Wind power frequency support adaptive slope exit method and system

Abstract

The invention provides a wind power frequency support self-adaptive slope quitting method and system, and belongs to the technical field of fan self-adaptive quitting, and the method comprises the steps: enabling the output change of a fan to be equivalent to a set load in a fan quitting frequency modulation process, obtaining a system frequency response time domain expression for applying the set load, and obtaining a system frequency response time domain expression; the system frequency response time domain expression is used for analyzing and expressing the frequency change of the fan in the slope frequency modulation quitting process; solving the minimum value of the system frequency response time domain expression, namely solving the optimal exit slope; solving fan mechanical characteristic constraints and system frequency constraints; based on the above solution result, the wind power plant adaptively quits the frequency modulation strategy: in a frequency support stage, according to the wind turbine rotor kinetic energy reserve proportion under different wind conditions, the disturbance is shared, and then the increment power and the support time of each wind turbine are determined; and in the frequency modulation quitting stage, the quitting slope of each fan in the wind power plant 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 massive access to new energy sources such as wind and solar has reduced the inertia of traditional machinery, forming a so-called low-inertia power system. The reduction in inertia has increased the frequency deviation and variation of the system, while the strong randomness and volatility of new energy sources have seriously weakened the regulation ability of the power system, bringing severe challenges to the safe operation of electricity, and power grid safety accidents occur from time to time.

[0004] In order to reduce the occurrence of such events and improve the stability of the power system, the power grids of many countries and regions have put forward new requirements for the operation of renewable energy, requiring renewable energy to have inertia response or primary frequency regulation functions. Taking wind power as an example, when an event disturbance occurs in the system and causes the frequency to drop, the wind turbine needs to release its own rotor kinetic energy or backup energy to provide short-term power support for the system, thereby suppressing the system frequency change rate and frequency deviation.

[0005] When new energy sources realize the above-mentioned inertia response or primary frequency modulation function, the fast frequency response (FFR) control method in the control method can effectively give play to the characteristics of fast response speed and high flexibility of the fan. When the system frequency drops, the fan can increase power sharply in a short time, thereby suppressing the decrease of 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; (1) Where: P w ( t ) is the electromagnetic power output by the fan, P MPPT is the maximum operating power of the fan.

[0007] 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 (2) Where: Δ P f (t ) is the incremental power output of the fan.

[0008] When the frequency is stable, the wind turbine needs to exit frequency modulation. At this time, it needs to 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.

[0009] 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.

[0010] 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" proposes a sequential exit frequency regulation control strategy by analyzing the corresponding relationship between the active power increment and the duration of frequency regulation in the process of wind turbines participating in system frequency regulation, which reduces 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 reduce 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 control method for wind turbine ramp exit 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.

[0011] 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 difficulty in analyzing the complex aerodynamic nonlinearity and time-varying characteristics of wind power, it is impossible to achieve an accurate quantitative characterization of wind power capacity; the frequency regulation capabilities of various wind turbines in wind farms 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 simple, accurate and effective task power allocation methods.

[0012] 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

[0013] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a wind power frequency support adaptive ramp exit method. The proposed strategy has obvious advantages and effectively reduces the secondary frequency drop of the system.

[0014] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: In a first aspect, a method for adaptively ramping out of wind power frequency support is disclosed, comprising: When the fan exits the frequency modulation process, 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 in the ramp exit frequency modulation process; Solve the minimum value of the time domain expression of the system frequency response, that is, solve the optimal exit slope; Solve the mechanical characteristic constraints of the fan and the system frequency constraints; Based on the above solution results, the wind farm adaptive exit frequency regulation strategy is obtained, including the strategy in the frequency support stage and the strategy in the exit frequency regulation stage; In the frequency support stage, the disturbance size is 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 are determined; During the phase of exiting frequency regulation, the exit slope of each wind turbine in the wind farm is allocated.

[0015] As a further technical solution, the process of obtaining the time domain expression of the system frequency response with a set load 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; Integrate the step response time domain expression to obtain the ramp response time domain expression of the system frequency response model; Based on the ramp response time domain expression, partial expressions of the frequency response characteristics of the analysis are obtained; After the partial expressions of the frequency response characteristics are combined, a set load is applied, and then the time domain expression of the system frequency response is obtained.

[0016] 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: a ramp component, a DC component and an exponentially decaying oscillation component.

