CN103915853B - The acquisition methods of Double-feed wind power field reactive capability - Google Patents

Abstract

The invention provides the acquisition methods of a kind of Double-feed wind power field reactive capability, comprise the following steps: the active power-reactive capability characteristic setting up unit; According to the active power-reactive capability characteristic of double-fed blower fan, linear regression is carried out in sampling, sets up unit active power-reactive capability linear regression model (LRM); The active power of unit-reactive capability regression model is equivalent to the fail safe of the active power-reactive capability characteristic of wind turbine cohort by checking, makes the reactive capability of the grid connected wind power machine group calculated be not more than the summation of the reactive capability of each double-fed fan motor unit; In conjunction with grid-connected blower fan number of units, calculate the double-fed fan motor field reactive capability of grid-connected blower fan number of units; And superpose the reactive capability of Reactive Compensation in Wind Farm equipment and the reactive capability of transformer absorption, calculate final double-fed fan motor field reactive capability.The acquisition methods of Double-feed wind power field provided by the invention reactive capability has higher precision.

Description

Acquisition method of reactive capacity of doubly-fed wind farm

technical field

The invention belongs to the field of new energy power generation in electric power systems, in particular to a method for accurately obtaining the reactive capacity of the doubly-fed wind farm when the doubly-fed wind farm participates in the reactive power optimization of the power grid.

Background technique

Wind power is an intermittent energy source. After grid connection, it will bring many adverse effects to the safe and stable operation of the power grid, especially the problem of reactive power and voltage after wind power grid connection is particularly prominent. Field operation experience shows that reactive power overcompensation and reactive power undercompensation exist at the same time after the wind farm is connected to the grid. When the wind speed is less than 5m/s, the overcompensation phenomenon of the doubly-fed wind farm is more prominent, and the power factor is basically all unqualified. In addition to unqualified power factor, wind farms also generally have problems such as excessive voltage fluctuations at public connection points and frequent voltage flicker, and frequent accidents of large-scale wind turbines going off-grid. Therefore, it is an important and urgent task to establish a reactive power and voltage control system for wind farms, enhance the dispatchability and controllability of wind power reactive power, and incorporate it into the three-level voltage control system of the power grid.

The reactive power and voltage control of the DFIG wind farm incorporated into the three-level voltage control system of the power grid requires the interaction between the power grid and the DFIG wind farm. Under the three-level voltage control system, when the power grid implements reactive power and voltage control for wind farms, it is first necessary to know the adjustable range of reactive power and voltage of the doubly-fed wind farm, and then the reactive power optimization of the regional power grid including the doubly-fed wind farm can be carried out , and then issue reactive voltage control commands to the wind farm. The reactive capacity of the DFIG wind farm is an important factor in determining the adjustable range of the reactive power and voltage of the DFIG wind farm. Therefore, the establishment of a method for obtaining the reactive capacity of the DFIG wind farm that participates in the reactive power optimization of the power grid is to carry out the DFIG wind farm Reactive voltage control is the key problem that needs to be solved first.

However, the current method for obtaining reactive capacity of DFIG wind farms has the following defects. On the one hand, the method based on real-time measurement needs the internal state and parameters of DFIG, and the measurement value is difficult to obtain and the cost is high; In a single period of power optimization, as the wind speed changes, the active power of the DFIG may have changed greatly, so the reactive capacity of the DFIG may have changed greatly, so that through real-time measurement It is unreasonable to determine the reactive power capacity of the DFIG wind farm participating in the reactive power optimization of the power grid by using the method. On the other hand, the method of determining reactive power capacity by using a single equivalent wind farm lacks theoretical basis and detailed derivation and demonstration, and the reliability of the reactive capacity determined by this method cannot be guaranteed.

Contents of the invention

To sum up, it is indeed necessary to provide an acquisition method that can accurately calculate the reactive capacity of a doubly-fed wind farm.

