Safety control method for double-layer hidden Markov jump power system
Technical Field
The invention relates to the technical field of control of Markov systems, in particular to a safety control method of a double-layer hidden Markov jump power system.
Background
As a complex nonlinear system, the power system often suffers from low frequency oscillations during operation. These continuous oscillations can seriously affect the stability of the system, resulting in significant economic losses. Power System Stabilizers (PSS) can provide supplementary damping for synchronous machine rotor oscillations, thus suppressing the oscillations, and thus have been widely studied and applied. Considering the change of the operation condition of the power system, the current method for stabilizing the power system on a large scale mainly comprises two methods, namely robust PSS and self-adaptive PSS. Robust PSS has received more attention than adaptive PSS which require relatively stringent continuous excitation conditions, since it can maintain good dynamic performance under conditions of large load variation and system nonlinearity. For example, experts discuss the control problem of nonlinear robust coordination PSS automatic voltage regulators. However, these studies did not consider the effect of random topological mutations on system stability. The research of the influence of the topological random mutation of the power system on the system stability is significant and challenging.
Faults and external disturbances experienced by the power system are unpredictable, and thus, abrupt changes in system structure and parameters may be modeled using markov theory, for example, some students have employed markov models to describe random abrupt changes in the power system. However, existing markov power system controller designs are mostly mode independent or mode dependent, and partial loss of system mode information may occur due to data loss or delay in the data transmission from the sensor to the controller, thereby possibly causing the controller to be out of sync with the system. Second, the acquisition of power system state information in actual operation is also a difficult challenge. In view of these factors, hidden Markov Models (HMMs) are certainly a better choice, and HMMs can not only characterize the phenomenon of dyssynchrony, but also solve the difficult problem of system mode information acquisition, so that it is necessary to study a power system based on HMMs.
On the other hand, data in a power system may be subjected to malicious network attacks during transmission, most often DoS attacks that lead to packet loss, and in addition, transmission failures are liable to occur due to unreliability of transmission channels. Faced with such challenges, some students employ discrete hidden Markov chains to model the probability of transmission failure. However, most of the current communication transmission studies ignore the possibility of DoS attacks and transmission failures occurring simultaneously. Notably, network failures that result in packet loss and energy-limited DoS attacks are different. Transmission failures are typically unintentional and random, while DoS attacks are intentional and may last for a period of time. Based on the above discussion, how to handle these stochastic processes in a hidden markov jump power system is the primary motivation for the present invention.
Similar to the acquisition of pattern information in a markov power system model, it is also challenging to acquire model information for communication transmissions. Fortunately, studies have shown that HMMs provide a viable solution to this challenge. Thus, the communication transmission process can be modeled as a hidden markov jump communication model. HMMs are effectively used in some studies to characterize channel dynamics. In other studies finite state HMMs have been used to study the problem of state estimation in unreliable communication channels, but these studies are limited by the assumption that the transition probability matrix or observation probability matrix is fully understood, and have great limitations in theory. To address this problem, some students consider using a partial information transition probability matrix when describing the random process of packet loss and time delay using HMMs. In addition, some scholars have studied markov jump systems based on sliding patterns, taking into account partly known observation probability matrices. Based on the above study, the present invention discusses a more general scenario in which both the transition probability matrix and the observation probability matrix may be partially known, or one of them may be partially unknown. Based on the above discussion, it is a very challenging problem to overcome the asynchronous behavior of controllers and system modes and asynchronous behavior of data in unreliable network transmissions, especially under unknown probability conditions.
Disclosure of Invention
The technical problem to be solved by the invention is how to overcome the asynchronous behavior problems of a controller and a system mode and data in unreliable network transmission, and provide a safety control method of a double-layer hidden Markov jump power system, which can realize the safety control of the system under the DoS attack by combining the control of the controller and the control of an H ∞ performance index.
