A frequency nadir quantification assessment method considering wind power low voltage ride through process

Abstract

The application discloses a frequency minimum point quantitative evaluation method considering a low-voltage ride-through wind turbine system, and comprises the following steps: in a multi-machine power system connected with wind power, non-step active power disturbance ΔP L (s) caused by wind power low-voltage ride-through to the system is analyzed, and a frequency response model of the system under the disturbance is established; the non-step active power disturbance ΔP L (s) is converted into a first step disturbance and a response of a virtual power generation device by using an equivalent device method; the frequency response model of the system is simplified by using a unified structure model, and unified structure parameters of each device are calculated; and the unified structure parameters are substituted into an empirical formula to quantitatively evaluate the system frequency minimum point in the low-voltage ride-through process. The frequency minimum point quantitative evaluation method considering the low-voltage ride-through wind turbine system can convert any non-step disturbance into frequency characteristics under the step disturbance for simplified analysis. Compared with existing methods, the disturbance range of quantitative evaluation is expanded, and the system frequency minimum point in the wind power low-voltage ride-through process is quantitatively analyzed.

Description

Technical Field

[0001] This invention belongs to the field of power system frequency characteristic quantification technology, and in particular relates to a method for quantitatively evaluating the lowest frequency point considering the low voltage ride-through process of wind power. Background Technology

[0002] With the large-scale integration of new energy sources such as wind power, traditional power systems dominated by synchronous machines are transforming into new power systems based on power electronics. This leads to a decrease in system inertia and frequency regulation capabilities, and a deterioration in the system's frequency response characteristics.

[0003] In high-proportion renewable energy power systems, the ability of wind turbines to maintain operation and provide support to the system during grid faults is increasingly valued. During low-voltage ride-through (LVRT) periods, wind turbines typically employ reactive power priority control, limiting active power output. Furthermore, after a fault is cleared, the active power output of the wind turbines does not immediately recover but increases at a slow, predetermined rate to avoid a sudden and significant increase in unit load, thus extending the turbine's lifespan. Therefore, the system will be continuously affected by active power deficits during this process, potentially leading to excessively low frequency minimums that trigger protection mechanisms and pose a risk of frequency instability. Thus, it is necessary to analyze and consider the system frequency response during the LVRT process to design frequency regulation control that improves system frequency stability.

[0004] Regarding the system frequency response during wind turbine low-voltage ride-through, current research reveals that when wind power does not participate in system frequency regulation, higher penetration rates and lower system inertia exacerbate frequency stability issues during low-voltage ride-through. However, these studies only qualitatively analyze the system frequency response during wind turbine low-voltage ride-through, lacking quantitative calculations of key factors influencing frequency stability, such as the minimum frequency point. To address this issue, some scholars have proposed using common-mode frequency to characterize the system's global frequency response, establishing a unified structural model for power generation equipment and deriving an empirical formula for the minimum frequency point. However, this empirical formula only applies to cases where the system power disturbance is a step, while the power deficit during wind turbine low-voltage ride-through is far more complex than a step, making it impossible to directly apply this empirical formula to analyze the minimum frequency point.

[0005] Therefore, it is necessary to study a quantitative evaluation method that takes into account the lowest system frequency point during the low-voltage ride-through process of the wind turbine. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the aforementioned existing problems, the present invention is proposed.

[0008] Therefore, the present invention provides a quantitative evaluation method for the lowest frequency point considering the low voltage ride-through process of wind power, which can quantitatively evaluate the lowest frequency point of a system considering the low voltage ride-through process.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution, including:

[0010] In a multi-machine power system with wind power grid connection, the non-step active power disturbance caused by wind power low voltage ride-through is analyzed, and a frequency response model of the system under the disturbance is established.

[0011] The equivalent device method is used to transform non-step active disturbances into a step disturbance and the response of a virtual power generation device.

[0012] The system frequency response model is simplified using a unified structural model, and the unified structural parameters of each device are calculated.

[0013] Substituting uniform structural parameters into empirical formulas, we can quantitatively evaluate the lowest system frequency point during the low-voltage ride-through process.

