Method and device for calculating positive sequence current of doubly-fed wind power generator under short-circuit fault

Abstract

The application discloses a kind of short-circuit fault under the positive sequence current calculation method and device of doubly-fed wind generator. Among them, method includes: judge the difference between the current round voltage of doubly-fed wind generator and last round voltage whether greater than preset threshold value, wherein the current round voltage is the result obtained by current round power flow calculation of the doubly-fed wind generator under short-circuit fault, and the last round voltage is the result obtained by last round power flow calculation of the doubly-fed wind generator under short-circuit fault;In the case where the difference is greater than the preset threshold value, the stator side short-circuit current of the doubly-fed wind generator, the grid side converter short-circuit current and filter circuit short-circuit current are calculated;According to the stator side short-circuit current, the grid side converter short-circuit current and the filter circuit short-circuit current, determine the positive sequence current of the doubly-fed wind generator under short-circuit fault.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment and electrical engineering technology, and more specifically, to a method and apparatus for calculating the positive sequence current of a doubly-fed wind turbine under short-circuit fault. Background Technology

[0002] Doubly fed induction generators (DFIGs) are widely used in large and medium-sized wind farms due to their high wind energy utilization efficiency and ability to achieve decoupled active and reactive power control. However, with the large-scale centralized integration of new energy sources into the grid, the calculation of the contribution of DFIGs to short-circuit current remains incomplete. The short-circuit current of DFIGs is essential for power system design (circuit breakers, busbars, etc.) and the setting of protection devices. Furthermore, the calculation of the short-circuit current of a single DFIG is fundamental to the calculation of short-circuit current for large-scale wind turbine integration into the power grid.

[0003] Existing software for power grid short-circuit calculation and analysis primarily treats doubly-fed induction generators (DFIGs) as equivalent to conventional synchronous motors (i.e., a series connection between voltage sources and impedance), or directly uses simplified models, limiting the short-circuit current contribution to a user-defined level (e.g., 1.2 pu), without considering the complex characteristics of the induction motors and related power electronic controls actually included in the DFIGs. Even when considering the control characteristics of the DFIGs and the transient response characteristics of the induction motors, these are based on time-domain simulations, the results of which cannot be directly used for calculating short-circuit currents in large power grids. Therefore, existing technologies cannot accurately calculate the positive-sequence current contributed by DFIGs under short-circuit fault conditions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and apparatus for calculating the positive sequence current of a doubly fed wind turbine under short-circuit fault conditions.

[0005] According to one aspect of the present invention, a method for calculating the positive sequence current of a doubly-fed induction generator (DFIG) under a short-circuit fault is provided, comprising:

[0006] Determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, wherein the current cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine under short-circuit fault.

[0007] If the difference is greater than the preset threshold, calculate the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine.

[0008] The positive sequence current of the doubly-fed wind turbine under a short-circuit fault is determined based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current.

[0009] Optionally, before determining whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, the method further includes:

[0010] The total short-circuit current obtained from the previous power flow calculation of the doubly fed wind turbine under short-circuit fault is used as the input parameter for the current power flow calculation to determine the voltage of the current cycle.

[0011] The total short-circuit current obtained from the power flow calculation of the previous cycle under short-circuit fault is used as the input parameter for the power flow calculation of the previous cycle to determine the voltage of the previous cycle.

[0012] Optionally, before calculating the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine, the method further includes:

[0013] Determine the voltage drop condition of the doubly-fed wind turbine, wherein the voltage drop condition is divided into minor voltage drop and severe voltage drop;

[0014] The slight voltage drop is used to indicate that the voltage of the doubly fed wind turbine is above a first percentage of the rated voltage after the voltage drop.

[0015] The severe voltage drop is used to indicate that the voltage of the doubly-fed wind turbine is below a first percentage of the rated voltage after the voltage drop.

[0016] Optionally, calculating the stator-side short-circuit current of the doubly-fed wind turbine includes:

[0017] When the voltage drop of the doubly-fed wind turbine is minor, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0018]

[0019] In the formula, i sq For the stator-side q-axis current in a synchronous rotating coordinate system, i sd P represents the stator-side d-axis current in a synchronous rotating coordinate system. DFIG The active power generated by the wind turbine; u sqi is the stator-side q-axis voltage in a synchronously rotating coordinate system; gq For the q-axis current on the mesh side in a synchronous rotating coordinate system, P RSC The active power generated by the rotor converter. u r For rotor voltage, i r Let L be the rotor current, j be the imaginary number, and L be the value of L. s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip Let ω be the slip angular velocity. s To achieve synchronous rotational angular velocity.

[0020] Optionally, calculating the stator-side short-circuit current of the doubly-fed wind turbine includes:

[0021] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0022]

[0023] In the formula, i sq I is the stator-side q-axis current in a synchronously rotating coordinate system. N This is the rated current; i sd U represents the stator-side d-axis current in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; N Rated voltage; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0024] Optionally, calculating the grid-side converter short-circuit current of the doubly-fed wind turbine includes:

[0025] When the voltage drop of the doubly-fed wind turbine is minor, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0026]

[0027] In the formula, i gq P represents the q-axis current on the mesh side in a synchronously rotating coordinate system. RSC The active power generated by the rotor converter; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gd The current on the d-axis of the network side in the synchronous rotating coordinate system.

[0028] Optionally, calculating the grid-side converter short-circuit current of the doubly-fed wind turbine includes:

[0029] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0030]

[0031] In the formula, i sq i is the rotor d-axis current in a synchronous rotating coordinate system; gq For the q-axis current on the mesh side in a synchronously rotating coordinate system; u sq I is the stator-side q-axis voltage in a synchronously rotating coordinate system. gmax I is the maximum current of the grid-side converter. N U is the rated current; k is a control coefficient under the low-voltage breakout strategy; U N This is the rated voltage.

[0032] Optionally, the stator-side short-circuit current includes the stator-side q-axis current and the stator-side d-axis current in a synchronous rotating coordinate system, and the grid-side converter short-circuit current includes the grid-side q-axis current and the grid-side d-axis current in a synchronous rotating coordinate system.

