Transient overvoltage analysis method for grid-connected direct-drive wind power system under asymmetric fault

Abstract

The application belongs to the technical field of new energy grid-connected system transient analysis, and particularly relates to a kind of direct-drive wind power grid-connected system transient overvoltage analysis method under asymmetric fault, comprising: obtaining three-phase asymmetric voltage and current, constructing positive and negative sequence double-synchronous positive and negative sequence dq control model of direct-drive wind power station;Establish the mapping relationship with symmetric component method and determine the positive sequence dynamic reactive current increment and negative sequence current suppression coefficient according to the converter control strategy;Establish the sequence network boundary condition under a variety of asymmetric faults;Equivalent direct-drive wind power station to frequency-dependent controlled sequence impedance source, obtain the equivalent sequence impedance of wind farm;Establish the sequence network equation considering wind power dynamic support;Calculate the current and sequence voltage of fault point and obtain three-phase voltage through symmetric component inverse transformation;Calculate the overvoltage coefficient and establish the quantitative relationship between overvoltage coefficient and negative sequence current suppression coefficient and apply it.The application provides theoretical support for parameter setting and capacity planning of wind power grid-connected system.

Description

Technical Field

[0001] This application belongs to the field of transient analysis technology for new energy grid-connected systems, specifically involving a transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults. Background Technology

[0002] With the accelerated global energy structure transformation, the penetration rate of new energy sources such as wind power in the power system continues to increase. Direct-drive wind turbines have become the mainstream technology for wind power due to their elimination of gearboxes and high operational reliability. However, direct-drive wind turbines are connected to the grid through a full-power converter, and their fault characteristics differ fundamentally from those of traditional synchronous generators.

[0003] When an asymmetrical fault occurs in the power grid, direct-drive wind turbines must inject positive-sequence dynamic reactive current to support the voltage, and simultaneously inject dynamic negative-sequence current to suppress voltage imbalance, as required by national standards. Existing calculation methods mostly focus on overvoltage analysis under symmetrical fault conditions, lacking analysis of transient overvoltage under asymmetrical faults. Furthermore, the impact mechanism of the negative-sequence current control strategy of wind power converters on overvoltage is unclear. The lack of quantitative relationships between negative-sequence control parameters and overvoltage levels in engineering projects makes control parameter tuning lack theoretical basis, and even leads to the phenomenon that negative-sequence support exacerbates overvoltage. These problems result in significant uncertainties in wind power capacity assessment, power grid planning and design, and protection setting, hindering the safe and stable operation of high-proportion renewable energy power systems. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults. The aim is to establish a transient overvoltage analysis and calculation method that integrates converter dynamic control characteristics and sequence network analysis, providing theoretical support for parameter tuning and capacity planning of wind power grid-connected systems, thereby overcoming or at least partially overcoming the shortcomings of existing technologies.

[0005] Firstly, this application provides a transient overvoltage analysis method for a direct-drive wind power grid-connected system under asymmetrical faults, including:

[0006] Control model construction steps: Obtain three-phase unbalanced voltage and current, and construct a positive and negative sequence dq control model for direct-drive wind farm with positive and negative sequence dual synchronization;

[0007] The steps for constructing the mapping relationship are as follows: establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and determine the positive sequence dynamic reactive current increment and the negative sequence current suppression coefficient according to the converter control strategy;

[0008] Boundary condition construction steps: Establish sequence network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit;

[0009] Sequence impedance equivalent steps: Equivalently convert the direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm;

[0010] Steps for constructing the sequence network equation: Combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power.

[0011] Fault point parameter calculation steps: Calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through symmetrical component inverse transformation;

[0012] Quantitative calculation and application steps: Calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be used in any scenario of wind farm control parameter tuning, access capacity planning and protection configuration.

[0013] Secondly, this application also provides a transient overvoltage analysis device for a direct-drive wind power grid-connected system under asymmetrical faults, the device comprising:

[0014] The control model building unit is used to obtain three-phase unbalanced voltage and current, and to build a positive and negative sequence dq control model for positive and negative sequence dual synchronization of direct-drive wind farm.

[0015] The mapping relationship construction unit is used to establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and to determine the positive sequence dynamic reactive current increment and negative sequence current suppression coefficient according to the converter control strategy.

[0016] Boundary condition construction unit is used to establish the sequence network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit.

[0017] Sequence impedance equivalent unit is used to convert a direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm.

[0018] The sequence network equation building unit is used to combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power.

[0019] The fault point parameter calculation unit is used to calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through the inverse transformation of symmetrical components.

[0020] The quantitative calculation and application unit is used to calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be used in any scenario of wind farm control parameter tuning, access capacity planning and protection configuration.

