Damping analysis method and device for low-frequency mode of offshore wind power flexible direct current station

Abstract

The present application provides a damping analysis method and device for the low-frequency mode of a wind power flexible direct current offshore station. The method includes: using a sweep frequency processing method under pre-set wind grid-side and flexible direct current sending-end control parameters to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies; determining the target oscillation frequency corresponding to the low-frequency mode under given control parameters based on the intersection of the oscillation frequency curve and the 0 axis; obtaining the target damping based on the target oscillation frequency and the damping curve; determining the stability of the low-frequency mode of the wind power flexible direct current offshore station based on the positive or negative value of the target damping, and determining the stability margin based on the numerical value of the target damping. In this way, the dimension of the mathematical model and the complexity of the analysis can be reduced.

Description

Technical Field

[0001] The present application relates to the field of power system safety technology, and in particular to a damping analysis method and device for low-frequency modes of offshore wind power flexible direct current stations. Background Art

[0002] Offshore direct-drive wind farms can achieve high-capacity and long-distance power transmission through flexible direct current (HVDC). The transmission system consists of an offshore station consisting of wind turbines and flexible direct current (HVDC) transmitters, and an onshore station consisting of flexible direct current (HVDC) receivers and an AC network. Offshore stations are essentially multi-timescale control systems composed of power electronic devices such as wind turbine converters and HVDC transmitters. Due to control interactions, there is a risk of oscillation instability in actual operation. Research has shown that the control mode of offshore stations is closely related to the control strategy, parameter settings, and operating conditions. Mode damping varies with operating scenarios, potentially posing a risk of oscillation instability. In the low-frequency range of 0–10 Hz, a pair of oscillation modes are jointly dominated by wind turbine phase-locked loop (PPL) control and flexible direct current (HVDC) transmitter q-axis V / F control. This is due to the interaction between the PLL and HVDC transmitter V / F control, and is prone to instability at high offshore wind turbine output.

[0003] To address the oscillation problem of wind power transmitted to offshore stations via flexible direct current (FDC), mainstream analysis methods include electromagnetic transient time-domain simulation technology, eigenvalue analysis technology based on small-signal state-space models, and impedance analysis technology based on small-signal impedance models. Among them, electromagnetic transient time-domain simulation technology requires the establishment of a detailed electromagnetic transient model of the case system. The calculation process requires the storage of a large amount of waveform data, which places high demands on computing power and storage space, making it difficult to quickly evaluate the stability of the system in a short period of time. Eigenvalue analysis technology based on small-signal state-space models is based on the small-signal state-space model of the analysis object. However, it is difficult to avoid the "curse of dimensionality" problem caused by the increase in system complexity. Impedance analysis technology based on small-signal impedance models also relies on small-signal models for stability analysis. However, due to the black-box processing of the impedance model, impedance analysis technology cannot distinguish the oscillation mode, cannot clearly define the model vibration shape, and cannot achieve targeted tracking and research of specific oscillation modes.

[0004] In summary, for the common low-frequency oscillation problem of offshore wind power flexible direct current stations, the existing technology has the problem of high complexity in stability assessment, which makes it impossible to quickly judge the stability. Summary of the Invention

[0005] The purpose of this application is to solve at least one of the above-mentioned technical deficiencies, especially the technical defect that the stability evaluation method in the prior art is highly complex and thus cannot quickly determine the stability.

[0006] In a first aspect, the present application provides a damping analysis method for a low-frequency mode of a wind power flexible direct current offshore station, the method comprising:

[0007] A frequency sweeping process is used under preset control parameters of the wind power grid side and the flexible direct current sending end to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies;

[0008] Determine the target oscillation frequency corresponding to the low-frequency mode under given control parameters according to the intersection of the oscillation frequency curve and the 0 axis;

[0009] Obtaining target damping according to the target oscillation frequency and the damping curve;

[0010] The stability of the low-frequency mode of the offshore wind power flexible direct current station is determined according to the positive or negative value of the target damping, and the stability margin is determined according to the numerical value of the target damping.