A method for obtaining reactive capacity of a double-fed wind farm, comprising the following steps: step S10, establishing the active power-reactive capacity characteristics of a single machine; step S20, sampling according to the active power-reactive capacity characteristics of the double-fed wind turbine Linear regression, establishing a single-machine active power-reactive capacity linear regression model; step S30, verifying that the single-machine active power-reactive capacity regression model is equivalent to the safety of the active power-reactive capacity characteristics of the wind turbine group, so that the calculation The obtained reactive capacity of the grid-connected wind turbine group is not greater than the sum of the reactive capacities of each DFIG; step S40, combining the number of grid-connected wind turbines, calculating the reactive capacity of the DFIG wind farm for the number of grid-connected wind turbines; and In step S50, the reactive power capacity of the reactive power compensation equipment of the wind farm and the reactive power capacity absorbed by the transformer are superimposed to obtain the final reactive power capacity of the doubly-fed wind farm.

Compared with the prior art, the method for obtaining the reactive capacity of the doubly-fed wind farm provided by the present invention is based on the active power-reactive capacity characteristics of a single machine, and uses a regression model to calculate the reactive capacity of the doubly-fed wind farm, which can accurately calculate the dual-fed wind farm’s reactive capacity. The reactive power capacity of the fed wind farm can be used for reactive power optimization of the power grid.

Description of drawings

Fig. 1 is a flowchart of a method for obtaining reactive capacity of a doubly-fed wind farm provided by the present invention.

Fig. 2 is a flow chart of the calculation process of the reactive capacity of the doubly-fed wind farm provided by the present invention.

detailed description

The technical solution of the present invention will be further described in detail below according to the drawings in the description and in combination with specific embodiments.

Please refer to Fig. 1 and Fig. 2 together, Fig. 1 is the flow chart of the method for obtaining the reactive capacity of the doubly-fed wind farm provided by the present invention, including the following steps:

Step S10, establishing the active power-reactive capacity characteristics of the single machine;

Step S20, according to the active power-reactive capacity characteristics of the doubly-fed fan, sampling and performing linear regression to establish a single-unit active power-reactive capacity linear regression model;

Step S30, verifying the safety of equating the active power-reactive capacity regression model of a single machine to the active power-reactive capacity characteristics of a wind turbine group, so that the calculated reactive capacity of the grid-connected wind turbine group is not greater than that of each wind turbine group The sum of the reactive capacity of the doubly-fed wind turbine;

Step S40, combining the number of grid-connected wind turbines, calculating the reactive capacity of the doubly-fed wind farm for the number of grid-connected wind turbines; and

In step S50, the reactive power capacity of the reactive power compensation equipment of the wind farm and the reactive power capacity absorbed by the transformer are superimposed to obtain the final reactive power capacity of the doubly-fed wind farm.

In step S10, the establishment of the active power-reactive capacity characteristics may mainly include the following steps:

Step S11, determining the operating range of the reactive power at the stator side of the doubly-fed machine.

First, limited by the rated capacity of the doubly-fed machine, the reactive power range of the doubly-fed machine stator side to the grid is calculated as:

(1-a)

(1-b)

In the formula, is the rated capacity of the doubly-fed motor, is the reactive power generated by the stator side of the doubly-fed motor to the grid, is the active power sent by the doubly-fed generator to the grid, is the fan speed.

Secondly, the operating range of active and reactive power on the stator side of the doubly-fed machine is also limited by the maximum current of the converter on the rotor side , the range of reactive power emitted by the stator side of the doubly-fed motor to the grid is calculated as:

(2-a)

(2-b)

To sum up, the ranges of the reactive power capacity on the stator side of the DFIG are as follows:

(3-a)

(3-b)

in is the stator side voltage, is the excitation inductance of the doubly-fed machine, is the stator inductance of the doubly-fed machine, is the synchronous speed.

It can be understood that the expression of the reactive capacity range on the stator side of the doubly-fed electric machine is only a specific embodiment, and can also be determined according to other physical parameters of the wind farm.

Step S12, determining the operating range of reactive power at the rotor side of the doubly-fed machine.