[0021] Thirdly, this application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the above-mentioned transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults.

[0022] Fourthly, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the above-described method for analyzing transient overvoltages in a direct-drive wind power grid-connected system under asymmetrical faults.

[0023] The above-mentioned at least one technical application used in the embodiments of this application can achieve the following beneficial effects:

[0024] First, this application constructs a positive and negative sequence dual synchronous dq control model for direct-drive wind farms and establishes its mapping relationship with the symmetrical component method, organically integrating the dynamic characteristics of converter control with sequence component analysis. This solves the limitation of traditional methods being difficult to adapt to asymmetrical fault scenarios and achieves accurate analysis of transient overvoltages under asymmetrical faults.

[0025] Second, this application equates direct-drive wind farms to frequency-dependent controlled sequence impedance sources and constructs sequence network equations that include dynamic support for wind power by combining grid sequence impedance. This approach better reflects the electrical characteristics of actual wind power grid-connected systems and provides a reliable analytical framework for calculating fault point parameters under different types of asymmetrical faults.

[0026] Third, this application establishes a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be directly applied to scenarios such as wind farm control parameter setting, grid connection capacity planning, or protection configuration. This effectively improves the analysis accuracy and application guidance of direct-drive wind power grid-connected systems under asymmetrical faults, and helps ensure the safe and stable operation of new energy power systems. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0028] Figure 1 A flowchart illustrating a transient overvoltage analysis method for a direct-drive wind power grid-connected system under asymmetrical faults according to an embodiment of this application is shown.

[0029] Figure 2 A schematic diagram of a transient overvoltage analysis device for a direct-drive wind power grid-connected system under asymmetrical faults according to an embodiment of this application is shown.

[0030] Figure 3A schematic diagram of the resulting electronic device according to an embodiment of this application is shown. Detailed Implementation

[0031] To make the objectives, technical claims, and advantages of this application clearer, the technical application of this application will be clearly and completely described below with reference to specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] The main concept of this application is to provide a method for transient overvoltage analysis and parameter tuning of a direct-drive wind power grid-connected system under asymmetrical faults. The core of this method is to unify the dq coordinate system control model of the direct-drive wind power converter with the symmetrical component method, obtain the frequency-related equivalent sequence impedance by deriving the converter closed-loop transfer function, and then establish the sequence network equation considering the dynamic support of wind power, so as to finally realize the calculation of transient overvoltage of the healthy phase under asymmetrical faults.

[0033] Figure 1 This paper illustrates a flowchart of a transient overvoltage analysis method for a direct-drive wind power grid-connected system under asymmetrical faults according to an embodiment of this application. Figure 1 As can be seen, this embodiment includes steps S100 to S700:

[0034] Control model construction step S100: Obtain three-phase unbalanced voltage and current, and construct a positive and negative sequence dq control model for direct-drive wind farm with positive and negative sequence dual synchronization.

[0035] Specifically, in some embodiments of this application, the control model construction step includes decoupling the three-phase unbalanced voltage and current into positive-sequence dq components and negative-sequence dq components through Park transformation, and establishing the voltage and current dynamic equations of the grid-side converter in the positive and negative sequence dq coordinate system.

[0036] A direct-drive permanent magnet synchronous generator system consists of a wind turbine, a permanent magnet synchronous generator, a machine-side converter (MSC), a DC bus, and a grid-side converter (GSC). In asymmetric fault analysis, the dynamic characteristics of the grid-side converter (GSC) are the primary focus.

[0037] When an asymmetrical fault occurs in the power grid, the three-phase voltage and current simultaneously contain both positive-sequence and negative-sequence components, and the traditional single synchronous rotating dq coordinate system cannot achieve complete decoupling. Therefore, this application introduces a dual synchronous dq coordinate system with positive and negative sequences: the positive-sequence dq coordinate system uses the positive-sequence voltage vector as a reference and rotates at a synchronous angular frequency of +ω; the negative-sequence dq coordinate system uses the negative-sequence voltage vector as a reference and rotates at an angular frequency of -ω.

[0038] Define the orthogonal Park transformation matrix for:

[0039] ;

[0040] in, ω is the phase angle of the positive sequence synchronization coordinate system, in radians (rad), and ω is the system synchronization angular frequency, in radians per second (rad / s). This is the initial phase angle. Using this transformation matrix, the three-phase voltage [...]. , , ] Convert to positive order dq components[ , ] .

[0041] Define the negative order Park transformation matrix for:

[0042] .