[0011] In one embodiment, the step of obtaining the oscillation frequency curve and the damping curve by using a sweep frequency processing method under preset wind grid side and flexible direct current sending end control parameters includes:

[0012] Determining the oscillation frequency curve and the damping curve according to a pre-constructed oscillation frequency function and a loop damping expression;

[0013] Wherein, the oscillation frequency function as follows:

[0014]

[0015] The loop damping The expression is as follows:

[0016]

[0017] in, is the phase-locked control proportional gain parameter, is the phase-locked control integral gain parameter, and is the relevant real number, For fixed damping, It is the additional damping and a function of the oscillation frequency, used to characterize the equivalent damping size corresponding to the external electrical and control links.

[0018] In one embodiment, the process of constructing the oscillation frequency function and the loop damping expression includes:

[0019] Determine the first characteristic equation of the second-order wind turbine phase-locked loop control system;

[0020] Performing a Laplace transform on the obtained small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating the intermediate variables of the frequency domain model to obtain a reduced-order model, and determining the second characteristic equation of the reduced-order model;

[0021] When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, the oscillation frequency function and the loop damping expression are constructed based on the first characteristic equation and the second characteristic equation.

[0022] In one embodiment, the first characteristic equation is expressed as follows:

[0023]

[0024] in, Refers to the eigenvalue.

[0025] In one embodiment, the steps of performing Laplace transform on the acquired small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating the intermediate variables of the frequency domain model to obtain a reduced-order model, and determining the second characteristic equation of the reduced-order model include:

[0026] The second characteristic equation is obtained according to the following expression:

[0027]

[0028] in, refers to the first-order coefficient, Refers to the coefficient of the zero-order term.

[0029] In one embodiment, when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, the step of constructing an oscillation frequency function based on the first characteristic equation and the second characteristic equation includes:

[0030] When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, based on the first characteristic equation and the second characteristic equation, the expression of the independent variable oscillation frequency is obtained as follows:

[0031]

[0032] The oscillation frequency function is constructed according to the expression of the independent variable oscillation frequency.

[0033] In one embodiment, the step of determining the stability of the low-frequency mode of the offshore wind power flexible direct current station according to the positive or negative value of the target damping includes:

[0034] If the target damping is greater than zero, the low-frequency mode of the offshore wind power flexible direct current station is in a stable state;

[0035] If the target damping is zero, the low-frequency mode of the wind power flexible direct current offshore station is in a critical stable state;

[0036] If the target damping is less than zero, the low-frequency mode of the offshore wind power flexible direct current station is in an unstable state.

[0037] In a second aspect, the present application provides a damping analysis device for a low-frequency mode of a wind power flexible direct current offshore station, the device comprising:

[0038] The curve acquisition module uses a sweep frequency processing method under preset wind grid side and flexible direct current sending end control parameters to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies;

[0039] a target oscillation frequency determination module, configured to determine, based on the intersection of the oscillation frequency curve and the zero axis, a target oscillation frequency corresponding to the low-frequency mode under given control parameters;

[0040] a target damping determination module, configured to obtain a target damping according to the target oscillation frequency and the damping curve;

[0041] The damping analysis module is used to determine the stability of the low-frequency mode of the offshore wind power flexible direct current station according to the positive or negative value of the target damping, and to determine the stability margin according to the numerical value of the target damping.

[0042] In a third aspect, the present application provides a storage medium storing computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the damping analysis method for the low-frequency mode of the offshore wind power flexible direct current station described in any of the above embodiments.

[0043] In a fourth aspect, the present application provides a computer device, comprising: one or more processors, and a memory;

[0044] The memory stores computer-readable instructions, and when the computer-readable instructions are executed by the one or more processors, the steps of the damping analysis method for the low-frequency mode of the offshore wind power flexible direct current station described in any of the above embodiments are executed.

[0045] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0046] The damping analysis method and device for the low-frequency mode of a wind power flexible direct current offshore station provided in the present application include: using a sweep frequency processing method under pre-set wind grid side and flexible direct current sending end control parameters to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies; determining the target oscillation frequency corresponding to the low-frequency mode under given control parameters according to the intersection of the oscillation frequency curve and the 0 axis; obtaining the target damping according to the target oscillation frequency and the damping curve; determining the stability of the low-frequency mode of the wind power flexible direct current offshore station according to the positive or negative value of the target damping, and determining the stability margin according to the numerical value of the target damping. Determining the target oscillation frequency and target damping according to the relationship between the oscillation frequency and the target oscillation frequency and the target damping in the function curve can reduce the dimension of the mathematical model. By analyzing the positive or negative and numerical value of the target damping, the stability and stability margin of the low-frequency mode of the wind power flexible direct current offshore station can be determined, thereby reducing the complexity of the analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0048] Figure 1 A flow chart of a damping analysis method for a low-frequency mode of a wind power flexible direct current offshore station provided in an embodiment of the present application;

