CN104504285A

CN104504285A - Doubly-fed wind power farm equivalent modeling method for crowbar protection

Info

Publication number: CN104504285A
Application number: CN201510005159.7A
Authority: CN
Inventors: 丁明; 朱乾龙; 韩平平; 贺敬
Original assignee: China Electric Power Research Institute Co Ltd CEPRI; Hefei University of Technology
Current assignee: State Grid Corp of China SGCC; China Electric Power Research Institute Co Ltd CEPRI; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd; Hefei University of Technology
Priority date: 2015-01-06
Filing date: 2015-01-06
Publication date: 2015-04-08

Abstract

The invention discloses a doubly-fed wind farm equivalent modeling method considering crowbar protection. Based on the relationship between them, a voltage drop criterion that can characterize the crowbar protection action of doubly-fed wind turbines is proposed; Based on the correction, the crowbar protection action of the unit is determined; then, the wind farm equivalent model is established based on the crowbar protection action as the cluster classification principle. The invention realizes the accurate characterization of the crowbar protection action of the internal unit of the doubly-fed wind farm, and improves the fitting accuracy of the wind farm equivalent model to the external characteristics of the wind farm power.

Description

An Equivalent Modeling Method for DFIG Wind Farm Considering Crowbar Protection

技术领域technical field

本发明涉及一种针对双馈风电场并网外特性的等值建模方法。The invention relates to an equivalent modeling method for the off-grid characteristics of a doubly-fed wind farm.

背景技术Background technique

双馈风电机组具有最大功率追踪、功率解耦控制、变流器容量小等特点，是当前风电场中的主流机型。为了提高双馈风电机组的低电压穿越能力，通常在其转子侧装设撬棒保护使功率变流器免受短路电流的冲击。撬棒保护电路的投入不仅使机组失去对输出功率的控制，有可能诱发风场内机组的连锁脱网，还由于撬棒电阻的接入导致风电场的弱馈程度增强。因此，撬棒保护的动作对风电场的运行特性具有重要影响。Doubly-fed wind turbines have the characteristics of maximum power tracking, power decoupling control, and small converter capacity, and are the mainstream models in current wind farms. In order to improve the low-voltage ride-through capability of doubly-fed wind turbines, a crowbar is usually installed on the rotor side to protect the power converter from the impact of short-circuit current. The input of the crowbar protection circuit not only makes the unit lose control of the output power, which may induce the chain disconnection of the unit in the wind farm, but also increases the weak feed of the wind farm due to the connection of the crowbar resistance. Therefore, the action of the crowbar protection has an important influence on the operating characteristics of the wind farm.

开展大规模风电并网特性研究时，为了减少风电场模型的阶数和仿真计算时间，风电场一般采用等值模型。目前，风电场多机等值模型的研究重点在于通过对风电机组特性的量化提取，确定合理的分群判据指标。常用的分群判据指标有风力机的输入风速、桨距角的动作情况、风电机组的直轴暂态电动势和风力发电机的转速向量。风电场单机等值模型的研究热点在于通过优化等值模型参数，进一步提高对风电场外特性的拟合精度。优化对象包括等值风力发电机参数、等值控制器参数和风电场内部的无源器件。但是，目前的研究成果均未计及撬棒保护对机组及风电场等值建模的影响。研究表明，如果考虑撬棒保护，传统的分群判据指标难以准确表征机组的撬棒保护动作情况，导致风电场等值模型产生较大误差。有学者对双馈风电机组端电压跌落深度与撬棒保护之间的关系进行研究，却没有考虑风电场拓扑结构对机组端电压跌落临界值的影响。When carrying out large-scale wind power grid-connected characteristics research, in order to reduce the order of the wind farm model and the simulation calculation time, the wind farm generally adopts an equivalent model. At present, the research focus of multi-generator equivalence model of wind farm is to determine the reasonable grouping criterion index through the quantitative extraction of the characteristics of wind turbines. Commonly used grouping criteria indicators include the input wind speed of the wind turbine, the action of the pitch angle, the direct axis transient electromotive force of the wind turbine and the speed vector of the wind turbine. The research hotspot of the wind farm stand-alone equivalent model is to further improve the fitting accuracy of the external characteristics of the wind farm by optimizing the parameters of the equivalent model. The optimization objects include equivalent wind turbine parameters, equivalent controller parameters and passive components inside the wind farm. However, the current research results do not take into account the impact of crowbar protection on the equivalent modeling of units and wind farms. The research shows that if the crowbar protection is considered, the traditional grouping criterion index is difficult to accurately represent the crowbar protection action of the unit, resulting in a large error in the equivalent model of the wind farm. Some scholars have studied the relationship between the depth of voltage drop at the terminal of double-fed wind turbines and the crowbar protection, but they have not considered the influence of the topological structure of the wind farm on the critical value of voltage drop at the terminal of the wind turbine.

发明内容Contents of the invention

本发明为了提高基于同调等值思想的双馈风电场等值建模方法对双馈风电机组撬棒保护动作情况的等效正确率，使风电场等值模型更加准确地拟合风电场的功率外特性。本发明提供一种计及撬棒保护的双馈风电场等值建模方法。In order to improve the equivalent accuracy of the doubly-fed wind farm equivalent modeling method based on the idea of coherent equivalents to the crowbar protection action of doubly-fed wind turbines, the invention makes the wind farm equivalent model more accurately fit the power of the wind farm external characteristics. The invention provides an equivalent modeling method of a doubly-fed wind farm considering crowbar protection.

本发明为解决技术问题采用如下技术方案：The present invention adopts following technical scheme for solving technical problems:

本发明计及撬棒保护的双馈风电场等值建模方法的特点是按如下步骤进行：The present invention considers the double-fed wind farm equivalent modeling method of crowbar protection to carry out according to the following steps:

步骤1、对风电场全年的实测风资源信息进行统计，所述风资源信息包括风电场风速的大小和风向，建立风电场风资源信息数据库；Step 1. Statistically measure the wind resource information of the wind farm throughout the year, the wind resource information includes the wind speed and direction of the wind farm, and establish a wind farm wind resource information database;

步骤2、基于双馈风电场的网络拓扑结构和模型参数，搭建风电场详细模型；Step 2. Build a detailed model of the wind farm based on the network topology and model parameters of the DFIG wind farm;

步骤3、设定机组的运行功率因数，从风资源信息数据库中随机读入一组风电场的风速信息，依据机组的位置分布和尾流效应计算推导出各台机组的输入风速，由输入风速对应确定各台机组的有功功率P_w，完成动态仿真前模型的潮流初始化；所述一组风电场的风速信息是指在机组切入风速v_in和切除风速v_out范围内的某一风速大小和0°到360°范围内某一风速方向的组合风速信息；所述机组为双馈风电机组；Step 3. Set the operating power factor of the unit, randomly read a group of wind speed information of the wind farm from the wind resource information database, and calculate and deduce the input wind speed of each unit according to the position distribution of the unit and the wake effect. The input wind speed Correspondingly determine the active power P _w of each unit, and complete the power flow initialization of the model before the dynamic simulation; the wind speed information of the group of wind _farms refers to a certain wind _speed and Combined wind speed information of a certain wind speed direction within the range of 0° to 360°; the unit is a double-fed wind turbine;

步骤4、采集风电场内部各台机组稳态运行时的端电压U_s0；Step 4. Collect the terminal voltage U _s0 of each unit in the wind farm during steady-state operation;

步骤5、设定0.1s时电网侧发生三相短路故障，150ms后故障消除，采集三相短路故障后1ms时刻各台机组的端电压跌落值U_sk；Step 5. Set that a three-phase short-circuit fault occurs on the grid side at 0.1 s, and the fault is eliminated after 150 ms, and collect the terminal voltage drop value U _sk of each unit at 1 ms after the three-phase short-circuit fault;

步骤6、若所述端电压跌落值U_sk小于修正前的相对应的端电压跌落临界值U₀，则判定机组撬棒保护动作，将撬棒保护动作机组划归至撬棒保护动作机群；反之，则计算该机组的虚拟线路阻抗Z_eq-k；Step 6. If the terminal voltage drop value U _sk is less than the corresponding terminal voltage drop critical value U ₀ before correction, it is determined that the crowbar protection action of the unit is performed, and the crowbar protection action unit is classified into the crowbar protection action group; Otherwise, calculate the virtual line impedance Z _eq-k of the unit;

步骤7、将步骤6中计算获得的虚拟线路阻抗Z_eq-k接入机组单机无穷大并网模型的机端变压器和中压母线之间，对机组的端电压跌落临界值U₀进行修正，获得修正后的端电压跌落临界值U₀′；Step 7. Connect the virtual line impedance Z _eq-k calculated in step 6 between the machine-side transformer and the medium-voltage bus of the single unit infinite grid-connected model, and correct the terminal voltage drop critical value U ₀ of the unit to obtain The corrected terminal voltage drop critical value U ₀ ′;

