure entering the fuel cell stack measured by sensor 1 and the actual value P2 of the hydrogen pressure 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; Step 3: Calculate the difference between P6 and the actual pressure value P2 of hydrogen entering the fuel cell stack, and use the 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, increase the 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, characterized in that: The hydrogen-air pressure difference maintenance algorithm includes the following steps: S1, determine whether D2 is in the interval [a, b], and the values ​​of a and b in the difference interval [a, b] are calibrated according to the performance of the battery stack; 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, and D1 is the difference between the ideal hydrogen and air pressures entering the fuel cell stack determined based on the fuel cell stack performance; S3. If D2 is not in the interval [a, b], calculate the target pressure of hydrogen entering the fuel cell stack P6 = P1 + D1.

3. The method for controlling hydrogen pressure in a hydrogen fuel cell according to claim 2, characterized in that: 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 accumulation 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 as the final result of PI regulation.

4. The method for controlling hydrogen pressure in a hydrogen fuel cell according to claim 3, characterized in that: 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 according to the target current I1 that the stack needs to output under the current working condition; A2, determining a correction value 1 of the proportional valve feedforward value according to the target current I1 and the temperature at the proportional valve; A3. Determine the correction value 2 of the proportional valve feedforward value according to the hydrogen medium pressure P3; 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.

5. The method for controlling hydrogen pressure in a hydrogen fuel cell according to claim 4, characterized in that: The hydrogen temperature at the proportional valve takes the coolant inlet temperature T1 as a reference value.

Images