Fan mppt control method based on virtual aerodynamic power compensation

Abstract

The application discloses a fan MPPT control method based on virtual aerodynamic power compensation, and improves an existing optimally tracking rotor (OTR) method, and comprises the following contents: on the basis of the traditional OTR method, a compensation loop of the difference between the filtered aerodynamic power and the optimal power is added in an electromagnetic power control loop, based on which, the aerodynamic power of the wind power generation system under the current wind speed state condition is virtually compensated by further dynamically switching the value of a compensation coefficient delta, then the imbalance torque of the fan is increased to increase the rotor acceleration, and finally the purpose of increasing the tracking performance of the rotor is achieved. Compared with the traditional OTR method, the method disclosed by the application can reduce the load consumption under the same wind energy capture efficiency.

Description

Technical Field

[0001] This invention relates to an improved optimal tracking rotor control method in the field of MPPT control for wind turbines, specifically a method for virtual compensation of the aerodynamic power of the wind turbine. Background Technology

[0002] Maximum Power Point Tracking (MPPT) is an important control mode in wind power generation system control strategies. Below rated wind speed, MPPT control strategies are used to maximize wind energy capture. Common low-wind-speed wind turbines operate below rated wind speed for a significant portion of the time, making improved MPPT efficiency crucial. Common MPPT control methods include Optimal Torque (OT), Tip Speed ​​Ratio (TSR), and Hill-Climbing Search (HCS). The most widely used method, Optimal Torque, adjusts the electromagnetic torque, thereby regulating the unbalanced torque of the wind turbine generator to accelerate or decelerate the rotor, indirectly achieving speed control.

[0003] Traditional optimal torque methods have some shortcomings in capturing wind energy. When wind turbines operate in turbulent winds, the tracking target of the OT method is the steady-state operating point of the electromagnetic torque, i.e., the optimal electromagnetic torque, which leads to poor wind energy capture. The Optimally Tracking Rotor (OTR) method, from a dynamic perspective, adds an extra torque command to the electromagnetic torque setpoint of the OT method. This allows the unbalanced torque of the wind turbine to be further increased as wind speed changes, thereby improving the dynamic tracking performance of the wind turbine. Similar methods include inertial compensation control, torque gain reduction control, and constant bandwidth control.

[0004] Because the energy contained in the low-frequency wind speed range is far greater than that in the high-frequency wind speed range, the energy contained in low-frequency wind speeds is more worthy of tracking. However, traditional OTR methods aim to capture the energy contained in wind speeds across the entire frequency band, tracking both high- and low-frequency wind speed ranges to the same degree. That is, they focus on tracking wind speeds with full effort in both the high- and low-frequency ranges, ignoring the load cost incurred in tracking both high- and low-frequency wind speeds. This leads to a linear increase in load on wind turbines as they pursue even small amounts of high-frequency wind energy. Therefore, how to improve the OTR method to increase the proportion of tracking in the low-frequency wind speed range, reduce the drastic increase in load caused by capturing high-frequency wind energy, and obtain greater tracking benefits is the focus of this invention. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of traditional OTR methods. Considering that MPPT is an important control mode in the control strategy of wind power generation systems, this invention addresses the problem of drastic load increase caused by the traditional OTR method tracking wind speeds to the same extent across the entire frequency band. It proposes an improved OTR control method that virtually compensates for the aerodynamic power of the wind turbine. A filter is added at the aerodynamic power of the wind turbine to further reduce the system load. A method for judging the current wind speed information is designed, and the compensation coefficient is dynamically adjusted based on the current wind turbine tracking status to increase the tracking ability of wind speeds in the gradually increasing low-frequency wind speed range, thereby enhancing wind energy capture.

[0006] The technical solution to achieve the purpose of this invention is: a wind turbine MPPT control method based on virtual aerodynamic power compensation. This method is an improvement on the traditional Optimally Tracking Rotor (OTR) method, which employs the following control strategy:

[0007] P g =K opt ω r 3 -G(P a -K opt ω r 3 )

[0008] In the formula, P a The calculated value of aerodynamic power is expressed as follows: For optimal electromagnetic power, ω r The rotational speed of the wind turbine is where ρ is the air density, R is the rotor radius, and when the wind turbine system is in the MPPT control phase, the pitch angle β = 0°, and the wind energy utilization coefficient C p The tip speed ratio λ = ω depends only on λ. r R / v, where v is the wind speed, when C p Achieving maximum wind energy utilization coefficient At that time, there exists an optimal tip velocity ratio λ. opt P g G is the electromagnetic power setpoint, and G is the control parameter.

