A wind farm frequency modulation power optimization distribution method based on stability improvement

Abstract

The application provides a wind farm frequency modulation power optimization distribution method based on stability improvement, and belongs to the technical field of active power distribution strategies of large-scale wind farm grid-connected systems. The technical problem of the decline of the stability margin of the grid-connected system in the scene where large-scale wind turbine generators participate in system frequency modulation is solved. The method comprises the following steps: S1, the wind turbine generator grid-connected system is equivalent to an interactive model of the source side and the power grid; S2, a wind farm grid-connected system frequency modulation power optimization distribution mathematical model is constructed; S3, a particle swarm algorithm is used to iteratively obtain an optimization distribution scheme of the frequency modulation power of each wind turbine generator; S4, when the wind farm responds to the frequency modulation demand, the dispatching center first determines the system frequency shortage information received and the current total output power of the wind farm; S5, the effectiveness of the optimization distribution scheme of the frequency modulation power is verified. The application takes into account the frequency modulation power response and the stability improvement of the grid-connected system, and breaks through the limitation of the traditional distribution strategy which only focuses on the power generation capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of active power distribution strategy of large-scale wind farm grid-connected system, and particularly relates to a wind farm frequency modulation power optimization distribution method based on stability improvement. BACKGROUND

[0002] In response to the grid frequency regulation requirement, the dispatch center determines the total power change required for frequency modulation based on the monitored system frequency shortage, and issues it to the wind farm central controller. After receiving the output change instruction, the wind farm central controller distributes power among the units according to a certain frequency modulation power distribution strategy. In this process, the active power output of each wind turbine changes continuously, thereby affecting the stability of the grid-connected system. At the same time, due to the differences in geographical location of wind turbines, the electrical distance from each wind turbine to the collection point also causes differences in the grid-connected port impedance parameters, which will also affect the stability of the grid-connected system when the output size does not match. Therefore, when designing the wind farm frequency modulation power distribution strategy, in addition to considering the frequency modulation capacity of each wind turbine, the technical problem of stability margin decline due to active power output change and mismatch between wind turbine port impedance during frequency modulation should also be considered.

[0003] At present, a large number of research results have been accumulated around the design of wind farm frequency modulation power distribution strategy at home and abroad. Despite this, the mainstream method follows the "proportional" or "generation capacity priority" principle, focusing on the influence of spatial differences in wind speed and wind turbine rated capacity. At the same time, some research takes into account the stability of the wind farm grid-connected system when distributing frequency modulation and virtual inertia power, and some research considers the technical problem of wind turbine fatigue load caused by frequent fluctuations in wind turbine output when distributing frequency modulation power, but does not involve the influence of wind turbine fatigue accumulation on the stability of the grid-connected system. In general, the current research on frequency modulation active distribution strategy still lacks a frequency modulation power distribution method that takes into account the matching of wind turbine output power and port impedance to improve the stability margin of the system.

[0004] How to solve the above technical problems is the problem faced by the present application. SUMMARY

[0005] In view of the technical problem that the mismatch of the output of each wind turbine and the port impedance of the wind farm participating in system frequency modulation will cause the stability to be reduced, and there is no wind farm frequency modulation power distribution method for solving the technical problem at present, in order to improve the system stability margin as the target, and taking into account the frequency modulation power distribution method of matching the output power of the wind turbine and the port impedance, the present application provides a wind farm frequency modulation power optimization distribution method based on stability improvement, establishes a multi-wind turbine frequency modulation power optimization model considering stability improvement, taking into account the frequency modulation power response and the stability improvement of the grid-connected system, and breaking through the limitation of the traditional distribution strategy which only focuses on the power generation capacity.

