Wind turbine frequency active support and recovery control strategy based on speed adaptation

Abstract

This invention belongs to the field of wind power generation technology, specifically relating to a wind turbine frequency active support and recovery control strategy based on speed adaptation. Addressing the shortcomings of existing wind turbine active frequency control in new energy power systems, which suffers from static control parameters and lacks a real-time adaptive adjustment mechanism, this invention adopts the following technical solution: The wind turbine frequency active support and recovery control strategy based on speed adaptation includes: obtaining a quadratic curve of mechanical power using an interval quadratic function approximation method; triggering a frequency regulation response when the grid frequency change exceeds a threshold, while simultaneously acquiring the wind turbine speed in real time; calculating the available rotor kinetic energy power and the reserve power or mechanical loss power of the wind turbine; determining the reference value of the wind turbine output active power based on the available frequency regulation power, adjusting the wind turbine speed to achieve active frequency support; and, when the recovery conditions are met, employing a speed adaptive recovery strategy to restore the wind turbine to overspeed load reduction mode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wind power generation, and particularly relates to a wind turbine frequency active support and recovery control strategy based on speed self-adaptation. BACKGROUND

[0002] With the growth of wind power installed capacity, the proportion of controllable power sources such as thermal power is decreasing. Since wind turbine generators are connected to the grid through power electronic converters, they lack the rotational inertia of traditional synchronous generators, and the overall inertia of the system is reduced, making it difficult for the capacity and response speed of traditional frequency modulation units to cope with load disturbances, and the active support capacity is insufficient, and the frequency stability is challenged. By pre-setting the frequency response strategy of the wind turbine generator, the output can be actively adjusted before the frequency exceeds the limit, solving the problem of frequency instability caused by low inertia and high volatility.

[0003] Permanent magnet direct drive wind turbines have dual frequency modulation potential of rotor kinetic energy reserve and overspeed load shedding reserve capacity, and can provide rapid power support in the initial stage of frequency disturbance. In view of this characteristic, through the study of reasonable control strategy, the accurate matching of frequency modulation energy under speed self-adaptation is realized, which is the current research hotspot. At present, the strategy of wind turbine generator participating in system frequency modulation mostly uses virtual inertia control, droop control and control method combining virtual inertia and droop control, and at the same time, overspeed load shedding method is used to reserve part of the power as frequency modulation reserve.

[0004] However, the existing method still has two major defects: first, the frequency modulation parameters are fixed, which cannot adapt to complex working condition changes; second, the rotor kinetic energy release and speed recovery process easily causes secondary frequency drop, aggravating the dynamic imbalance of the power grid. SUMMARY

[0005] The application provides a wind turbine frequency active support and recovery control strategy based on speed self-adaptation to solve the problems of static control parameters and lack of real-time self-adaptive adjustment mechanism in the active frequency control of wind turbine generators in existing new energy power systems. The rotor kinetic energy and load shedding reserve energy of the overspeed load shedding wind turbine generator are fully utilized to determine the wind turbine output active power reference value according to the available frequency modulation power. In the speed recovery stage, the speed recovery power reference value is determined according to the set speed recovery curve to reduce the power shortage during speed recovery, realize smooth and controllable speed recovery, and reduce the secondary frequency impact of speed recovery on the power grid.

[0006] To achieve the above purpose, the application adopts the following technical scheme: the wind turbine frequency active support and recovery control strategy based on speed self-adaptation includes:

[0007] Step S1: According to whether the wind turbine speed reaches the maximum power point speed, the mechanical power calculation is simplified by using the partition interval quadratic function approximation method to obtain the mechanical power quadratic curve;

[0008] Step S2: Real-time monitoring of the grid frequency variation, when the grid frequency variation exceeds the threshold value, the frequency modulation response is triggered, and the wind turbine speed is obtained in real time;

[0009] Step S3: According to the speed condition difference, the available frequency modulation power of the wind turbine is calculated, which is the available rotor kinetic energy power plus the load shedding reserve power or mechanical loss power;

[0010] Step S4: Combined with the frequency deviation and the frequency variation rate, the available frequency modulation power is calculated to determine the wind turbine output active power reference value, and the wind turbine speed is adjusted to realize active frequency support;

[0011] Step S5: When the speed variation rate and the frequency variation rate meet the recovery conditions, the speed adaptive recovery strategy is used to make the wind turbine return to the overspeed load shedding mode.