[0014] As a preferred embodiment of the frequency minimum point quantification evaluation method considering the low voltage ride-through process of wind power described in this invention, the power generation equipment in the multi-machine power system with wind power grid connection includes synchronous machines and wind turbine units.

[0015] As a preferred embodiment of the frequency minimum point quantification evaluation method considering the low voltage ride-through process of wind power described in this invention, the system frequency response model is represented by the frequency common-mode component Δω(s).

[0016] As a preferred embodiment of the frequency minimum point quantitative evaluation method considering the low-voltage ride-through process of wind power described in this invention, the establishment of the system frequency response model includes: the active power dynamic process of the wind turbine during the entire low-voltage ride-through process can be represented as follows:

[0017] ΔP d_LVRT (t)=-P0u(t-t0)+k(t-t1)u(t-t1)

[0018] Where t0 is the time of fault occurrence, which can be set to 0; t1 is the time of fault clearing; u(t) is the unit step function; P0 is the power deficit caused by the low voltage ride-through of the wind turbine at the moment of fault, P0 = P N0 k represents the active power recovery rate of the wind turbine after the fault is cleared.

[0019] Without loss of generality, consider a wind turbine grid-connected system with n generating units, where the first k units (numbered 1 to k) are synchronous machines, and the last nk units (numbered k+1 to n) are wind turbines. After a certain fault occurs in the system, assume that the first m wind turbines (numbered k+1 to k+m+1) enter low-voltage ride-through, p wind turbines (numbered k+m+2 to k+m+p+2) are disconnected from the grid, and the remaining wind turbines operate normally. Then, the frequency response model of the system can be represented by the frequency common-mode component Δω(s) as follows:

[0020]

[0021] Where s is the Laplace operator; ΔP d_LVRT,i (s) represents the active power disturbance caused by the low voltage ride-through of the wind turbine; ΔP d_off,i (s) represents the active power disturbance caused by the decommissioning of wind turbines; G sg,i (s) is the frequency-active power transfer function of the synchronous machine; G w,i (s) is the frequency-active power transfer function of a normally operating wind turbine.

[0022] As a preferred embodiment of the frequency minimum point quantification assessment method considering the low-voltage ride-through process of wind power described in this invention, the equivalent device method includes:

[0023] Consider an arbitrary n-machine system, assuming the disturbance power of each node is ΔP. d,i (s) (which may be a non-step disturbance), then the common-mode frequency of the system can be expressed as follows:

[0024]

[0025] Among them, G i (s) represents the frequency-active power transfer function of the equipment involved in frequency modulation; ΔP L1 (s)=1 T ΔP d Where 1 is an n-dimensional column vector with all elements equal to 1, and ΔP d =[ΔP d,1 ,L,ΔP d,n ] T ;

[0026] Note the arbitrary perturbation ΔP d,i (s) can all be decomposed into a first-order perturbation ΔP s,i (s) = -a / s and the remaining part ΔP r,i (s)=ΔP d,i The sum of (s) + a / s can be rewritten as:

[0027]

[0028] Among them, P L2(s)=1 T ΔP s ΔP s =[ΔP s,1 ,L,ΔP s,n ] T This refers to the step components decomposed from the perturbations at each node.

[0029] As a preferred embodiment of the frequency minimum point quantification assessment method considering the low-voltage ride-through process of wind power described in this invention, the method of converting disturbances using the equivalent device method includes:

[0030] First, we need to consider the active power disturbance ΔP caused by the low-voltage ride-through wind turbine. d_LVRT,i The step component is decomposed from (s); the decomposition method used is:

[0031] ΔP d_LVRT,i (s)=ΔP s,i (s)+ΔP r,i (s)

[0032] Where, ΔP s,i (s)=-P0 / s, that is, a power step disturbance of magnitude P0; That is, the active power that the wind turbine unit recovers at a fixed rate k after the fault is cleared;

[0033] Using the equivalent device method to transform the disturbance, the system frequency Δω(s) considering the low-voltage ride-through process of the wind turbine can be expressed as:

[0034]

[0035] Where, Δω L (s) represents the system frequency considering the low-voltage ride-through process of the wind turbine. Let be the frequency-active power transfer function of the virtual equivalent device. It is in the form of a step jump;

[0036] After transformation using the equivalent device method, the disturbance to the system is only a power disturbance. The device in the system is equivalent to adding a power response of ΔP at each node from k+1 to k+m+1. r,i The virtual equivalent device of (s).

