A method for analyzing frequency dynamic characteristics of islanded power grid based on droop control

Abstract

The application belongs to the technical field of islanded power grid frequency characteristic analysis, and discloses a kind of islanded power grid frequency dynamic characteristic analysis method based on droop control, the influence of different power supply of islanded power grid on system frequency dynamic characteristic is defined, the penetration rate of renewable energy and the droop control strategy of energy storage converter are considered simultaneously, a frequency response analysis model of system frequency dynamic characteristic is first constructed, then the frequency domain model is converted to time domain, the time domain analysis equation that can represent system frequency dynamic characteristic is obtained, and the system frequency under different disturbance conditions is analyzed using this equation, this method has strong universality for different islanded power grids, and can effectively avoid the complexity of traditional time domain simulation method which needs to be modeled and analyzed separately according to different islanded power grid characteristics.

Description

Technical Field

[0001] This invention relates to the technical field of frequency characteristic analysis of islanded power grids, and in particular to a method for analyzing the dynamic frequency characteristics of islanded power grids based on droop control. Background Technology

[0002] Islanded power grids are an effective means of efficiently developing and utilizing renewable energy. However, due to the high penetration rate of renewable energy in islanded power grids, the system frequency is prone to instability after active power disturbances. Traditional frequency characteristic analysis often employs time-domain simulation, but because different islanded power grids have varying topologies and power source compositions, traditional simulation methods lack universality and require modeling based on specific islanded power grid characteristics, increasing the difficulty of frequency characteristic analysis. Furthermore, the widespread integration of renewable energy sources such as energy storage into islanded power grids also integrates frequency regulation and control functions, with droop control being the simplest and most effective frequency control mode. Therefore, this paper proposes a method for analyzing the dynamic frequency characteristics of islanded power grids based on droop control. This method simultaneously considers the renewable energy penetration rate and the droop control mode of the energy storage converter, obtaining the time-domain equation of the system frequency response to analyze the dynamic frequency characteristics of the islanded power grid after active power disturbances. This method has a certain degree of universality for different islanded power grids, and its correctness and effectiveness are verified through the analysis of a real islanded power grid. Summary of the Invention

[0003] 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.

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is that the numerical simulation method of the prior art is not universal and cannot analyze the dynamic impact of the aforementioned factors on the system frequency.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control, comprising:

[0008] Based on the ratio of renewable energy capacity to synchronous machine capacity, a renewable energy proportion coefficient that can characterize islanded power grids is determined.

[0009] A dynamic frequency domain analysis model of the equivalent frequency of an isolated power grid is established through renewable energy droop frequency regulation control.

[0010] The time-domain model of the system's frequency dynamic response is calculated based on the dynamic frequency domain analysis model described above.

[0011] Substituting the system frequency into the time-domain model, the frequency dynamic characteristics of the islanded power grid are obtained by solving.

[0012] As a preferred embodiment of the frequency dynamic characteristic analysis of the islanded power grid based on droop control described in this invention, the frequency dynamic characteristics of the islanded power grid are determined by the synchronous machine, energy storage battery and load.

[0013] The dynamic response characteristics of the synchronous machine include its own inertia response process and the primary frequency regulation process of the governor and the steam turbine.

[0014] The inertial response process is represented as follows:

[0015]

[0016] The primary frequency modulation process is represented as follows:

[0017]

[0018] Where H is the inertial time constant of the synchronizer, D is the damping coefficient of the synchronizer, ω is the system frequency, and P... m P is the mechanical power input to the prime mover. e α is the electromagnetic power output by the synchronous machine, T is the equivalent time constant of the turbine, α is the turbine characteristic parameter, and R is the droop coefficient of the governor.

[0019] As a preferred embodiment of the islanded grid frequency dynamic characteristic analysis based on droop control described in this invention, the frequency-power droop control measures are applied at the active power outer loop based on the constant power control decoupling control strategy of the traditional energy storage converter, so that the energy storage battery has the ability to actively support the frequency of the islanded grid.

[0020] As a preferred embodiment of the frequency dynamic characteristic analysis of islanded power grids based on droop control described in this invention, the renewable energy proportion coefficient is expressed as:

[0021]

[0022] Where K is the penetration rate parameter of renewable energy. The higher the penetration rate of renewable energy, the smaller the value of K.

[0023] As a preferred embodiment of the frequency dynamic characteristic analysis of islanded power grids based on droop control described in this invention, the dynamic frequency domain analysis model is expressed as follows:

[0024]

[0025] in, ω is a constant term in the frequency domain analysis model. n It is the natural frequency; ζ represents the coefficient of the first-order term in the frequency domain analysis model, and ζ represents the damping ratio; D′=D+η(1-K) represents the equivalent damping considering the penetration rate of renewable energy, where the parameter η is the droop coefficient of the energy storage converter.

