Practical equivalent method for direct-drive wind farms suitable for frequency characteristics analysis

Abstract

The present invention belongs to the field of electric power systems, and specifically relates to a practical equivalent method for direct-driven wind farms suitable for frequency characteristic analysis. In order to solve the problem that the current wind farm aggregate equivalent modeling method suitable for frequency characteristic analysis is difficult to balance accuracy and computational complexity. A practical equivalent method for direct-driven wind farms suitable for frequency characteristic analysis is proposed. For direct-driven wind farms, the present invention establishes a detailed electromagnetic transient model of direct-driven wind turbines, and proposes a practical equivalent method for direct-driven wind farms suitable for frequency characteristic analysis using the clustering characteristics of the frequency regulation response of wind turbines in different wind speed ranges. Only three equivalent machines are needed at most to characterize the frequency regulation characteristics of complex wind farms under different operating scenarios. The equivalent accuracy is significantly better than that of the traditional single-machine equivalent method, and it can well simulate the frequency response characteristics of detailed stations and can better adapt to various wind speed scenarios.

Description

Technical Field

[0001] The present invention belongs to the field of power systems, and in particular relates to a practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis. Background Art

[0002] Renewable energy generation technologies, represented by wind power, are developing rapidly, and their installed capacity share in the power system is rapidly increasing. Taking into account factors such as economic efficiency and wind curtailment rates, wind turbines are mostly operated in Maximum Power Point Tracking (MPPT) mode and do not participate in the system's inertia support and primary frequency regulation. Furthermore, wind power output exhibits significant volatility and uncertainty, which worsens the frequency security situation of the power system. Accurately analyzing the frequency characteristics of the power system and optimizing the design of frequency-related control strategies requires establishing accurate wind farm simulation models. Unlike traditional synchronous generators, wind farms often include dozens or even hundreds of wind turbines, each with a small individual capacity and relatively dispersed locations. The complexity of detailed wind farm models and the simulation computation time increase exponentially, making it crucial to develop accurate and efficient wind farm equivalent modeling methods.

[0003] Researchers have developed a variety of solutions for equivalent modeling of wind farms, such as:

[0004] 1. Ding Xinhu et al., “Dynamic Equivalent Modeling of Wind Farms Based on GA-Optimized GRU-LSTM-FC Combined Network,” 2023, Hohai University. This paper proposes a data-driven modeling method for dynamic equivalent values ​​of wind farms based on a genetic algorithm and a GRU-LSTM-FC combined network. GA is used to optimize the number of FC layers and the number of neurons in each layer in the combined network, achieving good equivalent accuracy.

[0005] 2. Xia Anjun et al., “Study on Aggregation Model of Doubly Fed Asynchronous Generator Wind Farm,” 2015, State Key Laboratory of Control and Simulation of Power Systems and Power Generation Equipment (Tsinghua University). This paper designed a parameter calculation method for a single-unit equivalent unit based on the principle of keeping key parameters such as active and reactive output and kinetic energy change rate unchanged. The method achieved high accuracy in both electromechanical and electromagnetic transient simulations. However, the adaptability of these two methods to diverse fault scenarios has not been fully verified.

[0006] 3. "Fault Equivalent Modeling Method for Doubly Fed Wind Farms Based on Improved K-Means Algorithm" published by Jia Ke et al., 2023, State Key Laboratory of New Energy Power Systems (North China Electric Power University), achieved good short-circuit current equivalent accuracy, reduced the number of short-circuit current iterative calculation nodes, and improved calculation efficiency. However, this method involves four grouping indicators, including control mode, generator-end voltage phase, and voltage drop degree, and the calculation is relatively complex.

[0007] Currently, single-unit equivalent methods for wind farms are primarily focused on low-voltage ride-through conditions. While intelligent algorithms can improve errors, these algorithms are complex and difficult to apply to a wide range of operating scenarios. Multi-unit equivalent methods, while capable of achieving high accuracy, often focus on identifying clustering indicators that characterize the dynamic characteristics of unit fault ride-through, requiring the use of complex clustering or optimization algorithms.

