Wind power frequency support adaptive ramp exit method and system

Abstract

The present invention proposes a wind power frequency support adaptive ramp exit method and system, which belongs to the field of wind turbine adaptive exit technology, including: in the process of wind turbine exiting frequency modulation, the wind turbine output change is equivalent to a set load, and a system frequency response time domain expression of the set load is obtained, and the system frequency response time domain expression is used to analytically express the frequency change of the wind turbine in the ramp exit frequency modulation process; solving the minimum value of the system frequency response time domain expression, that is, solving the optimal exit slope; solving the wind turbine mechanical characteristic constraints and the system frequency constraints; based on the above solution results, a wind farm adaptive exit frequency modulation strategy is formulated: in the frequency support stage, the disturbance size is shared according to the kinetic energy reserve ratio of the wind turbine rotor under different wind conditions, and then the incremental power and support time of each wind turbine are determined; in the exit frequency modulation stage, the exit slope of each wind turbine in the wind farm is distributed.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind turbine adaptive exit, and in particular relates to a method and system for adaptive ramp exit of wind power frequency support. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The widespread integration of renewable energy sources such as wind and solar has reduced the inertia of traditional machinery, creating a so-called low-inertia power system. This reduced inertia increases system frequency deviation and variability. The high randomness and volatility of renewable energy sources have severely weakened the power system's regulatory capabilities, posing severe challenges to safe power operation and leading to frequent grid accidents.

[0004] To reduce the occurrence of such incidents and improve power system stability, power grids in many countries and regions have introduced new requirements for the operation of renewable energy systems, requiring them to have inertia response or primary frequency regulation capabilities. For example, when a system disturbance causes a frequency drop, wind turbines must release their own rotor kinetic energy or reserve energy to provide short-term power support, thereby suppressing the rate of change and frequency deviation of the system frequency.

[0005] When new energy sources implement the above-mentioned inertia response or primary frequency modulation function, the Fast Frequency Response (FFR) control method can effectively bring into play the characteristics of the wind turbine's fast response speed and high flexibility. When the system frequency drops, the wind turbine can increase power sharply in a short period of time, thereby suppressing the decrease in system frequency and helping the system frequency to recover quickly.

[0006] When the operating conditions remain unchanged and the system is running stably, the wind turbine operates in the Maximum Power Point Tracking (MPPT) state, and the output power remains unchanged;

[0007] (1)

[0008] Where: P w ( t ) is the electromagnetic power output by the fan, P MPPT is the maximum operating power of the fan.

[0009] When the system experiences a disturbance that causes the frequency to drop, the wind turbine provides power support to the grid by extracting its own rotor kinetic energy. At this time, the wind turbine output power can be expressed as

[0010] (2)

[0011] Where: Δ P f ( t ) is the incremental power output of the fan.

[0012] When the frequency stabilizes, the wind turbine needs to exit frequency modulation and absorb energy from the grid to supplement the rotor kinetic energy. The wind turbine outputs incremental power Δ P f ( t ) changes from positive to negative. P f ( t ) changes in a short time, especially when the power drops sharply, it is easy to cause a secondary drop in the system frequency.

[0013] Existing secondary drop measures: Domestic and foreign scholars have conducted research on changing the exit power size, adjusting the exit time, etc. to reduce the frequency secondary drop problem.

[0014] For example, the paper "Weiyu Bao, Lei Ding, Zhifan Liu, et al. Analytically derived fixed termination time for stepwise inertial control of wind turbines—Part I: Analytical derivation[J]. International Journal of Electrical Power&Energy Systems, 2020, 121: 106120" reasonably sets the time for wind turbine exit, superimposes the frequency drop caused by wind turbine exit and the overshoot point of the frequency curve caused by disturbance, thereby increasing the lowest point of the system's secondary drop. The paper "He Chengming, Wang Hongtao, Sun Huadong, et al. Analysis of frequency regulation characteristics of variable-speed wind turbines and sequential coordinated control strategy for wind farms[J]. Automation of Electric Power Systems, 2013, 37(09):1-6+59" analyzes the corresponding relationship between the active power increment and the duration of frequency regulation during the process of wind turbines participating in system frequency regulation, and proposes a sequential exit frequency regulation control strategy to reduce the power impact caused by the simultaneous exit of wind turbines. The paper “Z. Wang and W. Wu. Coordinated Control Method for DFIG-Based Wind Farm to Provide Primary Frequency Regulation Service[J]. IEEE Transactions on Power Systems, 2018, 33(3): 2644-2659.” proposed a distributed control method to ensure the safety of wind turbine operation by limiting energy release and reducing the secondary frequency drop, but this method affects the frequency regulation effect to a certain extent. The paper “S. El Itani,UD Annakkage and G. Joos. Short-term frequency support utilizing inertial response of DFIG wind turbines[C]. 2011 IEEE Power and Energy Society General Meeting, Detroit, MI, USA, 2011, pp. 1-8.” proposed a wind turbine ramp exit control method to reduce power impact, but only qualitative description was given, lacking the design scheme of the strategy and quantitative analysis of the parameters.At the same time, none of the above strategies have conducted research on the coordinated cooperation of wind power and synchronous machine energy links from a system level, and ultimately failed to achieve the optimal effect.

[0015] It can be seen that the existing methods have not conducted research on the coordinated cooperation of various energy links of wind power and synchronous machines from a system level, and ultimately cannot achieve the optimal effect; due to the complex aerodynamic nonlinearity and time-varying characteristics of wind power, which are difficult to analyze, it is impossible to achieve an accurate quantitative characterization of wind power capacity; the frequency regulation capabilities of various wind turbines in the wind farm vary greatly, and the existing methods have failed to reasonably allocate power according to the kinetic energy reserves of different wind turbines, resulting in some wind turbines facing the risk of speed exceeding the limit. Further research is needed on a simple, accurate and effective task power allocation method.

