A calculation method and system for short-circuit current provided by a double-fed wind turbine

Abstract

The present invention discloses a method and system for calculating the short-circuit current provided by a doubly-fed wind turbine, wherein the method comprises: determining the parameters of the doubly-fed wind turbine, determining that the control strategy of the doubly-fed wind turbine is a Crowbar input control strategy; based on the determined doubly-fed wind turbine parameters and the Crowbar input control strategy, calculating the short-circuit impedance Z of the doubly-fed wind turbine f1 , the calculated short-circuit impedance of the doubly-fed wind turbine is converted to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Z of the doubly-fed wind turbine f ; Based on the calculated short-circuit impedance of the doubly-fed wind turbine and the short-circuit impedance Z of the unit transformer t Calculation of short-circuit impedance Z of doubly-fed wind turbine power supply unit s ; Based on the transmission line, transformer impedance admittance parameters; synchronous and asynchronous motor direct-axis subtransient reactance; doubly-fed wind turbine power supply unit short-circuit impedance; rated voltage Un, etc., generate a node admittance matrix Y; based on the node admittance matrix Y, use the triangular decomposition method to obtain the node impedance matrix Z, and based on the node impedance matrix Z, calculate the short-circuit current.

Description

Technical Field

[0001] The present invention relates to the technical field of power system planning and operation, and more specifically, to a calculation method and system for a short-circuit current provided by a doubly-fed wind turbine. Background Art

[0002] In the planning, design and operation control of power systems, short-circuit current calculations are required for selecting system equipment capacity parameters, setting protection device settings and arranging operation modes. The results of short-circuit current calculations have a significant impact on the coordination of system safety and economy. If the calculated results are too large, it is necessary to select larger capacity switchgear equipment and increase investment; it may also cause the short-circuit level evaluation results of many sites to exceed the standard, increase investment in additional current limiting measures, and reduce system operation reliability. If the calculated results are too small, although the investment in primary equipment is saved, the circuit breaker equipment may face the problem of insufficient interrupting capacity, affecting the safety of equipment and systems. With the development of the power grid, the short-circuit current level in load centers and areas with dense power access has been close to the rated interrupting capacity of the circuit breaker, which has put forward higher requirements for the accuracy of short-circuit current calculations.

[0003] In the early stage of wind power and photovoltaic development, the short-circuit current provided to the grid connection point was much smaller than the short-circuit current of the grid connection point itself, which would not affect the safe and stable operation of the system. However, as the capacity and installed scale of such new energy units become larger and larger, and they are characterized by centralized access, the short-circuit current they provide cannot be ignored. As of the end of 2019, the installed capacity of wind power and photovoltaic power generation in the State Grid operating area reached 170 million kilowatts and 179 million kilowatts, respectively, which have reached a considerable proportion in many provinces. It is estimated that by 2020, the installed capacity of wind power will reach 230 million kilowatts and the installed scale of photovoltaic power will reach 260 million kilowatts. The calculation results of the short-circuit current provided by new energy have become one of the main reasons affecting the accuracy of short-circuit current calculation. New energy mainly considers wind turbines and photovoltaics, among which wind turbines include doubly fed wind turbines and direct-drive wind turbines. Researchers have proposed an electromechanical transient model for calculating short-circuit current in response to the short-circuit current provided by direct-drive wind turbines and photovoltaic power stations, but the electromechanical transient model for calculating short-circuit current of doubly fed wind turbines has not yet been studied clearly.

[0004] At present, my country's national standard for short-circuit current calculation, GB / T 15544.1-2013 "Three-phase AC system short-circuit current calculation Part 1: Current calculation", does not mention the calculation method for the short-circuit current provided by renewable energy. The IEC standard and my country's technical regulations for the access of renewable energy to the power system have some involvement in this aspect, but the two have different ways of handling the short-circuit current provided by the doubly-fed wind turbine.

[0005] IEC 60909-0:2016, Short-circuit current calculation in three-phase a.c. system—Part 0: Calculation of currents, proposes a voltage source model for short-circuited doubly-fed wind turbines, and the total positive sequence short-circuit impedance Z of the wind turbine WD , calculated by the following formula (1).