Limited by the capacity of the grid-side converter, the ranges of the reactive power generated by the grid-side converter like the grid are:

(4-a)

(4-b)

In the formula, is the reactive power sent by the grid-side converter to the grid, is the rated capacity of the grid-side converter.

It can be understood that the expression of the reactive power operating range on the rotor side of the doubly-fed generator is only a specific example, and can also be determined according to other physical parameters of the wind farm.

Step S13, according to the operating range of reactive power on the stator side and the rotor side of the doubly-fed machine, the reactive power adjustment range of the doubly-fed wind turbine is obtained:

(5-a)

(5-b)

In the formula, is the inductive reactive capacity of the doubly-fed wind turbine, is the capacitive reactive capacity of the doubly-fed wind turbine; is the inductive reactive capacity of the stator side, is the capacitive reactive capacity of the stator side; is the inductive reactive capacity of the grid-side converter, is the capacitive reactive capacity of the grid-side converter.

Step S14, eliminating the rotational speed in the reactive power adjustment range of the doubly-fed wind turbine, and obtaining the single machine active power-reactive capacity characteristic.

In the maximum power tracking mode, the speed of the doubly-fed wind turbine can be calculated according to the active power output value of the doubly-fed wind turbine:

(6)

k _opt is an inherent constant of the double-fed fan, which can be obtained from the factory parameters of the double-fed fan. Therefore, considering (5-a), (5-b) and (6), the characteristics of the active power-reactive capacity of the doubly-fed wind turbine can be obtained, that is, the function between the reactive capacity and the output value of active power:

(7)

It can be understood that the establishment of the active power-reactive capacity characteristics of the single machine can also be expressed by other physical quantities, and can also include other steps such as correction.

In step S20, by taking several sample points, a linear regression can be performed on the active power and reactive capacity of the single machine to obtain a regression model:

(8)

in is the estimated value of the reactive capacity regression of the doubly-fed machine, is the active power of the doubly-fed machine, , The expression is as follows:

(9)

In the formula,

(10)

(11)

(12)

(13)

Among them, _xi represents the active power of a single fan, is the average active power of the wind turbine group; _yi is the actual value of the reactive capacity sampling of a single fan, It is the average value of the reactive capacity sampling of the wind turbine group.

It can be understood that the manner of linear regression is only a specific example, and linear regression processing can also be performed according to other physical quantities of the wind farm, and correction can also be made according to the actual situation of the wind farm.

In step S30, the safety of equating the active power-reactive capacity regression model of a single machine to the active power-reactive capacity characteristics of a wind turbine group can be verified by the following method:

When the active power value of the double-fed fan in the wind turbine group is any value within the rated capacity, verify whether the following formula is true:

(14)

In the formula, , are the lower limit and upper limit of the equivalent reactive capacity range of the wind turbine group calculated by the regression model, respectively, , Respectively, the first wind turbine group The inductive reactive capacity and capacitive reactive capacity of a doubly-fed wind turbine, is the number of doubly-fed wind turbines in the wind turbine group.

Further, please also refer to FIG. 2 , if (14) is true, go to the next step; if (14) is not true, go back to step S20 for correction.

In step S40, by combining the number of grid-connected wind turbines, the reactive capacity of the doubly-fed wind farm considering the number of grid-connected wind turbines can be established, including the calculation method of capacitive reactive capacity and inductive reactive capacity, as shown in the following formula:

(15)

In the formula, is the total number of DFIGs in the DFIG wind farm, n is the number of grid-connected wind turbines, is the active power output value of the DFIG wind farm, and P represents the active power value of the wind farm.

In step S50, considering the reactive power capacity of the reactive power compensation equipment of the wind farm and the reactive power capacity absorbed by the transformer, the reactive power capacity of the final doubly-fed wind farm is obtained, which mainly includes:

Calculate the reactive power Q _T absorbed by the wind farm transformer:

(16)

In the formula, is the percentage of no-load current; is the percentage of short-circuit impedance; is the operating capacity of the transformer; is the nominal capacity of the transformer.