[0006] In order to achieve the above-mentioned application purpose, the technical scheme adopted by the present application is specifically as follows: a wind farm frequency modulation power optimization distribution method based on stability improvement, comprising the following steps:

[0007] 1) As shown in Figure (1), the grid-connected system of the wind turbine can be equivalent to an interactive model of the source side and the grid, and the stability of the grid-connected system of the wind farm is determined by / , and the expressions of the equivalent grid-side impedance , and the equivalent source-side impedance are respectively:

[0008] (1)

[0009] In the formula, Zs represents the equivalent source-side impedance, Zg represents the equivalent grid-side impedance, Zi represents the equivalent impedance of the i-th wind turbine, and Zpi represents the port impedance of the i-th wind turbine. The active power output of the wind turbine affects the equivalent impedance of the corresponding wind turbine , further affects the equivalent source-side impedance of the wind farm in formula (1)

[0010] , and the line impedance of each wind turbine affects the equivalent grid-side impedance , therefore, the stability margin of the grid-connected system is improved by optimizing the matching degree of the active power output of each wind turbine and the line impedance. The total impedance matrix of the grid-connected system of the wind farm is: (2)

[0011]

[0012] The stability margin of the wind power grid-connected system can be quantitatively represented by the damping ratio. For the impedance model of the wind farm grid-connected system shown in formula (2), the eigenvalue set is obtained by the characteristic equation, and the characteristic equation is:

[0013] (3)​​​​​

[0014] From equation (3), the n characteristic values ​​of the wind farm grid-connected system can be derived. The set is In the formula, , Corresponding to the i-th eigenvalue The real and imaginary parts of the eigenvalues. For a stable system, i.e., where the real part of the eigenvalue is less than 0, there exists a dominant eigenvalue that has the greatest impact on the stability of the wind farm grid-connected system. ,and At this point, the system damping ratio corresponding to the dominant eigenvalue is for:

[0015] (4)

[0016] In the formula, dominant eigenvalues The corresponding damping ratio of the wind farm grid-connected system, , Corresponding to the dominant eigenvalues The real and imaginary parts, <0 and The larger the value, the more stable the system. Therefore, this invention sets the stability margin index of the wind farm grid-connected system as:

[0017] (5)

[0018] In the formula, It is the critical stability damping ratio of the wind farm grid-connected system.

[0019] 2) Next, construct a mathematical model for frequency regulation power optimization allocation of the wind farm grid-connected system, considering stability improvement, based on the damping ratio margin of the wind farm grid-connected system. The objective function is to maximize the damping ratio while considering stability constraints, power balance constraints, and active power output constraints of the wind turbines, including stability margin and phase margin. Under the premise of ensuring that the wind turbine grid-connected system meets the system's frequency regulation power requirements and stability requirements, the stability margin of the wind farm grid-connected system is improved by maximizing the damping ratio. The wind farm frequency regulation power allocation optimization model is as follows:

[0020] (6)

[0021] In the formula, For the phase margin of the wind farm grid-connected system, h For the amplitude margin of the wind farm grid connection system, This is the total power adjustment amount. Indicates the first k The active power output of the typhoon generator unit This represents the minimum active power output that each wind turbine can provide. This represents the maximum active power output that each wind turbine can provide.

[0022] In the above optimization model, the wind farm grid-connected system needs to satisfy the inequality constraints on phase margin and gain margin when it is stable. The gain margin of the grid-connected system... h The expression is:

[0023] (7)

[0024] In the formula, ω g Represents the equivalent source-side impedance With equivalent network side impedance Crossing frequency.

[0025] Substituting further into equation (1), we can obtain

[0026] (8)

[0027] In the formula, , Let represent the equivalent impedance of the i-th wind turbine at the crossover frequency and the grid connection line impedance of the i-th wind turbine at the crossover frequency, respectively. , Let represent the equivalent impedance of the i-th wind turbine at the cross-frequency and the grid connection line impedance of the i-th wind turbine at the cross-frequency, respectively.

[0028] Meanwhile, during the frequency regulation process of the wind power grid-connected system, it is necessary to satisfy the equality constraint between the wind farm power adjustment amount and the system frequency regulation power demand, as well as the upper and lower limit output constraints of each wind turbine, namely:

[0029] (9)

[0030] The upper and lower limits of wind turbine output can be determined by considering factors such as the available rotor kinetic energy of each wind turbine and operating conditions such as wind speed.

[0031] 3) The particle swarm optimization algorithm is used to iteratively obtain the optimal allocation scheme of frequency regulation power for each wind turbine. It is assumed that the AC power grid is known, the line length from each wind turbine to the collection point is known, that is, the network topology and port impedance are given, and each wind turbine operates in maximum power point tracking mode.