[0033] Furthermore, based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current, the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault is determined, including: calculating the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault using the following formula:

[0034]

[0035] In the formula, i dfigq i is the positive sequence current of the doubly-fed wind turbine generator; sq i represents the stator-side q-axis current in a synchronously rotating coordinate system; sd i represents the stator-side d-axis current in a synchronously rotating coordinate system; gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. gd For the d-axis current on the mesh side in a synchronously rotating coordinate system; ω s C d u sq ω is the short-circuit current of the filter circuit. s For synchronous rotational angular velocity; C d The capacitance value of the filter circuit; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0036] Optionally, the method further includes: when the voltage drop of the doubly-fed wind turbine is a slight voltage drop, calculating the rotor current inside the doubly-fed wind turbine using the following formula:

[0037]

[0038] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; i gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. rq This refers to the rotor q-axis current in the synchronous rotating coordinate system.

[0039] Optionally, the method further includes: when the voltage drop of the doubly-fed wind turbine is a severe voltage drop, calculating the rotor current inside the doubly-fed wind turbine using the following formula:

[0040]

[0041] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq U is the stator-side q-axis voltage in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; U N This is the rated voltage; ω s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; i rq I is the rotor q-axis current in a synchronous rotating coordinate system. rmax This is the maximum rotor current.

[0042] According to another aspect of the present invention, a positive sequence current calculation device for a doubly-fed wind turbine generator under a short-circuit fault is provided, comprising:

[0043] The judgment module is used to determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, wherein the current cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the current cycle under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the previous cycle under short-circuit fault.

[0044] The first calculation module is used to calculate the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine when the difference is greater than the preset threshold.

[0045] The second calculation module is used to determine the positive sequence current of the doubly-fed wind turbine under a short-circuit fault based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current.

[0046] Optionally, the device further includes a voltage determination module for:

[0047] The total short-circuit current obtained from the previous power flow calculation of the doubly fed wind turbine under short-circuit fault is used as the input parameter for the current power flow calculation to determine the voltage of the current cycle.

[0048] The total short-circuit current obtained from the power flow calculation of the previous cycle under short-circuit fault is used as the input parameter for the power flow calculation of the previous cycle to determine the voltage of the previous cycle.

[0049] Optionally, the device also includes a drop condition determination module for:

[0050] Determine the voltage drop condition of the doubly-fed wind turbine, wherein the voltage drop condition is divided into minor voltage drop and severe voltage drop;

[0051] The slight voltage drop is used to indicate that the voltage of the doubly fed wind turbine is above a first percentage of the rated voltage after the voltage drop.

[0052] The severe voltage drop is used to indicate that the voltage of the doubly-fed wind turbine is below a first percentage of the rated voltage after the voltage drop.

[0053] Optionally, the first computing module is specifically used for:

[0054] When the voltage drop of the doubly-fed wind turbine is minor, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0055]

[0056] In the formula, i sq For the stator-side q-axis current in a synchronous rotating coordinate system, i sd P represents the stator-side d-axis current in a synchronous rotating coordinate system. DFIG The active power generated by the wind turbine; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gq For the q-axis current on the mesh side in a synchronous rotating coordinate system, P RSC The active power generated by the rotor converter. u r For rotor voltage, i r Let L be the rotor current, j be the imaginary number, and L be the value of L.s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip Let ω be the slip angular velocity. s To achieve synchronous rotational angular velocity.

[0057] Optionally, the first computing module is specifically used for:

[0058] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0059]

[0060] In the formula, i sq I is the stator-side q-axis current in a synchronously rotating coordinate system. N This is the rated current; i sd U represents the stator-side d-axis current in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; N Rated voltage; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0061] Optionally, the first computing module is specifically used for:

[0062] When the voltage drop of the doubly-fed wind turbine is minor, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0063]

[0064] In the formula, i gq P represents the q-axis current on the mesh side in a synchronously rotating coordinate system. RSC The active power generated by the rotor converter; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gd The current on the d-axis of the network side in the synchronous rotating coordinate system.

[0065] Optionally, the first computing module is specifically used for:

[0066] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0067]

[0068] In the formula, i sq i is the rotor d-axis current in a synchronous rotating coordinate system; gqFor the q-axis current on the mesh side in a synchronously rotating coordinate system; u sq I is the stator-side q-axis voltage in a synchronously rotating coordinate system. gmax I is the maximum current of the grid-side converter. N U is the rated current; k is a control coefficient under the low-voltage breakout strategy; U N This is the rated voltage.

[0069] Optionally, the stator-side short-circuit current includes the stator-side q-axis current and the stator-side d-axis current in a synchronous rotating coordinate system, and the grid-side converter short-circuit current includes the grid-side q-axis current and the grid-side d-axis current in a synchronous rotating coordinate system.

[0070] Furthermore, the second calculation module is specifically used for:

[0071] The positive sequence current of the doubly-fed wind turbine under a short-circuit fault is calculated using the following formula:

[0072]

[0073] In the formula, i dfigq i is the positive sequence current of the doubly-fed wind turbine generator; sq i represents the stator-side q-axis current in a synchronously rotating coordinate system; sd i represents the stator-side d-axis current in a synchronously rotating coordinate system; gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. gd For the d-axis current on the mesh side in a synchronously rotating coordinate system; ω s C d u sq ω is the short-circuit current of the filter circuit. s For synchronous rotational angular velocity; C d The capacitance value of the filter circuit; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0074] Optionally, the device further includes a third calculation module, used to calculate the rotor current inside the doubly-fed wind turbine generator using the following formula when the voltage drop of the doubly-fed wind turbine generator is a slight voltage drop:

[0075]

[0076] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; P DFIGThe active power generated by the wind turbine; i gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. rq This refers to the rotor q-axis current in the synchronous rotating coordinate system.