[0006]

[0007] Where U rTHV is the rated voltage of the high-voltage side of the unit transformer; κ WD is the short-circuit current peak calculation coefficient converted to the high-voltage side of the transformer; i WDmax is the highest instantaneous short-circuit current value when the three-phase short circuit occurs on the high-voltage side of the transformer. WD Related to the control and protection parameters of the converter, if κ WD Unknown, 1.7 can be used.

[0008] According to the calculation method of this standard, the short-circuit current provided by the doubly-fed wind turbine is equivalent to that of the traditional asynchronous motor, and the short-circuit impedance is still used to characterize the short-circuit current provided by the doubly-fed wind turbine. Although this method proposes a calculation method for the short-circuit impedance of the doubly-fed wind turbine, its key parameters, such as i WDmax It needs to be given by the manufacturer based on the experimental results. Due to the large number of manufacturers of double-fed wind turbines and the different types of units, the availability of this parameter is poor, resulting in insufficient practicality of this method.

[0009] GB / T 19963-2011 "Technical Regulations for Wind Farm Connection to Power System" proposes that for wind farms with a total installed capacity of one million kilowatts or more, when a three-phase short circuit fault occurs in the power system and causes a voltage drop, each wind farm should have dynamic reactive power support capabilities during the low voltage ride-through process. The dynamic reactive current injected into the power grid by the wind farm should meet the following requirements: ① From the moment the voltage drops at the grid connection point, the response time of the dynamic reactive current shall not exceed 75ms, and the duration shall not be less than 550ms; ② The reactive current I injected into the power system by the wind farm T satisfy:

[0010]

[0011] Where: U g I is the voltage per unit value at the wind farm grid connection point; N is the rated current of the wind farm.

[0012] In summary, there are currently two practical engineering algorithms for short-circuit current. The first one is based on the principle in IEC 60909-0:2016, using a voltage source model. The model properties are correct, and the short-circuit impedance is obtained by calculating the parameters of the induction motor, but the influence of the Crowbar resistor connected in series on the rotor side after the wind turbine is short-circuited is not considered, and the accuracy is poor; the second one is based on the principle of injecting reactive compensation into the system during the low voltage ride-through of the wind turbine in GB / T19963-2011, and uses a current source model, but this model is suitable for electromechanical transient processes after short circuits, and is not suitable for short-circuit current calculations that focus on electromagnetic transient processes tens of milliseconds after a fault.

[0013] Therefore, it is urgent to study the improved method of short-circuit current calculation of doubly fed wind turbines. Summary of the invention

[0014] The technical solution of the present invention provides a method and system for calculating the short-circuit current provided by a doubly-fed wind turbine, so as to solve the problem of how to calculate the short-circuit current provided by the doubly-fed wind turbine.

[0015] In order to solve the above problem, the present invention provides a method for calculating the short-circuit current provided by a doubly-fed wind turbine, the method comprising:

[0016] Determine the parameters of the doubly-fed wind turbine and determine that the control strategy of the doubly-fed wind turbine is the Crowbar input control strategy;

[0017] Based on the determined double-fed wind turbine parameters and Crowbar input control strategy, the short-circuit impedance Zf1 of the double-fed wind turbine is calculated, and the calculated short-circuit impedance of the double-fed wind turbine is converted to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Zf of the double-fed wind turbine;

[0018] The short-circuit impedance Zs of the doubly-fed wind turbine power supply unit is calculated based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer;

[0019] Generate a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactance, double-fed wind turbine power supply unit short-circuit impedance and rated voltage Un;

[0020] A node impedance matrix Z is obtained based on the node admittance matrix Y by using a triangular decomposition method, and a short-circuit current is calculated based on the node impedance matrix Z.

[0021] Preferably, it also includes:

[0022] After calculating the short-circuit current, calculate the high-voltage side voltage of the doubly-fed wind turbine unit transformer;

[0023] When the voltage on the high-voltage side of the doubly-fed wind turbine unit transformer is less than 0.9pu, it is determined that the doubly-fed wind turbine provides short-circuit current.

[0024] Preferably, the calculating of the short-circuit impedance of the doubly-fed wind turbine based on the determined doubly-fed wind turbine parameters and the Crowbar input control strategy comprises:

[0025] Calculate the Crowbar Resistance R CE The calculated value R' calculated to the stator side of the doubly fed wind turbine CE ,

[0026]

[0027] Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor;

[0028] The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is:

[0029] Z fl =R s +jX s +jX m / / (R' r +jX' r +R' CE )

[0030] R s is the stator resistance of the doubly-fed wind turbine, X s Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine;

[0031] R r ′ is the value of rotor resistance after being converted to the stator side, X r ' is the value of rotor reactance after being converted to the stator side.