[0012] As an improvement, in step S1, the maximum power point speed is obtained by dynamic calculation according to the real-time wind speed and the aerodynamic characteristic parameters of the wind turbine.

[0013] As an improvement, in step S1, according to the size relationship between the wind turbine speed and the maximum power point speed, when the speed is higher than the maximum power point speed, the maximum power point and the overspeed load shedding point are taken as the vertex and boundary point of the quadratic curve to fit the mechanical power curve.

[0014] When the speed is lower than the maximum power point speed, the maximum power point and the allowable minimum speed point are taken as the vertex and boundary point of the quadratic curve to fit the mechanical power curve.

[0015] As an improvement, in step S3, the available rotor kinetic energy power is the energy difference between the working speed and the minimum speed of the wind turbine, which is expressed as:

[0016]

[0017] In the formula: is the moment of inertia of the wind turbine, is the power factor, is the rated power, T is the expected average frequency modulation time, is the working speed of the wind turbine, is the minimum speed of the wind turbine.

[0018] As an improvement, in step S3, when the speed is greater than or equal to the maximum power point speed, the wind turbine operates in the overspeed load shedding interval, and the calculation formula of the load shedding reserve power of the wind turbine is:

[0019]

[0020] In the formula, The mechanical power at the point of maximum power under the same wind speed; This represents the mechanical power corresponding to the current rotational speed. The mechanical power at the overspeed unloading point under the same wind speed; The rotational speed corresponding to the maximum power point; The target speed for overspeed load reduction is given by the overspeed load reduction strategy; This represents the current angular velocity of the wind turbine rotor.

[0021] At this point, the formula for calculating frequency modulation power is:

[0022]

[0023] In the formula, The available rotor kinetic energy power; Mechanical power reserves for wind turbine units;

[0024] When the rotational speed is lower than the maximum power point speed, the wind turbine is operating in the deceleration range. The formula for calculating the mechanical energy loss caused by the wind turbine's deviation from the maximum power point is:

[0025] ;

[0026] In the formula, This represents the mechanical power corresponding to the current rotational speed. The mechanical power at the point of maximum power under the same wind speed;

[0027] At this point, the formula for calculating frequency modulation power is:

[0028]

[0029] In the formula, The available rotor kinetic energy power; This refers to the mechanical energy loss power generated by the maximum power point of the wind turbine's off-center.

[0030] As an improvement, in step S4, the reference value of the active power output by the wind turbine is... The formula for calculation is:

[0031]

[0032] In the formula: To reduce the output power of the wind turbine at the load reduction point, For frequency deviation, The rate of change of frequency, The inertia coefficient is constant. The drooping coefficient is fixed.

[0033] .

[0034] As an improvement, the formula for calculating the inertia fixation factor is:

[0035]

[0036] In the formula, As a baseline, the available power increment is taken as 10% of the rated capacity. express; The frequency change rate is 1.25 Hz / s, which is used as the design reference.

[0037] The formula for calculating the sag fixed coefficient is:

[0038] .

[0039] As an improvement, considering fast power tracking on the grid-connected side and neglecting damping, we take... The power form of the swing equation on the wind turbine side is obtained:

[0040]

[0041] In the formula: H The equivalent inertia constant of the wind turbine generator. This is the current rotational speed of the wind turbine. Its time derivative; This represents the mechanical power corresponding to the current rotational speed. The electromagnetic output power corresponding to the current rotational speed is given by the active power reference value. Give;

[0042] At the initial moment It is known that a custom time step is used. By using recursive relationships and numerical methods, the solution can be obtained step by step. The change in is used to derive the time-varying expression that adapts to the rotational speed:

[0043] .

[0044] As an improvement, in step S5, the speed adaptive recovery strategy includes:

[0045] The conditions for speed recovery are:

[0046] (1) Rate of change of frequency This trend continued for a period of time, indicating that the system frequency had gradually stabilized.

[0047] (2) Rate of change of rotational speed And this continued for a period of time, indicating that the wind turbine speed had gradually stabilized;

[0048] At this point, the mechanical power is approximately equal to the electromagnetic power. Usually, because the droop control is still in place, the electromagnetic power is higher than the load reduction power at the initial moment.

[0049] Let the speed of the wind turbine be when the recovery conditions are met. According to the fitted formula, the mechanical power at this time is: Let this point be the speed recovery point.