[0008] In summary, the existing technology has the problem that the wind farm aggregate equivalent modeling method suitable for frequency characteristic analysis is difficult to strike a balance between accuracy and computational complexity. Summary of the Invention

[0009] In order to solve the problem that the current wind farm aggregate equivalent modeling method suitable for frequency characteristic analysis is difficult to strike a balance between accuracy and computational complexity, this invention proposes a practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis.

[0010] S1: Construct a universal frequency regulation control model for direct-drive wind turbines; each type of direct-drive wind turbine shares a common set of universal frequency regulation control model parameters;

[0011] S2: For each type of direct-drive wind turbine, the direct-drive wind turbine is divided into three wind turbine groups according to the different wind speed ranges of the wind turbines in the direct-drive wind turbine.

[0012] S3: For each type of direct-drive wind turbine, the wind turbine group divided according to S2 is equivalent to 3 equivalent machines;

[0013] S4: For each type of direct-drive wind turbine, the equivalent machines divided in S3 are merged, and then the universal frequency regulation control model of the direct-drive wind turbine obtained in S1 is used to control the merged equivalent machines respectively.

[0014] The beneficial effects of the present invention are:

[0015] For direct-drive wind farms, the present invention establishes a detailed electromagnetic transient model of direct-drive wind turbines and proposes a practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis by utilizing the clustering characteristics of the frequency regulation response of wind turbines within different wind speed ranges. Multiple equivalent machines are divided according to wind speed to maintain the frequency stability of the power grid. When the grid frequency drops, the active power output of the wind turbines is increased to help increase the frequency; conversely, when the grid frequency rises, the output power is reduced. The present invention uses only three equivalent machines at most to characterize the frequency regulation characteristics of complex wind farms under different operating scenarios. The equivalent accuracy is significantly better than that of traditional single-machine equivalent methods. It can well simulate the frequency response characteristics of detailed stations and can better adapt to various wind speed scenarios. This solves the problem in the existing art that the aggregate equivalent modeling method of wind farms suitable for frequency characteristic analysis is difficult to strike a balance between accuracy and computational complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of a general frequency modulation control model for a direct-drive wind turbine generator system according to the present invention;

[0017] Figure 2 The wind energy utilization coefficient C of the present invention p Relationship curve with tip speed ratio λ and pitch angle β;

[0018] Figure 3 The wind turbine frequency modulation response curve diagram under different wind speeds of the present invention;

[0019] Figure 4 is a typical frequency modulation response curve diagram of different wind speed ranges of the present invention;

[0020] Figure 5 This is a diagram of the practical three-machine equal-value grouping method of the present invention. DETAILED DESCRIPTION

[0021] Specific implementation method 1: Combination Figure 1 The present invention is described as follows: a practical equivalent method for a direct-drive wind farm suitable for frequency characteristic analysis; the method comprises the following steps:

[0022] S1: Construct a universal frequency regulation control model for direct-drive wind turbines; each type of direct-drive wind turbine shares a common set of universal frequency regulation control model parameters;

[0023] S2: For each type of direct-drive wind turbine, the direct-drive wind turbine is divided into three wind turbine groups according to the different wind speed ranges of the wind turbines in the direct-drive wind turbine.

[0024] S3: For each type of direct-drive wind turbine, the wind turbine group divided according to S2 is equivalent to 3 equivalent machines;

[0025] S4: For each type of direct-drive wind turbine, the equivalent machines divided in S3 are merged, and then the universal frequency regulation control model of the direct-drive wind turbine obtained in S1 is used to control the merged equivalent machines respectively.

[0026] For direct-drive wind farms, the present invention establishes a detailed electromagnetic transient model of direct-drive wind turbines and proposes a practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis by utilizing the clustering characteristics of the frequency regulation response of wind turbines within different wind speed ranges. Multiple equivalent machines are divided according to wind speed to maintain the frequency stability of the power grid. When the grid frequency drops, droop control increases the active power output of the wind turbines to help increase the frequency; conversely, when the grid frequency rises, the output power is reduced. The present invention uses only three equivalent machines at most to characterize the frequency regulation characteristics of complex wind farms under different operating scenarios. The equivalent accuracy is significantly better than that of traditional single-machine equivalent methods. It can well simulate the frequency response characteristics of detailed stations and can better adapt to various wind speed scenarios. This solves the problem in the existing art that the aggregate equivalent modeling method of wind farms suitable for frequency characteristic analysis is difficult to strike a balance between accuracy and computational complexity.