[0032] Preferably, the calculation of the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the converted short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer comprises:

[0033] Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

[0034] Based on another aspect of the present invention, the present invention provides a calculation system for a short-circuit current provided by a doubly-fed wind turbine, the system comprising:

[0035] The initial unit is used to determine the parameters of the doubly-fed wind turbine and determine that the control strategy of the doubly-fed wind turbine is the Crowbar input control strategy;

[0036] The first calculation unit is used to calculate the short-circuit impedance Zf1 of the doubly fed wind turbine based on the determined doubly fed wind turbine parameters and the Crowbar input control strategy, and convert the calculated short-circuit impedance of the doubly fed wind turbine to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Zf of the doubly fed wind turbine unit transformer;

[0037] The second calculation unit is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer;

[0038] A generating unit, used for generating a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactances, double-fed wind turbine power supply unit short-circuit impedance and rated voltage Un;

[0039] The result unit is used to obtain the node impedance matrix Z based on the node admittance matrix Y by using the triangular decomposition method, and calculate the short-circuit current based on the node impedance matrix Z.

[0040] Preferably, the method further comprises a determining unit, configured to:

[0041] After calculating the short-circuit current, calculate the high-voltage side voltage of the doubly-fed wind turbine unit transformer;

[0042] When the voltage on the high-voltage side of the doubly-fed wind turbine unit transformer is less than 0.9pu, it is determined that the doubly-fed wind turbine provides short-circuit current.

[0043] Preferably, the first calculation unit is used to calculate the short-circuit impedance of the doubly-fed wind turbine based on the determined doubly-fed wind turbine parameters and the Crowbar input control strategy, including:

[0044] Calculate the Crowbar Resistance R CE The calculated value R' calculated to the stator side of the doubly fed wind turbine CE ,

[0045]

[0046] Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor;

[0047] The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is:

[0048] Z fl =R s +jX s +jX m / / (R' r +jX'r +R' CE )

[0049] R s is the stator resistance of the doubly-fed wind turbine, X s Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine;

[0050] R r ′ is the value of rotor resistance after being converted to the stator side, X r ' is the value of the rotor reactance after being referred to the stator side.

[0051] Preferably, the second calculation unit is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer, including:

[0052] Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

[0053] Based on another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the program is executed by a processor, any step of a method for calculating a short-circuit current provided by a doubly-fed wind turbine is implemented.

[0054] According to another aspect of the present invention, the present invention provides an electronic device, characterized in that it includes:

[0055] The computer-readable storage medium described above; and

[0056] One or more processors are used to execute the program in the computer-readable storage medium.

[0057] The technical solution of the present invention provides a calculation method and system for the short-circuit current provided by a doubly fed wind turbine, wherein the method comprises: determining the parameters of the doubly fed wind turbine, and determining that the control strategy of the doubly fed wind turbine is a Crowbar input control strategy; based on the determined doubly fed wind turbine parameters and the Crowbar input control strategy, calculating the short-circuit impedance Zf1 of the doubly fed wind turbine, and returning the calculated short-circuit impedance of the doubly fed wind turbine to the high-voltage side of the unit transformer to obtain the short-circuit impedance Zf of the doubly fed wind turbine after the return; calculating the short-circuit impedance Zs of the doubly fed wind turbine power supply unit based on the returned short-circuit impedance Zf of the doubly fed wind turbine and the short-circuit impedance Zt of the unit transformer; generating a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactances, short-circuit impedance of the doubly fed wind turbine power supply unit, and rated voltage Un; obtaining a node impedance matrix Z based on the node admittance matrix Y by using a triangular decomposition method, and calculating the short-circuit current based on the node impedance matrix Z. The technical solution of the present invention proposes a method for calculating the short-circuit current of a doubly-fed wind turbine. The technical solution of the present invention determines the control mode after a doubly-fed wind turbine fails, and the method for calculating the short-circuit current of a doubly-fed wind turbine is more rigorous. The technical solution of the present invention is applicable to the calculation of short-circuit current in the planning of power grid equipment selection, as well as the calculation of short-circuit current in the operating power grid and the formulation of short-circuit current limiting measures, and has strong robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0059] Figure 1 A flow chart of a method for calculating short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention;