[0026] As a preferred embodiment of the frequency dynamic characteristic analysis of islanded power grids based on droop control described in this invention, the time-domain model of the system's frequency dynamic response is expressed as follows:

[0027]

[0028] in, a and b are two eigenvalues ​​obtained by solving the frequency domain model. k1 and k2 are two coefficients in the time-domain model.

[0029] As a preferred embodiment of the frequency dynamic characteristic analysis of the islanded power grid based on droop control described in this invention, the frequency dynamic characteristics of the islanded power grid include steady-state frequency deviation, maximum frequency deviation, and time to the maximum frequency deviation.

[0030] The steady-state frequency deviation is expressed as:

[0031]

[0032] The maximum frequency deviation is expressed as:

[0033]

[0034] The time to the maximum frequency deviation is expressed as:

[0035]

[0036] Secondly, embodiments of the present invention provide a frequency dynamic characteristic analysis system for islanded power grids based on droop control, comprising:

[0037] The capacity acquisition module determines the renewable energy proportion coefficient that characterizes the islanded power grid based on the ratio of renewable energy capacity to synchronous machine capacity.

[0038] The frequency domain analysis module establishes a dynamic frequency domain analysis model of the equivalent frequency of the islanded power grid through renewable energy droop frequency regulation control.

[0039] The time-domain analysis module calculates the time-domain model of the system's dynamic frequency response based on the dynamic frequency-domain analysis model.

[0040] The characteristic analysis module substitutes the system frequency into the time-domain model to solve for the frequency dynamic characteristics of the islanded power grid.

[0041] Thirdly, embodiments of the present invention provide a computing device, including:

[0042] Memory and processor;

[0043] The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the one or more programs are executed by the one or more processors, the one or more processors implement the method for analyzing the frequency dynamic characteristics of islanded power grids based on droop control as described in any embodiment of the present invention.

[0044] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control.

[0045] The beneficial effects of this invention are as follows: This invention provides a method for analyzing the frequency dynamic characteristics of islanded power grids based on droop control. It clarifies the impact of different power sources on the system's frequency dynamic characteristics in an islanded power grid, while also considering the penetration rate of renewable energy and the droop control strategy of the energy storage converter. First, a frequency response analysis model of the system's frequency dynamic characteristics is constructed. Then, the frequency domain model is transformed into the time domain, resulting in a time domain analysis equation that can characterize the system's frequency dynamic characteristics. This equation is then used to analyze the system frequency under different disturbance conditions. This method has strong versatility for different islanded power grids and can effectively avoid the complexity of traditional time domain simulation methods that require separate modeling and analysis based on the characteristics of different islanded power grids. Attached Figure Description

[0046] 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:

[0047] Figure 1 This is an overall flowchart of the islanded power grid frequency dynamic characteristic analysis method based on droop control according to an embodiment of the present invention;

[0048] Figure 2This is a schematic diagram of the system structure of the islanded power grid frequency dynamic characteristic analysis method based on droop control according to an embodiment of the present invention;

[0049] Figure 3 This is a topology diagram of an actual islanded power grid based on the frequency dynamic characteristic analysis method of islanded power grids based on droop control, as described in an embodiment of the present invention.

[0050] Figure 4 This is a block diagram of the energy storage converter droop control in an embodiment of the islanded power grid frequency dynamic characteristic analysis method based on droop control according to an embodiment of the present invention.

[0051] Figure 5 This is a frequency analysis model diagram of the system frequency dynamic response characteristics of the islanded power grid frequency dynamic characteristic analysis method based on droop control according to an embodiment of the present invention.

[0052] Figure 6 The figure shows the calculated steady-state frequency deviation and maximum frequency deviation of the system as a function of the value of K in the frequency dynamic characteristic analysis method of islanded power grid based on droop control according to an embodiment of the present invention.

[0053] Figure 7 This is a frequency response curve of an actual islanded power grid, illustrating the frequency dynamic characteristic analysis method for islanded power grids based on droop control according to an embodiment of the present invention. Detailed Implementation

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Example 1

[0061] Reference Figure 1 —5, is an embodiment of the present invention, which provides a method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control, characterized in that it includes:

[0062] S100: Based on the ratio of renewable energy capacity to synchronous machine capacity, determine the renewable energy proportion coefficient that can characterize the islanded power grid;

[0063] Furthermore, the frequency dynamics of an islanded power grid are determined by the synchronous machine, energy storage batteries, and loads;

[0064] The dynamic response characteristics of a synchronous machine include its own inertial response process and the primary frequency regulation process of the governor and the turbine.