[0027] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the general frequency regulation control model of the direct-drive wind turbine constructed in S1 includes: virtual inertia control module Flag 1, droop control module Flag 2, overspeed load reduction standby control module Flag 3 and pitch angle standby control module Flag 4; other steps and parameters are the same as specific embodiment 1.

[0028] Specific embodiment 3: This embodiment differs from specific embodiments 1 to 2 in that:

[0029] The virtual inertia control module Flag 1 controls the active power output of the wind turbine according to the frequency change rate of the power grid system. The specific process is as follows:

[0030]

[0031] Where ΔP1 is the active power adjustment output by the virtual inertia control, f is the system frequency, K1 is the virtual inertia control coefficient, and d is the derivative;

[0032] Virtual inertia control is designed to provide an inertial response similar to that of a traditional synchronous generator. By simulating the inertial characteristics of a synchronous machine, virtual inertia control can rapidly adjust the generator's power output when the grid frequency changes, counteracting frequency fluctuations. This is particularly important for maintaining grid stability, especially in grids dominated by intermittent energy sources such as wind and solar.

[0033] The droop control module Flag 2: controls the active power output of the wind turbine according to the frequency deviation of the power grid system; the specific process is as follows:

[0034] ΔP2=-K2Δf (2)

[0035] Where ΔP2 is the active power adjustment output of the droop control, K2 is the droop control coefficient; Δf is the system frequency deviation;

[0036] It achieves control by adjusting the relationship between the active power output of the wind turbine and the grid frequency. Usually, this control strategy is similar to that of traditional generators. Droop control (also known as frequency droop control) is mainly used to maintain the frequency stability of the grid. When the grid frequency drops, droop control increases the active power output of the wind turbine to help increase the frequency; conversely, when the grid frequency rises, it reduces the output power.

[0037] The overspeed load reduction standby control module Flag 3: controls the wind turbine operating point according to the tip speed ratio λ of the wind turbine;

[0038] The operating point of the fan refers to the operating state of the fan under specific conditions, including parameters such as the fan's power output, speed, and blade angle.

[0039] When the wind speed is constant, there is a unique optimal speed ω opt and the optimal tip speed ratio λ opt Wind energy utilization coefficient C p It reaches its maximum value at the current pitch angle β. When the wind speed is too high, by changing the tip speed ratio λ, the wind turbine speed can be indirectly changed to control the wind turbine operating point and realize the load reduction operation of the wind turbine set; ω opt and λ opt The corresponding relationship is shown as follows:

[0040]

[0041] Where R is the radius of the wind wheel and v is the wind speed;

[0042] Reducing the speed to achieve load shedding may cause stability problems, so fans generally use overspeed control. Figure 2 As shown, the pitch angle is β1, that is, when the wind turbine runs on the β1 curve, the load reduction reserve coefficient η can be set del Move the fan operating point from A to C to achieve reduced load operation;

[0043] The pitch angle standby control module Flag 4: controls the wind turbine operating point according to the pitch angle β;

[0044] like Figure 2 As shown in the figure, by increasing the pitch angle from β1 to β2, the wind turbine operating point will move from A to B, which can also achieve a load reduction effect similar to overspeed control.

[0045] When using overspeed load reduction control, the wind turbine can simultaneously call on the rotor kinetic energy and standby power to participate in frequency regulation, and the response speed is fast, but it is limited by the upper and lower limits of the speed and is not suitable for high wind speed scenarios. Although pitch angle control can adapt to a wider range of wind speed scenarios, it involves the movement of large mechanical components, has a slow response speed, and will increase the wear of the mechanical system. Therefore, it is often necessary to adopt a coordinated control mode of comprehensive inertia control, overspeed load reduction control and pitch angle load reduction control to meet the frequency regulation requirements under different wind speed scenarios. The other steps and parameters are the same as those of specific implementation methods one to two.