[0060] Figure 2 A schematic diagram of an equivalent circuit of a doubly-fed wind turbine according to a Crowbar input control strategy in a preferred embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of an equivalent circuit of a fan in which the resistance on the rotor side is converted to the stator side according to a Crowbar input control strategy in a preferred embodiment of the present invention;

[0062] Figure 4 A schematic diagram of a power generation unit structure of a doubly-fed wind turbine and a unit transformer according to a preferred embodiment of the present invention;

[0063] Figure 5 A schematic diagram of a PSCAD simulation model of a doubly-fed wind turbine according to a preferred embodiment of the present invention;

[0064] Figure 6 A schematic diagram of a short-circuit calculation result provided by the machine side when a high-voltage side short-circuit fault occurs on the chassis transformer of a doubly-fed wind turbine according to a preferred embodiment of the present invention when the Crowbar resistor takes different values;

[0065] Figure 7 A schematic flow chart of a method for calculating short-circuit current for a doubly-fed wind turbine according to a preferred embodiment of the present invention; and

[0066] Figure 8 A structural 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

[0067] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0068] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0069] Figure 1 A flow chart of a calculation method for short-circuit current provided by a doubly-fed wind turbine according to a preferred embodiment of the present invention. In view of the contradiction between the current requirement for improving the accuracy of short-circuit current calculation in my country and the unclear principle and inaccurate calculation method of the short-circuit current calculation model of doubly-fed wind turbines, the present invention proposes a method for accurately calculating the short-circuit current provided by doubly-fed wind turbines. The implementation method of the present invention can be directly applied to the short-circuit current level verification of power grids in the planning and operation of power grids at all levels, and provide technical support and decision-making basis for the selection of electrical equipment capacity for power grid planning and design schemes, the preliminary demonstration and scheme comparison of major engineering projects, the scientific implementation of power grid planning and design, and the guarantee of safe operation.

[0070] like Figure 1 As shown, the present invention provides a method for calculating the short-circuit current provided by a doubly-fed wind turbine, the method comprising:

[0071] Step 101: Determine the parameters of the doubly-fed wind turbine and determine that the control strategy of the doubly-fed wind turbine is a Crowbar input control strategy;

[0072] The present invention, in step 101-1, first performs basic verification of calculation data, and checks whether the double-fed wind farms in the short-circuit current calculation data are all connected according to the year of commissioning and whether they are all in full-on mode.

[0073] Step 101-2: Calculate the voltage drop on the high-voltage side of the doubly-fed wind turbine unit transformer when a short-circuit fault occurs. If the voltage is greater than or equal to 0.9pu, the doubly-fed wind turbine is not considered to provide short-circuit current; if the voltage is less than 0.9pu, the doubly-fed wind turbine is considered to provide short-circuit current, and enter step 101-3.

[0074] There are two control modes for a doubly fed wind turbine after a short circuit fault. When the voltage drop is small, it is a continuous excitation control mode; when the voltage drops deeply, it switches to the Crowbar input control mode. A small voltage drop in the vicinity of the wind turbine indicates that the fault point is far from the wind turbine and the short-circuit current it provides is small; a deep voltage drop indicates that the fault point is close to the wind turbine and the short-circuit current provided by the wind turbine is large. Based on engineering experience, the present invention selects the high-voltage side voltage of the doubly fed wind turbine unit transformer after the fault as 0.9pu as a reference value. Under normal circumstances, the voltage at this point is 1.0pu. When the fault location is far away from the wind turbine and the voltage drop does not exceed 0.1pu, the short-circuit current it provides to the fault point is slight and its impact can be ignored; when the fault location is close to the wind turbine and the voltage drop is greater than 0.1pu, it can be considered that the voltage drops deeply, and the wind turbine control strategy switches to the Crowbar input control strategy, which provides a large short-circuit current to the fault point and should be considered.

[0075] Step 101-3: Check the parameters of the doubly-fed wind turbine. Check the stator resistance R of the doubly-fed wind turbine in the data. s , stator reactance X s , magnetizing reactance X m , calculated to the rotor resistance R on the stator side r ′、Rotor reactance X r ′、Crowbar resistance R CE Parameters and stator-rotor turns ratio n (or Crowbar resistance R' CE ) is filled in correctly.

