Wind power plant aggregation equivalence grouping, verification and equivalence method and device considering fan active amplitude limiting

Abstract

The invention discloses a wind power plant aggregation equivalence grouping, verification and equivalence method and device considering fan active amplitude limiting, and belongs to the technical field of wind power plant modeling. In order to solve the problem that an existing wind power plant equivalent modeling method is poor in engineering practicability, the method comprises the steps that firstly, whether the active power of a draught fan reaches an amplitude limiting value or not during a transient steady state is adopted as a draught fan grouping basis for grouping, and aggregation equivalent modeling is conducted based on grouping; classifying the fans reaching the active current amplitude limiting into a group, classifying the fans not reaching the active current amplitude limiting into a group, and verifying the effectiveness of grouping; and finally, performing aggregation based on a grouping result, calculating equivalent machine parameters, equivalent transformer parameters and equivalent current collection network parameters, and realizing equivalence.

Description

Technical Field

[0001] The invention belongs to the technical field of wind farm modeling, and relates to a wind farm aggregation equivalent grouping and verification method, as well as an equivalent method and corresponding equipment. Background Art

[0002] As energy and environmental issues become increasingly prominent, wind power generation accounts for an increasing proportion in the power grid with its advantages of cleanliness, flexibility and sustainability. Large-scale wind farms have been formed, with a large number of units and large differences in operating conditions. If each unit is modeled separately, it will not only greatly increase the scale of simulation operations and extend the simulation operation time, but also face great challenges in its effectiveness and accuracy. Establishing a wind farm equivalent model that can take into account both calculation and accuracy is a key issue that needs to be urgently solved in the current field of wind power grid connection research. Therefore, it is indispensable to perform equivalent processing on wind farms. The operating conditions of units in wind farms are time-varying and different. How to reasonably and effectively group wind turbines and how to calculate the collector network are issues that must be solved. The existing wind farm aggregation equivalent model mostly considers the equivalent error during the recovery period of the wind turbine, but lacks consideration of the equivalent error during the wind turbine failure period. As a result, the current wind farm equivalent modeling method has the problem of poor engineering practicality. Summary of the invention

[0003] In order to solve the problem of poor engineering practicality of the current wind farm equivalent modeling method, the present invention proposes a wind farm aggregate equivalent grouping method considering the active power limitation of wind turbines, and proposes a corresponding verification method, as well as an equivalent method and device based on the grouping results.

[0004] The wind farm aggregation equal value grouping method considering the active power limitation of wind turbines adopts whether the active power of wind turbines reaches the limit value during the transient steady state as the basis for grouping wind turbines.

[0005] A wind farm aggregate equivalent grouping verification method considering wind turbine active power limitation is provided, and a positive verification is performed on the grouping result obtained by the wind farm aggregate equivalent grouping method considering wind turbine active power limitation, comprising the following steps: According to the operating principle of the wind turbine, determine the active power P of the wind turbine during the transient steady state. i (t f ): Where U i (t f ) is the voltage of fan i during the transient steady state; I p_i (t f ) is the active current of wind turbine i during the transient steady state; P normal_i I is the active power of wind turbine i during the steady state before the fault; max is the maximum current of the fan; Iq_i (t f ) is the reactive current at the time of fault clearing, expressed as: In the formula, k Q1 is the reactive support coefficient; k Q2 is the reactive voltage threshold; I q_max is the reactive current limit value; In view of the nonlinear superposition relationship of the response characteristics of each unit in the wind farm during the fault drop process; first determine the active power expression of the wind turbine during the transient steady state when the wind turbine active power does not reach the limit: Based on the fact that the sum of the active power of all units in the same group of wind turbines during the steady-state period is equal to the active power of the equivalent unit, the active power expression of the wind turbine during the transient steady-state period is determined as follows: In the formula, , They are the active powers of fan 1 and fan 2 during the transient steady state; is the active power of the equivalent machine during the transient steady state; , are the active powers of wind turbine 1 and wind turbine 2 during the steady state before the fault respectively; Based on the above active power expression of the wind turbine during the transient steady state, verify whether the active power of the wind turbine during the transient steady state has a linear superposition characteristic when the wind turbine does not reach the limit. If it has a linear superposition characteristic, continue the subsequent rationality verification, otherwise, verify that the grouping result is unreasonable; Then determine the active power expression of the fan during the transient steady state when the fan active power reaches the limit: Will not have linear superposition characteristics Perform conversion analysis, first draw the curve of P and U based on the expression, and then perform linear regression analysis on the curve; through linear regression analysis, get the slope, intercept and R-square value of the fitting line, and determine whether the curve of P and U can be expressed as a straight line according to the R-square value corresponding to the approximate linear equation of P and U. If not, it is considered that the corresponding grouping is unreasonable; if so, it is considered that the grouping of fans whose active power reaches the limit value during the transient steady state is reasonable.