[0046] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 4 in that:

[0047] Each module is enabled and disabled through the status of a flag bit; the status of the flag bit includes "1" and "0", where "0" means disabling the control module and "1" means enabling the control module.

[0048] Each type of direct-drive wind turbine shares a common set of frequency regulation control model parameters. The specific process is as follows:

[0049] The general frequency regulation control model parameter of the direct-drive wind turbine with virtual inertia control module is Flag 1 = 1;

[0050] The general frequency control model parameter of the direct-drive wind turbine without the virtual inertia control module is Flag 1 = 0;

[0051] The general frequency regulation control model parameter Flag 2 = 1 for direct-drive wind turbines equipped with a droop control module;

[0052] The general frequency regulation control model parameter Flag 2 = 0 for direct-drive wind turbines without droop control module;

[0053] The general frequency regulation control model parameter Flag3 of the direct-drive wind turbine with overspeed load reduction standby control module is 1;

[0054] The general frequency regulation control model parameter Flag3 of the direct-drive wind turbine without overspeed load reduction backup control module is 0;

[0055] The general frequency regulation control model parameter of the direct-drive wind turbine with a pitch angle backup control module is Flag 4 = 1;

[0056] The general frequency regulation control model parameter of the direct-drive wind turbine with a pitch angle backup control module is Flag 4=0.

[0057] If the model of a certain type of wind turbine in a certain wind farm has a virtual inertia control module, a droop control module, an overspeed load reduction standby control module, and a pitch angle standby control module at the same time, then Flag 1 = 1, Flag 2 = 1, Flag 3 = 1, and Flag 4 = 1 for this type of wind turbine. If the general frequency control model of a certain type of wind turbine in a certain wind farm does not have a virtual inertia control module, a droop control module, an overspeed load reduction standby control module, and a pitch angle standby control module, then Flag 1 = 0, Flag 2 = 0, Flag 3 = 0, and Flag 4 = 0 for this type of wind turbine. Correspondingly, if the general frequency control model of a certain type of wind turbine in a certain wind farm only has some frequency control modules, it is only necessary to set the corresponding Flag of that part to 1, and set the Flags of the remaining parts to 0.

[0058] The other steps and parameters are the same as those in the first to third embodiments.

[0059] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that:

[0060] In S2, for each type of direct-drive wind turbine generator set, the direct-drive wind turbine generator set is divided into three wind turbine group groups according to the different wind speed ranges of the wind turbines in the direct-drive wind turbine generator set. The specific process is as follows:

[0061] S2.1: Determine the wind speed interval cut point;

[0062] S2.2: Divide the wind speed range into three intervals according to the cut points of the wind speed range divided in S2.1, and divide the direct-drive wind turbines into three direct-drive wind turbine groups according to the three divided wind speed ranges. The other steps and parameters are the same as those of the specific implementation methods one to four.

[0063] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that:

[0064] The wind speed interval cutting points in S2.1 include: cut-in wind speed point, first wind speed dividing point, second wind speed dividing point and cut-out wind speed point. The cut-in wind speed point is the minimum wind speed required for the wind turbine to start generating electricity.

[0065] The first wind speed segmentation point is when the active output of the wind turbine generator set is equal to the threshold value P th The corresponding wind speed;

[0066] The second wind speed split point refers to the wind speed corresponding to the time when the wind speed further increases during the operation of the wind turbine and the speed of the wind turbine reaches its designed maximum speed even if overspeed load reduction measures are taken;

[0067] The cut-out wind speed point is the maximum wind speed at which the wind turbine stops generating electricity.

[0068] When the wind speed exceeds the cut-out wind speed point, the generator will automatically stop running to protect the equipment from damage. Other steps and parameters are the same as those of the specific implementation methods 1 to 5.

