Adaptive frequency control method for wind turbines considering wind speed variation and speed recovery

Abstract

The present invention discloses an adaptive frequency control method for a wind turbine group considering wind speed change and speed recovery. In view of the shortcomings of weak dynamic adjustment capability and lack of consideration of wind speed change in the frequency droop control of traditional wind turbines, the reference power of the wind turbine in the frequency regulation process is adjusted in real time through adaptive frequency droop control, that is, in the frequency regulation control process, the wind speed frequency adjustment coefficient is obtained according to the real-time wind speed and wind speed change, and the basic frequency adjustment coefficient is determined according to the variable coefficient frequency control of the effective rotational kinetic energy of the wind turbine, so as to calculate and determine the output active power reference value; finally, in the speed recovery stage, the speed recovery control coefficient is determined according to the speed recovery function. The present invention enables the wind turbine to smoothly switch to the MPPT operation mode, thereby eliminating the secondary frequency impact of the speed recovery on the power grid while achieving smooth and controllable speed recovery, and enhancing the safety of the frequency response.

Description

Technical Field

[0001] The invention belongs to the technical field of wind power generation, and in particular relates to an adaptive frequency control method for a wind turbine generator set taking into account wind speed variation and rotation speed recovery. Background Art

[0002] Variable speed wind turbines are the mainstream models in wind farms. They realize the functional exchange between the rotor side and the grid side through the converter, resulting in the decoupling of their speed from the grid frequency. They use vector control technology and have the advantages of power decoupling control and maximum power point tracking (MPPT). However, MPPT operation decouples the frequency of wind turbines from the system frequency, making them incapable of inertial response. With the increasing penetration rate of wind turbines, the inertia and frequency control capabilities of the power system will be significantly reduced, deteriorating the frequency safety characteristics of the system and restricting the level of wind power consumption. When the system frequency deviation is too large, it will trigger protection actions such as low-frequency load reduction, thereby endangering the frequency safety and stability of the entire system, and reducing the overall inertia level and primary frequency regulation capability of the power system. After the disturbance occurs in the power grid, the maximum frequency deviation of the power grid increases. With the increasing penetration rate of wind power, this phenomenon will become more serious.

[0003] The wind turbine can reserve a certain amount of active power for system frequency regulation through overspeed control, pitch control and the coordinated control strategy of the two. Reference [Wang Jisong, Chen Mingliang. Experimental study on primary frequency regulation of wind turbine with virtual inertia and pitch control [J]. Electrical Measurement and Instrumentation, 2019, 56(23): 18-23] proposed a control strategy combining inertia control and pitch control, which effectively improved the steady-state characteristics of the system frequency. However, in actual operation, the frequent action of the pitch angle will increase the mechanical fatigue of the wind turbine and shorten the life of the pitch system. Reference [Cai Guowei, Zhong Chao, Wu Gang, et al. Power system unit combination strategy considering wind turbine overspeed load reduction and inertia control [J]. Automation of Electric Power Systems, 2021, 45(16): 134-142] proposed to use overspeed control and virtual inertia control collaborative control strategy to participate in system frequency regulation. Although this method is conducive to extending the life of the wind turbine variable pitch system, the wind turbine runs in load reduction mode for a long time, which reduces the speed adjustment range, weakens the wind turbine frequency regulation ability under high-frequency disturbance, and is not conducive to the economic operation of the wind farm. Reference [Zhao Jingjing, Li Min, He Xinqin, et al. Wind-storage joint frequency regulation control strategy based on torque limit control [J]. Transactions of the Chinese Society of Electrotechnical Engineering, 2019, 34(23): 4982-4990] proposed to use energy storage devices to eliminate secondary frequency drops while achieving rapid speed recovery. However, due to the high system cost of energy storage devices, large-scale configuration is not economical. The above studies mainly focus on the operating status of the wind turbine itself, and the research on the frequency regulation characteristics of the wind turbine under different wind speed scenarios is not in-depth enough. These controls no longer consider the impact of wind speed changes after the frequency regulation begins. In fact, during the frequency regulation period, the wind speed input to the wind turbine may change significantly, and continuous wind speed changes may have a significant impact on the wind turbine during the frequency regulation period. At the same time, the problem of rotor speed recovery is not considered. Summary of the invention

[0004] In order to enable the wind turbine to adapt to the continuous change of wind speed during the frequency regulation process and avoid the secondary frequency drop problem caused by the recovery of the rotor speed after the wind turbine participates in the frequency regulation process, so as to obtain a better frequency regulation effect, the present invention provides a wind turbine adaptive frequency control method considering wind speed change and speed recovery, which is improved on the basis of the existing control strategy based on the effective rotational kinetic energy of the wind turbine. In the power grid frequency support stage, the frequency control coefficient is coupled with the wind speed by means of an exponential function, which can effectively improve the adaptability of the control strategy to wind speed changes. In the speed recovery stage, the control coefficient is smoothly decayed to zero within a preset time with the help of a quadratic decreasing function.