[0006] Furthermore, the maximum current of the fan I max It is 1.345 times the rated current.

[0007] Furthermore, when it is considered that the wind turbine grouping for wind turbines whose active power reaches the limit value during the transient steady state is reasonable, the expression of the active power of the wind turbine when the limit is reached is simplified to: In the formula, is the slope of the fitted straight line; is the intercept of the fitted straight line; Then the active power of wind turbine 1 and wind turbine 2 during the transient steady state is expressed as: In the formula, , They are the voltages of fan 1 and fan 2 during the transient steady state; After equalization, the transient steady-state active power of the fan is expressed as: ; In the formula, is the voltage of the equivalent machine during the transient steady state; since the voltage after the equivalent value is approximately equal to the average value of the voltage drop of all units, , and the conclusion that "the wind turbine grouping when the active power of the wind turbine reaches the limit value during the transient steady state is reasonable" is correct.

[0008] A wind farm aggregation equivalent method considering wind turbine active power limitation is provided, firstly using the wind farm aggregation equivalent grouping method considering wind turbine active power limitation to obtain a grouping result, and then performing equivalent based on the grouping result, comprising the following steps: Based on the principle that the output power of wind turbines and wind farms remains unchanged, equivalent wind turbines are aggregated; for a wind farm containing x wind turbines, y wind turbines are aggregated into one equivalent wind turbine to obtain equivalent machine capacity and equivalent machine active power; The calculation method of "capacity weighting, impedance series and parallel connection" is used to calculate the equivalent value of box-type transformer parameters: In the formula, E T is the rated capacity of the box-type transformer; Z T is the impedance of the box-type transformer, the subscript eq represents the aggregate value, and the subscript i represents the box-type transformer of the i-th wind turbine unit; The calculation of the collector network parameters of the wind farm includes the following steps: A corresponding wind turbine group in the equivalent group is recorded as the Ath wind turbine group, and the equivalent power and equivalent current injected into the same node before and after the equivalent corresponding to the Ath wind turbine group are set to remain unchanged; when calculating the equivalent parameters, the equivalent of the Ath wind turbine group has the same power and current before and after the equivalent as follows: In the formula, t represents the tth moment; , , denote the complex power, current and voltage of the i-th unit respectively; , denote the complex power and current of the equivalent machine A respectively; Determine the equivalent impedance of the equivalent machine composed of the A-th group of wind turbines: In the formula, is the voltage at the outlet of the wind farm; , , They are the equivalent impedance, voltage and equivalent capacitance current to ground corresponding to the equivalent machine A formed by the Ath group of wind turbines; The equivalent impedance Z in the equivalent collector network at the outlet of the equivalent machine A Aeq The equivalent resistance R Aeq and equivalent reactance X Aeq It is expressed as: Among them, real(·) means to find the real part of a complex number, and imag(·) means to find the imaginary part of a complex number; Then calculate the equivalent capacitance of the collector network of the equivalent machine A to ground: In the formula, is the capacitance to ground of the collector network corresponding to the equivalent machine A; represents the voltage of the i-th unit, is the ground capacitance of the collector network corresponding to the i-th unit.

[0009] Furthermore, the equivalent machine capacity and the equivalent machine active power are as follows: Where E is the capacity of the wind turbine; P is the active power of the wind turbine, the subscript eq represents the aggregate value, and the subscript i represents the i-th wind turbine.

[0010] Furthermore, for a wind farm containing x wind turbines, in the process of aggregating y wind turbines into one equivalent wind turbine, the impedances of the wind turbines are processed in parallel.

[0011] Furthermore, the equivalent voltage corresponding to the equivalent machine A formed by the Ath group of wind turbines is for Here, * indicates conjugation.

[0012] Furthermore, the equivalent ground capacitance current corresponding to the equivalent machine A of the Ath group of wind turbines is for In the formula, , are the ground capacitance and ground capacitance current of the collector network corresponding to the i-th unit respectively; is the angular velocity.

[0013] An equivalent device for aggregating wind farms taking into account the active power limitation of wind turbines, the device comprising a processor and a memory, the memory storing at least one instruction, the at least one instruction being loaded and executed by the processor to implement the equivalent method for aggregating wind farms taking into account the active power limitation of wind turbines.

