A multi-agent-based additional frequency modulation control method for multi-terminal flexible HVDC system

Abstract

This invention discloses an additional frequency regulation control method for a multi-terminal flexible DC system based on multiple agents, comprising the following steps: configuring an Agent for each battery swapping station participating in frequency regulation control in the multi-terminal flexible DC system; adjacent Agents being connected via a communication network; each Agent including a weighted frequency calculation module and a frequency droop control module; the weighted frequency calculation module calculating the system weighted frequency using a discrete consensus algorithm based on information from the local and adjacent Agents. f ref The Agent information includes: the frequency droop control coefficient of the converter station. K f and weighted frequency f K Where, f is the frequency of the AC system connected to the converter station; the frequency droop control module is based on the system weighted frequency. f ref Calculate the additional frequency regulation power of the converter station P f The frequency droop control module will P f Superimposed on the converter station power setpoint P set The invention changes the output power of the converter station to participate in system frequency regulation. It has the advantages of low communication burden, high reliability, easy implementation of decentralized control, and easy expansion.

Description

Technical Field

[0001] This invention relates to the field of power transmission and distribution technology, specifically to an additional frequency regulation control method for a multi-terminal flexible DC system based on multiple agents. Background Technology

[0002] Multi-terminal flexible DC transmission is one of the main methods for achieving asynchronous grid interconnection. With the large-scale grid connection of new energy sources such as wind power and photovoltaics, fluctuations in new energy output pose a significant challenge to grid frequency regulation control. Multi-terminal flexible DC transmission has rapid power regulation capabilities and can improve converter station power to provide frequency support for the grid and enhance grid frequency stability when frequency events occur in the grid through additional frequency droop control. However, traditional frequency droop control can cause fluctuations in the DC voltage of the multi-terminal flexible DC system, which may threaten the operational safety of the DC system in severe cases. Multi-terminal flexible DC transmission with additional frequency control based on weighted frequency can decouple converter station frequency droop control and voltage droop control, thereby avoiding the impact of frequency droop control on the multi-terminal flexible DC voltage. However, in this control, each converter station needs to measure the frequency and frequency droop control coefficient of other converter stations to calculate the weighted frequency value, resulting in a heavy measurement and communication load, poor adaptability to communication failures, and difficulties in engineering applications. Summary of the Invention

[0003] The purpose of this invention is to provide a frequency modulation control method for a multi-terminal flexible DC system based on multiple agents, which has the advantages of low communication burden, high reliability, easy implementation of distributed control, and easy expansion.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] A method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents is provided, which includes the following steps:

[0006] S1: Configure an Agent for each battery swapping station participating in frequency regulation control in the multi-terminal flexible DC system, wherein adjacent Agents are connected through a communication network, and the Agent includes: a weighted frequency calculation module and a frequency droop control module;

[0007] S2: The weighted frequency calculation module calculates the system weighted frequency based on information from local and neighboring agents using a discrete consensus algorithm. f ref The Agent information includes: the frequency droop control coefficient of the converter station. K f and weighted frequency f K ,in, In the formula, f is the frequency of the AC system connected to the converter station;

[0008] S3: The frequency droop control module controls the frequency based on the system weighted frequency. f ref Calculate the additional frequency regulation power of the converter station P f ;

[0009] S4: Frequency droop control module will P f Superimposed on the converter station power setpoint P set The converter station's output power is changed to participate in system frequency regulation.

[0010] As a preferred embodiment of the additional frequency modulation control method for multi-terminal flexible DC systems based on multiple agents, the weighted frequency calculation module calculates the system weighted frequency using a discrete consensus algorithm based on information from local and neighboring agents. f ref Step S2 includes:

[0011] S21: Each Agent measures the local information of its corresponding converter station and transmits the information to neighboring Agents through the communication network, while also receiving information from neighboring Agents;

[0012] S22: Based on information from local and neighboring agents, update its own information values ​​in a discrete form and obtain the information exchange coefficient matrix. W ;

[0013] S23: The weighted frequency calculation module uses a consensus algorithm based on the information exchange coefficient matrix. W Iteratively calculate the information values ​​of each Agent to obtain the average weighted frequency of all participating frequency regulation control converter stations. and the average value of the frequency droop coefficient ;

[0014] S24: Based on the weighted frequency average and the average value of the frequency droop coefficient The system weighted frequency was calculated. f ref .

