A method for controlling pressure and flow of cathode gas in a fuel cell system

Abstract

The invention provides a method for controlling the pressure and flow of cathode gas in a fuel cell system. During the operation of the fuel cell system, the required values of the target pressure and target flow of the air supply system are calculated in real time according to the target operating current, and are compared with the measured air pressure and actual air flow. If the pressure difference or flow difference is not within the error range, the actual air pressure is adjusted to be within the pressure error range by controlling the air compressor speed, or the actual air flow is adjusted to be within the flow error range by controlling the electronic throttle valve, until the actual pressure and actual flow are both controlled within the error range. When the target operating current changes or other factors cause the pressure difference or flow difference to be outside the error range, the adjustment control is again activated until the actual pressure and actual flow are again controlled within the error range. This method ensures that the air supply system can provide the required air pressure and flow for the fuel cell, and ensures that the fuel cell system can operate in an optimal state.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell technology, in particular, and more particularly, to a method for stably controlling the pressure and flow of cathode gas of a fuel cell system. BACKGROUND

[0002] A fuel cell is a device that converts the chemical energy in fuel (hydrogen) and oxidant (oxygen) into electrical energy through electrochemical reactions, with very little pollution and high efficiency, and only needs to provide the required hydrogen and oxygen system to continuously supply energy. Fuel cells have the advantages of light weight, high power density, good stability, low operating temperature, and fast startup at low temperature, making them the most promising fuel cell technology and very suitable for providing power for vehicles.

[0003] Fuel cells have very strict requirements for air supply subsystems, and different operating states and working conditions require different air inlet pressures and air metering ratios. Only by meeting these requirements can the performance of the fuel cell be fully utilized and the service life of the fuel cell be ensured.

[0004] The air supply system mainly adjusts the pressure and flow of the cathode air path through an air compressor and an electronic throttle valve. Changes in the speed of the air compressor will simultaneously affect the pressure and flow of the air path, and changes in the opening of the electronic throttle valve will also simultaneously affect the pressure and flow of the air path. Therefore, this system is a strongly coupled system with double inputs and double outputs. The cathode air pressure and air flow of the fuel cell system are interrelated and interdependent when the system is running, making system control very difficult.

[0005] Current control methods for the inlet pressure and flow of the air system include open-loop control of the air compressor and electronic throttle valve lookup table, which has the disadvantage of being greatly affected by the environment and part consistency, and the control effect is not ideal. There are also closed-loop control methods based on PID or decoupling, which have complex parameter tuning and are prone to oscillation and overshoot. SUMMARY

[0006] According to the above-mentioned air system of fuel cell, the overshoot and oscillation of flow and pressure are suppressed, and a pressure and flow control method of cathode gas of fuel cell system is provided, which ensures that the actual pressure value and actual flow value are consistent with the target pressure and target flow when the fuel cell operates in various working conditions, and solves the problem that the fuel cell cathode gas is insufficient due to the deviation of the cathode gas pressure or flow from the actual target value, which causes the performance of the stack to decline and attenuate. Since the fuel cell system operates in the full working condition of the cycle variable load from the idle point to the peak point, the actual pressure and actual flow in the air supply system must meet the requirements of the air target pressure and air target flow at each working point, that is, the air target pressure and air target flow are calculated in real time during the full working condition of the fuel cell system, and the actual pressure and actual flow must be controlled within the target value range at the same time, otherwise the air supply system will be unbalanced, which will cause local air shortage in the stack and cause corrosion of key materials such as membrane electrode, thereby affecting the durability of the fuel cell system.