[0049] Figure 2 A schematic diagram of the process of constructing the oscillation frequency function and loop damping expression provided in the embodiment of the present application;

[0050] Figure 3 Wind power phase-locked loop second-order system control block diagram provided in the embodiment of this application

[0051] Figure 4 A schematic diagram of the damping analysis process provided in an embodiment of the present application;

[0052] Figure 5 A schematic diagram of an offshore wind power grid-connected system via flexible direct current provided in an embodiment of the present application;

[0053] Figure 6 Schematic diagram of damping analysis of a second-order system under different q-axis proportional gains provided in an embodiment of the present application;

[0054] Figure 7 A schematic diagram of the structure of a damping analysis device for a low-frequency mode of a wind power flexible direct current offshore station provided in an embodiment of the present application;

[0055] Figure 8 A schematic diagram of the internal structure of a computer device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0057] The low-frequency oscillation mode in the offshore wind power flexible direct current converter subsystem can be considered a control issue for maintaining synchronization between the gridside converter (GSC) and the output AC voltage of the flexible direct current sending end converter (SEC). Under high wind power output scenarios, this can lead to weak damping and the risk of oscillation instability. This paper follows a reduced-order selection model analysis approach, retaining the second-order phase-locked control equations for the wind power GSC. It then performs damping calculations and stability assessments for the low-frequency oscillation mode in offshore wind power flexible direct current stations.

[0058] This application provides a damping analysis method for low-frequency mode of offshore wind power flexible direct current station. The following embodiments are described by taking the application of this method to computer equipment as an example. It can be understood that the computer equipment can be any device with data processing function, including but not limited to a single server, a server cluster, a personal laptop computer, a desktop computer, etc. Figure 1 As shown, the damping analysis method for the low-frequency mode of the offshore wind power flexible direct current station of the present application may include the following steps:

[0059] S101: A frequency sweeping process is used under preset wind grid side and flexible direct current sending end control parameters to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies.

[0060] In this step, frequency sweeping refers to a signal processing technique used to analyze and process signals within a certain frequency range. This involves performing spectral analysis on the signal to determine the frequency components and their strengths. Control parameters for offshore wind power flexible direct current (FDC) stations include grid-side phase-locked control parameters and FDC sending-end SEC V / F control parameters. FDC sending-end V / F control refers to voltage / frequency control.

[0061] Furthermore, by performing frequency sweep processing on each parameter, an oscillation frequency curve and a damping curve are obtained, and the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies, so that the oscillation frequency curve and the damping curve can be associated through the oscillation frequency. For example, a certain independent variable can be determined through the oscillation frequency curve, and then the corresponding damping can be determined on the damping curve based on the independent variable. Alternatively, a certain independent variable can be determined through the damping curve, and then the corresponding value can be determined on the oscillation frequency curve based on the independent variable. Alternatively, after determining a certain independent variable, the corresponding value can be determined on the oscillation frequency curve and the damping curve.

[0062] S102: Determine, according to the intersection of the oscillation frequency curve and the zero axis, a target oscillation frequency corresponding to the low-frequency mode under given control parameters.

[0063] In this step, there is only one intersection point between the oscillation frequency curve and the 0 axis, and this intersection point is the target oscillation frequency corresponding to the low-frequency mode under given control parameters.

[0064] S103: Obtain target damping according to the target oscillation frequency and the damping curve.

[0065] In this step, the independent variable of the damping curve is the oscillation frequency. When the target oscillation frequency is obtained, the target oscillation frequency is substituted into the damping curve as an independent variable to obtain a unique target damping.

[0066] S104: Determine the stability of the low-frequency mode of the offshore wind power flexible direct current station according to the positive or negative value of the target damping, and determine the stability margin according to the numerical value of the target damping.