[0015] As a preferred embodiment of the frequency modulation control method for multi-terminal flexible DC systems based on multiple agents, the method updates its own information values ​​in a discrete form according to the information of the local and neighboring agents, and obtains the information exchange coefficient matrix. W In step S22, the formula for updating the information value is:

[0016]

[0017]

[0018] In the formula, x i ( k )and x j ( k ) are respectively the first k Next iteration Agent i and Agent j Information obtained; Agent i and Agent j Converter stations i and converter station j Configured Agent; x i ( k +1) is x i ( k The updated value; δ ij Agent i and Agent j The coefficient of information exchange between them; N The total number of agents participating in information exchange, whose value is equal to the number of converter stations participating in system frequency regulation; max( x i , x j ) for Agent i The maximum number of neighboring agents that each of its neighboring agents possesses; M i Indicates with Agent i The set of indices of adjacent Agents.

[0019] As a preferred embodiment of the frequency modulation control method for multi-terminal flexible DC systems based on multiple agents, the method updates its own information values ​​in a discrete form according to the information of the local and neighboring agents, and obtains the information exchange coefficient matrix. W In step S22, the Agent's information update matrix is ​​as follows:

[0020]

[0021]

[0022] In the formula, ; W This is the information exchange coefficient matrix.

[0023] As a preferred embodiment of the additional frequency modulation control method for multi-terminal flexible DC systems based on multiple agents, the weighted frequency calculation module employs a consensus algorithm based on the information exchange coefficient matrix.W Iteratively calculate the information values ​​of each Agent to obtain the average weighted frequency of all participating frequency regulation control converter stations. and the average value of the frequency droop coefficient In step S23, the iteration ends when the change in each Agent's information is less than 1% in two consecutive iterations.

[0024] As a preferred embodiment of the additional frequency modulation control method for multi-terminal flexible DC systems based on multiple agents, the method is based on the weighted average frequency. and the average value of the frequency droop coefficient The system weighted frequency was calculated. f ref In step S24, the system weighted frequency f ref for:

[0025]

[0026] In the formula, N The number of converter stations participating in frequency regulation control.

[0027] As a preferred embodiment of the additional frequency modulation control method for a multi-terminal flexible DC system based on multiple agents, the frequency droop control module adjusts the system weighted frequency according to the frequency droop control module. f ref Calculate the additional frequency regulation power of the converter station P f In step S3, the additional frequency modulation power P f for: .

[0028] The beneficial effects of this invention are as follows: The proposed multi-agent-based multi-terminal flexible DC system frequency modulation control method uses a consensus algorithm, where each agent can calculate the weighted frequency value of the system solely through interaction information with neighboring agents, significantly reducing the communication requirements for control. Furthermore, due to the use of a multi-agent approach, if a communication line between different agents fails during the control process, as long as the communication topology between the multi-agent systems remains connected, the control effect is not affected, greatly improving the robustness of control to communication failures. This results in the invention having advantages such as low communication burden, high reliability, ease of implementing distributed control, and easy expansion. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0030] Figure 1 This is a flowchart of an embodiment of the additional frequency modulation control method for a multi-terminal flexible DC system based on multiple agents according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the system flow of the multi-terminal flexible DC system with additional frequency modulation control based on multiple agents according to an embodiment of the present invention;

[0032] Figure 3 This is a six-terminal flexible DC system for offshore wind farm access as described in one embodiment of the present invention;

[0033] Figure 4 This is a graph showing the frequency response results of the power grid under different control conditions in one embodiment of the present invention;

[0034] Figure 2 middle:

[0035] K D This is the voltage droop factor. P This refers to the output power of the converter station. Detailed Implementation

[0036] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0037] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0038] Reference Figure 1 and Figure 2 An embodiment of the present invention provides an additional frequency modulation control method for a multi-terminal flexible DC system based on multiple agents, characterized by comprising the following steps:

[0039] S1: Configure an Agent for each battery swapping station participating in frequency regulation control in a multi-terminal flexible DC system, wherein adjacent Agents are connected through a communication network, and the Agent includes: a weighted frequency calculation module and a frequency droop control module;

[0040] S2: The weighted frequency calculation module calculates the system weighted frequency based on information from local and neighboring agents using a discrete consensus algorithm. f ref The Agent information includes: the frequency droop control coefficient of the converter station. K f and weighted frequency f K ,in, In the formula, f is the frequency of the AC system connected to the converter station;

[0041] S3: The frequency droop control module controls the frequency based on the system weighted frequency. f ref Calculate the additional frequency regulation power of the converter station P f The additional frequency modulation power P f for: ;

[0042] S4: Frequency droop control module will P f Superimposed on the converter station power setpoint P set The converter station's output power is changed to participate in system frequency regulation.