[0077] Optionally, the device further includes a fourth calculation module, used to calculate the rotor current inside the doubly-fed wind turbine generator using the following formula when the voltage drop condition of the doubly-fed wind turbine generator is a severe voltage drop:

[0078]

[0079] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq U is the stator-side q-axis voltage in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; U N This is the rated voltage; ω s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; i rq I is the rotor q-axis current in a synchronous rotating coordinate system. rmax This is the maximum rotor current.

[0080] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0081] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0082] This invention first determines whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed induction generator (DFIG) wind turbine is greater than a preset threshold. Then, if the difference is greater than the preset threshold, it calculates the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current of the DFIG wind turbine. Finally, based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current, it determines the positive-sequence current of the DFIG wind turbine under a short-circuit fault. This invention considers the short-circuit currents of the stator side, the grid-side converter, and the filter circuit under the control strategy of the DFIG wind turbine. By determining the positive-sequence current of the DFIG wind turbine under a short-circuit fault based on the short-circuit currents of these three circuits, it achieves accurate calculation of the positive-sequence current contributed by the DFIG wind turbine under grid fault conditions. Attached Figure Description

[0083] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0084] Figure 1 This is a flowchart illustrating a method for calculating the positive sequence current of a doubly fed wind turbine under a short-circuit fault, provided in an exemplary embodiment of the present invention.

[0085] Figure 2 This is a schematic diagram of the positive-sequence equivalent model of a doubly fed wind turbine provided in an exemplary embodiment of the present invention;

[0086] Figure 3 This is a schematic diagram of the overall process for calculating the positive sequence current of a doubly fed wind turbine under a short-circuit fault, provided by an exemplary embodiment of the present invention.

[0087] Figure 4 This is a schematic diagram of a dual-ended network provided in an exemplary embodiment of the present invention;

[0088] Figure 5 This is a schematic diagram of the positive sequence current calculation device for a doubly fed wind turbine under a short-circuit fault, provided in an exemplary embodiment of the present invention.

[0089] Figure 6 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. Detailed Implementation

[0090] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0091] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0092] Those skilled in the art will understand that the terms "first," "second," etc., in the embodiments of the present invention are only used to distinguish different steps, devices, or modules, and do not represent any specific technical meaning, nor do they indicate a necessary logical order between them.

[0093] It should also be understood that in the embodiments of the present invention, "multiple" can refer to two or more, and "at least one" can refer to one, two or more.

[0094] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more unless explicitly defined or given contrary instructions in the context.

[0095] Furthermore, the term "and / or" in this invention is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this invention generally indicates that the preceding and following related objects have an "or" relationship.

[0096] It should also be understood that the description of the various embodiments in this invention emphasizes the differences between the various embodiments, and the similarities or similarities can be referred to each other. For the sake of brevity, they will not be described in detail.

[0097] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0098] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0099] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0100] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0101] The embodiments of this invention can be applied to electronic devices such as terminal devices, computer systems, and servers, and can operate together with a wide range of other general-purpose or special-purpose computing system environments or configurations. Examples of well-known terminal devices, computing systems, environments, and / or configurations suitable for use with electronic devices such as terminal devices, computer systems, and servers include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments including any of the above systems, etc.

[0102] Electronic devices such as terminal devices, computer systems, and servers can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, program modules can include routines, programs, object programs, components, logic, data structures, etc., which perform specific tasks or implement specific abstract data types. Computer systems / servers can be implemented in distributed cloud computing environments, where tasks are executed by remote processing devices linked through communication networks. In distributed cloud computing environments, program modules can reside on local or remote computing system storage media, including storage devices.

[0103] Exemplary methods

[0104] Figure 1 This is a flowchart illustrating a method for calculating the positive sequence current of a doubly-fed induction generator (DFIG) under a short-circuit fault, provided in an exemplary embodiment of the present invention. This embodiment can be applied to electronic devices. Figure 1 As shown, the method 100 for calculating the positive sequence current of a doubly-fed induction generator under a short-circuit fault includes the following steps:

[0105] Step 101: Determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly fed wind turbine is greater than a preset threshold.

[0106] Wherein, the current cycle voltage is the result of the power flow calculation of the doubly-fed induction generator under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed induction generator under short-circuit fault.

[0107] In this embodiment of the invention, since doubly-fed induction generators (DFIGs) often have a Chopper device configured at the DC bus to limit the DC voltage and prevent the crowbar circuit from engaging, the converter can provide uninterrupted control when the external power grid of the DFIG experiences a fault. The DFIG is represented by a combination of a controlled current source and impedance. The control effects of the DFIG consider both normal and low-voltage ride-through operation modes, corresponding to slight and severe voltage drops on the stator side. The positive-sequence equivalent model of the DFIG is as follows: Figure 2 As shown.

[0108] Optionally, before determining whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed induction generator (DFIG) is greater than a preset threshold, the method further includes: using the total short-circuit current obtained from the power flow calculation of the DFIG under a short-circuit fault in the previous cycle as the input parameter for the current cycle to perform power flow calculation and determine the current cycle voltage; and using the total short-circuit current obtained from the power flow calculation of the DFIG under a short-circuit fault in the cycle two cycles prior as the input parameter for the previous cycle to perform power flow calculation and determine the previous cycle voltage.

[0109] In an embodiment of the present invention, see Figure 3 As shown, when the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is less than a preset threshold, that is, ... When the power flow calculation has converged, it proves that no further calculation is needed, and the process ends directly. However, if the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed induction generator (DFIG) is not less than a preset threshold, it means the power flow calculation has not converged, and the next cycle of power flow calculation is required. In this case, the positive sequence current of the DFIG needs to be calculated accurately and directly. The calculated positive sequence current It is used as input for the next round of power flow calculation.

[0110] Step 102: If the difference is greater than the preset threshold, calculate the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly fed wind turbine.

[0111] Optionally, before calculating the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine, the method further includes: determining the voltage sag of the doubly-fed wind turbine, wherein the voltage sag is divided into minor voltage sag and severe voltage sag; the minor voltage sag is used to indicate that the voltage of the doubly-fed wind turbine after the sag is above a first percentage of the rated voltage; the severe voltage sag is used to indicate that the voltage of the doubly-fed wind turbine after the sag is below a first percentage of the rated voltage.