[0016] As a result, existing wind turbines lack systematic theoretical guidance during the frequency support exit phase and are unable to determine the optimal exit slope, which may lead to a secondary drop in system frequency during the exit process. Summary of the Invention

[0017] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for adaptive ramp exit of wind power frequency support. The proposed strategy has obvious advantages and effectively reduces the secondary frequency drop of the system.

[0018] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0019] In a first aspect, a method for adaptively ramping out of wind power frequency support is disclosed, comprising:

[0020] During the process of the fan exiting the frequency modulation, the fan output change is equivalent to the set load, and the system frequency response time domain expression of the set load is obtained. The system frequency response time domain expression is used to analytically express the frequency change of the fan during the ramp exiting the frequency modulation process;

[0021] Solve the minimum value of the time domain expression of the system frequency response, that is, solve the optimal exit slope;

[0022] Solve the mechanical characteristic constraints of the fan and the system frequency constraints;

[0023] Based on the above solution results, the wind farm adaptive exit frequency regulation strategy is obtained, including the strategy in the frequency support phase and the strategy in the exit frequency regulation phase;

[0024] During the frequency support phase, the disturbance magnitude is apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, thereby determining the incremental power and support time of each wind turbine.

[0025] During the frequency regulation exit phase, the exit slope of each wind turbine in the wind farm is allocated.

[0026] As a further technical solution, the process of obtaining the time domain expression of the system frequency response with the set load is as follows:

[0027] Based on the set load equivalent to the change in fan output, the system frequency response model is used for analysis to obtain the time domain expression of the step response;

[0028] Integrating the step response time domain expression to obtain the ramp response time domain expression of the system frequency response model;

[0029] Based on the time domain expression of the ramp response, partial expressions of the frequency response characteristics of the analysis are obtained;

[0030] After merging the partial expressions of the frequency response characteristics and applying the set load, the time domain expression of the system frequency response is obtained.

[0031] As a further technical solution, based on the time-domain expression of the ramp response, the influence of the ramp response on the frequency mainly includes three parts: the ramp component, the DC component and the exponentially decaying oscillation component.

[0032] As a further technical solution, the process of solving the optimal exit slope is:

[0033] Substituting the exit slope expression into the system frequency response time domain expression, we can obtain the first monotonically decreasing nonlinear function;

[0034] For the first monotonically decreasing nonlinear function, different fan exit times are selected for simulation to obtain the system frequency response curve;

[0035] The optimal exit slope of the fan is obtained based on the system frequency response curve.

[0036] As a further technical solution, the optimal exit time of the fan should be set to , at this time the optimal exit slope of the fan is k opt Expressed as:

[0037]

[0038] Among them, Δ P is the power amplitude of the wind turbine exit, is the damped oscillation frequency.

[0039] Secondly, a wind power frequency support adaptive ramp exit system is disclosed, including:

[0040] The frequency change expression module is configured to: during the process of the fan exiting the frequency modulation, the fan output change is equivalent to the set load, and the system frequency response time domain expression of the set load is obtained. The system frequency response time domain expression is used to analytically express the frequency change of the fan during the process of ramping out of the frequency modulation;

[0041] The solving module is configured to: solve the minimum value of the time domain expression of the system frequency response, that is, solve the optimal exit slope;

[0042] Solve the mechanical characteristic constraints of the fan and the system frequency constraints;

[0043] The wind farm adaptive frequency regulation exit strategy module is configured to: obtain a wind farm adaptive frequency regulation exit strategy based on the above solution results, including a strategy for the frequency support phase and a strategy for exiting the frequency regulation phase;

[0044] During the frequency support phase, the disturbance magnitude is apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, thereby determining the incremental power and support time of each wind turbine.

[0045] During the frequency regulation exit phase, the exit slope of each wind turbine in the wind farm is allocated.

[0046] One or more of the above technical solutions have the following beneficial effects:

[0047] The present invention proposes an adaptive ramp exit method for wind turbine frequency support: First, a control method for ramping out frequency modulation of wind turbines is proposed, and the problem is transformed. Then, the optimal slope and optimal time for the wind turbine under the ramp exit method are derived and solved. Simultaneously, the wind turbine's own mechanical characteristic constraints and system frequency constraints are considered to determine the safe operating range of the wind turbine under different operating conditions. Finally, the power allocation scheme for each wind turbine in the wind farm during frequency support is simplified, and an adaptive exit strategy for wind farm frequency support is proposed. Results from an improved IEEE 39 simulation case show that the proposed strategy has significant advantages and effectively reduces the system's secondary frequency drop.

[0048] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0050] Figure 1 This is a schematic diagram of a wind turbine generator system participating in frequency modulation according to an embodiment of the present invention;

[0051] Figure 2 This is a schematic diagram of the system equivalent load felt by the synchronous machine according to an embodiment of the present invention;

[0052] Figure 3 A simulation diagram of an embodiment of the present invention, wherein Figure 3 (a) shows the load change of the synchronous machine under different exit slopes in the embodiment of the present invention. Figure 3 (b) is a schematic diagram of the frequency change of the system according to an embodiment of the present invention;

[0053] Figure 4 Schematic diagram of the corresponding relationship between the lowest point of the secondary drop in system frequency and the time required for wind turbine exit in an embodiment of the present invention;

[0054] Figure 5 Schematic diagram of frequency response characteristics analysis of two ramp loads according to an embodiment of the present invention;

[0055] Figure 6 The lowest frequency point of the embodiment of the present invention and t off Schematic diagram of the relationship between

[0056] Figure 7 This is a schematic diagram of power-speed during the frequency modulation process of a fan according to an embodiment of the present invention;

[0057] Figure 8 This is a power-time diagram of the process in which a wind turbine participates in frequency modulation according to an embodiment of the present invention;

[0058] Figure 9 Schematic diagram of an SFR model including a fan according to an embodiment of the present invention;