[0009] The MPPT control of the wind turbine based on virtual aerodynamic power compensation adopts the following control strategy:

[0010] P g =K opt ω r 3 -G(δP a_lpf -K opt ω r 3 )

[0011] In the formula, P a_lpf The value is the aerodynamic power calculated after filtering, where δ is the aerodynamic power compensation coefficient, and δ needs to be determined based on the fan tracking status.

[0012] Furthermore, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation is characterized by: first, in order to eliminate the load problem caused by the continuous change of high-frequency wind speed in the output of the wind power generation system, the aerodynamic power calculation signal of the traditional OTR method is filtered to obtain P. a_lpf Second, a virtual aerodynamic power compensation coefficient δ was designed. Its function is to set different values ​​of compensation coefficient δ during the MPPT control stage to virtually compensate the calculated aerodynamic power of the wind power generation system under the current wind speed conditions, adjust the magnitude of the electromagnetic power command value, increase the unbalanced torque of the wind turbine, thereby increasing the wind turbine acceleration, and ultimately improve the tracking performance of the wind turbine.

[0013] Furthermore, the aerodynamic power compensation coefficient δ is set based on the current tracking status of the wind turbine, including the following steps:

[0014] Step 1: Design the compensation coefficient δ, whose mathematical expression is as follows:

[0015]

[0016] In the formula, δ1 is the aerodynamic power compensation coefficient when the wind speed is in the deceleration phase, and δ2 is the aerodynamic power compensation coefficient when the wind speed is in the acceleration phase.

[0017] Step 2: To determine the wind turbine acceleration To determine the acceleration and deceleration states, it is necessary to collect current wind speed information and calculate the theoretically optimal rotational speed ω. ropt The expression is as follows:

[0018] ω ropt =λ opt v / R

[0019] Further based on the actual rotational speed ω r And the optimal tracking target ω of rotational speed ropt The magnitude of the value determines the acceleration / deceleration tracking state, and the determination principle is as follows:

[0020]

[0021] ω r >ω ropt And the duration T is greater than t1, so it is determined that this is the deceleration phase; when ω r <ω ropt If the duration T is greater than t1, it is determined that this is the acceleration phase.

[0022] Furthermore, regarding the aerodynamic power P a A first-order low-pass filter is introduced into the signal to reduce the dramatic increase in high-frequency load caused by capturing high-frequency wind speeds in turbulence. The expression after introducing the filter is as follows:

[0023]

[0024] In the formula, Let τ be the filter expression, τ be the filter parameter, and s be the frequency domain in the Laplace transform.

[0025] Furthermore, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation described above requires designing the value of the compensation coefficient δ, where δ1<1 during deceleration and δ2>1 during acceleration, with δ1∈[0.6,1] and δ2∈(1,1.5).

[0026] Furthermore, based on the aforementioned requirements for the value of δ, if the value of δ is too aggressive, it may lead to an over-limit of the electromagnetic power command. Therefore, the following constraints are required:

[0027]

[0028] In the formula, the threshold value of electromagnetic power is set to 110%P. gN , where P gN This is a rated power limit. When the output electromagnetic power command value exceeds the set threshold, P... g The value is set to a threshold; when the output electromagnetic power command value is between 0 and the set threshold, P g The value is itself; when the output electromagnetic power command value is less than 0, P g The value is 0.

[0029] Furthermore, in the wind turbine MPPT control strategy based on virtual aerodynamic power compensation described above, the value of t1 is between 0.5s and 1.5s.

[0030] Compared with the prior art, the beneficial effects of this invention are as follows:

[0031] a) The use of filtering steps reduces the dramatic increase in load caused by capturing high-frequency wind speeds, making the wind energy MPPT process focus more on capturing low-frequency wind energy.

[0032] b) The compensation coefficient δ is dynamically adjusted according to the current tracking status. This dynamic adjustment method is based on the tracking status judgment. When accelerating, δ2 is set to reduce the set value of electromagnetic power, increase the unbalanced torque and thus increase the wind turbine acceleration, thereby enhancing the wind turbine's tracking performance for gradually increasing wind speed. When decelerating, δ1 is set to increase the unbalanced torque, thereby reducing the wind turbine acceleration and enhancing the wind turbine's tracking performance for gradually decreasing wind speed. Attached Figure Description

[0033] Figure 1 The control block diagram is for the wind turbine MPPT control strategy based on virtual aerodynamic power compensation.

[0034] Figure 2 The diagram shows the rotational speed tracking trajectory of the OT method, the traditional OTR method, and the wind turbine MPPT control method based on virtual aerodynamic power compensation in the embodiments of the present invention. Detailed Implementation

[0035] The traditional OTR method and the wind turbine MPPT control method based on virtual aerodynamic power compensation described in this embodiment use the following parameters:

[0036] Table 1. Structure and Control Parameters of Wind Turbine Units

[0037]

[0038] Among them, C p The curve (λ,β) is expressed using the following mathematical expression:

[0039]

[0040] λ i = [1 / (λ+0.08β)-0.035 / (1+β)] 3 )] -1

[0041] In the above formula, when the wind turbine system is in the MPPT control phase, the pitch angle β = 0°, and the wind energy utilization coefficient C p The tip speed ratio λ = ω depends only on λ. g R / v, when C p To achieve the maximum wind energy utilization coefficient C pmax At that time, there exists an optimal tip velocity ratio λ. opt .