[0017] As a further technical solution, the process of solving the optimal exit slope is: Substituting the exit slope expression 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 a system frequency response curve; The optimal exit slope of the fan is obtained based on the system frequency response curve.

[0018] As a further technical solution, the optimal exit time of the fan should be set to , at this time the fan optimal exit slope k opt It is expressed as:

[0019] Among them, Δ P is the power amplitude of the wind turbine exit, is the damped oscillation frequency.

[0020] In the second aspect, a wind power frequency support adaptive ramp exit system is disclosed, including: The frequency change expression module is configured as follows: when the fan exits the frequency modulation process, 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 in the ramp exit frequency modulation process; The solution module is configured to: solve the minimum value of the system frequency response time domain expression, that is, solve the optimal exit slope; Solve the mechanical characteristic constraints of the fan and the system frequency constraints; The wind farm adaptive exit frequency modulation strategy module is configured to: obtain the wind farm adaptive exit frequency modulation strategy based on the above solution results, including the strategy of the frequency support stage and the strategy of exiting the frequency modulation stage; In the frequency support stage, the disturbance size is 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 are determined; During the phase of exiting frequency regulation, the exit slope of each wind turbine in the wind farm is allocated.

[0021] One or more of the above technical solutions have the following beneficial effects: The technical solution of the present invention is a method for adaptive ramp exit of wind power frequency support: first, a control method for ramp exit of wind turbine frequency modulation is proposed, and the problem is transformed; then, the optimal slope and optimal time of the wind turbine in the ramp exit mode are derived and solved; at the same time, the mechanical characteristic constraints of the wind turbine itself and the system frequency constraints are considered to determine the safe operating range of the wind turbine under different operating conditions; finally, the power allocation scheme of each wind turbine in the frequency support process of the wind farm is simplified, and an adaptive exit strategy for wind farm frequency support is proposed. Through the results of the improved IEEE 39 simulation case, it can be found that the strategy proposed by the technical solution of the present invention has obvious advantages and effectively reduces the secondary frequency drop of the system.

[0022] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, 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.

[0024] Figure 1 A schematic diagram of a wind turbine generator system participating in frequency modulation according to an embodiment of the present invention; Figure 2 A schematic diagram of the system equivalent load felt by the synchronous machine according to an embodiment of the present invention; 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; Figure 4 Schematic diagram of the corresponding relationship between the lowest point of the secondary drop of the system frequency and the time required for the fan to exit according to an embodiment of the present invention; Figure 5 Schematic diagram of frequency response characteristic analysis of two slope loads according to an embodiment of the present invention; Figure 6 The lowest frequency point of the embodiment of the present invention and t off Schematic diagram of the relationship between Figure 7 This is a schematic diagram of power-speed during frequency modulation of a fan according to an embodiment of the present invention; Figure 8 This is a power-time schematic diagram of the process in which the fan participates in frequency modulation according to an embodiment of the present invention; Fig. 9 Schematic diagram of an SFR model including a fan according to an embodiment of the present invention; Fig.10 It is a schematic diagram of a frequency response image of a fan when ramping out according to an embodiment of the present invention; Fig.11 For the embodiment of the present invention Δ P With Δ P f Relationship diagram; Fig.12 This is a schematic diagram of the centralized control architecture of a wind farm; Fig.13 It is the schematic diagram of the simulation system; Fig.14 It is a schematic diagram of wind turbine power distribution ratio under different wind speeds; Fig.15 The image of wind turbine speed change under different wind speeds in scene 1, where Fig.15 (a) is the image of wind turbine speed change in scene 1 with a wind speed of 7 m / s. Fig.15 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 1. Fig.15 (c) in the figure is the image of wind turbine speed change in scene 1 with a wind speed of 9 m / s. Fig.15 (d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 1; Fig.16 This is the wind turbine output change image under different wind speeds in scene 1, where Fig.16 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 1. Fig.16 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 1. Fig.16 (c) in the figure is the wind turbine output change image with a wind speed of 9 m / s in scene 1. Fig.16 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 1; Fig.17 This is the frequency change image of scene 1; Fig.18 The image of wind turbine speed change under different wind speeds in scene 2, where Fig.18 (a) is the image of wind turbine speed change in scene 2 with a wind speed of 7 m / s. Fig.18 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 2. Fig.18(c) is the wind turbine speed change image with a wind speed of 9 m / s in scene 2. Fig.18 (d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 2; Fig.19 This is the wind turbine output change image under different wind speeds in scene 1, where Fig.19 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 2. Fig.19 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 2. Fig.19 (c) is the wind turbine output change image with a wind speed of 9 m / s in scene 2. Fig.19 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 2; Fig. 20 This is the frequency change image of scene 2. DETAILED DESCRIPTION