[0059] Figure 10 This is a schematic diagram of a frequency response image of a wind turbine during ramp exit according to an embodiment of the present invention;

[0060] Figure 11 For the embodiment of the present invention Δ P With Δ P f Relationship diagram;

[0061] Figure 12 This is a schematic diagram of the centralized control architecture of a wind farm;

[0062] Figure 13 Schematic diagram of the simulation system;

[0063] Figure 14 This is a schematic diagram of wind turbine power distribution ratio at different wind speeds;

[0064] Figure 15 The image of wind turbine speed change under different wind speeds in scene 1 is shown below. Figure 15 (a) is the image of wind turbine speed change in scene 1 with a wind speed of 7 m / s. Figure 15 (b) is the image of wind turbine speed change in scene 1 with a wind speed of 8 m / s. Figure 15 (c) in the figure is the image of wind turbine speed change in scene 1 with a wind speed of 9 m / s. Figure 15(d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 1;

[0065] Figure 16 The wind turbine output changes at different wind speeds in scene 1, where Figure 16 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 1. Figure 16 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 1. Figure 16 (c) in the figure is the wind turbine output change image with a wind speed of 9 m / s in scene 1. Figure 16 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 1;

[0066] Figure 17 This is the frequency change image of scene 1;

[0067] Figure 18 The image of wind turbine speed change under different wind speeds in scene 2 is shown in the figure. Figure 18 (a) is the image of wind turbine speed change in scene 2 with a wind speed of 7 m / s. Figure 18 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 2. Figure 18 (c) is the wind turbine speed change image with a wind speed of 9 m / s in scene 2. Figure 18 (d) is the image of wind turbine speed change in scene 2 with a wind speed of 10 m / s;

[0068] Figure 19 The wind turbine output changes at different wind speeds in scene 1, where Figure 19 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 2. Figure 19 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 2. Figure 19 (c) is the wind turbine output change image with a wind speed of 9 m / s in scene 2. Figure 19 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 2;

[0069] Figure 20 This is the frequency change image of scene 2. DETAILED DESCRIPTION

[0070] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0071] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0072] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0073] Example 1

[0074] This embodiment discloses a method for adaptive ramp exit of wind power frequency support. The sub-technical solution of this embodiment focuses on the coordinated control of wind turbines and the multi-scale energy release characteristics of synchronous machines during the process of exiting frequency regulation, as well as the frequency secondary drop problem of the system. First, the process of wind power ramp exiting frequency regulation under FFR control is equivalent to load change, and the lowest point of the secondary frequency drop is obtained by analysis. Further considering the mechanical characteristic constraints of the wind turbine and the system frequency constraints, the constraint expression of the mechanical characteristics is formula (34); the system frequency constraint expression is formula f nadir1 > f nadir2 The optimal slope and time for the wind turbine to exit frequency regulation are obtained. These optimal slope and time are calculated by treating all wind turbines in the system as a whole. This result is then used to allocate power to each wind turbine. Finally, the power allocation problem for each wind turbine in the wind farm is transformed into a linear programming problem, improving the practicality of the proposed strategy.

[0075] The synchronous machine has different energy storage levels and release rates at various time scales, including electromagnetic energy, rotor kinetic energy, boiler heat storage, and fuel links. The sub-technical solution of this embodiment is mainly to coordinate the rapid frequency response of the fan with the rotor kinetic energy of the synchronous machine's single frequency modulation during the response phase; and to coordinate the ramp exit of the fan with the boiler heat storage of the synchronous machine during the exit phase.

[0076] In this embodiment, the specific steps of the wind power frequency support adaptive ramp exit method include:

[0077] Step 1: Problem transformation: In order to deal with the secondary frequency drop problem, this example improves on the basis of fast frequency response (FFR) control and adopts a ramp exit method to avoid a short-term power drop, such as Figure 1 shown.

[0078] During the wind turbine exit process, assuming the exit power amplitude Δ P Certainly, in t =- t off The output power of the fan is along the slope k slope The slope goes down, passingt off Exit time, t off is the fan exit time, when t = 0, it decreases to a stable value and keeps the current output power unchanged. The exit slope can be expressed as

[0079] (3)

[0080] For synchronous machines, the fan ramp exit process is equivalent to adding a Figure 2 Equivalent load shown: t =- t off When the load power along the slope - k slope Increase, when t =0, the load with equal slope and opposite direction is superimposed, and the equivalent load power becomes -Δ P , and remain constant.

[0081] Therefore, reducing the frequency secondary drop problem can be converted into improving Figure 2 The frequency minimum problem caused by the equivalent load is shown.

[0082] From the above analysis, we can see that when the fan exits the frequency modulation process, the system can be regarded as having only synchronous machines, and the fan output change is equivalent to Figure 2 For the load shown, the traditional system frequency response model (SFR) can be used, i.e., formulas (4)(5)(6)(7)(8)(9) for analysis. The SFR model is a frequency analysis model that describes the power grid dominated by traditional synchronous machines. For synchronous machines, the wind turbine ramp exit is to input a ramp load into the SFR model. During analysis, the output characteristics of the SFR for the input step load are first derived, and then integrated to obtain the SFR output characteristics for the ramp load.

[0083] The step response time domain expression of the above SFR model is:

[0084] (4)

[0085] (5)

[0086] (6)

[0087] (7)

[0088] (8)

[0089] (9)

[0090] Where: is the load change; is the frequency variation of the power grid under step disturbance; D is the equivalent damping coefficient of the power grid; H is the equivalent inertia time constant of the power grid; R 、 K m 、 T R 、 F H are the equivalent quantities of synchronous machine prime mover and speed governor parameters, namely droop coefficient, mechanical power gain coefficient, prime mover time constant and reheat power percentage; is the damped oscillation frequency, ζ is the damping ratio, is the natural frequency, φ 、 φ 1. φ 2 is the phase angle, a is the coefficient.