步骤8、若是步骤5采集的机组端电压跌落值U_sk小于步骤7中获得的修正后的端电压跌落临界值U₀′，则判定机组撬棒保护动作，将撬棒保护动作机组划归至撬棒保护动作机群；反之，则判定机组的撬棒保护未动作，将撬棒保护未动作的机组划归至撬棒保护未动作机群；Step 8. If the unit terminal voltage drop value U _sk collected in step 5 is less than the corrected terminal voltage drop critical value U ₀ ′ obtained in step 7, then it is determined that the unit crowbar protection action is performed, and the crowbar protection action unit is assigned to If the crowbar protection operates the group; otherwise, it is determined that the crowbar protection of the unit has not been operated, and the units that have not operated the crowbar protection are classified as the crowbar protection does not operate the group;

步骤9、令：撬棒保护动作机群中包含的机组用第一台等值机组WT_eq1表征，机组所在支路中其有功功率流出方向上的线路阻抗用第一个等值线路阻抗Z_eq1表征，机组的机端变压器用第一台等值机端变压器T_eq1表征；令：撬棒保护未动作机群中包含的机组用第二台等值机组WT_eq2表征，机组所在支路中其有功功率流出方向上的线路阻抗用第二个等值线路阻抗Z_eq2表征，机组的机端变压器用第二台等值机端变压器T_eq2表征；利用所述第一台等值机组WT_eq1和第二台等值机组WT_eq2、第一个等值线路阻抗Z_eq1和第二个等值线路阻抗Z_eq2、第一台等值机端变压器T_eq1和第二台等值机端变压器T_eq2的等值参数建立计及撬棒保护的双馈风电场等值模型。Step 9. Order: The units included in the crowbar protection action group are represented by the first equivalent unit WT _eq1 , and the line impedance in the direction of the active power outflow of the branch where the unit is located is represented by the first equivalent line impedance Z _eq1 , the machine-side transformer of the unit is represented by the first equivalent machine-side transformer T _eq1 ; and: the units contained in the crowbar protection group that does not operate are represented by the second equivalent unit WT _eq2 , and the active power of the unit in the branch is The line impedance in the outflow direction is characterized by the second equivalent line impedance Z _eq2 , and the machine-end transformer of the unit is characterized by the second equivalent machine-end transformer T _eq2 ; using the first equivalent unit WT _eq1 and the second Equivalent unit WT _eq2 , the first equivalent line impedance Z _eq1 and the second equivalent line impedance Z _eq2 , the first equivalent machine-side transformer T _eq1 and the second equivalent machine-side transformer T _eq2 , etc. The value parameters are used to establish the equivalent model of the doubly-fed wind farm considering the crowbar protection.

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：步骤2中所述风电场是由多台型号相同的机组组成，所述机组的额定端电压为U_N，经机端变压器升压至U_MV后通过架空线路接于中压母线，再经过风电场主变压器升压至U_HV，最终通过双回线路接入电网；相邻机组间的间隔为s；所述风电场详细模型包括风电场内各机组的单机模型、机组间线路模型、机端变压器以及主变压器模型。The feature of the double-fed wind farm equivalent modeling method considering crowbar protection in the present invention is that the wind farm described in step 2 is composed of multiple units of the same model, and the rated terminal voltage of the units is U _N , After being boosted to U _MV by the machine terminal transformer, it is connected to the medium-voltage bus through an overhead line, then boosted to U _HV through the main transformer of the wind farm, and finally connected to the power grid through a double-circuit line; the interval between adjacent units is s; The detailed model of the wind farm includes the stand-alone model of each unit in the wind farm, the line model between units, the transformer at the machine end and the main transformer model.

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：步骤3中各机组的输入风速按以下过程计算：The characteristics of the double-fed wind farm equivalent modeling method considering the crowbar protection of the present invention are also: the input wind speed of each unit in step 3 is calculated according to the following process:

步骤a、根据读入的风电场风速信息中的风向信息确定风电场内部机组间的上、下游位置关系；Step a, according to the wind direction information in the wind speed information of the wind farm that is read in, determine the upstream and downstream positional relationship between the internal units of the wind farm;

步骤b、风电场内部最上游机组的输入风速的大小等于读入的风电场风速信息中的风速大小；设定下游机组WT_j的输入风速v_j仅受其上游机组WT_k尾流效应的影响，则下游机组WT_j的输入风速v_j按公式(1)计算获得：Step b. The input wind speed of the most upstream unit in the wind farm is equal to the wind speed in the wind speed information of the wind farm; the input wind speed v _j of the downstream unit WT _j is only affected by the wake effect of the upstream unit WT _k , then the input wind speed v _j of the downstream unit WT _j is calculated according to formula (1):

${v v}_{j j} = = {v v}_{k k} [[11 - - {((\frac{r r}{0.08 0.08 {s the s}_{jk jk} + + r r}))}^{22} ((11 - - \sqrt{11 - - {C C}_{t t}}))]] - - - - - - ((11))$

式(1)中，v_k为上游机组WT_k的输入风速；r为机组圆形扫风截面的半径；s_jk为上游机组WT_k和下游机组WT_j的直线距离；C_t为推力系数；In formula (1), v _k is the input wind speed of the upstream unit WT _k ; r is the radius of the circular sweep section of the unit; s _jk is the straight-line distance between the upstream unit WT _k and the downstream unit WT _j ; C _t is the thrust coefficient;

步骤c、将机组WT_j作为上游机组，依据式(1)确定其下游机组的输入风速，依次类推，直至计算获得风电场内部各机组的输入风速。Step c, take the unit WT _j as the upstream unit, determine the input wind speed of its downstream unit according to formula (1), and so on, until the input wind speed of each unit inside the wind farm is calculated.

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：所述步骤3中机组的有功功率P_w由式(2)计算获得：The feature of the double-fed wind farm equivalent modeling method considering the crowbar protection of the present invention is also that: the active power _Pw of the unit in the step 3 is calculated by formula (2):

${P P}_{w w} = = 0.5 0.5 {ρπr ρπr}^{22} {c c}_{p p} {v v}_{w w}^{33} - - - - - - ((22))$

式(2)中，ρ为空气密度；v_w为机组的输入风速；c_p为风能利用系数；所述风能利用系数c_p由式(3)计算获得：In formula (2), ρ is the air density; v _w is the input wind speed of the unit; c _p is the wind energy utilization coefficient; the wind energy utilization coefficient c _p is calculated by formula (3):

$\{\begin{matrix} {c c}_{p p} = = 0.22 0.22 ((\frac{116116}{λ λ + + 0.08 0.08 β β} - - \frac{4.06 4.06}{{β β}^{33} + + 11} - - 0.4 0.4 β β - - 55)) {e e}^{- - ((\frac{12.5 12.5}{λ λ + + 0.08 0.08 β β} - - \frac{0.4375 0.4375}{{β β}^{33} + + 11}))} \\ λ λ = = \frac{{ω ω}_{t t} r r}{{v v}_{w w}} \end{matrix} - - - - - - ((33))$

式(3)中，λ为机组的叶尖速比；β为机组的桨距角；ω_t为机组中的风轮机转速。In formula (3), λ is the tip speed ratio of the unit; β is the pitch angle of the unit; _ωt is the speed of the wind turbine in the unit.

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：步骤6中机组修正前端电压跌落临界值U₀按如下过程确定：The feature of the double-fed wind farm equivalent modeling method in consideration of the crowbar protection of the present invention is that: in step 6, the unit corrects the front-end voltage drop critical value U ₀ according to the following process:

(1)、搭建机组单机无穷大并网模型，设定机组的运行功率因数；设定机组的有功功率P_w为0MW，稳态运行时的端电压为0.97pu；(1) Build a single-unit infinite grid-connected model, set the operating power factor of the unit; set the active power P _w of the unit to 0MW, and the terminal voltage during steady-state operation to be 0.97pu;

(2)、设定0.1s时电网侧发生三相短路故障，150ms后故障消除；(2) When setting 0.1s, a three-phase short-circuit fault occurs on the grid side, and the fault is eliminated after 150ms;

(3)、在三相短路故障发生后1ms时，若机组的撬棒保护未动作，则逐步减小短路接地阻抗Z_f，直至撬棒保护恰好动作；若机组的撬棒保护动作，则逐步增加短路接地阻抗Z_f，直至撬棒保护恰好不动作；(3) 1ms after the occurrence of the three-phase short-circuit fault, if the crowbar protection of the unit does not operate, then gradually reduce the short-circuit grounding impedance Z _f until the crowbar protection operates; if the crowbar protection of the unit operates, gradually Increase the short-circuit grounding impedance Z _f until the crowbar protection just does not operate;

(4)、记录撬棒保护由未动作到恰好动作时刻，或撬棒保护由动作到恰好不动作时刻机组的端电压跌落值U_sk，即为机组在有功功率P_w和稳态运行端电压U_s0组合情况下对应的修正前端电压跌落临界值U₀；(4) Record the terminal voltage drop value U _sk of the unit from the moment when the crowbar protection does not act to the moment when the crowbar protection acts to just stop, which is the active power P _w and the steady-state operating terminal voltage of the unit The corrected front-end voltage drop threshold value U ₀ corresponding to the combination of U _s0 ;