[0005] An adaptive frequency control method for wind turbines considering wind speed changes and speed recovery is proposed. For a grid-connected system including a wind turbine, an output active power reference value of a converter control unit on the wind turbine side is improved to improve the system's adaptability to wind speed changes during frequency regulation, and additional speed recovery control is performed after the frequency regulation is completed.

[0006] Furthermore, the specific process of improving the design of the output active power reference value is as follows:

[0007] (1) Obtain the grid frequency and real-time wind speed through monitoring, and then calculate the frequency change and wind speed change;

[0008] (2) Calculate and determine the basic frequency adjustment coefficient according to the variable coefficient frequency control strategy based on the effective rotational kinetic energy of the wind turbine generator;

[0009] (3) Calculate and determine the wind speed frequency control parameters based on the real-time wind speed and wind speed change;

[0010] (4) The output active power reference value is calculated and determined based on the basic frequency adjustment coefficient and wind speed frequency control parameters.

[0011] Furthermore, in step (1), the frequency change and wind speed change are calculated by the following formula:

[0012]

[0013] in: v is the real-time wind speed, Δ v is the wind speed change, Δ f is the frequency change, f s is the actual grid frequency, f 0 is the rated frequency of the power grid, t Indicates the current moment.

[0014] Furthermore, in step (2), the basic frequency adjustment coefficient is calculated and determined by the following formula:

[0015]

[0016] in: C is the basic adjustment coefficient of the wind turbine, k f is the basic frequency adjustment coefficient, oh min is the minimum rotational angular velocity of the wind turbine, oh r is the angular velocity of the wind turbine.

[0017] Furthermore, in step (3), the wind speed frequency control parameter is determined by calculating using the following formula:

[0018]

[0019] in: k v is the wind speed frequency control parameter, e is a natural constant, v is the real-time wind speed, Δ v is the wind speed change, α is the control coefficient.

[0020] Furthermore, the control coefficient α The size of is determined by the wind power penetration rate (i.e. the proportion of wind power capacity in the system to all power generation capacity). When the wind power penetration rate is low (by setting a threshold for comparison), increasing α The value of is conducive to the wind turbine to fully utilize the rotor kinetic energy of wind power to accelerate the operation recovery of the wind turbine; when the wind power penetration is high, reducing α The value of can be controlled to slow down the MPPT operation recovery speed of the wind turbine, which is beneficial to reduce the burden of other synchronous generators in the system to output more active power to adjust the frequency and prevent the occurrence of secondary frequency drop.

[0021] Furthermore, in step (4), the output active power reference value is calculated by the following formula:

[0022]

[0023] in: P ref is the output active power reference value, P MPPT is the active power output of the wind turbine in the MPPT operation mode, Δ P is the power compensation amount, Δ f is the frequency change, K is the intermediate variable coefficient, k f is the basic frequency adjustment coefficient, k v is the wind speed frequency control parameter.

[0024] Furthermore, the speed recovery control is specifically implemented as follows: when the actual speed of the wind turbine generator is monitored to converge, , start the rotor speed recovery link, adjust the coefficient of the original basic frequency k f and wind speed frequency control parameters k vBased on this, multiply it by a decreasing speed recovery function f rec ( t ), and obtain the speed recovery control coefficient k rec , and then the output active power reference value is determined by the following expression: P ref , used to control the wind turbine side converter;

[0025]

[0026] in: P MPPT is the active power output of the wind turbine in the MPPT operation mode, Δ P is the power compensation amount, Δ f is the frequency change, oh r ( t + T ) is the wind turbine generator t + T The angular velocity of rotation at the moment, oh r ( t ) is the wind turbine generator t The angular velocity of rotation at the moment, T is the sampling period, d To set the threshold, t Indicates the current moment.

[0027] Furthermore, the decreasing speed recovery function f rec ( t ) is as follows:

[0028]

[0029] in: t 0 represents the start time of the speed recovery link, Δ t Indicates the duration of the speed recovery phase.

[0030] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is used to execute the computer program to implement the above-mentioned wind turbine adaptive frequency control method considering wind speed change and rotation speed recovery.

[0031] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for adaptive frequency control of a wind turbine generator set taking into account wind speed variation and rotation speed recovery is implemented.

[0032] Based on the above technical solution, the present invention has the following beneficial technical effects:

[0033] 1. The invention improves on the control strategy of effective rotational kinetic energy of the wind turbine, effectively alleviates the problem of excessive deceleration that may occur in the deceleration stage of traditional droop control, enhances the safety of frequency response, and establishes a coupling relationship between the frequency control coefficient and the wind speed change with the help of an exponential function, so that the wind turbine generator set can fully utilize the rotor kinetic energy to provide high-quality frequency response services for the power grid under different wind speed change scenarios. In the speed recovery stage, with the help of a quadratic decreasing function, the control coefficient is smoothly decayed to zero within a preset time, so that the wind turbine can smoothly switch to the MPPT operation mode, thereby achieving a smooth and controllable speed recovery while eliminating the secondary frequency impact of the speed recovery on the power grid.