[0007] In the technical solution disclosed in the application, during the operation of the fuel cell system, the demand values of the target pressure and target flow of the air supply system are calculated in real time according to the target working current, and the measured air pressure and actual air flow are compared. If the pressure difference or flow difference is not within the error range, the actual air pressure is adjusted to be within the pressure error range by controlling the air compressor speed, or the actual air flow is adjusted to be within the flow error range by controlling the electronic throttle valve, until the actual pressure and actual flow are controlled within the error range, and the adjustment control ends and enters the pressure flow steady state. When the target working current changes or other factors cause the pressure difference or flow difference to be out of the error range, the adjustment control works again until the actual pressure and actual flow are controlled within the error range again. The specific scheme includes the following steps:

[0008] The target air pressure and target air flow under the current target loading current are calculated according to the current target working current and the ambient temperature of the fuel cell system, and the measured air pressure and actual air flow of the current air supply system are detected;

[0009] The air compressor speed variable step compensation value is calculated according to the deviation of the target air pressure from the measured air pressure, and the electronic throttle valve opening variable step compensation value is calculated according to the deviation of the target air flow from the actual air flow;

[0010] When the difference between the measured air pressure and the target air pressure of the air supply system is not within the pressure error range, and the measured air pressure is greater than the target air pressure, the speed of the air compressor is adjusted to decrease according to the modified step to reduce the air pressure;

[0011] When the difference between the measured air pressure and the target air pressure of the air supply system is not within the pressure error range, and the measured air pressure is less than the target air pressure, the rotational speed of the air compressor is adjusted to increase the air pressure according to the correction step;

[0012] When the difference between the actual air flow and the target air flow of the air supply system is not within the flow error range, and the actual air flow is greater than the target air flow, the opening of the electronic throttle valve is adjusted to decrease the air flow according to the correction step;

[0013] When the difference between the actual air flow and the target air flow of the air supply system is not within the flow error range, and the actual air flow is less than the target air flow, the opening of the electronic throttle valve is adjusted to increase the air flow according to the correction step;

[0014] When the difference between the measured air pressure and the target air pressure of the air supply system is within the pressure error range, and the difference between the actual air flow and the target air flow is within the flow error range, the rotational speed of the air compressor and the opening of the electronic throttle valve are controlled to remain unchanged.

[0015] Further, the target air pressure of the current fuel cell inlet is calculated according to the current ambient atmospheric pressure and the current power request of the fuel cell.

[0016] Further, the target air flow of the current fuel cell inlet is calculated according to the current ambient atmospheric pressure and the current power request of the fuel cell.

[0017] Further, the pressure error value of the fuel cell inlet is set as Pth, and when the absolute value of the difference between the target air pressure and the measured air pressure is less than the pressure error value Pth, the measured air pressure is no longer adjusted, and the pressure enters a steady state.

[0018] Further, the flow error value of the fuel cell inlet is set as Qth, and when the absolute value of the difference between the target air flow and the actual air flow is less than the flow error value Qth, the actual air flow is no longer adjusted, and the flow enters a steady state.

[0019] Further, when the measured air pressure and the actual air flow are both not within the error range, the air pressure is first adjusted to be within the error range, and then the air flow is adjusted to be within the error range; when the measured air pressure and the actual air flow are both not within the error range, the air flow is first adjusted to be within the error range, and then the air pressure is adjusted to be within the error range.

[0020] The application discloses a pressure and flow control method capable of stably controlling a cathode gas of a fuel cell system, and the method has good response characteristics and robustness through bench and vehicle verification under different systems and different environments. The method can precisely control the air inlet pressure and air inlet flow of the fuel cell system under different working states and different working conditions, and ensures that the fuel cell performance is always in the optimal state. The method adopts a variable step length adjustment or PID adjustment closed loop real-time adjustment control mode, ensures that the air supply system has good response characteristics, and simultaneously realizes high control precision through the closed loop control, and fully meets the application requirements of the fuel cell system. The variable step length or PID parameters and control period of the closed loop adjustment of the air compressor speed and the electronic throttle opening degree are given in a calibration mode, and the control effect can be ensured through calibration on a system test bench. In addition, the control mode is closed loop, and the air supply system can provide the air pressure and flow required by the fuel cell under the condition that the performance of parts is inconsistent or the long-time running state of parts changes, and the fuel cell system can be ensured to run in the optimal state. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 Flow chart of the method of the present application