[0067] In this step, the target damping can be greater than 0, less than 0, or even equal to 0. The stability of the low-frequency mode of the offshore wind power flexible direct current station can be determined based on the relationship between the target damping and 0. Stability can include stable, unstable, and critically stable. The stability margin of the low-frequency mode of the offshore wind power flexible direct current station refers to the distance from the system's critical stability when operating at the designed operating point. The stability margin of the low-frequency mode can be determined based on the value of the target damping.

[0068] In the above embodiment, the method includes: using a sweep frequency processing method under pre-set wind grid side and flexible direct current sending end control parameters to obtain an oscillation frequency curve and a damping curve, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies; determining the target oscillation frequency corresponding to the low-frequency mode under the proportional gain parameter according to the intersection of the oscillation frequency curve and the 0 axis; obtaining the target damping according to the target oscillation frequency and the damping curve; determining the stability of the low-frequency mode of the wind power flexible direct current offshore station according to the positive or negative value of the target damping, and determining the stability margin according to the numerical value of the target damping. Determining the target oscillation frequency and target damping based on the relationship between the oscillation frequency and the target oscillation frequency and the target damping in the function curve can reduce the dimension of the mathematical model. By analyzing the positive or negative and numerical value of the target damping, the stability and stability margin of the low-frequency mode of the wind power flexible direct current offshore station can be determined, which can reduce the complexity of the analysis.

[0069] In one embodiment, the step of obtaining the oscillation frequency curve and the damping curve by using a sweep frequency processing method under preset wind grid side and flexible direct current sending end control parameters includes:

[0070] Determining the oscillation frequency curve and the damping curve according to a pre-constructed oscillation frequency function and a loop damping expression;

[0071] Wherein, the oscillation frequency function as follows:

[0072]

[0073] The loop damping The expression is as follows:

[0074]

[0075] in, is the phase-locked control proportional gain parameter, is the phase-locked control integral gain parameter, and is the relevant real number, For fixed damping, It is the additional damping and a function of the oscillation frequency, used to characterize the equivalent damping size corresponding to the external electrical and control links.

[0076] Specifically, in addition to the inherent damping, the wind power phase-locked loop control loop has additional damping. The additional damping characterizes the equivalent damping size corresponding to the external electrical and control links. The loop damping state depends on the positive or negative sum of the inherent damping and the additional damping, and the additional damping is a function of the oscillation frequency. In order to obtain the value of the loop damping, it is necessary to calculate the intersection of the oscillation frequency function and the 0 axis in the low-frequency mode, estimate the target oscillation frequency, and then determine the target damping on the loop damping curve according to the target oscillation frequency.

[0077] It can be understood that determining the oscillation frequency curve and the damping curve based on the oscillation frequency function and the loop damping expression can reduce the dimension of the mathematical model and thus reduce the complexity of the analysis.

[0078] like Figure 2 As shown, in one embodiment, the process of constructing the oscillation frequency function and the loop damping expression includes:

[0079] S201: Determine the first characteristic equation of the wind power phase-locked loop control second-order system;

[0080] S202: performing a Laplace transform on the obtained small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating intermediate variables of the frequency domain model to obtain a reduced-order model, and determining a second characteristic equation of the reduced-order model;

[0081] S203: When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, constructing the oscillation frequency function and the loop damping expression based on the first characteristic equation and the second characteristic equation.

[0082] It can be understood that when the low-frequency mode of the offshore wind power flexible direct current station is in a weak damping state, constructing the oscillation frequency function and loop damping expression according to the first characteristic equation and the second characteristic equation can reduce the dimension of the mathematical model and thus reduce the complexity of the analysis.

[0083] In one embodiment, the first characteristic equation is expressed as follows:

[0084]

[0085] in, Refers to the eigenvalue.

[0086] Specifically, the wind power phase-locked loop control transfer function is as follows: Figure 3 As shown, is the reference signal, is the output signal, is the angular frequency, is the signal on the feedback path, is the integral in the frequency domain. The wind power phase-locked loop itself constitutes a closed-loop second-order system, from which the first characteristic equation can be obtained. The inherent damping corresponding to the design parameters of the second-order phase-locked loop system is and oscillation frequency They are:

[0087]

[0088]

[0089] It can be understood that the inherent damping of the second-order system is Proportional to the proportional gain of the PLL, since Is a positive number, inherent damping Shows positive value.

