阅读说明：本技术 一种双馈风机提供短路电流的计算方法及系统 (Calculation method and system for providing short-circuit current by double-fed fan ) 是由 张玉红 张彦涛 孙华东 陆润钊 贺静波 卜广全 李亚楼 郭强 王雪琼 张健 叶俭 于 2021-06-04 设计创作，主要内容包括：本发明公开了一种双馈风机提供短路电流的计算方法及系统,其中方法包括：确定双馈风机参数,确定双馈风机的控制策略为Crowbar投入控制策略；基于确定的双馈风机参数及Crowbar投入控制策略,计算双馈风机短路阻抗Z-(f1),将计算出的所述双馈风机短路阻抗归算至单元变压器高压侧,获取归算后的双馈风机的短路阻抗Z-(f)；基于归算后的双馈风机短路阻抗及单元变压器的短路阻抗Z-(t)计算双馈风机供电单元短路阻抗Z-(s)；基于输电线路、变压器阻抗导纳参数；同步、异步电动机直轴次暂态电抗；双馈风机供电单元短路阻抗；额定电压Un等,生成节点导纳矩阵Y；基于所述节点导纳矩阵Y利用三角分解法求得节点阻抗矩阵Z,基于所述节点阻抗矩阵Z计算短路电流。(The invention discloses a method and a system for calculating short-circuit current provided by a double-fed fan, wherein the method comprises the following steps: determining parameters of the double-fed fan, and determining that a control strategy of the double-fed fan is a Crowbar input control strategy; calculating the short-circuit impedance Z of the double-fed fan based on the determined parameters of the double-fed fan and the Crowbar input control strategy f1 The calculated short-circuit impedance of the double-fed fan is reduced to the high-voltage side of the unit transformer, and the reduced short-circuit impedance Z of the double-fed fan is obtained f (ii) a Short-circuit impedance Z of double-fed fan and unit transformer based on reduced double-fed fan t Calculating short circuit impedance Z of power supply unit of doubly-fed fan s (ii) a Based on impedance admittance parameters of the transmission line and the transformer; a direct-axis sub-transient reactance of a synchronous motor and an asynchronous motor; short-circuit impedance of a power supply unit of the doubly-fed fan; rated voltage Un, etc., to generate a node admittance matrix Y; solving the node impedance moment by utilizing a trigonometric decomposition method based on the node admittance matrix YAnd the array Z is used for calculating the short-circuit current based on the node impedance matrix Z.)

1. A calculation method for providing short-circuit current by a doubly-fed wind turbine comprises the following steps:

determining parameters of the double-fed fan, and determining that a control strategy of the double-fed fan is a Crowbar input control strategy;

calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, reducing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of a unit transformer, and obtaining the reduced short-circuit impedance Zf of the double-fed fan;

calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer;

generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

and solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y, and calculating the short-circuit current based on the node impedance matrix Z.

2. The method of claim 1, further comprising:

after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit;

and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

3. The method of claim 1, wherein the calculating of the short-circuit impedance of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and a Crowbar input control strategy comprises:

calculation of Crowbar resistance R_CEReturn value R 'to stator side of doubly-fed fan'_CE，

Wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan, U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R′_r+jX′_r+R′_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rThe rotor reactance is the value that is normalized to the stator side.

4. The method of claim 1, wherein the calculating of the short-circuit impedance Zs of the power supply unit of the doubly-fed wind turbine based on the reduced short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer comprises:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

5. A computing system for providing short circuit current for a doubly fed wind turbine, the system comprising:

the initial unit is used for determining parameters of the double-fed fan and determining that a control strategy of the double-fed fan is a Crowbar input control strategy;

the first calculation unit is used for calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, normalizing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of the unit transformer and acquiring the normalized short-circuit impedance Zf of the unit transformer of the double-fed fan;

the second calculation unit is used for calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer;

the generating unit is used for generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

and the result unit is used for solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y and calculating the short-circuit current based on the node impedance matrix Z.

6. The system of claim 5, further comprising a determination unit to:

after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit;

and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

7. The system of claim 5, wherein the first calculating unit is configured to calculate the short-circuit impedance of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and a Crowbar input control strategy, and includes:

calculation of Crowbar resistance R_CEReturn value R 'to stator side of doubly-fed fan'_CE，

Wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan，U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R′_r+jX′_r+R′_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rThe rotor reactance is the value that is normalized to the stator side.

