Composite MPPT (Maximum Power Point Tracking) control method suitable for small permanent magnet direct-driven wind power generation system

Abstract

The invention relates to the technical field of wind power generation, in particular to a composite MPPT (Maximum Power Point Tracking) control method suitable for a small permanent magnet direct-driven wind power generation system, which is realized by adopting the following steps of: S1, establishing a wind speed estimation model; s2, estimating the current wind speed; s3, the optimal tip speed ratio is initially set; s4, the optimal rotating speed corresponding to the current wind speed is calculated; s5, tracking by adopting an optimal tip speed ratio method; s6, whether the rotating speed difference value is larger than a switching threshold value or not is judged; step S7, tracking by adopting a hill-climbing search method; s8, whether the rotating speed difference value is larger than a switching threshold value or not is judged; step S9, tracking by adopting an optimal tip speed ratio method; s10, judging whether the slope is zero or not; and step S11, recalculating the optimal rotating speed corresponding to the current wind speed. The problems that an existing MPPT control method is low in tracking speed, poor in tracking stability and low in tracking success rate are solved, and the method is suitable for power supply in remote areas.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and specifically to a composite MPPT control method applicable to a small permanent magnet direct drive wind power generation system. Background Art

[0002] Small permanent magnet direct drive wind power generation systems are widely used in power supply for remote areas such as mountains, islands, and deserts due to their advantages of high efficiency, energy conservation, simple maintenance, high reliability, and strong adaptability. As Figure 1 shown, a small permanent magnet direct drive wind power generation system includes a wind turbine, a PMSG (Permanent Magnet Synchronous Generator), a rectifier, a boost chopper circuit, and a load. In practical applications, in order to make the small permanent magnet direct drive wind power generation system always output the maximum power, it is necessary to perform MPPT (Maximum Power Point Tracking) control on it. However, under the existing technical conditions, due to the limitations of its own principle, the MPPT control method has problems of slow tracking speed and poor tracking stability when applied to a small permanent magnet direct drive wind power generation system, and thus cannot well meet the control requirements. Based on this, it is necessary to invent a composite MPPT control method applicable to a small permanent magnet direct drive wind power generation system to solve the problems of slow tracking speed, poor tracking stability, and low tracking success rate of the existing MPPT control method when applied to a small permanent magnet direct drive wind power generation system. Summary of the Invention

[0003] The present invention provides a composite MPPT control method applicable to a small permanent magnet direct drive wind power generation system to solve the problems of slow tracking speed, poor tracking stability, and low tracking success rate of the existing MPPT control method when applied to a small permanent magnet direct drive wind power generation system.