[0090] In one embodiment, the steps of performing Laplace transform on the acquired small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating intermediate variables of the frequency domain model to obtain a reduced-order model, and determining a second characteristic equation of the reduced-order model include:

[0091] The second characteristic equation is obtained according to the following expression:

[0092]

[0093] in, refers to the coefficient of the first-order term, Refers to the coefficient of the zero-order term.

[0094] Specifically, the stability of wind power PLL control is related to the flexible direct current SEC control and other links. Based on the full-dimensional state space equation reduction of the offshore subsystem, the second-order control equation of the wind power PLL is retained, and the PLL characteristic equation that takes into account the influence of other system controls can be obtained. The small signal state space model of the low-frequency mode of the wind power flexible direct current offshore station is Laplace transformed to obtain the frequency domain model of the system. The state variables are sorted and organized into the following form:

[0095]

[0096] in, represents the frequency domain, is the wind power phase-locked loop state variable , is the column vector of the remaining state variables, 、 、 and is a matrix element.

[0097] Retain wind power phase-locked loop state variables , eliminating the intermediate variables , and obtain the reduced-order model:

[0098]

[0099] in, , is a 2×2 matrix, Refers to the identity matrix.

[0100] Therefore, the reduced-order model can be equivalent to:

[0101]

[0102] in, 、 、 and They are The four matrix elements of , rewrite the formula into a second-order small perturbation frequency domain equation:

[0103]

[0104]

[0105] The second characteristic equation can be obtained based on the second-order small perturbation frequency domain equation.

[0106] In one embodiment, when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, the step of constructing an oscillation frequency function based on the first characteristic equation and the second characteristic equation includes:

[0107] When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, based on the first characteristic equation and the second characteristic equation, the expression of the independent variable oscillation frequency is obtained as follows:

[0108]

[0109] The oscillation frequency function is constructed according to the expression of the independent variable oscillation frequency.

[0110] Specifically, when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, , approximately:

[0111]

[0112]

[0113] in, represents a complex variable, represents the imaginary unit, Indicates frequency.

[0114] The second characteristic equation can be rewritten as:

[0115]

[0116]

[0117] in, represents the real part of a complex number, It represents the imaginary part of a complex number.

[0118] According to the first characteristic equation and the rewritten second characteristic equation, let:

[0119]

[0120] Then we have:

[0121]

[0122]

[0123] when When considering the PLL control of external electrical and control links, the second-order system damping for:

[0124]

[0125] It can be understood that based on the inherent characteristics of the low-frequency mode, by selecting the mode analysis method and constructing a reduced-order analysis model, the dimension of the mathematical model and the complexity of the analysis are greatly reduced; the low-frequency mode of the offshore wind power flexible direct current station is analyzed, and the tracking study of the low-frequency oscillation mode of the offshore wind power flexible direct current station is carried out in a targeted manner; the frequency sweep based on the explicit expression and the calculation of the damping value can easily and quickly derive the oscillation damping of the low-frequency mode, thereby realizing a rapid judgment of the stability.

[0126] like Figure 4 As shown, in one embodiment, the step of determining the stability of the low-frequency mode of the offshore wind power flexible direct current station according to the positive or negative value of the target damping includes:

[0127] S301: If the target damping is greater than zero, the low-frequency mode of the offshore wind power flexible direct current station is in a stable state;

[0128] S302: If the target damping is zero, the low-frequency mode of the offshore wind power flexible direct current station is in a critical stable state;

[0129] S303: If the target damping is less than zero, the low-frequency mode of the offshore wind power flexible direct current station is in an unstable state.

[0130] Specifically, if the target damping is greater than zero, it indicates that the low-frequency mode of the wind power flexible direct current offshore station is in a stable state, which means that the damping effect of the low-frequency mode is strong enough to suppress the oscillation of the system and make it eventually stable; if the target damping is equal to zero, it indicates that the low-frequency mode of the wind power flexible direct current offshore station is in a critical stable state, which means that the damping effect of the low-frequency mode is weak, and the oscillation may continue for a period of time, but will eventually remain in a stable state; if the target damping is less than zero, it indicates that the low-frequency mode of the wind power flexible direct current offshore station is in an unstable state, which means that the damping effect of the low-frequency mode is not enough to suppress the oscillation, and the low-frequency mode will experience growing oscillations and cannot reach a stable state.