[0076] When the doubly-fed wind turbine control strategy is switched to the Crowbar input control strategy, its physical structure and electrical characteristics are equivalent to those of an asynchronous motor, such as Figure 2 shown.

[0077] Figure 2 In, R s , X s , X m , R r , X r , R CE They are the stator resistance, stator reactance, magnetizing reactance, rotor resistance, rotor reactance and Crowbar resistance of the doubly-fed wind turbine respectively.

[0078] The short-circuit current calculation of large power grids generally adopts per unit value, so the stator and rotor parameters generally adopt per unit value. r '、Rotor reactance X r ′、Crowbar resistance R′ CE All parameters should be the values ​​after being converted to the stator side. At this time, we can get Figure 3 Circuit diagram shown.

[0079] Among the rated parameters of the fan, generally, except for the Crowbar resistance R CE Except for the nominal value, all other values ​​will be given as per unit value after being converted to the stator side. CE When calculating, the stator-rotor turns ratio n must also be given. Among them, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine.

[0080] Step 102: Based on the determined parameters of the doubly-fed wind turbine and the Crowbar input control strategy, the short-circuit impedance Zf1 of the doubly-fed wind turbine is calculated, and the calculated short-circuit impedance of the doubly-fed wind turbine is converted to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Zf of the doubly-fed wind turbine;

[0081] Preferably, based on the determined double-fed wind turbine parameters and Crowbar input control strategy, the short-circuit impedance of the double-fed wind turbine is calculated, including:

[0082] Calculate the Crowbar Resistance R CE The calculated value is calculated to the stator side of the doubly fed wind turbine.

[0083]

[0084] Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor;

[0085] The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is:

[0086] Z fl =R s +jX s +jX m / / (R' r +jX' r +R' CE )

[0087] R s is the stator resistance of the doubly-fed wind turbine, Xs Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine;

[0088] R r ′ is the value of rotor resistance after being converted to the stator side, X r ' is the value of the rotor reactance after being referred to the stator side.

[0089] The present invention calculates the short-circuit impedance of the double-fed wind turbine and returns it to the high-voltage side of the unit transformer.

[0090] according to Figure 3 As shown in the figure, the calculation formula of short-circuit impedance of doubly fed wind turbine under Crowbar input control strategy is: fl =R s +jX s +jX m / / (R' r +jX' r +R' CE ).

[0091] The double-fed wind turbine is connected to the grid via a unit transformer. The IEC standard combines it with the unit transformer into one unit to take into account its short-circuit impedance. Figure 4 It is the power supply unit for the doubly-fed wind turbine and the unit transformer.

[0092] The calculation formula for converting the fan's own parameters to the high-voltage side of the unit transformer is:

[0093] Among them, S fN Rated capacity of doubly-fed wind turbine, S tN is the rated capacity of the unit transformer.

[0094] Step 103: Calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer;

[0095] Preferably, the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit is calculated based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer, including:

[0096] Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

[0097] The present invention calculates the short-circuit impedance of a double-fed wind turbine power supply unit.

[0098] Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t , where Z tis the short-circuit impedance of the unit transformer. In order to verify the correctness of the method of obtaining the short-circuit impedance and then calculating the short-circuit current, the present invention conducts a comparative study of the short-circuit current electromagnetic transient simulation analysis and theoretical results. CE Except for the above parameters, the remaining parameters are all basic parameters of asynchronous motor and box transformer, and they have been obtained by literature research and reference to existing parameters of mature models. The Crowbar resistance parameters are obtained by field research. The research results show that the variation range of Crowbar resistance value is basically 0.1Ω~0.6Ω, and the stator-rotor turns ratio of the doubly fed fan adopts the typical value in PSCAD. The present invention is established as follows Figure 5 In the PSCAD simulation model shown, the short-circuit point is selected at the high-voltage side outlet of the double-fed wind turbine unit transformer. At 0.998s, the voltage of one phase at the fault point crosses the zero point. When the setting time is 0.998s, a three-phase short-circuit metallic grounding fault occurs at the fault point, and the fault duration is 0.1s. The main parameters in the model are listed in Table 1.