[0112] In this embodiment of the invention, in order to accurately calculate the short-circuit current contributed by the doubly-fed induction generator (DFIG) under grid fault conditions, the control strategies of the DFIG under different voltage dip levels are considered. Therefore, before calculating the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the DFIG, it is also necessary to determine the voltage dip conditions of the DFIG.

[0113] The voltage drop of a doubly-fed induction generator (DFIG) is categorized into minor voltage drop and severe voltage drop. In this embodiment of the invention, a voltage drop below a first percentage of the rated voltage after a voltage drop is considered a minor voltage drop, while a voltage drop below a first percentage of the rated voltage after a voltage drop is considered a severe voltage drop.

[0114] For example, but not limited to, the first percentage is 90%. In this embodiment of the invention, a doubly-fed wind turbine is considered to have experienced a minor voltage dip when the voltage after a voltage drop is above 90% of the rated voltage. A doubly-fed wind turbine is considered to have experienced a severe voltage dip when the voltage after a voltage drop is below 90% of the rated voltage.

[0115] Optionally, calculating the stator-side short-circuit current of the doubly-fed wind turbine includes: when the voltage drop of the doubly-fed wind turbine is a slight voltage drop, calculating the stator-side short-circuit current of the doubly-fed wind turbine using the following formula:

[0116]

[0117] In the formula, i sq For the stator-side q-axis current in a synchronous rotating coordinate system, i sd P represents the stator-side d-axis current in a synchronous rotating coordinate system. DFIG The active power generated by the wind turbine; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gq For the q-axis current on the mesh side in a synchronous rotating coordinate system, P RSC The active power generated by the rotor converter. u r For rotor voltage, i r Let L be the rotor current, j be the imaginary number, and L be the value of L. s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip Let ω be the slip angular velocity. s To achieve synchronous rotational angular velocity.

[0118] In this embodiment of the invention, under the condition of a slight voltage drop, the doubly-fed induction generator (DFIG) continues to supply active power to the grid. Therefore, the stator-side short-circuit current of the DFIG can be expressed as:

[0119]

[0120] In the formula, i sq For the stator-side q-axis current in a synchronous rotating coordinate system, i sdP represents the stator-side d-axis current in a synchronous rotating coordinate system. DFIG The active power generated by the wind turbine; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gq For the q-axis current on the mesh side in a synchronous rotating coordinate system, P RSC The active power generated by the rotor converter. u r For rotor voltage, i r Let L be the rotor current, j be the imaginary number, and L be the value of L. s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip Let ω be the slip angular velocity. s To achieve synchronous rotational angular velocity.

[0121] Optionally, calculating the stator-side short-circuit current of the doubly-fed wind turbine includes: when the voltage drop of the doubly-fed wind turbine is a severe voltage drop, calculating the stator-side short-circuit current of the doubly-fed wind turbine using the following formula:

[0122]

[0123] In the formula, i sq I is the stator-side q-axis current in a synchronously rotating coordinate system. N This is the rated current; i sd U represents the stator-side d-axis current in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; N Rated voltage; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0124] In this embodiment of the invention, when a voltage dip fault occurs in the power grid, and the voltage at the connection point of the doubly-fed induction generator (DFIG) drops to below 90% of the rated voltage (e.g., but not limited to the range of 20% to 90%), the DFIG should provide reactive current to support the grid voltage under fault conditions. At this time, the stator-side short-circuit current of the DFIG can be expressed as:

[0125]

[0126] In the formula, i sq I is the stator-side q-axis current in a synchronously rotating coordinate system. N This is the rated current; i sd U represents the stator-side d-axis current in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; N Rated voltage; u sqThis refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0127] Optionally, calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine includes: when the voltage drop of the doubly-fed wind turbine is a slight voltage drop, calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine using the following formula:

[0128]

[0129] In the formula, i gq P represents the q-axis current on the mesh side in a synchronously rotating coordinate system. RSC The active power generated by the rotor converter; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gd The current on the d-axis of the network side in the synchronous rotating coordinate system.

[0130] In this embodiment of the invention, under a slight voltage drop, the doubly-fed induction generator (DFIG) can be considered to still operate at its rated power, with zero reactive power output, and the active power determined by the active power output from the rotor converter side. In this case, the grid-side converter short-circuit current of the DFIG can be expressed as:

[0131]

[0132] In the formula, i gq P represents the q-axis current on the mesh side in a synchronously rotating coordinate system. RSC The active power generated by the rotor converter; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gd The current on the d-axis of the network side in the synchronous rotating coordinate system.

[0133] Optionally, calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine includes: when the voltage drop of the doubly-fed wind turbine is a severe voltage drop, calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine using the following formula:

[0134]

[0135] In the formula, i sq i is the rotor d-axis current in a synchronous rotating coordinate system; gq For the q-axis current on the mesh side in a synchronously rotating coordinate system; u sq I is the stator-side q-axis voltage in a synchronously rotating coordinate system. gmax I is the maximum current of the grid-side converter. N U is the rated current; k is a control coefficient under the low-voltage breakout strategy; U N This is the rated voltage.

[0136] In this embodiment of the invention, under severe voltage dips, the reactive current injected by the rotor converter (RSC) may be insufficient to meet requirements due to inadequate reactive power. In this case, the grid-side converter (GSC) begins to inject reactive current, and the short-circuit current of the grid-side converter of the doubly-fed wind turbine can be expressed as:

[0137]

[0138] In the formula, i sq i is the rotor d-axis current in a synchronous rotating coordinate system; gq For the q-axis current on the mesh side in a synchronously rotating coordinate system; u sq I is the stator-side q-axis voltage in a synchronously rotating coordinate system. gmax I is the maximum current of the grid-side converter. N U is the rated current; k is a control coefficient under the low-voltage breakout strategy; U N This is the rated voltage.

[0139] Step 103: Determine the positive sequence current of the doubly-fed wind turbine under a short-circuit fault based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current.