At the same time, taking the reactive power of the reactive power compensation equipment and other equipment in the wind farm into consideration, the reactive power capacity of the doubly-fed wind farm is calculated, as follows:

(17)

(18)

In the formula, is the inductive reactive capacity of the doubly-fed wind farm, is the capacitive reactive capacity of the doubly-fed wind farm. is the total inductive reactive power capacity of all grid-connected DFIGs in the DFIG wind farm, is the total capacitive reactive power capacity of all grid-connected DFIGs in the DFIG wind farm. is the total inductive reactive capacity, is the total capacitive reactive power capacity of the reactive power compensation equipment in the double-fed wind farm.

The method for obtaining the reactive capacity of the doubly-fed wind farm provided by the present invention is based on the active power-reactive capacity characteristics of a single machine, and uses a regression model to calculate the reactive capacity of the doubly-fed wind farm, which can accurately calculate the reactive power of the doubly-fed wind farm capacity, which can be used for reactive power optimization of the power grid; and compared with the current method of determining the reactive power capacity of DFIG wind farms in equal proportions according to the rated capacity, it has theoretical basis and detailed derivation and demonstration, and improves the reactive power capacity of DFIG wind farms credibility.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included in the scope of protection claimed by the present invention.

Claims (9)

1. A method for obtaining reactive power capacity of a doubly-fed wind farm, comprising the following steps: Step S10, establishing the active power-reactive capacity characteristics of the single machine; Step S20, according to the active power-reactive capacity characteristics of the doubly-fed fan, sampling and performing linear regression to establish a single-unit active power-reactive capacity linear regression model; Step S30, verifying the safety of equating the active power-reactive capacity regression model of a single machine to the active power-reactive capacity characteristics of a wind turbine group, so that the calculated reactive capacity of the grid-connected wind turbine group is not greater than that of each wind turbine group The sum of the reactive capacity of the doubly-fed wind turbine; Step S40, combining the number of grid-connected wind turbines, calculating the reactive capacity of the doubly-fed wind farm for the number of grid-connected wind turbines; and Step S50, superimposing the reactive capacity of the reactive power compensation equipment of the wind farm and the reactive capacity absorbed by the transformer, and calculating the final reactive capacity of the doubly-fed wind farm; Among them, the reactive capacity of the final DFIG wind farm is calculated by the following method: Calculate the reactive power Q _T absorbed by the wind farm transformer: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ In the formula, I ₀ % is the percentage of no-load current; U _k % is the percentage of short-circuit impedance; S is the operating capacity of the transformer; S _n is the nominal capacity of the transformer; Considering the reactive power of the reactive power compensation equipment and other equipment in the wind farm, the reactive power capacity of the doubly-fed wind farm is calculated as: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ;</span>$ In the formula, is the inductive reactive capacity of the doubly-fed wind farm, is the capacitive reactive capacity of the doubly-fed wind farm; is the total inductive reactive power capacity of all grid-connected DFIGs in the DFIG wind farm, is the total capacitive reactive capacity of all grid-connected DFIGs in the DFIG; is the total inductive reactive power capacity of the reactive power compensation equipment in the double-fed wind farm, is the total capacitive reactive power capacity of the reactive power compensation equipment in the double-fed wind farm. 2. the acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 1, is characterized in that, The establishment of active power-reactive capacity characteristics of a single machine includes the following steps: Determine the operating range of reactive power at the stator side of the doubly-fed motor; Determine the operating range of reactive power on the rotor side of the doubly-fed machine; According to the operating range of reactive power on the stator side and the rotor side of the doubly-fed generator, the reactive power adjustment range of the doubly-fed wind turbine is obtained; and The speed in the reactive power adjustment range of the double-fed wind turbine is eliminated, and the single machine active power-reactive capacity characteristic is obtained. 