[0025] 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 meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0027] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0028] Embodiment 1 This embodiment discloses an adaptive ramp exit method for wind power frequency support. The sub-technical scheme of this embodiment focuses on the coordinated control of wind turbines and the multi-scale energy release characteristics of synchronous machines during the exit from frequency modulation, as well as the secondary frequency drop problem of the system. First, the process of wind power ramp exit from frequency modulation under FFR control is equivalent to load change, and the lowest point of the secondary frequency drop is obtained analytically. 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 optimal time for the wind turbine to exit frequency regulation are obtained by solving the problem. The optimal slope and optimal time here are the results obtained by considering all the wind turbines in the system as a whole. The subsequent step is to allocate power to each wind turbine based on this result. Finally, the power allocation problem of each wind turbine in the wind farm is transformed into a linear programming problem, which improves the practicality of the proposed strategy.

[0029] 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 exemplary 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 primary frequency modulation in the response phase; and to coordinate the ramp exit of the fan with the boiler heat storage of the synchronous machine in the exit phase.

[0030] In this implementation example, the specific steps of the wind power frequency support adaptive ramp exit method include: Step 1: Problem transformation: In order to deal with the secondary frequency drop problem, this example is improved 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.

[0031] During the wind turbine exit process, assuming the exit power amplitude Δ P Definitely, in t =- t off The output power of the fan is along the slope k slope The slope of the decline, through t 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 (3) 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.

[0032] Therefore, reducing the frequency secondary drop problem can be converted into improving Figure 2 The frequency minimum point problem caused by the equivalent load is shown.

[0033] From the above analysis, it can be seen that when the fan exits the frequency modulation process, the system can be regarded as having only a synchronous machine, and the fan output change is equivalent to Figure 2For the load shown, the traditional system frequency response model (System Frequency Response, SFR), that is, formula (4)(5)(6)(7)(8)(9) can be used for analysis. The SFR model is a frequency analysis model that describes the power grid dominated by the traditional synchronous machine. For the synchronous machine, the wind turbine ramp exit is to input a ramp load into the SFR model. During the analysis: first derive the output characteristics of the SFR for the input step load, and then integrate it to obtain the SFR output characteristics of the ramp load.

[0034] The step response time domain expression of the above SFR model is: (4) (5) (6) (7) (8) (9) Where: is the load variation; 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 the synchronous machine prime mover and speed governor parameters, which are the 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.

[0035] By integrating equation (4), we can obtain the time domain expression of the ramp response of the SFR model: (10) Where: is the frequency variation of the power grid under the ramp disturbance. It can be seen from formula (10) that the influence of the ramp response on the frequency mainly includes three parts: the ramp component, the DC component and the exponentially decayed oscillation component. Figure 2The disturbance shown is the superposition of two ramp loads at different times. Since the slopes of the 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 attenuated oscillation components mentioned above, that is, the frequency response characteristic part of the analysis is: (11) Formula (11) can be further simplified as (12) In the formula is the AC component of the power grid frequency change under ramp disturbance. Where: (13) (14) Imposition Figure 2 The time domain expression of the system frequency response of the load shown is It can be expressed as: (15) In summary, the frequency change of the fan during the ramp exit frequency modulation process can be analytically expressed using formula (15), and the minimum value of the secondary frequency drop is also converted into the minimum value of formula (15). Then, the secondary frequency drop problem can be reduced by solving the optimal exit slope.

[0036] Considering that the prior art only has qualitative analysis and does not further quantify the expression of the withdrawal process, the above process of this embodiment example realizes the solution of the system frequency time domain expression of the wind power withdrawal process.

[0037] Step 2: Analysis of the system's response demand for wind power.

[0038] 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 has 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 secondary 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.

[0039] (2-1) The first frequency minimum point f nadir1 .

[0040] By solving the lowest point of the frequency drop caused by the disturbance, f nadir1 > f nadir2 Translated into power response demand for the wind turbine.