8. The system of claim 5, wherein the second calculating unit is configured to calculate a short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the reduced doubly-fed wind turbine short-circuit impedance Zf and the unit transformer short-circuit impedance Zt, and includes:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 4.

10. An electronic device, comprising:

the computer-readable storage medium recited in claim 9; and

one or more processors to execute the program in the computer-readable storage medium.

Technical Field

The invention relates to the technical field of planning and operation of an electric power system, in particular to a method and a system for calculating short-circuit current provided by a double-fed fan.

Background

In the planning design and operation control of the power system, the selection of system equipment capacity parameters, the setting of protection device fixed values and the arrangement of operation modes are all required to be carried out by short-circuit current calculation. The short-circuit current calculation result has a great influence on the coordination of the safety and the economy of the system. If the calculation result is larger, switching electrical equipment with larger capacity needs to be selected, and the investment is increased; and the evaluation results of the short circuit level of more stations can exceed the standard, and the operation reliability of the system can be reduced while additional investment of current limiting measures is added. If the calculation result is smaller, although one-time equipment investment is saved, the breaker equipment may face the problem of insufficient breaking capacity, which affects the safety of the equipment and the system. With the development of a power grid, the short-circuit current level of a load center and a power supply intensive access area approaches the rated breaking capacity of a circuit breaker, and higher requirements are provided for the calculation accuracy of the short-circuit current.

The development of wind power and photovoltaic is in a dispersed form at the initial stage of development, and the short-circuit current provided for the grid-connected point is far smaller than the self short-circuit current of the grid-connected point, so that the safe and stable operation of the system is not influenced. However, as the capacity and the installed scale of the new energy single machine become larger and larger, and the new energy single machine has the characteristic of centralized access, the short-circuit current provided by the new energy single machine is not negligible. By the end of 2019, installed capacities of wind power generation and photovoltaic power generation in a national grid management area reach 1.70 hundred million kilowatts and 1.79 hundred million kilowatts respectively, a plurality of provinces reach considerable specific gravity, and the installed capacity of the wind power generation reaches 2.3 hundred million kilowatts and the installed scale of the photovoltaic power generation reaches 2.6 hundred million kilowatts in 2020. The calculation result of the short-circuit current provided by the new energy becomes one of the main reasons influencing the calculation accuracy of the short-circuit current. The new energy mainly considers a fan and a photovoltaic, wherein the fan comprises a double-fed fan and a direct-drive fan. The scientific research personnel provide an electromechanical transient model for calculating the short-circuit current aiming at the condition that the direct-drive fan and the photovoltaic power station provide the short-circuit current, but the electromechanical transient model for calculating the short-circuit current of the double-fed fan is not clearly researched.

At present, the national standard for calculating the short-circuit current in China is GB/T15544.1-2013 part 1 for calculating the short-circuit current of a three-phase alternating-current system: current calculation, no method is mentioned for calculating the short circuit current provided by the new energy source. The IEC standard and the technical regulation of the new energy access electric power system in China are related in the aspect, but the processing modes of the IEC standard and the new energy access electric power system for providing the short-circuit current for the double-fed wind turbine are different.

IEC 60909-0: 2016, Short-circuit current calculation in three-phase a.c. system-Part 0: calculation of currents, a voltage source model is adopted when the double-fed fan is in short circuit, and the total positive sequence short-circuit impedance Z of the fan_WDThis is calculated from the following formula (1).

In the formula of U_rTHVSetting the rated voltage for the high-voltage side of the transformer of the unit; kappa_WDCalculating a coefficient for converting a short-circuit current peak value to a high-voltage side of the transformer; i.e. i_WDmaxThe instantaneous value of the highest short-circuit current when the high-voltage side of the transformer is in three-phase short circuit is obtained. The standard states that κ_WDIn relation to the control protection parameters of the converter, if κ_WDUnknown, 1.7 can be used.

According to the standard calculation method, the short-circuit current provided by the double-fed fan is equivalent to that provided by the traditional asynchronous motor, and the short-circuit impedance is still adopted to represent the condition of providing the short-circuit current. Although the method provides a calculation method of the short-circuit impedance of the doubly-fed wind turbine, the key parameters, such as i, of the method_WDmaxThe test result is required to be given by a manufacturer. Due to the fact that the double-fed wind turbine generator manufacturers are numerous, the models of the double-fed wind turbine generator are different, and the availability of the parameters is poor, the practicability of the method is insufficient.