[0014] Beneficial effects: The present invention first performs clustering feature analysis, analyzes the power response characteristics of wind turbines during LVRT, and according to the measured active and reactive power response curves and the active power steady-state value change curve during the transient steady state, it can be seen that the obvious clustering effect; then, whether the active current of the model reaches the active power limit value is used as the clustering standard, and the wind turbines that reach the active current limit are grouped together, and the wind turbines that do not reach the active current limit are grouped together, and the effectiveness of the clustering method is verified; finally, the equivalent machine parameter calculation, the equivalent transformer parameter calculation and the equivalent collector network parameter calculation are combined to form an aggregated equivalent model of the wind farm. The present invention can solve the problem of poor engineering practicality of the existing wind farm multi-machine equivalent model, and effectively improve the accuracy of the wind farm equivalent model in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the active power response curve; Figure 2 It is the active power response curve during the transient steady state; Figure 3 It is the reactive power response curve; Figure 4 It is a curve diagram of active power steady-state value during transient steady-state corresponding to different active outputs; Figure 5 This is a comparison chart of the original active power and the fitted active power values ​​under different voltage drop levels; Figure 6 It is a detailed model schematic diagram of a wind farm with m rows and n columns; Figure 7 It is a schematic diagram of a multi-machine equivalent model of an m-row n-column wind farm; Figure 8 This is a topological diagram of a typical wind farm; Fig. 9 It is a real power (active power) scenario diagram selected from the actual power scenario; Fig.10is a real power (reactive power) scenario diagram selected from actual power scenarios; Fig.11 It is a real power (voltage) scenario diagram selected from the actual power scenario; Fig.12 It is a real power (current) scenario diagram selected from the actual power scenario; Fig.13 This is the equivalent effect diagram when the voltage drops to 0.35pu; Fig.14 is a real power scenario diagram selected from actual power scenarios; Fig.15 It is the mean absolute error curve of active power of different models under each power scenario; Fig.16 This is the equivalent effect diagram (active power) when the voltage drops to 0.35pu in scenario 1; Fig.17 This is the equivalent effect diagram (reactive power) when the voltage drops to 0.35pu in scenario 1; Fig.18 This is the equivalent effect diagram (voltage) when the voltage drops to 0.35pu in scenario 1; Fig.19 This is the equivalent effect diagram (current) when the voltage drops to 0.35pu in scenario 1. DETAILED DESCRIPTION

[0016] In order to solve the problem of poor engineering practicality of the current wind farm equivalent modeling method, the present invention proposes a wind farm aggregate equivalent grouping and equivalent method considering the active power limitation of wind turbines, and finds the optimal grouping strategy based on the active power limitation of wind turbines, thereby establishing the most accurate wind farm equivalent model. The present invention analyzes the clustering characteristics by analyzing the power response characteristics of wind turbines during LVRT (low voltage ride-through), and uses whether the active current of the model reaches the active power limitation as the grouping standard, and combines the calculation of equivalent machine parameters, equivalent transformer parameters and equivalent collector network parameters to form an aggregate equivalent model of the wind farm. Through verification in an actual wind farm, the proposed method can find the optimal grouping strategy based on the active power limitation of wind turbines, and the multi-machine equivalent model under the optimal grouping can well characterize the response of the detailed model, verifying the effectiveness of the proposed method. The present invention is further described below in conjunction with specific implementation methods. Specific implementation method one: This implementation method is a wind farm aggregation equivalent grouping and verification method considering wind turbine active power limitation, including the following steps: Step 1: Analysis of wind turbine power response characteristics during LVRT: The transient characteristics of wind turbines during the LVRT process can be characterized by voltage, current and power, among which the power characteristic is the most important characteristic in the analysis of electromagnetic transient characteristics of wind farms connected to power systems. This characteristic is widely used in the design of wind farm control strategies and electromagnetic transient analysis of wind farms connected to power systems. Therefore, analyzing the power response characteristics of wind turbines during LVRT is a prerequisite for dynamic equivalent modeling of wind farms. Increase the wind turbine power from 0.025pu, in intervals of 0.025pu, to 1p.u. At the same time, set a three-phase symmetrical short-circuit grounding fault at the wind farm grid connection point. The fault starts at 3s and is cleared at 4s. The measured active power response is shown in the attached figure. Figure 1 As shown in the attached figure, the reactive power response is Figure 3 As shown, each curve corresponds to the simulation result at a starting power.

[0018] From the attached Figure 1 It can be seen that the overall linearity of the active power response curve is very high. As the active power increases, the steady-state value during the transient steady-state period also increases, but it remains basically unchanged after reaching a certain level. Figure 3 It can be seen that the reactive power response curves of the whole fault ride-through process are similar. Figure 2 and attached Figure 4 It can be seen that the attached Figure 4 During the temporary steady state period, the steady-state value of active power increases with the increase of the initial active power of the wind turbine, but remains unchanged after reaching a certain level. Figure 2 The active power during the transient steady state of the red curve part has entered the limit, while the active power during the transient steady state of the blue curve part has not entered the limit; the steady-state values ​​during the transient steady state corresponding to the red curve are basically the same, while the steady-state values ​​during the transient steady state corresponding to the blue curve are different, and an obvious grouping effect can be seen. Therefore, the present invention adopts whether the active power of the wind turbine during the transient steady state reaches the limit value as the grouping basis of the wind turbine, and divides the wind turbines that reach the active power limit into one group, and the wind turbines that do not reach the active power limit into one group, thereby forming a grouping strategy in the aggregated equal value grouping of the wind farm.

