A method for controlling cathode gas subsystem of a fuel cell system when load varies

Abstract

The present invention provides a method for controlling a cathode gas subsystem of a fuel cell system under variable load, which specifically comprises the following steps: calculating a loading current value corresponding to the power of a whole vehicle, a target air pressure and a target air flow rate of the cathode gas at the current power, and if the actual air pressure or the actual air flow rate is not within an error range, adjusting and controlling the air compressor speed and the electronic throttle opening to reduce the pressure deviation and the flow deviation, until the pressure and the flow rate at the idle power point are controlled within the error range; calculating the current target air pressure and the target air flow rate according to the current actual loading current value, calculating the deviation value between the actual pressure and the target pressure, and calculating the deviation value between the actual flow rate and the target flow rate, and if the pressure deviation value or the flow rate deviation value is not within an allowable error range, controlling the air compressor speed or the electronic throttle opening to reduce the pressure deviation or the flow rate deviation, until the pressure deviation and the flow rate deviation enter the allowable error range, and reaching a steady state of pressure and flow control.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell technology, and in particular to a method for controlling a cathode gas subsystem of a fuel cell system when the load is variable. Background Art

[0002] A fuel cell is a device that converts the chemical energy in fuel (hydrogen) and oxidant (oxygen) into electrical energy through an electrochemical reaction. It has very few pollutants and high efficiency. It only needs to provide the required hydrogen and oxygen to continuously supply energy. Fuel cells have the advantages of light weight, high power density, good stability, low operating temperature and the ability to start quickly at low temperatures. It is currently the most promising fuel cell technology and is very suitable for powering vehicles.

[0003] The operation requirements of the cathode gas supply system are very strict when the fuel cell system is working. Different working conditions have different requirements for the air pressure and air flow of the cathode system. Only by meeting the requirements can the fuel cell performance be fully utilized and the fuel cell have a long service life. The cathode gas subsystem is a strongly coupled system with dual input and dual output. The control of air pressure and air flow is interrelated and affects each other, making system control very difficult. Therefore, an excellent cathode system control algorithm is a reliable guarantee for the long-term stable operation of the fuel cell system.

[0004] At present, when the fuel cell system is running in the process of adding and reducing load, the control of cathode gas is mainly based on table lookup open-loop control of the air compressor and electronic throttle, or table lookup open-loop pre-control and decoupling closed-loop control at the same time.

[0005] The disadvantage of table lookup open-loop control is that it cannot guarantee that the pressure and flow control of the cathode gas in different environments and when component parameters change meet the target requirements of pressure and flow. As the ambient temperature changes drastically or the difference in component parameters becomes larger, the table lookup control data calibrated in a single environment no longer has full coverage. The actual air pressure and air flow of the cathode gas deviate from the required target air pressure and air flow, which can easily cause an imbalance in the cathode gas supply, resulting in local gas shortages in the stack and corrosion of key materials such as the membrane electrode, thereby affecting the durability of the fuel cell system.

[0006] The disadvantages of table lookup open-loop pre-control and decoupling closed-loop simultaneous control are: although some disadvantages of table lookup open-loop control are solved, the open-loop table lookup data requires a lot of manpower and time to calibrate, and it is only calibration data under limited environments. Similarly, with the drastic changes in ambient temperature or the increasing differences in component parameters, dual errors of air pressure and air flow are introduced into the operation control, increasing the control time and control fluctuations of the decoupling control. Summary of the invention

[0007] According to the technical problems raised above, a method for controlling the cathode gas subsystem of a fuel cell system under variable load is provided, which suppresses the introduction of control errors, shortens the control time and control fluctuations, and saves a lot of manpower and time for data calibration.

[0008] During operation, the fuel cell system receives power requests and enable commands from the entire vehicle. After receiving the power command from the entire vehicle, the FCU controller starts to control the cathode gas subsystem, anode gas system, water thermal management system, and power distribution system in accordance with the startup and operation process of the fuel cell system. The output power meets the power requirements of the entire vehicle. The following specifically explains how the air pressure and air flow of the cathode gas subsystem, which is difficult to control, are controlled when the fuel cell system is running at different operating points.