(5)、在机组运行功率0～2MW范围内以0.1MW为步长逐渐增加机组的有功功率P_w，重复步骤(2)到步骤(4)；(5) Gradually increase the active power P _w of the unit with a step size of 0.1MW within the operating power range of the unit from 0 to 2MW, and repeat steps (2) to (4);

(6)、在机组稳态运行端电压0.97～1.07pu范围内以0.01pu为步长逐渐增加机组的稳态运行端电压U_s0，重复步骤(2)到步骤(5)；(6) Gradually increase the steady-state operating terminal voltage U _s0 of the unit within the range of 0.97 to 1.07 pu with a step size of 0.01 pu, and repeat steps (2) to (5);

(7)、以有功功率P_w为X轴，稳态运行时端电压U_s0为Y轴，修正前端电压跌落临界值U₀为Z轴，建立机组修正前的端电压跌落临界值三维坐标图。(7) Take the active power P _w as the X axis, the terminal voltage U _s0 during steady state operation as the Y axis, and the corrected front-end voltage drop critical value U ₀ as the Z axis to establish a three-dimensional coordinate diagram of the terminal voltage drop critical value of the unit before correction .

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：步骤6中机组的虚拟线路阻抗Z_eq-k按式(4)计算获得：The present invention considers the double-fed wind farm equivalent modeling method of crowbar protection to also be characterized in that: in step 6, the virtual line impedance Z _eq-k of the unit is calculated according to formula (4):

${Z Z}_{eq eq - - k k} = = \frac{{Σ Σ}_{l l = = k k}^{N N} (({Z Z}_{l l} {Σ Σ}_{i i = = 11}^{l l} {S S}_{i i}^{* *}))}{{S S}_{k k}^{* *}} - - - - - - ((44))$

式(4)中，Z_l为机组WT_l所在支路中其有功功率P_w流出支路的线路阻抗；为第i台机组WT_i视在功率的共轭值；N为机组WT_i所在的一条馈线上的机组的台数。In formula (4), Z _l is the line impedance of the branch where the active power P _w of the unit WT _l is located; is the conjugate value of the apparent power of the i-th unit WT _i ; N is the number of units on a feeder where the unit WT _i is located.

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：步骤7中对机组端电压跌落临界值U₀的修正按如下过程进行：The feature of the double-fed wind farm equivalent modeling method considering the crowbar protection of the present invention is also that: in step 7, the correction of the critical value _U0 of the voltage drop at the unit terminal is carried out according to the following process:

(a)、将机组的线路虚拟阻抗Z_eq-k串联接入机组单机无穷大并网模型的机端变压器和中压母线之间；(a), the line virtual impedance Z _eq-k of the unit is connected in series between the machine terminal transformer and the medium-voltage busbar of the single unit infinite grid-connected model of the unit;

(b)、设定机组的运行功率因数与步骤3中设定的运行功率因数相同，并设定机组有功功率P_w与步骤3中机组有功功率P_w保持相同，调节电网电压使机组稳态运行时的端电压U_s0与步骤4采集到的端电压相同U_s0；(b) Set the operating power factor of the unit to be the same as that set in step 3, and set the active power P _w of the unit to be the same as the active power P _w of the unit in step 3, and adjust the grid voltage to make the unit stable The terminal voltage U _s0 during operation is the same as the terminal voltage U _s0 collected in step 4;

(c)、设定0.1s时电网侧发生三相短路故障，150ms后故障消除；(c) When setting 0.1s, a three-phase short-circuit fault occurs on the grid side, and the fault is eliminated after 150ms;

(d)、在三相短路故障发生后1ms时，若机组的撬棒保护未动作，则逐步减小短路接地阻抗Z_f，直至撬棒保护恰好动作；若撬棒保护动作，则逐步增加短路接地阻抗Z_f，直至撬棒保护恰好不动作；(d) 1ms after the occurrence of the three-phase short-circuit fault, if the crowbar protection of the unit does not operate, gradually reduce the short-circuit grounding impedance Z _f until the crowbar protection operates; if the crowbar protection operates, gradually increase the short circuit Grounding impedance Z _f until the crowbar protection just does not operate;

(e)、记录撬棒保护由未动作到恰好动作时刻，或撬棒保护由动作到恰好不动作时刻机组的端电压跌落值U_sk，即为机组有功功率P_w和稳态运行端电压U_s0组合情况下对应的修正后端电压跌落临界值U′₀。(e) Record the terminal voltage drop value U _sk of the unit from the moment when the crowbar protection does not act to the moment when the crowbar protection acts to just stop, which is the active power P _w of the unit and the steady-state operating terminal voltage U In the case of the combination of _s0 , the corresponding corrected rear-end voltage drop critical value U′ ₀ .

本发明计及撬棒保护的双馈风电场等值建模方法的特点也在于：所述步骤9中等值机组包含的各等值参数：视在功率S_eq、发电机阻抗Z_{G_eq}、惯性时间常数H_eq、轴系刚度系数K_eq、轴系阻尼系数D_eq，以及等值机端变压器包含的各等值参数：视在功率S_{T_eq}、阻抗Z_{T_eq}按式(5)计算获得：The feature of the equivalent modeling method of the doubly-fed wind farm considering the crowbar protection of the present invention is that: the equivalent parameters included in the equivalent unit in the step 9: apparent power S _eq , generator impedance Z _{G_eq} , inertia time The constant H _eq , the shafting stiffness coefficient K _eq , the shafting damping coefficient D _eq , and the equivalent parameters included in the equivalent machine-side transformer: apparent power S _{T_eq} and impedance Z _{T_eq} are obtained by formula (5):

$\{\begin{matrix} {S S}_{eq eq} = = {Σ Σ}_{i i = = 11}^{m m} {S S}_{i i},, {Z Z}_{G G__eq eq} = = \frac{{Z Z}_{Gi Gi}}{m m},, {H h}_{eq eq} = = {Σ Σ}_{i i = = 11}^{m m} {H h}_{i i} \\ {K K}_{eq eq} = = {Σ Σ}_{i i = = 11}^{m m} {K K}_{i i},, {D D.}_{eq eq} = = {Σ Σ}_{i i = = 11}^{m m} {D D.}_{i i} \\ {S S}_{T T__eq eq} = = {Σ Σ}_{i i = = 11}^{m m} {S S}_{Ti Ti},, {Z Z}_{T T__eq eq} = = \frac{{Z Z}_{Ti Ti}}{m m} \end{matrix} - - - - - - ((55))$

式(5)中，S_i、Z_Gi、H_i、K_i和D_i分别表示第i台机组的视在功率、发电机阻抗、惯性时间常数、轴系刚度系数和轴系阻尼系数；S_Ti、Z_Ti为第i台机组的机端变压器的额定容量和阻抗；m为相应机群中机组的台数；In formula (5), S _i , Z _Gi , H _i , K _i and D _i represent the apparent power, generator impedance, inertial time constant, shafting stiffness coefficient and shafting damping coefficient of unit i respectively; S _Ti and Z _Ti are the rated capacity and impedance of the machine-side transformer of the i-th unit; m is the number of units in the corresponding unit;

等值线路的阻抗Z_l-eq按式(6)计算获得：The impedance Z _l-eq of the equivalent line is calculated according to formula (6):

${Z Z}_{l l - - eq eq} = = \frac{{Σ Σ}_{i i = = 11}^{m m} {Z Z}_{l l - - i i} {S S}_{i i}^{* *} {S S}_{i i}}{(({Σ Σ}_{i i = = 11}^{m m} {S S}_{i i})) (({Σ Σ}_{i i = = 11}^{m m} {S S}_{i i}^{* *}))} - - - - - - ((66))$

式(6)中，Z_l-i为第i台机组WT_i所在支路中其有功功率P_w流出方向上的线路阻抗。In formula (6), Z _li is the line impedance in the outflow direction of the active power P _w in the branch where the i-th unit WT _i is located.

与已有技术相比，本发明有益效果体现在：Compared with the prior art, the beneficial effects of the present invention are reflected in:

1、本发明以机组撬棒保护动作情况为机群分类原则建立双馈风电场等值模型，将机组在电网侧发生三相短路故障后1ms时刻的端电压跌落值依次与其相对应的修正前和经过修正后的端电压跌落临界值进行两轮判别比较，能够有效区分风电场内部撬棒保护动作和撬棒保护未动作的机组并将其划归至相应机群，提高了风电场等值模型对机组撬棒保护动作的等效正确率，是一种等值机组数目较少、实现较方便、更加准确拟合风电场功率外特性的双馈风电场等值建模方法。1. The present invention establishes a doubly-fed wind farm equivalent model based on the crowbar protection action of the unit as the group classification principle, and compares the terminal voltage drop value of the unit at 1 ms after a three-phase short-circuit fault occurs on the power grid side to its corresponding pre-correction and After two rounds of discriminant comparison of the corrected terminal voltage drop critical value, it can effectively distinguish the crowbar protection action and the crowbar protection non-action unit in the wind farm and classify them into the corresponding cluster, which improves the wind farm equivalent model. The equivalent accuracy rate of the unit crowbar protection action is an equivalent modeling method for double-fed wind farms with fewer equivalent units, more convenient implementation, and more accurate fitting of the external characteristics of wind farm power.

