Background
The electro-hydraulic servo system has the outstanding advantages of large transmission torque, high transmission efficiency and the like, and is widely applied to various important industrial fields, such as engineering machinery, machine tools, aerospace and the like. With the rapid development of these fields, the position tracking performance of the electro-hydraulic system is more and more required, and the performance of the system is closely related to the design of the controller. The electrohydraulic servo system is a typical nonlinear system, and many modeling uncertainties including parameter uncertainties and unmodeled disturbances are encountered in the process of designing a controller, wherein the disturbance entering the system through the same channel as the control input of the controller is called matched disturbance, and the disturbance entering the system through different channels as unmatched disturbance. These modeling uncertainties can severely degrade the desired control performance, resulting in less than ideal control accuracy, making the design of the controller difficult.
In the face of these model uncertainties in electro-hydraulic servo systems, numerous scholars have proposed corresponding controller design methods. The problem of parameter uncertainty in the design process of the controller is solved by introducing a parameter adaptive method. Other unmodeled interference problems in the controller design process are overcome by a robust control method. However, in the robust control method, the interference of the interference on the control performance is mainly suppressed by designing the gain of the controller, and when the system is faced with a large disturbance, the gain of the controller must be increased to ensure the stability of the system, which may deteriorate the tracking performance of the system.
The unmodeled interference is observed by a disturbance observer, and then the interference is compensated by utilizing the interference estimation value in the design process of the controller, so that a good effect can be achieved. The stability of the system is ensured, and the position tracking performance of the system is improved. Most of the existing interference observers can only observe matched disturbance, but cannot observe the matched disturbance. Some observers can observe two kinds of disturbances at the same time, but the design process is very complicated, and engineering practice is not facilitated. Therefore, a simple and feasible interference observation compensation control method for the electro-hydraulic position servo system, which can observe matched and unmatched disturbance simultaneously, is urgently needed.
Detailed Description
The invention provides a simple and easy-to-implement method for designing the interference observer of the electro-hydraulic servo system, so that matching and non-matching interference can be compensated, and the control precision of the electro-hydraulic servo system is improved.
An electro-hydraulic position servo system control method based on interference compensation comprises the following steps:
step 1, establishing a mathematical model of the electro-hydraulic position servo system, wherein according to Newton's second law, a motion equation of the electro-hydraulic position servo system is as follows:
in the formula (1), m is an inertial load parameter, y is inertial load displacement,
and
respectively inertial load velocity and acceleration, P
LTo load pressure, D
mIs the displacement of the hydraulic motor, B is the coefficient of viscous friction, F
eThe uncertainty items of external interference and unmodeled friction and the like.
Wherein the load pressure PLCan be expressed as
V in formula (2)
tIs the total volume of the hydraulic cylinder; beta is a
eThe effective elastic modulus of the hydraulic oil; c
tIs the internal leakage coefficient;
representing the total uncertainty present in equation (2). Q
LFor load flow, the expression is:
k in formula (3)tIs the total flow gain, PsIs the oil supply pressure; sign (#) is a sign function, and a specific expression is
Defining the state variables of the system as
The state equation of the system is:
wherein
In the formula (6), δ1And delta2Is a known constant.
And 2, establishing a mathematical model of the disturbance term observer.
In the formula (7), the first and second groups,
as interference term d
1Is determined by the estimated value of (c),
as interference term d
2Estimate of (a) ("lambda
1And λ
2Is the gain of the observer. p is a radical of
1And p
2Variables were designed for the observer's assistance.
And
are each p
1And p
2A derivative value with respect to time;
from the equations (5) and (7), it can be found
In the formula (8), e1As interference term d1Observation error of (e)2As interference term d2The observation error of (2).
And 3, designing the controller of the electro-hydraulic position servo system based on interference compensation.
The goal of the controller design is to make the position output x of the motor position servo system1Tracking as accurately as possible the position instruction x desired to be tracked1d。
The variables are defined as follows
Wherein alpha is2And alpha3Is a virtual control quantity;
defining a semi-positive definite function V1As follows
Derivation of V1Is expressed as
Wherein
The command is tracked for the desired speed, so that the virtual control quantity alpha can be designed
2Is composed of
In the formula (12), k1The gain is designed for the controller.
According to the formulae (11) and (12), it is possible to obtain
Defining a semi-positive definite function V2As follows
Derivation of V2Is expressed as
Thereby, the virtual control quantity alpha can be designed3Is composed of
In the formula (16), k2The gain is designed for the controller.
From the equations (15) and (16), it is found that
Defining a semi-positive definite function V3As follows
Derivation of V3Is expressed as
So that the controller output u can be designed to be
Wherein
From the equations (19), (20) and (21), it is found that
And 4, analyzing the stability of the electro-hydraulic position servo system:
according to the stability analysis of the system in the control theory:
wherein λ is the minimum feature root of matrix Λ
The stability is proved by applying the Lyapunov stability theory, and the stability can be obtained according to a formula (24):
so that the system can be made to be bounded stable.
The present invention will be described in detail with reference to the following examples and drawings.
Examples
The values of the parameters of the motor servo system are as follows:
m=30kg,B=10N·m·rad-1·s-1,Vt=7.962e-5m3,βe=700e6pa,Dm=9e-4m2,Ct=3e-12m3/s/pa,kt=1.18e-8m3/s/V/pa-1/2,Ps=10e6pa。
to verify the control performance of the controller, the controller proposed by the present invention is named NRDC controller, and the controller used for comparison is named FLC controller, and the two controllers have the same expression but different parameters. The FLC controller does not have an interference compensation item for interference.
NRDC controller parameter k1=1000,k2=2000,k3=1000,λ1=100,λ2=2000。
FLC controller parameter k1=1000,k2=2000,k3=1000,λ1=0,λ2=0。
Position command signal x1d(t)=0.04sin(t)·[1-exp(-0.01t3)]
FIG. 2 is a graph of a position command signal and FIG. 3 is a graph of tracking error versus time for two controllers, and it can be seen that the controller designed by the present invention is significantly superior to the FLC controller. FIG. 4 shows disturbance d under the action of the controller designed by the present invention1Fig. 5 shows the interference d under the action of the controller designed according to the present invention2And estimating an error map. According to the figure4 and 5, it can be seen that the estimation performance of the disturbance observer is excellent. The superior performance of a controller designed according to the present invention in the face of interference is fully illustrated with respect to fig. 3, 4 and 5. Fig. 6 is a time-varying control input curve of the controller designed by the present invention, and it can be seen from the graph that the control input signal obtained by the present invention is continuous, which is beneficial to the application in engineering practice.