The invention solves the technical problems through the following technical proposal, and the invention comprises the following steps:
S1, taking into consideration the action of a breaker switch caused by line faults in a power system and the asynchronous behavior between the power system and a controller, introducing a hidden Markov jump power system model;
s2, in order to deal with data packet loss and DoS attack which can be encountered when data is transmitted in an unreliable network channel, another independent hidden Markov model is adopted to describe the situation, and a transition probability matrix and an observation probability matrix in the hidden Markov model can be unknown;
s3, constructing a controller model to obtain a closed-loop system model of the system under the DoS attack;
s4, giving a linear matrix inequality condition that the system obtained in the step S3 is randomly stable under disturbance and meets the performance index sigma of H ∞;
s5, proving that the inequality condition of the step S4 is effective by utilizing a Lyapunov function and a performance index function;
S6, solving a gain matrix of the controller;
And S7, realizing the safety control of the double-layer hidden Markov power system according to the gain matrix of the controller and the given system parameters in the step S6.
Further, in the step S1, the specific processing procedure is as follows:
s11, establishing a dynamic model of the power system as follows:
where δ is the rotor angle, x d is the synchronous reactance along the d-axis, x ' d is the transient reactance along the d-axis, T e is the electric torque, V is the infinite bus voltage, E fd is the generator field voltage, u is the stationary signal, T do ' is the d-axis open-circuit transient time constant, V t is the terminal voltage, E q ' is the q-axis voltage after transient reactance, x e is the external line reactance, M is the inertia coefficient, k E,TE is the exciter gain and time constant, T m is the mechanical torque;
s12, representing the fourth-order state space model of the power system in the step S11 as:
Wherein:
xT(υ)=[Δδ Δω ΔE′q ΔEfd];
x (v) and u (v) respectively represent the state variable and the control input of the v-th node, y (v) is the measurement output, Is an internal coupling matrix between nodes, w (v) is a segmentAn additional disturbance on the surface of the substrate,Is the measurement matrix of the sensor and,Is the output matrix of the system, k 1,k2...k6 is the linearization model constant of the synchronous motor, and Δω is the speed deviation;
s13, introducing a hidden Markov process with unknown part of information, and establishing a hidden Markov jump power system as follows:
Wherein, the Is a discrete-time markov chain;
The transition probability matrix r= { η ψj } in the hidden markov jump power system is as follows:
wherein eta ψj epsilon [0,1],
Observation probability matrix in hidden Markov jump power systemThe following are provided:
Wherein, the
Further, in the step S2, the DoS attack has limited energy, and may last until the nth time point, and the DoS attack mode is as follows:
Mode 1, which shows that data transmission is successful (lambda (mu) =1), wherein in the mode, the probability of the system continuing to succeed in the next time step is τ 11, the probability of occurrence of transmission channel faults is τ 12, and the probability of DoS attack is τ 13;
Mode 2, which represents communication transmission failure (lambda (mu) =2), wherein in the mode, the probability of successful transmission of the system in the next time step is τ 21, the probability of occurrence of transmission channel failure is τ 22, and the probability of DoS attack is τ 23;
mode 3, representing transmission under DoS attack (λ (μ) =3), wherein the probability of normal transmission of the system in the next time step is τ 31, the probability of occurrence of transmission channel failure is τ 32, and the probability of possible continued DoS attack is τ 34;
According to the same principle, the system is extended to the mode λ (μ) =n+1, and the system may return to the mode 1 or the mode 2 with probabilities τ (N+2)1 and τ (N+2)2, respectively, in the next time step, due to the limited attack energy when the attack reaches λ (μ) =n+2.