GB/T19963 plus 2011 'technical regulation for accessing wind power plant to power system', proposes a wind power plant group with total installed capacity of more than million kilowatts, and when a three-phase short-circuit fault occurs in a power system and voltage drop is caused, each wind power plant has dynamic reactive power support capability in a low-voltage ride-through process. The dynamic reactive current injected into the grid by the wind farm should meet the following requirements: starting from the voltage drop moment of a grid-connected point, the response time of dynamic reactive current is not more than 75ms, and the duration time is not less than 550 ms; ② reactive current I of wind power plant injection power system_TSatisfies the following conditions:

in the formula: u shape_gThe voltage per unit value of the wind power plant grid-connected point is obtained; i is_NThe rated current of the wind power plant.

In summary, there are two practical short-circuit current engineering algorithms. The first is based on IEC 60909-0: 2016, a voltage source model is adopted, the model property is correct, the short-circuit impedance is obtained through parameter calculation of the induction motor, but the influence of Crowbar resistance connected in series at the rotor side after the fan is short-circuited is not considered, and the accuracy is not good; and the second principle is based on reactive compensation injected into the system in the low voltage ride through process of the fan in GB/T19963-2011, a current source model is adopted, but the model is suitable for the electromechanical transient process after short circuit and is not suitable for short-circuit current calculation in the electromagnetic transient process of tens of milliseconds after a fault is concerned.

Therefore, an improved method for researching the calculation of the short-circuit current of the doubly-fed wind turbine is needed.

Disclosure of Invention

The technical scheme of the invention provides a method and a system for calculating short-circuit current provided by a double-fed fan, which are used for solving the problem of how to calculate the short-circuit current provided by the double-fed fan.

In order to solve the above problem, the present invention provides a method for calculating a short-circuit current provided by a doubly-fed wind turbine, where the method includes:

determining parameters of the double-fed fan, and determining that a control strategy of the double-fed fan is a Crowbar input control strategy;

calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, reducing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of a unit transformer, and obtaining the reduced short-circuit impedance Zf of the double-fed fan;

calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer;

generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

and solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y, and calculating the short-circuit current based on the node impedance matrix Z.

Preferably, the method further comprises the following steps:

after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit;

and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

Preferably, the calculating of the short-circuit impedance of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and the Crowbar input control strategy includes:

calculation of Crowbar resistance R_CEReturn value R 'to stator side of doubly-fed fan'_CE，

Wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan, U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R'_r+jX'_r+R'_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rThe rotor reactance is the value that is normalized to the stator side.

Preferably, the calculating of the short-circuit impedance Zs of the power supply unit of the doubly-fed wind turbine based on the reduced short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer includes:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

Based on another aspect of the present invention, the present invention provides a calculation system for providing short-circuit current for a doubly-fed wind turbine, where the system includes:

the initial unit is used for determining parameters of the double-fed fan and determining that a control strategy of the double-fed fan is a Crowbar input control strategy;

the first calculation unit is used for calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, normalizing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of the unit transformer and acquiring the normalized short-circuit impedance Zf of the unit transformer of the double-fed fan;

the second calculation unit is used for calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer;

the generating unit is used for generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

and the result unit is used for solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y and calculating the short-circuit current based on the node impedance matrix Z.

Preferably, the method further comprises a determining unit, configured to:

after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit;

and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

Preferably, the first calculating unit is configured to calculate the short-circuit impedance of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and a Crowbar input control strategy, and includes:

calculation of Crowbar resistance R_CEReturn value R 'to stator side of doubly-fed fan'_CE，

Wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan, U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R'_r+jX'_r+R'_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rThe rotor reactance is the value that is normalized to the stator side.

Preferably, the second calculating unit is configured to calculate a short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the reduced doubly-fed wind turbine short-circuit impedance Zf and the unit transformer short-circuit impedance Zt, and includes:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

According to another aspect of the present invention, the present invention provides a computer readable storage medium, on which a computer program is stored, wherein the program is executed by a processor to implement the steps of any one of the calculation methods for providing a short-circuit current by a doubly-fed wind turbine.