[0019] Based on the grouping strategy, whether the active power of the wind turbine reaches the limit value during the transient steady state is used as the basis for grouping the wind turbines.

[0020] Step 2: Mathematical verification of wind turbine clustering strategy: The purpose of grouping is to divide the units with linear superposition characteristics into a group, so that the wind farm model after equalization can fully characterize the response characteristics of the wind farm model before equalization. To this end, the present invention proposes a mathematical verification method for the wind turbine grouping strategy. Through formula derivation, it is verified whether the response characteristics of the units in each group have linear superposition characteristics. After the fault begins, the unit i in the detailed wind farm reaches the steady-state value P during the transient steady state after a short-term transient state.i (t f ). The port power and port voltage of each wind turbine are different, resulting in different active power steady-state values ​​of each wind turbine during the transient steady-state period. According to the active power response curve, it can be seen that the difference in active power mainly comes from the deviation of the steady-state value during the transient steady-state period.

[0021] According to the operating principle of the wind turbine, the active power P of the wind turbine during the transient steady state i (t f ), which is determined by the reactive support value required by the grid connection standard, the power priority function, and the steady-state active power and voltage drop level before the unit fails: Where U i (t f ) is the voltage of fan i during the transient steady state; I p_i (t f ) is the active current of wind turbine i during the transient steady state; P normal_i I is the active power of wind turbine i during the steady state before the fault; max is the maximum current of the fan. In this embodiment, I max 1.345 times the rated current; I q_i (t f ) is the reactive current at the time of fault clearing, which can be expressed as: In the formula, k Q1 is the reactive power support coefficient, which is determined by the grid connection standard; k Q2 is the reactive voltage threshold; I q_max is the reactive current limit value.

[0022] According to the above formula, the active current is and The smaller value is taken between the two. The steady-state active power of the wind farm units before the fault and the voltage drop during the fault are different, which will cause the active current of some units to be , the active current of some units is Therefore, the response characteristics of each unit in the wind farm during the fault drop process are not a simple linear superposition relationship.

[0023] In order to verify the effectiveness of the grouping strategy proposed in the present invention, the rationality of using whether the active power of the wind turbine reaches the limit value during the transient steady state as the basis for wind turbine grouping is proved based on mathematical methods. To simplify the derivation process, the following only studies the case where two wind turbines are equivalent to one equivalent machine, and explores whether there is a linear relationship between their active outputs. If there is a linear relationship, then the method of merging the two wind turbines is reasonable, and this conclusion is still applicable when extended to x units.

[0024] The active power expression of the wind turbine during the transient steady state is: When the active power of the fan does not reach the limit, the active power expression of the fan during the transient steady state is: According to the equivalent theory of wind turbines, during steady state, the sum of the active power of all units in the same group of wind turbines is equal to the active power of the equivalent unit, which can be expressed as: In the formula, , are the active powers of wind turbine 1 and wind turbine 2 during the steady state before the fault respectively; is the active power of the equivalent machine during the steady state before the fault.

[0025] Then the active power expression of the wind turbine during the transient steady state can be derived as: In the formula, , They are the active powers of fan 1 and fan 2 during the transient steady state; is the active power of the equivalent machine during the transient steady state; From the above formula, it can be seen that when the wind turbine does not reach the limit, the active power of the wind turbine during the temporary steady state has a linear superposition characteristic, so it is reasonable to combine the two wind turbines into one wind turbine with equal value; When the active power of the fan reaches the limit, the active power expression of the fan during the transient steady state is: According to the formula, P is a function of U, and is a nonlinear function. Apparently, the formula does not have a linear superposition characteristic. Therefore, the present invention draws a curve of P and U according to the formula, and performs a linear regression analysis on the curve. When performing linear regression analysis, the R-squared value is an important statistical indicator used to measure the degree to which the fitted line explains the data variation; it represents the proportion of the data variation explained by the fitted line, and its calculation formula is as follows: In the formula, R 2 is the R-square value, SS res is the residual sum of squares, which represents the sum of squares of the differences between the predicted values ​​of the fitted line and the actual data values, SS totIt is the total sum of squares, which represents the sum of squares of the differences between the actual data values ​​and the data mean. The R-square value ranges from 0 to 1. The closer it is to 1, the better the fitted line can explain the variation in the data and the better the fit. The R-square value can be obtained by calculating the ratio of the residual sum of squares of the linear regression model to the total sum of squares.

[0026] Through linear regression analysis, the slope, intercept and R-square value of the fitting line were obtained. The fitting results are shown in the attached figure. Figure 5 As shown, the approximate linear equation obtained is P=1.6694U-0.27173, and the R-square value is 0.99964, which is approximately equal to 1, indicating that the curve can almost be approximated as a straight line, and the formula has a linear superposition characteristic.