2、本发明将机组撬棒保护的动作判据由机组转子电流简化为故障后机组端电压跌落临界值，其值求取方便，易于撬棒保护动作的判别，兼顾了判别指标表达的简洁性和执行的高效性。2. The present invention simplifies the operation criterion of the unit crowbar protection from the unit rotor current to the critical value of the terminal voltage drop of the unit after a fault, which is convenient to obtain and easy to discriminate the action of the crowbar protection, taking into account the simplicity of the expression of the discrimination index and execution efficiency.

3、本发明考虑到风电场内部拓扑结构对机组端电压跌落临界值影响，通过引入虚拟线路阻抗对机组端电压跌落临界值进行修正，提高了机组撬棒保护动作判别的准确度。3. The present invention takes into account the influence of the internal topological structure of the wind farm on the critical value of the voltage drop at the unit terminal, and corrects the critical value of the voltage drop at the unit terminal by introducing a virtual line impedance, thereby improving the accuracy of the judgment of the crowbar protection action of the unit.

附图说明Description of drawings

图1为本发明计及撬棒保护的双馈风电场等值建模流程图；Fig. 1 is the equivalent modeling flowchart of the doubly-fed wind farm taking crowbar protection into account in the present invention;

图2为本发明中双馈风电场网络拓扑结构图；Fig. 2 is the topological structure diagram of doubly-fed wind farm network in the present invention;

图3为本发明中确定机组修正前电压跌落临界值流程图；Fig. 3 is the flow chart of determining the voltage drop critical value before unit correction in the present invention;

图4为本发明中机组单机无穷大并网结构图；Fig. 4 is the structure diagram of unit single unit infinite grid connection in the present invention;

图5为本发明中单位功率因数运行时机组修正前的端电压跌落临界值三维坐标图；Fig. 5 is a three-dimensional coordinate diagram of the terminal voltage drop critical value before the unit is corrected when the unit power factor is running in the present invention;

图6为本发明中风电场链式结构图；Fig. 6 is a chain structure diagram of a wind farm in the present invention;

图7为本发明中双馈风电场等值模型结构图；Fig. 7 is a doubly-fed wind farm equivalent model structural diagram in the present invention;

图8为本发明中单位功率因数运行时双馈风电场有功功率动态响应过程；Fig. 8 is the dynamic response process of the active power of the doubly-fed wind farm when operating at unit power factor in the present invention;

图9为本发明中单位功率因数运行时双馈风电场无功功率动态响应过程；Fig. 9 is the reactive power dynamic response process of the doubly-fed wind farm during unit power factor operation in the present invention;

具体实施方式Detailed ways

如图1所示，本实施例中计及撬棒保护的双馈风电场等值建模方法按如下步骤进行：As shown in Figure 1, in this embodiment, the equivalent modeling method of DFIG considering crowbar protection is carried out as follows:

步骤1、根据气象数据惯例，将0°-360°的风向均分为16个区域，风速的间隔步长取为1m/s，对风电场全年的实测风资源信息进行统计，风资源信息包括风电场风速的大小和风向，建立风电场风资源信息数据库。Step 1. According to the meteorological data convention, the wind direction of 0°-360° is divided into 16 areas, and the interval step of wind speed is set to 1m/s, and the actual wind resource information of the wind farm throughout the year is counted, and the wind resource information Including the wind speed and wind direction of the wind farm, a wind resource information database of the wind farm is established.

步骤2、基于双馈风电场的网络拓扑结构和模型参数，利用DIgSILENT/Power Factory软件平台搭建风电场详细模型。Step 2. Based on the network topology and model parameters of the double-fed wind farm, use the DIgSILENT/Power Factory software platform to build a detailed model of the wind farm.

本步骤2中风电场是由多台型号相同的机组组成，机组的额定端电压为U_N，经机端变压器升压至U_MV后通过架空线路接于中压母线，再经过风电场主变压器升压至U_HV，最终通过双回线路接入电网；相邻机组间的间隔为s；双馈风电场的网络拓扑结构如图2所示，模型参数如表1所示。当机组的转子电流大于撬棒保护门槛值的持续时间超过1ms，则撬棒保护信号触发，2ms后撬棒电路投入。风电场详细模型包括风电场内各机组的单机模型、机组间线路模型、机端变压器以及主变压器模型。In step 2, the wind farm is composed of multiple units of the same model. The rated terminal voltage of the units is U _N , which is boosted to U _MV by the machine-side transformer and connected to the medium-voltage bus through an overhead line, and then through the main transformer of the wind farm. The voltage is boosted to U _HV , and finally connected to the grid through a double-circuit line; the interval between adjacent units is s; the network topology of the doubly-fed wind farm is shown in Figure 2, and the model parameters are shown in Table 1. When the rotor current of the unit is greater than the crowbar protection threshold for more than 1ms, the crowbar protection signal is triggered, and the crowbar circuit is activated after 2ms. The detailed model of the wind farm includes the stand-alone model of each unit in the wind farm, the line model between units, the transformer at the machine end and the main transformer model.

步骤3、设定机组的运行功率因数，从风资源信息数据库中随机读入一组风电场的风速信息，依据机组的位置分布和尾流效应计算推导出各台机组的输入风速，由输入风速对应确定各台机组的有功功率P_w，完成动态仿真前模型的潮流初始化；一组风电场的风速信息是指在机组切入风速v_in和切除风速v_out范围内的某一风速大小和0°到360°范围内某一风速方向的组合风速信息；机组为双馈风电机组。Step 3. Set the operating power factor of the unit, randomly read a group of wind speed information of the wind farm from the wind resource information database, and calculate and deduce the input wind speed of each unit according to the position distribution of the unit and the wake effect. The input wind speed Correspondingly determine the active power P _w of each unit, and complete the power flow initialization of the model before dynamic simulation; the wind speed information of a group of wind farms refers to a certain wind speed within the range of cut-in wind speed v _in and cut-off wind speed v _out of the unit and 0° Combined wind speed information of a certain wind speed direction within the range of 360°; the unit is a double-fed wind turbine unit.

本步骤3中各机组的输入风速按以下过程计算：In this step 3, the input wind speed of each unit is calculated according to the following process:

式(1)中，v_k为上游机组WT_k的输入风速；r为机组圆形扫风截面的半径；s_jk为上游机组WT_k和下游机组WT_j的直线距离；C_t为推力系数；推力系数C_t是由机组制造厂家提供的指标，可通过查表获得。In formula (1), v _k is the input wind speed of the upstream unit WT _k ; r is the radius of the circular sweep section of the unit; s _jk is the straight-line distance between the upstream unit WT _k and the downstream unit WT _j ; C _t is the thrust coefficient; The thrust coefficient C _t is an index provided by the unit manufacturer and can be obtained by looking up a table.

本步骤3中机组的有功功率P_w由式(2)计算获得：The active power Pw of the unit in step 3 is calculated by _formula (2):

步骤4、采集风电场内部各台机组稳态运行时的端电压U_s0。Step 4. Collect the terminal voltage U _s0 of each unit in the wind farm when it is running in a steady state.

步骤5、设定0.1s时电网侧发生三相短路故障，150ms后故障消除，采集三相短路故障后1ms时刻各台机组的端电压跌落值U_sk。Step 5. It is set that a three-phase short-circuit fault occurs on the grid side at 0.1 s, and the fault is eliminated after 150 ms, and the terminal voltage drop value U _sk of each unit at 1 ms after the three-phase short-circuit fault is collected.

步骤6、若端电压跌落值U_sk小于修正前的相对应的端电压跌落临界值U₀，则判定机组撬棒保护动作，将撬棒保护动作机组划归至撬棒保护动作机群；反之，则计算该机组的虚拟线路阻抗Z_eq-k。Step 6. If the terminal voltage drop value U _sk is less than the corresponding terminal voltage drop critical value U ₀ before correction, it is determined that the crowbar protection action of the unit is determined, and the crowbar protection action unit is classified into the crowbar protection action group; otherwise, Then calculate the virtual line impedance Z _eq-k of the unit.

