Disclosure of Invention
In accordance with the above-presented series of problems with constrained nonlinear system control, the present invention presents an adaptive control method for nonlinear systems with input skew and state constraints. The technical scheme of the invention comprises the following specific steps:
1. A method for adaptive control of a nonlinear system having input skew and state constraints, the method comprising the steps of:
step 1, establishing a nonlinear system equation with input time lag and state constraint:
Wherein the method comprises the steps of As a state variable of the system,Is a real space of n dimension, andAs the first derivative of state x i,Is the first derivative of state x n; is a state vector consisting of states x 1,...,xi, Is i-dimensional real space, u is control input of the system, and Is a real number set, θ is an uncertain parameter item, and I and n both represent the order of the system for d-dimensional real spaceIs thatThe function has f 1 (0, θ) =0,The function is a function set with continuous first-order partial derivatives, d i (t) represents bounded external disturbance in the ith-order system, d n (t) represents bounded external disturbance in the nth-order system, τ >0 represents input time lag, and t represents t moment;
step 2, processing the input time lag of the nonlinear system by using a Pade approximation method, and obtaining according to the Laplace time lag theorem:
where l {.cndot. } represents the Laplace transform process and s is the Laplace variable;
subsequently, an intermediate variable x n+1 is introduced, which satisfies
From (3), it can be seen that
From the Laplace transform and (4) can be obtained
The combination of systems (1), (3) and (5) gives the following new systems
Wherein η is defined intermediate variable andF n (x, θ) is a nonlinear function of the system.
Step 3, introducing state coordinate transformation
And define the adaptive parameters as follows
Wherein z 1,...,zi,...,zn is the state of the system after coordinate transformation, Θ is the adaptive parameter, α 2,...,αn is the virtual control law to be designed, reference signal y d,I-th derivative ofBounded on Ω d, where Ω d is the set that satisfies the reference signal constraint andIs positive constant, and can be obtained according to the formulas (6) - (7)
Wherein, the As the estimated value of theta,D 2,di,dj,dn are respectively bounded external disturbances of the corresponding order system;
and 4, setting constraint conditions of the system as follows:
Where k bi is a known constant. The introduction of the obstacle Lyapunov function (BLF) according to the constraint conditions is:
Wherein k ci >0 is a positive constant and Γ >0 is an adaptive gain constant; is Θ and its estimated value Error values between the two.
Step 5, designing an adaptive controller of a nonlinear system with input time lag and state constraint as follows:
Wherein, the C n,σ0,εn,kcn >0 is a known positive constant; representing the nth derivative of the reference signal.
Compared with the prior art, the invention has the following advantages:
1. the invention firstly tries to consider the influence of input time lag, state constraint and parameter uncertainty at the same time, and solves the control problem of a more general nonlinear system.
2. By combining the Pade approximation method, BLF and self-adaptive backstepping design in a unified framework, the difficulties brought to the design of a system controller by input time lag, state constraint and parameter uncertainty are successfully compensated;
3. The invention designs a new BLF-based self-adaptive state feedback controller, which proves that all signals in a closed loop system are consistent and finally bounded, and the tracking error of the system always converges to a small neighborhood of an origin. In particular, the state of the system never violates constraint limits.
Detailed Description
In order to make the design concept of the present invention more clear, the following will describe in detail the design, principle and demonstration of the state feedback controller, and the following will describe in detail the drawings in conjunction with the accompanying drawings.
As shown in fig. 1, the present invention provides an adaptive control method for a nonlinear system with input skew and state constraints. The technical scheme comprises the following specific steps:
step 1, establishing a nonlinear system equation with input time lag and state constraint:
Wherein the method comprises the steps of As a state variable of the system,Is a real space of n dimension, andAs the first derivative of state x i,Is the first derivative of state x n; is a state vector consisting of states x 1,...,xi, Is i-dimensional real space, u is control input of the system, and Is a real number set, θ is an uncertain parameter item, and I and n both represent the order of the system for d-dimensional real spaceIs thatThe function has f 1 (0, θ) =0,The function is a function set with continuous first-order partial derivatives, d i (t) represents bounded external disturbance in the ith-order system, d n (t) represents bounded external disturbance in the nth-order system, τ >0 represents input time lag, and t represents t moment;
step 2, processing the input time lag of the nonlinear system by using a Pade approximation method, and obtaining according to the Laplace time lag theorem:
where l {.cndot. } represents the Laplace transform process and s is the Laplace variable;
subsequently, an intermediate variable x n+1 is introduced, which satisfies
From (3), it can be seen that
From the Laplace transform and (4) can be obtained
The combination of systems (1), (3) and (5) gives the following new systems
Wherein η is defined intermediate variable andF n (x, θ) is a nonlinear function of the system.