[0043] In the positive-sequence dq coordinate system, the voltage and current dynamic equations of the grid-side converter GSC are as follows:

[0044] ;

[0045] ;

[0046] In the above equation, and These are the positive sequence d-axis and q-axis currents, respectively; and These are the output voltages of the positive-sequence d-axis and q-axis converters, respectively. and ω represents the positive sequence d-axis and q-axis grid voltages, respectively; L is the filter inductance; R is the equivalent resistance, including the line resistance of the filter inductance and the equivalent resistance of switching losses; ω is the synchronization angular frequency.

[0047] In the negative-sequence dq coordinate system, the voltage and current dynamic equations of the grid-side converter GSC are as follows:

[0048] ;

[0049] ;

[0050] In the above equation, and These are the negative sequence d-axis and q-axis currents, respectively. and These are the output voltages of the negative sequence d-axis and q-axis converters, respectively. and These represent the negative sequence d-axis and q-axis grid voltages, respectively.

[0051] Mapping relationship construction step S200: Establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and determine the positive sequence dynamic reactive current increment and negative sequence current suppression coefficient according to the converter control strategy.

[0052] Specifically, in some embodiments of this application, the mapping relationship construction step includes: constructing a mapping relationship between the positive and negative sequence dq control model and the symmetric component method, and converting the positive and negative sequence dq current amplitudes into positive sequence currents represented by symmetric components. and negative sequence current And determine the positive-sequence dynamic reactive current increment according to the converter control strategy. and negative sequence current suppression coefficient .

[0053] Specifically, a mapping relationship is established between the magnitude of the dq current and the magnitude of its sequence component. Based on the properties of the Park transform, when positive-sequence voltage orientation is adopted (i.e., letting...), =0, When =|E1|), the positive sequence current amplitude is | The relationship with the positive-sequence dq current is:

[0054] ;

[0055] Among them, | | represents the positive sequence current amplitude.

[0056] Similarly, the magnitude of the negative sequence current | The relationship with the negative sequence dq current is:

[0057] ;

[0058] Among them, | | represents the amplitude of the negative sequence current.

[0059] According to national standards, when the grid connection voltage drops, wind farms should inject dynamic reactive current to support the voltage. The formula for calculating the positive-sequence dynamic reactive current increment is:

[0060] ;

[0061] in, This represents the positive-sequence reactive current increment, in A. The positive-sequence reactive power support factor has a value range of 1.5 ≤ ≤2.0; The per-unit value of the positive sequence voltage at the grid connection point is defined as follows: =|U1| / Where |U1| is the positive sequence voltage amplitude, Rated voltage; This is the rated current of the converter.

[0062] The reference value for the positive sequence q-axis current is:

[0063] ;

[0064] in, This is the reference value for the positive-sequence q-axis current. This represents the positive-sequence q-axis current before the fault. In voltage-oriented control, the q-axis current corresponds to the reactive current.

[0065] The positive sequence d-axis current must be limited by the converter's maximum current.

[0066] ;

[0067] in, This is the reference value for the positive sequence d-axis current. This is the maximum output current of the converter. This represents the positive-sequence d-axis current before the fault.

[0068] For negative sequence control, a negative sequence current suppression strategy is adopted:

[0069] ;

[0070] ;

[0071] in, , This is the reference value for the negative sequence dq-axis current. , Z is the negative sequence dq-axis current suppression coefficient. eq This represents the system's equivalent impedance magnitude. The purpose of the negative sequence suppression strategy is to counteract the influence of the negative sequence voltage and reduce voltage imbalance by injecting a negative sequence current that is opposite to the negative sequence voltage.

[0072] Boundary condition construction step S300: Establish sequential network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit.

[0073] Specifically, in some embodiments of this application, the boundary condition construction step includes: for three fault types—single-phase grounding, two-phase grounding, and two-phase short circuit—deriving the relationship between zero-sequence current, positive-sequence current, and negative-sequence current, as well as the relationship between zero-sequence voltage, positive-sequence voltage, and negative-sequence voltage.

[0074] For three typical asymmetric faults, their order component boundary conditions are derived:

[0075] (1) Single-phase ground fault

[0076] Assume phase a is grounded, and the grounding impedance is Z. f Based on the fault boundary conditions, we have:

[0077] ;

[0078] ;

[0079] ;

[0080] Using symmetric component transformation, we can obtain:

[0081] ;

[0082] ;

[0083] This boundary condition indicates that during a single-phase ground fault, the three sequence currents are equal, and the sum of the three sequence voltages is equal to three times the product of the grounding impedance and the sequence current.