[0004] The present invention is implemented by the following technical solutions: A composite MPPT control method applicable to a small permanent magnet direct drive wind power generation system, which is implemented by the following steps: Step S1: Establish a wind speed estimation model; Step S2: Start the small permanent magnet direct drive wind power generation system, collect the current speed and current power of the wind turbine in the system, and send the collected results into the wind speed estimation model. The wind speed estimation model estimates the current wind speed according to the collected results; Step S3: Perform an initial setting on the optimal tip speed ratio; Step S4: Calculate the optimal speed corresponding to the current wind speed according to the optimal tip speed ratio and the current wind speed. The specific calculation formula is as follows: ωref = λ opt · V w / R ; In the formula: ω ref represents the optimal rotational speed corresponding to the current wind speed; λ opt represents the optimal tip speed ratio; V w represents the current wind speed; R represents the blade radius of the wind turbine; Step S5: Track the maximum power point of the wind turbine using the optimal tip speed ratio method; Step S6: Determine whether the rotational speed difference is greater than the switching threshold; the rotational speed difference refers to the absolute difference between the optimal rotational speed corresponding to the current wind speed and the current rotational speed of the wind turbine; If the rotational speed difference is greater than the switching threshold, return to Step S5; If the rotational speed difference is less than or equal to the switching threshold, switch the tracking method from the optimal tip speed ratio method to the hill climbing search method, and then execute Step S7; Step S7: Track the maximum power point of the wind turbine using the hill climbing search method; Step S8: Determine whether the rotational speed difference is greater than the switching threshold; If the rotational speed difference is less than or equal to the switching threshold, return to Step S7; If the rotational speed difference is greater than the switching threshold, switch the tracking method from the hill climbing search method to the optimal tip speed ratio method, and then execute Step S9; Step S9: Track the maximum power point of the wind turbine using the optimal tip speed ratio method; Step S10: Determine whether the slope of the current power point of the wind turbine in its rotational speed - power curve is zero; If the slope is zero, return to Step S5; If the slope is not zero, determine whether the slope is greater than zero; If the slope is greater than zero, adaptively update the optimal tip speed ratio according to the following formula, and then execute Step S11; the specific update formula is as follows: λ opt = λ opt + α + β · k ; In the formula: λ opt represents the optimal tip speed ratio; α represents the step size increase factor; βRepresents the step size coefficient; k Represents the slope of the current power point of the wind turbine in its speed-power curve; If the slope is less than zero, adaptively update the optimal tip speed ratio according to the following formula, and then execute step S11; the specific update formula is as follows: λ opt = λ opt - γ + β · k ; In the formula: λ opt Represents the optimal tip speed ratio; γ Represents the step size reduction factor; β Represents the step size coefficient; k Represents the slope of the current power point of the wind turbine in its speed-power curve; Step S11: Substitute the optimal tip speed ratio into the formula in step S4, recalculate the optimal speed corresponding to the current wind speed, and then return to step S6.

[0005] Furthermore, in step S1, the wind speed estimation model is established by using support vector regression or gated recurrent unit or optimized backpropagation neural network; the optimized backpropagation neural network is obtained by optimizing the traditional backpropagation neural network using the improved parrot optimization algorithm.

[0006] Furthermore, in step S3, the initially set optimal tip speed ratio is 6.4; in step S10, α The value of β is 0.06, γ The value of

[0007] Furthermore, in steps S5 and S9, the specific tracking process is as follows: Send the speed difference into the proportional-integral controller, and the proportional-integral controller performs pulse width modulation on the duty cycle of the boost chopper circuit according to the speed difference, so that the current speed of the wind turbine quickly approaches the optimal speed corresponding to the current wind speed.

[0008] Furthermore, in step S7, the specific tracking process is as follows: Based on the current duty cycle of the boost chopper circuit, increase or decrease the duty cycle of the boost chopper circuit according to the positive or negative slope of the current power point of the wind turbine in its speed-power curve, so that the current speed of the wind turbine gradually approaches the optimal speed corresponding to the current wind speed.

[0009] Compared with the existing MPPT control methods, the composite MPPT control method for a small permanent magnet direct drive wind power generation system described in the present invention has the following advantages: First, the present invention adopts a composite control strategy combining the optimal tip speed ratio method and the hill climbing search method. On the one hand, it realizes the rapid tracking of the maximum power point of the wind turbine at the start of the wind turbine and in the initial stage of wind speed change. On the other hand, it ensures the stability of tracking when the wind speed is stable. Second, the present invention uses a brand-new update formula to adaptively update the optimal tip speed ratio, avoiding the failure of maximum power point tracking caused by inappropriate initial setting of the optimal tip speed ratio when the parameters of the wind turbine are unknown, thus ensuring the success rate of tracking when the wind speed is variable.