[0023] Figure 2 Schematic diagram of the air supply system of the fuel cell in the method of the present application

[0024] Figure 3 Logic state diagram of the air compressor speed and the electronic throttle opening degree in the method of the present application

[0025] Figure 4 PID control flow chart in the method of the present application

[0026] In the drawings: 100, fuel cell, 101, air filter, 102, air flow meter, 104, air compressor, 105, intercooler, 106, inlet electronic throttle, 109, outlet electronic throttle, 110, controller, 103, first temperature and pressure sensor, 107, second temperature and pressure sensor, 108, third temperature and pressure sensor DETAILED DESCRIPTION

[0027] In order to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present application.

[0028] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product, or device.

[0029] The fuel cell system operates in a full working condition process of a cycle variable load from an idle point to a peak point. When operating at each working point, the actual pressure and the actual flow rate in the air supply system must simultaneously meet the requirements of the air target pressure and the air target flow rate, that is, the fuel cell system calculates the air target pressure and the air target flow rate in real time in the full working condition, and at the same time, the actual pressure and the actual flow rate must be controlled within the target value range, otherwise, air supply imbalance of the air system will occur, causing local air deficiency in the stack and leading to corrosion of key materials such as membrane electrodes, and further affecting the durability of the fuel cell system.

[0030] As shown in Figure 1 During the operation of the fuel cell system, the demand values of the target pressure and the target flow rate of the air supply system are calculated in real time according to the target working current, and are compared with the measured air pressure and the actual air flow rate. If the pressure difference or the flow difference is not within the error range, the actual pressure of the air is adjusted to be within the pressure error range by controlling the air compressor speed, or the actual flow rate of the air is adjusted to be within the flow error range by controlling the electronic throttle valve, until the actual pressure and the actual flow rate are both controlled within the error range, and the adjustment control ends to enter the pressure flow steady state. When the target working current changes or other factors cause the pressure difference or the flow difference to be not within the error range, the adjustment control works again until the actual pressure and the actual flow rate are again controlled within the error range.

[0031] The present application discloses a kind of pressure and flow control method capable of stable control of fuel cell system cathode gas, based asFigure 3 The system shown, wherein the fuel cell system specifically includes the following:

[0032] Fuel cell 100: convert hydrogen and oxygen into electricity through electrochemical reaction;

[0033] Air filter 101: filter impurities, dust, etc. in the air;

[0034] Air flow meter 102: measure air flow in the air path;

[0035] Air compressor 104: provide fresh air to the fuel cell stack through the cathode air flow path, control the air pressure inside the air path;

[0036] Intercooler 105: cool the air temperature before entering the fuel cell;

[0037] Inlet electronic throttle 106: located at the air inlet position of the fuel cell stack, after shutdown, cooperate with the outlet electronic throttle to seal the air chamber;

[0038] Outlet electronic throttle 109: located at the air outlet position of the fuel cell stack, adjust the air flow inside the air path;

[0039] Controller 110: measure the pressure, temperature, and flow information in the air supply system, and control the electronic throttle and air compressor;

[0040] First temperature and pressure sensor 103: measure the air pressure and temperature before the air compressor, for ambient temperature use;

[0041] Second temperature and pressure sensor 107: measure the air temperature and air pressure at the inlet of the fuel cell;

[0042] Third temperature and pressure sensor 108: measure the air temperature and air pressure at the outlet of the fuel cell; pressure sensor 111: measure the ambient atmospheric pressure

[0043] In working condition, the fuel cell system measures the current ambient temperature and atmospheric pressure in real time, and calculates the current system load target current, and calculates the air target pressure and air target flow of the air supply system in real time according to the load target current, atmospheric pressure and ambient temperature. The control diagram of air pressure and air flow is shown in Figure 3 .