[0042] In this embodiment, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation is an improved method based on the traditional Optimally Tracking Rotor (OTR) method. The traditional OTR method adopts the following control strategy:

[0043] P g =K opt ω r 3 -G(P a -K opt ω r 3 )

[0044] In the formula, P aThe calculated value of aerodynamic power is expressed as follows: For optimal electromagnetic power, ω r The rotational speed of the wind turbine is where ρ is the air density, R is the rotor radius, and when the wind turbine system is in the MPPT control phase, the pitch angle β = 0°, and the wind energy utilization coefficient C p The tip speed ratio λ = ω depends only on λ. r R / v, where v is the wind speed, when C p Achieving maximum wind energy utilization coefficient At that time, there exists an optimal tip velocity ratio λ. opt P g G is the electromagnetic power setpoint, and G is the control parameter.

[0045] The MPPT control of the wind turbine based on virtual aerodynamic power compensation adopts the following control strategy:

[0046] P g =K opt ω r 3 -G(δP a_lpf -K opt ω r 3 )

[0047] In the formula, P a_lpf The value is the aerodynamic power calculated after filtering, where δ is the aerodynamic power compensation coefficient, and δ needs to be determined based on the fan tracking status.

[0048] In this embodiment, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation is characterized by: first, in order to eliminate the load problem caused by the continuous change of high-frequency wind speed in the output of the wind power generation system, the aerodynamic power calculation signal of the traditional OTR method is filtered to obtain P. a_lpf Second, a virtual aerodynamic power compensation coefficient δ was designed. Its function is to set different values ​​of compensation coefficient δ during the MPPT control stage to virtually compensate the calculated aerodynamic power of the wind power generation system under the current wind speed conditions, adjust the magnitude of the electromagnetic power command value, increase the unbalanced torque of the wind turbine, thereby increasing the wind turbine acceleration, and ultimately improve the tracking performance of the wind turbine.

[0049] In this embodiment, the aerodynamic power compensation coefficient δ is set according to the current tracking status of the wind turbine, including the following steps:

[0050] Step 1: Design the compensation coefficient δ, whose mathematical expression is as follows:

[0051]

[0052] In the formula, δ1 is the aerodynamic power compensation coefficient when the wind speed is in the deceleration phase, and δ2 is the aerodynamic power compensation coefficient when the wind speed is in the acceleration phase.

[0053] Step 2: To determine the wind turbine acceleration To determine the acceleration and deceleration states, it is necessary to collect current wind speed information and calculate the theoretically optimal rotational speed ω. ropt The expression is as follows:

[0054] ω ropt =λ opt v / R

[0055] Further based on the actual rotational speed ω r And the optimal tracking target ω of rotational speed ropt The magnitude of the value determines the acceleration / deceleration tracking state, and the determination principle is as follows:

[0056]

[0057] When ω r >ω ropt And the duration T is greater than t1, so it is determined that this is the deceleration phase; when ω r <ω ropt If the duration T is greater than t1, it is determined that this is the acceleration phase.

[0058] In this embodiment, the aerodynamic power P a A first-order low-pass filter is introduced into the signal to reduce the dramatic increase in high-frequency load caused by capturing high-frequency wind speeds in turbulence. The expression after introducing the filter is as follows:

[0059]

[0060] In the formula, Here is the filter expression, τ is the filter parameter, set to τ = 1.5, and s represents the frequency domain in the Laplace transform.

[0061] In this embodiment, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation described above requires designing the value of the compensation coefficient δ, where δ1 = 0.8 during deceleration and δ2 = 1.2 during acceleration.

[0062] In this embodiment, based on the aforementioned requirement for the value of δ, if the value of δ is too aggressive, it may lead to an over-limit of the electromagnetic power command value. Therefore, the following constraint needs to be adopted:

[0063]

[0064] In the formula, the threshold value of electromagnetic power is set to 110%P. gN , where P gNThis is a rated power limit. When the output electromagnetic power command value exceeds the set threshold, P... g The value is set to a threshold; when the output electromagnetic power command value is between 0 and the set threshold, P g The value is itself; when the output electromagnetic power command value is less than 0, P g The value is 0.

[0065] In this embodiment, the wind turbine MPPT control strategy based on virtual aerodynamic power compensation described above has a value of 1s for t1.