[0043] Specifically, the weighted frequency calculation module calculates the system weighted frequency using a discrete consensus algorithm based on information from local and neighboring agents. f ref Step S2 includes:

[0044] S21: Each Agent measures the local information of its corresponding converter station and transmits the information to neighboring Agents through the communication network, while also receiving information from neighboring Agents;

[0045] S22: Based on information from local and neighboring agents, update its own information values ​​in a discrete form and obtain the information exchange coefficient matrix. W ;

[0046] In this step, the formula for updating the information value is:

[0047]

[0048]

[0049] In the formula, x i ( k )and x j ( k ) are respectively the first k Next iteration Agent i and Agent j Information obtained; Agent i and Agent j Converter stations i and converter station j Configured Agent; x i ( k +1) is x i ( k The updated value; δ ij Agent i and Agent j The coefficient of information exchange between them; N The total number of agents participating in information exchange, whose value is equal to the number of converter stations participating in system frequency regulation; max( x i , x j ) for Agent i The maximum number of neighboring agents that each of its neighboring agents possesses; M i Indicates with Agent i The set of indices of adjacent Agents.

[0050] The agent's information update matrix is:

[0051]

[0052]

[0053] In the formula, ; W This is the information exchange coefficient matrix.

[0054] S23: The weighted frequency calculation module uses a consensus algorithm based on the information exchange coefficient matrix. W Iteratively calculate the information values ​​of each Agent to obtain the average weighted frequency of all participating frequency regulation control converter stations. and the average value of the frequency droop coefficient ;

[0055] In this step, after several iterations, the iteration ends when the change in the information of each Agent is less than 1% in two consecutive iterations. According to the consensus algorithm, the information variables of all Agents can asymptotically reach consensus and eventually converge to the average of the initial values ​​of all information variables, that is, the average weighted frequency of all converter stations participating in frequency regulation control. and the average value of the frequency droop coefficient

[0056] S24: Based on the weighted frequency average and the average value of the frequency droop coefficient The system weighted frequency was calculated. f ref The system weighted frequency f ref for:

[0057]

[0058] In the formula, N The number of converter stations participating in frequency regulation control.

[0059] In this embodiment, by using a consensus algorithm, each Agent can calculate the weighted frequency value of the system simply by using the interaction information with neighboring Agents, which greatly reduces the communication requirements for control. Furthermore, due to the use of a multi-agent approach, if a communication line between different Agents fails during the control process, as long as the communication topology between the multi-agent systems remains connected, the control effect will not be affected, greatly improving the robustness of control to communication failures. This makes the present invention have the advantages of low communication burden, high reliability, easy implementation of distributed control, and easy expansion.

[0060] Reference Figure 3 Taking a power system comprising a six-terminal flexible DC transmission system as a specific application example, converter station 6 is connected to an offshore wind farm and performs voltage-frequency control, but does not participate in the frequency regulation control of the multi-terminal flexible DC system. Converter stations 1-5 are connected to their respective power grids, all performing DC voltage droop control and participating in system frequency regulation control. Each power grid includes a synchronous generator equipped with a speed control system and a load. Frequency events of the power grid are simulated by controlling changes in the output of the load or the synchronous generator. A corresponding Agent is configured for each converter station according to the above method. The Agent... i Converter station i Configured Agent. Frequency droop control coefficients for each converter station. K f As shown in Table 1 below.

[0061] Table 1 Frequency droop control coefficients for each converter station

[0062]

[0063] The network connectivity between the agents is shown in Table 2.

[0064] Table 2 Network connectivity between agents

[0065]

[0066] Taking steady-state frequency as an example, the convergence value and time of the information iteration of the weighted frequency calculation module in the test agent were measured. The convergence condition was that the information change was less than 1% between two consecutive iterations. The system converged through 30 iterations. Taking a communication rate of 2 Mbit / s and a communication data bit width of 16 as an example, the convergence calculation time was 0.00192 seconds, which is much smaller than the time scale of frequency control and can therefore be ignored. The calculation results for each agent are shown in Table 3. It can be seen that each agent can accurately converge to the true value.

[0067] Table 3. Convergence values ​​of information for each Agent

[0068]

[0069] Considering a communication failure between Agent1 and Agent5, the robustness of the weighted frequency calculation module to this failure was tested. The system iterated and converged 32 times, with a convergence calculation time of 0.00203 seconds, which is much smaller than the time scale of frequency control and can still be ignored. The calculation results are shown in Table 4, demonstrating that the communication failure does not affect the accuracy of the weighted frequency calculation module.

[0070] Table 4. Information convergence values ​​of each agent under communication failure.

[0071]

[0072] A load surge of 200MW is simulated in AC power grid 5, representing 10% of the total load change in grid 5. Considering the multi-terminal flexible DC system, two control methods are implemented: traditional weighted frequency-based supplementary frequency regulation control and multi-agent supplementary frequency regulation control. The frequency response of grid 5 under different control methods is as follows: Figure 4 As shown, the two overlap. The additional frequency modulation control based on multiple agents can achieve essentially the same control effect as the traditional additional frequency modulation control based on weighted frequency while significantly reducing communication requirements.