[0034] 2. The present invention introduces a frequency control coefficient that takes wind speed changes into consideration, and establishes a coupling relationship between the frequency control coefficient and the wind speed change with the help of an exponential function. This enables the wind turbine to further release more rotor kinetic energy to participate in the frequency modulation process when the wind speed rises rapidly, and to slow down the kinetic energy release of the wind turbine to prevent the problem of excessive deceleration when the wind speed drops rapidly, so that the wind turbine can smoothly return to the MPPT control mode and prepare for the next frequency modulation control. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a flow chart of a method for adaptive frequency control of a wind turbine generator system in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0037] The present invention is a wind turbine adaptive frequency control method that takes into account wind speed changes and speed recovery. For a grid-connected system including a wind turbine, an output active power reference value of the wind turbine is improved and designed. The system further considers wind speed changes during the frequency response process, adaptively adjusts the wind turbine output active power reference value, and adds speed recovery control after the frequency adjustment is completed. The specific implementation process is as follows: Figure 1 As shown:

[0038] (1) Obtain the grid frequency and real-time wind speed changes of the wind turbine to be controlled, and then obtain the frequency change, measured wind speed, and wind speed change.

[0039] The real-time wind speed monitored by this implementation method v , wind speed change Δ v And the frequency change Δ f , designed to achieve wind speed frequency adjustment coefficient kv ,in , Δ v =d v / d t , f s is the actual grid frequency, f 0 is the rated frequency of the power grid.

[0040] (2) Determine the basic frequency adjustment coefficient based on the variable coefficient frequency control of the effective rotational kinetic energy of the wind turbine k f .

[0041] In this embodiment, the basic frequency adjustment coefficient is obtained based on the variable coefficient frequency control coefficient formula of the effective rotational kinetic energy of the wind turbine. k f , the specific formula is as follows:

[0042]

[0043] in: C is the basic adjustment coefficient of the wind turbine, oh min is the minimum rotational angular velocity of the wind turbine, oh r is the angular velocity of the wind turbine, It represents the effective rotational kinetic energy of the wind turbine, so that the wind turbine can effectively utilize the rotor kinetic energy to participate in system frequency regulation under different wind speed scenarios, while avoiding wind turbine stall.

[0044] (3) Calculate and determine the wind speed frequency control parameters based on the measured wind speed and wind speed change k v .

[0045] This embodiment uses the following formula to calculate and determine the wind speed frequency control parameter:

[0046]

[0047] Among them: The improved control strategy can flexibly adjust the control coefficient according to the change of wind speed k v , control coefficient α The size of is determined by the wind power penetration rate (i.e. the proportion of wind power capacity in the system to all power generation capacity). When the wind power penetration rate is low (by setting a threshold for comparison), increasing α The value of is conducive to the wind turbine to fully utilize the rotor kinetic energy of wind power to accelerate the operation recovery of the wind turbine; when the wind power penetration is high, reducing αThe value of can be controlled to slow down the MPPT operation recovery speed of the wind turbine, which is beneficial to reduce the burden of other synchronous generators in the system to output more active power to adjust the frequency and prevent the occurrence of secondary frequency drop.

[0048] (4) Calculate and determine the output active power reference value based on the basic frequency adjustment coefficient and wind speed frequency control parameters P ref .

[0049] In this implementation, the output active power reference value is calculated by the following formula:

[0050]

[0051] in: P ref is the output active power reference value, P MPPT is the active power output of the wind turbine in the MPPT operation mode, Δ P is the power compensation amount, K is the coefficient of the intermediate variable.

[0052] (5) Determine the speed recovery control coefficient based on the speed recovery function k rec , when the actual rotor speed meets the convergence condition When the speed is restored, the fan will resume operation in MPPT mode after frequency modulation.

[0053] This embodiment is to set a speed recovery link for the wind turbine adaptive frequency control method, that is, when the actual rotor speed converges, that is, ,in T is the sampling period of the wind turbine rotor speed, d is a small value close to 0, which can be configured as required. When convergence is detected, the rotor speed recovery link is started, and the original coefficient K The basis is multiplied by the decreasing speed recovery function f rec ( t ) to obtain the speed recovery control coefficient k rec ; The speed recovery process of the wind turbine is determined by the recovery function, and the specific formula is expressed as:

[0054]

[0055] in: t 0 represents the start time of the speed recovery link, Δ t Indicates the duration of the speed recovery phase.

