Method for analyzing frequency supporting capability of high-proportion new energy access system

Abstract

The invention discloses a method for analyzing the frequency supporting capacity of a high-proportion new energy access system, and the method comprises the steps: constructing a frequency response model containing new energy hybrid equipment, solving a corresponding mathematical analysis formula through pull-type inverse transformation, calculating a frequency safety index based on the frequency response model, and calculating the frequency supporting capacity of a new energy access system. Related control parameters of single new energy equipment are changed, the supporting characteristics of the equipment on system frequency are observed, then the equipment is expanded into hybrid new energy equipment, the supporting effect of the equipment is evaluated, the influence rule is summarized, and finally actual simulation verification is carried out. According to the method, the supporting characteristics of the new energy equipment on the frequency can be effectively evaluated, so that more efficient power system frequency stability prevention and control can be realized.

Description

Technical Field

[0001] The present invention relates to the field of stable operation analysis of power systems, and in particular to a method for analyzing the frequency support capability of a system with a high proportion of new energy access. Background Art

[0002] As the proportion of renewable energy access systems increases, the frequency stability issues brought about by large-scale renewable energy access to the power system have begun to attract attention. The support capabilities and impacts of renewable energy equipment on frequency urgently require in-depth research. Currently, mainstream renewable energy power generation equipment control structures are mainly divided into grid-following and grid-forming types. Under power fluctuations, renewable energy equipment such as wind turbines and photovoltaics may cause the system's frequency safety to exceed the limit due to the intermittent and uncertain output, resulting in significant losses to the power grid operation. Therefore, studying the support role of renewable energy equipment on frequency is of great significance to the safe operation of the system.

[0003] Based on this, this patent proposes a method for analyzing the frequency support capability of a high-proportion new energy access system. First, a frequency response aggregation model containing grid-following and grid-forming devices is established. Then, based on the aggregation model, the influence characteristics of the control parameters of the grid-following devices on the frequency support are analyzed. Then, by changing the following / grid-forming control parameters, the impact analysis of the hybrid scenario of new energy devices on the frequency support is discussed. Finally, the law of the effect of new energy devices on frequency support is summarized, and actual simulation verification is carried out. Summary of the Invention

[0004] The purpose of the present invention is to provide an analysis method for the frequency support capability of a high-proportion renewable energy access system. The principle is to obtain the frequency support characteristics of renewable energy equipment by changing the control parameters of the equipment on the basis of constructing a frequency response model, and finally verify the conclusion through simulation.

[0005] To this end, a technical solution adopted by the present invention is: a method for analyzing the frequency support capability of a high-proportion new energy access system, which includes:

[0006] Step 1: Obtain the power frequency response characteristics of new energy and generator sets, and establish a frequency response model containing grid-following and grid-forming new energy based on these characteristics.

[0007] Step 2: Based on the frequency response model obtained in step 1, calculate frequency security-related indicators, change the network control parameters, and observe the impact of a single new energy device on frequency support.

[0008] Step 3: Change the system control parameters in the hybrid scenario and discuss the impact of the hybrid scenario of new energy equipment on frequency support.

[0009] Step 4: Summarize the frequency support effects of new energy equipment and verify the conclusions through actual simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0011] Figure 1 This is a diagram showing the accuracy of the frequency response model provided by the embodiment of the present invention;

[0012] Figure 2 The impact of network tracking and network construction equipment on the system frequency damping ratio under different parameter values ​​provided in the embodiment of the present invention;

[0013] Figure 3 The impact of network tracking and network building equipment on the lowest point of system frequency under different parameter values ​​provided in the embodiment of the present invention;

[0014] Figure 4 The present invention provides an example of the actual simulation verification of the impact of new energy hybrid equipment on frequency. DETAILED DESCRIPTION

[0015] Furthermore, in step 1, the power-frequency response characteristics of the new energy and the generator set are obtained, and a frequency response model containing grid-following and grid-forming new energy is established, which includes the second-order rotor motion equation of the synchronous generator, represented by the transfer function G1(s), the hysteresis link of the grid-following device, represented by the transfer function G2(s), and the active support link of the grid-forming device, represented by the transfer function G3(s). Finally, the various transfer functions are integrated to form an aggregated frequency response model. The frequency response transfer function is as follows:

