Background
With the advance of science and technology, a spacecraft is used in various military and civil activities, the attitude motion of the spacecraft refers to the motion relative to the self mass center, the attitude control is a precondition for the spacecraft to complete various tasks, in the design of an actual controller, the nonlinear characteristic of an actuator also needs to be considered, namely, the problem of saturation is input, in the actual spacecraft, the actuator cannot output infinite moment, if the problem is not considered by the controller, the actuator can be always kept in a saturated state, the performance degradation and even the failure of the actuator can be caused, finally, the system instability and even the failure of the task can be caused, along with the improvement of the refinement degree of the space mission, the transient performance of the spacecraft also needs to be considered in the design of the controller, the transient performance comprises the size of overshoot and the preset convergence speed, in the operation process of the space system, if the attitude change overshoot is too large, not only more fuel is consumed, but also the system stability is possibly affected, so the spacecraft attitude controller is designed to take the output constraint and input saturation into consideration.
Disclosure of Invention
The invention aims to provide a control scheme aiming at the problems of actuator saturation and attitude constraint in the attitude control process of a spacecraft.
In order to achieve the purpose, the invention provides the following technical scheme:
a spacecraft attitude tracking control algorithm is based on a back stepping method, virtual variables are introduced into a spacecraft attitude error dynamics submodel, a virtual control rate is designed, further, a finite time control law is designed based on the virtual control rate, the stability of a finite time controller is proved, a time optimal design concept is adopted, a transition process is designed to smooth input signals, a jump step signal is changed into a slowly rising signal, a system keeps a small error in the whole process of tracking the input signals, the generation of input saturation is avoided, and the obstacle Lyapunov function is used in the process of designing the spacecraft attitude tracking controller by the back stepping method, so that the tracking performance and the constraint requirement of a spacecraft attitude subsystem are guaranteed.
Preferred as the present invention: the input anti-saturation processing adopts a time optimal design method, and a jumping step signal can be changed into a slowly rising signal, so that the generation of an input saturation phenomenon is avoided.
Preferred as the present invention: the spacecraft carries out attitude constraint control, and the constraint control of the state quantity is realized through an obstacle Lyapunov function.
Compared with the prior art, the invention has the beneficial effects that: compared with other spacecraft attitude tracking algorithms, the spacecraft attitude tracking control algorithm takes the input saturation problem and the attitude constraint problem into consideration and provides an improved scheme.
The specific implementation mode is as follows:
the following detailed description of the embodiments of the present invention is provided, and it is obvious that the embodiments described are only a part of the present invention, and not all of the embodiments, and those skilled in the art can obtain the embodiments of the present invention without creative efforts, and all of them are within the protection scope of the present invention.
In the embodiment of the invention: a spacecraft attitude tracking control algorithm is based on a backstepping method, a spacecraft attitude controller is designed by utilizing a barrier Lyapunov function, the state constraint of a spacecraft attitude angle can be guaranteed, and a step control input instruction is processed into a relatively smooth input signal by adopting a time optimal design concept, so that a system keeps a small error in the whole process of tracking the input signal.
1. Spacecraft attitude control model
The method for representing the attitude control model of the spacecraft comprises an Euler angle, a quaternion, a rotation matrix, a modified Rodrigue parameter and the like, the description mode of the rotation matrix is compared with the description mode of the Euler angle, so that the occurrence of a singular problem can be avoided, and the attitude kinematics and dynamics model of the spacecraft based on the rotation matrix is as follows:
in the formula: rcE, S0(3) represents a rotation matrix of the spacecraft attitude from a body coordinate system to an inertia coordinate system; omegac∈R3 ×1Representing the attitude angular velocity of the spacecraft in a body coordinate system; j. the design is a squarec∈R3×3Is a rotational inertia matrix of the spacecraft; u is an element of R3×1And d ∈ R3×1Respectively representing the control moment and the disturbance moment of the spacecraft under a body coordinate system.
R
eAnd ω
eRespectively, an attitude error and an angular velocity error, defined as
And
wherein R is
tAnd ω
tRespectively desired attitude and desired angular velocity.
Attitude error ReIs a matrix, is difficult to be applied to the design of a controller, and adopts a posture error representation form of a structure
In the formula: tr (R)e) Represents Re"V" represents the inverse of the cross product: SO (3) → R3×1。
According to the limit
The available spacecraft attitude control model is
2. Design of controller
Considering that the output omega of a spacecraft system is constrained, a first-order low-pass filter is introduced to realize dynamic surface control by using the thought of designing virtual control quantity layer by using backstepping control, and BLF is introduced to process the output constraint problem, so that a spacecraft rendezvous and docking attitude tracking control algorithm is provided, and the design steps are as follows:
step1 defines the actual attitude error e and the expectationAttitude error edHas a dynamic surface error of x1I.e. by
x1=e-ed
Get edX is 01E. The error dynamic equation is
Choosing a logarithmic BLF function:
wherein k isb1Is to the state quantity x1The constraint parameter of (2).
The derivation is carried out on the above formula
Fetch stabilization function
In the formula: sig (x)1,i)γ=sign(x1,i)|x1,i|γ,i=1,2,3,r1=(2-γ)ηγ-1,r2=(γ-1)ηγ-20 < gamma < 1, eta is a very small positive number, beta1>0,β2>0。
Easy to verify: when ω is
tAnd
in hundreds of bounds, using a virtual controller
Can make convergence to the region | x in a limited time
1,i|≤η。
Step2 pair
Filtering is carried out, with
Where τ > 0, is the sampling time.
Selecting a second BLF function:
wherein k isb2Is to the state quantity x2The constraint parameter of (2).
The derivation is carried out on the above formula
Derived along the system trajectory
Is convenient to use
And obtaining an experimental result through a simulation test by using a designed controller.
The technical solutions and advantages of the present invention have been clearly described above, and it is obvious for those skilled in the art that the present invention is not limited by the above embodiments, and the above described embodiments and descriptions are only technical solutions and principles of the present invention and do not represent all of them, and the invention is implemented by performing corresponding algorithm modifications without departing from the spirit and content of the present invention, and within the scope of the claims of the present invention, the experimental results of the present invention are implemented in a specific form, and the scope of the present invention is defined by the appended claims and the equivalent.