[0050] As an improvement, in step S5, at the start of speed recovery, the reference power is first reduced to a mechanical power slightly lower than the recovery point. Typically, a 3% decrease from the mechanical power reference at the recovery point is used as the reference starting point for the speed recovery curve. Subsequently, a quadratic recovery curve strategy is adopted, and the set quadratic recovery curve passes through both the speed recovery reference starting point and the overspeed unloading point. The specific values ​​are as follows:

[0051]

[0052] In the formula: To restore the mechanical power of the point, This refers to the rotational speed at which the rotational speed recovers.

[0053] Rotational speed is also obtained through a recursive expression: .

[0054] The wind turbine frequency active support and recovery control strategy based on speed adaptation of this invention simplifies mechanical power calculation by using a quadratic function approximation method with intervals. This simplification of mechanical power calculation and the wider dynamic adaptation range cover the minimum allowable speed and the speed at the overspeed and load shedding point, with high approximation accuracy. The constructed wind turbine output power reference value based on speed adaptation considers both rotor kinetic energy and energy reserves or mechanical losses during load shedding, accurately matching the dynamic demand of the power grid and avoiding rotor speed exceeding limits during active frequency support. During speed recovery, it reduces power surges caused by speed recovery, ensuring a smooth speed transition and effectively alleviating secondary dynamic imbalances in the power grid. This provides a frequency stabilization solution for high-proportion renewable energy power systems that combines rapid response, accurate matching, and smooth recovery characteristics. Attached Figure Description

[0055] Figure 1 This is a flowchart illustrating the wind turbine frequency active support and recovery control strategy based on speed adaptation, according to an embodiment of the present invention.

[0056] Figure 2 This is a power-speed curve diagram of the wind turbine frequency active support and recovery control strategy based on speed adaptation according to an embodiment of the present invention.

[0057] Figure 3(a) is a frequency comparison diagram between the speed adaptive strategy of the present invention and the traditional fixed parameter strategy when the frequency is actively supported.

[0058] Figure 3(b) is a comparison of the mechanical speed of the speed adaptive strategy of the present invention and the traditional fixed parameter strategy when the frequency is actively supported.

[0059] Figure 3(c) is a comparison of the reference power of the wind turbine with the speed adaptive strategy of the present invention and the traditional fixed parameter strategy when the frequency is actively supported.

[0060] Figure 4(a) is a frequency comparison diagram of the speed adaptive strategy of the present invention under different load reduction coefficients when the frequency is actively supported.

[0061] Figure 4(b) is a comparison of mechanical speeds of the speed adaptive strategy of the present invention under different load reduction coefficients when the frequency is actively supported.

[0062] Figure 4(c) is a comparison of the reference power of the wind turbine generator under different load reduction coefficients of the speed adaptive strategy of the present invention in the embodiment of the present invention when the frequency is actively supported.

[0063] Figure 5(a) is a frequency comparison diagram between the speed recovery adaptive strategy of the present invention and the traditional direct recovery strategy.

[0064] Figure 5(b) is a comparison of mechanical speeds between the adaptive speed recovery strategy of the present invention and the traditional direct recovery strategy.

[0065] Figure 5(c) is a comparison of the reference power of wind turbines using the adaptive speed recovery strategy of this invention and the traditional direct recovery strategy. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be explained and described below. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0067] See Figure 1 The wind turbine frequency active support and recovery control strategy based on speed adaptation in this embodiment of the invention includes:

[0068] Step S1: Based on whether the wind turbine speed has reached the maximum power point speed, the mechanical power calculation is simplified by using the interval quadratic function approximation method to obtain the mechanical power quadratic curve;

[0069] Step S2: Monitor the change in grid frequency in real time. When the change in grid frequency exceeds the threshold, trigger the frequency regulation response and simultaneously acquire the wind turbine speed in real time.

[0070] Step S3: Calculate the available frequency-regulating power of the wind turbine based on the difference in operating speed. The available frequency-regulating power is the available rotor kinetic energy power plus the load-reduced reserve power or mechanical loss power.

[0071] Step S4: Combining frequency deviation and frequency change rate, calculate and determine the reference value of the active power output of the wind turbine based on the available frequency regulation power (available frequency regulation power = available rotor kinetic energy power + load reduction reserve or mechanical loss power), and adjust the wind turbine speed to achieve active frequency support;

[0072] Step S5: When the speed change rate and frequency change rate meet the recovery conditions, the speed adaptive recovery strategy is adopted to restore the fan to the overspeed unloading mode.

