Disclosure of Invention
Aiming at the defects of the prior art, the invention discloses a leader following multi-agent system fault-tolerant consistency method based on network attack and fault distribution. In order to improve the stability of the control system, H is provided when the system has actuator failure fault∞The invention designs a fault-tolerant controller leading to follow the multi-agent system, so that the system can keep the stable performance when an actuator fails and network attacks occur.
Aiming at the leader, selecting the following state system model:
wherein x is
0(t)∈R
nIs the state quantity of the system leader,
is the input of the system leader.
The equation of state for the ith follower agent:
wherein x is
i(t)∈R
nIs the state quantity of the ith follower,
representing the control input of the follower actuator,
is an external disturbance of the system. Matrix B
wSatisfies B
wBF A, B and B
wIs the state matrix of the system with the appropriate dimensions and F is the known real matrix.
And (2) constructing a failure model of the executor with the leaders following the multi-agent. A general fault model for an actuator is now given as follows:
wherein: m isi=diag{mi,1,mi,2,...mi,s}ui=diag{ui,1,ui,2,...ui,s}i=1,2,...,N,j=1,2,....,s,
Redefining the model of the partial failure matrix:
wherein: m is
i,jRepresenting the coefficient of the ith agent for the jth actuator failing,
and
represents the failure coefficient m
i,jUpper and lower bounds.
According to the failure characteristics and upper and lower boundaries:
redefining the failure matrix may result in:
the form of the amplification matrix is as follows:
wherein:
augmented form of probability of failure of ith agent jth actuator of representative leadership multi-agent system, Γ
i0And
two failure coefficients selected from the segmented failure intervals are selected, based on the provided failure model,
can be rewritten as:
step (3) designs the network attack model of the invention
In the present invention, network attacks are considered, which are implemented by injecting misleading numbers into regular transmission data. To reduce system performance, the invention uses a non-linear function fj(x (t)) to represent a random network attack.
Wherein:
is represented by the x
i(t) the signal received by the agent is from the xth agent
j(t) the signals of the agents under network attack, alpha is more than or equal to 0
j(t) 1 is the x-th
i(t) the signal received by the agent is from the xth agent
j(t) probability of network-attacked signal, (reduced to network-attacked signal)
The possibility of occurrence).
Step (4) is to establish a consistent control law equation of the whole system aiming at steps (1), (2) and (3):
first, a consistent control law is given for the whole leader-follower multi-agent system, i.e. for any initial conditions, if satisfied,
the entire system may implement a fault-tolerant mean square consistency protocol.
Designing a fault-tolerant controller:
ui(t)=Kei(t),i=1,...,N (9)
wherein:
the combination of equations (1), (2), (3), (7), (8), (10) yields the consistency equation for the entire system:
wherein: giIs representative of the strength of the communication link between the leader and the follower, aijThe information communication strength between follower agents is represented, and the follower agents and the information communication strength form a topological structure between the whole leader-following multi-agent agents.
Step (5) is to establish an error state equation of the whole system for steps (1), (2), (3) and (4):
the invention adopts a method of segmenting a topological structure to write an error state equation of the whole system into a form of an augmentation matrix:
wherein:
and (6) aiming at the state equation of the system described in the step four, selecting a proper Lyapunov function as follows, so that the system (11) can realize consistent stability of mean square and H-infinity performance index.
The designed Lyapunov function of the invention is as follows:
i.e. given the correct controller gain K>0, constant number
Variable c
m>0, i-1, 2,3,4, and a matrix Q, T, F of the appropriate dimension, if given a positive definite matrix P of the appropriate dimension>0, N, satisfying the following linear matrix inequality holds, the system of step (5) can be implemented in the mean square sense with H
∞And achieving the fault-tolerant consistency of leader-following multi-agent under the condition of the interference level gamma.
Wherein:
in classical H∞In theory, the zero initial condition must be satisfied, based on this build performance index J:
wherein:
step (7) is a further optimization for step (6), i.e. designing the gain of the controller.