[0099] Table 1 Main parameters of PSCAD simulation model

[0100]

[0101]

[0102] When the Crowbar resistance value changes from 0.1Ω to 0.6Ω, the high-voltage side of the double-fed wind turbine box is short-circuited. The short-circuit current provided by the machine side is as follows: Figure 6 The simulation results and theoretical calculation results are recorded in Table 2. It can be seen that the short-circuit impact current i provided by the double-fed wind turbine to the short-circuit point is p The theoretical value is 0.1810~0.1189kA, and the simulation value is 0.1630~0.1134kA. The difference between the two is less than 10%, which is within the allowable range of engineering application. Short-circuit current I' k 'Through i p Divided by the fixed coefficient, it is feasible to use the model of asynchronous motor connected in series with Crowbar resistor to simulate the short-circuit situation of the Crowbar input control strategy of the doubly fed wind turbine.

[0103] Under this set of parameters, if the Crowbar resistor is not considered, the theoretical value of the short-circuit impact current provided by the doubly fed wind turbine is 0.1926 kA. It can be seen that compared with considering the Crowbar resistor, the error is between 15% and 41%, and the error is close to 30% when the middle value of the Crowbar resistor is 0.3Ω. It can be seen that the method proposed in the present invention greatly improves the calculation accuracy of the short-circuit current provided by the doubly fed wind turbine.

[0104] Table 2 Differences between calculated and simulated short-circuit current values ​​at 35kV side

[0105] Crowbar resistance value (Ω) Calculated value (kA) Simulation value grid-side current (kA) Difference between simulation value and calculated value (%) 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％

[0106] Step 104: Generate a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactances, double-fed wind turbine power supply unit short-circuit impedance, and rated voltage Un;

[0107] Step 105: derive the node impedance matrix Z based on the node admittance matrix Y by using the triangular decomposition method, and calculate the short-circuit current based on the node impedance matrix Z.

[0108] Preferably, the method further comprises: after calculating the short-circuit current, calculating the high-voltage side voltage of the double-fed wind turbine unit transformer;

[0109] When the voltage on the high-voltage side of the doubly-fed wind turbine unit transformer is less than 0.9pu, it is determined that the doubly-fed wind turbine provides short-circuit current.

[0110] Step 6: Input the line, transformer, generator parameters, etc. to form the node admittance matrix Y -1 , use the triangular decomposition method to solve the node impedance matrix X -1 , calculate the short-circuit current I" k .

[0111] The basic process of this step is the calculation process of the short-circuit current provided by the voltage source. In the input parameters, the relevant parameters of the doubly fed wind turbine are added. In addition, a link for calculating and comparing the high-voltage side voltage of the doubly fed wind turbine unit is added to the calculation process. In the initial calculation, the doubly fed wind turbine is not considered, and the high-voltage side voltage U of the doubly fed wind turbine unit is calculated according to the obtained short-circuit current. ft . If U ft ≥0.9pu, it is considered that the short-circuit current provided by the doubly fed wind turbine to the short-circuit point is limited and close to 0, and the calculation ends; otherwise, the proposed calculation method is used to calculate the short-circuit impedance of the doubly fed wind turbine and the short-circuit impedance of the doubly fed wind turbine power supply unit, and the node admittance matrix Y is calculated again. -1 , node impedance matrix X -1 , calculate the short-circuit current I" k .

[0112] The present invention proposes a method for calculating the short-circuit current provided by a doubly-fed wind turbine. The method is based on the rated parameters of the doubly-fed wind turbine, does not change the basic process of short-circuit current calculation based on the traditional voltage source, and proposes a method for accurately calculating the short-circuit current provided by the doubly-fed wind turbine. This method is further compared with the two existing methods for calculating the short-circuit current provided by the doubly-fed wind turbine in engineering, which verifies the correctness of the voltage source model used by the doubly-fed wind turbine and improves the accuracy of the short-circuit current calculation results. The present invention starts from the investigation of the short-circuit current calculation standards and methods of the doubly-fed wind turbine, refers to the control method after the doubly-fed wind turbine fails, and combines simulation analysis with theoretical derivation, with rigorous logic. From the principle of the implementation method of the present invention, the present invention is suitable for short-circuit current calculation in the planning of power grid equipment selection, and is also suitable for short-circuit current calculation in the operating power grid and the formulation of short-circuit current limiting measures, and has strong robustness.

[0113] Compared with the current engineering calculation method based on IEC 60909-0:2016 principle, which adopts a voltage source model but does not consider the influence of Crowbar resistance, the present invention improves the calculation accuracy by about 30% and the settlement result is more accurate.

