Control method and system of maximum power point of fuel cell based on improved step length

Abstract

The embodiment of the present invention provides a control method and system for the maximum power point of a fuel cell based on an improved step length, which belongs to the technical field of new energy vehicles. The control method includes: obtaining the current output current of the fuel cell; determining the corresponding second-order change rate on the corresponding relationship curve of the power and output current of the preset fuel cell according to the output current; judging whether the second-order change rate is greater than a first preset value; in the case where the second-order change rate is judged to be greater than the first preset value, updating the step length of the conductance increment method according to formula (1); in the case where the second-order change rate is judged to be less than or equal to the first preset value, calculating the change rate corresponding to the selected point; judging whether the change rate is greater than or equal to the second preset value of the maximum change rate; in the case where the change rate is judged to be greater than or equal to the second preset value of the maximum change rate, updating the step length of the conductance increment method according to formula (1); and adjusting the duty cycle of the fuel cell by the conductance increment method.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy vehicles, and in particular to a control method and system for a maximum power point of a fuel cell based on an improved step length. Background Art

[0002] In recent years, the global energy crisis and environmental pollution problems have become increasingly serious, and countries around the world have begun to vigorously develop renewable energy. Under the background that countries around the world are gradually banning the sale of fuel vehicles, major automakers are in urgent need of a clean energy to replace fuel. Among various clean energy sources, fuel cells, as a power generation equipment that directly converts chemical energy into electrical energy, are considered to be one of the most promising green energy sources. Among them, proton exchange membrane fuel cells (PEMFC) have the advantages of clean power generation, high reliability, high efficiency and low noise, and have gradually been applied to the research and development of new energy vehicles. However, the high maintenance cost and short service life of proton exchange membrane fuel cells have seriously hindered their large-scale application. The use of advanced control methods is an important means to improve the overall performance of fuel cells. Among them, the use of maximum power point tracking (MPPT) technology is currently the most commonly used solution to improve the overall performance of fuel cells. Although the fuel efficiency and output power of fuel cells cannot be optimized at the same time, in some practical applications, power density is more important than fuel efficiency. Therefore, controlling the fuel cell to output at the maximum power point is gradually becoming a research hotspot.

[0003] At present, a large number of domestic and foreign scholars have conducted in-depth research on MPPT technology and adopted the perturbation observation method (P&O). The advantage of this method is that the algorithm is simple and easy to implement, but it will produce oscillations in the steady state, seriously reducing the efficiency of the fuel cell; combining the perturbation observation method with the prediction model, by establishing the objective function of the system performance and estimating the position of the control variable at the next moment, to predict the direction of power movement on the curve, but its prediction model formula is relatively complex and difficult to implement under actual circumstances; using the fixed voltage method, the output voltage of the battery is continuously adjusted through the pre-set output voltage until the preset value is reached. This method is simple and easy to implement, but when external conditions change, the preset voltage needs to be continuously changed to achieve MPPT control, so it is not practical in actual operation. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to provide a control method and system for the maximum power point of a fuel cell based on an improved step size, wherein the control method and system can improve the output power of the fuel cell.

[0005] In order to achieve the above object, an embodiment of the present invention provides a method for controlling the maximum power point of a fuel cell based on an improved step size, comprising:

[0006] Get the current output current of the fuel cell;

[0007] Determining a corresponding second-order change rate according to the output current on a preset corresponding relationship curve between the power and the output current of the fuel cell;

[0008] Determining whether the second-order change rate is greater than a first preset value;

[0009] When it is determined that the second-order rate of change is greater than the first preset value, the step size of the conductance increment method is updated according to formula (1):

[0010]

[0011] Where D(k) is the duty cycle of the boost circuit at time k, D(k-1) is the duty cycle of the boost circuit at time k-1, and N1 is the step size factor. is the rate of change;

[0012] When it is determined that the second-order change rate is less than or equal to the first preset value, calculating the change rate corresponding to the selected point;

[0013] Determining whether the change rate is greater than or equal to a second preset value of a maximum change rate;

[0014] When it is determined that the change rate is greater than or equal to the second preset value of the maximum change rate, updating the step size of the conductance increment method according to formula (1);

[0015] The duty cycle of the fuel cell is adjusted by using a conductance increment method.