[0073] In step S1, the maximum power point speed is dynamically obtained by real-time wind speed and aerodynamic characteristic parameters of the fan (such as blade radius, air density, and optimal tip speed ratio). Based on the comparison between the fan speed and the maximum power point speed, when the speed is higher than the maximum power point speed, the maximum power point and the overspeed unloading point are used as the apex and boundary points of the quadratic curve to fit the mechanical power curve; when the speed is lower than the maximum power point speed, the maximum power point and the minimum allowable speed point are used as the apex and boundary points of the quadratic curve to fit the mechanical power curve.

[0074] The real-time wind speed and aerodynamic characteristics of the fan have been measured in the example. Figure 2 The fitted mechanical power curve is shown in the figure.

[0075] Specifically, for safety reasons, it is generally believed that when the rotor speed drops to... When the speed is 0.65pu (assuming the maximum power point speed at a certain wind speed is the reference speed), the mechanical power corresponding to this speed is denoted as... The fan needs to be taken out of frequency regulation mode.

[0076] According to aerodynamic theory, the wind turbine operates at a wind speed of... The mechanical power that can be obtained at that time is:

[0077]

[0078] In the formula: This is the density of air, usually taken as 1.225. Where is the radius of the wind turbine. This refers to wind speed.

[0079]

[0080] In the formula: It is the wind energy utilization coefficient, which meets the requirements. (Bez limit), in practice it is mostly 0.3~0.5; For the tip speed ratio, ; The pitch angle is usually taken as 0.

[0081]

[0082] In the formula: It is the corrected tip speed ratio, which is an intermediate variable.

[0083] When the wind speed is fixed, the wind energy captured by the wind turbine depends only on the wind energy utilization coefficient, and the optimal wind energy utilization coefficient corresponds to the optimal tip speed ratio. Therefore, it is only necessary to keep the wind turbine at the optimal tip speed ratio under different wind speeds. Once operational, maximum power point tracking (MPPT) control of the fan can be achieved. The maximum power point speed and power are obtained through dynamic calculation using real-time wind speed and fan aerodynamic characteristic parameters.

[0084]

[0085]

[0086] When the wind turbine enters overspeed unloading mode, in order to provide frequency regulation backup, the rotational speed is actively increased to deviate from the optimal operating point, thereby achieving power load reduction.

[0087] unload speed Calculated using the reduced blade tip speed ratio: .

[0088] The power at the unloading point is related to the preset unloading rate d:

[0089] .

[0090] Typically, the load reduction rate is 10%-30%, and the power at the load reduction point is usually greater than the power at which the wind turbine is disconnected. Based on the comparison between the wind turbine speed and the maximum power point speed, when the speed is higher than the maximum power point speed, the maximum power point and the overspeed unloading point are used as the vertices and boundary points of a quadratic curve to fit the mechanical power curve; when the speed is lower than the maximum power point speed, the maximum power point and the minimum allowable speed point are used as the vertices and boundary points of a quadratic curve to fit the mechanical power curve. Among these, according to the power characteristics of the wind turbine, the speed satisfies... After fitting, we obtain Mechanical power curve of the interval:

[0091] .

[0092] In step S2, the frequency change of the power grid is monitored in real time, the frequency change rate is calculated, and the rotor speed of the wind turbine is acquired in real time for subsequent interval judgment. When the frequency change exceeds the threshold, a frequency regulation response is triggered. In this step, the monitoring of frequency change and speed can be achieved using existing methods for monitoring frequency change and speed in actual power grid applications.

[0093] In step S3, the released rotor kinetic energy is the energy difference between the wind turbine's operating speed and its minimum speed, expressed as:

[0094] ;

[0095] Available rotor kinetic power The energy difference between the operating speed and the minimum speed of the wind turbine is expressed as:

[0096]

[0097] In the formula: The moment of inertia of the wind turbine. For power factor, Where R is the rated power, and T is the desired average frequency modulation time. The operating speed of the wind turbine. This is the minimum speed of the wind turbine.

[0098] When the rotational speed is greater than or equal to the maximum power point speed, the wind turbine is operating in the overspeed and load shedding range. The formula for calculating the load shedding reserve power of the wind turbine is:

[0099]

[0100] In the formula, The mechanical power at the point of maximum power under the same wind speed; This represents the mechanical power corresponding to the current rotational speed. The mechanical power at the overspeed unloading point under the same wind speed; The rotational speed corresponding to the maximum power point; The target speed for overspeed load reduction is given by the overspeed load reduction strategy; This represents the current angular velocity of the wind turbine rotor.