Further, in the step S2, the specific processing procedure is as follows:
S21, considering the use of Markov variable q (mu) to simulate the switching of a DoS attack, determining a transition probability matrix The following are provided:
Wherein, the
S22. variable lambda (μ) is observed through q (μ) and is shown inTakes the value of the middle, and determines the observation probability matrixThe following are provided:
Wherein, the
S23, analyzing the situation that the transition probability matrix and the observation probability matrix are partially unknown: Wherein:
The specific cases are divided into the following three types:
Further, in the step S3, the specific processing procedure is as follows:
s31, constructing the following asynchronous state feedback controller based on the hidden Markov model:
Wherein, the Representing the gain matrix of the controller,The variable theta ζ belongs toIndicating the state of transmission,When ζ=1, it indicates that the data transmission was successful, and when ζ+.1, it indicates that the current state information cannot be obtained, and the last successfully transmitted data is used
And S32, further obtaining the following double-layer hidden Markov jump power system:
where x (t+1) represents the state variable of the (t+1) th node, y (t) is the measurement output, Is given as a system parameter matrix, w (t) is the belonging intervalAn additional disturbance on the surface of the substrate,Is the measurement matrix of the sensor and,Is the output matrix of the system;
S33, performing augmentation processing on the double-layer hidden Markov jump power system in the step S32 to obtain a closed-loop system model as follows:
Wherein, the
Further, in said step S4, given a scalar σ >0, if a matrix K i is present,Ρ=a, b; and symmetric matrixThe system in step S32 is able to achieve random stabilization at a given H ∞ performance index σ when the following inequality condition holds:
Wherein:
further, in the step S5, the specific processing procedure is as follows:
S51 for w (t) ≡0 and any initial value, when the condition is When established, the system in step S32 is randomly stable, when all non-zeroAnd the zero initial state satisfies the following inequality, the system in step S32 can reach the specified performance index σ of H ∞:
S52, considering selecting the following Lyapunov functional:
Wherein, the
Order theThe method comprises the following steps:
Wherein, the
The following inequality and the above equation in step S51 are used to obtain:
Wherein:
s53, obtaining by the upper inequality in the inequality condition in the step S4:
Wherein, the
S54, substituting the inequality in step S53 into the inequality below the inequality condition in step S4, yields:
S55, then, based on inequality And Schur complement, capable of obtaining the lower inequality of the inequality condition in the step S4;
S56, according to the inequality in step S54, obtaining:
If w (t) ≡0, then The system is randomly stable;
Under zero initial conditions, w (t) +.0, knowing
The system is randomly stable and meets the specified H ∞ performance index σ.
Further, in the step S6, the specific processing procedure is as follows:
S61, enabling K i=Ti -1Ui to be the same as that of the original;
S62, performing equivalent transformation on the inequality below the inequality condition of the step S4 as follows:
Wherein:
and S63, using simulation software, calculating the values of the gain matrix of the controller through given matrix parameters.
Compared with the prior art, the invention has the following advantages:
1. Secondly, based on the random process of communication transmission (transmission success, transmission failure and DoS attack) and the difficulty of acquiring the mode information of the communication process, an HMM describing the communication process is established, and a novel double-layer hidden Markov jump power system is further established;
2. for random processes in communication HMMs are described that employ limited information, which may be present in the transition probability matrix, the observation probability matrix, or both.
Drawings
FIG. 1 is a flow diagram of a method of security control with a dual layer hidden Markov jump power system in an embodiment of the invention;
FIG. 2 is a diagram of system modalities and controller modalities in an embodiment of the invention;
FIG. 3 is a sequence diagram of different attacks in an embodiment of the present invention that take into account the impact of a hybrid network attack on the stability of the power system;
FIG. 4 is a graph of the trajectory of the controller under the gain matrix of the controller solved in an embodiment of the present invention;
FIG. 5 is a diagram of a system state trace without a controller in an embodiment of the invention;
FIG. 6 is a diagram of a system state trace with a controller according to an embodiment of the present invention;
FIG. 7 is a state trace diagram of x 1 (t) in an embodiment of the present invention;
FIG. 8 is a top view of x 4 (t) under an open loop system in an embodiment of the present invention;
FIG. 9 is a three-dimensional view of x 4 (t) under an open loop system in an embodiment of the present invention;
FIG. 10 is a top view of x 4 (t) under a closed loop system in an embodiment of the present invention;
FIG. 11 is a top view of x 4 (t) under a closed loop system in an embodiment of the present invention;
fig. 12 is a schematic diagram of a transmission information construction structure in an embodiment of the present invention.
Detailed Description
The following describes in detail the examples of the present invention, which are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of protection of the present invention is not limited to the following examples.