[0066] As a specific example, the invention will be further described in detail in one embodiment.

[0067] Wind speed files were generated using Turbsim, and a turbulent wind speed sequence with a duration of 10 minutes and a sampling period of 0.05 seconds was randomly generated. MPPT control was applied to the OT method, the traditional OTR method, and the improved OTR method based on virtual aerodynamic power compensation. A constant compensation coefficient was set to optimize the wind energy capture efficiency P of the traditional OTR and the improved OTR method based on virtual aerodynamic power compensation. favg When the loads are the same, calculate the loads corresponding to the two methods. and load growth rate At this point, the constant compensation coefficient G = 0.5 is obtained for this method, while the constant compensation coefficient G = 0.7 for the traditional OTR method.

[0068] Furthermore, the wind turbine speed tracking trajectories and corresponding compensation coefficients under the three methods are as follows: Figure 2 As shown, the wind energy capture efficiency P is given. favg Efficiency improvement rate load and load growth rate As shown in Table 2.

[0069] Table 2 Comparison of data results for the three MPPT methods

[0070]

[0071] As shown in the table above, the wind energy capture efficiency of the traditional OTR method and the method proposed in this invention is equal, with an improvement of 2.42%. At this point, the load growth rate of the method proposed in this invention is only 30.19%, while the average load reduction rate of the traditional OTR method is 21.52%, achieving the same average wind energy capture efficiency at a lower load cost. Figure 2 It can be seen that the method proposed in this paper increases the tracking ability of wind speed in the gradually increasing low-frequency wind speed range, thereby enhancing the capture of wind energy.

[0072] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this invention should be included within the protection scope of this invention. The protection scope of this invention should be determined by the scope of the claims.

Claims

1. A wind turbine MPPT control method based on virtual aerodynamic power compensation, characterized in that, The aerodynamic power calculation signal is filtered to reduce the drastic increase in load caused by capturing high-frequency wind speeds; a virtual aerodynamic power compensation coefficient is set according to the wind turbine acceleration state to virtually compensate the aerodynamic power calculation value of the wind power generation system under the current wind speed state, and the magnitude of the electromagnetic power command value is adjusted to increase the tracking performance of the wind turbine. The specific control strategy is as follows: In the formula, P a_lpf The value is the aerodynamic power after filtering, where δ is the aerodynamic power compensation coefficient, and δ is determined based on the fan tracking status. , Here is the filter expression, where τ is the filter parameter; P a The calculated value of aerodynamic power is expressed as follows: , For optimal electromagnetic power, ω r The rotational speed of the wind turbine is where ρ is the air density, R is the rotor radius, and when the wind turbine system is in the MPPT control phase, the pitch angle β = 0°, and the wind energy utilization coefficient C p Tip speed ratio is only related to λ. v is the wind speed, when C p Achieving maximum wind energy utilization coefficient At that time, there exists an optimal tip velocity ratio λ. opt P g G is the electromagnetic power setpoint, and G is the control parameter. Its aerodynamic power compensation coefficient δ is set according to the current tracking status of the wind turbine, including the following steps: Step 1: Design the compensation coefficient δ, whose mathematical expression is as follows: In the formula, δ1 is the aerodynamic power compensation coefficient when the wind speed is decelerating, and δ2 is the aerodynamic power compensation coefficient when the wind speed is accelerating. The value of the compensation coefficient δ is δ1 < 1 when decelerating and δ2 > 1 when accelerating, δ1 ∈ [0.6, 1], δ2 ∈ (1, 1.5]. Step 2, to determine the wind turbine acceleration To determine the acceleration and deceleration states, it is necessary to collect current wind speed information and calculate the theoretically optimal rotational speed ω. ropt The expression is as follows: Based on the actual rotational speed ω r And the optimal tracking target ω of rotational speed ropt The magnitude of the acceleration / deceleration tracking state is determined by the following expression: ω r >ω ropt And the duration T is greater than t1, so it is determined that this is the deceleration phase; when ω r <ω ropt If the duration T is greater than t1, it is determined that this is the acceleration phase.

2. The wind turbine MPPT control method based on virtual aerodynamic power compensation according to claim 1, wherein the value of δ is subject to the following constraints: In the formula, the threshold value of electromagnetic power is set to 110%P. gN , where P gN This is a rated power limit; when the output electromagnetic power command value exceeds the set threshold, P... g The value is set to a threshold; when the output electromagnetic power command value is between 0 and the set threshold, P g The value is itself; when the output electromagnetic power command value is less than 0, P g The value is 0.

3. In the wind turbine MPPT control method based on virtual aerodynamic power compensation according to claim 2, the value of t1 in step 2 ranges from 0.5s to 1.5s.

4. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1 to 3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1 to 3.

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