[0101] At this point, the formula for calculating frequency modulation power is:

[0102]

[0103] In the formula, The available rotor kinetic energy power; Mechanical power reserves for wind turbine units;

[0104] When the rotational speed is lower than the maximum power point speed, the wind turbine is operating in the deceleration range. The formula for calculating the mechanical energy loss caused by the wind turbine's deviation from the maximum power point is:

[0105] ;

[0106] In the formula, This represents the mechanical power corresponding to the current rotational speed. The mechanical power at the point of maximum power under the same wind speed;

[0107] At this point, the formula for calculating frequency modulation power is:

[0108]

[0109] In the formula, The available rotor kinetic energy power; This refers to the mechanical energy loss power generated by the maximum power point of the wind turbine's off-center.

[0110] In step S4, the reference value of the output active power of the wind turbine is determined using the following method.

[0111] The frequency-modulated power can be taken as a per-unit value, and the initial fixed parameters are set according to the power grid standard.

[0112] .

[0113] Based on integrated inertia control, the formula for calculating the reference value of the generator set's output active power is:

[0114]

[0115] In the formula: The output power of the wind turbine at the unloading point, For frequency deviation, The rate of change of frequency, The inertia coefficient is constant. This is a fixed droop coefficient.

[0116] Inertia constant factor This represents the power adjustment caused by the frequency change rate. Based on grid requirements, for example, if the frequency change rate is required to not exceed 1.25 Hz / s within 0.5 seconds, it can provide inertial support for disturbances of 10% of rated power. The setting value is:

[0117]

[0118] The droop fixation factor is based on power grid requirements, such as the required frequency deviation. At 1Hz, the fan provides 10% of its rated power, and the setting value is:

[0119]

[0120] In the formula: This is the rated capacity.

[0121] In step S4, the process of obtaining the adaptive speed of the wind turbine is as follows.

[0122] Considering fast power tracking on the grid-connected side and neglecting damping, take The power form of the swing equation from the wind turbine side:

[0123]

[0124] In the formula: H The equivalent inertia constant of the wind turbine generator. This is the current rotational speed of the wind turbine. Its time derivative; This represents the mechanical power corresponding to the current rotational speed. The electromagnetic output power corresponding to the current rotational speed is given by the active power reference value. Give;

[0125] At the initial moment It is known that a custom time step is used. By using recursive relationships and combining numerical methods (such as the Runge-Kutta method), the solution is obtained step by step. The change in speed, recursively yielded as follows:

[0126] .

[0127] Figure 2 In the figure, curve AB is an example of the speed adaptive frequency active support strategy in this embodiment.

[0128] from Figure 2 As can be seen, the load reduction curve (black curve) allows the wind turbine to operate in the overspeed load reduction zone (power slightly lower than the maximum power point, speed higher than the maximum speed). This allows for more mechanical power and higher rotational kinetic energy to be reserved.

[0129] The frequency modulation curve (purple curve) represents the trajectory of the electrical output reference during the frequency support period. When the frequency drops, the unit can utilize the rotor kinetic energy, so the instantaneous electromagnetic power can exceed the mechanical power curve at the same speed.

[0130]

[0131] Only when the electromagnetic power is greater than the mechanical power Only then will the wind turbine's speed decrease, releasing kinetic energy to provide active support power.

[0132] As shown in Figure 3(a), compared with the traditional fixed-parameter strategy, this embodiment can respond more quickly when the grid frequency drops, significantly improve the minimum frequency point, and achieve a higher steady-state recovery value, effectively improving the frequency stability of the system. Figure 3(b) shows that the strategy of this embodiment fully utilizes the rotor kinetic energy during frequency regulation, allowing the mechanical speed to decrease more within a safe range, thereby releasing more energy to participate in grid frequency support, while ensuring that the speed is always within the allowable limit, avoiding the risk of overspeeding or deep deceleration. In addition, as shown in Figure 3(c), the reference power output of this embodiment is significantly higher than that of the traditional strategy, providing stronger active power support under the same disturbance conditions. At the same time, by dynamically optimizing the power recovery trajectory, it avoids the secondary impact of power surges on the grid, ensuring the stable operation of the wind turbine throughout the frequency regulation process.