[0037] As a preferred embodiment of the frequency minimum point quantification evaluation method considering the low-voltage ride-through process of wind power described in this invention, the unified structural model includes:

[0038] Δω L (s) If the damping sine curve approaches the normal value for a period of time after the disturbance, then the unified structural model shown below can be used to approximate the characteristics of each device G. sg,i (s), G w,i (s) and Geq,i (s) Dynamics during this time period:

[0039]

[0040]

[0041]

[0042] Among them, J usg,i D usg,i and 1 / K usg,i For G sg,i The unified structural parameters of (s) are called effective inertia, effective damping coefficient, and effective dynamic droop coefficient, respectively; J uw,i D uw,i and 1 / K uw,i and J ueq,i D ueq,i and 1 / K ueq,i Similarly.

[0043] As a preferred embodiment of the frequency minimum point quantification evaluation method considering the low-voltage ride-through process of wind power described in this invention, the simplified system frequency response model includes: under power disturbance ΔP dis The common-mode frequency of the system under (s) can be approximately expressed as:

[0044]

[0045] Among them, J us D us and 1 / K us These are the unified structural parameters for the system.

[0046] As a preferred embodiment of the frequency minimum point quantitative evaluation method considering the low-voltage ride-through process of wind power described in this invention, the unified structural parameters of each device are respectively represented as follows:

[0047]

[0048]

[0049]

[0050] As a preferred embodiment of the frequency minimum point quantification evaluation method considering the low-voltage ride-through process of wind power described in this invention, the empirical formula is expressed as:

[0051]

[0052] Among them, P s For ΔP dis The amplitude of (s).

[0053] The beneficial effects of this invention are as follows: The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power provided by this invention can transform any non-step disturbance into a step disturbance for simplified analysis of frequency characteristics, and quantitatively evaluate the lowest system frequency point considering the low-voltage ride-through process of wind power. Compared with existing methods, this method expands the range of disturbances for quantitative evaluation and quantitatively analyzes the lowest system frequency point during the low-voltage ride-through process of wind power. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0055] Figure 1 This is a flowchart illustrating a method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power, as described in the first embodiment of the present invention.

[0056] Figure 2 This is a schematic diagram of 10 machines and 39 nodes in the simulation verification of a method for quantitatively evaluating the lowest frequency point considering the low voltage ride-through process of wind power, as described in the second embodiment of the present invention.

[0057] Figure 3 This is a model diagram of a turbine governor system in the simulation verification of a method for quantitatively evaluating the lowest frequency point considering the low voltage ride-through process of wind power, as described in the second embodiment of the present invention.

[0058] Figure 4 This is a power control diagram of a wind turbine in the simulation verification of a method for quantitatively evaluating the lowest frequency point considering the low voltage ride-through process of wind power, as described in the second embodiment of the present invention.

[0059] Figure 5 The active power waveform diagram of the wind turbine in the simulation verification of the frequency minimum point quantification evaluation method considering the low voltage ride-through process of wind power, as described in the second embodiment of the present invention.

[0060] Figure 6 This is a comparison diagram of the simulated trajectory of the wind turbine participating in frequency regulation and the approximate trajectory under the simplified frequency response model in the simulation verification of a method for quantitative evaluation of the lowest frequency point considering the low voltage ride-through process of wind power, as described in the second embodiment of the present invention. Detailed Implementation

[0061] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0062] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0063] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0064] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0065] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0066] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0067] Example 1

[0068] Reference Figure 1This is the first embodiment of the present invention, which provides a method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power, including:

[0069] S1: In a multi-machine power system with wind power grid connection, analyze the non-step active power disturbance ΔP caused by wind power low-voltage ride-through. L (s), establish the frequency response model of the system under the disturbance;

[0070] It should be noted that the power generation equipment in the multi-machine power system with wind power grid connection includes synchronous machines and wind turbines.

[0071] It should also be noted that the system frequency response model is represented by the frequency common-mode component Δω(s).