[0114] Compared with the current calculation method based on the reactive power compensation principle injected into the system during the low voltage ride-through of wind turbines in GB / T 19963-2011, which adopts the current source model, the present invention adopts the voltage source model and has a correct calculation principle.

[0115] Figure 8 A structural 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. Figure 8 As shown, the present invention provides a calculation system for a short-circuit current provided by a double-fed wind turbine, the system comprising:

[0116] An initial unit 801 is used to determine the parameters of the doubly-fed wind turbine and determine that the control strategy of the doubly-fed wind turbine is a Crowbar input control strategy;

[0117] The first calculation unit 802 is used to calculate the short-circuit impedance Zf1 of the doubly fed wind turbine based on the determined doubly fed wind turbine parameters and Crowbar input control strategy, and convert the calculated short-circuit impedance of the doubly fed wind turbine to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Zf of the doubly fed wind turbine unit transformer.

[0118] Preferably, the first calculation unit 802 is used to calculate the short-circuit impedance Zf1 of the doubly-fed wind turbine based on the determined doubly-fed wind turbine parameters and the Crowbar input control strategy, including:

[0119] Calculate the Crowbar Resistance R CE The calculated value R' calculated to the stator side of the doubly fed wind turbine CE ,

[0120]

[0121] Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor;

[0122] The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is:

[0123] Z fl =R s +jX s +jX m / / (R' r +jX' r +R' CE )

[0124] R s is the stator resistance of the doubly-fed wind turbine, X s Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine;

[0125] R r ′ is the value of rotor resistance after being converted to the stator side, X r ' is the value of rotor reactance after being converted to the stator side.

[0126] The second calculation unit 803 is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer. Preferably, the second calculation unit 803 is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer, including:

[0127] Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

[0128] A generating unit 804 is used to generate a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactances, double-fed wind turbine power supply unit short-circuit impedance and rated voltage Un;

[0129] The result unit 805 is used to obtain the node impedance matrix Z based on the node admittance matrix Y by using the triangular decomposition method, and calculate the short-circuit current based on the node impedance matrix Z.

[0130] Preferably, the system further comprises a determination unit, which is used to: calculate the high-voltage side voltage of the doubly-fed wind turbine unit transformer after calculating the short-circuit current; and determine that the doubly-fed wind turbine provides the short-circuit current when the high-voltage side voltage of the doubly-fed wind turbine unit transformer is less than 0.9pu.

[0131] A calculation system 800 for a doubly-fed wind turbine providing a short-circuit current in a preferred embodiment of the present invention corresponds to a calculation method 100 for a doubly-fed wind turbine providing a short-circuit current in a preferred embodiment of the present invention, and will not be described in detail herein.

[0132] The present invention provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, any step of a calculation method for a short-circuit current provided by a doubly-fed wind turbine is implemented.

[0133] The present invention provides an electronic device, which includes: the above-mentioned computer-readable storage medium; and one or more processors for executing the program in the computer-readable storage medium.

[0134] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0135] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0136] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0137] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0138] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0139] 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 / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of the means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

Claims

1. A method for calculating the short-circuit current provided by a doubly-fed wind turbine, the method comprising: Determine the parameters of the doubly fed wind turbine, the doubly fed wind turbine parameters include: the stator resistance R of the doubly fed wind turbine s , stator reactance X s , magnetizing reactance X m ; By equating the physical structure and electrical characteristics of the doubly fed wind turbine to those of an asynchronous motor, the control strategy of the doubly fed wind turbine is determined to be the Crowbar input control strategy; Based on the determined doubly fed wind turbine parameters and the Crowbar input control strategy, the short-circuit impedance Z of the doubly fed wind turbine is calculated f1 , the calculated short-circuit impedance of the doubly-fed wind turbine is converted to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Z of the doubly-fed wind turbine f ; The calculation of the short-circuit impedance of the doubly-fed wind turbine based on the determined doubly-fed wind turbine parameters and Crowbar input control strategy includes: Calculate the Crowbar Resistance R CE The calculated value R' calculated to the stator side of the doubly fed wind turbine CE , Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor; The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is: Z f1 =R s +jX s +jX m / / (R′ r +jX′ r +R′ CE ) R s is the stator resistance of the doubly-fed wind turbine, X s Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine; R′ r is the value of the rotor resistance after being converted to the stator side, X′ r is the value of rotor reactance after being converted to the stator side; Based on the short-circuit impedance Z of the double-fed wind turbine after calculation f and the short-circuit impedance Z of the unit transformer t Calculation of short-circuit impedance Z of doubly-fed wind turbine power supply unit s ; Generate a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactance, double-fed wind turbine power supply unit short-circuit impedance and rated voltage Un; A node impedance matrix Z is obtained based on the node admittance matrix Y by using a triangular decomposition method, and a short-circuit current is calculated based on the node impedance matrix Z.