[0032] When the frequency modulation controller issues a frequency modulation command to the central controller of the wind farm, the specific algorithm steps for solving the frequency modulation power optimization configuration are as follows:

[0033] Step 1: Input the control parameters, port impedance, network structure parameters, and system frequency regulation power requirements of each wind turbine in the wind farm grid connection system;

[0034] Step 2: Using the particle swarm optimization algorithm, initialize the frequency regulation active power configuration, calculate the equivalent impedance model of the wind farm grid-connected system under this configuration, derive the corresponding damping ratio of the wind farm grid-connected system, and calculate the current damping ratio stability margin.

[0035] Step 3: Determine whether the wind farm grid connection system under this configuration meets the constraints. If it does, proceed to the next step; otherwise, jump to step 2.

[0036] Step 4: Record the damping ratio stability margin calculated from the configurations that satisfy the constraints generated in the first group as the maximum damping ratio stability margin. Compare the damping ratio stability margin under the current configuration. With maximum damping ratio stability margin The size of the damping ratio stability margin under the current configuration. >0 and | |>| |, update the maximum value;

[0037] Step 5: Output maximum damping ratio stability margin And the corresponding frequency regulation active power optimization configuration results of the wind farm grid-connected system.

[0038] 4) When a wind farm responds to frequency regulation requirements, the dispatch center first determines the frequency deficit information Δ based on the received system frequency deficit information. f and the total output power of the wind farm at present Calculate the total power adjustment Δ required to meet the primary frequency regulation requirements. P The central controller at the wind farm level receives this Δ P When giving the instruction, Δ is not immediately divided equally. P Instead of allocating power to individual wind turbines, an active power optimization allocation strategy based on stability margin enhancement is implemented. The inputs to this strategy include the current maximum generating capacity of each wind turbine in the site. And the real-time evaluation results of the stability margin of the wind farm grid-connected system. The specific power adjustment amount for each wind turbine is calculated through optimization strategies, and then superimposed on the original power setpoint of that wind turbine to generate a new active power target command. The optimization scheme aims to effectively improve the grid connection stability margin of the entire wind farm while meeting the frequency regulation command. Its schematic diagram is shown in Figure (2).

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. The application proposes a wind farm frequency modulation power optimization distribution method based on stability improvement, establishes a multi-wind turbine frequency modulation power optimization model considering stability improvement, and takes into account the frequency modulation power response and the stability improvement of the wind farm grid-connected system, breaking through the limitation of traditional distribution strategy which only focuses on power generation capacity.

[0041] 2. The application establishes a wind farm grid-connected system equivalent impedance model of wind turbine active power and port impedance difference. The traditional impedance model usually ignores the direct influence of wind turbine output change on impedance characteristics, or is based on the homogenization assumption for simplified analysis, while the application couples the wind turbine output level and port impedance parameters into the impedance model through small signal modeling method. The model first quantifies the influence of output-impedance matching degree on stability, provides a theoretical basis for subsequent optimization distribution strategy, and improves the accuracy of stability analysis of wind farm grid-connected system.

[0042] 3. The wind turbine port impedance difference frequency modulation power differentiated distribution strategy proposed by the application analyzes the influence of impedance-output matching degree in different scenarios, and establishes the matching rule of "high impedance wind turbine is allocated low output, and low impedance wind turbine is allocated high output". By improving the matching degree of port impedance and frequency modulation output of each wind turbine in the wind farm grid-connected system, the strategy shortens the stability time of the wind farm grid-connected system, and the damping ratio stability margin is improved compared with the other two methods. The strategy embeds the impedance matching mechanism into the frequency modulation command decomposition process, and solves the stability deterioration problem caused by ignoring the electrical distance in the traditional method. BRIEF DESCRIPTION OF DRAWINGS

[0043] The accompanying drawings are used to provide a further understanding of the application, and constitute a part of the specification, together with the embodiments of the application, to explain the application, and do not constitute a limitation of the application.

[0044] Figure 1 is a wind farm grid-connected equivalent impedance model schematic diagram of the embodiment of the application.