[0091] By integrating Equation (4), we can obtain the time domain expression of the ramp response of the SFR model:

[0092] (10)

[0093] Where: is the frequency variation of the power grid under the ramp disturbance. As can be seen from formula (10), the influence of the ramp response on the frequency mainly includes three parts: the ramp component, the DC component and the exponentially decaying oscillation component. Figure 2 The disturbance shown is the superposition of two ramp loads at different times. Since the slopes of these two ramp loads are the same but the polarities are opposite, the polarities of the ramps, DC components, and oscillation components of the corresponding frequencies of the two ramp loads are opposite. t ∈(- t off , 0), the ramp load is reflected as a change in steady-state frequency; t >0, the ramp components and DC components of the frequencies corresponding to the two ramp loads cancel each other out, and the oscillation component has no effect. The frequency response can be considered as the superposition of the two continuously attenuating oscillation components mentioned above. That is, the frequency response characteristics analyzed are:

[0094] (11)

[0095] Formula (11) can be further simplified as

[0096] (12)

[0097] In the formula is the AC component of the grid frequency variation under ramp disturbance.

[0098] (13)

[0099] (14)

[0100] Imposition Figure 2 The time domain expression of the system frequency response of the load shown is It can be expressed as:

[0101] (15)

[0102] In summary, the frequency change of the fan during the ramp exit frequency modulation process can be analytically expressed using Equation (15). The minimum value of the secondary frequency drop is also converted into the minimum value of Equation (15). The secondary frequency drop problem can then be reduced by solving the optimal exit slope.

[0103] Considering that the prior art only conducts qualitative analysis and does not further quantitatively analyze the expression of the exit process, the above process of this embodiment realizes the solution of the system frequency time domain expression of the wind power exit process.

[0104] Step 2: Analysis of the system's response demand for wind power.

[0105] The lowest frequency point is an important indicator of the frequency response effect during frequency control. In order to maintain the safe and stable operation of the system, the lowest frequency point needs to be limited to a certain range. When the system encounters an event disturbance that causes the frequency to drop, the system will have the first lowest frequency point. f nadir1 At the same time, the second frequency drop caused by the fan exiting the frequency modulation will lead to the second frequency minimum point f nadir2 In order to reflect the superiority of the strategy in this paper, it is stipulated that the lowest point of the second drop in frequency should be higher than the first lowest point, that is, f nadir1 > f nadir2 The following is an analysis of the two lowest frequency points.

[0106] (2-1) The first frequency minimum point f nadir1 .

[0107] By solving the lowest point of the frequency drop caused by the disturbance, f nadir1 > f nadir2 Converted into power response demand for the wind turbine.

[0108] Frequency minimum f nadir1 It can be solved by the SFR model under step disturbance, such as Figure 6 、 7 , 8, where Δ P f represents the power change caused by the event disturbance, Δ P L Indicates the change in fan output, and the system equivalent step disturbance can be expressed as P step = Δ P f - Δ P L From formula (4), we can see that when d(Δ ω step ) / d t = 0, the frequency reaches its lowest point, and the lowest frequency time t nadir1 It can be expressed as:

[0109] (16)

[0110] Substituting equation (16) into equation (4), we can obtain the lowest point of the system: f nadir1 for

[0111] (17)

[0112] (2-2) The second lowest frequency point f nadir2 .

[0113] During the fan exit phase, if the fan ramp exit time is too short, it will cause a large power surge and a serious secondary frequency drop. If the fan ramp exit time is too long, the fan will consume rotor kinetic energy for a long time, which may cause the fan speed to drop too low and cause the fan to trip. Therefore, it is necessary to reasonably set the fan exit time to achieve the optimal frequency dynamic effect.

[0114] By solving the lowest point of the system frequency drop during the fan ramp exit process, f nadir1 > f nadir2 Converted into power response demand for the wind turbine.

[0115] Substituting formula (3) into formula (15), we can get

[0116] (18)

[0117] Obviously, formula (18) is a monotonically decreasing nonlinear function, but it is difficult to solve itst off The analytical expression of the minimum value change under this condition is t off Perform simulations such as Figure 3 As shown, Figure 3 (a) shows the load change of the synchronous machine under different exit slopes in the embodiment of the present invention. Figure 3 (b) is a schematic diagram of the frequency change of the system according to the embodiment of the present invention. The frequency secondary drop lowest point curve corresponding to different exit times is as follows: Figure 4 As shown. It can be found that: as the fan exits t off As the frequency increases, the lowest point of the secondary frequency increases continuously and shows a trend of "fast at first and then slow". That is, there is an inflection point. The speed of change of the lowest point of the secondary frequency drop before and after the inflection point is significantly different. After the inflection point, the change of the lowest point of the secondary frequency drop becomes slow, and then increases. t off The lowest point of the second frequency drop does not change much, but it will increase energy loss. Therefore, the wind turbine exit slope corresponding to this point can be regarded as a relatively ideal optimal exit slope. The following will focus on the analysis of this inflection point.

[0118] Discrete Analysis:

[0119] Hypothesis Function The extreme points of Consistent, that is, exponential decay does not affect the phase of the trigonometric function and the time corresponding to the extreme point, then and When the two oscillations are in phase, When , the two oscillation signals are at their peak values ​​at the same time. The response characteristics in this case are as follows Figure 5 As shown, for and The difference is obviously hour , Reaching the minimum , which can be expressed as

[0120] (19)

[0121] From the proof, we can see that along with t off The proof process is as follows.