[0069] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that:

[0070] In S2.2, the wind speed interval cut points divided in S2.1 are used to divide the wind speed interval into three intervals, and the direct-drive wind turbines are divided into three direct-drive wind turbine groups according to the three divided wind speed intervals. The specific process is as follows:

[0071] Wind speed interval 1 ranges from the cut-in wind speed point to the first wind speed dividing point; wind turbines in wind speed interval 1 are divided into the first wind turbine group; it usually includes the starting area and some MPPT areas with lower wind speeds;

[0072] The second wind speed interval ranges from the first wind speed dividing point to the second wind speed dividing point; the wind turbines in the second wind speed interval are divided into a second wind turbine group;

[0073] The wind speed interval three ranges from the second wind speed dividing point to the cut-out wind speed point; the wind turbines in the wind speed interval three are divided into a third wind turbine group; the other steps and parameters are the same as those of one of the specific implementation methods one to six.

[0074] Specific embodiment eight: This embodiment differs from specific embodiments one to seven in that:

[0075] In said S3, each type of direct-drive wind turbine is divided into three equivalent wind turbine groups according to the wind turbine group group divided in S2; the specific process is: for each type of direct-drive wind turbine, the first wind turbine group divided in S2 is equal to the first equivalent wind turbine group;

[0076] The second wind turbine group divided in S2 is equal to the second equivalent machine; the third wind turbine group divided in S2 is equal to the third equivalent machine. Other steps and parameters are the same as those in the first to seventh embodiments.

[0077] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that:

[0078] The specific process of setting the first wind turbine group as the first equivalent machine is as follows:

[0079] The active power of a first-class wind turbine equals the sum of the active power of all generators in the first wind turbine group; the capacity of a first-class wind turbine equals the sum of the capacities of all generators in the first wind turbine group. Within the first wind speed range, wind speeds and rotational speeds are low, resulting in low active power output and rotor kinetic energy. If a wind turbine increases its active power output in response to changes in system frequency, this will result in a decrease in rotational speed, which can easily cause the wind turbine to stall. To ensure stable operation, wind turbines in this area will not be placed in load-shedding standby mode or participate in system frequency regulation.

[0080] The specific process of setting the second wind turbine group to be equal to the second equivalent machine is as follows:

[0081] The active power of the second-equal-value machine is equal to the sum of the active powers of all generators in the second wind turbine group; the capacity of the second-equal-value machine is the sum of the capacities of all generators in the second wind turbine group;

[0082] In the second wind speed range, the wind speed and wind turbine speed increase for the second equivalent unit. Under MPPT control, the wind turbine pitch angle is always maintained at 0°. The unit adopts overspeed control to achieve load reduction operation, and cooperates with the integrated inertia control to participate in system frequency regulation.

[0083] During steady-state operation, the overspeed load reduction control causes the rotor to overspeed to the load reduction operating speed based on the current wind speed and the load reduction reserve coefficient. At this time, the mechanical power and electromagnetic power are balanced and the speed remains stable. The load reduction power tracking equation is:

[0084]

[0085] k del =(1-η del )k opt (5)

[0086] Where, P del is the load-reduced operating power, k opt is the maximum power tracking coefficient, k del It is the tracking coefficient of load shedding operation.

[0087] When the system frequency drops, integrated inertia control increases electromagnetic power output, reducing speed and improving the wind energy utilization factor until a new balance is reached between the mechanical power captured by the wind turbine and the electromagnetic power output by the generator. Conversely, when the system frequency rises, the wind turbine will further increase speed to reduce active power output, continuing to participate in frequency regulation. When overspeed load shedding control fails to meet load shedding standby requirements, pitch angle control is typically used to achieve load shedding standby.

[0088] The specific process of equating the third wind turbine group to a third equivalent machine is as follows:

[0089] The active power of the third equivalent machine is equal to the sum of the active powers of all generators in the third wind turbine group; the capacity of the third equivalent machine is the sum of the capacities of all generators in the third wind turbine group.

[0090] The third-level value machine operates within the third wind speed range. The wind turbine uses pitch angle control to achieve load reduction and cooperates with integrated inertia control to participate in system frequency regulation. When the system frequency drops or rises, integrated inertia control will increase or decrease the electromagnetic power output, causing the speed to deviate from the steady-state value. At this time, pitch angle control will adjust the pitch angle in real time until the speed stabilizes at the rated speed again. Therefore, the maximum wind speed in range three is the wind turbine's cut-out wind speed point. This range typically spans part of the MPPT range, the entire constant speed range, and the entire constant power range.