[0084] (2) Two-phase ground fault

[0085] Assume that phases b and c are grounded through the grounding impedance Zf. According to the fault boundary conditions, we have:

[0086] ;

[0087] ;

[0088] Using symmetric component transformation, we can obtain:

[0089] ;

[0090] ;

[0091] This boundary condition indicates that during a two-phase ground fault, the positive-sequence voltage equals the negative-sequence voltage, and the zero-sequence current equals the negative of the sum of the positive-sequence current and the negative-sequence current.

[0092] (3) Two-phase short circuit fault

[0093] Assume a short circuit in phases b and c (without grounding). Based on the fault boundary conditions, we have:

[0094] ;

[0095] ;

[0096] Using symmetric component transformation, we can obtain:

[0097] ;

[0098] ;

[0099] ;

[0100] This boundary condition indicates that during a two-phase short-circuit fault, the zero-sequence current is zero, the negative-sequence current is equal to the negative of the positive-sequence current, and the positive-sequence voltage is equal to the negative-sequence voltage.

[0101] In the above formula, This refers to the phase a fault current, which is the total fault current when phase a is grounded. This refers to the zero-sequence current at the fault point, which is the zero-sequence component decomposed from the three-phase current in an asymmetrical fault. This refers to the positive sequence current at the fault point, which is the positive sequence component of the three-phase current decomposed in an asymmetrical fault. The negative sequence current at the fault point is the negative sequence component of the three-phase current decomposed in an asymmetrical fault. This refers to the phase b current, which is the current in phase b during a fault. This refers to the current in phase c during a fault. This refers to the voltage of phase a during a fault. This is the grounding impedance; that is, when phase a is grounded, the faulty phase is connected to the ground through this impedance. This refers to the zero-sequence voltage at the fault point, which is the zero-sequence component decomposed from the three-phase voltage in an asymmetrical fault. This refers to the positive-sequence voltage at the fault point, which is the positive-sequence component of the three-phase voltage decomposed in an asymmetrical fault. The negative sequence voltage at the fault point is the negative sequence component of the three-phase voltage decomposed in an asymmetrical fault.

[0102] Sequence impedance equivalent step S400: Equivalently convert the direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm.

[0103] Specifically, in some embodiments of this application, the sequence impedance equivalent step specifically includes: controlling the positive and negative sequence parameters. , , , Calculate the equivalent positive sequence impedance of a wind farm and equivalent negative sequence impedance .

[0104] Among them, the positive and negative sequence control parameters include , , , . The proportional gain of the positive sequence PI controller; The integral coefficient of the positive-sequence PI controller; The proportional gain of the negative-sequence PI controller. The integral coefficient of the negative-sequence PI controller is expressed in seconds. - ¹.

[0105] The control strategy of the wind farm grid-connected system adopts a dual closed-loop control structure: the outer loop is for voltage / power control, and the inner loop is for current control. During fault transients, since the response speed of the inner current loop is much faster than that of the outer loop, the dynamics of the outer loop can be ignored, and only the PI controller of the inner current loop is considered.

[0106] For the ascending sequence channel, a PI controller is used:

[0107] ;

[0108] ;

[0109] in, The proportional gain of the positive sequence PI controller; is the integral coefficient of the positive-sequence PI controller; s is the Laplace operator.

[0110] Substituting the positive-order dynamic equation from step S100 and performing a Laplace transform, we obtain:

[0111] ;

[0112] After sorting, the voltage from the power grid is obtained. To output current Closed-loop transfer function:

[0113] ;

[0114] in, For the Laplace transform of the positive-sequence grid voltage, This is the Laplace transform of the positive-sequence output current.

[0115] The equivalent positive-sequence impedance of a wind farm is defined as the reciprocal of this transfer function:

[0116] ;

[0117] Similarly, for negative sequence channels, a PI controller is used. The equivalent negative sequence impedance can be obtained as follows:

[0118] ;

[0119] in, The proportional gain of the negative-sequence PI controller. The integral coefficient of the negative-sequence PI controller is expressed in seconds. - ¹.

[0120] It can be seen that the equivalent positive-sequence impedance and the equivalent negative-sequence impedance of a wind farm can be uniformly expressed as the following formula:

[0121] ;

[0122] in, , For the Laplace transform of positive and negative sequence voltages, , For the Laplace transform of positive and negative sequence currents, , These are the proportional and integral parameters of the positive-sequence PI controller. These are the proportional and integral parameters of the negative-sequence PI controller.

[0123] In the steady-state analysis at power frequency, letting s = jω, we can obtain:

[0124] ;

[0125] The equivalent impedance is a complex number, and its magnitude and phase angle are both related to the control parameters. , Related.

[0126] Step S500 in constructing the sequence network equation: Combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power.