[0133] Meanwhile, this embodiment can significantly optimize frequency regulation reserve capacity by adjusting the load reduction coefficient of the wind turbine. As shown in Figure 4(a), with the increase of the load reduction coefficient (10%, 20%, 30%), the overspeed load reduction reserve power reserved by the wind turbine increases accordingly, which significantly improves the frequency regulation energy that can be released when the grid frequency drops, thereby achieving a better frequency regulation effect. Figures 4(b) and 4(c) show that, under the premise of ensuring that the mechanical speed is always within the safe operating range, the turbine speed can be controllably reduced with the increase of the load reduction coefficient, and the output reference power based on speed adaptation provides the grid with a more flexible and reliable frequency support capability.

[0134] After the frequency active support is completed, the speed recovery process is as follows.

[0135] The speed adaptive recovery curve is constructed based on the following conditions:

[0136] Conditions for speed recovery:

[0137] (1) Rate of change of frequency This trend continued for a period of time, indicating that the system frequency had gradually stabilized.

[0138] (2) Rate of change of rotational speed This continues for a period of time, indicating that the wind turbine speed has gradually stabilized; at this point, the mechanical power is approximately equal to the electromagnetic power, usually due to the droop control still existing (Δ). f (≠0), at this time the electromagnetic power is higher than the load reduction power at the initial moment.

[0139] Let the rotational speed at the moment when the recovery condition is met be . The mechanical power at this point can be obtained from the fitted formula: Let this point be the speed recovery point.

[0140] At the start of speed recovery, first reduce the reference power to slightly below the mechanical power at the recovery point. Typically, a 3% decrease from the mechanical power reference at the recovery point is used as the reference starting point for the speed recovery curve. Subsequently, a quadratic curve recovery strategy is adopted, where the set quadratic curve passes through both the speed recovery reference starting point and the overspeed unloading point. The specific values ​​are as follows:

[0141]

[0142] In the formula: To restore the mechanical power of the point, This is the rotational speed at which the rotational speed recovers.

[0143] Rotational speed is also obtained through a recursive expression: .

[0144] Figure 2 In the figure, curve CC'DA is an example implementation of the speed adaptive recovery strategy in this embodiment.

[0145] from Figure 2 It can be seen that the key point of the speed recovery curve (green curve CC'DA) is its position rather than its shape: the rotor needs to accelerate back to the unloading point during the recovery phase, therefore, the electromagnetic power should be less than the mechanical power at the same speed throughout the entire recovery range. On the one hand, compared with the linear recovery curve that directly connects the recovery start point and the unloading point, the convex quadratic speed recovery curve has better dynamic characteristics. At the same speed, the electromagnetic power given by this curve is generally lower than that of the linear recovery curve, which can reserve a larger acceleration power margin for the rotor, which is beneficial to shorten the overall speed recovery time while suppressing torque shocks and power fluctuations. On the other hand, compared with the traditional direct speed recovery strategy, the convex quadratic curve avoids the sudden drop in power when entering the recovery phase, and can gradually approach the unloading point in the later stage of recovery, achieving smooth convergence to the unloading point. In addition, the quadratic curve has fewer parameters and a simpler form, which facilitates rapid tuning and flexible online adjustment in engineering implementation, taking into account both control effect and practical feasibility.

[0146] As shown in Figure 5(a), compared with the traditional direct speed recovery strategy, the method in this embodiment can effectively suppress the secondary frequency drop during the speed recovery process, avoiding additional impact on the power grid. Figures 5(b) and 5(c) further demonstrate that the adaptive speed recovery process of the method in this embodiment is stable and controllable, achieving a smooth transition in power output and improving the reliability and stability of wind turbines participating in grid frequency regulation.