本步骤6中机组修正前端电压跌落临界值U₀的确定流程如图3所示，具体按如下过程确定：In this step 6, the determination process of the critical value U ₀ of the unit’s corrected front-end voltage drop is shown in Figure 3, and it is specifically determined according to the following process:

(1)、利用DIgSILENT/Power Factory软件平台搭建机组单机无穷大并网模型，模型结构如图4所示，设定机组的运行功率因数；设定机组的有功功率P_w为0MW，稳态运行时的端电压为0.97pu；(1) Use the DIgSILENT/Power Factory software platform to build a single unit infinite grid-connected model. The model structure is shown in Figure 4. Set the operating power factor of the unit; set the active power P _w of the unit to 0MW. The terminal voltage is 0.97pu;

电网侧发生三相短路故障后，机组的转子电流i_r(t)由式(4-1)计算获得。After a three-phase short-circuit fault occurs on the grid side, the rotor current i _r (t) of the unit is calculated by formula (4-1).

$\begin{matrix} {i i}_{r r} ((t t)) = = - - \frac{{L L}_{m m}}{{L L}_{s the s} {L L}_{r r} - - {L L}_{m m}^{22}} [[\frac{{u u}_{sk sk}}{{jω jω}_{11}} + + ((\frac{{u u}_{s the s 00}}{{jω jω}_{11}} - - \frac{{u u}_{sk sk}}{{jω jω}_{11}})) {e e}^{- - j j {ω ω}_{11} t t} {e e}^{- - \frac{t t}{{T T}_{s the s}}}]] \\ + + \frac{{L L}_{s the s}}{{L L}_{s the s} {L L}_{r r} - - {L L}_{m m}^{22}} [[\frac{\frac{22}{33} \frac{11}{{ω ω}_{11} {L L}_{m m} | | {u u}_{s the s 00} | |} (({R R}_{r r} {ω ω}_{11} {L L}_{s the s} {P P}_{s the s} + + {R R}_{s the s} {ω ω}_{s the s} {L L}_{r r} {P P}_{s the s} + + {ω ω}_{11} {ω ω}_{s the s} {L L}_{s the s} {L L}_{r r} {σQ σQ}_{s the s} - - {R R}_{s the s} {R R}_{r r} {Q Q}_{s the s} + + \frac{33}{22} {ω ω}_{s the s} {L L}_{r r} {| | {u u}_{s the s 00} | |}^{22}))}{{jω jω}_{s the s} + + \frac{11}{{T T}_{r r}}} \\ + + \frac{j j \frac{22}{33} \frac{11}{{ω ω}_{11} {L L}_{m m} | | {u u}_{s the s 00} | |} (({ω ω}_{11} {ω ω}_{s the s} {L L}_{s the s} {L L}_{r r} {σP σP}_{s the s} - - {R R}_{s the s} {R R}_{r r} {P P}_{s the s} - - {R R}_{r r} {ω ω}_{11} {L L}_{s the s} {Q Q}_{s the s} - - {R R}_{s the s} {ω ω}_{s the s} {L L}_{r r} {Q Q}_{s the s} - - \frac{33}{22} {R R}_{r r} {| | {u u}_{s the s 00} | |}^{22}))}{{jω jω}_{s the s} + + \frac{11}{{T T}_{r r}}} \\ - - \frac{{AR AR}_{r r} {u u}_{sk sk}}{{jω jω}_{11} (({jω jω}_{s the s} + + \frac{11}{{T T}_{r r}}))} - - \frac{{AR AR}_{r r} (({u u}_{s the s 00} - - {u u}_{sk sk}))}{{jω jω}_{11} ((- - {jω jω}_{r r} + + \frac{11}{{T T}_{r r}} - - \frac{11}{{T T}_{s the s}}))} {e e}^{- - {jω jω}_{11} t t} {e e}^{- - \frac{t t}{{T T}_{s the s}}} + + {C C}_{11} {e e}^{- - {jω jω}_{s the s} t t} {e e}^{- - \frac{t t}{{T T}_{r r}}} \\ = = f f (({R R}_{s the s},, {L L}_{s the s},, {R R}_{r r},, {L L}_{r r},, {L L}_{m m},, {P P}_{s the s},, {Q Q}_{s the s},, {u u}_{sk sk},, {u u}_{s the s 00},, {ω ω}_{11},, {ω ω}_{s the s},, {ω ω}_{r r},, t t)) \end{matrix} t t &GreaterEqual; &Greater Equal; 00 . . - - - - - - ((44 - - 11))$

式(4-1)中，R_s和R_r分别为机组中发电机定转子侧的电阻；L_s、L_r和L_m分别为机组中发电机定转子侧的自感和互感；P_s和Q_s分别为机组定子向电网发出的有功功率和无功功率；u_sk和u_s0分别为故障后机组的端电压跌落矢量和稳态运行时的端电压矢量；ω₁为同步旋转角速度；ω_s为机组的转差角速度；ω_r为机组的转子角速度；为定子衰减时间常数； $T_{r} = (L_{s} L_{r} - L_{m}^{2}) / (L_{s} R_{r}),$ 为转子衰减时间常数；C₁为积分常数； $A = - L_{m} / (L_{s} L_{r} - L_{m}^{2});$ $σ = 1 - L_{m}^{2} / (L_{s} L_{r}) .$ In formula (4-1), R _s and R _r are the resistances on the stator and rotor sides of the generator in the unit, respectively; L _s , L _r and L _m are the self-inductance and mutual inductance on the stator and rotor sides of the generator in the unit, respectively; P _s and Q _s are the active power and reactive power sent by the unit stator to the grid, respectively; us _sk and u _s0 are the terminal voltage drop vector of the unit after a fault and the terminal voltage vector during steady-state operation, respectively; ω ₁ is the synchronous rotation angular velocity; ω _s is the slip angular velocity of the unit; ω _r is the rotor angular velocity of the unit; is the stator decay time constant; $T_{r} = (L_{the s} L_{r} - L_{m}^{2}) / (L_{the s} R_{r}),$ is the rotor decay time constant; C ₁ is the integral constant; $A = - L_{m} / (L_{the s} L_{r} - L_{m}^{2});$ $σ = 1 - L_{m}^{2} / (L_{the s} L_{r}) .$

根据式(4-1)可知，三相短路故障后机组的转子电流i_r(t)由发电机定转子侧的电阻R_s和R_r、发电机定转子侧的自感和互感L_s和L_r及L_m、有功功率P_s和无功功率Q_s、故障后的端电压跌落矢量u_sk、稳态运行时的端电压矢量u_s0以及机组中发电机的转差角转速ω_s和转子角速度ω_r共同决定。对于具有最大功率点追踪特性的机组，其发电机的转差角转速ω_s和转子角速度ω_r与有功功率P_s之间存在对应关系，发电机的转差角转速ω_s和转子角速度ω_r对转子电流i_r(t)的影响可包含在有功功率P_s中。通过机组运行功率因数反映的有功功率P_s和无功功率Q_s之间的关系，无功功率Q_s对转子电流i_r(t)的影响也可以包含在有功功率P_s中。因此，当发电机定转子侧的电阻R_s和R_r，定转子侧的自感和互感L_s、L_r和L_m以及转子电流i_r(t)的门槛值固定时，故障后端电压跌落矢量u_sk仅是机组的有功功率P_s和稳态运行时端电压矢量u_s0的函数。机组采用定子电压矢量定向控制方式运行时，则u_sk＝U_sk，u_s0＝U_s0。综上所述，可以将机组撬棒保护的动作判据指标由转子电流i_r(t)转化为故障后机组的端电压跌落值U_sk，进而确定使撬棒保护恰好动作时的端电压跌落临界值U₀。当故障后机组的端电压跌落值U_sk低于该临界值U₀时撬棒保护动作，反之则不动作。According to formula (4-1), after a three-phase short-circuit fault, the rotor current i _r (t) of the unit is determined by the resistances R _s and R _r on the stator and rotor sides of the generator, the self-inductance and mutual inductance L _s on the stator and rotor sides of the generator and L _r and L _m , active power P _s and reactive power Q _s , terminal voltage drop vector u _sk after a fault, terminal voltage vector u _s0 in steady state operation, and the slip angular speed ω _s and The rotor angular velocity ω _r is jointly determined. For a unit with maximum power point tracking characteristics, there is a corresponding relationship between the generator's slip angular speed ω _s and rotor angular speed ω _r and the active power P _s , and the generator's slip angular speed ω _s and rotor angular speed ω _r The influence on the rotor current i _r (t) can be contained in the active power P _s . Through the relationship between active power P _s and reactive power Q _s reflected by the operating power factor of the unit, the influence of reactive power Q _s on rotor current _ir (t) can also be included in active power P _s . Therefore, when the resistances R _s and R _r on the stator and rotor side of the generator, the self-inductance and mutual inductance L _s , L _r and L _m on the stator and rotor side, and the threshold value of the rotor current _ir (t) are fixed, the fault back-end voltage The drop vector u _sk is only a function of the active power P _s of the unit and the terminal voltage vector u _s0 in steady state operation. When the unit operates in the stator voltage vector directional control mode, then _usk = _Usk , u _s0 = U _s0 . To sum up, the operation criterion index of crowbar protection can be converted from rotor current _ir (t) to the terminal voltage drop value U _sk of the unit after a fault, and then the terminal voltage drop when the crowbar protection just operates can be determined Critical value U ₀ . When the terminal voltage drop value U _sk of the unit after the fault is lower than the critical value U ₀ , the crowbar protection will act, otherwise it will not act.