[0127] Specifically, in some embodiments of this application, the sequence network equation construction step includes: according to the fault type, the equivalent sequence impedance of the wind farm and the sequence impedance of the power grid are combined in parallel or in series to form the total sequence impedance of the system that includes the influence of wind power.

[0128] The equivalent sequence impedance of the wind farm calculated in step S400 is incorporated into the fault sequence network. Taking a single-phase ground fault as an example, in the positive sequence network, the equivalent positive sequence impedance of the wind farm is... With the positive sequence impedance of the power grid Connected in parallel, forming the total positive sequence impedance of the system:

[0129] ;

[0130] in, The positive-sequence equivalent impedance (Ω) is the impedance seen from the fault point into the power grid, including the internal impedance of the power source, the transformer impedance, and the line impedance.

[0131] Similarly, the total negative sequence impedance of the system is:

[0132] ;

[0133] in, The negative sequence impedance of the power grid (Ω).

[0134] Specifically, considering the negative-sequence current suppression strategy, negative-sequence support introduces an additional voltage modulation effect. This effect can be equivalent to a correction of the negative-sequence impedance, and the corrected equivalent total negative-sequence impedance is:

[0135] ;

[0136] in, The negative sequence impedance (Ω) of the line from the wind farm to the grid connection point. The equivalent impedance magnitude of the system (Ω). This is the negative-sequence q-axis current suppression coefficient. This formula shows that the negative-sequence suppression coefficient... The larger the value, the smaller the equivalent negative sequence impedance, and the stronger the "short circuit" effect on negative sequence voltage.

[0137] System zero-sequence impedance It is determined solely by the power grid and is not affected by the wind farm, because the wind farm uses delta or star-connected ungrounded transformers, thus blocking the zero-sequence path.

[0138] Fault point parameter calculation step S600: Calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through symmetrical component inverse transformation.

[0139] Specifically, in some embodiments of this application, the fault point parameter calculation steps include: calculating the current, zero-sequence voltage, positive-sequence voltage, and negative-sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtaining the three-phase voltage through symmetrical component inverse transformation.

[0140] Based on the boundary conditions in step S300 and the total impedance in step S500, the sequence network equations are established. Taking a single-phase ground fault as an example, based on the boundary conditions... = = and + + =3 Combining Kirchhoff's voltage law for ordered networks, we can obtain:

[0141] ;

[0142] ;

[0143] ;

[0144] ;

[0145] in, The positive-sequence electromotive force (V) of the power supply before the fault.

[0146] Solving the above equations simultaneously, we obtain the positive sequence current:

[0147] ;

[0148] This leads to the expressions for each sequence voltage:

[0149] ;

[0150] ;

[0151] ;

[0152] The three-phase voltages can be obtained by inverse transformation of the symmetrical components:

[0153] ;

[0154] Where a = e^(j2π / 3) is the rotation operator.

[0155] Quantitative calculation and application steps S700: Calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be used in any scenario of wind farm control parameter tuning, access capacity planning and protection configuration.

[0156] Specifically, in some embodiments of this application, the quantitative calculation and application steps specifically include: calculating the amplitude of the healthy phase voltage, defining the overvoltage coefficient as the ratio of the amplitude of the healthy phase voltage to the rated voltage, and establishing the overvoltage coefficient and the negative sequence current suppression coefficient. The quantitative relationship is derived. The calculation results are then applied to any scenario in wind farm control parameter tuning, grid connection capacity planning, and protection configuration.

[0157] For a single-phase ground fault (phase a grounded), the voltage amplitudes of the healthy phases b and c increase. The voltage of phase b is:

[0158] ;

[0159] Substituting the sequence voltage expression obtained in step S600:

[0160] ;

[0161] Summarized as follows:

[0162] ;

[0163] Will Substituting the expression and simplifying it, we can obtain the b-phase overvoltage coefficient considering the negative sequence support of wind power:

[0164] ;

[0165] in, Rated phase voltage, The overvoltage coefficient of phase b is taken into account for the influence of wind power.

[0166] Furthermore, it can be achieved through... about By finding the partial derivatives, we can analyze their changing patterns:

[0167] ;

[0168] in:

[0169] ;

[0170] make The optimal negative sequence current suppression coefficient is obtained by solving the problem.

[0171] ;

[0172] The optimal negative sequence suppression coefficient depends on the grid impedance, the wind farm equivalent impedance, and the ratio of the zero-sequence to the positive-sequence impedance of the system.

[0173] In engineering applications, the actual setting value should take into account the converter's current capacity limitation:

[0174] ;

[0175] in, The maximum current of the converter and positive sequence rated current Sure:

[0176] ;

[0177] This optimized tuning method ensures that the overvoltage level of the healthy phase is reduced to the greatest extent possible while meeting equipment safety constraints.