[0091] The other steps and parameters are the same as those in the first to eighth embodiments.

[0092] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that:

[0093] In S4, the equal-value machines divided in S3 are merged. The specific process is as follows:

[0094] For direct-drive wind turbines with Flag 1 = 0 and Flag 2 = 0, wind speed intervals 1, 2, and 3 are merged, and the first-class, second-class, and third-class wind turbines are merged into the first-class wind turbine.

[0095] For direct-drive wind turbines with Flag 3 = 0, wind speed intervals 2 and 3 are merged, and the second and third equivalent wind turbines are merged into the second equivalent wind turbine. If the number of wind turbines in a group is zero after the wind turbines in the wind farm are grouped according to wind speed intervals, the equivalent wind turbines corresponding to that group are automatically eliminated.

[0096] The present invention is described in conjunction with specific embodiments 1 to 10. Figure 1 , an electromagnetic transient model of a direct-drive wind farm was established on the MATLAB / Simulink software platform, and the following test scenario was designed to analyze the frequency regulation characteristics. The frequency regulation response curves of wind turbines under different wind speeds are as follows: Figure 3 As shown:

[0097] Test scenario 1 step disturbance: The frequency steps up and down to 50.5Hz and 49.5Hz respectively, and then returns to 50Hz after 5s; the wind speed changes from 3m / s at the start to 22m / s at the end, and the power interval is 0.01pu. The test results of the frequency step down and up are as follows: Figure 3 As shown in (a) and (b), each curve in the figure corresponds to the frequency modulation response result under a certain wind speed.

[0098] Test scenario 2 ramp disturbance: the frequency decreases / increases at a rate of ±0.5Hz / s, reaches 49.5Hz and 50.5Hz, and then maintains for 5s, and then returns to 50Hz at the opposite rate. The wind speed scenario is the same as test scenario 1. The test results of the frequency slope decrease and increase are as follows: Figure 3 As shown in (c) and (d), each curve in the figure corresponds to the FM response result under a certain wind speed.

[0099] It can be seen that the active power response curves of wind turbines in different wind speed ranges under the same frequency disturbance are significantly different. Specifically, they can be divided into: wind speed range 1 for low wind speed range, wind speed range 2 for medium and low wind speed range, and wind speed range 3 for medium and high wind speed range. The typical frequency modulation curves in different wind speed ranges are as follows: Figure 4 shown.

[0100] Step disturbance: 1) Wind speed range 1: The wind turbine has no response to frequency disturbance and does not participate in system frequency regulation; 2) Wind speed range 2: The wind turbine adjusts the active power output according to the drop / increase of frequency. The droop control is coordinated with the overspeed load reduction control, and the adjustment speed is faster; 3) Wind speed range 3: The wind turbine adjusts the active power output according to the drop / increase of frequency. The droop control is coordinated with the pitch angle load reduction control. The adjustment speed is slower, and the response time is about twice that of wind speed range 2.

[0101] Ramp disturbance: 1) Wind speed range 1: Same as step disturbance, does not participate in system frequency regulation; 2) Wind speed range 2: On the basis of overspeed load reduction control providing active power reserve, virtual inertia control and droop control jointly provide active power regulation during the frequency ramp phase; after the ramp phase, virtual inertia control is discontinued, while droop control continues to operate, and the active power regulation suddenly decreases and then enters a stable state; during the frequency recovery phase, the active power regulation changes with the slope. 3) Wind speed range 3: On the basis of pitch angle load reduction control providing active power reserve, the response process is the same as wind speed range 2; the response speed is similar to that of step response, slower than that of wind speed range 2. However, due to the relatively slow change rate of frequency ramp disturbance, the speed difference between wind speed ranges 2 and 3 is small.

[0102] From the above analysis results of the frequency modulation response characteristics, it can be seen that the wind turbines operating in the three wind speed ranges have obvious differences in frequency response characteristics due to different control modes, and each shows obvious clustering characteristics.