[0009] After the fuel cell system is successfully started, it works at the minimum power value, that is, the idle power point. The controller calculates the loading current value corresponding to the idle power, and calculates the cathode gas target air pressure and target air flow of the current power through the loading current value. If the actual air pressure or the actual air flow is not within the error range, the air compressor speed and the electronic throttle opening are adjusted to reduce the pressure deviation and flow deviation until the pressure and flow control at the idle power point are within the error range. After the fuel cell system receives the power request command of the whole vehicle (the requested power is between the idle power value and the peak power value), the controller calculates the final loading target current value of the system through the power request value. At the same time, the actual loading current is controlled to change toward the final target current according to the current loading slope. During the current loading change process, the controller calculates the current target air pressure and target air flow in the cathode gas subsystem according to the current actual loading current value, and measures the actual air pressure and actual air flow of the cathode gas in real time, and then calculates the deviation value between the actual pressure and the target pressure, and the deviation value between the actual flow and the target flow. If the pressure deviation value or the flow deviation value is not within the allowable error range, the air compressor speed or the electronic throttle opening is controlled to reduce the pressure deviation or flow deviation until the pressure deviation and the flow deviation enter the allowable error range to achieve a steady state of pressure and flow control.

[0010] The controller of the fuel cell system receives the power request and enable command of the whole vehicle, executes the startup process of the fuel cell system, enters the idle working point after successful startup, operates according to the air compressor speed and electronic throttle opening of the preset idle point, and the system outputs the idle power value;

[0011] The fuel cell controller detects the actual air pressure, actual air flow, ambient temperature and ambient atmospheric pressure information of the cathode gas subsystem in real time;

[0012] Calculate the target loading current value according to the vehicle's requested power, compare the target loading current value with the loading current of the current working point Cn, and execute the loading control strategy when the target loading current value is greater than the loading current of the current working point; and execute the load reduction control strategy when the target loading current value is less than the loading current of the current working point;

[0013] When the loading control strategy is executed, the loading current value of the next working point Cn+1 is calculated, and the target air pressure and target air flow of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point;

[0014] When the load reduction control strategy is executed, the loading current value of the next working point Cn-1 is calculated, and the target air pressure and target air flow of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point;

[0015] Obtain the target air pressure and target air flow of the new working point, measure the actual pressure and actual flow of the cathode gas in real time, and calculate the pressure difference between the actual pressure and the target pressure, and the difference between the actual flow and the target flow;

[0016] During cathode gas pressure regulation:

[0017] Determine whether the actual air pressure is within the target pressure allowable range. If not, perform pressure adjustment at the new working point. Based on the air compressor speed at the working point Cn, calculate the compensation value per unit time through the pressure difference PID, and add it to the air compressor speed at the working point Cn as the new air compressor speed that tends to the steady-state working point Cn+1 or Cn-1. Repeat the above control until the actual pressure enters the target pressure range and the actual pressure at the working point Cn+1 or Cn-1 reaches a steady state; if yes, perform the next step of cathode gas flow adjustment process;

[0018] During cathode gas flow regulation:

[0019] Determine whether the actual air flow is within the target flow allowable range. If not, execute the flow adjustment of the new working point. Based on the electronic throttle opening of the working point Cn, calculate the compensation value per unit time through the flow difference PID, and add it to the electronic throttle opening of the working point Cn as the new electronic throttle opening of the steady-state working point Cn+1 or Cn-1. Repeat the above control until the actual flow enters the target flow range and the actual flow of the working point Cn+1 or Cn-1 reaches a steady state; if yes, the actual flow and actual pressure of the working point Cn+1 or Cn-1 reach a steady state, the pressure and flow adjustment control of the new working point ends, and the working point Cn+1 or Cn-1 is regarded as the new current working point, and the next working point is executed. Repeat the above process until the vehicle request power point is reached.

[0020] Furthermore, during the variable load operation of the fuel cell, the PID control algorithm of the air compressor speed is used to output a maximum limit value, and the maximum limit value is used as the air compressor speed at the peak power point.

[0021] Furthermore, during the variable load operation of the fuel cell, the PID control algorithm of the air compressor speed is used to output a minimum limit value, and the minimum limit value is used as the air compressor speed at the idle power point.