[0122] Proof: Let

[0123] (20)

[0124] Taking its derivative we get

[0125] (twenty one)

[0126] make

[0127] (twenty two)

[0128] Taking the derivative we get

[0129] (twenty three)

[0130] exist t >0, h ’ ( t )<0 is always established, h ( t )exist t >0 is monotonically decreasing, so

[0131] (twenty four)

[0132] Multiply both sides by 1 / t 2

[0133] (25)

[0134] Right now

[0135] (26)

[0136] exist t >0, so f ( t )exist t When >0, it is monotonically increasing. f ( t ) is the limit of

[0137] (27)

[0138] (28)

[0139] therefore, exist t >0, considering only discrete time points, that is, When you can get

[0140] (29)

[0141] (30)

[0142] Continuous analysis: Next The response at continuous time continues to be analyzed.

[0143] It can be seen from the proof that when t off =0, Dissatisfied t off The response characteristic is discrete, mainly because t off =0, The phase and , The phase of is inconsistent. The proof is as follows:

[0144] (31)

[0145] (32)

[0146] Obviously, ， ,therefore , so when t off =0, The phase lags behind and .

[0147] The discrete frequency characteristic curve in formula (19) t off Replaced with a continuous quantity, the dynamic response obtained at this time means: at the exit time t off When any value is taken, it is determined The envelope of the decaying oscillation of Stay consistent, so Always t = t The lowest point is obtained at 0, and the phase relationship is always the same Figure 6 shown.

[0148] However, in reality, only when ,and n When is a positive integer, and The phase of t = t The extreme value is obtained at 0, and at other times and There is a phase deviation between the two. When there is a phase deviation, t = t 0 o'clock, Must be less than The proof is as follows:

[0149] (33)

[0150] because ), are all less than 0, so

[0151] (34)

[0152] Specific relationships such as Figure 7 As shown, in hour and In order to ensure that the fan can be restored to the MPPT operating state as soon as possible, it can be considered that It is the best choice.

[0153] Therefore, the optimal exit time of the fan should be set to , is the damped oscillation frequency, at which point the fan has the optimal exit slope k opt It can be expressed as:

[0154] (35)

[0155] Step 1 has achieved an analytical solution for the frequency response of the secondary frequency drop. According to formula (18), a simulation image can be further made, such as Figure 10 Before the fan exits the frequency modulation, the frequency change rate is 0; in the first stage, the fan begins to exit the frequency modulation in a ramp manner, and the system frequency decreases monotonically, with the lowest frequency point f nadir2 It must happen Figure 8 After the 0 moment of the equivalent load shown, that is Figure 10 The second stage is shown.

[0156] The following is for f nadir2 Continue to analyze. From the derivation, we can know that when When , formula (18) can be written as

[0157] (36)

[0158] Derivative of Equation (36)

[0159] (37)

[0160] (38)

[0161] Assume that t = t 0:00 Reaching the minimum value, minimum momentt 0 can be represented as

[0162] (39)

[0163] Where: n 0 means t 0 is the smallest positive integer greater than zero.

[0164] According to the superposition theorem, the lowest frequency point f nadir2 It can be expressed as

[0165] (40)

[0166] Therefore, the sub-technical solution of this embodiment realizes the analytical solution of the magnitude of the two lowest frequency points.

[0167] Step 3: Parameter adjustment method considering the mechanical characteristics of the fan.

[0168] Step 2 describes the system's response requirements for wind power; step 3 solves its own capabilities based on the mechanical characteristics constraints of the wind turbine, and then determines the actual safe operating parameter range of the wind turbine.

[0169] While meeting the system's response requirements for wind power, wind turbines, due to their inherent mechanical characteristics, must also meet constraints such as speed, output power, and load during actual operation. This chapter begins with the time-domain expression of wind turbine mechanical power and, using the principle of "area approximation," characterizes the wind turbine's actual frequency support capability, solving for operating parameters that meet the wind turbine's mechanical characteristics.

[0170] Due to its own characteristics, the wind turbine grid-connected converter has certain limitations on the output electromagnetic power. Figure 9 As shown in the figure, in the early stage of wind turbine frequency support, the maximum power should not exceed 1.1 pu. At the same time, the safe operating range of DFIG wind turbine speed is required to be between 0.70 pu and 1.25 pu. In order to meet this requirement, the kinetic energy released by the wind turbine during the system frequency support process should be guaranteed. E k Less than its maximum available rotor kinetic energy E kmax ,Right now

[0171] (41)

[0172] The maximum available rotor kinetic energy E kmax It can be expressed as

[0173] (42)

[0174] Where: is the initial speed of the fan before the system frequency support process begins, is the minimum speed of the fan, which is the 0.7 pu mentioned above.

[0175] like Figure 11 In order to further simplify the calculation, the curve of mechanical power changing with time is approximated as linear. Figure 11 The red dotted line shows the actual kinetic energy released by the fan. E k That is Figure 11 The area of ​​the blue shaded part can be expressed as:

[0176] (43)

[0177] By combining (41), (42), and (43), the slope range of the fan during the ramp exit process can be obtained as:

[0178] (44)

[0179] because k slope <0, formula (44) can be further written as:

[0180] (45)

[0181] Therefore, the exit slope considering the mechanical characteristics of the wind turbine should meet the requirements of formula (45). The actual optimal exit slope of each wind turbine is k opt.pr It can be expressed as:

[0182] (46)

[0183] In order to simultaneously meet the system's power response requirements for the fan and the fan's safe operation constraints, the fan needs to reasonably adjust its own operating parameters, mainly including the power parameter Δ P , Δ P f and time parameters t on 、 t off , where exit time t off The optimal value of Δ P , Δ P f 、 t on Conduct key analysis:

[0184] First is the power parameter Δ P , Δ Pf On the one hand, from equations (17) and (40), in order to make the two lowest frequency points relatively high, it is required that Δ P , Δ P f As large as possible; but on the other hand, in order to ensure the safe operation of the fan in the frequency process and avoid excessive release of the fan rotor kinetic energy, it is required that Δ P , Δ P f This leads to a set of contradictions.