[0103] Wind turbines operating within the same wind speed range have the same frequency regulation control strategy and similar response characteristics. Wind turbines operating in different wind speed ranges have different frequency regulation control strategies and response characteristics. Wind speed range one does not participate in system frequency regulation. Wind speed ranges two and three utilize overspeed load reduction and pitch angle load reduction, respectively, for standby operation. Wind turbines exhibit significant differences in frequency regulation response speed under the same regulation amount. The active power regulation speed achieved using pitch angle control for load reduction is significantly lower than that achieved using overspeed load reduction. Other steps and parameters are the same as those in Specific Implementations 1 to 9.

[0104] The above only describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above-mentioned specific implementation methods. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent replacements and improvements made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis, characterized in that: The following steps are involved: S1: Construct a universal frequency regulation control model for direct-drive wind turbines; each type of direct-drive wind turbine shares a common set of universal frequency regulation control model parameters; S2: For each type of direct-drive wind turbine, the direct-drive wind turbine is divided into three wind turbine groups according to the different wind speed ranges of the wind turbines in the direct-drive wind turbine. S3: For each type of direct-drive wind turbine, the wind turbine group divided according to S2 is equivalent to 3 equivalent machines; S4: For each type of direct-drive wind turbine, the equivalent machines divided in S3 are merged, and then the universal frequency regulation control model of the direct-drive wind turbine obtained in S1 is used to control the merged equivalent machines respectively; The general frequency regulation control model of the direct-drive wind turbine generator system constructed in S1 includes: a virtual inertia control module Flag 1, a droop control module Flag 2, an overspeed load reduction standby control module Flag 3, and a pitch angle standby control module Flag 4; The virtual inertia control module Flag 1 controls the active power output of the wind turbine according to the frequency change rate of the power grid system. The specific process is as follows: Where ΔP1 is the active power adjustment output by the virtual inertia control, f is the system frequency, K1 is the virtual inertia control coefficient, and d is the derivative; The droop control module Flag 2: controls the active power output of the wind turbine according to the frequency deviation of the power grid system; the specific process is as follows: ΔP2=-K2Δf (2) Where ΔP2 is the active power adjustment output of the droop control, K2 is the droop control coefficient; Δf is the system frequency deviation; The overspeed load reduction standby control module Flag3 controls the wind turbine operating point according to the tip speed ratio λ of the wind turbine; The pitch angle standby control module Flag4 controls the wind turbine operating point according to the pitch angle β; The virtual inertia control module Flag 1, the droop control module Flag 2, the overspeed load reduction standby control module Flag 3, and the pitch angle standby control module Flag 4 are all enabled and disabled through the status control module of the flag bit; The state of the flag bit includes "1" and "0", the "0" state represents disabling the control module, and the flag bit being in the "1" state represents enabling the control module; Each type of direct-drive wind turbine generator system shares a common set of frequency modulation control model parameters. The specific process is as follows: The general frequency regulation control model parameter of the direct-drive wind turbine with virtual inertia control module is Flag 1 = 1; The general frequency regulation control model parameter of the direct-drive wind turbine without the virtual inertia control module is Flag 1 = 0; The general frequency regulation control model parameter Flag 2 = 1 for direct-drive wind turbines equipped with a droop control module; The general frequency regulation control model parameter Flag 2 = 0 for direct-drive wind turbines without droop control module; The general frequency regulation control model parameter Flag 3 = 1 for direct-drive wind turbines equipped with an overspeed load reduction standby control module; The general frequency regulation control model parameter Flag 3 = 0 for direct-drive wind turbines without overspeed load reduction backup control module; The general frequency regulation control model parameter of the direct-drive wind turbine with a pitch angle backup control module is Flag 4 = 1; The general frequency regulation control model parameter of the direct-drive wind turbine without a pitch angle backup control module is Flag 4 = 0; In S2, for each type of direct-drive wind turbine generator set, the direct-drive wind turbine generator set is divided into three wind turbine group groups according to the different wind speed ranges of the wind turbines in the direct-drive wind turbine generator set. The specific process is as follows: S2.1: Determine the wind speed interval cut point; S2.2: Divide the wind speed interval into three intervals according to the cut-off points of the wind speed interval divided in S2.1, and divide the direct-drive wind turbines into three direct-drive wind turbine groups according to the three divided wind speed intervals; The specific process of determining the wind speed interval cut point in S2.1 is as follows: The wind speed interval cut-off points are obtained based on the clustering characteristics of the active power response curves participating in the frequency regulation process in the power system frequency reduction scenario and the power system frequency increase scenario according to the general frequency regulation control model of direct-drive wind turbines. The power system frequency reduction scenario includes: a power system frequency step-down scenario and a power system frequency slope reduction scenario; The power system frequency decreases in the range of 50.0Hz-49.5Hz; The power system frequency rising scenario includes: a power system frequency step-up scenario and a power system frequency slope rising scenario; The power system frequency rises in a range of 50.0 Hz to 50.5 Hz.