[0131] It is understandable that the stability of the low-frequency mode can be quickly judged based on the positive or negative value of the damping.

[0132] To facilitate understanding of the solution of this application, the following is an explanation through specific examples. Figure 5 As shown in the figure, a 1000MW wind farm cluster consists of 182 5.5MW permanent magnet direct-drive synchronous wind turbines connected to a flexible DC offshore converter station via a 10km-long 220kV AC submarine cable. The flexible DC onshore converter station is then connected to the 500kV AC main grid. The converter station has a capacity of 1000MVA, a DC voltage level of ±320kV, and a 90km-long DC submarine cable. Control parameters are specified based on typical project bandwidths: a 20Hz wind turbine phase-locked control bandwidth and a 12Hz flexible DC V / F control bandwidth.

[0133] Keep other parameters unchanged and set the V / F control q-axis proportional gain K of the flexible DC SEC to p9 Set to 0.81, 0.8, and 0.79, under the three parameter conditions, through frequency sweep processing, calculate the curve for estimating the oscillation frequency and damping, such as Figure 6 It should be noted that the SEC's q-axis control-related transmission function is included in the additional damping term In the equation ( ), the change of the q-axis control parameter of SEC will cause the value of the added damping to change, which will be superimposed on the inherent damping and ultimately determine the positive or negative value of the total damping.

[0134] according to The intersection of the curve and the horizontal axis can give the oscillation frequency corresponding to the mode. In the three cases of 0.81, 0.8 and 0.79, the oscillation frequencies are approximately 3.83Hz, 3.79Hz and 3.73Hz; according to the horizontal axis coordinate projected by the oscillation frequency, The curve can be used to obtain the size of the equivalent total damping of the mode. When it is 0.81, D=1.4>0, the low-frequency mode damping is positive, the system is in a stable state, and the inherent damping is 42s-1 , additional damping -40.6s -1 ;when When it is 0.8, D≈0, the low-frequency mode is in a critical stable state, and the inherent damping 42s -1 , additional damping -42s -1 ;when When it drops to 0.79, =-1.6s -1 <0, the low-frequency mode is in a negative damping state, the system tends to oscillate and diverge, and the inherent damping 42s -1 , additional damping -43.6s -1 Therefore, we can get The damping state of the low-frequency oscillation mode under specific values, and the stability is judged based on the damping state.

[0135] The damping analysis device for the low-frequency mode of a wind power flexible direct current offshore station provided by the embodiment of the present application is described below. The damping analysis device for the low-frequency mode of a wind power flexible direct current offshore station described below and the damping analysis method for the low-frequency mode of a wind power flexible direct current offshore station described above can be referred to each other. Figure 7 As shown, the damping analysis device for the low-frequency mode of a wind power flexible direct current offshore station provided by the present application may include the following structure:

[0136] The curve acquisition module 401 is used to obtain an oscillation frequency curve and a damping curve by using a sweep frequency processing method under preset wind grid side and flexible direct current sending end control parameters, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies;

[0137] A target oscillation frequency determination module 402 is configured to determine a target oscillation frequency corresponding to the low-frequency mode under given control parameters according to an intersection of the oscillation frequency curve and the zero axis;

[0138] a target damping determination module 403, configured to obtain a target damping according to the target oscillation frequency and the damping curve;

[0139] The damping analysis module 404 is used to determine the stability of the low-frequency mode of the offshore wind power flexible direct current station according to the positive or negative value of the target damping, and to determine the stability margin according to the numerical value of the target damping.

[0140] In one embodiment, the curve acquisition module 401 includes:

[0141] A curve acquisition submodule, configured to determine the oscillation frequency curve and the damping curve according to a pre-constructed oscillation frequency function and a loop damping expression;

[0142] Wherein, the oscillation frequency function as follows:

[0143]

[0144] The loop damping The expression is as follows:

[0145]

[0146] in, is the phase-locked control proportional gain parameter, is the phase-locked control integral gain parameter, and is the relevant real number, For fixed damping, It is the additional damping and a function of the oscillation frequency, used to characterize the equivalent damping size corresponding to the external electrical and control links.

