JPS63148302A - Controller using sliding mode control - Google Patents

Abstract

PURPOSE:To enable a controller of the sliding mode control to quickly respond by shortening the time required for arrival of a signal at a switching line independently of the extent of deviation or the like. CONSTITUTION:A VSS controller 1 which performs the normal sliding mode control observes the state of a control system in accordance with the deviation between an input signal 11 and an output signal 12 from a process 2 and the variation of the deviation and gives the state signal to a switching rule operating means 5 through a signal line 15. The switching rule operating means 5 discriminates whether the state is on the outside or the inside of a preliminarily set area, and the discrimination result is given to a switching means 4 through a signal line 16. The switching means 4 switches an output signal 17 to a process 2 to give it to a signal line 13 from a saturation output operating means 3 if the state is on the outside of the area preliminarily set near the switching line. If it is within this area, the output signal 17 to the process 2 is switched and given to a signal line 14 from the VSS controller 1 of the sliding mode control.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to process control, and particularly to VSS (Varia
ble 5structure system) Concerning the application of control methods.

[Prior Art] FIG. 6 is a block diagram showing a process control system in conventional vSS control. 1 is an SS controller which outputs a control output 16 based on the deviation between the output 12 of the process 2 and the input 11;

■SS control attempts to obtain the optimal control state by switching and using control systems with different structures.Even if the control system is unstable, it can be stabilized depending on the switching method. This system has the characteristics that it is possible to obtain a controlled system, and furthermore, it is possible to realize control that is more advanced than normal PID control. Also,
A special case of this vSS control is a method called sliding mode control. This means that by setting the switching conditions in vSS control to a certain predetermined state, a system that meets various requirements can be obtained, and the present invention relates to the application of this sliding mode control.

Here, sliding mode control will be explained in more detail. FIG. 7 is a phase plane trajectory diagram for explaining the concept of sliding mode control. Now, consider a controlled object having dynamic characteristics expressed by a certain first-order differential equation. Figure 7 shows the deviation e on the horizontal axis and the speed on the vertical axis, and plots the trajectory of the motion of two unstable control systems on these coordinates as e=o...(1) and 5=Ce+5=O・・ ・(2) (e is deviation, S and C are arbitrary constants) It shows the phase plane trajectory of the new control system pasted together by two straight lines. Here, the straight line of e=o and S=O is called a switching line, and when this switching line is crossed, the parameters of the system are switched and the control system is shifted to a different control system.

A system in a certain state transitions along the trajectory, but when it crosses the switching line S-0 and enters the region on the opposite side, it is pushed back by the trajectory in the opposite direction. This process is repeated on the switching line, causing a transition toward the origin while making small vibrations.

This is called a sliding mode, and once the straight line of switching line S=O is reached, the process continues along the switching line toward the origin and reaches an equilibrium state. The transient response at this time is S=0, that is, Ce+M=
Follow Q. This control method also has the advantage of being resistant to system parameter fluctuations.

Based on the above theory, a plurality of systems are switched within the vSS controller 1 according to conditions such as position and speed, and a control output U that responds quickly to input is provided to the process 2.

[Problems to be solved by the invention] However, in the conventional sliding mode control,
The time it takes to shift to the sliding mode largely depends on the magnitude of the deviation and other factors, resulting in the problem that the system does not have sufficient high-speed response.

[Means for Solving the Problems] In view of the above problems, the present invention aims to provide a controller using sliding mode control that minimizes the time required to reach the switching line regardless of the magnitude of deviation, etc. shall be.

As shown in FIG. 1, the configuration of the present invention includes a VSS controller 1 that performs normal sliding mode control, a saturated output control means 3 that uses the control output before entering the sliding mode control as a saturated output, and a A switching means 4 for switching between a saturated output and a sliding mode control output, and a switching law calculation means 5 for determining the state of the switching means.
The switching law calculating means 5 is configured to switch the control output by the switching means 4 to the saturated output side outside a preset area near the switching line, and to the sliding mode control output side within the area. has been done.

■The SS controller 1 observes the state of the control system based on the deviation between the input signal 11 and the output signal 12 from the process 2 and the amount of change in the deviation, and sends a state signal to the switching rule calculation means 5 via the signal line 15. is given, the switching law calculation means 5 determines whether the state is outside or inside a preset area, and sends this determination result to the switching means 4 via the signal line 16, and the switching means 4 A vSS controller 1 is connected to the signal line 13 from the saturation output calculation means 3 outside a preset area near the switching line, and a vSS controller 1 that performs sliding mode control within the area.
The output signal 17 to process 2 is switched to the signal line 14 side from .

[Embodiment] FIG. 2 is a block diagram showing an embodiment of the present invention, in which a vSS controller that performs control based on sliding mode control and a switching means 5 that switches the output of the saturation output calculation means 3. , a switching law calculating means (not shown) for observing the state quantity and switching the switching means 4,
Controls process 2.

The input value, that is, the target value r input via the signal line 11, and the output value X fed back from the process 2 via the signal line 12 are added together at a point 21, and the difference is taken as the deviation e. (e=r-x) The deviation e is further block 22
The velocity is determined by differentiation. The deviation e is multiplied by each of the two control parameters α1 and β1 in blocks 23.24, and the speed is similarly multiplied by each of the two control parameters α1 and β8 in blocks 25.26. Blocks 23 to 26 represent gain parameters that are switched depending on the state of the system and are summed at summing point 27. As a result, A, = αle + α, 6 ・
...(3) Or, A = β1e + β3 ...(4) Select the two types of gains to switch the control characteristics.