[0072] Furthermore, establishing the system frequency response model includes: the active power dynamic process of the wind turbine during the entire low-voltage ride-through process can be represented as follows:

[0073] ΔP d_LVRT (t)=-P0u(t-t0)+k(t-t1)u(t-t1)

[0074] Where t0 is the time of fault occurrence, which can be set to 0; t1 is the time of fault clearing; u(t) is the unit step function; P0 is the power deficit caused by the low voltage ride-through of the wind turbine at the moment of fault, P0 = P N0 k represents the active power recovery rate of the wind turbine after the fault is cleared.

[0075] Without loss of generality, consider a wind turbine grid-connected system with n generating units, where the first k units (numbered 1 to k) are synchronous machines, and the last nk units (numbered k+1 to n) are wind turbines. After a certain fault occurs in the system, assume that the first m wind turbines (numbered k+1 to k+m+1) enter low-voltage ride-through, p wind turbines (numbered k+m+2 to k+m+p+2) are disconnected from the grid, and the remaining wind turbines operate normally. Then, the frequency response model of the system can be represented by the frequency common-mode component Δω(s) as follows:

[0076]

[0077] Where s is the Laplace operator; ΔP d_LVRT,i (s) represents the active power disturbance caused by the low voltage ride-through of the wind turbine; ΔP d_off,i (s) represents the active power disturbance caused by the decommissioning of wind turbines; G sg,i (s) is the frequency-active power transfer function of the synchronous machine; G w,i (s) is the frequency-active power transfer function of a normally operating wind turbine.

[0078] S2: Using the equivalent device method, the non-step active power disturbance ΔP is transformed.L (s) is transformed into a step disturbance and the response of a virtual power generation device;

[0079] It should be noted that the equivalent device method includes:

[0080] Consider an arbitrary n-machine system, assuming the disturbance power of each node is ΔP. d,i (s) (which may be a non-step disturbance), then the common-mode frequency of the system can be expressed as follows:

[0081]

[0082] Among them, G i (s) represents the frequency-active power transfer function of the equipment involved in frequency modulation; ΔP L1 (s)=1 T ΔP d Where 1 is an n-dimensional column vector with all elements equal to 1, and ΔP d =[ΔP d,1 ,L,ΔP d,n ] T ;

[0083] Note the arbitrary perturbation ΔP d,i (s) can all be decomposed into a first-order perturbation ΔP s,i (s) = -a / s and the remaining part ΔP r,i (s)=ΔP d,i The sum of (s) + a / s can be rewritten as:

[0084]

[0085] Among them, P L2 (s)=1 T ΔP s ΔP s =[ΔP s,1 ,L,ΔP s,n ] T This refers to the step components decomposed from the perturbations at each node.

[0086] Furthermore, the transformation of the disturbance using the equivalent device method includes:

[0087] First, we need to consider the active power disturbance ΔP caused by the low-voltage ride-through wind turbine. d_LVRT,i The step component is decomposed from (s); the decomposition method used is:

[0088] ΔP d_LVRT,i (s)=ΔP s,i (s)+ΔP r,i (s)

[0089] Where, ΔP s,i(s)=-P0 / s, that is, a power step disturbance of magnitude P0; That is, the active power that the wind turbine recovers at a fixed rate k after the fault is cleared;

[0090] Using the equivalent device method to transform the disturbance, the system frequency Δω(s) considering the low-voltage ride-through process of the wind turbine can be expressed as:

[0091]

[0092] Where, Δω L (s) represents the system frequency considering the low-voltage ride-through process of the wind turbine. Let be the frequency-active power transfer function of the virtual equivalent device. It is in the form of a step jump;

[0093] After transformation using the equivalent device method, the disturbance to the system is only a power disturbance. The device in the system is equivalent to adding a power response of ΔP at each node from k+1 to k+m+1. r,i The virtual equivalent device of (s).