[0010] Through simulation tests, when the initially set optimal tip speed ratio is too large ( λ opt the value of Figure 3 is 9), the wind energy utilization coefficient curve of the wind turbine (as shown in Figure 4 ), and the output power curve (as shown in λ opt the value of Figure 5 is 6.4), the wind energy utilization coefficient curve of the wind turbine (as shown in Figure 6 ), and the output power curve (as shown in Figure 7 ), and the wind energy utilization coefficient curve of the wind turbine after adaptively updating the optimal tip speed ratio (as shown in Figure 8 ) and the output power curve (as shown in

[0011] are obtained respectively. Figure 3 、 Figure 5 、 Figure 7 By comparing

[0012] 、 Figure 4 、 Figure 6 、 Figure 8

[0013]

[0013] it can be seen that when the initially set optimal tip speed ratio is too large, the average value of the wind energy utilization coefficient of the wind turbine is about 0.47. When the initially set optimal tip speed ratio is too small, the average value of the wind energy utilization coefficient of the wind turbine is about 0.44. After adaptively updating the optimal tip speed ratio, the average value of the wind energy utilization coefficient of the wind turbine is about 0.48 (this value is greater than 0.47 and 0.44).

[0012] By comparing Figure 4 、 Figure 6 、 Figure 8

[0013]

[0013] it can be seen that when the initially set optimal tip speed ratio is too large, the maximum value of the output power of the wind turbine is about 390W. When the initially set optimal tip speed ratio is too small, the maximum value of the output power of the wind turbine is about 375W. After adaptively updating the optimal tip speed ratio, the maximum value of the output power of the wind turbine is about 410W (this value is greater than 390W and 375W).

[0013] It can be seen that by adaptively updating the optimal tip speed ratio, the present invention successfully tracks the maximum power point in the case where the parameters of the wind turbine are unknown.

[0014] The present invention effectively solves the problems of slow tracking speed, poor tracking stability, and low tracking success rate of existing MPPT control methods when applied to small permanent magnet direct drive wind power generation systems, and is applicable to power supply in remote areas such as mountains, islands, and deserts. Brief Description of the Drawings

[0015] Figure 1 is a schematic structural diagram of a small permanent magnet direct drive wind power generation system.

[0016] Figure 2 is a flowchart of steps S3 to S11 in the present invention.

[0017] Figure 3 is a curve graph of the wind energy utilization coefficient of the wind turbine when the initially set optimal tip speed ratio is too large.

[0018] Figure 4 is a curve graph of the output power of the wind turbine when the initially set optimal tip speed ratio is too large.

[0019] Figure 5 is a curve graph of the wind energy utilization coefficient of the wind turbine when the initially set optimal tip speed ratio is too small.

[0020] Figure 6 is a curve graph of the output power of the wind turbine when the initially set optimal tip speed ratio is too small.

[0021] Figure 7 is a curve graph of the wind energy utilization coefficient of the wind turbine after adaptively updating the optimal tip speed ratio.

[0022] Figure 8 is a curve graph of the output power of the wind turbine after adaptively updating the optimal tip speed ratio.

[0023] In the figure: λ opt represents the optimal tip speed ratio; ω ref represents the optimal rotational speed corresponding to the current wind speed; ω r represents the current rotational speed of the wind turbine; | ω ref - ω r | represents the rotational speed difference; ε represents the switching threshold; k represents the slope of the current power point of the wind turbine in its rotational speed-power curve; α represents the step increase factor; γrepresents the step - down factor; β represents the step - size coefficient. Specific implementation mode