2. The practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis according to claim 1, characterized in that: The wind speed interval cutting points in S2.1 include: cut-in wind speed point, first wind speed dividing point, second wind speed dividing point and cut-out wind speed point. The cut-in wind speed point is the minimum wind speed required for the wind turbine to start generating electricity; The first wind speed segmentation point is the wind turbine active power threshold P th The corresponding wind speed; The second wind speed split point refers to the wind speed corresponding to the maximum speed of the wind turbine when overspeed load reduction measures are taken during the operation of the wind turbine; The cut-out wind speed point is the maximum wind speed at which the wind turbine stops generating electricity.

3. The practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis according to claim 2, characterized in that: In S2.2, the wind speed interval cut points divided in S2.1 are used to divide the wind speed interval into three intervals, and the direct-drive wind turbines are divided into three direct-drive wind turbine groups according to the three divided wind speed intervals. The specific process is as follows: The wind speed interval 1 ranges from the cut-in wind speed point to the first wind speed dividing point; the wind turbines in the wind speed interval 1 are divided into a first wind turbine group; The second wind speed interval ranges from the first wind speed dividing point to the second wind speed dividing point; the wind turbines in the second wind speed interval are divided into a second wind turbine group; The wind speed interval three ranges from the second wind speed dividing point to the cut-out wind speed point; the wind turbines in the wind speed interval three are divided into a third wind turbine group.

4. The practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis according to claim 3, characterized in that: In S3, each model of direct-drive wind turbine group is equivalent to 3 equivalent machines according to the wind turbine group groups divided in S2; the specific process is: for each model of direct-drive wind turbine group, the first wind turbine group divided in S2 is equivalent to the first equivalent machine; the second wind turbine group divided in S2 is equivalent to the second equivalent machine; the third wind turbine group divided in S2 is equivalent to the third equivalent machine.

5. The practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis according to claim 4, characterized in that: The specific process of setting the first wind turbine group as the first-class value machine is as follows: The active power of the first-class value machine is equal to the sum of the active powers of all generators in the first wind turbine group; the capacity of the first-class value machine is the sum of the capacities of all generators in the first wind turbine group; The specific process of equating the second wind turbine group to the second equivalent unit is as follows: The active power of the second-equal-value machine is equal to the sum of the active powers of all generators in the second wind turbine group; the capacity of the second-equal-value machine is the sum of the capacities of all generators in the second wind turbine group; The specific process of equating the third wind turbine group to the third equivalent unit is as follows: The active power of the third equivalent machine is equal to the sum of the active powers of all generators in the third wind turbine group; the capacity of the third equivalent machine is the sum of the capacities of all generators in the third wind turbine group.

6. The practical equivalent method for direct-drive wind farms suitable for frequency characteristic analysis according to claim 5, characterized in that: In S4, the equal-value machines divided in S3 are merged. The specific process is as follows: For direct-drive wind turbines with Flag 1 = 0 and Flag 2 = 0, wind speed intervals 1, 2, and 3 are merged, and the first-class, second-class, and third-class wind turbines are merged into the first-class wind turbine. For the direct-drive wind turbine generator set with Flag 3=0, wind speed intervals 2 and 3 are merged, and the second and third value units are merged into the second value unit.

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