Step 3, introducing state coordinate transformation
And define the adaptive parameters as follows
Wherein z 1,...,zi,...,zn is the state of the system after coordinate transformation, Θ is the adaptive parameter, α 2,...,αn is the virtual control law to be designed, reference signal y d,I-th derivative ofBounded on Ω d, where Ω d is the set that satisfies the reference signal constraint andIs positive constant, and can be obtained according to the formulas (6) - (7)
Wherein, the As the estimated value of theta,D 2,di,dj,dn are respectively bounded external disturbances of the corresponding order system;
and 4, setting constraint conditions of the system as follows:
Where k bi is a known constant. The introduction of the obstacle Lyapunov function (BLF) according to the constraint conditions is:
Wherein k ci >0 is a positive constant and Γ >0 is an adaptive gain constant; is Θ and its estimated value Error values between the two.
Step 5, designing an adaptive controller of a nonlinear system with input time lag and state constraint as follows:
Wherein, the C n,σ0,εn,kcn >0 is a known positive constant; representing the nth derivative of the reference signal.
To better illustrate the inventive technique, a designed adaptive state feedback controller will be demonstrated. The following assumptions and quotients will be used in the proving process.
Assuming 1, there is a positive constant d iM such that for i=1..n, the external disturbance satisfies |d i(t)|≤diM
Assuming a 2, correlated reference signal y d,I-th derivative thereofIn the closed setIn the inner part of the inner part,Y 1,Yi (i=2., n) is a normal number.
Lemma 1, k ci >0 for arbitrary constant and allSatisfying the requirements of |z i|≤kci,This is true.
2, For real variable x >0, y >0, there areWherein m is a real number and is more than or equal to 1.
Lemma 3 for i=1, the combination of the first and second components, n,Function ofSatisfy the following requirements
Wherein the method comprises the steps ofIs a non-negative smooth function and Θ 0 is not less than 1, which is a design constant.
4, For any k ci >0, setAnd (3) withIs an open set. Consider a systemWherein the method comprises the steps ofIs a state variable, where z= (z 1,z2,...,zn)T,With respect to t segment continuum, with respect to z i local Lipoz continuum, atAnd is consistent with the above. Assuming that there is a continuously differentiable positive definite functionAndSuch that when z i→kci or z i→-kci there is V 1→∞,γ1(||ω||)≤W(||ω||)≤γ2 (|ω||), where γ 1 and γ 2 areA function. Definition V (κ) =v 1 +w (ω), where z (0) ∈Ω 1, if inequalityAt the position ofThe above holds, where μ, Δ is a positive constant, ω is bounded and z i∈Ω1,
The proving process is as follows:
and the first step, designing a self-adaptive controller.
For the system (6), the invention uses a back-stepping method to design the controller, and the design steps are divided into n steps:
the first step is to select Lyapunov function as
Wherein k c1 >0 is a design constant, Γ >0 is an adaptive gain constant; is Θ and its estimated value Error values between the two. Obviously, V 1 is atThe inner is conductive. From (9) - (10), the derivative of V 1 is
From the quotients 2-3, it is assumed that 1-2 and (7) - (8) are known
Wherein the method comprises the steps of
Substituting (16) - (18) into (15) can result in
Wherein, the Thus, the first virtual control law is selected as follows
Substituting (20) into (19) to obtain
Wherein c 1 >0 and sigma 0 >0 are design constants, and there are
Step two, selecting Lyapunov function V 2 as
Obviously, V 2 is atAnd (3) internal conduction. Deriving the above and using (9) and (21)
From hypothesis 1-2 and lemma 2-3
Wherein ε 21>0,ε22 >0 is the design constant;
substituting (25) - (27) into (24) to obtain
In the middle of
The virtual control laws are now selected as follows
Where c 2 >0 is the design constant. Substituting (29) into (28) to obtain
Wherein σ 2 >0 is a design constant, and has
Step i (i=3, 4.,. N-1) this step uses induction. Assume that there is a positive Lyapunov function in step i-1 asAnd has a series of virtual control laws
So that
Wherein σ i-1 is a non-negative continuous function and Δ i-1 is a positive constant.
We demonstrate that (33) is true for step i. Lyapunov function V i is defined asFrom (9) and (33), it can be seen that the derivative of V i is
For further derivation, the following inequality can be obtained by using the lemma 2-3 and hypothesis 1
Wherein the method comprises the steps ofAnd ε i >0 is a constant.
Substituting (35) - (37) into (34) and constructing alpha i+1 as
Can be made (34) to satisfy
Wherein c i >0 is a design constant;
Step one, selecting Lyapunov function V n as
Similar to the construction process of the i step, the controller and the adaptive control law are designed as follows
Finally can lead to
Where c n,Δn is a positive constant and γ n,φn is a non-negative continuous function.
And secondly, analyzing stability.