[0178] Finally, the obtained calculation results can be applied to various scenarios such as wind farm control parameter tuning, grid connection capacity planning, and protection configuration.

[0179] First, this application constructs a positive and negative sequence dual synchronous dq control model for direct-drive wind farms and establishes its mapping relationship with the symmetrical component method, organically integrating the dynamic characteristics of converter control with sequence component analysis. This solves the limitation of traditional methods being difficult to adapt to asymmetrical fault scenarios and achieves accurate analysis of transient overvoltages under asymmetrical faults.

[0180] Second, this application equates direct-drive wind farms to frequency-dependent controlled sequence impedance sources and constructs sequence network equations that include dynamic support for wind power by combining grid sequence impedance. This approach better reflects the electrical characteristics of actual wind power grid-connected systems and provides a reliable analytical framework for calculating fault point parameters under different types of asymmetrical faults.

[0181] Third, this application establishes a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be directly applied to scenarios such as wind farm control parameter setting, grid connection capacity planning, or protection configuration. This effectively improves the analysis accuracy and application guidance of direct-drive wind power grid-connected systems under asymmetrical faults, and helps ensure the safe and stable operation of new energy power systems.

[0182] Figure 2 This diagram illustrates a schematic of a transient overvoltage analysis device for a direct-drive wind power grid-connected system under asymmetrical faults according to an embodiment of this application. Figure 2 It can be seen that the transient overvoltage analysis device 200 for direct-drive wind power grid-connected systems under asymmetrical faults includes:

[0183] The control model building unit 210 is used to obtain three-phase unbalanced voltage and current, and to build a positive and negative sequence dq control model for positive and negative sequence dual synchronization of direct-drive wind farm.

[0184] The mapping relationship construction unit 220 is used to establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and to determine the positive sequence dynamic reactive current increment and negative sequence current suppression coefficient according to the converter control strategy.

[0185] Boundary condition construction unit 230 is used to establish sequential network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit.

[0186] Sequence impedance equivalent unit 240 is used to convert a direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm.

[0187] The sequence network equation building unit 250 is used to combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power.

[0188] The fault point parameter calculation unit 260 is used to calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through the inverse transformation of symmetrical components.

[0189] The quantitative calculation and application unit 270 is used to calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient, which can be used in any scenario of wind farm control parameter setting, access capacity planning and protection configuration.

[0190] It should be noted that the aforementioned transient overvoltage analysis device for direct-drive wind power grid-connected systems under asymmetrical faults can implement the aforementioned transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults. The implementation details will not be elaborated here.

[0191] Figure 3 This invention illustrates a schematic diagram of the structure of an electronic device according to an embodiment of the present application. Figure 3 As shown, the electronic device includes a processor, memory, network interface, and database connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile and / or volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface is used for communication with external devices via a network connection. When the computer program is executed by the processor, it implements the functions or steps of a transient overvoltage analysis method for a direct-drive wind power grid-connected system under asymmetrical faults.

[0192] In one embodiment, the electronic device provided in this application includes a memory and a processor. The memory stores a database and a computer program that can run on the processor. When the processor executes the computer program, it implements the steps of the aforementioned transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults.

[0193] The above is as stated in this application. Figure 2The method for analyzing transient overvoltages in a direct-drive wind power grid-connected system under asymmetrical faults, as disclosed in the illustrated embodiment, can be applied to a processor or implemented by a processor. During implementation, each step of the above method can be completed by integrated logic circuits in the processor's hardware or by instructions in software form. The processor can be a general-purpose processor, including a Central Processing Unit (CPU), a Network Processor (NP), etc.; it can also be a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field-Programmable Gate Array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. The steps of the method disclosed in the embodiments of this application can be directly implemented by a hardware decoding processor, or by a combination of hardware and software modules in the decoding processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method.

[0194] In one embodiment, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the aforementioned transient overvoltage analysis method for direct-drive wind power grid-connected systems under asymmetrical faults.

[0195] It should be noted that the functions or steps that the above-mentioned electronic devices or computer-readable storage media can achieve can be referred to the relevant descriptions in the foregoing method embodiments. To avoid repetition, they will not be described one by one here.

[0196] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0197] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above.