Giving an appropriate constant
Variable c
m>0, i-1, 2,3,4 and a matrix Q, T, F of the appropriate dimension, if there is one positive dimensionDefinite matrix P>0, N, and gain of the controller
The system of step (5) can be implemented in the mean square sense with H
∞And achieving the fault-tolerant consistency of leading and following the multiple agents under the condition of the interference level gamma.
Wherein:
step (8) is further optimized for step (7), and the failure coefficients in step (6) and step (7) are unknown.
Giving an appropriate constant
Variable c
m>0, i-1, 2,3,4 and moments Q, T, F of the appropriate dimension, if there is a matrix P of the appropriate dimension positive>0, N, gain of controller
The system of step (5) can be implemented in the mean square sense with H
∞And achieving the fault-tolerant consistency of leading and following the multiple agents under the condition of the interference level gamma.
Wherein:
the invention has the beneficial effects that: the stability and dynamic performance index of the system formula (11) have H while considering the system stability∞And (4) performance. In order to improve the safety and reliability of the leading-following multi-agent system, the device is provided withA fault-tolerant controller is designed, so that the system can still keep stable operation when an actuator failure fault and a network attack exist in the system.
Detailed Description
The invention will now be described in further detail with reference to examples shown in the accompanying drawings.
Aiming at the leader, selecting the following state system model:
wherein x is
0(t)∈R
nIs the state quantity of the leader and is,
an input that is a leader of the system.
The equation of state for the ith follower agent:
wherein: x is the number of
i(t)∈R
nIs the state quantity of the ith follower,
representing the control input of the follower actuator,
is an external disturbance of the system. Matrix B
wSatisfies B
wBF A, B, F and B
wIs a known real state matrix with the appropriate dimensions.
Step (2) constructs a failure model for the leader-follower multi-agent actuator of the invention. A general fault model for an actuator is now given as follows:
wherein: m isi=diag{mi,1,mi,2,...mi,s}ui=diag{ui,1,ui,2,...ui,s}i=1,2,...,N,j=1,2,....,s。
According to the characteristics of the failure fault of the actuator, redefining the model of a partial failure matrix:
wherein: m is
i,jRepresenting the failure coefficient of the jth actuator of the ith agent,
and
represents the failure coefficient m
i,jUpper and lower bounds.
According to the failure characteristics, the upper and lower bounds and the failure coefficients of the failure, the distribution rule of the failure satisfies Bernoulli distribution, and the failure matrix is redefined to obtain:
the form of the amplification matrix is as follows:
wherein:
probability of failure of the ith agent of the representative leader-follower multi-agent system for the jth actuator, Γ
i0And
two failure coefficients selected from the partitioned failure regions are used to follow the control input of the actuator based on the provided failure model
Can be rewritten as:
step (3) designs the network attack model of the invention
In the present invention, network attacks are considered, which are implemented by injecting misleading numbers into regular transmission data. To reduce system performance, the invention uses non-linear functionsfj(x (t)) to represent random cyber attacks, wherein the random cyber attacks satisfy the Bernoulli distribution.
Wherein:
is represented by the x
i(t) the signal received by the agent is from the xth agent
j(t) a signal under network attack, 0. ltoreq. alpha
j(t) 1 is the x-th
i(t) the signal received by the agent is from the xth agent
j(t) probability of network-attacked signal, (reduced to network-attacked signal)
The possibility of occurrence).
And (4) establishing a fault-tolerant consistency control law of the whole system aiming at the steps (1), (2) and (3).
First, the fault-tolerant consistent control law of the whole leader-follower multi-agent system is given, i.e. for any initial conditions, if satisfied,
the entire system may implement a fault-tolerant mean square consistency protocol.
Designing a fault-tolerant controller:
ui(t)=Kei(t),i=1,...,N (10)
wherein:
the combination of equations (1), (2), (3), (8), (9), (10) yields the consistency equation for the entire system:
wherein: giIs representative of the strength of the communication link between the leader and the follower, aijThe communication strength of the information between follower agents is represented, and the follower agents and the information form the communication strength of the topological structure between the whole leader-follower multi-agent agents.