From the above derivation, the present invention gives the following theorem:
Theorem 1 considers that the system (1) under the condition of assuming 1-2, when the actual controller is designed as (41) and the adaptive controller is designed as (42), there are
(I) All signals in the closed loop system are consistent and ultimately bounded;
(ii) The tracking error converging to within a certain closed set of origin, i.e
(Iii) The system state satisfies |x i|<kbi, i.e., the constraint is not violated.
And (3) proving:
(i) First by (43) Can be written as
Wherein the method comprises the steps ofFrom the quotation mark 1, it can be seen that
In combination (40) and (46), formula (45) can be written as
Where c=min {2c i,Γσ0, i=1,..n }.
From (40), (47) and lemma 4, it can be seen that z i (t) andIs consistent and eventually bounded, since Θ is a constant value, soAlso consistently ultimately bounded, as known from z 1=x1-yd, state x 1 consistently ultimately bounded, as known from equation (20) a 2 consistently ultimately bounded, again as known from equation (7) x 2=z2+α2, x 2 consistently ultimately bounded, and so on, we can obtain a 3,α4,...,αn,x3,x4,...,xn+1 and u consistently ultimately bounded. In summary, all signals in a closed loop system are consistent and ultimately bounded.
(Ii) Multiplying equation (47) by e ct and integrating the two sides of the inequality over [0, t ] to obtain
And can be seen from (40)Is obtained by arrangement
From equation (7), we can define the tracking error as y (t) -y d(t)=z1 (t), combined with (49) to know the error forThe tracking error satisfies
That is, the tracking error remains within a small neighborhood of the origin, which is a bounded tight set
(Iii) Assume thatWherein the method comprises the steps ofIs a positive constant. From x 1=z1+yd and hypothesis 2It can be seen thatOrder theCan obtain |x 1|<kb1. Again byAnd (3) withIt can be seen thatOrder theLet us get |x 2|<kb2 by analogy we can finally get |x i|<kbi, i=1, 2.
The effectiveness of the controller designed by the invention is verified by a single-link mechanical arm system. Consider a single link mechanical arm system as in FIG. 2, which is coupled to a DC motor by a rigid link through gears, the system dynamics being expressed as
Wherein m=1 kg·m 2 is inertia, m=1 kg is link mass, q is the angular position of the link; the unit is rad/s for the angular velocity of the connecting rod; The unit is the angular acceleration of the connecting rod, rad/s 2;g=9.8m/s2 is the gravitational acceleration, and F is the control force of the connecting rod. We regard i as a parameter uncertainty term and define the state variable x 1 = q, And a control input u=f, wherein the state constraint satisfies |x 1|<kb1=1.5,|x2|<kb2 =1.8, equation (51) can be written as
Wherein f 2=-0.5mgsin(x1) and θ=l. In the simulation, the disturbance signal is selected as d 2 (t) =0.2 sint, the reference signal is selected as y d =0.1 sint, and |d 2 (t) |is less than or equal to 0.2 from the assumption 1-2,AndIn addition, in the case of the optical fiber,Wherein Θ 0 =θ, select
The adaptive controller is designed according to the above-described controller design process as follows
Wherein the method comprises the steps of
And is also provided with
C 1,c2,ε2 >0 is a design constant.
In the simulation, assuming an input skew τ=0.01, the other parameters are chosen as ε 2=2,Γ=10,c1=1,c2=2,σ0 =1. The initial conditions of the system are chosen as [x1(0),x2(0)]T=[0.3,0.2]T,[x1(0),x2(0)]T=[1.2,0.2]T,[x1(0),x2(0)]T=[-1.1,0.2]T and respectivelyIt can be seen from fig. 3 that under different initial conditions the tracking error of the system can converge to a small neighborhood of the origin, i.e. the system output signal y can track the reference signal y d very well, that under different initial conditions the system state is not against the constraint, the adaptive parameters are consistent and eventually bounded, and that from fig. 7 the control input u of the system is also consistent and eventually bounded. In summary, all signals of the closed loop system are consistent and ultimately bounded.
The invention researches the tracking control problem of a state constraint nonlinear system with input time lag and parameter uncertainty. The parameter nonlinearity of the system is treated by combining the self-adaptive back-off method and the parameter separation method. Combining Pade approximation with BLF in a unified framework successfully addresses the uncertainty caused by input skew and state constraints. An adaptive state feedback controller is obtained through rigorous stability analysis. The research result shows that all signals in the closed loop system are consistent and finally bounded, the tracking error of the system always converges to a small neighborhood of the origin, and the state of the system never violates the constraint limit. Further work will focus on adaptive time-controlled assignment of constrained nonlinear systems.
The foregoing is merely illustrative of general procedures and is not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. which fall within the spirit and principles of the present invention should be included in the scope of the present invention.