[0198] The above-described embodiments are only used to illustrate the technical application of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical applications described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical applications to deviate from the spirit and scope of the technical applications of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for analyzing transient overvoltages in a direct-drive wind power grid-connected system under asymmetrical faults, characterized in that, include: Control model construction steps: Obtain three-phase unbalanced voltage and current, and construct a positive and negative sequence dq control model for direct-drive wind farm with positive and negative sequence dual synchronization; The steps for constructing the mapping relationship are as follows: establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and determine the positive sequence dynamic reactive current increment and the negative sequence current suppression coefficient according to the converter control strategy; Boundary condition construction steps: Establish sequence network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit; Sequence impedance equivalent steps: Equivalently convert the direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm; Steps for constructing the sequence network equation: Combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power. Fault point parameter calculation steps: Calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through symmetrical component inverse transformation; Quantitative calculation and application steps: Calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient; The quantitative calculation and application steps specifically include: calculating the amplitude of the healthy phase voltage, defining the overvoltage coefficient as the ratio of the healthy phase voltage amplitude to the rated voltage, and establishing the relationship between the overvoltage coefficient and the negative sequence q-axis current suppression coefficient. The quantitative relationship is obtained; the calculation results are applied to any scenario in wind farm control parameter tuning, access capacity planning and protection configuration; By analyzing the overvoltage coefficient... Find the partial derivatives, set them to 0, and solve for the optimal negative sequence current suppression coefficient. The optimal negative sequence current suppression coefficient depends on the grid impedance, the wind farm equivalent impedance, and the ratio of the zero-sequence impedance to the positive-sequence impedance of the system.

2. The method according to claim 1, characterized in that, The control model construction steps specifically include: decoupling the three-phase unbalanced voltage and current into positive-sequence dq components and negative-sequence dq components through Park transformation, and establishing the voltage and current dynamic equations of the grid-side converter in the positive and negative sequence dq coordinate system; The specific steps for constructing the mapping relationship include: converting the positive and negative sequence dq current amplitudes into positive sequence currents represented by symmetrical components. and negative sequence current And determine the positive-sequence dynamic reactive current increment according to the converter control strategy. and negative sequence q-axis current suppression coefficient ; The specific steps for constructing boundary conditions include: for three fault types—single-phase grounding, two-phase grounding, and two-phase short circuit—deriving the relationships between zero-sequence current, positive-sequence current, and negative-sequence current, as well as the relationships between zero-sequence voltage, positive-sequence voltage, and negative-sequence voltage; The sequence impedance equivalent steps specifically include: controlling the positive and negative sequence parameters. , , , Calculate the equivalent positive sequence impedance of a wind farm and equivalent negative sequence impedance ,in, The proportional gain of the positive sequence PI controller; The integral coefficient of the positive-sequence PI controller; The proportional gain of the negative-sequence PI controller. The integral coefficients of the negative-sequence PI controller; The specific steps for constructing the sequence network equation include: according to the fault type, the equivalent sequence impedance of the wind farm and the sequence impedance of the power grid are combined in parallel or in series to form the total sequence impedance of the system that includes the influence of wind power. The specific steps for calculating fault point parameters include: calculating the current, zero-sequence voltage, positive-sequence voltage, and negative-sequence voltage at the fault point according to the sequence network connection method corresponding to the fault type, and obtaining the three-phase voltage through inverse transformation of symmetrical components.

3. The method according to claim 1 or 2, characterized in that, In the positive-sequence dq coordinate system, the voltage and current dynamic equations of the grid-side converter are: ； ； In the negative-sequence dq coordinate system, the voltage and current dynamic equations of the grid-side converter are: ； ； Where L is the filter inductance; R is the equivalent resistance. and These are the positive sequence d-axis and q-axis currents, respectively; and These are the output voltages of the positive-sequence d-axis and q-axis converters, respectively. and These represent the positive-sequence d-axis and q-axis grid voltages, respectively. and These are the negative sequence d-axis and q-axis currents, respectively. and These are the output voltages of the negative sequence d-axis and q-axis converters, respectively. and These represent the negative sequence d-axis and q-axis grid voltages, respectively.

4. The method according to claim 1 or 2, characterized in that, The mapping relationship between the positive and negative sequence dq current amplitudes and the symmetrical components is as follows: ； ; The formula for calculating the positive-sequence dynamic reactive current increment is: ; The formula for calculating the negative sequence current reference value is: ; ; in, This is the per-unit value of the positive sequence voltage at the grid connection point. This is the positive sequence reactive power support coefficient. Rated current, , Z is the negative sequence dq-axis current suppression coefficient. eq The equivalent impedance magnitude of the system. and These are the positive sequence d-axis and q-axis currents, respectively. and These are the negative sequence d-axis and q-axis currents, respectively. and These represent the negative sequence d-axis and q-axis grid voltages, respectively.