[0094] It should be noted that a prerequisite for simplifying the system frequency response model using a unified structural model is that the system frequency trajectory under a step disturbance is close to a damped sine curve. However, the disturbance caused by wind power low-voltage ride-through is not a simple step disturbance, but requires the superposition of a slope-like disturbance. Conventional methods generally use the system frequency response model directly for analysis, which is very complex and lacks a simple empirical formula. Therefore, this invention addresses this problem by transforming the slope disturbance into a virtual equivalent device, whose power response corresponds to the original slope form. The equivalent device method is used to transform the non-step active power disturbance ΔP... L (s) is transformed into a step disturbance and the response of a virtual power generation device, and then simplified using a unified structural model.

[0095] S3: Simplify the system frequency response model using a unified structural model and calculate the unified structural parameters of each device;

[0096] It should be noted that the unified structural model includes:

[0097] Δω L (s) If the damping sine curve approaches the normal value for a period of time after the disturbance, then the unified structural model shown below can be used to approximate the characteristics of each device G. sg,i (s), G w,i (s) and G eq,i (s) Dynamics during this time period:

[0098]

[0099]

[0100]

[0101] Among them, J usg,i D usg,i and 1 / K usg,i For G sg,i The unified structural parameters of (s) are called effective inertia, effective damping coefficient, and effective dynamic droop coefficient, respectively; J uw,i D uw,i and 1 / K uw,i and J ueq,i D ueq,i and 1 / K ueq,i Similarly.

[0102] Furthermore, the simplified system frequency response model includes: under power disturbance ΔP dis The common-mode frequency of the system under (s) can be approximately expressed as:

[0103]

[0104] Among them, J us D us and 1 / K us These are the unified structural parameters for the system.

[0105] It should also be noted that the unified structural parameters of each device are expressed as follows:

[0106]

[0107]

[0108]

[0109] S4: Substitute the uniform structural parameters into the empirical formula to quantitatively evaluate the lowest system frequency point during the low voltage ride-through process.

[0110] It should be noted that the empirical formula is expressed as:

[0111]

[0112] Among them, P s For ΔP dis The amplitude of (s). J us D us and 1 / K us These are the unified structural parameters for the system.

[0113] Example 2

[0114] Reference Figure 2-6This is the second embodiment of the present invention, which provides a quantitative evaluation method for the lowest frequency point considering the low voltage ride-through process of wind power. In order to verify the beneficial effects of the present invention, a simulation experiment is conducted for scientific demonstration.

[0115] Build a 10-machine, 39-bus power system in Matlab / Simulink software, such as Figure 2 As shown in the figure. G1 to G10 represent power generation equipment, all with a capacity of 1000MVA (this is used as a baseline for standardizing all parameters in the example). Among them, G4, G7, and G10 are wind turbine generators (with an active power reference value of 0.4 pu during normal operation, equipped with low voltage ride-through control, an active current reference value of 0, an active power recovery rate of 0.2 pu / s, and additional frequency regulation control; the initial frequency regulation parameter is set to J). WTG =8, D WTG =20), the rest are synchronous units. The load is a constant power load. The line impedance and inductance are shown in Table 1.

[0116] Table 1. Line impedance values ​​in simulation verification of the embodiment.

[0117]

[0118]

[0119] Frequency-active power transfer function G of steam turbine unit SG (s) is

[0120] G SG (s)=J SG s+D SG +G T (s)

[0121] In the formula, J SG and D SG These are the inertia and damping coefficient of the synchronous machine, respectively; G T (s) is the transfer function of the turbine speed control system (input is frequency Δω, output is mechanical power ΔP). M ), model such Figure 3 As shown.

[0122] Wind turbines using the DFIG model, such as Figure 4 As shown, the frequency-active power transfer function G in the electromechanical scale is... WTG (s) is

[0123]

[0124] In the formula, J WTG and D WTG These are the virtual inertia and damping coefficient, T, respectively. f_PLL T is the time constant of the filter.f_P K is the time constant of the low-pass filter. P and K I These are the proportional and integral parameters of the PI controller of the phase-locked loop, K. P_PC and K I_PC These are the proportional and integral parameters of the PI controller in the active power outer loop.

[0125] The parameter values ​​for steam turbine units and wind turbine units are shown in Table 2.

[0126] Table 2. Parameter values ​​of the equipment in the simulation verification of the embodiment.