[0022] Furthermore, during the variable load operation of the fuel cell, the PID control algorithm of the electronic throttle opening is used to output a maximum limit value, and the maximum limit value is used as the electronic throttle opening at the peak power point.

[0023] Furthermore, during the variable load operation of the fuel cell, the PID control algorithm of the electronic throttle opening is used to output a minimum limit value, and the minimum limit value is used as the electronic throttle opening at the idle power point.

[0024] Furthermore, during the variable load operation of the fuel cell, there is an allowable pressure deviation value M Kpa to meet the target pressure at any power point. When the actual pressure is within the range of the target pressure ±M Kpa, the pressure requirement is met.

[0025] Furthermore, during the variable load operation of the fuel cell, there is an allowable pressure deviation value N Kpa to meet the target pressure at any power point. When the actual pressure is within the range of ±N Kpa of the target pressure, the pressure requirement is met.

[0026] The present invention discloses a method for controlling the cathode gas subsystem of a fuel cell system when the load is changed. In this method, when the fuel cell system is operated with load increase or decrease, a control method based on the air pressure and flow in the cathode system is used. This control method can save a lot of manpower and time consumed in data calibration, and also solves the introduction of double errors, reducing control fluctuations and control time. This method has good response characteristics and robustness. It can accurately control the pressure and flow of the cathode system to ensure that the performance of the fuel cell is always in the optimal state. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 Flow chart of the method of the present invention.

[0029] Figure 2 This is a power / current schematic diagram of the present invention when the load is changed.

[0030] Figure 3 It is a schematic diagram of the structure of the fuel cell system in the present invention.

[0031] In the figure: 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, 111, pressure sensor. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0034] This patent aims at the shortcomings of the existing control scheme and discloses a method for controlling the cathode gas subsystem of a fuel cell system under variable load, which suppresses the introduction of control errors, shortens the control time and control fluctuations, and saves a lot of manpower and time for data calibration. The method specifically includes the following steps:

[0035] After the fuel cell system controller receives the power request and enable command of the whole vehicle, the controller executes the startup work of the fuel cell system. After the system is successfully started, it enters the idle working point and operates according to the air compressor speed and electronic throttle opening of the idle point given in advance. The system outputs the idle power value.

[0036] During the operation of the fuel cell system, the controller detects the actual air pressure and actual air flow of the cathode gas subsystem in real time.

[0037] During the operation of the fuel cell system, the controller detects the ambient temperature and ambient atmospheric pressure in real time.

[0038] The controller calculates the target loading current according to the idle power value, and then calculates the target air pressure and target air flow of the cathode gas subsystem in combination with the ambient temperature and the ambient atmospheric pressure.

[0039] During the operation of the fuel cell system, the actual air pressure is controlled within the range of the target air pressure ±2Kpa, which meets the pressure control requirements of the system operation.

[0040] During the operation of the fuel cell system, the actual air flow rate is controlled within the range of ±2g / s of the target air flow rate, which meets the flow control requirements of the system operation.

[0041] The fuel cell system operates at the idle power point, and the controller calculates the deviation between the actual pressure and the target pressure, and the deviation between the actual flow and the target flow in real time. If the pressure deviation is not within the allowable error range, the pressure deviation is reduced to within the allowable range by adjusting the air compressor speed based on the idle air compressor speed. If the flow deviation is not within the allowable error range, the flow deviation is reduced to within the allowable range by adjusting the electronic throttle opening based on the idle electronic throttle opening, until the actual pressure and actual flow at the idle point are controlled within the allowable error range.