[0041] Frequency minimum f nadir1 It can be solved by the SFR model under step disturbance, such as Figure 6 , 7 , as shown in 8, where Δ P f represents the power change caused by the event disturbance, Δ P L Represents the change in fan output, and the equivalent step disturbance size of the system 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: (16) Substituting equation (16) into equation (4), we can obtain the lowest point of the system: f nadir1 for (17) (2-2) The second lowest frequency point f nadir2 .

[0042] In the exit phase, if the fan ramp exit time is very short, it will cause a large power impact and a serious frequency secondary drop problem; 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 be too low and the machine to be cut off. Therefore, it is necessary to reasonably set the fan exit time to achieve the optimal frequency dynamic effect.

[0043] By solving the lowest point of the system frequency drop during the fan ramp exit process, f nadir1 > f nadir2 Translated into power response demand for the wind turbine.

[0044] Substituting formula (3) into formula (15), we can get (18) Obviously, formula (18) is a monotonically decreasing nonlinear function, but it is difficult to solve its t off The analytical expression of the minimum value change under this condition is t off Perform simulation 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 in 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 first and then slow", that is, there is an inflection point. The change speed of the lowest point of the secondary drop in frequency before and after the inflection point is significantly different. After the inflection point, the change of the lowest point of the secondary drop in frequency becomes slow, and then increases. t off , the lowest point of the second drop in frequency does not change much, but it will increase energy loss. Therefore, the fan exit slope corresponding to this point can be used as a relatively ideal optimal exit slope. Next, this inflection point will be analyzed in detail.

[0045] Discrete Analysis: Assumption Function The extreme points of is consistent, that is, the 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 (19) From the proof, we can see that along with t off The proof process is as follows.

[0046] Proof: Order (20) Taking its derivative, we get (twenty one) make (twenty two) The derivative is (twenty three) exist t >0, h ’ ( t )<0 is always established, h ( t )exist t >0 is monotonically decreasing, so (twenty four) Multiply both sides by 1 / t 2 (25) Right now (26) exist t >0, so f ( t )exist t >0, it is monotonically increasing. f ( t ) has a limit of (27) (28) therefore, exist t >0, when only considering discrete time points, that is When you can get (29) (30) Continuous analysis: Next, The response at continuous time continues to be analyzed.

[0047] It can be seen from the proof that when t off =0, Dissatisfiedt off The main reason for the discrete response characteristic is t off =0, The phase and , The phases of are inconsistent. The proof is as follows: (31) (32) Obviously, ， ,therefore , so when t off =0, The phase lags behind and .

[0048] 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 0 The lowest point is obtained when the phase relationship is always the same Figure 6 shown.

[0049] However, in reality, only when ,and n When is a positive integer, and The phases of t = t 0 At other times and There is a phase deviation between the two. When there is a phase deviation, t = t 0 hour, Must be less than The proof is as follows: (33) because ), are all less than 0, so (34) 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.

[0050] 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: (35) Step 1 has achieved an analytical solution for the frequency response of the second frequency drop. According to equation (18), a simulation image can be further produced, such as Fig.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 in Figure 8 After the 0 moment of the equivalent load shown, that is Fig.10 Stage ② is shown.

[0051] The following is for f nadir2 Continue to analyze. From the derivation, we can know that when When , formula (18) can be written as (36) Derivative of equation (36) (37) (38) Assume that t = t 0 hour Reaching the minimum value, minimum moment t 0 It can be expressed as (39) Where: n 0 Indicates t 0 The smallest positive integer greater than zero.

[0052] From the superposition theorem, we know that the lowest frequency point f nadir2 It can be expressed as (40) Therefore, the sub-technical solution of this embodiment realizes the analytical solution of the size of the two lowest frequency points.

[0053] Step 3: Parameter setting method considering the mechanical characteristics of the fan.

[0054] 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.

[0055] While meeting the system's demand for wind power response, wind turbines also need to meet speed, output power, load and other restrictions in actual operation due to their own mechanical characteristics. This chapter starts with the time-domain expression of wind turbine mechanical power, uses the principle of "area approximation" to characterize the actual frequency support capacity of the wind turbine, and solves the operating parameters that meet the mechanical characteristics of the wind turbine.

[0056] Due to its own characteristics, the wind turbine grid-connected converter has certain limitations on the output electromagnetic power. Fig. 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 the 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 (41) The maximum available rotor kinetic energy E kmax It can be expressed as (42) 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.