[0045] Figure 2 is a wind farm frequency modulation power distribution schematic diagram of the embodiment of the application.

[0046] Figure 3 is a wind farm grid-connected system simulation topology structure diagram of embodiment 1 of the application.

[0047] Figure 4 is a wind turbine output distribution situation and wind farm output active power diagram under different schemes of embodiment 1 of the application.

[0048] Figure 5 is a simulation frequency response diagram of embodiment 1 of the application.

[0049] Figure 6 This is a diagram showing the relationship between the simulation stability margin and the output distribution in Embodiment 1 of the present invention.

[0050] Figure 7 These are active power output diagrams of wind farms under different schemes in Embodiment 2 of the present invention.

[0051] Figure 8 This is the simulated frequency response diagram of Embodiment 2 of the present invention.

[0052] Figure 9 This is a diagram showing the relationship between the simulation stability margin and the output distribution in Embodiment 2 of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0054] Example 1: See Figure 1 and Figure 6 This embodiment provides a technical solution: a wind farm frequency regulation power optimization allocation method based on stability improvement, comprising the following steps:

[0055] 1) As shown in Figure (1), the wind turbine grid-connected system can be equivalent to an interaction model between the source side and the power grid. The stability of the grid-connected system is determined by... / The decision, and the equivalent network-side impedance Equivalent source-side impedance The expressions are as follows:

[0056] (1)

[0057] In the formula, Indicates the equivalent source-side impedance. Indicates the equivalent network-side impedance. , , ..., These represent the equivalent impedances of the 1st, 2nd, ..., ith wind turbine units, respectively. , , ..., These represent the port impedances of the 1st, 2nd, ..., ith wind turbine units, respectively. This represents the equivalent grid impedance; the active power output of the wind turbine affects its equivalent impedance. This further affects the equivalent source-side impedance of the wind farm in equation (1). The impedance of each wind turbine's grid connection line affects the equivalent grid-side impedance. Therefore, the stability margin of the wind farm grid-connected system can be improved by optimizing the matching degree of the active power of each wind turbine and the line impedance. The total impedance matrix of the wind farm grid-connected system is

[0058] (2)

[0059] The stability margin of the wind farm grid-connected system can be quantitatively represented by the damping ratio. For the impedance model of the wind farm grid-connected system shown in equation (2), the characteristic value set is obtained from the characteristic equation, and the characteristic equation is:

[0060] (3)

[0061] It can be deduced from equation (3) that the n characteristic values of the wind farm grid-connected system are , wherein , respectively correspond to the real part and the imaginary part of the i-th characteristic value . For a stable system (i.e., the real part of the characteristic root is less than 0), there is a dominant characteristic root that has the greatest impact on the stability of the grid-connected system, and , at this time, the system damping ratio corresponding to the dominant characteristic root is

[0062] (4)

[0063] In equation (4), is the damping ratio corresponding to the dominant characteristic value , and , respectively correspond to the real part and the imaginary part of the dominant characteristic value . <0 and , the system is more stable. Therefore, the stability margin index of the wind farm grid-connected system is set as:

[0064] (5)

[0065] In equation (5), is the critical stability damping ratio of the wind farm grid-connected system, and is taken as 0.03.

[0066] 2) Then, a frequency regulation power optimization distribution mathematical model of the wind farm grid-connected system considering stability improvement is constructed, and the damping ratio margin ​The objective function is to maximize the damping ratio while simultaneously considering stability constraints, power balance constraints, and active power output constraints of the wind turbines, including stability margin and phase margin. Under the premise of ensuring that the wind turbine grid-connected system meets the system's frequency regulation power requirements and stability requirements, the stability margin of the system is improved by maximizing the damping ratio. The wind farm frequency regulation power allocation optimization model is as follows:

[0067] (6)

[0068] In the formula, For the phase margin of the wind farm grid-connected system, h For the amplitude margin of the wind farm grid connection system, This is the total power adjustment amount. Indicates the first k The active power output of the typhoon generator unit This represents the minimum active power output that each wind turbine can provide. This represents the maximum active power output that each wind turbine can provide.