[0027] Therefore, when the limit is reached, the active power expression of the wind turbine can be simplified to: In the formula, is the slope of the fitted straight line; is the intercept of the fitted straight line; in the present invention, When the fan model changes, resulting in changes in control parameters, the slope and intercept obtained by fitting will change.

[0028] Therefore, the active power of wind turbine 1 and wind turbine 2 during the transient steady state can be expressed by the following formulas: In the formula, , They are the voltages of fan 1 and fan 2 during the transient steady state.

[0029] After equalization, the transient steady-state active power of the wind turbine can be expressed as: In the formula, is the voltage of the equivalent machine during the transient steady state.

[0030] Since the voltage after equalization is approximately equal to the average voltage drop of all units, it can be proved that: From the above derivation process, it can be seen that when the wind turbine reaches the limit, the active power of the wind turbine during the transient steady state has a linear superposition characteristic, and the active power of the equivalent machine during the transient steady state is equal to the sum of the active power of all wind turbines during the transient steady state before the equivalent. Therefore, the method of merging two wind turbines into one wind turbine is reasonable.

[0031] The following is an analysis from the perspective of mathematical derivation as to why the units that have reached the limit and those that have not reached the limit cannot be grouped together. Assuming that under symmetrical drop, wind turbine 1 has not reached the limit and wind turbine 2 has reached the limit, the active power of wind turbine 1 and wind turbine 2 during the transient steady state can be expressed as follows: In the formula, , They are the active currents of fan 1 and fan 2 during the transient steady state.

[0032] For the equivalent wind turbine, there are two possible expressions for the active power during the transient steady state: At this time, regardless of Which of the following is the active power expression of .

[0033] In summary, it is proved that wind turbines in the same group can be linearly superimposed, which verifies the effectiveness of the clustering method from a mathematical perspective. At the same time, it is also proved from a mathematical perspective why units with different clustering characteristics cannot be grouped together, because there is no linear superposition relationship between functions, and the active functions of wind turbines with different clustering characteristics cannot be directly superimposed, nor are they equal to the active power of equivalent units. Specific implementation method 2: This implementation method is a wind farm aggregation equivalent method considering the active power limitation of wind turbines. It is based on the grouping results obtained by the wind farm aggregation equivalent grouping method considering the active power limitation of wind turbines, that is, whether the active power of wind turbines reaches the limit value during the temporary steady state is used as the grouping basis for wind turbines. Wind turbines that reach the limit value are grouped into one group, and wind turbines that do not reach the limit value are grouped into another group; then, equivalent values ​​are performed based on the equivalent model corresponding to the grouping. First, the equivalent machine parameters are calculated; then, the box transformer parameters are equivalently calculated using the calculation method of "capacity weighted, impedance series-parallel connection"; finally, the equivalent collector network parameters are calculated, which specifically includes the following steps: When calculating equivalent parameters of a wind farm, the equivalent wind turbines should be aggregated based on the principle that the output power of the wind turbines and wind farms remain unchanged.

[0035] For a wind farm with x wind turbines, if y wind turbines are aggregated into one equivalent wind turbine, the equivalent turbine capacity is: Where E is the capacity of the wind turbine; P is the active power of the wind turbine, the subscript eq represents the aggregate value, and the subscript i represents the i-th wind turbine.

[0036] Considering that the terminal voltage difference of each wind turbine in the wind farm is very small, the terminal voltage difference is ignored and it is assumed that the terminal voltage of each wind turbine is the same. The impedance of the wind turbine generator set can be simply connected in parallel.

[0037] When considering a wind farm with one machine and one transformer connection mode, the calculation method of "capacity weighted, impedance series and parallel" is used to calculate the equivalent value of box-type transformer parameters: In the formula, E T is the rated capacity of the box-type transformer; Z T is the impedance of the box-type transformer, the subscript eq represents the aggregate value, and the subscript i represents the box-type transformer of the i-th wind turbine unit.

[0038] For the equivalent calculation of the collector network parameters of wind farms, the present invention adopts a fast analytical method, aiming to promote its application to wind farms with more complex structures. This method focuses on realizing the rapid calculation of the dynamic equivalent parameters of the collector network, and can be effectively applied to wind farms with larger scale and more complex topological structures. While ensuring the accuracy of the equivalent model, it meets the needs of system-level simulation and stability analysis of wind farms. Considering the attached Figure 6 The wind farm shown in the figure contains wind turbines with m rows and n columns. Its equivalent model is shown in the attached figure. Figure 7 shown.