[0042] If the vehicle's requested power Pm is greater than the idle power P1, the controller calculates the target loading current value Cm corresponding to the requested power Pm. The target loading current value Cm is greater than the idle operating current value C1. The controller performs current loading control according to the current loading strategy. The current loading current gradually increases and is loaded to the target loading current value Cm after some time. In the process of gradually increasing the loading current (C1…Cn-1 Cn Cn+1…Cm, C1 is the idle current point for calculating the idle power, Cm is the target loading current point for calculating the vehicle request power, and Cn is the process current point), the controller calculates the target air pressure and target air flow rate at the current loading current point in real time according to the current loading current point Cn, the ambient temperature and the ambient atmospheric pressure, and detects the actual air pressure and actual air flow rate at this time in real time. If the actual pressure is not within the error range or the actual flow rate is not within the error range, the controller will execute the PID control algorithm based on the air compressor speed and the electronic throttle opening at the last loading current point Cn-1, change the air compressor speed or the electronic throttle opening to make the actual air pressure and the actual air flow rate change in the direction of the target air pressure and the target air flow rate, until the actual pressure and the actual flow rate are controlled within the allowable error range of the target pressure and the target flow rate; the controller then executes the control of the next loading current point Cn+1, which is the same as the process of executing the control of the loading current point Cn, and the above process is repeated. Finally, after the loading current point Cm is executed, the target loading current point is reached, that is, the vehicle power request is reached.

[0043] If the latest vehicle power request Pk is less than the last vehicle power request Pm, the controller calculates the target loading current value Ck corresponding to the latest requested power Pk. The target loading current value Ck is less than the last vehicle requested working current value Cm. The controller performs current load reduction control according to the current load reduction strategy. The current load reduction current gradually decreases and after some time, it is reduced to the target loading current value Ck. When the load reduction current gradually decreases (Cm…Cn-1 Cn Cn+1…Ck, Cm is the current point for calculating the power requested by the whole vehicle last time, Ck is the target loading current point for calculating the power requested by the whole vehicle at present, and Cn is the process current point), the controller calculates the target air pressure and the target air flow rate of the current loading current point in real time according to the current loading current point Cn, the ambient temperature and the ambient atmospheric pressure, and detects the actual air pressure and the actual air flow rate at this time in real time. If the actual pressure is not within the error range or the actual flow rate is not within the error range, the controller will execute the PID control algorithm based on the air compressor speed and the electronic throttle opening at the last loading current point Cn-1, change the speed of the air compressor or the opening of the electronic throttle to make the actual air pressure and the actual air flow rate change in the direction of the target air pressure and the target air flow rate, until the actual pressure and the actual flow rate are controlled within the allowable error range of the target pressure and the target flow rate; the controller then executes the control of the next loading current point Cn+1, which is the same as the process of executing the control of the loading current point Cn, and the above process is repeated. Finally, after the loading current point Ck is executed, the target loading current point is reached, that is, the latest vehicle power request is reached.

[0044] Example:

[0045] The controller receives the vehicle control command, executes the fuel cell system startup process according to the enable command, and runs at the idle power point 200 after successful startup. At this time, the controller calculates the target loading current value according to the vehicle request power, and compares it with the loading current of the current working point Cn 201. When the target loading current value is greater than the loading current of the current working point, the loading control strategy is executed, and when the target loading current value is less than the loading current of the current working point, the load reduction control strategy is executed;

[0046] If the loading control strategy is executed, the loading current value of the next working point Cn+1 is calculated, and the target air pressure and target air flow 203 of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point.

[0047] If the load reduction control strategy is executed, the loading current value of the next working point Cn-1 is calculated, and the target air pressure and target air flow 204 of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point.

[0048] The target air pressure and target air flow rate of the new working point are obtained, the actual pressure and actual flow rate of the cathode gas are measured in real time, and the difference between the actual pressure and the target pressure, and the difference between the actual flow rate and the target flow rate are calculated.

[0049] Cathode gas pressure regulation:

[0050] It is determined whether the actual air pressure is within the allowable range of the target pressure 206. If not, the pressure adjustment of the new working point is performed. Based on the air compressor speed at the working point Cn, the compensation value per unit time is calculated through the pressure difference PID, and added to the air compressor speed at the working point Cn as the new air compressor speed tending to the steady-state working point Cn+1 or Cn-1. The above control is repeatedly performed until the actual pressure enters the target pressure range and the actual pressure of the working point Cn+1 or Cn-1 reaches a steady state 207.

[0051] If yes, proceed to the next step of cathode gas flow adjustment.

[0052] Cathode gas flow regulation:

[0053] Determine whether the actual air flow is within the target flow allowable range 208. If not, perform flow regulation at the new working point. Based on the electronic throttle opening at the working point Cn, calculate the compensation value per unit time through the flow difference PID, and add it to the electronic throttle opening at the working point Cn as the new electronic throttle opening that tends to the steady-state working point Cn+1 or Cn-1. Repeat the above control until the actual flow enters the target flow range and the actual flow at the working point Cn+1 or Cn-1 reaches a steady state 209.