[0185] The relationship between the two can be Figure 14 The blue shaded area represents the power parameter range that satisfies both the system's power response requirements and the wind turbine's safe operation constraints. To minimize these conflicts, the wind turbine's control parameters during frequency support should be appropriately tuned within a safe range based on operational requirements. Here, the wind turbine's safe operating range is provided. Given the parameter constraints, the parameter allocation tuning process proceeds according to step 4.

[0186] Step 4: Wind farm adaptive exit frequency regulation strategy:

[0187] At different wind speeds, the frequency support capabilities of various wind turbines vary significantly. If wind turbine groups lack coordination and fail to allocate frequency modulation power appropriately based on their frequency modulation capabilities, some turbines may experience excessive frequency modulation and consequently shut down, while others may not fully utilize their frequency modulation capabilities. Therefore, a reasonable capacity assessment should be conducted during the frequency support and shutdown process of wind turbines to fully utilize their frequency support capabilities at various wind speeds and achieve optimal frequency response.

[0188] In the frequency support stage, the disturbance size should be apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, and then the incremental power and support time of each wind turbine should be determined, which can be expressed as

[0189] (47)

[0190] (48)

[0191] (49)

[0192] Where: E ki 、H wi 、 and Respectively represent i The available rotor kinetic energy, moment of inertia, speed and minimum speed of the typhoon turbine; Δ P fi For thei Incremental power of typhoon turbines, Δ P f is the total incremental power of the wind farm, n Indicates the number of wind turbines in the wind farm; t oni For the i The frequency support time of the typhoon, t on is the frequency support time of the wind farm.

[0193] During the frequency regulation exit phase, it is necessary to allocate the exit slopes of each wind turbine in the wind farm. The optimal exit slope of the wind farm can be obtained from the above formula (35), and the exit slope allocation target can be set to make the actual exit slope of the wind farm as close to the optimal exit slope as possible. Define the actual exit slope of the wind farm k With the optimal slope k opt The error between , the objective function is to minimize the absolute value of the error, which can be expressed as:

[0194] (50)

[0195] During the process of wind power exiting frequency regulation, the exit time of each wind turbine should remain the same, which is the optimal exit time.

[0196] (51)

[0197] Where: t offi Indicates the i The time for the typhoon turbine to ramp out.

[0198] At the same time, considering the differences in mechanical characteristic limitations of each wind turbine under different operating conditions, the exit slope should also meet its own constraints, which can be expressed as:

[0199] (52)

[0200] (53)

[0201] Where: k i For the i The actual slope of the typhoon's ramp exit, k imax For the i The maximum value of the typhoon turbine ramp exit slope, n is the number of wind turbines in the wind farm. It can be expressed as

[0202] (54)

[0203] Where: ΔP i Indicates the i Power changes during the typhoon turbine's withdrawal from frequency regulation, and Respectively represent i The initial speed of the typhoon and the minimum speed required to meet safe operation requirements.

[0204] This problem can be further organized into

[0205] (55)

[0206] Obviously, this is a multivariable linear programming problem, which can be solved using the simplex method: Let p i = -k i , the problem can be further transformed into:

[0207] (56)

[0208] When the disturbance size exceeds the maximum adjustable margin of the wind farm, each wind turbine performs frequency support according to its maximum adjustable capacity.

[0209] In the overall steps of the technical solution of this embodiment, step one completes the problem transformation, realizes the analytical transformation of the wind power exit process, and obtains the system frequency time-domain expression during the wind power ramp exit; step two establishes the mapping relationship between the frequency response characteristics and the key characteristics of the wind power curve (such as exit slope, exit time, support power, etc.); based on the analysis results, the basic power response requirements of wind power under fast frequency response and ramp exit methods are defined at the system level; step three simplifies the solution method of the wind turbine mechanical power time-domain expression, and uses the principle of "area approximation" to characterize the frequency support capability of wind power to participate in the above-mentioned basic power response requirements under the constraints of its own mechanical characteristics, wind speed conditions, etc.; step four simplifies the power allocation problem of each wind turbine in the wind farm at the system / site level, transforms the ramp allocation of the exit process into a linear programming problem, realizes the simple and rapid formulation of the wind power response curve, and ensures that each wind turbine operates at a fixed curve under the constraints, thereby ensuring the feasibility and universality of the strategy.

[0210] The simulation results demonstrate the effectiveness and superiority of the strategy proposed in this example in improving frequency dynamics: when exiting the frequency regulation link, through the coordinated control of the wind turbine and the synchronous machine energy link, the wind turbine can fully utilize its own energy while ensuring the safety of the unit. The secondary frequency drop problem is effectively improved, thereby improving the safe and stable operation of the power system.

[0211] When the above scheme is implemented, the control of wind power frequency support and exit frequency regulation mainly includes two parts: wind farm controller and wind turbine controller. Figure 12 As shown, the implementation process is as follows:

[0212] (1) Calculation of disturbance magnitude. When a power disturbance occurs in the system, in order to more accurately increase the power output, it is necessary to first estimate the disturbance magnitude. The sub-technical solution of this embodiment uses the initial frequency change rate of the system inertia center (CoI) to determine the disturbance magnitude, which can be expressed as

[0213] (57)

[0214] (58)

[0215] (59)

[0216] Where: f COI is the center frequency of inertia, S i 、 f i 、 H i Respectively i The capacity, node frequency, inertia of each synchronous machine, Δ P L is the power disturbance magnitude, H is the time constant of the equivalent inertia center of the system.

[0217] (2) Wind farm output curve design and power allocation of each wind turbine. In the frequency support stage, the wind farm central controller first determines the total wind farm output Δ according to equations (47) (48) (49). P f and frequency support time t on , and according to the operating status of each fan 、 P i 、 v wi and wind turbine operating constraints P ilim and k imax Determine the output of each fan Δ P fi ; In the phase of exiting frequency regulation, the wind farm controller determines the optimal slope of the exit phase according to formula (35): k opt and exit time t off , select the appropriate exit power ΔP , and then allocate the power of each wind turbine Δ according to scheme (55) P i and exit slope k i .