[0147] In one embodiment, the curve acquisition submodule includes:

[0148] A first characteristic equation determining unit, used to determine a first characteristic equation of a second-order wind power phase-locked loop control system;

[0149] a second characteristic equation determination unit, configured to perform a Laplace transform on the acquired small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminate intermediate variables of the frequency domain model to obtain a reduced-order model, and determine a second characteristic equation of the reduced-order model;

[0150] An oscillation frequency function construction unit is used to construct the oscillation frequency function and the loop damping expression based on the first characteristic equation and the second characteristic equation when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state.

[0151] In one embodiment, the first characteristic equation is expressed as follows:

[0152]

[0153] in, Refers to the eigenvalue.

[0154] In one embodiment, the second characteristic equation determining unit includes:

[0155] The second characteristic equation determining subunit is configured to obtain the second characteristic equation according to the following expression:

[0156]

[0157] in, refers to the first-order coefficient, Refers to the coefficient of the zero-order term.

[0158] In one embodiment, the oscillation frequency function construction unit includes:

[0159] The expression construction subunit is used to obtain the expression of the independent variable oscillation frequency based on the first characteristic equation and the second characteristic equation when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state as follows:

[0160]

[0161] The oscillation frequency function construction subunit is used to construct the oscillation frequency function according to the expression of the independent variable oscillation frequency.

[0162] In one embodiment, the damping analysis module 404 includes:

[0163] A first damping analysis submodule is configured to determine that if the target damping is greater than zero, the low-frequency mode of the offshore wind power flexible direct current station is in a stable state;

[0164] A second damping analysis submodule is configured to determine that if the target damping is zero, the low-frequency mode of the offshore wind power flexible direct current station is in a critical stable state;

[0165] The third damping analysis submodule is used to determine that if the target damping is less than zero, the low-frequency mode of the wind power flexible direct current offshore station is in an unstable state.

[0166] In one embodiment, the present application also provides a storage medium storing computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the damping analysis method for the low-frequency mode of a wind power flexible direct current offshore station as described in any of the above embodiments.

[0167] In one embodiment, the present application also provides a computer device, which stores computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the damping analysis method for the low-frequency mode of a wind power flexible direct current offshore station as described in any of the above embodiments.

[0168] Schematically, as Figure 8 As shown, Figure 8 This is a schematic diagram of the internal structure of a computer device provided in an embodiment of the present application. The computer device 500 can be provided as a server. Figure 8 Computer device 500 includes a processing component 502, which further includes one or more processors, and memory resources represented by memory 501 for storing instructions executable by processing component 502, such as application programs. The application programs stored in memory 501 may include one or more modules, each corresponding to a set of instructions. Furthermore, processing component 502 is configured to execute the instructions to perform the damping analysis method for low-frequency modes of offshore wind turbine flexible direct current (FDC) stations according to any of the aforementioned embodiments.

[0169] The computer device 500 may further include a power supply component 503 configured to perform power management of the computer device 500, a wired or wireless network interface 504 configured to connect the computer device 500 to a network, and an input / output (I / O) interface 505. The computer device 500 may operate based on an operating system stored in the memory 501, such as Windows Server™, Mac OS X™, Unix™, Linux™, Free BSD™, or the like.

[0170] Those skilled in the art will understand that Figure 8 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0171] Finally, it should be noted that, in this article, relational terms such as first and second are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. Without further restriction, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element. Herein, "one," "said," "the," and "its" may also include plural forms unless the context clearly indicates otherwise. A plurality refers to at least two, such as 2, 3, 5, or 8. "And / or" includes any and all combinations of the relevant listed items.

[0172] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referenced to each other.

[0173] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A damping analysis method for low-frequency mode of offshore wind power flexible direct current station, characterized in that: The method comprises: Determine the first characteristic equation of the second-order wind turbine phase-locked loop control system; Performing a Laplace transform on the obtained small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating the intermediate variables of the frequency domain model to obtain a reduced-order model, and determining the second characteristic equation of the reduced-order model; When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, an oscillation frequency function and a loop damping expression are constructed based on the first characteristic equation and the second characteristic equation; Determine an oscillation frequency curve and a damping curve according to the oscillation frequency function and the loop damping expression, wherein the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies; Wherein, the oscillation frequency function as follows: ； The loop damping The expression is as follows: ； in, is the phase-locked control proportional gain parameter, is the phase-locked control integral gain parameter, and is the relevant real number, For fixed damping, is the additional damping and is a function of the oscillation frequency, used to characterize the equivalent damping size corresponding to the external electrical and control links; Determine the target oscillation frequency corresponding to the low-frequency mode under given control parameters according to the intersection of the oscillation frequency curve and the 0 axis; Obtaining target damping according to the target oscillation frequency and the damping curve; If the target damping is greater than zero, the low-frequency mode of the wind power flexible direct current offshore station is in a stable state; if the target damping is equal to zero, the low-frequency mode of the wind power flexible direct current offshore station is in a critical stable state; if the target damping is less than zero, the low-frequency mode of the wind power flexible direct current offshore station is in an unstable state, and the stability margin is determined according to the numerical value of the target damping.