(3)、在三相短路故障发生后1ms时，若机组的撬棒保护未动作，则通过逐步减小短路接地阻抗Z_f降低机组的端电压跌落值U_sk，直至撬棒保护恰好动作；若通过机组的撬棒保护动作，则逐步增加短路接地阻抗Z_f提升机组的端电压跌落值U_sk，直至撬棒保护恰好不动作；(3) 1 ms after the occurrence of the three-phase short-circuit fault, if the crowbar protection of the unit does not operate, the terminal voltage drop value U _sk of the unit is reduced by gradually reducing the short-circuit grounding impedance Z _f until the crowbar protection just operates; If the crowbar protection action of the unit is activated, then gradually increase the short-circuit grounding impedance Z _f to increase the terminal voltage drop value U _sk of the unit until the crowbar protection just does not operate;

(7)、以有功功率P_w为X轴，稳态运行时端电压U_s0为Y轴，修正前端电压跌落临界值U₀为Z轴，建立机组修正前的端电压跌落临界值三维坐标图。单机无穷大系统中，单位功率因数运行的机组其端电压跌落临界值如图5所示。(7) Take the active power P _w as the X axis, the terminal voltage U _s0 during steady state operation as the Y axis, and the corrected front-end voltage drop critical value U ₀ as the Z axis to establish a three-dimensional coordinate diagram of the terminal voltage drop critical value of the unit before correction . In the single-unit infinite system, the terminal voltage drop critical value of the unit operating at unit power factor is shown in Figure 5.

本步骤6中机组的虚拟线路阻抗Z_eq-k按式(4)计算获得：In this step 6, the virtual line impedance Z _eq-k of the unit is calculated according to formula (4):

风电场内部各台机组端电压的差异主要源于其到中压母线电气距离的不同。与单机无穷大并网结构相比，当电网侧发生三相短路故障时，在如图6所示的风电场链式拓扑结构下单台机组到中压母线电气距离的增加效应使线路阻抗不容忽视。此时，机组与短路点之间串联了线路阻抗。基于式(4)的函数形式，如果把该阻抗并入发电机的定子侧，则发电机定子侧电阻R_s和电抗L_s的改变将影响定子衰减时间常数T_s和转子衰减时间常数T_r，从而影响机组的端电压跌落值U_sk与转子电流i_r(t)的关系。因此，需要对机组的端电压跌落临界值U₀进行修正。The difference in the terminal voltage of each unit in the wind farm is mainly due to the difference in the electrical distance to the medium voltage bus. Compared with the single-unit infinite grid-connected structure, when a three-phase short-circuit fault occurs on the grid side, the increase in the electrical distance between a single unit and the medium-voltage bus in the wind farm chain topology shown in Figure 6 makes the line impedance not negligible . At this time, the line impedance is connected in series between the unit and the short-circuit point. Based on the functional form of equation (4), if the impedance is incorporated into the stator side of the generator, the change of the generator stator side resistance R _s and reactance L _s will affect the stator decay time constant T _s and the rotor decay time constant T _r , thus affecting the relationship between the terminal voltage drop value U _sk of the unit and the rotor current i _r (t). Therefore, it is necessary to correct the terminal voltage drop critical value U ₀ of the unit.

步骤7、将步骤6中计算获得的虚拟线路阻抗Z_eq-k接入机组单机无穷大并网模型的机端变压器和中压母线之间，对机组的端电压跌落临界值U₀进行修正，获得修正后的端电压跌落临界值U₀′。Step 7. Connect the virtual line impedance Z _eq-k calculated in step 6 between the machine-side transformer and the medium-voltage bus of the single unit infinite grid-connected model, and correct the terminal voltage drop critical value U ₀ of the unit to obtain The corrected terminal voltage drop critical value U ₀ ′.

本步骤7中对机组端电压跌落临界值U₀的修正按如下过程进行：In this step 7, the correction of the critical value _U0 of the unit terminal voltage drop is carried out as follows:

(a)、将机组的线路虚拟阻抗Z_eq-k串联接入机组单机无穷大并网模型的机端变压器和中压母线之间。(a) Connect the line virtual impedance Z _eq-k of the unit in series between the machine-end transformer and the medium-voltage bus of the single unit infinite grid-connected model of the unit.

(b)、设定机组的运行功率因数与步骤3中设定的运行功率因数相同，并设定机组有功功率P_w与步骤3中机组有功功率P_w保持相同，调节电网电压使机组稳态运行时的端电压U_s0与步骤4采集到的端电压相同U_s0。(b) Set the operating power factor of the unit to be the same as that set in step 3, and set the active power P _w of the unit to be the same as the active power P _w of the unit in step 3, and adjust the grid voltage to make the unit stable The terminal voltage U _s0 during operation is the same as the terminal voltage U _s0 collected in step 4.

(c)、设定0.1s时电网侧发生三相短路故障，150ms后故障消除。(c) When setting 0.1s, a three-phase short-circuit fault occurs on the grid side, and the fault is eliminated after 150ms.

(d)、在三相短路故障发生后1ms时，若机组的撬棒保护未动作，则通过逐步减小短路接地阻抗Z_f降低机组的端电压跌落值U_sk，直至撬棒保护恰好动作；若撬棒保护动作，则通过逐步增加短路接地阻抗Z_f提升机组的端电压跌落值U_sk，直至撬棒保护恰好不动作。(d) 1 ms after the three-phase short-circuit fault occurs, if the crowbar protection of the unit does not act, then reduce the terminal voltage drop value U _sk of the unit by gradually reducing the short-circuit grounding impedance Z _f until the crowbar protection just operates; If the crowbar protection operates, the terminal voltage drop value U _sk of the unit is increased by gradually increasing the short-circuit grounding impedance Z _f until the crowbar protection just does not operate.

步骤8、若是步骤5采集的机组端电压跌落值U_sk小于步骤7中获得的修正后的端电压跌落临界值U₀′，则判定机组撬棒保护动作，将撬棒保护动作机组划归至撬棒保护动作机群；反之，则判定机组的撬棒保护未动作，将撬棒保护未动作的机组划归至撬棒保护未动作机群。Step 8. If the unit terminal voltage drop value U _sk collected in step 5 is less than the corrected terminal voltage drop critical value U ₀ ′ obtained in step 7, then it is determined that the unit crowbar protection action is performed, and the crowbar protection action unit is assigned to If the crowbar protection operates the group; on the contrary, it is determined that the crowbar protection of the unit has not operated, and the units that have not operated the crowbar protection are classified as the crowbar protection does not operate the group.

步骤9、令：撬棒保护动作机群中包含的机组用第一台等值机组WT_eq1表征，机组所在支路中其有功功率流出方向上的线路阻抗用第一个等值线路阻抗Z_eq1表征，机组的机端变压器用第一台等值机端变压器T_eq1表征；令：撬棒保护未动作机群中包含的机组用第二台等值机组WT_eq2表征，机组所在支路中其有功功率流出方向上的线路阻抗用第二个等值线路阻抗Z_eq2表征，机组的机端变压器用第二台等值机端变压器T_eq2表征；利用第一台等值机组WT_eq1和第二台等值机组WT_eq2、第一个等值线路阻抗Z_eq1和第二个等值线路阻抗Z_eq2、第一台等值机端变压器T_eq1和第二台等值机端变压器T_eq2的等值参数建立计及撬棒保护的双馈风电场等值模型。风电场等值模型的结构如图7所示。Step 9. Order: The units included in the crowbar protection action group are represented by the first equivalent unit WT _eq1 , and the line impedance in the direction of the active power outflow of the branch where the unit is located is represented by the first equivalent line impedance Z _eq1 , the machine-side transformer of the unit is represented by the first equivalent machine-side transformer T _eq1 ; and: the units contained in the crowbar protection group that does not operate are represented by the second equivalent unit WT _eq2 , and the active power of the unit in the branch is The line impedance in the outflow direction is characterized by the second equivalent line impedance Z _eq2 , and the machine-end transformer _of the unit is characterized by the second equivalent machine-end transformer T _eq2 ; The equivalent parameters of the check-in group WT _eq2 , the first equivalent line impedance Z _eq1 and the second equivalent line impedance Z _eq2 , the first equivalent terminal transformer T _eq1 and the second equivalent terminal transformer T _eq2 Establish the equivalent model of doubly-fed wind farm considering crowbar protection. The structure of the wind farm equivalent model is shown in Fig. 7.