[0057] like Fig.11 In order to further simplify the calculation, the curve of mechanical power changing with time is approximated as linear. Fig.11 The red dotted line shows the actual kinetic energy released by the fan. E k That is Fig.11 The area of ​​the blue shaded part can be expressed as: (43) Combining (41), (42), and (43), the slope range of the fan during the ramp exit process can be obtained as: (44) because k slope <0, formula (44) can be further written as: (45) 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: (46) 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 has been solved. Next, P , Δ P f , t on Conduct key analysis: First, the power parameter Δ P , Δ P f 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.

[0058] The relationship between the two can be Fig.14 Indicates that the blue shaded part represents the power parameter range that satisfies both the system's power response requirements for the wind turbine and the wind turbine's safe operation constraints. In order to minimize the above contradictions, the control parameters of the wind turbine during the frequency support period should be reasonably adjusted within the safety range according to the operation requirements. Here, the wind turbine's safe operation range is provided. Given the parameter constraints, the parameter allocation adjustment process is carried out according to step 4.

[0059] Step 4: Wind farm adaptive exit frequency regulation strategy: At different wind speeds, the frequency support capabilities of each wind turbine vary greatly. If the wind turbine group lacks coordination and cannot reasonably allocate frequency modulation power according to its own frequency modulation capabilities, it may cause some units to be cut off due to excessive frequency modulation, while the frequency modulation capabilities of other units cannot be fully utilized. Therefore, a reasonable capacity assessment should be carried out during the frequency support and withdrawal process of the wind turbine to fully utilize the frequency support capabilities of the wind turbine at each wind speed and achieve the optimal frequency response effect.

[0060] In the frequency support stage, the disturbance size should be apportioned according to the proportion of wind turbine rotor kinetic energy reserve under different wind conditions, and then the incremental power and support time of each wind turbine should be determined, which can be expressed as (47) (48) (49) Where: E ki 、H wi 、 and Respectively represent i The available rotor kinetic energy, moment of inertia, speed and minimum speed of the wind turbine; Δ P fi For the i Incremental power of typhoon generator set, 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 generator, t on It is the frequency support time of the wind farm.

[0061] In the phase of exiting frequency regulation, it is necessary to allocate the exit slope 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: (50) 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.

[0062] (51) Where: t offi Indicates i The time for the typhoon turbine to ramp out.

[0063] At the same time, considering the differences in mechanical characteristic limitations of each fan under different working conditions, the exit slope should also meet its own constraints, which can be expressed as: (52) (53) Where: k i For the i The actual slope of the typhoon machine ramp exit, k imax For the i The maximum value of the typhoon machine ramp exit slope, n is the number of wind turbines in the wind farm. It can be expressed as (54) Where: Δ P i Indicates i Power changes of typhoon turbines during the period of frequency regulation withdrawal, and Respectively represent i The initial speed of the typhoon fan and the minimum speed required for safe operation.

[0064] This problem can be further organized into (55) Obviously, this is a multivariable linear programming problem, which can be solved using the simplex method: p i = -k i , the problem can be further transformed into: (56) When the disturbance size exceeds the maximum adjustable margin of the wind farm, each wind turbine provides frequency support according to its maximum adjustable capacity.

[0065] In the overall steps of the technical solution of this embodiment, step one completes the problem transformation, realizes analytical transformation of the wind power withdrawal process, and obtains the system frequency time domain expression when the wind power ramps out; step two establishes the mapping relationship between the frequency response characteristics and the key characteristics of the wind power curve (such as withdrawal slope, withdrawal time, support power, etc.); according to the analysis results, the basic power response requirements of wind power under fast frequency response and ramp withdrawal are defined from 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 from the system / station level, transforms the slope allocation of the withdrawal process into a linear programming problem, realizes the formulation of a simple and fast wind power response curve, and ensures that each wind turbine realizes fixed curve operation under the constraints, thereby ensuring the feasibility and universality of the strategy.

[0066] The simulation results prove 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, and the secondary frequency drop problem is effectively improved, thereby improving the safe and stable operation of the power system.

[0067] When the above scheme is implemented, the control of wind power in frequency support and exit frequency regulation mainly includes two parts: wind farm controller and wind turbine controller. Fig.12 As shown, the implementation process is as follows: (1) Calculation of disturbance size. 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 size. The sub-technical solution of this embodiment uses the initial frequency change rate of the system center of inertia (CoI) to determine the disturbance size, which can be expressed as (57) (58) (59) Where: f COI is the center frequency of inertia, S i , f i , H i Respectively i The capacity, node frequency, and inertia of each synchronous machine, Δ P L is the power disturbance magnitude, His the system equivalent inertia center time constant.

