Wind turbine generator frequency modulation parameter design method based on improved frequency response model

Abstract

The application relates to a wind turbine frequency modulation parameter design method based on an improved frequency response model and belongs to the technical field of new energy grid-connected frequency modulation. On the basis of a traditional frequency response model, a wind turbine virtual inertia control branch is added, the influence of an inertia control link and a time delay parameter is comprehensively considered, an improved frequency response model of a wind power interconnected system is established, and the interaction mechanism of synchronous machines and wind turbines in a frequency modulation process can be reflected. The application is based on the improved frequency response model, the selection range of wind turbine parameters is determined through system stability analysis, the maximum frequency deviation index is considered, the relationship between the maximum frequency deviation and the time delay is analyzed according to a transfer function, the selection principle of the time delay parameter of the virtual inertia control link is designed, and the method has important significance for the reasonable setting of wind turbine frequency modulation parameters. The application provides theoretical support for the control parameter design of a wind power plant active support system frequency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid-connected frequency modulation, and particularly relates to a wind turbine generator set frequency modulation parameter design method based on an improved frequency response model. BACKGROUND

[0002] At present, most of the mainstream wind turbine generators in China are variable speed constant frequency wind turbine generators such as doubly-fed wind turbine generators and permanent magnet direct-drive wind turbine generators. The rotor speed and grid frequency of these wind turbine generators controlled by power electronic conversion are in a decoupled state, and it is difficult for them to provide inertia and primary frequency modulation support to the grid like traditional synchronous generators. In order to expand the application of wind power and other new energy and improve the frequency stability of future power grids dominated by wind power and other new energy, the state requires that wind farms must have flexible power control capability and actively participate in frequency control to improve the frequency stability of the power grid.

[0003] In the traditional power system, the frequency response model is often used to analyze the frequency response of the power system after active disturbance, so as to analyze the system frequency stability and design synchronous machine parameters. However, the traditional power grid frequency response model does not consider the influence of large-scale wind power access, so it is necessary to modify the traditional frequency response model to describe the frequency dynamic process of the power grid under wind power access. At present, the system frequency response model considering wind turbine generators mainly considers that wind power does not participate in system frequency regulation, and mainly analyzes the influence of wind power access on the dynamic response of power grid frequency and the calculation of maximum wind power penetration rate. At present, more and more grid-connected wind turbine generators are being modified in China to participate in power grid frequency modulation. However, the research on grid-connected wind turbine frequency modulation often ignores its time delay characteristics, but grid-connected wind turbines have inherent time delay when participating in frequency modulation, which affects the frequency characteristics of the power grid. It is necessary to modify the traditional frequency response model according to the characteristics of frequency modulation control, build an improved system frequency response model suitable for grid-connected wind turbine generators participating in system frequency modulation, analyze the interaction mechanism between synchronous machines and wind turbines, and analyze the frequency stability problem of new-type power system after large-scale wind power access, and design wind farm frequency modulation related parameters. SUMMARY

[0004] The application aims to provide a wind turbine frequency modulation parameter design method based on an improved frequency response model, which modifies the traditional system frequency response model, solves the problem that the traditional system frequency response model cannot reflect the system frequency characteristics after the wind turbine participates in frequency modulation, and provides theoretical support for the control parameter design of the wind farm active support system frequency.

[0005] The above-mentioned purpose of the application is realized by the following technical scheme:

[0006] The wind turbine frequency modulation parameter design method based on the improved frequency response model first establishes an improved system frequency response model considering the wind turbine virtual inertia control delay, reflects the interaction mechanism of the synchronous machine and the wind turbine during the frequency modulation process, and facilitates the analysis of the influence of the wind turbine on the system frequency after participating in the frequency modulation. Secondly, the open-loop transfer function of the system is obtained, and the wind turbine frequency modulation parameter range is determined through the Nyquist stability criterion to ensure the stability of the system in which the synchronous machine and the wind turbine jointly participate in frequency modulation. Finally, the maximum frequency deviation is reduced as the target, the relationship between the transfer function overshoot and the phase angle margin is analyzed, and the control delay parameter selection principle suitable for the wind farm active support system inertia is designed. Including the following steps:

[0007] Including the following steps:

[0008] (1) The improved system frequency response model considering the wind turbine virtual inertia control delay is established as follows:

[0009]

[0010] Among them:

[0011]

[0012]

[0013]

[0014] In the formula, s is the Laplace operator; K WT1 is the droop control coefficient; K WT2 is the inertia control coefficient; H g is the inertia time constant of the synchronous machine; D gis the damping coefficient of the synchronous machine; Δω is the frequency deviation; ΔP L is the load power variation; R g is the governing coefficient of the prime mover; F H is the reheat constant of the turbine; T R is the reheat time constant; T WT is the inertia control link time delay parameter;

[0015] (2) determining the wind turbine frequency modulation parameter selection range based on the improved system frequency response model;

[0016] (3) the time delay parameter design method of the inertia control link with the target of reducing the maximum frequency deviation.