[0140] Optionally, the stator-side short-circuit current includes the stator-side q-axis current and the stator-side d-axis current in a synchronous rotating coordinate system, and the grid-side converter short-circuit current includes the grid-side q-axis current and the grid-side d-axis current in a synchronous rotating coordinate system.

[0141] Furthermore, based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current, the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault is determined, including: calculating the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault using the following formula:

[0142]

[0143] In the formula, i dfigq i is the positive sequence current of the doubly-fed wind turbine generator; sq i represents the stator-side q-axis current in a synchronously rotating coordinate system; sd i represents the stator-side d-axis current in a synchronously rotating coordinate system; gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. gd For the d-axis current on the mesh side in a synchronously rotating coordinate system; ω s C d u sq ω is the short-circuit current of the filter circuit. s For synchronous rotational angular velocity; Cd The capacitance value of the filter circuit; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0144] In this embodiment of the invention, under a short-circuit fault, the positive-sequence current contributed by the doubly-fed wind turbine is:

[0145]

[0146] In the formula, i dfigq i is the positive sequence current of the doubly-fed wind turbine generator; sq i represents the stator-side q-axis current in a synchronously rotating coordinate system; sd i represents the stator-side d-axis current in a synchronously rotating coordinate system; gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. gd For the d-axis current on the mesh side in a synchronously rotating coordinate system; ω s C d u sq ω is the short-circuit current of the filter circuit. s For synchronous rotational angular velocity; C d The capacitance value of the filter circuit; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0147] Optionally, the method further includes: when the voltage drop of the doubly-fed wind turbine is a slight voltage drop, calculating the rotor current inside the doubly-fed wind turbine using the following formula:

[0148]

[0149] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; i gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. rq This refers to the rotor q-axis current in the synchronous rotating coordinate system.

[0150] Optionally, the method further includes: when the voltage drop of the doubly-fed wind turbine is a severe voltage drop, calculating the rotor current inside the doubly-fed wind turbine using the following formula:

[0151]

[0152] In the formula, ird The rotor d-axis current in a synchronous rotating coordinate system; u sq U is the stator-side q-axis voltage in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; U N This is the rated voltage; ω s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; i rq I is the rotor q-axis current in a synchronous rotating coordinate system. rmax This is the maximum rotor current.

[0153] In this embodiment of the invention, when the doubly-fed wind turbine adopts a q-axis voltage-oriented control strategy, the stator d-axis current i output under fault conditions is... sd With rotor d-axis current i rd The relationship between them is

[0154]

[0155] In the formula, u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance.

[0156] Therefore, the rotor current inside the doubly-fed wind turbine should be during a slight voltage dip.

[0157]

[0158] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; i gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. rq This refers to the rotor q-axis current in the synchronous rotating coordinate system.

[0159] During a severe voltage dip, the rotor current inside the doubly-fed wind turbine should be:

[0160]

[0161] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sqU is the stator-side q-axis voltage in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; U N This is the rated voltage; ω s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; i rq I is the rotor q-axis current in a synchronous rotating coordinate system. rmax This is the maximum rotor current.

[0162] Therefore, the rotor current inside the doubly fed wind turbine can be accurately calculated under different voltage drop levels, so that the rotor current can be used to check whether the protection on the rotor side operates under short-circuit fault, and to check whether the short-circuit current on the rotor side exceeds the converter capacity under short-circuit fault.

[0163] The following will combine Figure 4 The dual-ended network shown verifies the accuracy of the positive sequence current calculation method for a doubly fed wind turbine under short-circuit faults proposed in this embodiment of the invention.

[0164] See Figure 4 As shown in the figure, when the external power grid experiences three-phase short-circuit faults at Fault1 and Fault2 respectively, the short-circuit current contributed by the doubly-fed induction generator (DFIG) is calculated using time-domain simulation and the calculation method proposed in this invention, as shown in Tables 1 and 2. Tables 1 and 2 show that the positive-sequence current calculation method for DFIG under short-circuit faults proposed in this invention has an error of less than 4.5%, demonstrating high accuracy and practicality.

[0165] Table 1. Calculation results of short-circuit current of the doubly-fed wind turbine after a three-phase short-circuit fault at Fault 1.

[0166]

[0167] Table 2 shows the calculation results of the short-circuit current of the doubly-fed wind turbine after a three-phase short-circuit fault at Fault 2.

[0168]

[0169] This invention proposes a method for calculating the positive sequence current of a doubly-fed induction generator (DFIG) under fault conditions, based on the control strategies of DFIGs under different operating modes. The DFIG is represented by a conventional combination of controlled current sources and impedance elements. The impact of DFIG control is considered in both normal and low-voltage ride-through operating modes, corresponding to slight and severe stator voltage dips. This invention considers the equivalent circuits of the stator-side converter, grid-side converter, and filter circuit of the DFIG, enabling accurate calculation of the current level contributed by the DFIG during external grid faults. This method can be directly applied to existing short-circuit current calculation software.

[0170] Exemplary device

[0171] Figure 5 This is a schematic diagram of the positive sequence current calculation device for a doubly-fed wind turbine under a short-circuit fault, provided in an exemplary embodiment of the present invention. Figure 5 As shown, the device 500 includes:

[0172] The judgment module 510 is used to determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, wherein the current cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the current cycle under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the previous cycle under short-circuit fault.

[0173] The first calculation module 520 is used to calculate the stator-side short-circuit current, grid-side converter short-circuit current and filter circuit short-circuit current of the doubly fed wind turbine when the difference is greater than the preset threshold.

[0174] The second calculation module 530 is used to determine the positive sequence current of the doubly-fed wind turbine under a short-circuit fault based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current.

[0175] Optionally, the device further includes a voltage determination module for:

[0176] The total short-circuit current obtained from the previous power flow calculation of the doubly fed wind turbine under short-circuit fault is used as the input parameter for the current power flow calculation to determine the voltage of the current cycle.

[0177] The total short-circuit current obtained from the power flow calculation of the previous cycle under short-circuit fault is used as the input parameter for the power flow calculation of the previous cycle to determine the voltage of the previous cycle.