[0016] Optionally, the control method further includes:

[0017] In the case where it is determined that the change rate is less than the second preset value of the maximum change rate, determining whether the change rate is greater than or equal to a third preset value of the maximum change rate;

[0018] When it is determined that the change rate is greater than or equal to the third preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (2):

[0019]

[0020] Among them, N2 is the step size factor.

[0021] Optionally, the control method further includes:

[0022] When it is determined that the change rate is less than the third preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (3):

[0023]

[0024] Among them, N3 is the step size factor.

[0025] Optionally, the first preset value is 0.

[0026] Optionally, the second preset value is 2 / 3 of the maximum value of the change rate.

[0027] Optionally, the third preset value is 1 / 3 of the maximum value of the change rate.

[0028] Optionally, the conductance increment method comprises:

[0029] Determining whether the output current of the fuel cell is located to the left of the maximum power point;

[0030] When it is determined that the output current of the fuel cell is located on the left side of the maximum power point, the duty ratio of the output current of the fuel cell is increased.

[0031] Optionally, the conductance increment method comprises:

[0032] In the case where it is determined that the output current of the fuel cell is not located on the left side of the maximum power point, determining whether the output current of the fuel cell is located on the right side of the maximum power point;

[0033] When it is determined whether the output current of the fuel cell is located on the right side of the maximum power point, the duty cycle of the output current of the fuel cell is reduced.

[0034] Optionally, N1=10N2, N3=0.1N2

[0035] On the other hand, the present invention further provides a control system for a maximum power point of a fuel cell based on an improved step size, wherein the control system comprises a processor configured to execute any of the control methods described above.

[0036] Through the above technical scheme, the control method and system of the maximum power point of the fuel cell based on the improved step size provided by the present invention divides the corresponding relationship curve of the fuel cell into multiple intervals, and determines the step size of the conductance increment method according to the characteristics of each interval, so that the output power of the fuel cell is always maintained near the maximum power point, thereby improving the output efficiency of the fuel cell.

[0037] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0039] Figure 1 is a flow chart of a method for controlling a maximum power point of a fuel cell based on an improved step size according to an embodiment of the present invention;

[0040] Figure 2 is an exemplary diagram of a corresponding relationship curve between power and output current of a fuel cell according to an embodiment of the present invention;

[0041] Figure 3 is a flow chart of a conductance increment method according to one embodiment of the present invention;

[0042] Figure 4 is a comparison diagram of the output power of a fuel cell from 0 to 0.015 s according to an example of the present invention;

[0043] Figure 5 is a comparison chart of the convergence time of four algorithms at a temperature of 328K according to an example of the present invention;

[0044] Figure 6 is a comparison diagram of steady-state power fluctuations of four algorithms at 328K temperature according to an example of the present invention;

[0045] Figure 7 is a comparison chart of the convergence time of four algorithms at a temperature of 358K according to an example of the present invention;

[0046] Figure 8 This is a comparison chart of the convergence time of four algorithms at a temperature of 348K according to an example of the present invention. DETAILED DESCRIPTION

[0047] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0048] like Figure 1 FIG. 1 is a flow chart of a method for controlling the maximum power point of a fuel cell based on an improved step size according to an embodiment of the present invention. Figure 1 In the control method, the control method may include:

[0049] In step S10, the current output current of the fuel cell is obtained;

[0050] In step S11, a corresponding second-order change rate is determined on a preset corresponding relationship curve between the power and the output current of the fuel cell according to the output current;

[0051] In step S12, determining whether the second-order change rate is greater than a first preset value;

[0052] In step S13, when it is determined that the second-order rate of change is greater than the first preset value, the step size of the conductance increment method is updated according to formula (1):

[0053]

[0054] Where D(k) is the duty cycle of the boost circuit at time k, D(k-1) is the duty cycle of the boost circuit at time k-1, and N1 is the step size factor. is the rate of change;

[0055] In step S14, when it is determined that the second-order change rate is less than or equal to the first preset value, the change rate corresponding to the selected point is calculated;

[0056] In step S15, determining whether the change rate is greater than or equal to a second preset value of the maximum change rate;

[0057] When it is determined that the change rate is greater than or equal to the second preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (1), that is, step S13 is executed.