[0069] In the above optimization model, the grid-connected system needs to satisfy the inequality constraints between phase margin and gain margin when it is stable. Gain margin of the wind farm grid-connected system. h The expression is:

[0070] (7)

[0071] In the formula, ω g Represents the equivalent source-side impedance With equivalent network side impedance Crossing frequency.

[0072] Substituting further into equation (1), we can obtain

[0073] (8)

[0074] In the formula, , Let represent the equivalent impedance of the i-th wind turbine at the crossover frequency and the grid connection line impedance of the i-th wind turbine at the crossover frequency, respectively. , Let represent the equivalent impedance of the i-th wind turbine at the cross-frequency and the grid connection line impedance of the i-th wind turbine at the cross-frequency, respectively.

[0075] Meanwhile, during the frequency regulation process of the wind power grid-connected system, it is necessary to satisfy the equality constraint between the wind farm power adjustment and the frequency regulation power demand of the wind farm grid-connected system, as well as the upper and lower limit output constraints of each wind turbine, i.e.

[0076] (9)

[0077] The upper and lower limits of wind turbine output can be determined by considering factors such as the available rotor kinetic energy of each wind turbine and operating conditions such as wind speed.

[0078] 3) The optimal allocation scheme for the frequency regulation power of each wind turbine is obtained iteratively using the particle swarm optimization algorithm. It is assumed that the AC power grid is known, the line length from each wind turbine to the collection point is known, that is, the network topology and port impedance are given, and each wind turbine operates in MPPT mode.

[0079] When the frequency modulation controller issues a frequency modulation command to the wind farm central controller, the specific algorithm steps for solving the frequency modulation power optimization configuration are as follows:

[0080] Step 1: Input the control parameters, port impedance, network structure parameters, and system frequency regulation power requirements for each wind turbine in the grid-connected system;

[0081] Step 2: Using the particle swarm optimization algorithm, initialize the frequency regulation active power configuration, calculate the equivalent impedance model of the wind farm grid-connected system under this configuration, derive the corresponding damping ratio of the wind farm grid-connected system, and calculate the current damping ratio stability margin.

[0082] Step 3: Determine whether the wind farm grid connection system under this configuration meets the constraints. If it does, proceed to the next step; otherwise, jump to step 2.

[0083] Step 4: Record the damping ratio stability margin calculated from the configurations that satisfy the constraints generated in the first group as the maximum damping ratio stability margin. Compare the damping ratio stability margin under the current configuration. With maximum damping ratio stability margin The size of the damping ratio stability margin under the current configuration. >0 and | |>| |, update the maximum value;

[0084] Step 5: Output maximum damping ratio stability margin And the corresponding frequency regulation active power optimization configuration results of the wind farm grid-connected system.

[0085] 4) When a wind farm responds to frequency regulation requirements, the dispatch center first determines the frequency deficit information Δ based on the received system frequency deficit information. f and the total output power of the wind farm at present Calculate the total power adjustment Δ required to meet the primary frequency regulation requirements. P The central controller at the wind farm level receives this total power adjustment Δ P When the command is given, the total power adjustment Δ is not immediately and evenly distributed. Pto each unit, but a strategy of active power optimization distribution based on stability margin improvement is executed. The input of the strategy includes the current maximum available power of each wind turbine in the field and the real-time evaluation result of the stability margin of the wind farm grid-connected system. Through the optimization strategy, the specific power adjustment of each wind turbine is calculated, which is superimposed on the original power set point of the wind turbine to generate a new active power target instruction , which is then issued to the corresponding wind turbine. The goal of the optimization scheme is to effectively improve the grid-connected stability margin of the entire wind farm under the premise of meeting the frequency modulation instruction, and the schematic diagram is shown in FIG. 2.

[0086] 5) In order to verify the effectiveness of the frequency modulation power distribution scheme proposed in the application, a wind farm composed of direct-drive wind turbines is taken as an example for calculation verification. The structure and control parameters of the direct-drive wind turbine are shown in Table 1, and the grid-connected parameters are shown in Table 2.