[0147] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the content described in the above specific embodiments. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A speed adaptive based wind turbine frequency active support and restoration control strategy, characterized in that: The wind turbine frequency active support and recovery control strategy based on the rotational speed self-adaption comprises: Step S1: according to whether the rotational speed of the wind turbine reaches the maximum power point rotational speed, a partitioned quadratic function approximation method is used to simplify the mechanical power calculation, and a mechanical power quadratic curve is obtained; Step S2: the grid frequency variation is monitored in real time, and the frequency regulation response is triggered when the grid frequency variation exceeds a threshold value, and the rotational speed of the wind turbine is obtained in real time; Step S3: according to the rotational speed working condition difference, the available frequency regulation power of the wind turbine is calculated, and the available frequency regulation power is the available rotor kinetic energy power plus the load shedding reserve power or the mechanical loss power; Step S4: the frequency deviation and the frequency variation rate are combined, the available frequency regulation power is calculated to determine the wind turbine output active power reference value, the rotational speed of the wind turbine is adjusted, and the frequency active support is realized; Step S5: when the rotational speed variation rate and the frequency variation rate meet the recovery conditions, the rotational speed self-adaption recovery strategy is used to make the wind turbine recover to the overspeed load shedding mode; In step S4, the active power reference value output by the wind turbine The calculation formula is: wherein: is the output power of the wind turbine, is the available frequency regulation power, is the frequency deviation, is the rate of change of frequency, is the inertia constant, is the droop constant. wherein, is the moment of inertia of the wind turbine, T is the desired average frequency modulation time, is the rated power, is the power factor, is the operating speed of the wind turbine, is the minimum speed of the wind turbine; is the speed corresponding to the maximum power point; is the overspeed trip target speed, given by the overspeed trip strategy; is the mechanical power at the overspeed trip point at the same wind speed; is the power at which the wind turbine is tripped off; is the mechanical power at the maximum power point at the same wind speed.

2. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 1, wherein: In step S1, the maximum power point rotational speed is obtained by dynamically searching the real-time wind speed and the aerodynamic characteristic parameters of the wind turbine.

3. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 1, wherein: In step S1, when the rotational speed is higher than the maximum power point rotational speed, the maximum power point and the overspeed load shedding point are taken as the vertex and the boundary point of the quadratic curve to fit the mechanical power curve; When the rotational speed is lower than the maximum power point rotational speed, the maximum power point and the allowable minimum rotational speed point are taken as the vertex and the boundary point of the quadratic curve to fit the mechanical power curve.

4. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 1, wherein: In step S3, the available rotor kinetic energy power is the energy difference between the working rotational speed and the minimum rotational speed of the wind turbine.

5. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 4, wherein: In step S3, when the rotational speed is greater than or equal to the maximum power point rotational speed, the wind turbine operates in the overspeed load shedding interval, and the load shedding reserve power of the wind turbine is the mechanical power of the maximum power point at the same wind speed minus the mechanical power corresponding to the current rotational speed: When the rotational speed is less than the maximum power point rotational speed, the wind turbine operates in the speed reduction interval, and the calculation formula of the mechanical loss power of the wind turbine deviated from the maximum power point is the mechanical power corresponding to the current rotational speed minus the mechanical power of the maximum power point at the same wind speed.

6. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 1, wherein: The calculation formula of the inertia fixed coefficient is: wherein is the reference available power increment; is the frequency change rate; is the rated capacity; The calculation formula of the droop fixed coefficient is: 。 7. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 6, wherein: Considering the fast tracking of grid-side power and ignoring the damping, take , get the power form of the swing equation on the side of the wind turbine wherein: H is an equivalent inertia constant of the wind turbine, is a current rotational speed of the wind turbine, is a time derivative thereof; is a mechanical power corresponding to the current rotational speed; is an electromagnetic output power corresponding to the current rotational speed, given by an active reference value Pm,ref. At an initial time instant It is known that, by adopting a custom time step , the variation of the function is solved step by step by means of a numerical method, combined with a recurrence relation, which leads to a time-varying expression adapted to the rotational speed: 。 8. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 1, wherein: In step S5, the rotational speed self-adaption recovery strategy comprises: The condition for the rotational speed recovery is: (1) rate of change of frequency and for a period of time indicating that the system frequency has gradually stabilized; (2) rate of change of speed and for a period of time, indicating that the wind turbine speed has gradually stabilized; At this time, the mechanical power is approximately equal to the electromagnetic power, and usually due to the droop control, the electromagnetic power is higher than the load shedding power at the initial moment; Let n0 be the speed of the wind turbine when the recovery condition is met , and the mechanical power at this moment is , according to the fitted formula.

9. The speed adaptive based wind turbine frequency active support and restoration control strategy of claim 8, wherein: In step S5, at the beginning of the speed recovery, the reference power is first reduced to a mechanical power slightly lower than the recovery point ; then the recovery parabola recovery strategy is used, the set recovery parabola passing through both the speed recovery reference starting point and the overspeed trip point.

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