本步骤9中等值机组包含的各等值参数：视在功率S_eq、发电机阻抗Z_{G_eq}、惯性时间常数H_eq、轴系刚度系数K_eq、轴系阻尼系数D_eq，以及等值机端变压器包含的各等值参数：视在功率S_{T_eq}、阻抗Z_{T_eq}按式(5)计算获得：The equivalent parameters included in the equivalent unit in step 9: apparent power S _eq , generator impedance Z _{G_eq} , inertial time constant H _eq , shafting stiffness coefficient K _eq , shafting damping coefficient D _eq , and equivalent machine end The equivalent parameters included in the transformer: apparent power S _{T_eq} and impedance Z _{T_eq} are calculated according to formula (5):

为验证本发明中机组修正后的端电压跌落临界值U′₀对撬棒保护动作情况判别的准确性，依据表2设定66台单位功率因数运行的机组的有功功率P_w，0.1s时电网侧发生三相短路，150ms后故障消除。考虑短路接地阻抗分别为Z_f＝j5.5Ω和Z_f＝j7Ω两种情况，此时风电场中压母线电压U_MV相应跌落至其额定值的53.7％和55.7％。将机组的端电压跌落值U_sk分别与其修正前和修正后的端电压跌落临界值U₀和U′₀进行比较，判断撬棒保护的动作情况，并以详细模型的仿真结果为基准，对上述撬棒保护动作情况判断的正确性进行统计，如表3所示。可以看出，当Z_f＝j5.5Ω和Z_f＝j7Ω时，依据修正前的端电压跌落临界值U₀，撬棒保护动作误判的机组台数分别为8台和7台；使用修正后的端电压跌落临界值U′₀，误判台数分别减小至2台和0台。可见，采用修正后的端电压跌落临界值U′₀可以提高对风电场内机组撬棒保护动作情况判别的准确性。In order to verify the accuracy of the corrected terminal voltage drop critical value U′ ₀ of the unit in the present invention on the judgment of the crowbar protection action, the active power P _w of 66 unit power factor operating units is set according to Table 2, when 0.1s A three-phase short circuit occurs on the grid side, and the fault is eliminated after 150ms. Considering the two situations where the short-circuit grounding impedance is Z _f =j5.5Ω and Z _f =j7Ω respectively, the medium-voltage bus voltage U _MV of the wind farm drops to 53.7% and 55.7% of its rated value respectively. Compare the terminal voltage drop value U _sk of the unit with its critical value U ₀ and U′ ₀ of terminal voltage drop before and after correction respectively to judge the action of the crowbar protection, and based on the simulation results of the detailed model, The correctness of the judgment of the above crowbar protection action is counted, as shown in Table 3. It can be seen that when Z _f ＝j5.5Ω and Z _f ＝j7Ω, according to the terminal voltage drop critical value U ₀ before the correction, the number of generating units misjudged by the crowbar protection action is 8 and 7 respectively; The terminal voltage drops critical value U′ ₀ , and the number of misjudged units is reduced to 2 and 0 respectively. It can be seen that using the corrected terminal voltage drop critical value U′ ₀ can improve the accuracy of judging the crowbar protection action of the unit in the wind farm.

为验证本发明中依据撬棒保护动作情况分类建立风电场等值模型的有效性，依据风电场实测风速数据的概率分布随机产生风电场初始风速(风速11m/s，风向0°)。机组采用单位功率因数运行方式。基于撬棒动作分类、风速分类、转速向量分类的风电场等值模型及详细模型在风电场出口处的功率响应过程如图8和图9所示。图8中曲线a为详细模型在风电场出口处的有功功率响应过程，曲线b为基于撬棒动作分类等值模型在风电场出口处的有功功率响应过程，曲线c为基于风速分类等值模型在风电场出口处的有功功率响应过程，曲线d为基于转速向量分类等值模型在风电场出口处的有功功率响应过程。图9中曲线a为详细模型在风电场出口处的无功功率响应过程，曲线b为基于撬棒动作分类等值模型在风电场出口处的无功功率响应过程，曲线c为基于风速分类等值模型在风电场出口处的无功功率响应过程，曲线d为基于转速向量分类等值模型在风电场出口处的无功功率响应过程。In order to verify the validity of the wind farm equivalent model based on the crowbar protection action classification in the present invention, the initial wind speed of the wind farm (wind speed 11m/s, wind direction 0°) is randomly generated according to the probability distribution of the wind farm measured wind speed data. The unit adopts the unit power factor operation mode. Figure 8 and Figure 9 show the power response process of the wind farm equivalent model and detailed model based on crowbar action classification, wind speed classification, and rotational speed vector classification at the outlet of the wind farm. Curve a in Fig. 8 is the active power response process of the detailed model at the exit of the wind farm, curve b is the active power response process of the equivalent model based on the crowbar action classification at the exit of the wind farm, and curve c is the equivalent model based on the wind speed classification The active power response process at the wind farm outlet, curve d is the active power response process at the wind farm outlet based on the rotational speed vector classification equivalent model. Curve a in Fig. 9 is the reactive power response process of the detailed model at the wind farm outlet, curve b is the reactive power response process of the equivalent model based on crowbar action classification at the wind farm outlet, and curve c is based on wind speed classification, etc. The value model is the reactive power response process at the wind farm outlet, and the curve d is the reactive power response process at the wind farm outlet based on the rotational speed vector classification equivalent model.

以风电场详细模型仿真结果为基准，定义等值模型的误差指标为：Based on the simulation results of the wind farm detailed model, the error index of the equivalent model is defined as:

${E E.}_{r r} = = \frac{11}{n no} {Σ Σ}_{i i = = 11}^{n no} | | \frac{{Y Y}_{fi the fi} ((k k)) - - {Y Y}_{i i} ((k k))}{{Y Y}_{i i} ((k k))} | | - - - - - - ((77))$

$δ δ = = \underset{11 \leq \leq i i \leq \leq n no}{max max} | | {Y Y}_{fi the fi} ((k k)) - - {Y Y}_{i i} ((k k)) | | - - - - - - ((88))$

式(7)和式(8)中，Y_i(k)、Y_fi(k)分别为风电场详细模型、等值模型在风电场出口处的电气量；n为采样点数。In Equation (7) and Equation (8), Y _i (k) and Y _fi (k) are the electrical quantities of the wind farm detailed model and the equivalent model at the outlet of the wind farm respectively; n is the number of sampling points.

风电场等值模型对详细模型中机组撬棒动作情况的等效正确率及模型误差指标如表4所示，其中模型误差指标的分析时间范围从故障初始时刻(0.1s)到系统趋于稳定时刻(0.6s)，数据采样步长为0.2ms。故障期间，机组撬棒保护动作与否决定着其对系统的无功支撑能力，进而影响风电场的电压跌落深度以及风电场的有功功率。由于本发明所提方法具有更高的撬棒动作情况等效正确率，因此更好地拟合了风电场的功率外特性。The equivalent accuracy rate and model error index of the wind farm equivalent model to the unit crowbar action in the detailed model are shown in Table 4, where the analysis time range of the model error index is from the initial moment of fault (0.1s) to the system tends to be stable At time (0.6s), the data sampling step is 0.2ms. During the fault period, whether the unit crowbar protection operates or not determines its reactive power support capability to the system, which in turn affects the voltage drop depth of the wind farm and the active power of the wind farm. Since the method proposed in the present invention has a higher equivalent correct rate of crowbar action, it better fits the external power characteristics of the wind farm.

表1 双馈风电机组及线路模型参数Table 1 DFIG and line model parameters

表2 双馈风电机组有功功率Table 2 Active power of doubly-fed wind turbines

表3 撬棒保护动作的双馈风电机组Table 3 DFIG with crowbar protection action

表4 撬棒动作情况的等效正确率及模型误差指标Table 4 Equivalent accuracy rate and model error index of crowbar action

Claims

1. take into account a double-fed fan motor station equivalent modeling method for crow bar protection, it is characterized in that described method is carried out as follows:

Step 1, add up the actual measurement wind-resources information of wind energy turbine set whole year, described wind-resources information comprises size and the wind direction of wind farm wind velocity, sets up wind energy turbine set wind-resources information database;

Step 2, based on the network topology structure of double-fed fan motor field and model parameter, build wind energy turbine set detailed model;

The operate power factor of step 3, setting unit, the wind speed information of one group of wind energy turbine set is read at random from wind-resources information database, position distribution and the wake effect of foundation unit calculate the input wind speed deriving each unit, are determined the active-power P of each unit by input wind speed correspondence _w, complete the trend initialization of model before dynamic simulation; The wind speed information of described one group of wind energy turbine set refers at unit incision wind speed v _inwith excision wind speed v _outthe combination wind speed information of a certain wind speed direction within the scope of a certain wind speed size in scope and 0 ° to 360 °; Described unit is double-fed fan motor unit;

Terminal voltage U when step 4, each the unit steady-state operation in inside of collection wind energy turbine set _s0;

Grid side generation three phase short circuit fault when step 5, setting 0.1s, Failure elimination after 150ms, after gathering three phase short circuit fault, the terminal voltage of 1ms moment each unit falls value U _sk;