[0065] The inertial response process is represented as:

[0066]

[0067] A single frequency modulation process is represented as:

[0068]

[0069] Where H is the inertial time constant of the synchronizer, D is the damping coefficient of the synchronizer, ω is the system frequency, and P... m P is the mechanical power input to the prime mover. e α is the electromagnetic power output by the synchronous machine, T is the equivalent time constant of the turbine, α is the turbine characteristic parameter, and R is the droop coefficient of the governor.

[0070] It should be noted that, as Figure 3 As shown, the islanded power grid mainly consists of four parts: synchronous motors, photovoltaic (PV) power generation, energy storage batteries, and loads. The synchronous motor is the main power source of the islanded power grid, primarily providing a stable AC voltage and a grid connection reference for PV power generation and energy storage batteries. PV power generation always operates in maximum power point tracking (MPPT) mode, characterized by maintaining its original active power output regardless of grid frequency changes. The energy storage battery employs a droop control strategy, providing active frequency support to the system based on the frequency deviation of the islanded power grid. Loads constitute the power consumption component of the islanded power grid and are also the main source of active power disturbance; the active power disturbances in this invention are mainly provided by the connection or disconnection of large loads. Therefore, the frequency dynamic characteristics of the entire islanded power grid are mainly determined by the synchronous motor, energy storage batteries, and loads.

[0071] Furthermore, based on the constant power control decoupling control strategy of traditional energy storage converters, frequency-power droop control measures are applied at the active power outer loop, enabling the energy storage battery to actively support the frequency of the islanded grid. The droop control block diagram of the energy storage converter is shown below. Figure 4 As shown.

[0072] Furthermore, the renewable energy share coefficient is expressed as:

[0073]

[0074] Where K is the penetration rate parameter of renewable energy. The higher the penetration rate of renewable energy, the smaller the value of K.

[0075] S200: Establish an equivalent frequency dynamic frequency domain analysis model for islanded power grids through renewable energy droop frequency regulation control;

[0076] Furthermore, a frequency domain analysis model of the system's dynamic frequency response, including the coefficient K and the droop control characteristics of the energy storage battery, is constructed, such as... Figure 5 As shown. The dynamic frequency domain analysis model is expressed as:

[0077]

[0078] in, ω is a constant term in the frequency domain analysis model. n It is the natural frequency; ζ represents the coefficient of the first-order term in the frequency domain analysis model, and ζ represents the damping ratio; D′=D+η(1-K) represents the equivalent damping considering the penetration rate of renewable energy, where the parameter η is the droop coefficient of the energy storage converter.

[0079] S300: A time-domain model for calculating the dynamic frequency response of a system based on a dynamic frequency domain analysis model;

[0080] Furthermore, the time-domain model of the system's frequency dynamic response is expressed as:

[0081]

[0082] in, a and b are two eigenvalues ​​obtained by solving the frequency domain model. k1 and k2 are two coefficients in the time-domain model.

[0083] S400: Substitute the system frequency into the time-domain model to obtain the frequency dynamic characteristics of the islanded power grid.

[0084] Furthermore, the frequency dynamic characteristics of an islanded power grid include steady-state frequency deviation, maximum frequency deviation, and time to the maximum frequency deviation.

[0085] The steady-state frequency deviation is expressed as:

[0086]

[0087] The maximum frequency deviation is expressed as:

[0088]

[0089] The time to the maximum frequency deviation is expressed as:

[0090]

[0091] The above is a schematic scheme of an islanded power grid frequency dynamic characteristic analysis method based on droop control according to this embodiment. It should be noted that the technical solution of this islanded power grid frequency dynamic characteristic analysis system based on droop control belongs to the same concept as the technical solution of the islanded power grid frequency dynamic characteristic analysis method based on droop control described above. Details not described in detail in the technical solution of the islanded power grid frequency dynamic characteristic analysis system based on droop control in this embodiment can be found in the description of the technical solution of the islanded power grid frequency dynamic characteristic analysis method based on droop control described above.

[0092] Figure 2This is a schematic diagram of the structure of the islanded power grid frequency dynamic characteristic analysis system based on droop control provided by the present invention. This embodiment can be applied to the case of islanded power grid frequency dynamic characteristic analysis method based on droop control.

[0093] See Figure 2 The islanded power grid frequency dynamic characteristic analysis system based on droop control in this embodiment includes:

[0094] The capacity acquisition module 101 determines the renewable energy proportion coefficient that can characterize the islanded power grid based on the ratio of renewable energy capacity to synchronous machine capacity.

[0095] Frequency domain analysis module 201 establishes an equivalent frequency dynamic frequency domain analysis model for the islanded power grid through renewable energy droop frequency regulation control;

[0096] Time-domain analysis module 301 calculates the time-domain model of the system's frequency dynamic response based on the dynamic frequency-domain analysis model;

[0097] The characteristic analysis module 401 substitutes the system frequency into the time domain model and solves for the frequency dynamic characteristics of the islanded power grid.

