Low-voltage alternating-current micro-grid secondary control strategy for unconstrained attack

Abstract

The invention belongs to the technical field of micro-grid secondary control in control engineering, and particularly relates to a low-voltage alternating-current micro-grid secondary control strategy oriented to unconstrained attacks, which can counteract the adverse effect of general unconstrained network physical attacks on a control input channel by designing a compensation signal, and improves the control accuracy. Therefore, the defense capability of the AC micro-grid is improved. Compared with an existing method, the strategy can process more common unbounded attack signals, limitation on bounded high-order time derivatives is more loose, and therefore unlimited network physical attack signals with a wider range can be resisted. According to the method, the final limits of the frequency and the voltage of each inverter are flexibly adjusted by adjusting the adaptive gain in the adaptive adjustment method, so that the performance of the alternating-current micro-grid is further optimized.

Description

Technical Field

[0001] This invention belongs to the field of microgrid secondary control technology in control engineering, specifically relating to a low-voltage AC microgrid secondary control strategy for unconstrained attacks. Background Technology

[0002] Microgrids are cyber-physical systems that integrate the physical layer of a distribution network with the network layer of distributed local controllers and sparse communication networks. They face the potential threat of cyber-physical attacks, which can target various components such as sensors, actuators, and communication channels, disrupting the overall performance and stability of the microgrid in a coordinated manner. Existing microgrid research mainly focuses on two approaches to addressing cyber-physical attacks. One approach is to detect compromised agents and then implement recovery or isolation strategies; the core premise of the "detect and recover or isolate" approach is that the attack signal is detectable. However, attack detection methods cannot always protect against and prevent stealthy and intelligent attackers. Therefore, enhancing the self-healing capabilities of large-scale microgrids through the development of anti-attack control protocols is an important method to ensure the safe and stable operation of microgrid systems. Distributed anti-attack control protocols can maintain acceptable performance levels by mitigating the adverse effects of external disturbances and attacks propagating within the system. The main focus is on designing local distributed control methods to enhance the self-recovery capabilities of microgrids against malicious attacks without needing to detect and identify compromised agents. It is worth noting that in existing methods, interference, noise, faults, or attacks are generally considered bounded signals. However, in reality, attackers may intentionally inject unbounded attack signals into cyber-physical systems to maximize damage. Therefore, developing cyber-physical defense strategies capable of resisting general unbounded attacks is crucial for ensuring the reliability and security of AC microgrids.

[0003] The invention disclosed in CN114899823 A presents a design method for a distributed secondary controller in a variable topology microgrid, belonging to the field of distributed secondary controllers for microgrids in control engineering. This design method includes: constructing distributed secondary controllers for each node under different modes; then establishing a distributed secondary control model for a single node and a complete model of the microgrid under distributed secondary control in different modes; establishing a new Lyapunov-Krasovsky function based on the microgrid model and providing a new microgrid stability criterion; proving the stability of the variable topology microgrid based on the linear matrix inequality in the stability criterion; and finally calculating the maximum controller gain of the variable topology microgrid under asymptotic stability conditions using a particle swarm optimization algorithm. Summary of the Invention

[0004] The purpose of this invention is to provide a secondary control method for low-voltage AC microgrids against unconstrained attacks, addressing the problems existing in the prior art. This method is designed for fully distributed, attack-resistant secondary control of AC microgrids to cope with unrestricted cyber-physical attacks.

[0005] The technical solution of this invention is:

[0006] A two-stage control strategy for low-voltage AC microgrids resistant to unconstrained attacks includes the following steps:

[0007] S1: Select a microgrid containing N inverters, and define an attack with bounded α-order derivative. In a microgrid, the attributes of each node can be represented by a time-varying weighted graph G at the information layer. Let the physical layer of the k-th node in the information layer be the connection point to the main grid; then this node is the leader node. Define the adjacency matrix A = [aij] ∈ RN × N, and define b... ik It is the gain from the k-th dominant node to the i-th inverter, denoted by the diagonal matrix Bk = diag(b ik In this context, a general unconstrained FDI attack is introduced on the local input channels of the frequency and voltage control loops. For the i-th inverter, the droop mechanism is as follows:

[0008]

[0009]

[0010] S2: Definition

[0011]

[0012] S3:

[0013]

[0014] S4: Recovery signal R fi R vi The solution method is as follows:

[0015]

[0016] Where ηfi and ηvi are positive exponential decay functions, such as ηfi(t)=et(t), Rfi and Rvi are compensation signals, χfi and χvi are adaptive adjustment parameters, adaptive gain βfi and βvi are positive constants, and τ∈(0,1) is the time adjustment coefficient.