[0058] In step S16, when it is determined that the change rate is less than the second preset value of the maximum change rate, it is determined whether the change rate is greater than or equal to the third preset value of the maximum change rate;

[0059] In step S17, when it is determined that the change rate is greater than or equal to the third preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (2):

[0060]

[0061] Among them, N2 is the step size factor.

[0062] In step S18, when it is determined that the rate of change is less than the third preset value of the maximum rate of change, the step size of the conductance increment method is updated according to formula (3):

[0063]

[0064] Among them, N3 is the step size factor.

[0065] The traditional conductivity increment method is mainly used to adjust the duty cycle of the output current so that the output power of the fuel cell is always near the maximum power point, thereby improving the output efficiency of the fuel cell. However, the corresponding relationship curve between the power and output current of the fuel cell shows different change characteristics at different output current points. For example, when it is far away from the maximum power point, When the maximum power point is close, the tracking speed needs to be increased, that is, a larger step size needs to be provided. is smaller, so the accuracy needs to be increased, that is, a shorter step length needs to be provided. The step length change rule is shown in the following formula (4) and formula (5):

[0066]

[0067]

[0068] Where N is a fixed step size.

[0069] However, the step size of the conductivity increment method commonly used in the prior art is fixed. When the step size is a fixed value, if the step size is set too large, it will cause data oscillation; on the contrary, if the step size is set too small, although the data oscillation can be reduced, when the external conditions change rapidly, the system cannot respond in time, causing the power of the fuel cell to deviate from the maximum power point. Therefore, in the case of Figure 1 In the control method shown, step S10 is used to obtain the current output current of the fuel cell, and step S11 determines the corresponding second-order change rate on the corresponding relationship curve between power and output current for the obtained output current, and then combines steps S12 to S18 to divide the corresponding relationship curve into four regions, namely, when the second-order change rate is greater than or equal to 0, it is in region I; when the second-order change rate is less than 0 and the change rate is greater than or equal to 2 / 3 of the maximum value of the change rate, it is in region II; when the change rate is greater than or equal to 1 / 3 of the maximum value of the change rate and less than 2 / 3 of the maximum value, it is in region III; when the change rate is less than 1 / 3 of the maximum value, it is in region IV. It is known that when the change rate is less than 1 / 3 of the maximum value, the output power of the fuel cell is closest to the maximum power point, so the method of updating the step size of the conductance increment method can be improved in combination with the characteristics of each region, namely formula (1) to formula (3). When using formula (1), the corresponding relationship curves of zone I and zone II are farthest from the maximum power point, so a larger step size can be set, that is, N1 with a larger value; when using formula (2), zone III is closer to the maximum power point, so a smaller step size can be set, that is, N2 with a smaller value; when using formula (3), zone IV is closest to the maximum power point, so a larger step size can be set, that is, N3 with the smallest value. For the specific numerical relationship between N1, N2 and N3, N1, N2 and N3 can be any values ​​as long as the size relationship is satisfied. In a preferred example of the present invention, N1=10N2, N3=0.1N2.

[0070] In this embodiment, the conductance increment method may be in various forms known to those skilled in the art. However, in one example of the present invention, the conductance increment method may include: Figure 3 In the steps shown in Figure 3 In the invention, the conductance increment method may include:

[0071] In step S20, it is determined whether the output current of the fuel cell is located to the left of the maximum power point;

[0072] In step S21, when it is determined that the output current of the fuel cell is located to the left of the maximum power point, the duty cycle of the output current of the fuel cell is increased;

[0073] In step S22, when it is determined that the output current of the fuel cell is not located on the left side of the maximum power point, it is determined whether the output current of the fuel cell is located on the right side of the maximum power point;

[0074] In step S23 , when it is determined whether the output current of the fuel cell is located on the right side of the maximum power point, the duty ratio of the output current of the fuel cell is reduced.

[0075] Through the above technical scheme, the control method and system of the maximum power point of the fuel cell based on the improved step size provided by the present invention divides the corresponding relationship curve of the fuel cell into multiple intervals, and determines the step size of the conductance increment method according to the characteristics of each interval, so that the output power of the fuel cell is always maintained near the maximum power point, thereby improving the output efficiency of the fuel cell.