3. The acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 2, is characterized in that, the operating range of doubly-fed machine stator side reactive power is determined by the following method: First, limited by the rated capacity of the doubly-fed machine, the reactive power range of the doubly-fed machine stator side to the grid is calculated as: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span><span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&le;</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ In the formula, S _n is the rated capacity of the DFIG, Q _s is the reactive power generated by the stator side of the DFIG to the grid, P _d is the active power generated by the DFIG to the grid, and ω _r is the fan speed; Secondly, the operating range of active and reactive power on the stator side of the doubly-fed machine is also limited by the maximum current _Irmax of the converter on the rotor side. The range of reactive power sent from the stator side of the doubly-fed machine to the grid is calculated as: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&le;</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; +</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ To sum up, it can be obtained that the ranges of the reactive power capacity on the stator side of the doubly-fed motor are: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; +</span>\sqrt{{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ Where U _s is the voltage on the stator side, L _m is the excitation inductance of the DFIG, L _s is the stator inductance of the DFIG, and ω _s is the synchronous speed. 4. The acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 3, is characterized in that, the operating range of doubly-fed machine rotor side reactive power is determined by the following manner: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ In the formula, Q _g is the reactive power sent by the grid-side converter to the grid, and S _g is the rated capacity of the grid-side converter. 5. The method for obtaining reactive power capacity of doubly-fed wind farms as claimed in claim 4, wherein the reactive power adjustment range of doubly-fed wind turbines is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; )</span>$ ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span>$ In the formula, is the inductive reactive capacity of the doubly-fed wind turbine, is the capacitive reactive capacity of the doubly-fed wind turbine; is the inductive reactive capacity of the stator side, is the capacitive reactive capacity of the stator side; is the inductive reactive capacity of the grid-side converter, is the capacitive reactive capacity of the grid-side converter. 6. The method for obtaining reactive capacity of a doubly-fed wind farm as claimed in claim 5, wherein the rotational speed of the doubly-fed fan is calculated according to the active power output value of the doubly-fed wind turbine: ${\mathrm{\&omega;}}_r=\sqrt[3]{\frac{P_d}{k_{opt}}}---\left(6\right),$ in, Where k _opt is the inherent constant of double-fed fan; Consider (5-a), (5-b) and (6) to obtain the characteristics of the active power-reactive capacity of the DFIG, that is, the function between the reactive capacity and the output value of active power: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; .</span>$ 7. The acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 6, is characterized in that, the doubly-fed wind farm reactive capacity of grid-connected wind turbine number is calculated by the following method: $\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ;</span>$ In the formula, N is the total number of DFIGs in the DFIG wind farm, n is the number of grid-connected wind turbines, _Pwf is the active power output value of the DFIG wind farm, and P represents the active value of the wind farm. 8. The acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 1, is characterized in that, carrying out linear regression to the active power of stand-alone and reactive capacity comprises the steps: make $\widehat{\mathrm{the\; y}}=\hat{a}+\hat{b}x;$ in is the estimated value of the reactive capacity regression of the doubly-fed machine, x is the active power of the doubly-fed machine, The expression is as follows: $\left\{\begin{array}{c}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}\\ \stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}\end{array}\right.<span\; class="notranslate">\; ;</span>$ In the formula, $\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ;</span>$ $\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$ Among them, _xi represents the active power of a single fan, is the average active power of the wind turbine group; _yi is the actual value of the reactive capacity sampling of a single fan, It is the average value of the reactive capacity sampling of the wind turbine group. 9. The acquisition method of doubly-fed wind farm reactive capacity as claimed in claim 1, is characterized in that, the active power-reactive capacity regression model of stand-alone is equivalent to the active power- Security of reactive capacity characteristics: When the active power value of the double-fed fan in the wind turbine group is any value within the rated capacity, verify whether the following formula is true: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}\\ {\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; \&le;</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}\end{array}\right.<span\; class="notranslate">\; ;</span>$ In the formula, are the lower limit and upper limit of the equivalent reactive capacity range of the wind turbine group calculated by the regression model, respectively, are the inductive reactive capacity and capacitive reactive capacity of the i-th DFIG of the wind turbine group, respectively, and n is the number of DFIGs in the wind turbine group.