[0073] In the description of this invention, it should be understood that the terms "middle," "length," "upper," "lower," "front," "rear," "vertical," "horizontal," "inner," "outer," "radial," "circumferential," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and 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 this invention.

[0074] In this invention, unless otherwise expressly specified and limited, the first feature "on" the second feature may be in direct contact with the first and second features, or indirect contact with the first and second features through an intermediate medium. "A plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0075] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0076] The above description is merely illustrative of the embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made without creative effort within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents, characterized in that, Includes the following steps: S1: Configure an Agent for each battery swapping station participating in frequency regulation control in the multi-terminal flexible DC system, wherein adjacent Agents are connected through a communication network, and the Agent includes: a weighted frequency calculation module and a frequency droop control module; S2: The weighted frequency calculation module calculates the system weighted frequency based on information from local and neighboring agents using a discrete consensus algorithm. f ref The Agent information includes: the frequency droop control coefficient of the converter station. K f and weighted frequency f K ,in, In the formula, f is the frequency of the AC system connected to the converter station; S3: The frequency droop control module controls the frequency based on the system weighted frequency. f ref Calculate the additional frequency regulation power of the converter station P f ; S4: Frequency droop control module will P f Superimposed on the converter station power setpoint P set The converter station's output power is changed to participate in system frequency regulation.

2. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 1, characterized in that, The weighted frequency calculation module calculates the system weighted frequency using a discrete consensus algorithm based on information from local and neighboring agents. f ref Step S2 includes: S21: Each Agent measures the local information of its corresponding converter station and transmits the information to neighboring Agents through the communication network, while also receiving information from neighboring Agents; S22: Based on information from local and neighboring agents, update its own information values ​​in a discrete form and obtain the information exchange coefficient matrix. W ; S23: The weighted frequency calculation module uses a consensus algorithm based on the information exchange coefficient matrix. W Iteratively calculate the information values ​​of each Agent to obtain the average weighted frequency of all participating frequency regulation control converter stations. and the average value of the frequency droop coefficient ; S24: Based on the weighted frequency average and the average value of the frequency droop coefficient The system weighted frequency was calculated. f ref .

3. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 2, characterized in that, Based on information from local and neighboring agents, the system updates its own information values ​​in a discrete form and obtains an information exchange coefficient matrix. W In step S22, the formula for updating the information value is: In the formula, x i ( k )and x j ( k ) are respectively the first k Next iteration Agent i and Agent j The information obtained; Agent i and Agent j Converter stations i and converter station j Configured Agent; x i ( k +1) is x i ( k The updated value; δ ij Agent i and Agent j The coefficient of information exchange between them; N The total number of agents participating in information exchange, whose value is equal to the number of converter stations participating in system frequency regulation; max( x i , x j ) for Agent i The maximum number of neighboring agents that each of its neighboring agents possesses; M i Indicates with Agent i The set of indices of adjacent Agents.

4. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 2, characterized in that, Based on information from local and neighboring agents, the system updates its own information values ​​in a discrete form and obtains an information exchange coefficient matrix. W In step S22, the Agent's information update matrix is ​​as follows: In the formula, , X ( k )and X ( k+1 ) are respectively the first k Agent information vectors before and after each iteration; W This is the information exchange coefficient matrix; δ ij Agent i and Agent j The coefficient of information exchange between them; N The total number of agents participating in information exchange, which is equal to the number of converter stations participating in system frequency regulation; x i ( k ) ( i =1,2,…,N) is the first k Next iteration Agent i The information obtained.

5. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 2, characterized in that, The weighted frequency calculation module employs a consensus algorithm based on the information exchange coefficient matrix. W Iteratively calculate the information values ​​of each Agent to obtain the average weighted frequency of all participating frequency regulation control converter stations. and the average value of the frequency droop coefficient In step S23, the iteration ends when the change in each Agent's information is less than 1% in two consecutive iterations.

6. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 2, characterized in that, According to the average value of the weighted frequency and the average value of the frequency droop coefficient The system weighted frequency was calculated. f ref In step S24, the system weighted frequency f ref for: In the formula, N The number of converter stations participating in frequency regulation control.

7. The method for additional frequency modulation control of a multi-terminal flexible DC system based on multiple agents according to claim 1, characterized in that, The frequency droop control module is based on the system weighted frequency. f ref Calculate the additional frequency regulation power of the converter station P f In step S3, the additional frequency modulation power P f for: .

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