5. The method according to claim 1 or 2, characterized in that, The method for calculating the equivalent sequence impedance of a wind farm is as follows: Establish the closed-loop transfer function from grid voltage to output current: ; ; The equivalent sequence impedance of a wind farm is defined as the reciprocal of its transfer function: ; in, , For the Laplace transform of positive and negative sequence voltages, , For the Laplace transform of positive and negative sequence currents, , These are the proportional and integral parameters of the positive-sequence PI controller. These are the proportional and integral parameters of the negative-sequence PI controller, respectively; L is the filter inductance; and R is the equivalent resistance.

6. The method according to claim 5, characterized in that, When the fault is a single-phase ground fault, the total positive sequence impedance The parallel connection of the grid positive-sequence impedance and the wind farm equivalent positive-sequence impedance: ; Total negative sequence impedance The negative sequence impedance of the power grid is connected in parallel with the equivalent negative sequence impedance of the wind farm: ; For total negative sequence impedance By introducing an equivalent negative sequence impedance correction factor, the corrected equivalent total negative sequence impedance is obtained. for: ； in, , These are the positive and negative sequence impedances of the power grid, respectively. This represents the negative sequence impedance of the line from the wind farm to the grid connection point. This is the equivalent positive sequence impedance. This is the equivalent negative sequence impedance. This is the negative sequence q-axis current suppression coefficient. The equivalent impedance magnitude of the system is Ω.

7. The method according to claim 6, characterized in that, When the fault is a single-phase ground fault, according to the boundary conditions = = and + + =3 Combining Kirchhoff's voltage law for sequence networks, the positive sequence current is obtained as: ; Thus, the sequence voltages are obtained: ; ; ; The three-phase voltage is obtained by inverse transformation of symmetrical components: ; Where a = e^(j2π / 3) is the rotation operator.

8. The method according to claim 7, characterized in that, When the fault is a single-phase ground fault, the voltage of the healthy phase b is: ; Substituting into the expression for sequence voltage, we obtain the following expression: ; The expression obtained after simplification is as follows: ; Will Substituting the expression and simplifying it, we obtain the b-phase overvoltage coefficient considering the negative sequence support of wind power: ; in, Rated phase voltage, The overvoltage coefficient of phase b is taken into account for the influence of wind power.

9. The method according to claim 8, characterized in that, Establish overvoltage coefficient and negative sequence q-axis current suppression coefficient The specific quantitative relationships include: Establish the partial derivative of the overvoltage coefficient with respect to the negative-sequence q-axis current suppression coefficient: ; Solve for the optimal negative sequence current suppression coefficient: ; Choose the smaller of the actual setting value and the theoretical optimal value and the current capacity constraint value: ; in, The maximum current of the converter and positive sequence rated current Sure: 。 10. A transient overvoltage analysis device for a direct-drive wind power grid-connected system under asymmetrical faults, characterized in that, The device includes: The control model building unit is used to obtain three-phase unbalanced voltage and current, and to build a positive and negative sequence dq control model for positive and negative sequence dual synchronization of direct-drive wind farm. The mapping relationship construction unit is used to establish the mapping relationship between the positive and negative sequence dq control model and the symmetrical component method, and to determine the positive sequence dynamic reactive current increment and negative sequence current suppression coefficient according to the converter control strategy. Boundary condition construction unit is used to establish the sequence network boundary conditions under various asymmetric faults, including: single-phase grounding, two-phase grounding, and two-phase short circuit. Sequence impedance equivalent unit is used to convert a direct-drive wind farm into a frequency-dependent controlled sequence impedance source to obtain the equivalent sequence impedance of the wind farm. The sequence network equation building unit is used to combine the equivalent sequence impedance of the wind farm with the sequence impedance of the power grid in parallel or series to establish the sequence network equation considering the dynamic support of wind power. The fault point parameter calculation unit is used to calculate the current and sequence voltage of the fault point according to the sequence network connection method corresponding to the fault type, and obtain the three-phase voltage through the inverse transformation of symmetrical components. The quantitative calculation and application unit is used to calculate the overvoltage coefficient and establish a quantitative relationship between the overvoltage coefficient and the negative sequence current suppression coefficient. The quantitative calculation and application steps specifically include: calculating the amplitude of the healthy phase voltage, defining the overvoltage coefficient as the ratio of the healthy phase voltage amplitude to the rated voltage, and establishing the relationship between the overvoltage coefficient and the negative sequence q-axis current suppression coefficient. The quantitative relationship is obtained; the calculation results are applied to any scenario in wind farm control parameter tuning, access capacity planning and protection configuration; By analyzing the overvoltage coefficient... Find the partial derivatives, set them to 0, and solve for the optimal negative sequence current suppression coefficient. The optimal negative sequence current suppression coefficient depends on the grid impedance, the wind farm equivalent impedance, and the ratio of the zero-sequence impedance to the positive-sequence impedance of the system.

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