[0044] Figure 3The pressure-flow chart of the air supply system is constituted by fitting together the rotation performance chart of the air compressor and the electronic throttle opening performance chart. As can be seen from the air compressor rotation curve and the electronic throttle opening curve in the chart, when the air pressure is not within the pressure error range or the air flow is not within the flow error range, the air pressure and the air flow can be controlled to reach the target requirement by adjusting the air compressor rotation or the electronic throttle opening to control the air pressure and the air flow within the appropriate pressure error and flow error range.

[0045] In Figure 3 , two working points A and B in the operation process of the fuel cell system are shown. The working points A and B are vertically projected onto the horizontal coordinate axis (air flow coordinate axis) and the vertical coordinate axis (air pressure coordinate axis) to correspond to the actual air flow value and the measured air pressure value respectively. It can be seen that the air pressure value of point B is greater than that of point A, and the air flow value of point B is greater than that of point A.

[0046] If the control working point is operated from point A to point B, first, the air compressor rotation is controlled to increase to increase the air pressure until the air pressure enters the pressure error range. Then, the electronic throttle opening is controlled to increase to increase the air flow. If the air pressure exceeds the pressure error range in the process of controlling the flow, the air compressor rotation is controlled again until the air pressure enters the pressure error range. Then, the electronic throttle is controlled to increase to increase the air flow. This is repeated until the air pressure and the air flow enter the respective error ranges. In this way, the working point is operated from point A to point B.

[0047] If the control working point is operated from point B to point A, first, the air compressor rotation is controlled to decrease to decrease the air pressure until the air pressure enters the pressure error range. Then, the electronic throttle opening is controlled to decrease to decrease the air flow. If the air pressure exceeds the pressure error range in the process of controlling the flow, the air compressor rotation is controlled again until the air pressure enters the pressure error range. Then, the electronic throttle is controlled to decrease to decrease the air flow. This is repeated until the air pressure and the air flow enter the respective error ranges. In this way, the working point is operated from point B to point A.

[0048] Among them, there are two schemes for controlling the air pressure and the air flow in the air supply system: variable step control and PID control, Figure 1 The variable step control flow chart is schematically shown, Figure 4 The PID control flow chart is schematically shown.

[0049] Example 1:

[0050] For the deviation of the air pressure and the air flow, the variable step control scheme one of the air compressor rotation and the electronic throttle opening is as follows:

[0051] The target air pressure and the target air flow of the air supply system are calculated in real time according to the target current, the ambient atmospheric pressure and the ambient temperature 200. The air pressure and the air flow at the inlet of the fuel cell system are measured in real time 201.

[0052] When the measured air pressure in the air supply system is greater than the target air pressure, the actual air flow is greater than the target air flow, or the measured air pressure is less than the target air pressure, and the actual air flow is less than the target air flow 202, the difference between the current measured air pressure and the target air pressure is calculated, the correction step value of the air compressor speed is calculated according to the pressure difference, and the air compressor speed is reduced according to the step value 203 to reduce the air pressure in the air supply system.

[0053] When the measured air pressure in the air supply system is greater than the target air pressure, the actual air flow is greater than the target air flow, or the measured air pressure is less than the target air pressure, and the actual air flow is greater than the target air flow 204, the difference between the current actual air flow and the target air flow is calculated, the correction step value of the electronic throttle valve is calculated according to the flow difference, and the opening of the electronic throttle valve is reduced according to the step value 205 to reduce the air flow in the air supply system.

[0054] When the actual air flow in the air supply system is within the flow error range, and the measured air pressure is within the pressure error range 206, the air supply system enters a flow and pressure stable state, at this time, the air compressor speed and the electronic throttle valve are not controlled, and the last control state is maintained.

[0055] Embodiment 2

[0056] PID control scheme two of the air compressor speed and the opening of the electronic throttle valve for the deviation of the air pressure and the air flow:

[0057] As shown in Figure 4 The target air pressure and the target air flow of the air supply system are calculated in real time according to the target current, the ambient atmospheric pressure and the ambient temperature 300. The air pressure and the air flow at the inlet of the fuel cell system are measured in real time 301.