[0017] The improved system frequency response model considering the time delay of the wind turbine virtual inertia control in step (1) builds a wind turbine virtual inertia control branch in the traditional frequency response model, and considers the influence of the inertia control link time delay parameter on the system frequency response.

[0018] The wind turbine frequency modulation parameter selection range based on the improved system frequency response model in step (2) is determined according to the improved system frequency response model, and the open-loop transfer function is as follows, and the Nyquist stability criterion is used to determine the wind turbine control parameter selection range that makes the system stable.

[0019]

[0020] Wherein:

[0021]

[0022]

[0023]

[0024] The time delay parameter design method of the inertia control link with the target of reducing the maximum frequency deviation in step (3) redesigns the time delay parameter on the basis of the fixed time delay of the wind turbine inertia control, so that the system maximum frequency deviation is reduced; according to the relationship between the phase angle margin and the damping ratio, and the relationship between the damping ratio and the overshoot, the qualitative relationship between the phase angle margin and the overshoot is obtained, and then the qualitative relationship between the system maximum frequency deviation and the time delay parameter of the wind turbine inertia control is given; after the actual system parameters are brought in, the quantitative analytical expression of the phase angle margin about the time delay parameter is written, and the intersection of the amplitude margin and 0dB is satisfied, the maximum value of the phase angle margin in the analytical expression is calculated, and the corresponding time delay parameter is the optimal time delay parameter of the inertia control link that makes the system maximum frequency deviation minimum.

[0025] The beneficial effects of the present application are as follows:

[0026] The current research on frequency modulation of the grid-following wind turbine ignores its response delay, but its delay characteristics are inherent and have an impact on the frequency response, the application proposes an improved frequency response model considering the delay characteristics of the grid-following wind turbine participating in grid frequency modulation, and on the basis of the improved model, the optimal control delay parameter is designed to reduce the maximum frequency deviation. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings described herein are used to provide further understanding of the application, and form a part of the application, the illustrative examples of the application and the description thereof are used to explain the application, and do not constitute improper limitation on the application.

[0028] Figure 1 The traditional system frequency response model is as follows:

[0029] Figure 2 The wind turbine participating in frequency modulation after considering the delay system frequency response model is as follows:

[0030] Figure 3 The Bode diagram for stabilizing the system is as follows. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings, obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application. In order to make the above-mentioned purposes, characteristics and advantages of the application more obvious and easy to understand, the application will be further described in detail below with reference to the drawings and specific embodiments.

[0032] Reference Figure 2As shown, the wind turbine frequency modulation parameter design method based on the improved frequency response model of the application solves the problem that the traditional system frequency response model cannot accurately reflect the description of the system frequency characteristics after the wind turbine participates in frequency modulation, and provides theoretical support for the parameter design of the actual engineering wind farm. Based on the traditional system frequency response model, according to the frequency response characteristics of the virtual inertia control of the wind turbine participating in frequency modulation, considering the delay parameter of the inertia link, an improved system frequency response model is built. With the help of the improved frequency response model, the system stability is analyzed, the parameter selection range of the wind turbine is determined, and the selection principle of the delay parameter of the virtual inertia control link is provided. Based on the traditional frequency response model, the wind turbine virtual inertia control branch is added, and the influence of the inertia control link and its delay parameter is considered, and an improved frequency response model of the wind power interconnected system is established, which can reflect the interaction mechanism of synchronous machines and wind turbines in the frequency modulation process. Based on the improved frequency response model, the selection range of the wind turbine parameters is determined through system stability analysis, and the maximum frequency deviation index is also considered. According to the transfer function analysis of the relationship between the maximum frequency deviation and the delay, the selection principle of the delay parameter of the virtual inertia control link is designed, which is of great significance for the reasonable setting of the wind turbine frequency modulation parameters.

[0033] 1. Traditional system frequency response model

[0034] The traditional system frequency response model is as shown in Figure 1 , which is used to describe the frequency change of the traditional power system when subjected to power disturbance from the system level. The specific parameter meanings are as follows: H g is the inertia time constant of the synchronous machine; D g is the damping coefficient of the synchronous machine; Δω is the frequency deviation; ΔP L is the load power change; R g is the governor coefficient of the prime mover; F H is the reheat constant of the steam turbine; T R is the reheat time constant.

[0035] 2. Improved system frequency response model considering wind turbine virtual inertia control delay

[0036] The wind turbine participates in system frequency regulation through virtual inertia control as shown in formula (1), and the frequency information of the system is obtained by phase-locked loop phase locking. The inertia control link needs to calculate the system frequency change rate, according to the national standard "GB / T19963.1-2021", the window time for calculating the frequency change rate is not less than 100ms, that is, there is inherent delay in this link, which cannot be ignored. A commonly used first-order inertia link is used to represent the delay, and formula (2) is used to represent the delay T(s) in this application, where T WTis the time delay parameter of the inertia control link, the larger the parameter, the later the inertia support of the fan is reflected, in the system where the synchronous machine and the fan participate in frequency modulation together, the common action mechanism of the synchronous machine and the fan in frequency modulation is reflected, the parameter needs to be designed within the range required by the national standard, the frequency modulation functions of the synchronous machine and the fan are coordinated, so as to achieve the goal of optimizing the frequency response.