[0087] Table 1 Wind turbine parameter table

[0088]

[0089] Table 2 Grid-connected parameter table

[0090]

[0091] Figure 3 The effectiveness of the frequency modulation output distribution optimization strategy proposed in the application is verified by the grid-connected system of the two wind turbines shown in FIG. 1. The port impedance of the two wind turbines and the preset wind speed are different, the initial active output of the wind turbine is set to 0.9pu, and the wind farm grid-connected system runs in a stable state after t=2.0s. At 2.1s, the wind farm responds to the system frequency modulation instruction, and on the basis of the conventional maximum power point tracking mode, the frequency modulation output of the two wind turbines is appropriately adjusted and optimized according to the following three schemes:

[0092] Scheme one: according to the rated power output, that is, according to the rated capacity of each wind turbine, the frequency modulation power is distributed in proportion. The active power ratio of the two wind turbines under this scheme is 1:1, and the distribution is shown in Figure 4 (a).

[0093] Scheme two: according to the available power output, that is, according to the preset wind speed, the total active power is distributed. The active power ratio under this scheme is 1:1.16, and the distribution is shown in Figure 4 (b).

[0094] Scheme three: according to the wind farm active power distribution scheme considering stability improvement. The optimal active power ratio under this scheme is 1.25:1, and the distribution is shown in Figure 4 (c).

[0095] To verify the effectiveness of the strategy proposed in the present application, the wind farm is set to respond to the dispatching instruction of the power grid when t = 2.1 s, and the output active power is stepped from 0.9 pu to 1.0 pu. The time-domain simulation results of the output active power of the wind farm grid-connected system in this scenario are shown in (d) of FIG. 6, and the frequency response diagram is shown in (5) of FIG. 6. Figure 4

[0096] The influence of disturbance on the stability of the system under different active power output allocation schemes is compared and analyzed. As shown in (d) of FIG. 6, the frequency modulation effects are the same under the three schemes, because the frequency modulation output allocation strategy only affects the output allocation between the two wind turbines, and the external active power output of the wind farm is always the same under the three schemes. As shown in (d) of FIG. 6, the system enters a stable working state at about 2.0 s, and under the power instruction disturbance of scenario one, the output active power of the wind farm under the equal proportion allocation strategy fluctuates, and then enters a new stable operating state at 3.26 s. For scenario one, the grid-connected system using scenario two experiences a larger amplitude oscillation, and the overshoot is larger, and the system reaches a stable working point at 3.33 s; scenario three uses the active power output allocation scheme proposed in the present application, which considers the improvement of stability, and only 2.92 s is needed to reach a new stable operating point. Compared with scenario two, the grid-connected system of the wind farm under this scheme recovers to a stable operating state more quickly after fluctuation, and the overshoot is the smallest. Figure 5 The damping ratio stability margin of the wind farm grid-connected system under different output allocation schemes is shown in (d) of FIG. 6. The damping ratio stability margins of scenario one and scenario two are 56% and 34% respectively, and the damping ratio stability margin of the wind farm grid-connected system using the active power output allocation scheme of the wind farm considering the improvement of stability rises to 61%, verifying the effectiveness of the scheme proposed in the present application in improving the stability of the wind farm grid-connected system. Figure 4 Figure 6 It can be seen that the stability of the wind farm grid-connected system of scenario three is the best, and the difference allocation of the active power output of each wind turbine of the wind farm based on the port impedance of the wind turbine can improve the stability margin of the grid-connected system, and the system can always maintain stability during the operation of the wind farm. Even in the scenario affected by disturbance, the grid-connected system of the wind farm using scenario three reaches a new stable working point in a shorter time and with a smaller oscillation amplitude, verifying the effectiveness of the present application.

[0097] It can be seen that the stability of the wind farm grid-connected system of scenario three is the best, and the difference allocation of the active power output of each wind turbine of the wind farm based on the port impedance of the wind turbine can improve the stability margin of the grid-connected system, and the system can always maintain stability during the operation of the wind farm. Even in the scenario affected by disturbance, the grid-connected system of the wind farm using scenario three reaches a new stable working point in a shorter time and with a smaller oscillation amplitude, verifying the effectiveness of the present application.