Based on another aspect of the present invention, the present invention provides an electronic device, comprising:

the computer-readable storage medium described above; and

one or more processors to execute the program in the computer-readable storage medium.

The technical scheme of the invention provides a method and a system for calculating short-circuit current provided by a double-fed fan, wherein the method comprises the following steps: determining parameters of the double-fed fan, and determining that a control strategy of the double-fed fan is a Crowbar input control strategy; calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, reducing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of the unit transformer, and obtaining the reduced short-circuit impedance Zf of the double-fed fan; calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer; generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un; and solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y, and calculating the short-circuit current based on the node impedance matrix Z. The technical scheme of the invention provides a method for calculating the short-circuit current of the double-fed fan, determines the control mode of the double-fed fan after the fault, and is more rigorous for the method for calculating the short-circuit current of the double-fed fan. The technical scheme of the invention is not only suitable for calculating the short-circuit current in planning the selection of the power grid equipment, but also suitable for calculating the short-circuit current in the operating power grid and making short-circuit current limiting measures, and has stronger robustness.

Drawings

A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:

fig. 1 is a flowchart of a calculation method for providing short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention;

fig. 2 is a schematic diagram of an equivalent circuit of a double-fed wind turbine according to a Crowbar input control strategy in the preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of an equivalent circuit of a wind turbine with rotor side resistance reduced to stator side according to a Crowbar input control strategy in a preferred embodiment of the present invention;

FIG. 4 is a schematic diagram of a power generation unit structure of a double-fed fan and a unit transformer according to a preferred embodiment of the invention;

FIG. 5 is a schematic diagram of a PSCAD simulation model of a doubly-fed wind turbine according to a preferred embodiment of the invention;

fig. 6 is a schematic diagram of a short-circuit calculation result provided by a machine side when a double-fed fan box becomes a high-voltage side short-circuit fault when Crowbar resistors take different values according to the preferred embodiment of the present invention;

fig. 7 is a schematic flow chart of a calculation method for providing short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention; and

fig. 8 is a block diagram of a calculation system for providing short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention.

Detailed Description

The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.

Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.

Fig. 1 is a flowchart of a calculation method for providing a short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention. Aiming at the contradiction between the improvement of the requirement on the calculation precision of the short-circuit current in China and the unclear principle and inaccurate calculation method of the calculation model of the short-circuit current of the double-fed fan, the invention provides a method for accurately calculating the short-circuit current provided by the double-fed fan. The embodiment of the invention can be directly applied to power grid short-circuit current level check in power grid planning and operation at all levels, and provides technical support and decision basis for power grid planning design scheme electrical equipment capacity selection, large engineering project early-stage argument and scheme comparison, scientific power grid planning design development and safe operation guarantee.

As shown in fig. 1, the invention provides a method for calculating a short-circuit current provided by a doubly-fed wind turbine, which comprises the following steps:

step 101: determining parameters of the double-fed fan, and determining that a control strategy of the double-fed fan is a Crowbar input control strategy;

the invention, at step 101-1: firstly, basic check of the calculation data is carried out. And in the short-circuit current calculation data, whether the double-fed wind power plant is accessed according to the production year or not and whether the double-fed wind power plant is in a full-open mode or not is checked.

Step 101-2: and calculating the voltage drop condition of the high-voltage side of the transformer of the double-fed fan unit when the short-circuit fault occurs. If the voltage is greater than or equal to 0.9p.u., the double-fed fan is not considered to provide short-circuit current; if the voltage is less than 0.9p.u., considering that the doubly-fed wind turbine provides the short-circuit current, the step 101-3 is performed.

After the double-fed fan is in short circuit fault, two control modes are provided, and when the voltage drop is small, the control mode is a continuous excitation control mode; and when the voltage drops deeply, switching to a Crowbar input control mode. The voltage drop of the fan in the near area is small, which indicates that the fault point is far away from the fan, and the short-circuit current provided by the fan is small; the voltage drops deeply, which shows that the fault point is closer to the fan and the short-circuit current provided by the fan is larger. According to engineering experience, the voltage of the high-voltage side of the doubly-fed fan unit after the fault is selected to be 0.9p.u. as a reference value, and the voltage of the point is 1.0p.u. under normal conditions. When the fault point is far away from the fan and the voltage drop does not exceed 0.1p.u., the short-circuit current provided by the fault point is slight, and the influence of the short-circuit current can be ignored; when the fault point is close to the fan and the voltage drop is greater than 0.1p.u., the voltage is considered to be deeply dropped, the fan control strategy is switched to a Crowbar input control strategy, and the short-circuit current provided by the fault point is large and needs to be considered.