[0178] Optionally, the device also includes a drop condition determination module for:

[0179] Determine the voltage drop condition of the doubly-fed wind turbine, wherein the voltage drop condition is divided into minor voltage drop and severe voltage drop;

[0180] The slight voltage drop is used to indicate that the voltage of the doubly fed wind turbine is above a first percentage of the rated voltage after the voltage drop.

[0181] The severe voltage drop is used to indicate that the voltage of the doubly-fed wind turbine is below a first percentage of the rated voltage after the voltage drop.

[0182] Optionally, the first computing module 520 is specifically used for:

[0183] When the voltage drop of the doubly-fed wind turbine is minor, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0184]

[0185] In the formula, i sq For the stator-side q-axis current in a synchronous rotating coordinate system, i sd P represents the stator-side d-axis current in a synchronous rotating coordinate system. DFIG The active power generated by the wind turbine; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gq For the q-axis current on the mesh side in a synchronous rotating coordinate system, P RSC The active power generated by the rotor converter. u r For rotor voltage, i r Let L be the rotor current, j be the imaginary number, and L be the value of L. s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip Let ω be the slip angular velocity. s To achieve synchronous rotational angular velocity.

[0186] Optionally, the first computing module 520 is specifically used for:

[0187] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula:

[0188]

[0189] In the formula, i sqI is the stator-side q-axis current in a synchronously rotating coordinate system. N This is the rated current; i sd U represents the stator-side d-axis current in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; N Rated voltage; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0190] Optionally, the first computing module 520 is specifically used for:

[0191] When the voltage drop of the doubly-fed wind turbine is minor, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0192]

[0193] In the formula, i gq P represents the q-axis current on the mesh side in a synchronously rotating coordinate system. RSC The active power generated by the rotor converter; u sq i is the stator-side q-axis voltage in a synchronously rotating coordinate system; gd The current on the d-axis of the network side in the synchronous rotating coordinate system.

[0194] Optionally, the first computing module 520 is specifically used for:

[0195] When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula:

[0196]

[0197] In the formula, i sq i is the rotor d-axis current in a synchronous rotating coordinate system; gq For the q-axis current on the mesh side in a synchronously rotating coordinate system; u sq I is the stator-side q-axis voltage in a synchronously rotating coordinate system. gmax I is the maximum current of the grid-side converter. N U is the rated current; k is a control coefficient under the low-voltage breakout strategy; U N This is the rated voltage.

[0198] Optionally, the stator-side short-circuit current includes the stator-side q-axis current and the stator-side d-axis current in a synchronous rotating coordinate system, and the grid-side converter short-circuit current includes the grid-side q-axis current and the grid-side d-axis current in a synchronous rotating coordinate system.

[0199] Furthermore, the second computing module 530 is specifically used for:

[0200] The positive sequence current of the doubly-fed wind turbine under a short-circuit fault is calculated using the following formula:

[0201]

[0202] In the formula, i dfigq i is the positive sequence current of the doubly-fed wind turbine generator; sq i represents the stator-side q-axis current in a synchronously rotating coordinate system; sd i represents the stator-side d-axis current in a synchronously rotating coordinate system; gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. gd For the d-axis current on the mesh side in a synchronously rotating coordinate system; ω s C d u sq ω is the short-circuit current of the filter circuit. s For synchronous rotational angular velocity; C d The capacitance value of the filter circuit; u sq This refers to the q-axis voltage on the stator side in a synchronously rotating coordinate system.

[0203] Optionally, the device further includes a third calculation module, used to calculate the rotor current inside the doubly-fed wind turbine generator using the following formula when the voltage drop of the doubly-fed wind turbine generator is a slight voltage drop:

[0204]

[0205] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sq ω is the stator-side q-axis voltage in a synchronously rotating coordinate system. s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; i gq i represents the q-axis current on the mesh side in a synchronously rotating coordinate system. rq This refers to the rotor q-axis current in the synchronous rotating coordinate system.

[0206] Optionally, the device further includes a fourth calculation module, used to calculate the rotor current inside the doubly-fed wind turbine generator using the following formula when the voltage drop condition of the doubly-fed wind turbine generator is a severe voltage drop:

[0207]

[0208] In the formula, i rd The rotor d-axis current in a synchronous rotating coordinate system; u sqU is the stator-side q-axis voltage in a synchronous rotating coordinate system; k is a control coefficient under the low-voltage penetration strategy; U N This is the rated voltage; ω s For synchronous rotational angular velocity; L s For stator-side inductance; L m For magnetizing inductance; i rq I is the rotor q-axis current in a synchronous rotating coordinate system. rmax This is the maximum rotor current.

[0209] The positive sequence current calculation device 500 for a doubly-fed wind turbine under a short-circuit fault in an embodiment of the present invention corresponds to the positive sequence current calculation method 100 for a doubly-fed wind turbine under a short-circuit fault in another embodiment of the present invention, and will not be described again here.

[0210] Exemplary electronic devices

[0211] Figure 6 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. The electronic device may be either or both of a first device and a second device, or a standalone device independent of them. The standalone device may communicate with the first device and the second device to receive acquired input signals from them. Figure 6 A block diagram of an electronic device according to an embodiment of the present invention is illustrated. Figure 6 As shown, the electronic device 60 includes one or more processors 61 and a memory 62.

[0212] The processor 61 may be a central processing unit (CPU) or other form of processing unit with data processing and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0213] The memory 62 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 61 may execute the program instructions to implement the methods for information mining of historical change records and / or other desired functions of the software programs of the various embodiments of the present invention described above. In one example, the electronic device may also include an input device 63 and an output device 64, which are interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0214] In addition, the input device 63 may also include, for example, a keyboard, a mouse, etc.

[0215] The output device 64 can output various information to the outside. The output device 64 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices, etc.

[0216] Of course, for the sake of simplicity, Figure 6 Only some of the components of the electronic device relevant to the present invention are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device may include any other suitable components depending on the specific application.