[0098] This embodiment also provides a computing device applicable to the frequency dynamic characteristic analysis method of islanded power grids based on droop control, including:

[0099] The system includes a memory and a processor. The memory stores computer-executable instructions, and the processor executes these instructions to implement the method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control, as proposed in the above embodiments.

[0100] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0101] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control, as proposed in the above embodiments.

[0102] The storage medium proposed in this embodiment and the data storage method proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0103] Example 2

[0104] Reference Figure 6 —7 is an embodiment of the present invention, which provides a method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through specific implementation methods and implementation effects.

[0105] Based on the aforementioned frequency response characteristics of the isolated power grid, this embodiment calculates the steady-state frequency deviation and maximum frequency deviation of the system as the penetration rate of renewable energy changes.

[0106] like Figure 6 As shown, it should be noted that the values ​​of the parameters used in the calculation are: D = 0.01, R = 0.05, T = 6, 2H = 12, α = 1 / 3, and the power disturbance of the system at 250s is ΔPL* = 0.02. Figure 7 This is the frequency response curve of an actual isolated power grid. By comparing the calculated values ​​with the actual frequency response curve, it can be demonstrated that the frequency characteristic analysis method proposed in this invention is correct and effective.

[0107] 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 method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control, characterized in that, include: Based on the ratio of renewable energy capacity to synchronous machine capacity, a renewable energy proportion coefficient that can characterize islanded power grids is determined. A dynamic frequency domain analysis model of the equivalent frequency of an isolated power grid is established through renewable energy droop frequency regulation control. The time-domain model of the system's frequency dynamic response is calculated based on the dynamic frequency domain analysis model described above. Substituting the system frequency into the time-domain model, the frequency dynamic characteristics of the islanded power grid are obtained by solving the problem. The frequency dynamic characteristics of the isolated power grid are determined by the synchronous machine, energy storage battery, and load. The dynamic response characteristics of the synchronous machine include its own inertia response process and the primary frequency regulation process of the governor and the steam turbine. The inertial response process is represented as follows: The primary frequency modulation process is represented as follows: in, The inertial time constant of the synchronous machine, This is the damping coefficient of the synchronous machine. For system frequency, The mechanical power input to the prime mover. The electromagnetic power output by the synchronizer. Let be the equivalent time constant of the steam turbine. These are the characteristic parameters of the steam turbine. This refers to the droop coefficient of the speed controller; Based on the constant power control decoupling control strategy of traditional energy storage converters, frequency-power droop control measures are applied at the active power outer loop to enable the energy storage battery to have the ability to actively support the frequency of the islanded grid. The renewable energy proportion coefficient is expressed as follows: in, K is a parameter representing the penetration rate of renewable energy. The higher the penetration rate of renewable energy, the smaller the value of K. The dynamic frequency domain analysis model is expressed as follows: in, , which is a constant term in the frequency domain analysis model. ω n It is the natural frequency; , where is the coefficient of the first-order term in the frequency domain analysis model, and ζ is the damping ratio; To account for the equivalent damping of renewable energy penetration, the parameter is... This represents the droop factor of the energy storage converter.

2. The method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control as described in claim 1, characterized in that: The time-domain model of the system's frequency dynamic response is expressed as follows: in, , , a , b These are two eigenvalues ​​obtained through the frequency domain model. , , k 1. k 2 represents two coefficients in the time-domain model.

3. The method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control as described in claim 2, characterized in that: The frequency dynamic characteristics of the isolated power grid include steady-state frequency deviation, maximum frequency deviation, and time to the maximum frequency deviation. The steady-state frequency deviation is expressed as: The maximum frequency deviation is expressed as: The time to the maximum frequency deviation is expressed as: 。 4. A frequency dynamic characteristic analysis system for an islanded power grid based on droop control, employing the method described in claim 1, characterized in that, include: The capacity acquisition module (101) determines the renewable energy proportion coefficient that can characterize the islanded power grid based on the ratio of renewable energy capacity to synchronous machine capacity; The frequency domain analysis module (201) establishes an equivalent frequency dynamic frequency domain analysis model for the islanded power grid through renewable energy droop frequency regulation control; The time-domain analysis module (301) calculates the time-domain model of the system's frequency dynamic response based on the dynamic frequency-domain analysis model. The characteristic analysis module (401) substitutes the system frequency into the time domain model and solves for the frequency dynamic characteristics of the islanded power grid.

5. A computing device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control as described in any one of claims 1 to 3.

6. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the method for analyzing the frequency dynamic characteristics of an islanded power grid based on droop control as described in any one of claims 1 to 3.

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