[0058] When the measured air pressure in the air supply system is greater than the target air pressure, the actual air flow is greater than the target air flow, or the measured air pressure is less than the target air pressure, and the actual air flow is less than the target air flow 302, the difference between the current measured air pressure and the target air pressure is calculated, the current air compressor speed value is calculated by the PID control algorithm, and the air compressor speed is reduced according to the calculated speed value 303 to reduce the air pressure in the air supply system.

[0059] When the measured air pressure in the air supply system is greater than the target air pressure, the actual air flow is less than the target air flow, or the measured air pressure is less than the target air pressure, and the actual air flow is greater than the target air flow 304, the difference between the current actual air flow and the target air flow is calculated, the PID control algorithm calculates the current electronic throttle opening value, and the electronic throttle opening is reduced according to the calculated opening value 305, so as to reduce the air flow in the air supply system.

[0060] When the actual air flow in the air supply system is within the flow error range, and the measured air pressure is within the pressure error range, the air supply system enters a flow and pressure stable state 306, at this time the air compressor speed and the electronic throttle are not controlled, and the last control state is maintained.

[0061] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pressure and flow control method capable of stably controlling a cathode gas of a fuel cell system, characterized by, The method comprises the following steps: calculating the target air pressure and target air flow under the current target loading current according to the current target working current of the fuel cell system and the ambient temperature, and detecting the measured air pressure and actual air flow of the current air supply system; calculating the air compressor speed variable step compensation value according to the deviation of the target air pressure and the measured air pressure; calculating the electronic throttle opening variable step compensation value according to the deviation of the target air flow and the actual air flow; when the difference between the measured air pressure and the target air pressure of the air supply system is not within the pressure error range, and the measured air pressure is greater than the target air pressure, then the speed of the air compressor is adjusted according to the correction step to reduce the air pressure; when the difference between the measured air pressure and the target air pressure of the air supply system is not within the pressure error range, and the measured air pressure is less than the target air pressure, then the speed of the air compressor is adjusted according to the correction step to increase the air pressure; when the difference between the actual air flow and the target air flow of the air supply system is not within the flow error range, and the actual air flow is greater than the target air flow, then the opening of the electronic throttle is adjusted according to the correction step to reduce the air flow; when the difference between the actual air flow and the target air flow of the air supply system is not within the flow error range, and the actual air flow is less than the target air flow, then the opening of the electronic throttle is adjusted according to the correction step to increase the air flow; when the difference between the measured air pressure and the target air pressure of the air supply system is within the pressure allowable error range, and the difference between the actual air flow and the target air flow is within the flow allowable error range, then the speed of the air compressor and the opening of the electronic throttle are controlled to remain unchanged in the adjusted state.

2. The method of claim 1, wherein: calculating the target air pressure of the current fuel cell inlet according to the current ambient atmospheric pressure and the current power request of the fuel cell.

3. The method of claim 1, wherein: calculating the target air flow of the current fuel cell inlet according to the current ambient atmospheric pressure and the current power request of the fuel cell.

4. The method of claim 1, wherein: setting the pressure error value of the fuel cell inlet as Pth, when the absolute value of the difference between the target air pressure and the measured air pressure is less than the pressure error value Pth, then the measured air pressure is no longer adjusted, and the pressure enters the steady state.

5. The method of claim 1, wherein: setting the flow error value of the fuel cell inlet as Qth, when the absolute value of the difference between the target air flow and the actual air flow is less than the flow error value Qth, then the actual air flow is no longer adjusted, and the flow enters the steady state.

6. The method according to claim 1, characterized in that: when the measured air pressure and the actual air flow are both not within the error range, then the air pressure is first adjusted to be within the error range, and then the air flow is adjusted to be within the error range; when the measured air pressure and the actual air flow are both not within the error range, then the air flow is first adjusted to be within the error range, and then the air pressure is adjusted to be within the error range.

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