Step 101-3: and (5) checking parameters of the doubly-fed wind turbine. Double-fed fan stator resistance R in inspection data_sStator reactance X_sExciting reactance X_mCalculated to the stator side rotor resistance R'_rAnd rotor reactance X'_rCrowbar resistance R_CEParameter and stator-to-rotor turns ratio n (or Crowbar resistance regression value R'_CE) Whether it is filled in correctly.

When the control strategy of the doubly-fed wind turbine is switched to the Crowbar input control strategy, the physical structure and the electrical characteristics of the doubly-fed wind turbine are equal to those of an asynchronous motor, as shown in fig. 2.

In FIG. 2, R_s、X_s、X_m、R_r、X_r、R_CEThe resistance values are respectively stator resistance, stator reactance, excitation reactance, rotor resistance, rotor reactance and Crowbar resistance of the doubly-fed fan.

The short-circuit current of the large power grid is calculated by a per unit value generally, so the parameters of the stator and the rotor are generally calculated by per unit values. Wherein, the rotor resistance R'_rAnd rotor reactance X'_rCrowbar resistance R'_CEThe parameters should be values that are normalized to the stator side. At this time, a circuit diagram as shown in fig. 3 can be obtained.

In rated parameters of the fan, the resistance R is generally divided from Crowbar_CEThe given value is not named, and other values are given as per unit values after being reduced to the stator side. During Crowbar resistance R_CEDuring the reduction, the turn ratio n of the stator and the rotor is also required to be given,wherein, U_nRated voltage of doubly-fed wind turbine, S_fnThe rated power of the doubly-fed wind turbine is.

Step 102: calculating the short-circuit impedance Zf1 of the double-fed fan based on the determined parameters of the double-fed fan and a Crowbar input control strategy, reducing the calculated short-circuit impedance Zf of the double-fed fan to the high-voltage side of the unit transformer, and obtaining the reduced short-circuit impedance Zf of the double-fed fan;

preferably, calculating the short-circuit impedance of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and a Crowbar input control strategy, and the method comprises the following steps:

calculation of Crowbar resistance R_CEThe reduced value to the stator side of the doubly-fed fan,

wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan, U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R'_r+jX'_r+R'_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rThe rotor reactance is the value that is normalized to the stator side.

The method carries out calculation on the short-circuit impedance of the double-fed fan and reduces the short-circuit impedance to the high-voltage side of the unit transformer.

According to the graph shown in fig. 3, the calculation formula of the short-circuit impedance of the doubly-fed wind turbine under the Crowbar input control strategy is X_f1＝R_s+jX_s+jX_m//(R'_r+jX'_r+R'_CE)。

The double-fed fan is connected to a power grid through the unit transformer. The IEC standard combines it with a cell transformer into one cell to take into account its short circuit impedance. Fig. 4 shows a power supply unit of the doubly-fed wind turbine and the unit transformer.

The formula for reducing the parameters of the fan to the high-voltage side of the unit is as follows:

wherein S is_fNRated capacity, S, of doubly-fed wind turbine_tNIs the rated capacity of the unit transformer.

Step 103: calculating the short-circuit impedance Zs of the power supply unit of the double-fed fan based on the reduced short-circuit impedance Zf of the double-fed fan and the short-circuit impedance Zt of the unit transformer;

preferably, calculating the short-circuit impedance Zs of the power supply unit of the doubly-fed wind turbine based on the reduced short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer, and the method comprises the following steps:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

The method carries out calculation on the short-circuit impedance of the power supply unit of the double-fed fan.