Step (5) is to establish an error state equation of the whole leader-follower multi-agent system aiming at steps (1), (2), (3) and (4):
the invention adopts a method of segmenting a topological structure to write an augmentation matrix form of an error state equation of the whole system:
wherein:
and (6) aiming at the state equation of the system described in the step (4), selecting a proper Lyapunov function as follows, so that the system (11) can realize the consistent stability of fault-tolerant mean square and the performance index of H infinity.
The designed Lyapunov function of the invention is as follows:
i.e. if given the correct controller gain K>0, constant number
Variable c
m>0, i-1, 2,3,4, and a matrix Q, T, F of appropriate dimension, and a positive matrix P of appropriate dimension>0, N, satisfying the following linear matrix inequality holds, the described system of step (5) can be implemented in the mean square sense with H
∞And achieving the fault-tolerant consistency of leading and following the multiple agents under the condition of the interference level gamma.
Wherein:
in classical H∞In theory, the zero initial condition must be satisfied, based on this build performance index J:
wherein
Step (7) is a further optimization for step (6), i.e. designing the gain of the controller.
Giving an appropriate constant
Variable c
m>0, i-1, 2,3,4 and moments Q, T, F of the appropriate dimension, if there is a matrix P of the appropriate dimension positive>0, N, and gain of the controller
The system of step (5) can be implemented in the mean square sense with H∞And achieving the fault-tolerant consistency of leading and following the multiple agents under the condition of the interference level gamma.
Wherein:
step (8) is further optimized for step (7), and the failure coefficients in step (6) and step (7) are known, but in most cases are unknown, and based on this, the following theorem is designed.
Giving an appropriate constant
Variable c
m>0, i-1, 2,3,4 and moments Q, T, F of the appropriate dimension, if there is a matrix P of the appropriate dimension positive>0, N, the gain of the controller is full
The system of step (5) can be implemented in the mean square sense with H
∞And achieving the fault-tolerant consistency of leading and following the multiple agents under the condition of the interference level gamma.
Wherein:
for ease of understanding, step (8) is now explained as follows: the fault-tolerant controller is designed to ensure that the system keeps the mean square consistency of the whole system under the fault condition and the network attack and has H∞The performance index γ.
(2) Firstly, a digital simulation example is used for verifying the effectiveness of the fault-tolerant control design method:
firstly, parameters of digital simulation are given:
A=[-0.59 0.496;-5.513 -0.939]
B=[0.06 0.06;1.879 2.328]
F=[0.2 0;0.3 -0.5]
leader-Laplace array L following multiple agents satisfies:
follower actuator failure coefficient:
ρi1=0.65 ρi2=0.84 i=1,2....4.
leader input: r is0(t)=[sin(t)+14;cos(0.5×t-2.2)-12]T
External disturbance: w is ai(t)=[sin(t);1]T,i=1,2,3,4
Probability of network attack occurrence: alpha is alphaj(t) ═ 0.3, performance index: gamma is 0.3
Through the step (8), the gains of the fault-tolerant controller of the invention can be obtained respectively:
K=[2.2687 0.3449;26.6989 6.5273]
FIG. 1 illustrates a leader-follower multi-agent topology, and the present invention is directed to a system of five agents in a directed and directed topology.
Fig. 2, fig. 3, fig. 4, and fig. 5 are attack signals based on a case where the network attack occurrence probability is 30%.
FIGS. 6 and 7 show that the leaders-follow the tracks traced by the multi-agent in
states 1,2, the tracks of the operations tend to be identical, i.e. the tracks of the operations tend to be identical
Thus, fault-tolerant consistency of five agents is achieved.
Fig. 8 and 9 show the tracking errors of five agents in two states, as shown in the figure, the tracking error will gradually converge to 0, so the controller gain obtained by theorem 3 can also realize the fault-tolerant consistency under the condition of actuator failure fault and network attack of the system.
The invention researches the consistency of the leader following the multi-agent system when the actuator fault and the network attack occur. First, a fault model suitable for a leader-follower multi-agent is established based on fault characteristics. The network attack model is described by mutually independent random Bernoulli variables, and a topological structure segmentation method is adopted for solving. Then, sufficient conditions for realizing the mean square consistency of the system are given, and finally, the effectiveness of the method is verified through a specific digital simulation example.