[0068] (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), and (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 equation (35): k opt and exit time t off , select the appropriate exit power Δ P , and then allocate the power of each wind turbine Δ according to scheme (55) P i and exit slope k i .

[0069] In order to achieve efficient solution, wind turbines with the same wind speed can be grouped together. In the output calculation process, wind turbines in the same group are equivalent to one unit and then evenly distributed.

[0070] (3) Wind turbine fixed curve operation. After receiving the command from the wind farm controller, the wind turbine controller controls the wind turbine to operate safely on a fixed curve.

[0071] Case Introduction This example builds the following in the DIgSILENT\PowerFactory simulation software: Fig.13 The improved IEEE 39-node system model shown in the figure is used to verify the effectiveness and superiority of the strategy proposed in the sub-technical solution of this embodiment in a large-scale power system. Among them, G1-G10 are synchronous generators, all equipped with standard IEESGO speed regulators. A wind farm is connected to bus No. 24, which contains 300 DFIG wind turbines with a capacity of 5 MW. The wind speed is set to 7 m / s, 8 m / s, 9 m / s, and 10 m / s, and there are 75 wind turbines with the same parameters at each wind speed.

[0072] 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: Fig.14 As shown, the values ​​are set to 0.02, 0.16, 0.32, and 0.50 from small to large.

[0073] In order to verify the superiority of the proposed strategy, this paper sets 5 strategies for comparison: Strategy 1: The wind turbine does not participate in frequency regulation; Strategy 2: Traditional fast frequency response method, wind turbines use a step-by-step method to exit frequency regulation; Strategy 3: Exit at a fixed time; Strategy 4: Timed exit; Strategy 5: Ramp exit, which is the strategy proposed in this article.

[0074] At the same time, two typical scenarios are used to verify the performance of the strategy proposed in this article: Scenario 1: Synchronous machine G8 cutting; Scenario 2: The active power of load 4 suddenly increases by 100%.

[0075] Simulation comparison: Table 1 Simulation results

[0076] Fig.16 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 1. Fig.16 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 1. Fig.16 (c) in the figure is the wind turbine output change image with a wind speed of 9 m / s in scene 1. Fig.16 (d) is the wind turbine output change image with a wind speed of 10 m / s in scene 1. Fig.19 (a) is the wind turbine output change image with a wind speed of 7 m / s in scene 2. Fig.19 (b) is the wind turbine output change image with a wind speed of 8 m / s in scene 2. Fig.19 (c) is the wind turbine output change image with a wind speed of 9 m / s in scene 2. Fig.19 (d) is the wind turbine output change image with a wind speed of 10m / s in scene 2; Fig.16 (a), (b), (c), (d) and Fig.19 From the wind turbine output curves (a), (b), (c), and (d), we can find that strategies 2, 3, 4, and 5 all perform well in the early stage of the disturbance; but in the later stage of wind turbine exit, due to the sudden drop in power, strategies 2, 3, and 4 all have a certain degree of power oscillation, and as the wind speed decreases, the oscillation problem becomes more serious. The strategies in this paper demonstrate their superiority.

[0077] at the same time, Fig.15 (a) is the image of wind turbine speed change in scene 1 with a wind speed of 7 m / s. Fig.15 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 1. Fig.15 (c) in the figure is the image of wind turbine speed change in scene 1 with a wind speed of 9 m / s. Fig.15 (d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 1; Fig.18 (a) is the image of wind turbine speed change in scene 2 with a wind speed of 7 m / s. Fig.18 (b) is the wind turbine speed change image with a wind speed of 8 m / s in scene 2. Fig.18 (c) is the wind turbine speed change image with a wind speed of 9 m / s in scene 2. Fig.18 (d) is the wind turbine speed change image with a wind speed of 10 m / s in scene 2; Fig.15 (a), (b), (c) and (d) Fig.18 It can be seen from the speed change curves of (a), (b), (c), and (d) in the figure 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.

[0078] Depend on Fig.17 and Fig. 20 It can be seen that in two typical scenarios, compared with the situation where the fan does not participate in frequency regulation, the use of fast frequency response can effectively improve the lowest frequency point. As can be seen from Table 1, the lowest frequency point is increased from 0.9903 and 0.9922 to 0.9925 and 0.9936 respectively. At the same time, in the frequency recovery process, the strategy in this paper significantly improves the problem of secondary frequency drop in the system. In the two scenarios, the minimum value of the secondary frequency drop is increased to 0.9957 pu and 0.9967 pu respectively, which is significantly higher than other strategies, effectively improving the system dynamic frequency and ensuring the safe operation of the fan during the system frequency support process.