[0017] The beneficial effects of this invention are as follows: Compared with existing methods, this invention proposes a fully distributed anti-attack defense strategy for the secondary frequency and voltage control of AC microgrids. Specifically, it designs a compensation signal by incorporating an adaptive adjustment parameter reflecting relative neighborhood information to offset the adverse effects of general unrestricted cyber-physical attacks on the control input channel. The provided strategy can more broadly address unrestricted attacks on the control input channel, considering more unbounded cyber-physical attacks injected into the control input channel, requiring the higher-order time derivatives (α-th order) of the attack signal to be bounded. Existing solutions can only handle a limited range of unbounded attack signals, and their first-order time derivatives must be bounded. In contrast, the cyber-physical defense strategy proposed in this invention can handle more general unbounded attack signals, with a more relaxed restriction on bounded higher-order time derivatives. This relaxation enables AC microgrids using the proposed control method to resist a wider range of unrestricted cyber-physical attack signals, thereby enhancing the AC microgrid's defense capability against malicious cyber-physical attacks. The defense strategy successfully mitigates the comprehensive adverse effects caused by general unbounded attacks. Furthermore, by appropriately adjusting the adaptive gain in the adaptive adjustment method, the final limits of frequency and voltage for each inverter can be adjusted. Attached Figure Description

[0018] Figure 1 This is a control block diagram of the control strategy provided by the present invention;

[0019] Figure 2 This is a schematic diagram illustrating the pre-defined problem of the control strategy provided by the present invention;

[0020] Figure 3 This is a schematic diagram of the IEEE 9 bus structure;

[0021] Figure 4 yes Figure 3 Equivalent diagram;

[0022] Figure 5 This is a schematic diagram of the frequency performance of traditional secondary control under unconstrained attack signals.

[0023] Figure 6 This is a schematic diagram of the performance of a traditional secondary control voltage under an unconstrained attack signal.

[0024] Figure 7 This is a schematic diagram of the secondary control frequency performance proposed in this invention under unconstrained attack signals.

[0025] Figure 8 This is a schematic diagram of the performance of the secondary control voltage proposed in this invention under an unconstrained attack signal.

[0026] Figure 9 This is a schematic diagram comparing the frequency performance of unconstrained actuators under attack with different adaptive gain values ​​βfi. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] like Figure 1 The diagram shown is a principle block diagram of a two-stage control strategy for a low-voltage AC microgrid resistant to unconstrained attacks provided in this embodiment, including the following steps:

[0030] S1: Select a microgrid containing N inverters, and define an attack with bounded α-order derivative. In a microgrid, the attributes of each node can be represented by a time-varying weighted graph G at the information layer. Let the physical layer of the k-th node in the information layer be the connection point to the main grid; then this node is the leader node. Define the adjacency matrix A = [aij] ∈ RN × N, and define b... ik It is the gain from the k-th dominant node to the i-th inverter, denoted by the diagonal matrix Bk = diag(b ik In this context, a general unconstrained FDI attack is introduced on the local input channels of the frequency and voltage control loops. For the i-th inverter, such as... Figure 2 The diagram shows an example of an independent microgrid. In the figure, ①②③④ represent four distributed generation sources, and the left diagram represents a single distributed generation source, i.e., an expansion of ①. The droop mechanism is as follows:

[0031]

[0032]

[0033] S2: Definition

[0034]

[0035] S3:

[0036]

[0037] S4: Recovery signal R fi R vi The solution method is as follows:

[0038]

[0039] Where ηfi and ηvi are positive exponential decay functions, such as ηfi(t)=et(t), Rfi and Rvi are compensation signals, χfi and χvi are adaptive adjustment parameters, adaptive gain βfi and βvi are positive constants, and τ∈(0,1) is the time adjustment coefficient.