The embodiment provides a technical scheme that a safety control method of a double-layer hidden Markov jump power system is provided, firstly, a hidden Markov jump power system model is introduced in consideration of the switching action of a circuit breaker caused by line faults in the power system and the asynchronous behavior between the power system and a controller. To address packet loss and denial of service attacks (DoS attacks) that may be encountered when data is transmitted in an unreliable network channel, another separate Hidden Markov Model (HMM) is used to describe this situation, and the Transition Probability Matrix (TPM) and Observation Probability Matrix (OPM) in the HMM may be unknown. Secondly, based on the electric power system with the double-layer hidden Markov jump structure, some sufficient conditions are established to ensure that the closed-loop system realizes random stability in the mode asynchronous and unreliable data network transmission process. And finally, verifying the correctness of the double-layer hidden Markov jump structure power system theory through a simulation example.
As shown in fig. 1, the safety control method with the double-layer hidden markov jump power system specifically includes the following steps:
step S1, a hidden Markov jump power system model is introduced in consideration of the switching action of a circuit breaker caused by line faults in a power system and the asynchronous behavior between the power system and a controller;
the dynamic model of the power system is built as follows:
where δ is the rotor angle, x d is the synchronous reactance along the d-axis, x ' d is the transient reactance along the d-axis, T e is the electric torque, V is the infinite bus voltage, E fd is the generator field voltage, u is the stationary signal, T do ' is the d-axis open-circuit transient time constant, V t is the terminal voltage, E q ' is the q-axis voltage after transient reactance, x e is the external line reactance, M is the inertia coefficient, k E,TE is the exciter gain and time constant, T m is the mechanical torque;
the fourth-order state space model of the power system (1) is expressed as:
Wherein:
xT(υ)=[Δδ Δω ΔE′q ΔEfd];
x (v) and u (v) respectively represent the state variable and the control input of the v-th node, y (v) is the measurement output, Is an internal coupling matrix between nodes, w (v) is a segmentAn additional disturbance on the surface of the substrate,Is the measurement matrix of the sensor and,Is the output matrix of the system, k 1,k2...k6 is the linearization model constant of the synchronous motor, Δω is the speed deviation.
And (3) introducing a hidden Markov process with unknown part information, and establishing a hidden Markov jump power system as follows:
Wherein, the Is a discrete-time markov chain;
transition probability matrix r= { η ψj }:
wherein eta ψj epsilon [0,1],
In view of the asynchronous behavior and the difficulty in acquiring system state information, a hidden markov jump power system model is built in this embodiment. S (t) related to r (t) follows the following observation probability matrix
Wherein, the
In order to handle packet loss and denial of service attacks that may be encountered when data is transmitted in an unreliable network channel, another separate hidden markov model is used to describe this situation, where both the transition probability matrix and the observation probability matrix may be unknown.
In power system research, communication channels may experience transmission failures and denial of service attacks (DoS attacks) during transmission. These conditions can damage or even lose data packets, severely affecting system stability. Where the DoS attack has limited energy, it may last until the nth time point, the DoS attack mode is as follows:
Mode 1, which shows that the data transmission is successful (lambda (mu) =1), in which the probability of the system continuing to succeed in the next time step is τ 11, and the probability of being subjected to DoS attack is τ 13 because the probability of the transmission channel failure is τ 12;
Mode 2, which represents communication transmission failure (lambda (mu) =2), wherein in the mode, the probability of successful transmission of the system in the next time step is τ 21, the probability of occurrence of transmission channel failure is τ 22, and the probability of DoS attack is τ 23;
mode 3, representing transmission under DoS attack (λ (μ) =3), wherein the probability of normal transmission of the system in the next time step is τ 31, the probability of occurrence of transmission channel failure is τ 32, and the probability of possible continued DoS attack is τ 34;
according to the same principle, it is extended to the pattern λ (μ) =n+1. Since the attack energy is limited when the attack reaches λ (μ) =n+2, the system may return to either mode 1 or mode 2 with probabilities τ (N+2)1 and τ (N+2)2, respectively, in the next time step.
Considering the use of a Markov variable q (μ) to simulate the switching of a DoS attack, a transition probability matrix
Wherein, the
The variable lambda (mu) is observed through q (mu) and is shown inTakes the value of the middle, and observes the probability matrix
Wherein, the
Analyzing the cases where the transition probability matrix and the observation probability matrix are partially unknown,
Wherein, the
And step S3, constructing a controller model to obtain a closed-loop system model of the system under the DoS attack.