[0039] Take the following example to illustrate the calculation steps of the equivalent parameters of the collector network corresponding to the equivalent machine of the A-th group of wind turbines (one of the equivalent units): In the process of calculating before and after the equivalent value, the principle is to ensure that the equivalent power and equivalent current injected into the same node before and after the equivalent value of the equivalent machine of the A group remain unchanged. Then, when calculating the equivalent parameters, the characteristic that the equivalent machine of the A group of wind turbines has the same power and current before and after the equivalent value can be expressed by the formula: In the formula, t represents the tth moment; , , denote the complex power, current and voltage of the i-th unit respectively; , denote the complex power and current of the equivalent machine A respectively, and * denotes conjugate.

[0040] Based on the principle of Ohm's law, it can be deduced that the equivalent impedance of the equivalent machine composed of the A-th group of wind turbines is: In the formula, is the voltage at the outlet of the wind farm; , , They are the equivalent impedance, voltage and equivalent capacitance current to ground corresponding to the equivalent machine A formed by the Ath group of wind turbines; It can be expressed as: Wherein, * indicates conjugation; 50% of the total ground capacitance current in the collector network at the outlet of all fans in group A: In the formula, , are the ground capacitance and ground capacitance current of the collector network corresponding to the i-th unit respectively; is the angular velocity.

[0041] Therefore, the equivalent impedance Z in the equivalent collector network at the outlet of the equivalent machine A is Aeq The equivalent resistance R Aeq and equivalent reactance X Aeq It can be expressed as: Among them, real(·) means to find the real part of a complex number, and imag(·) means to find the imaginary part of a complex number; Substituting the above formula, the equivalent impedance of the collector network at the outlet of the equivalent machine A corresponding to the Ath group of wind turbines can be calculated.

[0042] The next step is to calculate the equivalent capacitance of the collector network of the equivalent machine A to the ground. Before performing the equivalent calculation, the reactive power loss to the ground on the collector line connected to the wind farm unit before the equivalent machine A can be calculated. : The next task is to calculate the equivalent value of the collector network capacitance to ground of the equivalent machine A and the reactive power loss to ground on the collector circuit connected to the equivalent machine A. It can be expressed as: In the formula, is the capacitance to ground of the collector network corresponding to the equivalent machine A.

[0043] When calculating the equivalent value of the collector network capacitance, it is necessary to ensure that the reactive power loss generated by the collector line capacitance before and after the equivalent value is equal, that is, Through this condition, the equivalent capacitance of the collector line corresponding to the equivalent machine A can be obtained: . Specific implementation method three: This embodiment is an equivalent device for wind farm aggregation considering active power limitation of wind turbines, the device includes a processor and a memory, and it should be understood that including any device including a processor and a memory described in the present invention, the device may also include other units and modules that perform display, interaction, processing, control, etc. and other functions through signals or instructions; At least one instruction is stored in the memory, and the at least one instruction is loaded and executed by the processor to implement the equivalent method for wind farm aggregation considering active power limitation of wind turbines.

[0045] Those skilled in the art will appreciate that at least one instruction stored is a computer program product corresponding to the method or system. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The solutions in the embodiments of the present application may be implemented in various computer languages, for example, object-oriented programming language Java and interpreted scripting language JavaScript, etc.

[0046] The present application is described with reference to the flowcharts and / or block diagrams of the methods, systems, and computer program products according to the embodiments of the present application, and may also be used for corresponding devices. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0047] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0048] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0049] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0050] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

[0051] Example A typical wind farm topology diagram is shown in the attached figure. Figure 8 As shown, it includes 30 8.3MW full-power wind turbines and 37 6.8MW full-power wind turbines. The wind farm mainly consists of wind turbines, machine-end transformers, collection network lines and wind farm booster stations. The machine-end voltage is 1.14kV, and the machine-end transformer voltage ratio is 1.14kV / 36.75kV. After the units are boosted by the machine-end transformer, they are connected through the collection network, collected through 17 branches to the wind farm booster station, and connected to the power grid.

[0052] Taking this wind farm as an example, three models were constructed on the PSCAD software platform: detailed model, single-machine equivalent model and dual-machine equivalent model. Figure 8 The electromagnetic transient model is established based on the wind farm topology diagram shown in the figure to ensure that all parameters are consistent with the actual wind farm parameters. The single-machine equivalent model uses the above-mentioned equivalent parameter calculation method to equate the entire wind farm to one unit, where the initial active power of the wind turbine is the average power of all wind turbines, and the wind farm's collector network line is equivalent to the series impedance of the equivalent machine according to the above method. The dual-machine equivalent model follows the above-mentioned unit grouping principle to group the wind turbines, and calculates the initial active power and equivalent parameters of each group of direct-drive wind turbines.

[0053] In order to verify the effectiveness of the proposed wind farm practical equivalent method, the attached Figure 8 The wind farm shown in the figure is the research object. The actual wind speed data is selected as shown in the attached figure. Figure 9-12The 428th set of real wind speed data shown in the figure shows that a three-phase ground short circuit fault occurred at the outlet of the wind farm in 3s, and the fault was cleared in 3.25s. The voltage at the fault point was set to drop to around 0.35pu. The simulation results are shown in the attached figure. Fig.13 As shown in the figure, it can be seen that the proposed wind farm practical equivalent method can significantly improve the accuracy of the single-machine equivalent model, and the tracking effects of active power, reactive power, voltage and current at the wind farm outlet are all good. Therefore, the practical equivalent method has good adaptability.