[0040] Example 2

[0041] like Figure 3 As shown, we validated the fully distributed, attack-resistant secondary defense strategy proposed in Example 1 on an IEEE 9 bus system, which is islanded at bus 100 and contains three inverter-based DERs and two leaders (reference). All inverters have the same power rating. The inverter droop gain is set to m. P1 =9.4×10⁻⁵, m P2 =18.8×10⁻⁵, m P3 =28.2×10⁻⁵, n Q1 = 1.3×10⁻³, n Q2 = 2.6 × 10⁻³, n Q3 = 3.9×10⁻³. The inverter communicates on a bidirectional communication network, with an adjacency matrix of A = [0 1 1; 1 0 1; 1 1 0]. The gain is g = 1. The frequency reference, upper voltage limit reference, and lower voltage limit reference are 50 Hz, 390V, and 370V, respectively. The traditional secondary control strategy is designed as follows:

[0042] (11)

[0043] In this case study, the unconstrained attack injections into the frequency and voltage control loops are set to AT, respectively. v1 =0.5t 2 AT v2 =0.4t 2 AT v3 =0.3t 2 and AT f1 =0.3t 2 AT f2 =0.4t 2 AT f3 =0.5t 2 The performance of the anti-attack defense strategy was compared with that of the traditional two-level control method in (6). The constant gain of the traditional control protocol was set as kfi = 20, kvi = 10, i = 1, 2, 3; the adaptive gain of the anti-attack defense strategy was set as βvi = 20, βfi = 350, i = 1, 2, 3. Figure 5 and Figure 6 The voltage and frequency responses of conventional strategies and the proposed resilient secondary defense strategy in response to unrestricted attacks were compared. Figure 7 This is a schematic diagram of the secondary control frequency performance proposed in this invention under unconstrained attack signals. Figure 8This is a schematic diagram illustrating the performance of the secondary control voltage proposed in this invention under an unconstrained attack signal. It can be seen that after the attack is injected at t=5s, both the voltage and frequency diverge. Therefore, traditional methods cannot maintain system stability. In contrast, by employing the proposed anti-attack secondary defense strategy, the voltage of each inverter converges to a value within the range of 370-390V, and the frequency converges to the reference value of 50Hz. These results verify that the proposed resilient defense strategy can achieve convergence in frequency regulation.

[0044] like Figure 9 This diagram illustrates the frequency performance comparison of unconstrained actuator attacks under different adaptive gain values ​​βfi. Different βfi values ​​are represented by different types of lines. It can be seen that by appropriately adjusting the βfi value, the limiting constraint is reduced, and the transient response is improved.

[0045] This invention designs a compensation signal, a strategy that can offset the adverse effects of general unrestricted cyber-physical attacks on the control input channel, thereby enhancing the defense capability of AC microgrids. Compared to existing methods, this strategy can handle more common unrestricted attack signals and has more relaxed restrictions on bounded higher-order time derivatives, thus resisting a wider range of unrestricted cyber-physical attack signals. Furthermore, this invention allows for flexible adjustment of the final limits of frequency and voltage for each inverter by adjusting the adaptive gain in the adaptive adjustment method, thereby achieving further optimization of AC microgrid performance. In summary, the purpose of this invention is to improve the defense capability of AC microgrids against malicious cyber-physical attacks and ensure their stable operation. Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this invention and not to limit it; although the invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solution of this invention, and all such modifications should be covered within the scope of the technical solution claimed in this invention.

Claims

1. A two-stage control strategy for low-voltage AC microgrids resistant to unconstrained attacks, characterized in that, Includes the following steps: S1: Select a microgrid containing N inverters, and define an attack with bounded α-order derivative. , In a microgrid, the attributes of each node at the information layer can be represented by a time-varying weighted graph G. Let the physical layer of the k-th node at the information layer be the connection point to the main grid; then this node is the leader node. Define the adjacency matrix of the information graph as A = [aij] ∈ RN × N, and define b... ik It is the gain from the k-th dominant node to the i-th inverter, denoted by the diagonal matrix Bk = diag(b ik In this context, a general unconstrained FDI attack is introduced on the local input channels of the frequency and voltage control loops. For the i-th inverter, the droop mechanism is as follows: (6) (7) S2: Definition (8) S3： (9) S4: Restore signal , The solution method is as follows: (10) Where ηfi and ηvi are positive exponential decay functions, such as ηfi(t) = et(t), Rfi and Rvi are compensation signals, χfi and χvi are adaptive adjustment parameters, and the adaptive gain βfi and βvi are positive constants. It is the time adjustment coefficient.

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