2. The damping analysis method for low-frequency mode of offshore wind power flexible direct current station according to claim 1 is characterized in that: The expression of the first characteristic equation is as follows: ； in, Refers to the eigenvalue.

3. The damping analysis method for low-frequency mode of offshore wind power flexible direct current station according to claim 2 is characterized in that: The steps of performing Laplace transform on the acquired small signal state space model of the low-frequency mode of the offshore wind power flexible direct current station to obtain a frequency domain model, eliminating intermediate variables of the frequency domain model to obtain a reduced-order model, and determining a second characteristic equation of the reduced-order model include: The second characteristic equation is obtained according to the following expression: ； in, refers to the first-order coefficient, Refers to the coefficient of the zero-order term.

4. The damping analysis method for low-frequency mode of offshore wind power flexible direct current station according to claim 3 is characterized in that: When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, the step of constructing an oscillation frequency function based on the first characteristic equation and the second characteristic equation includes: When the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, based on the first characteristic equation and the second characteristic equation, the expression of the independent variable oscillation frequency is obtained as follows: ； The oscillation frequency function is constructed according to the expression of the independent variable oscillation frequency.

5. A damping analysis device for low-frequency mode of a wind power flexible direct current offshore station, characterized in that: The device comprises: A curve acquisition module is used to determine the first characteristic equation of the second-order system of the wind power phase-locked loop control; perform Laplace transform on the small signal state space model of the low-frequency mode of the obtained wind power flexible direct current offshore station to obtain a frequency domain model, eliminate the intermediate variables of the frequency domain model to obtain a reduced-order model, and determine the second characteristic equation of the reduced-order model; when the low-frequency mode of the wind power flexible direct current offshore station is in a weak damping state, construct an oscillation frequency function and a loop damping expression based on the first characteristic equation and the second characteristic equation; determine the oscillation frequency curve and the damping curve according to the oscillation frequency function and the loop damping expression, and the independent variables of the oscillation frequency curve and the damping curve are both oscillation frequencies; wherein, the oscillation frequency function as follows: ； The loop damping The expression is as follows: ； in, is the phase-locked control proportional gain parameter, is the phase-locked control integral gain parameter, and is the relevant real number, For fixed damping, is the additional damping and is a function of the oscillation frequency, used to characterize the equivalent damping size corresponding to the external electrical and control links; a target oscillation frequency determination module, configured to determine, based on the intersection of the oscillation frequency curve and the zero axis, a target oscillation frequency corresponding to the low-frequency mode under given control parameters; a target damping determination module, configured to obtain a target damping according to the target oscillation frequency and the damping curve; The damping analysis module is used to determine that if the target damping is greater than zero, the low-frequency mode of the wind power flexible direct current offshore station is in a stable state; if the target damping is equal to zero, the low-frequency mode of the wind power flexible direct current offshore station is in a critical stable state; if the target damping is less than zero, the low-frequency mode of the wind power flexible direct current offshore station is in an unstable state; and determine the stability margin according to the numerical value of the target damping.

6. A storage medium, characterized in that: The storage medium stores computer-readable instructions, which, when executed by one or more processors, enable the one or more processors to perform the steps of the damping analysis method for the low-frequency mode of a wind power flexible direct current offshore station as described in any one of claims 1 to 4.

7. A computer device, characterized in that: include: one or more processors, and memory; The memory stores computer-readable instructions, which, when executed by the one or more processors, execute the steps of the damping analysis method for the low-frequency mode of a wind power flexible direct current offshore station as claimed in any one of claims 1 to 4.

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