[0217] Exemplary computer program products and computer-readable storage media

[0218] In addition to the methods and devices described above, embodiments of the present invention may also be computer program products, which include computer program instructions that, when executed by a processor, cause the processor to perform the steps of the methods for information mining of historical change records according to various embodiments of the present invention as described in the "Exemplary Methods" section of this specification.

[0219] The computer program product can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of the present invention. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0220] Furthermore, embodiments of the present invention may also be computer-readable storage media storing computer program instructions thereon, which, when executed by a processor, cause the processor to perform the steps of the methods for information mining of historical change records according to various embodiments of the present invention as described in the "Exemplary Methods" section above.

[0221] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or any combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0222] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the specific details described above.

[0223] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0224] The block diagrams of devices, systems, devices, and apparatuses involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, systems, devices, and apparatuses can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0225] The methods and systems of the present invention may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of the present invention are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present invention may also be implemented as a program recorded on a recording medium, the program comprising machine-readable instructions for implementing the methods according to the present invention. Thus, the present invention also covers recording media storing programs for performing the methods according to the present invention.

[0226] It should also be noted that in the systems, apparatus, and methods of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered equivalents of the present invention. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0227] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for calculating the positive sequence current of a doubly-fed induction generator (DFIG) under a short-circuit fault, characterized in that, include: Determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, wherein the current cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine under short-circuit fault. If the difference is greater than the preset threshold, calculate the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine. The positive sequence current of the doubly-fed wind turbine under a short-circuit fault is determined based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current. Before calculating the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine, the following steps are also included: Determine the voltage drop condition of the doubly-fed wind turbine, wherein the voltage drop condition is divided into minor voltage drop and severe voltage drop; The slight voltage drop is used to indicate that the voltage of the doubly fed wind turbine is above a first percentage of the rated voltage after the voltage drop. The severe voltage drop is used to indicate that the voltage of the doubly-fed wind turbine is below a first percentage of the rated voltage after the voltage drop. Based on slight voltage dips and severe voltage dips, the stator-side short-circuit current and the grid-side converter short-circuit current are calculated respectively.

2. The method according to claim 1, characterized in that, Before determining whether the difference between the current cycle voltage and the previous cycle voltage of a doubly-fed wind turbine is greater than a preset threshold, the following steps are also included: The total short-circuit current obtained from the power flow calculation of the doubly fed wind turbine under short-circuit fault in the previous cycle is used as the input parameter for the current cycle to perform power flow calculation and determine the voltage of the current cycle. The total short-circuit current obtained from the power flow calculation of the previous cycle of the doubly fed wind turbine under short-circuit fault is used as the input parameter for the power flow calculation of the previous cycle to determine the voltage of the previous cycle.

3. The method according to claim 1, characterized in that, The calculation of the stator-side short-circuit current of the doubly-fed wind turbine includes: When the voltage drop of the doubly-fed wind turbine is minor, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Stator side in synchronous rotating coordinate system q shaft current, Stator side in synchronous rotating coordinate system d shaft current; P DFIG The active power generated by the wind turbine; Stator side in synchronous rotating coordinate system q Shaft voltage; For the mesh side in the synchronous rotating coordinate system q shaft current, , P RSC The active power generated by the rotor converter. , , u r For rotor voltage, i r For rotor current, j It is an imaginary number. L s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip For slip angular velocity, ω s To achieve synchronous rotational angular velocity.

4. The method according to claim 1, characterized in that, The calculation of the stator-side short-circuit current of the doubly-fed wind turbine includes: When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Stator side in synchronous rotating coordinate system q shaft current; I N Rated current; Stator side in synchronous rotating coordinate system d shaft current; k This is a control coefficient under the low-penetration strategy; U N Rated voltage; Stator side in synchronous rotating coordinate system q Shaft voltage.

5. The method according to claim 1, characterized in that, Calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine includes: When the voltage drop of the doubly-fed wind turbine is minor, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, For the mesh side in the synchronous rotating coordinate system q shaft current; P RSC The active power generated by the rotor converter; Stator side in synchronous rotating coordinate system q Shaft voltage; For the mesh side in the synchronous rotating coordinate system d Axis current.

6. The method according to claim 1, characterized in that, Calculating the short-circuit current of the grid-side converter of the doubly-fed wind turbine includes: When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; For the mesh side in the synchronous rotating coordinate system q shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; This represents the maximum current of the grid-side converter. I N Rated current; k This is a control coefficient under the low-penetration strategy; U N This is the rated voltage.

7. The method according to claim 1, characterized in that, The stator-side short-circuit current includes the stator-side current in the synchronous rotating coordinate system. q shaft current and stator side d The short-circuit current of the grid-side converter includes the grid-side current in the synchronous rotating coordinate system. q shaft current and grid side d shaft current; Furthermore, based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current, the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault is determined, including: calculating the positive-sequence current of the doubly-fed wind turbine under a short-circuit fault using the following formula: ； In the formula, This represents the positive sequence current of the doubly-fed wind turbine. Stator side in synchronous rotating coordinate system q shaft current; Stator side in synchronous rotating coordinate system d shaft current; For the mesh side in the synchronous rotating coordinate system q shaft current; For the mesh side in the synchronous rotating coordinate system d shaft current; This is the short-circuit current of the filter circuit; ω s To synchronize rotational angular velocity; This is the capacitance value of the filter circuit; Stator side in synchronous rotating coordinate system q Shaft voltage.

8. The method according to claim 1, characterized in that, Also includes: When the voltage drop of the doubly-fed wind turbine is minor, the rotor current inside the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; ω s To synchronize rotational angular velocity; L s Stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; For the mesh side in the synchronous rotating coordinate system q shaft current; Rotor in synchronous rotating coordinate system q Axis current.

9. The method according to claim 1, characterized in that, Also includes: When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the rotor current inside the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; k This is a control coefficient under the low-penetration strategy; U N Rated voltage; ω s To synchronize rotational angular velocity; L s Stator-side inductance; L m For magnetizing inductance; Rotor in synchronous rotating coordinate system q shaft current; This is the maximum rotor current.