[0127]

[0128] Using the method of this invention, after transforming the disturbance using the equivalent device method, the relationship between the equivalent step disturbance and the frequency response is obtained:

[0129]

[0130] A three-phase short-circuit fault occurred at node 23 at t = 0.5s, and the fault was cleared after 100ms. G4 experienced low-voltage ride-through, G7 was de-energized, and G10 operated normally. The active power waveform is as follows: Figure 5 As shown. The unified structural parameters of each power generation device are calculated using a unified structural approximation method, where the unified structural parameter of the generator set is J. usg,i =7.69, D usg,i =1.29, 1 / K usg,i =2.82, the unified structural parameter of the wind turbine is J uw,i =2.53, D uw,i =24.40, 1 / K uw,i = -3.46, the unified structural parameter of the equivalent equipment is J ueq,i =-0.47, D ueq,i =8.87, 1 / K ueq,i =18.95.

[0131] According to the method of the present invention, the frequency response model is simplified based on the unified structural approximation representation method to obtain a comparison between the frequency trajectory and the system common mode trajectory, for example... Figure 6 As shown. By Figure 6 It can be seen that the frequency trajectory obtained based on the simplified frequency response model basically matches the system's common-mode trajectory, and the frequency trajectories of each device fluctuate around the common-mode frequency in the simulation. The established equivalent device method, after converting the disturbance, combined with the unified structure approximation method, can analyze the system's common-mode frequency characteristics. The experimental data demonstrates the superior performance of the proposed method compared to current methods in various performance indicators.

[0132] It should be recognized that embodiments of the present invention can be implemented or carried out by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer-readable storage medium. The method can be implemented using standard programming techniques—including a non-transitory computer-readable storage medium configured with a computer program, wherein such a storage medium causes the computer to operate in a specific and predefined manner—according to the methods and drawings described in the specific embodiments. Each program can be implemented in a high-level procedural or object-oriented programming language to communicate with the computer system. However, if desired, the program can be implemented in assembly or machine language. In any case, the language can be a compiled or interpreted language. Furthermore, for this purpose, the program can run on a programmed application-specific integrated circuit (ASIC).

[0133] Furthermore, the procedures described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by the context. The procedures described herein (or variations and / or combinations thereof) may be executed under the control of one or more computer systems configured with executable instructions, and may be implemented by hardware or a combination thereof as code (e.g., executable instructions, one or more computer programs, or one or more applications) that commonly executes on one or more processors. The computer program comprises a plurality of instructions executable by one or more processors.

[0134] Furthermore, the method can be implemented in any suitable type of computing platform, including but not limited to personal computers, minicomputers, mainframes, workstations, networked or distributed computing environments, standalone or integrated computer platforms, or in communication with charged particle tools or other imaging devices, etc. Aspects of the invention can be implemented as machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optical read and / or write storage medium, RAM, ROM, etc., such that it is readable by a programmable computer, and when the storage medium or device is read by the computer, it can be used to configure and operate the computer to perform the processes described herein. Furthermore, the machine-readable code, or portions thereof, can be transmitted via wired or wireless networks. The invention described herein includes these and other different types of non-transitory computer-readable storage media when such media comprises instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor. When programmed according to the methods and techniques described herein, the invention also includes the computer itself. A computer program can be applied to input data to perform the functions described herein, thereby transforming the input data to generate output data stored in non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the invention, the converted data represents physical and tangible objects, including specific visual depictions of physical and tangible objects generated on a display.

[0135] As used herein, the terms “component,” “module,” “system,” etc., are intended to refer to a computer-related entity, which may be hardware, firmware, a combination of hardware and software, software, or running software. For example, a component may be, but is not limited to, a process running on a processor, a processor, an object, an executable file, a running thread, a program, and / or a computer. As an example, an application running on a computing device and the computing device itself can both be components. One or more components may reside in a running process and / or thread, and components may be located in a single computer and / or distributed among two or more computers. Furthermore, these components are capable of execution from various computer-readable media having various data structures thereon. These components may communicate locally and / or remotely via signals, such as based on one or more data packets (e.g., data from a component that interacts with a local system, another component in a distributed system, and / or signals that interact with other systems via a network such as the Internet).