[0056] Then, the output active power reference value is calculated and determined according to the following expression to control the wind turbine side converter;

[0057]

[0058] Finally, the control coefficient decreases smoothly with time and is t 0+Δ t ) seconds later, it converges smoothly to zero, thus achieving a smooth and controllable speed recovery and effectively avoiding the secondary frequency shock caused by the sudden change of the active reference value of the wind turbine.

[0059] For simulation verification, we used a fast simulation system that provides a system frequency response (SFR) model, and the wind speed changes come from the measured data of the actual wind farm. In order to verify the improvement of the frequency response effect of the wind turbine system under wind speed changes, we took a data interval with faster wind speed changes to conduct comparative simulation experiments under different control methods. According to the changes in the active output power and rotor speed of the wind turbine under the same wind speed changes and system frequency changes, we compared the control effects of different control strategies. The experimental data are shown in Table 1:

[0060] Table 1

[0061]

[0062] It can be seen that due to the frequency support coefficient of the method of the present invention K The wind speed change is directly considered in the correction, that is, the wind speed frequency control parameter is determined by calculating the measured wind speed and the wind speed change. k v , so the power increment brought by the increase in wind speed can be fully utilized. In the frequency regulation process to reach the same minimum frequency point, the method of the present invention can provide a greater output power for the wind turbine, and the minimum speed value is also smaller, which fully releases the rotor kinetic energy of the wind turbine to provide the energy required for frequency regulation.

[0063] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and speed recovery, characterized in that: For the grid-connected system including wind turbines, the output active power reference value of the wind turbine side converter control unit is improved to improve the system's adaptability to wind speed changes during frequency regulation, and additional speed recovery control is added after the frequency regulation is completed. By decreasing the speed recovery function f rec (t) realizing speed recovery control; Where: t0 represents the start time of the speed recovery link, Δt represents the duration of the speed recovery link, and t represents the current time; The specific process of improving the design of the output active power reference value is as follows: (1) Obtain the grid frequency and real-time wind speed through monitoring, and then calculate the frequency change and wind speed change; (2) calculating and determining the basic frequency adjustment coefficient according to a variable coefficient frequency control strategy based on the effective rotational kinetic energy of the wind turbine generator; (3) The wind speed frequency control parameter is determined by calculating the following formula based on the real-time wind speed and wind speed change; Where: k v is the wind speed frequency control parameter, e is the natural constant, v is the real-time wind speed, Δv is the wind speed change, and α is the control coefficient, whose size is determined by the wind power penetration rate; (4) The output active power reference value is determined based on the basic frequency adjustment coefficient and the wind speed frequency control parameter.

2. The method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and speed recovery according to claim 1, characterized in that: In step (1), the frequency change and wind speed change are calculated by the following formula: Where: Δf is the frequency change, f s is the actual grid frequency, and f0 is the rated grid frequency.

3. The method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and speed recovery according to claim 1, characterized in that: In the step (2), the basic frequency adjustment coefficient is calculated and determined by the following formula; Where: C is the basic adjustment coefficient of the wind turbine, k f is the basic frequency adjustment coefficient, ω min is the minimum rotational angular velocity of the wind turbine, ω r is the angular velocity of the wind turbine.

4. The method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and speed recovery according to claim 1, characterized in that: In step (4), the output active power reference value is calculated by the following formula: Where: P ref is the output active power reference value, P MPPT is the active power output by the wind turbine in the MPPT operation mode, ΔP is the power compensation, Δf is the frequency change, K is the intermediate variable coefficient, k f is the basic frequency adjustment coefficient, k v is the wind speed frequency control parameter.

5. The method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and speed recovery according to claim 1, characterized in that: The specific implementation method of the speed recovery control is: when the actual speed of the wind turbine is monitored to converge, that is, |ω r (t+T)-ω r (t)|≤δ, start the rotor speed recovery link, and adjust the coefficient k at the original basic frequency f and wind speed frequency control parameter k v Based on this, it is multiplied by a decreasing speed recovery function f rec (t), and obtain the speed recovery control coefficient k rec , and then the output active power reference value P is determined by the following expression: ref , used to control the wind turbine side converter; Where: P MPPT is the active power output by the wind turbine in the MPPT operation mode, ΔP is the power compensation, Δf is the frequency change, ω r (t+T) is the rotational angular velocity of the wind turbine at time t+T, ω r (t) is the rotation angular velocity of the wind turbine at time t, T is the sampling period, and δ is the set threshold.

6. A computer device comprising a memory and a processor, characterized in that: The memory stores a computer program, and the processor is used to execute the computer program to implement the method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and rotation speed recovery as claimed in any one of claims 1 to 5.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for adaptive frequency control of a wind turbine generator system taking into account wind speed variation and rotation speed recovery as claimed in any one of claims 1 to 5 is implemented.

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