[0016]

[0017] Where H gfl Indicates the equivalent virtual inertia coefficient of the network-following device, D gfl Indicates the damping coefficient of the grid-following equipment, T gfl Indicates the hysteresis time constant of the network-following device, H gfm 、D gfm They are respectively expressed as the equivalent inertia and equivalent damping coefficient of the network-type equipment, x g 、x gfl 、x gfm They represent the proportion of synchronous machines, grid-following power supplies, and grid-forming power supplies respectively. The proportion mainly depends on the percentage of active output of each type of equipment in the total system output, which can be expressed as:

[0018]

[0019] Perform the inverse Lagrange transform on the original transfer function to obtain the corresponding time domain analytical expression:

[0020]

[0021] Furthermore, in step 2, the frequency safety-related indicators are calculated, mainly considering the frequency minimum point constraint, the frequency maximum change rate constraint, and their impact on the damping ratio of the system. The former characterizes the safety characteristics of frequency stability, and the latter characterizes the stable state of the system.

[0022] Furthermore, in step 2, the control parameters of the network are changed to observe the impact of a single new energy device on the frequency support. The proportion of another new energy device in the corresponding single scenario in the frequency response model in step 1 is set to 0, and the corresponding H of the device is changed. gfl 、D gfl 、H gfm 、H gfm Parameter range, and observe its impact characteristics on frequency safety indicators.

[0023] Furthermore, in step 3, to change the system control parameters in the hybrid scenario, it is necessary to fix the proportion of new energy based on the frequency support characteristics obtained in step 2, change the ratio between following the grid and building the grid, and observe the support effect of the hybrid system on the frequency.

[0024] Furthermore, in step 4, according to the frequency support characteristics obtained in step 3, simulation is performed in an actual system to verify the correctness and applicability of the law.

[0025] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0026] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. The scope of protection of the present invention should be based on the scope of protection of the claims.

[0027] Application Examples

[0028] Taking a four-machine two-area system as an example, the method of the present invention is demonstrated:

[0029] Step 1: First, a frequency response model of grid-following and grid-forming new energy hybrid is established based on the characteristics. The model includes the synchronous generator transfer function G1(s), the grid-following device transfer function G2(s), and the grid-forming device transfer function G3(s). The frequency response model verification is as follows: Figure 1 shown.

[0030] Step 2: Based on the frequency response model obtained in step 1, calculate the frequency safety related indicators through the time domain analytical formula, specifically the lowest frequency point:

[0031]

[0032] in

[0033]

[0034] Damping ratio:

[0035]

[0036] Where P is the total proportion of new energy, representing the sum of the proportion of grid-connected and grid-building, x l Indicates the proportion of new energy and grid-type equipment, ΔP d Indicates the magnitude of the disturbance applied to the system.

[0037] Maximum frequency change rate:

[0038]

[0039] Based on the above frequency security indicators, the control parameters of the follow / build network are changed to observe the impact of a single new energy device on frequency support. The results are as follows: Figure 2 、 3 shown

[0040] Step 3: Based on the frequency support characteristics of the single new energy scenario obtained in step 2, continue to change the system control parameters in the hybrid scenario and discuss the impact of the hybrid scenario of new energy equipment on frequency support. Figure 2 It can be concluded that:

[0041] From Figures (a) and (b), we can see that for the following network damping D gl , improve D gl Will reduce the system damping ratio, and the proportion of the grid is x gl The larger the value is, the greater the sensitivity of the network damping to the system damping is, and the virtual inertia H gl The increase of can reduce the sensitivity. For the inertia of following the network, increase H gl Can improve the damping ratio, D gl For H gl The sensitivity is not affected. The greater the proportion of the network, the greater the sensitivity. gl From the fixed value range, increase x gl The damping ratio will decrease, while the opposite is true when it is greater than a fixed value. The fixed value depends on D gl Parameter value of .

[0042] As shown in Figures (c) and (d), compared with the network access system, D gm The increase of can improve the system damping and increase H gm The sensitivity of H gm Will reduce the system damping, H gm Increasing will decrease D gm The sensitivity of D gm When the value is 0-5, increase the proportion of network x gm It will reduce the damping, and increase it in other cases. The increase in proportion can generally improve the sensitivity of each parameter.