[0218] To achieve an efficient solution, wind turbines with the same wind speed can be grouped together. During the output calculation, wind turbines in the same group are treated as one unit and then evenly distributed.

[0219] (3) Wind turbine fixed curve operation. After receiving the instruction from the wind farm controller, the wind turbine controller controls the wind turbine to operate safely according to the fixed curve.

[0220] Case Introduction

[0221] This example builds the following simulation software in DIgSILENT\PowerFactory: Figure 13 The improved IEEE 39-bus system model shown in Figure 1 is used to verify the effectiveness and superiority of the strategy proposed in this embodiment's sub-technical solution in large-scale power systems. G1-G10 are synchronous generators, each equipped with a standard IEESGO speed regulator. A wind farm is connected to bus 24, consisting of 300 5 MW DFIG wind turbines. Wind speeds are set at 7 m / s, 8 m / s, 9 m / s, and 10 m / s, with 75 wind turbines with identical parameters at each wind speed.

[0222] First, according to the operating conditions of the wind turbines, the central controller of the wind farm distributes the power disturbance according to the maximum releasable kinetic energy of each rotor. The distribution ratio is as follows: Figure 14 As shown, the values ​​are set to 0.02, 0.16, 0.32, and 0.50 from small to large.

[0223] In order to verify the superiority of the proposed strategy, this paper sets 5 strategies for comparison:

[0224] Strategy 1: The wind turbine does not participate in frequency regulation;

[0225] Strategy 2: Traditional fast frequency response method, wind turbines use a step-by-step method to exit frequency regulation;

[0226] Strategy 3: Exit at a fixed time;

[0227] Strategy 4: Timing Exit;

[0228] Strategy 5: Ramp Exit, which is the strategy proposed in this article.

[0229] At the same time, two typical scenarios are used to verify the performance of the strategy proposed in this article:

[0230] Scenario 1: Synchronous machine G8 cutting;

[0231] Scenario 2: The active power of load 4 suddenly increases by 100%.

[0232] Simulation comparison:

[0233] Table 1 Simulation results

[0234]

[0235] Figure 16 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 1. Figure 16 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 1. Figure 16 (c) in the figure is the wind turbine output change image with a wind speed of 9 m / s in scene 1. Figure 16 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 1. Figure 19 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 2. Figure 19 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 2. Figure 19 (c) is the wind turbine output change image with a wind speed of 9 m / s in scene 2. Figure 19 (d) is the wind turbine output change image with a wind speed of 10m / s in scene 2; Figure 16 (a), (b), (c), (d) and Figure 19 From the wind turbine output curves (a), (b), (c), and (d), we can see that strategies 2, 3, 4, and 5 all perform well in the early stages of the disturbance. However, during the later stages of wind turbine exit, due to a sudden drop in power, strategies 2, 3, and 4 all experience a certain degree of power oscillation, and as the wind speed decreases, the oscillation problem becomes more severe. This strategy demonstrates its superiority.

[0236] at the same time, Figure 15 (a) is the image of wind turbine speed change in scene 1 with a wind speed of 7 m / s. Figure 15 (b) is the image of wind turbine speed change in scene 1 with a wind speed of 8 m / s. Figure 15 (c) in the figure is the image of wind turbine speed change in scene 1 with a wind speed of 9 m / s. Figure 15 (d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 1; Figure 18 (a) is the image of wind turbine speed change in scene 2 with a wind speed of 7 m / s. Figure 18 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 2. Figure 18 (c) is the wind turbine speed change image with a wind speed of 9 m / s in scene 2. Figure 18(d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 2; Figure 15 (a), (b), (c) and (d) Figure 18 It can be seen from the speed change curves of (a), (b), (c), and (d) in Figure 1 that the strategy proposed in this paper can release the rotor kinetic energy more fully, and the rotor kinetic energy recovery time is roughly the same as that of strategies 2, 3, and 4.

[0237] Depend on Figure 17 and Figure 20 It can be seen that in two typical scenarios, compared with the case where the wind turbine does not participate in frequency regulation, the use of a fast frequency response method can effectively improve the lowest frequency point. As shown in Table 1, the lowest frequency points are increased from 0.9903 and 0.9922 to 0.9925 and 0.9936, respectively. Furthermore, during the frequency recovery process, this strategy significantly improves the secondary frequency drop problem of the system. In the two scenarios, the minimum secondary frequency drop value is increased to 0.9957 pu and 0.9967 pu, respectively, which is significantly higher than other strategies. This effectively improves the system dynamic frequency and ensures the safe operation of the wind turbine during the system frequency support process.

[0238] Example 2

[0239] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0240] Example 3

[0241] The purpose of this embodiment is to provide a computer-readable storage medium.

[0242] A computer-readable storage medium stores a computer program, which, when executed by a processor, performs the steps of the above method.

[0243] Example 4

[0244] The purpose of this embodiment is to provide a wind power frequency support adaptive ramp exit system, including:

[0245] The frequency change expression module is configured to: during the process of the fan exiting the frequency modulation, the fan output change is equivalent to the set load, and the system frequency response time domain expression of the set load is obtained. The system frequency response time domain expression is used to analytically express the frequency change of the fan during the process of ramping out of the frequency modulation;

[0246] The solving module is configured to: solve the minimum value of the time domain expression of the system frequency response, that is, solve the optimal exit slope;

[0247] Solve the mechanical characteristic constraints of the fan and the system frequency constraints;

[0248] The wind farm adaptive frequency regulation exit strategy module is configured to: obtain a wind farm adaptive frequency regulation exit strategy based on the above solution results, including a strategy for the frequency support phase and a strategy for exiting the frequency regulation phase;

[0249] During the frequency support phase, the disturbance magnitude is apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, thereby determining the incremental power and support time of each wind turbine.