[0136] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A quantitative assessment method for the lowest frequency point considering the low-voltage ride-through process of wind power, characterized in that, include: In a multi-machine power system with wind power grid connection, analyze the non-step active power disturbance caused by wind power low-voltage ride-through. Establish a frequency response model of the system under the disturbance; The system's frequency response model uses common-mode components. express; Establishing the frequency response model of the system under the aforementioned disturbance includes: The active power dynamic process of the wind turbine during the entire low-voltage ride-through process is represented as follows: in, At the moment the fault occurs, it can be set ; This is the time when the fault is cleared. It is a unit step function; This refers to the power deficit caused by the low voltage ride-through of the wind turbine during a fault. ; The active power recovery rate of the wind turbine unit after the fault is cleared; Without loss of generality, consider a wind turbine grid-connected system with n generating units, where the first k units (numbered 1~k) are synchronous generators, and the last nk units (numbered k+1~n) are wind turbines. After a system fault occurs, assume that the first m wind turbines (numbered k+1~k+m+1) enter low-voltage ride-through, p wind turbines (numbered k+m+2~k+m+p+2) are disconnected from the grid, and the remaining wind turbines operate normally. Then, the frequency response model of the system can be represented by the common-mode component. It is expressed as follows: in, For the Laplace operator; Active power disturbance caused by low voltage ride-through of wind turbines; Active power disturbance caused by decommissioned wind turbines; This is the frequency-active power transfer function of the synchronous machine; The frequency-active power transfer function of a normally operating wind turbine; Using the equivalent device method to transform non-step active power disturbances This is transformed into a first-step disturbance and the response of a virtual power generation device; The transformation of disturbances using the equivalent equipment method includes: First, let's look at the active power disturbance caused by low-voltage ride-through wind turbines. The step component is decomposed from the middle part; the decomposition method used is: in, That is, the size is The power step disturbance; That is, after the fault is cleared, the wind turbine will operate at a fixed rate. The restored active power; The disturbance is transformed using the equivalent device method, and the system frequency is considered during the low-voltage ride-through process of the wind turbine. It can be represented as: in, To account for the system frequency during the low-voltage ride-through of the wind turbine, Let be the frequency-active power transfer function of the virtual equivalent device. It is in the form of a step jump; After transformation using the equivalent device method, the disturbance to the system is only a power disturbance. The system's devices are equivalent to adding power responses at nodes k+1 to k+m+1. Virtual equivalent device; The system frequency response model is simplified using a unified structural model, and the unified structural parameters of each device are calculated. Substituting uniform structural parameters into empirical formulas, we can quantitatively evaluate the lowest system frequency point during the low-voltage ride-through process.

2. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 1, characterized in that, The power generation equipment in the multi-machine power system with wind power grid connection includes synchronous machines and wind turbine units.

3. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 2, characterized in that, The equivalent equipment method includes: Consider an arbitrary n-machine system, assuming the disturbance power of each node is... The common-mode frequency of the system is expressed as follows: in, The frequency-active transfer function of the equipment involved in frequency modulation; ,in, It is an array where all elements are 1. 3D column vector, ; Notice arbitrary perturbations Decomposed into a first-order perturbation and the remainder The sum of these terms, rewritten as the common-mode frequency of the system, is: in, , This refers to the step components decomposed from the perturbations at each node.

4. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 3, characterized in that, The unified structural model includes: After a period of time following the disturbance, the structure approximates a damped sine curve. The unified structural model shown below is used to approximate the characteristics of each device. , and exist Dynamics over a period of time after the disturbance: in, , and for The unified structural parameters are referred to as effective inertia, effective damping coefficient, and effective dynamic droop coefficient, respectively. , and as well as , and Similarly.

5. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 4, characterized in that, The simplified system frequency response model includes: under power disturbance The common-mode frequency of the lower system can be approximated as: in, , and These are the unified structural parameters for the system.

6. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 5, characterized in that, The unified structural parameters of each device are represented as follows: 。 7. The method for quantitatively evaluating the lowest frequency point considering the low-voltage ride-through process of wind power as described in claim 6, characterized in that, The empirical formula is expressed as follows: in, for The amplitude.

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