[0043] Description Figure 3 Perform analysis:

[0044] From Figures (a) and (b), we can see that the damping D gl and virtual inertia H gl The increase of H can increase the lowest frequency point. gl The sensitivity of D gl This rule is more obvious when the proportion of the network is larger. gl The increase of D gl The sensitivity of the lowest point is increased, and the initial value of the lowest point is increased. The larger the proportion, the more significant the effect. gl Increasing the system ratio will also have a similar effect. For the system ratio, the increase in the ratio will reduce the initial value of the lowest point, but in turn will increase D gl and H gl sensitivity.

[0045] From Figure (c) and (d), we can see that D gm Increasing can improve the lowest frequency point, but increasing H gm Increasing the initial value of the lowest frequency point will reduce D gm The sensitivity of D gm When it is greater than a certain value, it is beneficial to the system. The value depends on H gm Size, H gm The larger it is, the smaller the fixed value is. gm Increasing D can improve the lowest frequency point, but the sensitivity to frequency deviation is small, and as D gm The greater the change, the smaller the sensitivity, and D gm Similarly, the impact of increasing the proportion on the system depends on H gm parameter changes.

[0046] Step 4: Summarize the frequency support effects of new energy equipment, as follows:

[0047]

[0048] Consider three different scenarios, set different proportions of new energy, improve the corresponding system control parameters, and conduct actual simulation verification of the conclusions obtained in step 3. The specific verification results are shown in the figure. Figure 4 shown.

[0049] At this point, through the support analysis method provided by the present invention, the frequency support capability of the high-proportion new energy access system can be preliminarily evaluated, providing a reference basis for the formulation of subsequent frequency support improvement strategies, which has important research significance.

Claims

1. A method for analyzing the frequency support capability of a system with a high proportion of new energy access, characterized by comprising the following steps: Step 1: Obtain the power-frequency response characteristics of new energy and generator sets, and establish a frequency response model containing grid-following and grid-forming new energy based on the response characteristics. Step 2: Based on the frequency response model obtained in step 1, calculate frequency security-related indicators, change the network control parameters, and observe the impact of a single new energy device on frequency support. Step 3: Change the network control parameters and discuss the impact of hybrid new energy equipment on frequency support. Step 4: Summarize the frequency support effects of new energy equipment and conduct actual simulation verification.

2. A method for analyzing the frequency support capability of a high-proportion new energy access system according to claim 1, characterized in that: In step 1, when a disturbance such as power outage or load mutation occurs in the high-proportion renewable energy power system, an active unbalance ΔP is generated. d According to the rotor motion equation, a frequency deviation Δf will be generated. For different new energy equipment, the power-frequency response characteristics are different. Establishing a frequency response model containing grid-following and grid-forming new energy can accurately reflect the frequency response dynamic characteristics of the system.

3. A method for analyzing the frequency support capability of a high-proportion new energy access system according to claim 1, characterized in that: In step 2, first, the frequency response analytical expression is derived and solved based on the frequency response model as follows: Where H gm 、H gl and H1 are the equivalent inertia of the grid-forming type, grid-following type, and traditional synchronous unit systems, respectively. gm 、D gl , D1 are the equivalent damping of the grid-forming type, grid-following type, and traditional synchronous unit systems respectively. gm and x gl Indicates the proportion of network construction and network following. Based on the existing frequency response model, relevant indicators for solving frequency safety are obtained: lowest point, frequency steady-state deviation, maximum frequency change rate and system damping ratio. The specific expression is as follows: Set the network following and network building ratio parameters to 0 respectively, change the corresponding network following and network building control structure parameters, and observe the impact of the equipment on the system frequency response to determine its frequency support characteristics.

4. The method for analyzing the frequency support capability of a high-proportion new energy access system according to claim 1 is characterized by: In step 3, the proportion of new energy is fixed, and the ratio between grid-following and grid-configuration is adjusted to observe the impact of parameter changes on the system frequency response when new energy devices are connected in parallel. Attention should be paid to the interaction mechanism of device parameters.

5. The method for analyzing the frequency support capability of a high-proportion new energy access system according to claim 1 is characterized by: In step 4, the access conditions of the single new energy and hybrid new energy devices to the system are analyzed, and finally the obtained supporting rules are summarized and the conclusions are verified by simulation in the actual system.

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