Short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_tWherein Z is_tIs the short-circuit impedance of the cell transformer. In order to verify the correctness of the method for calculating the short-circuit current by calculating the short-circuit impedance, the invention carries out comparison research on short-circuit current electromagnetic transient simulation analysis and theoretical results. Resistance R except for Crowbar_CEBesides, other parameters are basic parameters of the asynchronous motor and the box transformer substation, and a literature investigation mode and a reference mature model are adopted for obtaining the existing parameters. And acquiring the Crowbar resistance parameter by adopting an on-site investigation mode. According to the research result, the change range of the Crowbar resistance value is basically 0.1-0.6 omega, and the turn ratio of the stator and the rotor of the double-fed fan adopts a typical value in PSCAD. According to the method, a PSCAD simulation model shown in figure 5 is established, a short-circuit point is selected at the high-voltage side outlet of a double-fed fan unit transformer, a zero crossing point occurs to one-phase voltage of the fault point when 0.998s is set, a three-phase short-circuit metallic grounding fault occurs to the fault point when 0.998s is set, and the fault duration time is 0.1 s. The main parameters of the model are listed in table 1.

TABLE 1 PSCAD simulation model Main parameter Table

When the Crowbar resistance value is changed from 0.1 omega to 0.6 omega, the double-fed fan box becomes a high-voltage side short-circuit fault, and the short-circuit current provided by the machine side is as shown in fig. 6. The simulation result and the theoretical calculation result are recorded in table 2, and it can be seen that the double-fed fan provides the short-circuit impact current i to the short-circuit point_pThe theoretical value is 0.1810-0.1189 kA, and the simulation value is0.1630-0.1134 kA, the difference between the two is less than 10%, and the method is within the engineering application allowable range. Short-circuit current I'_kThrough i_pThe method is obtained by dividing the voltage of the double-fed fan Crowbar by a fixed coefficient, so that the model of connecting a Crowbar resistor in series into an asynchronous motor is feasible for simulating the short circuit condition of the Crowbar input control strategy of the double-fed fan.

Under the set of parameters, if Crowbar resistance is not considered, the theoretical value of short-circuit impact current provided by the doubly-fed fan is 0.1926 kA. It can be seen that compared with the Crowbar resistor, the error is 15% -41%, the intermediate value of the Crowbar resistor is taken as 0.3 omega, and the error is close to 30%. The method provided by the invention can greatly improve the calculation precision of the short-circuit current provided by the double-fed fan.

TABLE 235 kV side short-circuit current calculation value and simulation value difference

Crowbar resistance value (omega)	Calculated value (kA)	Simulation value net side current (kA)	Simulation value and calculated value difference (%)
				0.1	0.1810	0.1630	9.94％
0.2	0.1682	0.1515	9.93％
				0.3	0.1551	0.1398	9.86％
0.4	0.1422	0.1303	8.37％
				0.5	0.1301	0.1217	6.46％
0.6	0.1189	0.1134	4.63％

Step 104: generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

step 105: and solving a node impedance matrix Z by utilizing a trigonometric decomposition method based on the node admittance matrix Y, and calculating the short-circuit current based on the node impedance matrix Z.

Preferably, the method further comprises the following steps: after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit;

and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

Step 6: inputting the parameters of the line, the transformer, the generator and the like to form a node admittance matrix Y^-1Solving the node impedance matrix X by adopting a triangular decomposition method^-1Calculating the short-circuit current I'_k。

The basic process of the step is a calculation process for providing the short-circuit current by the voltage source, the related parameters of the double-fed fan are added in the input parameters, and in addition, a calculation and comparison link for calculating the voltage of the variable high-voltage side of the double-fed fan unit is added in the calculation process. Initially calculating, without considering the doubly-fed fan, and calculating the voltage U of the variable high-voltage side of the doubly-fed fan unit according to the solved short-circuit current_ft. If U is_ftIf the current is more than or equal to 0.9p.u., the double-fed fan is considered to provide limited short-circuit current close to 0 to the short-circuit point, and the calculation is finished; otherwise, calculating the short-circuit impedance of the double-fed fan and the short-circuit impedance of the power supply unit of the double-fed fan by adopting the calculation method, and calculating the node admittance matrix Y again^-1Node impedance matrix X^-1Calculating the short-circuit current I'_k。

The invention provides a method for calculating short-circuit current provided by a double-fed fan, which is based on rated parameters of the double-fed fan and does not change the basic flow of short-circuit current calculation based on the traditional voltage source. Compared with two existing short-circuit current calculation methods considering the double-fed fan in engineering, the method verifies the correctness of the double-fed fan adopting a voltage source model and improves the accuracy of a short-circuit current calculation result. The method is based on the research of the calculation standard and method of the short-circuit current of the double-fed fan, refers to the control mode of the double-fed fan after the fault, combines the simulation analysis and the theoretical derivation, and has strict logic. From the principle of the implementation mode of the invention, the method is suitable for short-circuit current calculation in planning power grid equipment selection, is also suitable for short-circuit current calculation and short-circuit current limitation measure formulation in an operating power grid, and has stronger robustness.