[0098] Example 2: Based on example 1, the effectiveness and applicability of the analysis results and the proposed allocation scheme are further verified. A wind farm grid-connected system as shown in FIG. 7 is built, and the system parameters are shown in Table 3. In example 2, different numbers of wind turbines, wind turbine parameters in the field, wind turbine port impedance and wind turbine operating conditions are considered. Wind farm 1 and wind farm 2 are represented by equivalent wind turbines, representing the grid-connected parameters and operating state of the wind farm. Figure 7 ​​​

[0099] Table 3 Grid Connection Parameter Table

[0100]

[0101] The initial total active power output of the wind farm is set at 90% of its rated capacity. At 2.1 seconds, in response to the frequency regulation command issued by the dispatch center, the total active power output is increased to 100% of the rated capacity. Three power distribution schemes are employed: based on rated active power output, based on available active power output, and based on the wind farm active power output allocation scheme considering stability improvement proposed in Example 1. Frequency regulation power is allocated between wind farms 1 and 2. The output active power and system frequency response of the wind farm grid-connected system are as follows: Figure 8 , Figure 9 As shown.

[0102] Of the three schemes, Scheme 3 remains the frequency regulation power allocation scheme that minimizes the overshoot of the wind farm's active power output during frequency regulation and reaches the new steady state the fastest. Scheme 3 also features a damping ratio stability margin. The active power output reached 52.67%, which is 12.78% and 17.84% higher than Scheme 1 and Scheme 2, respectively, significantly improving the stability margin of the wind farm grid-connected system. Meanwhile, the frequency response of the three schemes remained consistent. Although the scale of the wind farm increased, the different schemes did not affect the total active power output, only the active power output configuration among the wind turbine clusters. Simulation results show that the analysis results and the proposed allocation schemes are still applicable when considering different wind farm grid-connected scenarios.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A stability-improvement-based wind farm frequency regulation power optimization allocation method, characterized in that, The method comprises the following steps: S1, the wind turbine generator system is equivalent to the interaction model of source side and power grid, and the stability of the wind turbine generator system is determined by / the expression of equivalent source side impedance , and equivalent grid side impedance is respectively: (1); wherein , ,..., denote the equivalent impedances of the 1st, 2nd,..., i-th wind turbine generator, , ,..., denote the port impedances of the 1st, 2nd,..., i-th wind turbine generator, denotes the equivalent grid impedance; S2, construct a mathematical model for optimizing distribution of frequency modulation power of a wind farm grid-connected system, so as to improve damping ratio margin of the wind farm grid-connected system The maximum is a target function, and the stability constraints, power balance constraints and active power output constraints of the wind turbine are considered in terms of stability margin and phase margin. S3, the particle swarm algorithm is used to iteratively obtain an optimal allocation scheme of the frequency modulation power of the wind turbine; assuming that the AC power grid is known, the line length from each wind turbine to the collection point is known, the network topology and port impedance are given, and each wind turbine operates in a maximum power point tracking mode; In the step S2, the mathematical model of the optimal allocation of the frequency modulation power of the wind farm grid-connected system is as follows: （6）； In the formula, is the phase margin of the wind farm grid-connected system, h is the amplitude margin of the wind farm grid-connected system, Δ P is the total power adjustment amount, represents the first k active power output of the wind turbine, is the minimum active power output of each wind turbine, is the maximum active power output of each wind turbine; In the optimization model, when the grid-connected system is stable, the inequality constraints of phase margin and amplitude margin are met, and the amplitude margin of the grid-connected system h The expression of the amplitude margin of the grid-connected system is: （7）； wherein ω g representing the equivalent source-side impedance and the equivalent grid-side impedance of the crossover frequency; Substituting equation (1) into equation (2) gives （8）； In the formula, , respectively represent the equivalent impedance of the i th wind turbine at the cross frequency and the grid connection line impedance of the i th wind turbine at the cross frequency, , respectively represent the equivalent impedance of the i th wind turbine at the cross frequency and the grid connection line impedance of the i th wind turbine at the cross frequency; In the frequency modulation process of the wind farm grid-connected system, the equality constraint of the wind farm power adjustment amount and the system frequency modulation power demand amount, and the upper and lower output constraints of each wind turbine need to be met, that is: （9）； S4. When the wind farm responds to frequency regulation requirements, the dispatch center first bases its response on the received system frequency deficit information. and the total output power of the wind farm at present Calculate the total power adjustment required to meet the primary frequency regulation requirements. The central controller at the wind farm level receives total power adjustment. When the command is given, the total power adjustment amount is not immediately distributed evenly. To each generating unit, it is used to execute an active power optimization allocation strategy based on stability margin improvement; S5, the effectiveness of the optimal allocation scheme of the frequency modulation power of each wind turbine is verified, and a wind farm composed of direct-drive wind turbines is developed for example verification based on a power system computer-aided design simulation platform.