[0054] In order to verify the effectiveness of the practical equivalent strategy proposed in this invention under different wind speed scenarios, 10 sets of actual scenarios were selected from actual wind field data for verification, as shown in the attached figure. Fig.14 In these scenarios, a three-phase ground short circuit fault occurred at the wind farm outlet at 3.2 seconds, and the fault was cleared at 3.55 seconds, with the voltage dropping to about 0.35 pu. The average absolute error of the active power during the transient steady state of the single-machine equivalent, practical equivalent method and the detailed wind farm is shown in the attached figure. Fig.15 As shown in the attached Fig.15 It can be seen that the proposed practical equivalent method shows excellent adaptability to various wind speed scenarios during the symmetric fall.

[0055] In order to more intuitively demonstrate the equivalent effect of the practical equivalent strategy proposed in the present invention, the third and seventh groups of actual scenarios are selected to show the time domain simulation results of voltage, current, active power and reactive power of the actual wind farm model, the single machine equivalent model and the practical equivalent model at the grid connection point. The equivalent effect of the third group of actual scenarios is shown in the attached figure. Figure 16-Figure 19 shown.

[0056] By observing the Figure 16-Figure 19 From the simulation results shown, it can be seen that the practical equivalent method proposed in the present invention can significantly improve the accuracy of the traditional single-machine equivalent model. The method performs well in tracking the voltage, current, active power and reactive power of the detailed wind field model. Whether in steady state or transient state, the error is controlled within 1%, and the transient error is controlled below 5%. Therefore, the practical equivalent method proposed in the present invention has shown excellent adaptability to various wind speed scenarios.

[0057] In summary, the present invention proposes a wind farm aggregation equivalent method considering the active power limitation of wind turbines, realizes finding the optimal grouping strategy based on the active power limitation of wind turbines, and establishes the most accurate wind farm equivalent model.

[0058] It should be noted that the specific implementation is only an explanation and description of the technical solution of the present invention, and cannot be used to limit the scope of protection of the rights. Any partial changes made according to the claims and description of the present invention should still fall within the scope of protection of the present invention.

Claims

1. A wind farm aggregation equal value grouping method considering wind turbine active power limitation, characterized in that: The fans are grouped based on whether their active power reaches the limit value during the transient steady state.

2. A wind farm aggregation equivalent grouping verification method considering wind turbine active power limitation is characterized in that: A positive verification is performed on the grouping result obtained by the wind farm aggregation equivalent grouping method considering the wind turbine active power limitation as described in claim 1, comprising the following steps: According to the operating principle of the wind turbine, determine the active power P of the wind turbine during the transient steady state. i (t f ): Where U i (t f ) is the voltage of fan i during the transient steady state; I p_i (t f ) is the active current of wind turbine i during the transient steady state; P normal_i I is the active power of wind turbine i during the steady state before the fault; max is the maximum current of the fan; I q_i (t f ) is the reactive current at the time of fault clearing, expressed as: In the formula, k Q1 is the reactive support coefficient; k Q2 is the reactive voltage threshold; I q_max is the reactive current limit value; In view of the nonlinear superposition relationship of the response characteristics of each unit in the wind farm during the fault drop process; first determine the active power expression of the wind turbine during the transient steady state when the wind turbine active power does not reach the limit: Based on the fact that the sum of the active power of all units in the same group of wind turbines during the steady-state period is equal to the active power of the equivalent unit, the active power expression of the wind turbine during the transient steady-state period is determined as follows: In the formula, , They are the active powers of fan 1 and fan 2 during the transient steady state; is the active power of the equivalent machine during the transient steady state; , are the active powers of wind turbine 1 and wind turbine 2 during the steady state before the fault respectively; Based on the above active power expression of the wind turbine during the transient steady state, verify whether the active power of the wind turbine during the transient steady state has a linear superposition characteristic when the wind turbine does not reach the limit. If it has a linear superposition characteristic, continue the subsequent rationality verification, otherwise, verify that the grouping result is unreasonable; Then determine the active power expression of the fan during the transient steady state when the fan active power reaches the limit: Will not have linear superposition characteristics Perform conversion analysis, first draw the curve of P and U based on the expression, and then perform linear regression analysis on the curve; through linear regression analysis, get the slope, intercept and R-square value of the fitting line, and determine whether the curve of P and U can be expressed as a straight line according to the R-square value corresponding to the approximate linear equation of P and U. If not, it is considered that the corresponding grouping is unreasonable; if so, it is considered that the grouping of fans whose active power reaches the limit value during the transient steady state is reasonable.