10. A device for calculating the positive sequence current of a doubly-fed wind turbine under a short-circuit fault, characterized in that, include: The judgment module is used to determine whether the difference between the current cycle voltage and the previous cycle voltage of the doubly-fed wind turbine is greater than a preset threshold, wherein the current cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the current cycle under short-circuit fault, and the previous cycle voltage is the result of the power flow calculation of the doubly-fed wind turbine in the previous cycle under short-circuit fault. The first calculation module is used to calculate the stator-side short-circuit current, grid-side converter short-circuit current, and filter circuit short-circuit current of the doubly-fed wind turbine when the difference is greater than the preset threshold. The second calculation module is used to determine the positive sequence current of the doubly-fed wind turbine under a short-circuit fault based on the stator-side short-circuit current, the grid-side converter short-circuit current, and the filter circuit short-circuit current. It also includes a drop condition determination module, used for: Determine the voltage drop condition of the doubly-fed wind turbine, wherein the voltage drop condition is divided into minor voltage drop and severe voltage drop; The slight voltage drop is used to indicate that the voltage of the doubly fed wind turbine is above a first percentage of the rated voltage after the voltage drop. The severe voltage drop is used to indicate that the voltage of the doubly-fed wind turbine is below a first percentage of the rated voltage after the voltage drop. Based on slight voltage dips and severe voltage dips, the stator-side short-circuit current and the grid-side converter short-circuit current are calculated respectively.

11. The apparatus according to claim 10, characterized in that, It also includes a voltage determination module, used for: The total short-circuit current obtained from the power flow calculation of the doubly fed wind turbine under short-circuit fault in the previous cycle is used as the input parameter for the current cycle to perform power flow calculation and determine the voltage of the current cycle. The total short-circuit current obtained from the power flow calculation of the previous cycle under short-circuit fault is used as the input parameter for the power flow calculation of the previous cycle to determine the voltage of the previous cycle.

12. The apparatus according to claim 10, characterized in that, The first calculation module is specifically used for: When the voltage drop of the doubly-fed wind turbine is minor, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Stator side in synchronous rotating coordinate system q shaft current, Stator side in synchronous rotating coordinate system d shaft current; P DFIG The active power generated by the wind turbine; Stator side in synchronous rotating coordinate system q Shaft voltage; For the mesh side in the synchronous rotating coordinate system q shaft current, , P RSC The active power generated by the rotor converter. , , u r For rotor voltage, i r For rotor current, j It is an imaginary number. L s For stator-side inductance, i s For stator current, L m For magnetizing inductance, ω slip For slip angular velocity, ω s To achieve synchronous rotational angular velocity.

13. The apparatus according to claim 10, characterized in that, The first calculation module is specifically used for: When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the stator-side short-circuit current of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Stator side in synchronous rotating coordinate system q shaft current; I N Rated current; Stator side in synchronous rotating coordinate system d shaft current; k This is a control coefficient under the low-penetration strategy; U N Rated voltage; Stator side in synchronous rotating coordinate system q Shaft voltage.

14. The apparatus according to claim 10, characterized in that, The first calculation module is specifically used for: When the voltage drop of the doubly-fed wind turbine is minor, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, For the mesh side in the synchronous rotating coordinate system q shaft current; P RSC The active power generated by the rotor converter; Stator side in synchronous rotating coordinate system q Shaft voltage; For the mesh side in the synchronous rotating coordinate system d Axis current.

15. The apparatus according to claim 10, characterized in that, The first calculation module is specifically used for: When the voltage drop of the doubly-fed wind turbine is a severe voltage drop, the short-circuit current of the grid-side converter of the doubly-fed wind turbine is calculated using the following formula: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; For the mesh side in the synchronous rotating coordinate system q shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; This represents the maximum current of the grid-side converter. I N Rated current; k This is a control coefficient under the low-penetration strategy; U N This is the rated voltage.

16. The apparatus according to claim 10, characterized in that, The stator-side short-circuit current includes the stator-side current in the synchronous rotating coordinate system. q shaft current and stator side d The short-circuit current of the grid-side converter includes the grid-side current in the synchronous rotating coordinate system. q shaft current and grid side d shaft current; Furthermore, the second calculation module is specifically used for: The positive sequence current of the doubly-fed wind turbine under a short-circuit fault is calculated using the following formula: ； In the formula, This represents the positive sequence current of the doubly-fed wind turbine. Stator side in synchronous rotating coordinate system q shaft current; Stator side in synchronous rotating coordinate system d shaft current; For the mesh side in the synchronous rotating coordinate system q shaft current; For the mesh side in the synchronous rotating coordinate system d shaft current; This is the short-circuit current of the filter circuit; ω s To synchronize rotational angular velocity; This is the capacitance value of the filter circuit; Stator side in synchronous rotating coordinate system q Shaft voltage.

17. The apparatus according to claim 10, characterized in that, Also includes: The third calculation module is used to calculate the rotor current inside the doubly-fed wind turbine using the following formula when the voltage drop of the doubly-fed wind turbine is a slight voltage drop: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; ω s To synchronize rotational angular velocity; L s Stator-side inductance; L m For magnetizing inductance; P DFIG The active power generated by the wind turbine; For the mesh side in the synchronous rotating coordinate system q shaft current; Rotor in synchronous rotating coordinate system q Axis current.

18. The apparatus according to claim 10, characterized in that, Also includes: The fourth calculation module is used to calculate the rotor current inside the doubly-fed wind turbine generator when the voltage drop is severe, using the following formula: ； In the formula, Rotor in synchronous rotating coordinate system d shaft current; Stator side in synchronous rotating coordinate system q Shaft voltage; k This is a control coefficient under the low-penetration strategy; U N Rated voltage; ω s To synchronize rotational angular velocity; L s Stator-side inductance; L m For magnetizing inductance; Rotor in synchronous rotating coordinate system q shaft current; This is the maximum rotor current.

19. A computer-readable storage medium, characterized in that, The storage medium stores a computer program for performing the method described in any one of claims 1-9.

20. An electronic device, characterized in that, The electronic device includes: processor; Memory used to store the processor's executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1-9.

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