2. The method according to claim 1, further comprising: After calculating the short-circuit current, calculate the high-voltage side voltage of the doubly-fed wind turbine unit transformer; When the voltage on the high-voltage side of the doubly-fed wind turbine unit transformer is less than 0.9pu, it is determined that the doubly-fed wind turbine provides short-circuit current.

3. The method according to claim 1, wherein the short-circuit impedance Z of the doubly-fed wind turbine after the calculation is f And the unit transformer short-circuit impedance Z t Calculation of short-circuit impedance Z of doubly-fed wind turbine power supply unit s ,include: Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

4. A calculation system for a short-circuit current provided by a doubly-fed wind turbine, the system comprising: The initial unit is used to determine the parameters of the doubly fed wind turbine, the parameters of the doubly fed wind turbine include: the stator resistance R of the doubly fed wind turbine s , stator reactance X s , magnetizing reactance X m ; By equating the physical structure and electrical characteristics of the doubly-fed wind turbine to those of an asynchronous motor, the control strategy of the doubly-fed wind turbine is determined to be the Crowbar input control strategy; The first calculation unit is used to calculate the short-circuit impedance Zf1 of the doubly fed wind turbine based on the determined doubly fed wind turbine parameters and Crowbar input control strategy, and convert the calculated short-circuit impedance of the doubly fed wind turbine to the high-voltage side of the unit transformer to obtain the converted short-circuit impedance Zf of the doubly fed wind turbine unit transformer; the calculation of the short-circuit impedance of the doubly fed wind turbine based on the determined doubly fed wind turbine parameters and Crowbar input control strategy includes: Calculate the Crowbar Resistance R CE The calculated value R' calculated to the stator side of the doubly fed wind turbine CE , Where n is the turns ratio of the stator and rotor of the doubly fed wind turbine, U n is the rated voltage of the doubly fed wind turbine, S fn is the rated power of the doubly fed wind turbine, R CE is the Crowbar resistor; The calculation formula of short-circuit impedance of doubly-fed wind turbine under Crowbar input control strategy is: Z f1 =R s +jX s +jX m / / (R′ r +jX′ r +R′ CE ) R s is the stator resistance of the doubly-fed wind turbine, X s Doubly-fed wind turbine stator reactance, X m is the magnetizing reactance of the doubly-fed wind turbine; R′ r is the value of the rotor resistance after being converted to the stator side, X′ r is the value of rotor reactance after being converted to the stator side; The second calculation unit is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer; A generating unit, used for generating a node admittance matrix Y based on transmission line parameters, transformer impedance admittance parameters, synchronous and asynchronous motor direct-axis subtransient reactances, double-fed wind turbine power supply unit short-circuit impedance and rated voltage Un; The result unit is used to obtain the node impedance matrix Z based on the node admittance matrix Y by using the triangular decomposition method, and calculate the short-circuit current based on the node impedance matrix Z.

5. The system according to claim 4, further comprising a determining unit, configured to: After calculating the short-circuit current, calculate the high-voltage side voltage of the doubly-fed wind turbine unit transformer; When the voltage on the high-voltage side of the doubly-fed wind turbine unit transformer is less than 0.9pu, it is determined that the doubly-fed wind turbine provides short-circuit current.

6. The system according to claim 4, wherein the second calculation unit is used to calculate the short-circuit impedance Zs of the doubly-fed wind turbine power supply unit based on the calculated short-circuit impedance Zf of the doubly-fed wind turbine and the short-circuit impedance Zt of the unit transformer, comprising: Short-circuit impedance Z of the double-fed wind turbine power supply unit s =Z f +Z t .

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 3 are implemented.

8. An electronic device, characterized in that: include: The computer readable storage medium as claimed in claim 7; as well as One or more processors are used to execute the program in the computer-readable storage medium.

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