[0079] Embodiment 2 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.

[0080] Embodiment 3 The purpose of this embodiment is to provide a computer-readable storage medium.

[0081] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0082] Embodiment 4 The purpose of this embodiment is to provide a wind power frequency support adaptive ramp exit system, including: The frequency change expression module is configured as follows: when the fan exits the frequency modulation process, 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 in the ramp exit frequency modulation process; The solution module is configured to: solve the minimum value of the system frequency response time domain expression, that is, solve the optimal exit slope; Solve the mechanical characteristic constraints of the fan and the system frequency constraints; The wind farm adaptive exit frequency modulation strategy module is configured to: obtain the wind farm adaptive exit frequency modulation strategy based on the above solution results, including the strategy of the frequency support stage and the strategy of exiting the frequency modulation stage; In the frequency support stage, the disturbance size is 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 are determined; During the phase of exiting frequency regulation, the exit slope of each wind turbine in the wind farm is allocated.

[0083] Embodiment 5 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. The steps involved in the apparatus of the above embodiment correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0084] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0085] Although the above describes the specific implementation mode 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 creative work are still within the scope of protection of the present invention.

Claims

1. A wind power frequency support adaptive ramp exit method, characterized in that: include: When the fan exits the frequency modulation process, 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 in the ramp exit frequency modulation process; Solve the minimum value of the time domain expression of the system frequency response, that is, solve the optimal exit slope; Solve the mechanical characteristic constraints of the fan and the system frequency constraints; Based on the above solution results, the wind farm adaptive exit frequency regulation strategy is as follows: In the frequency support stage, the disturbance size is 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 are determined; During the phase of exiting frequency regulation, the exit slope of each wind turbine in the wind farm is allocated.

2. The wind power frequency support adaptive ramp exit method according to claim 1, characterized in that: 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; Integrate the step response time domain expression to obtain the ramp response time domain expression of the system frequency response model; Based on the ramp response time domain expression, partial expressions of the frequency response characteristics of the analysis are obtained; After the partial expressions of the frequency response characteristics are combined and the set load is applied, the time domain expression of the system frequency response is obtained.

3. The wind power frequency support adaptive ramp exit method according to claim 2, 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 decayed oscillation component.

4. The wind power frequency support adaptive ramp exit method according to claim 1, characterized in that: The process of solving the optimal exit slope is: Substituting the exit slope expression 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 a system frequency response curve; The optimal exit slope of the fan is obtained based on the system frequency response curve.

5. The wind power frequency support adaptive ramp exit method according to claim 4, characterized in that: The optimal fan exit time should be set to , at this time the fan optimal exit slope k opt It is expressed as: Among them, Δ P is the power amplitude of the wind turbine exit, is the damped oscillation frequency.

6. Wind power frequency support adaptive ramp exit system, characterized by: include: The frequency change expression module is configured as follows: when the fan exits the frequency modulation process, 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 in the ramp exit frequency modulation process; The solution module is configured to: solve the minimum value of the system frequency response time domain expression, that is, solve the optimal exit slope; Solve the mechanical characteristic constraints of the fan and the system frequency constraints; The wind farm adaptive exit frequency modulation strategy module is configured to: obtain the wind farm adaptive exit frequency modulation strategy based on the above solution results, including the strategy of the frequency support stage and the strategy of exiting the frequency modulation stage; In the frequency support stage, the disturbance size is 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 are determined; During the phase of exiting frequency regulation, the exit slope of each wind turbine in the wind farm is allocated.

7. The wind power frequency support adaptive ramp exit system according to claim 6, characterized in that When exiting the frequency regulation phase, first select the appropriate exit platform period based on the wind farm capacity, determine the optimal slope of the exit phase, and then limit the output distribution based on the mechanical characteristics of each wind turbine; In the process of calculating the wind turbine output, the wind turbines in the same group are aggregated into one unit, and then the power of each wind turbine is evenly distributed according to the size of the shared disturbance.

8. 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 5 is implemented.

9. 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 5 are implemented.

10. 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 described in any one of claims 1 to 5 are performed.

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