[0054] If yes, then the actual flow and actual pressure of the working point Cn+1 or Cn-1 reach a steady state 210. The pressure and flow regulation control of the new working point ends, and then the working point Cn+1 or Cn-1 is regarded as the new current working point, and the next working point is executed, and the above process is repeated until the vehicle request power point is reached.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling a cathode gas subsystem of a fuel cell system when the load is variable. It is characterized in that include: The controller of the fuel cell system receives the power request and enable command of the whole vehicle, executes the startup process of the fuel cell system, enters the idle working point after successful startup, operates according to the air compressor speed and electronic throttle opening of the preset idle point, and the system outputs the idle power value; The fuel cell controller detects the actual air pressure, actual air flow, ambient temperature and ambient atmospheric pressure information of the cathode gas subsystem in real time; Calculate the target loading current value according to the vehicle's requested power, compare the target loading current value with the loading current of the current working point Cn, and execute the loading control strategy when the target loading current value is greater than the loading current of the current working point; and execute the load reduction control strategy when the target loading current value is less than the loading current of the current working point; When the loading control strategy is executed, the loading current value of the next working point Cn+1 is calculated, and the target air pressure and target air flow of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point; When the load reduction control strategy is executed, the loading current value of the next working point Cn-1 is calculated, and the target air pressure and target air flow of this working point are calculated in combination with the ambient temperature value and the ambient atmospheric pressure as the control target of the new working point; Obtain the target air pressure and target air flow of the new working point, measure the actual pressure and actual flow of the cathode gas in real time, and calculate the pressure difference between the actual pressure and the target pressure, and the difference between the actual flow and the target flow; During cathode gas pressure regulation: Determine whether the actual air pressure is within the target pressure allowable range. If not, perform pressure adjustment at the new working point. Based on the air compressor speed at the working point Cn, calculate the compensation value per unit time through the pressure difference PID, and add it to the air compressor speed at the working point Cn as the new air compressor speed that tends to the steady-state working point Cn+1 or Cn-1. Repeat the above control until the actual pressure enters the target pressure range and the actual pressure at the working point Cn+1 or Cn-1 reaches a steady state; if yes, perform the next step of cathode gas flow adjustment process; During cathode gas flow regulation: Determine whether the actual air flow is within the target flow range. If not, perform flow adjustment at the new working point. Based on the electronic throttle opening at the working point Cn, calculate the compensation value per unit time through the flow difference PID, and add it to the electronic throttle opening at the working point Cn as the new electronic throttle opening that tends to the steady-state working point Cn+1 or Cn-1. Repeat the above control until the actual flow enters the target flow range and the actual flow at the working point Cn+1 or Cn-1 reaches a steady state. If yes, then the actual flow and actual pressure of the working point Cn+1 or Cn-1 reach a steady state, the pressure and flow regulation control of the new working point ends, the working point Cn+1 or Cn-1 is regarded as the new current working point, and the next working point is executed, and the above process is repeated until the vehicle request power point is reached; During the variable load operation of the fuel cell, the PID control algorithm of the air compressor speed is used to output the maximum limit value, and the maximum limit value is used as the air compressor speed at the peak power point; During the variable load operation of the fuel cell, the PID control algorithm of the air compressor speed is used to output the minimum limit value, and the minimum limit value is used as the air compressor speed at the idle power point; During the variable load operation of the fuel cell, the PID control algorithm of the electronic throttle opening is used to output the maximum limit value, and the maximum limit value is used as the electronic throttle opening at the peak power point; During the variable load operation of the fuel cell, the PID control algorithm of the electronic throttle opening is used to output the minimum limit value, and the minimum limit value is used as the electronic throttle opening at the idle power point.

2. The method according to claim 1 is characterized in that: during the variable load operation of the fuel cell, there is an allowable pressure deviation value M Kpa to meet the target pressure at any power point, and the pressure requirement is met when the actual pressure is within the range of the target pressure ±M Kpa.

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