[0037]

[0038]

[0039] In the formula: K WT1 is the droop control coefficient; K WT2 is the inertia control coefficient; P ω is the frequency change of the grid-following fan after disturbance.

[0040] According to the above analysis, by using the characteristics of the fan participating in frequency modulation through virtual inertia control, a virtual inertia branch is added to the traditional system frequency response model to obtain an improved system frequency response model considering the time delay of the virtual inertia control of the fan as shown in formula (2). According to the improved system frequency response model, the frequency response at this time can be obtained as shown in formula (3). Figure 2

[0041]

[0042] Among them:

[0043]

[0044]

[0045]

[0046] 3. Fan parameter range design method based on improved system frequency response model

[0047] According to the improved system frequency response model of formula (2), the system open-loop transfer function H(s) at this time can be obtained as shown in formula (4). Figure 2

[0048] Among them:

[0049]

[0050]

[0051]

[0052]

[0053] ​​The application is based on Nyquist criterion for stability analysis on the basis of improving system frequency stability model. After substituting system parameters, the relational expression of amplitude-frequency characteristic and phase-frequency characteristic of the transfer function about wind turbine frequency modulation parameter K WT1 、 WT2 and delay parameter T WT can be written. When there is intersection between amplitude-frequency characteristic and 0dB in Bode diagram of open-loop transfer function, and phase angle margin is in stable range, as shown in Figure 3 , the overall system is stable at this time. The selection range of wind turbine frequency modulation parameter K WT1 、 WT2 and delay parameter T WT which make the system stable is determined according to the above criterion.

[0054] 4. Inertial control link delay parameter design method aiming at reducing maximum frequency deviation

[0055] Virtual inertia control of wind turbine can improve system frequency, but because there is inherent delay in inertia control link, wind turbine inertia cannot reduce the maximum frequency change rate of the system. But with the increase of delay parameter, the maximum deviation of frequency first decreases and then increases, that is, there is a delay parameter which can make the maximum deviation of system frequency minimum. Its physical meaning is that providing power support for the system at a proper time can improve the maximum deviation of frequency to the greatest extent.

[0056] Substituting system parameters can obtain the qualitative relationship between delay parameter and system phase angle margin. According to automatic control theory, phase angle margin is proportional to damping ratio, and damping ratio is inversely proportional to overshoot (maximum frequency deviation), so phase angle margin is inversely proportional to overshoot. The analytical expression related to delay parameter and phase angle margin can be obtained by using actual system parameters. Through quantitative calculation, the delay parameter which can make the phase angle margin maximum can be obtained. At this time, the delay parameter is the optimal delay parameter which can make the maximum frequency deviation of the system minimum.

[0057] The above only describes the preferred examples of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made to the application shall be included in the protection scope of the application.

Claims

1. A method for designing frequency modulation parameters of a wind turbine based on an improved frequency response model, characterized in that: Includes the following steps: (1) An improved system frequency response model considering the delay of the virtual inertia control of the wind turbine is constructed. The virtual inertia control branch of the wind turbine is built in the traditional frequency response model. At the same time, the influence of the delay parameter of the inertia control link on the system frequency response is considered. The improved system frequency response model is as follows: ； in: ； ； ； where s is Laplace operator; K WT1 is droop control coefficient; K WT2 is inertia control coefficient; H g is inertia time constant of synchronous machine; D g is damping coefficient of synchronous machine; is frequency deviation; is load power variation; R g is governing coefficient of prime mover; F H is reheat constant of steam turbine; T R is reheat time constant; T WT is inertia control loop time delay parameter; (2) Based on the improved system frequency response model, the selection range of wind turbine frequency regulation parameters is determined. The open-loop transfer function is obtained according to the improved system frequency response model as follows. The selection range of wind turbine control parameters that make the system stable is determined using the Nyquist stability criterion: ； in: ； ； ； (3) The delay parameter design method of the inertia control loop with the goal of reducing the maximum frequency deviation is to redesign the delay parameter on the basis of the fixed delay of the inertia control of the wind turbine to reduce the maximum frequency deviation of the system. According to the relationship between phase margin and damping ratio, and the relationship between damping ratio and overshoot, the qualitative relationship between phase margin and overshoot is obtained, and then the qualitative relationship between the maximum frequency deviation of the system and the delay parameter of the inertia control of the wind turbine is given. After substituting the actual system parameters, the quantitative analytical expression of phase margin with respect to delay parameter is written. At the same time, the gain margin and 0dB have an intersection point. The maximum value of phase margin in the analytical expression is obtained. The corresponding delay parameter is the optimal delay parameter of the inertia control loop that minimizes the maximum frequency deviation of the system.

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