The following asynchronous state feedback controller based on the hidden Markov model is constructed:
Wherein, the The two subscripts representing the controller gain matrix, K, represent the system mode and the observed mode, respectively.
The block diagram may be constructed from the modeling information of transmission success, transmission failure, and DoS attack, as shown in fig. 12. The variable theta ζ belongs toRepresenting the transmission status.
When ζ=1, it indicates that the data transmission was successful, on the contrary, when ζ+.1, it indicates that the current state information cannot be acquired, so that the last successfully transmitted data is usedThe specific expression is as follows:
in summary, the following two-layer hidden markov jump power system can be obtained:
where x (t+1) represents the state variable of the (t+1) th node, y (t) is the measurement output, Is given as a system parameter matrix, w (t) is the belonging intervalAn additional disturbance on the surface of the substrate,Is the measurement matrix of the sensor and,Is the output matrix of the system.
The augmentation treatment is carried out on the formula (6), and a closed-loop system model can be obtained as follows:
Wherein, the
And step S4, giving a linear matrix inequality condition that the system in the step S3 is randomly stable under disturbance and meets the performance index sigma of H ∞.
Given a scalar σ >0, if a matrix K i is present,Ρ=a, b and symmetric matrixThen the system (7) can achieve random stabilization at a given H ∞ performance index σ when the following inequality condition holds:
Wherein:
and S5, proving that the inequality condition of the step S4 is effective by using a Lyapunov function and a performance index function.
When the system (7) is established under given conditions, it not only appears to be randomly stable, but also meets the H ∞ performance index σ.
For w (t) ≡0 and any initial value, the system (7) is randomly stable, when the condition isWhen the method is established, the following steps are carried out:
when all are non-zero And the zero initial state satisfies the inequality below, the system (7) can reach the specified H ∞ performance index sigma.
Consider the following Lyapunov functional to be selected:
Wherein, the
Order theThe method can obtain:
Wherein, the
Obtainable by formula (10) and above:
Wherein: obtained by the formula (8):
Wherein, the Substituting the above inequality into equation (9), it is possible to obtain:
then, based on the inequality And Schur complement, can obtain formula (9);
from equation (12), it follows:
If w (t) ≡0, it can be seen that The system is randomly stable.
Under zero initial conditions, w (t) +.0, can be obtainedThe system is randomly stable and meets the specified H ∞ performance index σ.
And step S6, solving a gain matrix of the controller.
Let K i=Ti -1Ui.
The partial inequality condition of step S4 is equivalently transformed as follows:
Wherein:
At this point, the values of the controller gain matrix K i may be calculated by given matrix parameters using simulation software.
And S7, realizing the safety control of the double-layer hidden Markov power system according to the gain matrix of the controller and the given system parameters in the step S6.
When a line fails, the hidden Markov jump power system shown in the formula (3) has two modes according to the on-off state of the circuit breaker, and specific parameters are as follows:
Mode 1:
Mode 2:
the remaining parameters in this embodiment are assumed as follows:
σ=20,w(t)=0.3*cos(0.3t)e-0.56t,S1=[0.6 0.6 0.45 0.3]T,S2=[1.2 0.45 0.45 0.45]T;
Then the controller gain matrix is as follows:
K1=[-0.0076 -0.048 0.0393 0.0043];
K2=[-0.0239 -0.2067 0.0107 -0.0021]。
From the above parameters, the following simulation graphs can be obtained. Fig. 4 shows the output response u (t) over 10 sampling paths. Fig. 2 shows the evolution of the system and controller modes over time. Also, fig. 3 depicts three transmission modes under HMM. Fig. 5 shows that the system state trace is unstable over 10 sampling paths if there is no controller. In fig. 7, the state trace x 1 (t) clearly shows that the system eventually stabilized after the controller is applied. Fig. 6 illustrates that all state traces have reached stability. In addition, fig. 8-11 show three-dimensional diagrams of x 4 (t) of a single sampling path. The system state in fig. 8 and 9 is divergent from a three-dimensional perspective (without controller) and then stabilizes under the intervention of the controller, as shown in fig. 10 and 11.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.