[0250] During the frequency regulation exit phase, the exit slope of each wind turbine in the wind farm is allocated.

[0251] Example 5

[0252] The purpose of this embodiment is to provide a computer program product containing instructions, which, when running on a computer, enables the computer to execute the methods and functions involved in any of the above embodiments.

[0253] The steps involved in the apparatus of the above embodiment correspond to those of the method embodiment 1. For detailed implementation, please refer to the relevant description of embodiment 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any method of the present invention.

[0254] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0255] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. The wind power frequency support adaptive ramp exit method is characterized by: include: During the process of the fan exiting the frequency modulation, the fan output change is equivalent to the set load, and the system frequency response time domain expression of the set load is obtained. The system frequency response time domain expression is used to analytically express the frequency change of the fan during the ramp exiting the frequency modulation process; The process of obtaining the time domain expression of the system frequency response with a set load applied is: Based on the set load equivalent to the change in fan output, the system frequency response model is used for analysis to obtain the time domain expression of the step response; Integrating the step response time domain expression to obtain the ramp response time domain expression of the system frequency response model; Based on the time domain expression of the ramp response, partial expressions of the frequency response characteristics of the analysis are obtained; Substitute the frequency response characteristic part expression into the ramp response time domain expression and apply the set load to obtain the system frequency response time domain expression; Solve the minimum value of the time-domain expression of the system frequency response, that is, solve the optimal exit slope. The process is: The process of wind power ramping out of frequency regulation under fast frequency response control is equated to load change, and the exit slope expression is obtained. The exit slope expression is substituted into the system frequency response time domain expression to obtain the first monotonically decreasing nonlinear function; For the first monotonically decreasing nonlinear function, different fan exit times are selected for simulation to obtain the system frequency response curve; Obtain the optimal exit slope of the fan based on the system frequency response curve; Considering the mechanical characteristics constraints of the wind turbine and the system frequency constraints, the optimal exit slope of the wind turbine is obtained. Based on the above solution results, the wind farm adaptive exit frequency regulation strategy is obtained: During the frequency support phase, the disturbance magnitude is apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, thereby determining the incremental power and support time of each wind turbine. During the frequency regulation exit phase, the goal is to minimize the absolute value of the error between the actual exit slope of the wind farm and the optimal exit slope of the wind turbine, maintain the optimal exit time for each wind turbine, and at the same time, consider the differences in the mechanical characteristics of each wind turbine under different working conditions, and allocate the exit slope of each wind turbine in the wind farm.

2. The wind power frequency support adaptive ramp exit method according to claim 1, characterized in that: Based on the time domain expression of the ramp response, the influence of the ramp response on the frequency mainly includes three parts: the ramp component, the DC component and the exponentially decaying oscillation component.

3. The wind power frequency support adaptive ramp exit method according to claim 1, characterized in that: The optimal exit time of the fan should be set to , at this time the optimal exit slope of the fan is k opt Expressed as: Among them, Δ P is the power amplitude of the wind turbine exit, is the damped oscillation frequency.

4. Wind power frequency support adaptive ramp exit system, which is characterized by: include: The frequency change expression module is configured to: during the process of the fan exiting the frequency modulation, the fan output change is equivalent to the set load, and the system frequency response time domain expression of the set load is obtained. The system frequency response time domain expression is used to analytically express the frequency change of the fan during the process of ramping out of the frequency modulation; The process of obtaining the time domain expression of the system frequency response with a set load applied is: Based on the set load equivalent to the change in fan output, the system frequency response model is used for analysis to obtain the time domain expression of the step response; Integrating the step response time domain expression to obtain the ramp response time domain expression of the system frequency response model; Based on the time domain expression of the ramp response, partial expressions of the frequency response characteristics of the analysis are obtained; Substitute the frequency response characteristic part expression into the ramp response time domain expression and apply the set load to obtain the system frequency response time domain expression; The solution module is configured to solve the minimum value of the system frequency response time domain expression, that is, to solve the optimal exit slope. The process is: The process of wind power ramping out of frequency regulation under fast frequency response control is equated to load change, and the exit slope expression is obtained. The exit slope expression is substituted into the system frequency response time domain expression to obtain the first monotonically decreasing nonlinear function; For the first monotonically decreasing nonlinear function, different fan exit times are selected for simulation to obtain the system frequency response curve; Obtain the optimal exit slope of the fan based on the system frequency response curve; Considering the mechanical characteristics constraints of the wind turbine and the system frequency constraints, the optimal exit slope of the wind turbine is obtained. The wind farm adaptive frequency regulation exit strategy module is configured to: obtain a wind farm adaptive frequency regulation exit strategy based on the above solution results, including a strategy for the frequency support phase and a strategy for exiting the frequency regulation phase; During the frequency support phase, the disturbance magnitude is apportioned according to the proportion of wind turbine rotor kinetic energy reserves under different wind conditions, thereby determining the incremental power and support time of each wind turbine. During the frequency regulation exit phase, the goal is to minimize the absolute value of the error between the actual exit slope of the wind farm and the optimal slope, maintain the optimal exit time for each wind turbine, and allocate the exit slope of each wind turbine in the wind farm taking into account the differences in the mechanical characteristics limitations of each wind turbine under different operating conditions.

5. The wind power frequency support adaptive ramp exit system according to claim 4, characterized in that When exiting the frequency regulation phase, the appropriate exit power is selected based on the wind farm capacity, the optimal slope of the exit phase is determined, and then the output is limited and allocated according to the mechanical characteristics of each wind turbine; In the process of calculating the wind turbine output, wind turbines with the same wind speed are grouped together. Wind turbines in the same group are equivalent to one unit. The power of each wind turbine is then evenly distributed according to the size of the shared disturbance.

6. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 3 is implemented.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method described in any one of claims 1 to 3 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 3 are performed.

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