3. The wind farm aggregation equivalent grouping verification method considering wind turbine active power limitation according to claim 2 is characterized in that: Maximum current of fan I max It is 1.345 times the rated current.

4. The wind farm aggregation equivalent grouping verification method considering wind turbine active power limitation according to claim 2 is characterized in that: When it is considered that the wind turbine grouping is reasonable when the wind turbine active power reaches the limit value during the transient steady state, the expression of the wind turbine active power when reaching the limit is simplified to: In the formula, is the slope of the fitted straight line; is the intercept of the fitted straight line; Then the active power of wind turbine 1 and wind turbine 2 during the transient steady state is expressed as: In the formula, , They are the voltages of fan 1 and fan 2 during the transient steady state; After equalization, the transient steady-state active power of the fan is expressed as: ; In the formula, is the voltage of the equivalent machine during the transient steady state; since the voltage after the equivalent value is approximately equal to the average value of the voltage drop of all units, , and the conclusion that "the wind turbine grouping is reasonable when the active power of the wind turbine reaches the limit value during the transient steady state" is correct.

5. An equivalent method for wind farm aggregation considering wind turbine active power limitation, characterized in that: First, the grouping result is obtained by using the wind farm aggregate equivalent grouping method considering the wind turbine active power limitation as described in claim 1, and then equivalent is performed based on the grouping result, including the following steps: Based on the principle that the output power of wind turbines and wind farms remains unchanged, equivalent wind turbines are aggregated; for a wind farm containing x wind turbines, y wind turbines are aggregated into one equivalent wind turbine to obtain equivalent machine capacity and equivalent machine active power; The calculation method of "capacity weighting, impedance series and parallel connection" is used to calculate the equivalent value of box-type transformer parameters: In the formula, E T is the rated capacity of the box-type transformer; Z T is the impedance of the box-type transformer, the subscript eq represents the aggregate value, and the subscript i represents the box-type transformer of the i-th wind turbine unit; The calculation of the collector network parameters of the wind farm includes the following steps: A corresponding wind turbine group in the equivalent group is recorded as the Ath wind turbine group, and the equivalent power and equivalent current injected into the same node before and after the equivalent corresponding to the Ath wind turbine group are set to remain unchanged; when calculating the equivalent parameters, the equivalent of the Ath wind turbine group has the same power and current before and after the equivalent as follows: In the formula, t represents the tth moment; , , denote the complex power, current and voltage of the i-th unit respectively; , denote the complex power and current of the equivalent machine A respectively; Determine the equivalent impedance of the equivalent machine composed of the A-th group of wind turbines: In the formula, is the voltage at the outlet of the wind farm; , , They are the equivalent impedance, voltage and equivalent capacitance current to ground corresponding to the equivalent machine A formed by the Ath group of wind turbines; The equivalent impedance Z in the equivalent collector network at the outlet of the equivalent machine A Aeq The equivalent resistance R Aeq and equivalent reactance X Aeq It is expressed as: Among them, real(·) means to find the real part of a complex number, and imag(·) means to find the imaginary part of a complex number; Then calculate the equivalent capacitance of the collector network of the equivalent machine A to ground: In the formula, is the capacitance to ground of the collector network corresponding to the equivalent machine A; represents the voltage of the i-th unit, is the ground capacitance of the collector network corresponding to the i-th unit.

6. The equivalent method of wind farm aggregation considering wind turbine active power limitation according to claim 5 is characterized in that: The equivalent machine capacity and equivalent machine active power are as follows: Where E is the capacity of the wind turbine; P is the active power of the wind turbine, the subscript eq represents the aggregate value, and the subscript i represents the i-th wind turbine.

7. The equivalent method of wind farm aggregation considering wind turbine active power limitation according to claim 5 is characterized in that: For a wind farm with x wind turbines, when y wind turbines are aggregated into one equivalent wind turbine, the impedance of the wind turbines is processed in parallel.

8. The equivalent method of wind farm aggregation considering wind turbine active power limitation according to any one of claims 5 to 7, characterized in that: The equivalent voltage corresponding to the equivalent machine A formed by the Ath group of wind turbines for Here, * indicates conjugation.

9. The equivalent method of wind farm aggregation considering wind turbine active power limitation according to claim 8, characterized in that: The equivalent ground capacitance current corresponding to the equivalent machine A of the Ath group of wind turbines for In the formula, , are the ground capacitance and ground capacitance current of the collector network corresponding to the i-th unit respectively; is the angular velocity.

10. An equivalent device for wind farm aggregation considering wind turbine active power limitation, characterized in that: The device includes a processor and a memory, wherein the memory stores at least one instruction, and the at least one instruction is loaded and executed by the processor to implement an equivalent method for wind farm aggregation considering active power limitation of wind turbines as described in any one of claims 5 to 9.

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