[0024] A composite MPPT control method applicable to a small - scale permanent - magnet direct - drive wind power generation system, and this method is implemented by the following steps: Step S1: Establish a wind speed estimation model; Step S2: Start the small - scale permanent - magnet direct - drive wind power generation system, collect the current rotational speed and current power of the wind turbine in the system, and send the collected results into the wind speed estimation model. The wind speed estimation model estimates the current wind speed according to the collected results; Step S3: Initialize the optimal tip - speed ratio; Step S4: Calculate the optimal rotational speed corresponding to the current wind speed according to the optimal tip - speed ratio and the current wind speed. The specific calculation formula is as follows: ω ref = λ opt · V w / R ; In the formula: ω ref represents the optimal rotational speed corresponding to the current wind speed; λ opt represents the optimal tip - speed ratio; V w represents the current wind speed; R represents the blade radius of the wind turbine; Step S5: Use the optimal tip - speed ratio method to track the maximum power point of the wind turbine; Step S6: Judge whether the rotational speed difference is greater than the switching threshold; the rotational speed difference refers to the absolute difference between the optimal rotational speed corresponding to the current wind speed and the current rotational speed of the wind turbine; If the rotational speed difference is greater than the switching threshold, return to Step S5; If the rotational speed difference is less than or equal to the switching threshold, switch the tracking method from the optimal tip - speed ratio method to the hill - climbing search method, and then execute Step S7; Step S7: Use the hill - climbing search method to track the maximum power point of the wind turbine; Step S8: Judge whether the rotational speed difference is greater than the switching threshold; If the rotational speed difference is less than or equal to the switching threshold, return to Step S7; If the rotational speed difference is greater than the switching threshold, switch the tracking method from the hill - climbing search method to the optimal tip - speed ratio method, and then execute Step S9; Step S9: Use the optimal tip - speed ratio method to track the maximum power point of the wind turbine; Step S10: Determine whether the slope of the current power point of the wind turbine in its speed-power curve is zero; If the slope is zero, return to Step S5; If the slope is not zero, determine whether the slope is greater than zero; If the slope is greater than zero, adaptively update the optimal tip speed ratio according to the following formula, and then execute Step S11; the specific update formula is as follows: λ opt = λ opt + α + β · k ; In the formula: λ opt represents the optimal tip speed ratio; α represents the step increase factor; β represents the step coefficient; k represents the slope of the current power point of the wind turbine in its speed-power curve; If the slope is less than zero, adaptively update the optimal tip speed ratio according to the following formula, and then execute Step S11; the specific update formula is as follows: λ opt = λ opt - γ + β · k ; In the formula: λ opt represents the optimal tip speed ratio; γ represents the step decrease factor; β represents the step coefficient; k represents the slope of the current power point of the wind turbine in its speed-power curve; Step S11: Substitute the optimal tip speed ratio into the formula in Step S4, recalculate the optimal speed corresponding to the current wind speed, and then return to Step S6.

[0025] In Step S1, the wind speed estimation model is established by using support vector regression or gated recurrent unit or optimized backpropagation neural network; the optimized backpropagation neural network is obtained by optimizing the traditional backpropagation neural network using the improved parrot optimization algorithm.

[0026] In Step S3, the initially set optimal tip speed ratio is 6.4; in Step S10, α the value of β is 0.06, γ the value of

[0027] In the said step S5 and step S9, the specific tracking process is as follows: The rotational speed difference is sent into a proportional-integral controller, and the proportional-integral controller performs pulse width modulation on the duty cycle of the boost chopper circuit according to the rotational speed difference, so that the current rotational speed of the wind turbine rapidly approaches the optimal rotational speed corresponding to the current wind speed.

[0028] In the said step S7, the specific tracking process is as follows: Based on the current duty cycle of the boost chopper circuit, the duty cycle of the boost chopper circuit is increased or decreased according to the positive or negative slope of the current power point of the wind turbine in its rotational speed-power curve, so that the current rotational speed of the wind turbine gradually approaches the optimal rotational speed corresponding to the current wind speed.