[0076] In order to further verify the technical effect of the control method and system provided by the present invention, in one embodiment of the present invention, a fuel cell model can be built in MATLAB / Simulink, and the control method provided by the present invention and various methods in the prior art are used to control the fuel cell model respectively, and the output power is compared to determine the technical effect of the method provided by the present invention (segmented variable step conductance increment method, I-VINC). The parameters of the fuel cell model are shown in Table 1.

[0077] Table 1 Basic parameters of Boost circuit

[0078]

[0079] Several methods in the prior art are perturbation and observation (P&O), fixed step size conductivity increment (INC) and fixed step size factor variable step size conductivity increment (VINC). The simulation time is set to 0.015s. From 0 to 0.006s, the temperature is set to 328K; from 0.006 to 0.012s, the temperature is increased to 358K; from 0.012 to 0.015s, the temperature is reduced to 348K. The experimental results are as follows Figures 4 to 8 shown.

[0080] Based on this Figures 4 to 8 The curve comparison data shown in , and the numerical comparison data are shown in Table 2,

[0081] Table 2 Comparison of four algorithms

[0082]

[0083] Aiming at the problem that the traditional variable step size conductance increment method cannot take into account both speed and accuracy at the same time, this paper proposes a segmented variable step size conductance increment method. This algorithm can select the appropriate step size factor according to the different working point positions of the fuel cell. By comparing with the perturbation observation method, conductance increment method and traditional variable step size conductance increment method in MATLAB / Simulink simulation, it is proved that this method has faster response speed and smaller power fluctuation, reduces the power loss of the fuel cell, and prolongs the life of the fuel cell.

[0084] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0085] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A control method for the maximum power point of a fuel cell based on an improved step size, characterized in that: The control method comprises: Get the current output current of the fuel cell; Determining a corresponding second-order change rate according to the output current on a preset corresponding relationship curve between the power and the output current of the fuel cell; Determining whether the second-order change rate is greater than a first preset value; When it is determined that the second-order rate of change is greater than the first preset value, the step size of the conductance increment method is updated according to formula (1): ，（1） in, for The duty cycle of the boost circuit corresponding to the moment, for The duty cycle of the boost circuit corresponding to the moment, is the step size factor, is the rate of change; When it is determined that the second-order change rate is less than or equal to the first preset value, calculating the change rate corresponding to the selected point; Determining whether the change rate is greater than or equal to a second preset value of a maximum change rate; When it is determined that the change rate is greater than or equal to the second preset value of the maximum change rate, updating the step size of the conductance increment method according to formula (1); Using a conductance increment method to adjust the duty cycle of the fuel cell; The control method further comprises: In the case where it is determined that the change rate is less than the second preset value of the maximum change rate, determining whether the change rate is greater than or equal to a third preset value of the maximum change rate; When it is determined that the change rate is greater than or equal to the third preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (2): ，（2） in, is the step size factor; When it is determined that the change rate is less than the third preset value of the maximum change rate, the step size of the conductance increment method is updated according to formula (3): ，（3） in, is the step size factor.

2. The control method according to claim 1, characterized in that: The first preset value is 0.

3. The control method according to claim 1, characterized in that: The second preset value is 2 / 3 of the maximum value of the change rate.

4. The control method according to claim 1, characterized in that: The third preset value is 1 / 3 of the maximum value of the change rate.

5. The control method according to claim 1, characterized in that: The conductance increment method comprises: Determining whether the output current of the fuel cell is located to the left of the maximum power point; When it is determined that the output current of the fuel cell is located on the left side of the maximum power point, the duty ratio of the output current of the fuel cell is increased.

6. The control method according to claim 5, characterized in that: The conductance increment method comprises: In the case where it is determined that the output current of the fuel cell is not located on the left side of the maximum power point, determining whether the output current of the fuel cell is located on the right side of the maximum power point; When it is determined whether the output current of the fuel cell is located on the right side of the maximum power point, the duty cycle of the output current of the fuel cell is reduced.

7. The control method according to claim 1, characterized in that: ， 。 8. A control system for a maximum power point of a fuel cell based on an improved step size, the control system comprising a processor configured to execute the control method according to any one of claims 1 to 7.

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