2. The stability-lifting-based wind farm frequency regulation power optimization allocation method according to claim 1, characterized in that, In the step S1, the active power of the wind turbine influences the equivalent impedance of the corresponding wind turbine, and further influences the equivalent source-side impedance of the wind farm in the formula (1) The grid-connected line impedance of each wind turbine influences the equivalent grid-side impedance The total impedance matrix of the grid-connected system of the wind farm is ​ （2）； The stability margin of the wind farm grid-connected system is quantitatively characterized by a damping ratio. For the impedance model of the wind farm grid-connected system shown in equation (2), a set of characteristic values is obtained from a characteristic equation, which is: (3); From formula (3), n eigenvalues of the wind farm grid-connected system are derived as The set is , wherein , respectively correspond to the real part and the imaginary part of the ith eigenvalue ; for a stable system, there is a dominant eigenvalue which has the greatest impact on the stability of the grid-connected system, and the system damping ratio corresponding to the dominant eigenvalue is: (4). In the formula, is the dominant eigenvalue is the corresponding system damping ratio, , respectively correspond to the real part and the imaginary part of the dominant eigenvalue , the stability margin index of the grid-connected system of the wind farm is set as: (5). In the formula, is the critical stability damping ratio of the grid-connected system.

3. The method of claim 1, wherein, The input of the active power optimization distribution strategy in the step S4 includes the current maximum available power of each wind turbine in the wind farm and the real-time evaluation result of the stability margin of the grid-connected system of the wind farm. The specific power adjustment amount of each wind turbine is calculated through the active power optimization distribution strategy, which is superimposed on the original power set point of the wind turbine to generate a new active power target instruction , which is issued to the corresponding wind turbine.

4. The method of claim 1, wherein, In the step S3, when the frequency modulation controller issues a frequency modulation instruction to the wind farm central controller, the frequency modulation power optimization configuration solving comprises the following steps: S31: data input and parameter initialization The control parameters of each wind turbine in the wind farm grid-connected system are input, including the rated capacity of the wind turbine, the control loop proportional integral coefficient, the node port impedance parameter, the network topology structure parameter, and the system-level frequency modulation power total demand value; S32: frequency modulation configuration optimization iteration Improved particle swarm optimization algorithm is used to initialize the configuration of active power: N groups of wind turbine active power distribution schemes are randomly generated as initial particle swarm, each group of scheme needs to meet the power balance condition, for each configuration scheme, the equivalent impedance model of the wind farm grid-connected system is established, by solving the corresponding characteristic equation, according to the damping ratio formula The damping characteristics under the current configuration are calculated, and the damping ratio stability margin , is defined as the critical stable damping ratio of the wind farm grid-connected system; S33: multi-dimensional constraint condition checking It is judged whether the current configuration meets the following constraint conditions: (1) wind turbine output constraint; (2) power system stability constraint: the amplitude margin and phase margin of the wind farm grid-connected system are greater than zero; (3) system frequency modulation power demand constraint: in the frequency modulation process of the wind farm grid-connected system, the equality constraint of the wind farm power adjustment amount and the system frequency modulation power demand amount needs to be met, and if any condition is not met, the particle swarm mutation operator is triggered to generate a configuration scheme again; S34: dynamic update of optimal solution The damping ratio stability margin calculated from the configurations that satisfy the constraints generated in the first group is denoted as the maximum damping ratio stability margin. Compare the damping ratio stability margin under the current configuration. With maximum damping ratio stability margin The size of the damping ratio stability margin under the current configuration. >0 and | |>| |, update the maximum value; S35: output the maximum damping ratio stability margin and the corresponding wind farm frequency modulation power optimal allocation scheme result.

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