Compared with the prior art based on IEC 60909-0: 2016, a voltage source model is adopted, but an engineering calculation method of Crowbar resistance influence is not considered, the calculation precision is improved by about 30%, and the settlement result is more accurate.

Compared with the current method based on the principle that reactive compensation is injected into a system in the low-voltage ride through process of the fan in GB/T19963-2011, the method adopts a current source model, adopts a voltage source model, and is correct in calculation principle.

Fig. 8 is a block diagram of a calculation system for providing short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention. As shown in fig. 8, the present invention provides a computing system for providing short-circuit current by a doubly-fed wind turbine, and the system includes:

an initial unit 801, configured to determine parameters of a doubly-fed wind turbine, and determine that a control strategy of the doubly-fed wind turbine is a Crowbar input control strategy;

the first calculating unit 802 is configured to calculate a short-circuit impedance Zf1 of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and a Crowbar input control strategy, reduce the calculated short-circuit impedance of the doubly-fed wind turbine to a high-voltage side of the unit transformer, and obtain the reduced short-circuit impedance Zf of the unit transformer of the doubly-fed wind turbine.

Preferably, the first calculating unit 802 is configured to calculate the short-circuit impedance Zf1 of the doubly-fed wind turbine based on the determined parameters of the doubly-fed wind turbine and the Crowbar input control strategy, and includes:

calculation of Crowbar resistance R_CEReturn value R 'to stator side of doubly-fed fan'_CE，

Wherein n is the turn ratio of the stator and the rotor of the doubly-fed fan, U_nRated voltage of doubly-fed wind turbine, S_fnRated power, R, of doubly-fed wind turbines_CEIs a Crowbar resistance;

the calculation formula of the short-circuit impedance of the double-fed fan under the Crowbar input control strategy is as follows:

X_f1＝R_s+jX_s+jX_m//(R'_r+jX'_r+R'_CE)

R_sfor doubly-fed fan stator resistance, X_sDoubly-fed fan stator reactance, X_mIs a doubly-fed fan excitation reactance;

R′_ris a value X 'after the rotor resistance is reduced to the stator side'_rFor the reactance of the rotor being reduced toStator side rear value.

And the second calculating unit 803 is configured to calculate a short-circuit impedance Zs of the power supply unit of the doubly-fed wind turbine based on the reduced short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer. Preferably, the second calculating unit 803 is configured to calculate a short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the reduced doubly-fed wind turbine short-circuit impedance Zf and the unit transformer short-circuit impedance Zt, and includes:

short-circuit impedance Z of power supply unit of doubly-fed fan_s＝Z_f+Z_t。

The generating unit 804 is used for generating a node admittance matrix Y based on the power transmission line parameters, the transformer impedance admittance parameters, the direct-axis sub-transient reactance of the synchronous and asynchronous motors, the short-circuit impedance of the power supply unit of the double-fed fan and the rated voltage Un;

and a result unit 805 configured to calculate a node impedance matrix Z by using a trigonometric decomposition method based on the node admittance matrix Y, and calculate a short-circuit current based on the node impedance matrix Z.

Preferably, the system further comprises a determining unit for: after the short-circuit current is calculated, calculating the voltage of the high-voltage side of the transformer of the double-fed fan unit; and when the voltage of the high-voltage side of the transformer of the double-fed fan unit is less than 0.9p.u., determining that the double-fed fan provides short-circuit current.

The calculation system 800 for providing a short-circuit current by a doubly-fed wind turbine in the preferred embodiment of the present invention corresponds to the calculation method 100 for providing a short-circuit current by a doubly-fed wind turbine in the preferred embodiment of the present invention, and details thereof are not repeated herein.

The invention provides a computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, realizes the steps of any one of the calculation methods for providing a short-circuit current by a doubly-fed wind turbine.

The present invention provides an electronic device, including: the computer-readable storage medium described above; and one or more processors for executing the program in the computer-readable storage medium.

The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.