If the described terminal voltage of step 6 falls value U _skbe less than the corresponding terminal voltage before correction and fall critical value U ₀, then judge unit crow bar protection act, crow bar protection act unit incorporated into a crow bar protection act group of planes; Otherwise, then the virtual circuit impedance Z of this unit is calculated _eq-k;

Step 7, the virtual circuit impedance Z of acquisition will be calculated in step 6 _eq-kaccess unit Infinite bus power system also, between the machine end transformer of pessimistic concurrency control and middle pressure bus, falls critical value U to the terminal voltage of unit ₀revise, obtain revised terminal voltage and fall critical value U ₀';

If the set end Voltage Drop value U that step 8 step 5 gathers _skbe less than the revised terminal voltage obtained in step 7 and fall critical value U ₀', then judge unit crow bar protection act, crow bar protection act unit is incorporated into a crow bar protection act group of planes; Otherwise, then judge that the crow bar protection of unit is not operating, protected by crow bar not operating unit to incorporate into crow bar and protect a not operating group of planes;

Step 9, order: the equivalent unit WT of the unit First comprised in a crow bar protection act group of planes _eq1characterize, in the branch road of unit place, its active power flows out line impedance first the equivalent line impedance Z on direction _eq1characterize, the machine end transformer First equivalent machine end transformer T of unit _eq1characterize; Order: crow bar protects unit second the equivalent unit WT comprised in a not operating group of planes _eq2characterize, in the branch road of unit place, its active power flows out line impedance second the equivalent line impedance Z on direction _eq2characterize, machine end transformer second equivalent machine end transformer T of unit _eq2characterize; Utilize the equivalent unit WT of described First _eq1with second equivalent unit WT _eq2, first equivalent line impedance Z _eq1with second equivalent line impedance Z _eq2, First equivalent machine end transformer T _eq1with second equivalent machine end transformer T _eq2equivalent parameters set up take into account crow bar protection double-fed fan motor field Equivalent Model.

2. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, it is characterized in that wind energy turbine set described in step 2 is made up of the unit that multiple stage model is identical, the specified terminal voltage of described unit is U _n, through machine end transformer boost to U _mVbe connected to middle pressure bus by overhead transmission line afterwards, then boost to U through wind energy turbine set main-transformer _hV, eventually through double-circuit line access electrical network; S is spaced apart between adjacent unit; Described wind energy turbine set detailed model comprises circuit model, machine end transformer and main-transformer model between the unit model of each unit in wind energy turbine set, unit.

3. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the input wind speed of each unit in step 3 is by following process computation:

Upstream and downstream position relationship between the inner unit of wind direction information determination wind energy turbine set in the wind farm wind velocity information that step a, basis are read in;

The size of the input wind speed of step b, wind energy turbine set inner most upstream unit equals the wind speed size in the wind farm wind velocity information of reading in; Setting downstream unit WT _jinput wind speed v _jonly by its upstream unit WT _kthe impact of wake effect, then downstream unit WT _jinput wind speed v _jcalculate by formula (1) and obtain:

v_{j} = v_{k} [1 - {(\frac{r}{0.08 s_{jk} + r})}^{2} (1 - \sqrt{1 - C_{t}})] - - - (1)

In formula (1), v _kfor upstream unit WT _kinput wind speed; R is the radius that unit circle sweeps wind cross section; s _jkfor upstream unit WT _kwith downstream unit WT _jair line distance; C _tfor thrust coefficient;

Step c, by unit WT _jas upstream unit, determine the input wind speed of its downstream unit according to formula (1), the like, until calculate the input wind speed obtaining the inner each unit of wind energy turbine set.

4. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the active-power P of unit in described step 3 _wcalculated by formula (2) and obtain:

P_{w} = 0.5 ρπ r^{2} c_{p} v_{w}^{3} - - - (2)

In formula (2), ρ is atmospheric density; v _wfor the input wind speed of unit; c _pfor power coefficient; Described power coefficient c _pcalculated by formula (3) and obtain:

\{\begin{matrix} c_{p} = 0.22 (\frac{116}{λ + 0.08 β} - \frac{4.06}{β^{3} + 1} - 0.4 β - 5) e^{- (\frac{12.5}{λ + 0.08 β} - \frac{0.4375}{β^{3} + 1})} \\ λ = \frac{ω_{t} r}{v_{w}} \end{matrix} - - - (3)

In formula (3), λ is the tip speed ratio of unit; β is the propeller pitch angle of unit; ω _tfor the wind turbine rotating speed in unit.

5. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that in step 6, unit correction front voltage falls critical value U ₀determine according to the following procedure:

(1), unit Infinite bus power system is built and pessimistic concurrency control, the operate power factor of setting unit; The active-power P of setting unit _wfor 0MW, terminal voltage during steady-state operation is 0.97pu;

(2), setting 0.1s time grid side generation three phase short circuit fault, Failure elimination after 150ms;

(3), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively short circuit grounding impedance Z is reduced _f, until crow bar protects lucky action; If the crow bar protection act of unit, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

(4), record crow bar protection by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit at active-power P _wwith steady-state operation terminal voltage U _s0correction front voltage corresponding under combined situation falls critical value U ₀;

(5), within the scope of unit operation power 0 ~ 2MW, with 0.1MW be the active-power P that step-length increases unit gradually _w, repeat step (2) to step (4);

(6), within the scope of unit steady-state operation terminal voltage 0.97 ~ 1.07pu, with 0.01pu be the steady-state operation terminal voltage U that step-length increases unit gradually _s0, repeat step (2) to step (5);

(7), with active-power P _wfor X-axis, terminal voltage U during steady-state operation _s0for Y-axis, revise front voltage and fall critical value U ₀for Z axis, the terminal voltage set up before unit correction falls critical value three-dimensional coordinate figure.

6. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the virtual circuit impedance Z of unit in step 6 _eq-kcalculate by formula (4) and obtain:

Z_{eq - k} = \frac{Σ_{l = k}^{N} (Z_{l} Σ_{i = 1}^{l} S_{i}^{*})}{S_{k}^{*}} - - - (4)

In formula (4), Z _lfor unit WT _lits active-power P in the branch road of place _wflow out the line impedance of branch road; be i-th unit WT _ithe conjugate of applied power; N is unit WT _ithe number of units of the unit on a feeder line at place.

7. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that in step 7 set end Voltage Drop critical value U ₀correction carry out according to the following procedure:

(a), by the circuit virtual impedance Z of unit _eq-kseries connection access unit Infinite bus power system between the machine end transformer of pessimistic concurrency control and middle pressure bus;

B the operate power factor of (), setting unit is identical with the operate power factor set in step 3, and set unit active-power P _wwith unit active-power P in step 3 _wkeep identical, adjustment line voltage makes terminal voltage U during unit steady-state operation _s0u identical with the terminal voltage that step 4 collects _s0;

Grid side generation three phase short circuit fault when (c), setting 0.1s, Failure elimination after 150ms;

(d), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively reduce short circuit grounding impedance Z _f, until crow bar protects lucky action; If crow bar protection act, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

E (), record crow bar are protected by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit active-power P _wwith steady-state operation terminal voltage U _s0correction rear end Voltage Drop critical value U ' corresponding under combined situation ₀.

8. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that each equivalent parameters that described step 9 medium value unit comprises: applied power S _eq, generator impedance Z _{g_eq}, inertia time constant H _eq, axis rigidity COEFFICIENT K _eq, axle system ratio of damping D _eq, and each equivalent parameters that equivalent machine end transformer comprises: applied power S _{t_eq}, impedance Z _{t_eq}calculate by formula (5) and obtain:

\{\begin{matrix} S_{eq} = Σ_{i = 1}^{m} S_{i}, Z_{G_eq} = \frac{Z_{Gi}}{m}, H_{eq} = Σ_{i = 1}^{m} H_{i} \\ K_{eq} = Σ_{i = 1}^{m} K_{i}, D_{eq} = Σ_{i = 1}^{m} D_{i} \\ S_{T_eq} = Σ_{i = 1}^{m} S_{Ti}, Z_{T_eq} = \frac{Z_{Ti}}{m} \end{matrix} - - - (5)

In formula (5), S _i, Z _gi, H _i, K _iand D _irepresent the applied power of i-th unit, generator impedance, inertia time constant, axis rigidity coefficient and axle system ratio of damping respectively; S _ti, Z _tibe rated capacity and the impedance of the machine end transformer of i-th unit; M is the number of units of unit in a corresponding group of planes;

The impedance Z of equivalent circuit _l-eqcalculate by formula (6) and obtain:

Z_{l - eq} = \frac{Σ_{i = 1}^{m} Z_{l - i} S_{i}^{*} S_{i}}{(Σ_{i = 1}^{m} S_{i}) (Σ_{i = 1}^{m} S_{i}^{*})} - - - (6)

In formula (6), Z _l-ibe i-th unit WT _iits active-power P in the branch road of place _wflow out the line impedance on direction.