[0029] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only illustrative examples, and the protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A composite MPPT control method suitable for a small permanent magnet direct-drive wind power generation system, characterized in that: This method is implemented by the following steps: Step S1: Establish a wind speed estimation model; Step S2: starting the small permanent magnet direct-drive wind power generation system, collecting the current speed and current power of the wind turbine in the system, sending the collected results to the wind speed estimation model, and the wind speed estimation model estimates the current wind speed according to the collected results; Step S3: Initially setting the optimal tip speed ratio; Step S4: Calculate the optimal rotation speed corresponding to the current wind speed according to the optimal tip speed ratio and the current wind speed; the specific calculation formula is as follows: ω ref = λ opt · V w / R ； Where: ω ref Indicates the optimal speed corresponding to the current wind speed; λ opt represents the optimum tip speed ratio; V w Indicates the current wind speed; R Indicates the blade radius of the wind turbine; Step S5: Tracking the maximum power point of the wind turbine using the optimal tip speed ratio method; Step S6: determining whether the speed difference is greater than a switching threshold; the speed difference refers to the absolute difference between the optimal speed corresponding to the current wind speed and the current speed of the wind turbine; If the speed difference is greater than the switching threshold, return to step S5; If the speed difference is less than or equal to the switching threshold, the tracking method is switched from the optimal tip speed ratio method to the hill climbing search method, and then step S7 is executed; Step S7: Tracking the maximum power point of the wind turbine using a hill climbing search method; Step S8: determining whether the speed difference is greater than a switching threshold; If the speed difference is less than or equal to the switching threshold, return to step S7; If the speed difference is greater than the switching threshold, the tracking method is switched from the hill climbing search method to the optimal tip speed ratio method, and then step S9 is executed; Step S9: Tracking the maximum power point of the wind turbine using the optimal tip speed ratio method; Step S10: determining whether the slope of the current power point of the wind turbine in its speed-power curve is zero; If the slope is zero, return to step S5; If the slope is not zero, determine whether the slope is greater than zero; If the slope is greater than zero, the optimal tip speed ratio is adaptively updated according to the following formula, and then step S11 is executed; the specific updating formula is as follows: λ opt = λ opt + α + β · k ； Where: λ opt represents the optimum tip speed ratio; α represents the step-length increase factor; β represents the step size coefficient; k Indicates the slope of the wind turbine's current power point in its speed-power curve; If the slope is less than zero, the optimal tip speed ratio is adaptively updated according to the following formula, and then step S11 is executed; the specific updating formula is as follows: λ opt = λ opt - γ + β · k ； Where: λ opt represents the optimum tip speed ratio; γ represents the step length reduction factor; β represents the step size coefficient; k Indicates the slope of the wind turbine's current power point in its speed-power curve; Step S11: Substitute the optimal tip speed ratio into the formula in step S4, recalculate the optimal rotation speed corresponding to the current wind speed, and then return to step S6.

2. A composite MPPT control method suitable for a small permanent magnet direct-drive wind power generation system according to claim 1, characterized in that: In step S1, the wind speed estimation model is established by using support vector regression or gated recurrent unit or optimized back propagation neural network; the optimized back propagation neural network is obtained by optimizing the traditional back propagation neural network by using the improved Parrot optimization algorithm.

3. The composite MPPT control method for a small permanent magnet direct-drive wind power generation system according to claim 1 is characterized in that: In step S3, the optimal tip speed ratio is initially set to 6.4; in step S10, α The value of is 0.06, β The value of is 0.02, γ The value of is 0.

02.

4. The composite MPPT control method for a small permanent magnet direct-drive wind power generation system according to claim 1 is characterized in that: In step S5 and step S9, the specific tracking process is as follows: the speed difference is sent to the proportional-integral controller, and the proportional-integral controller performs pulse width modulation on the duty cycle of the boost chopper circuit according to the speed difference, so that the current speed of the wind turbine quickly approaches the optimal speed corresponding to the current wind speed.

5. The composite MPPT control method for a small permanent magnet direct-drive wind power generation system according to claim 1 is characterized in that: In step S7, the specific tracking process is as follows: taking the current duty cycle of the boost chopper circuit as a reference, the duty cycle of the boost chopper circuit is increased or decreased according to the positive or negative slope of the current power point of the wind turbine in its speed-power curve, so that the current speed of the wind turbine gradually approaches the optimal speed corresponding to the current wind speed.

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