At a summing point 28, the signal is summed with signals from various compensation means 29 such as friction compensation and disturbance compensation to obtain a normal sliding mode control output.

The deviation e is also input to the saturation output calculation means 3 via the signal line 30. The saturated output calculation means 3 outputs a positive saturated output if e>Q. The sliding mode control output and the saturation output are determined by a switching sub-calculation means (not shown) whether or not the system state 3=06+e is within a predetermined region So on the phase plane trajectory diagram; If it is outside S0, the switching agent is determined to be the saturated output side, and if it is within So, the switching agent is determined to be the sliding mode control output side, and the switching means 4 switches the output to the process 2.

FIG. 2 is a phase plane trajectory diagram for explaining the state of control according to the present invention, in which the horizontal axis represents the deviation e, and the vertical axis represents the variation amount 6 of the deviation. Here, in the equation of state 5=Ce+e, S=O is the switching line 6, and so that the switching line 6 is included,
Consider an area So sandwiched between two straight lines passing through the origin: C1e+6=O (5) C1e+a=OI e ·(6) (CI-CI is a constant). The switching means 4 is e,
When the state of 6 is outside So, the output is switched to saturation, and when it is within S, the output is switched to sliding mode control output. For example, when in state a, the switching means 4 is switched to the saturated output side, so the input to the process 2 is in a saturated state, that is, the process operates when the deviation is assumed to be infinite. Approach the target value in the shortest possible time (.

When the state reaches a point where the state intersects the straight line (5) and enters the region S0, the switching means 4 switches to the sliding mode control output side. From b to point C, where it intersects with the switching line 6, it travels on a preset control system trajectory, and when it crosses C, it is pushed back by the trajectory of another control system and repeats small vibrations on the switching line 6. While doing so, it advances to the origin d and reaches equilibrium.

FIG. 3 shows another example of setting the area S0 by sliding mode control, in which two straight lines parallel to the switching line 6, Ce+2=S1 a #-('y)Ce+6=
This is a case where a region surrounded by S t (8) (C, Sl, and S are constants) is considered. This embodiment works to enter sliding mode control relatively quickly when the deviation is small. Further, the region S only needs to include the switching line 6, and is not limited to being divided by a straight line.

The flowchart in FIG. 4 shows the calculation process when the controller according to the present invention is constructed using a digital computer.

In block 61, the current deviation e is sampled at a certain sampling time. In block 62, the previous deviation stored in memory is subtracted from this deviation and divided by the sampling time to obtain the difference. If the amount is observable with a sensor or the like, sampling may be used instead as in block 61. In block 63, the state quantity S of the system is calculated based on aSe obtained in block 61.62.
Find the value of. In block 64, it is determined from the value of S just found whether the state exists in So.

If YES, the process goes to block 65 and outputs parameters for sliding mode control, and if NO, parameters for saturation are output. In the next block 67, e, 5 at the time of sampling this time is shifted and stored, and is used as the next calculation data.

Although the above flowchart is an example for a first-order differential equation, the same procedure can be used for an n-th order differential equation (3 equations).

FIG. 5 is a diagram showing the drive characteristics of the valve by a step response when the controller of the present invention is used as a valve drive shaft. (a) shows the present invention, and (b) shows the conventional sliding mode control, where the horizontal axis shows time and the vertical axis shows valve position. Furthermore, the magnitude of each target value is divided into three levels, and differences in response to the magnitude of deviation are compared.

In contrast to the conventional sliding mode control shown in (b), where differences occur in the rise depending on the size of the deviation,
In the control according to the present invention in (a), saturation input is applied to the valve actuator up to the vicinity of the target value, so the rise is constant and fast regardless of the magnitude of the deviation. When sliding mode control is entered near the target value, its robustness against external disturbances prevents deterioration of tracking performance due to Coulomb friction generated between the valve drive shaft and seal packing, and the target value is reached at high speed. .

[Effects] As described above, the controller according to the present invention can realize high-speed response by using the saturation output calculation means while taking advantage of the robustness against disturbances that sliding mode control has. Furthermore, this controller can be applied to all kinds of servo mechanisms, and its effects are particularly remarkable in control systems where fluctuations in deviation are large and high-speed response is required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention. FIG. 2 is a diagram showing an embodiment of the present invention. Figure 3(a)
, (b) are phase plane trajectory diagrams for explaining the control state of the present invention. FIG. 4 is a flowchart when the present invention is implemented using a digital computer. FIG. 5(a) is a diagram showing the step response of a valve when the present invention is applied to a valve positioner, and FIG. 5(b) is a diagram plotting the step response in the case of conventional sliding mode control. be. FIG. 6 is a diagram showing the configuration of a control system using a conventional SS controller. FIG. 7 is a phase plane trajectory diagram for explaining SS control. 1...■SS controller, 2...process, 3.
...Saturated output calculation means, 4. Switching means, 5. Switching law calculation means, 6. Switching line. Figure 1 10 B 16 12 Figure 4 Figure 5 (b) Figure 6 Figure 7

Claims (1)

[Claims] In a controller that controls a process based on sliding mode control, a saturated output calculation means for giving a saturated output to the process, a switching means for switching between the saturated output and the sliding mode control output according to a state quantity,
switching law calculating means for determining the state of the switching means, and the switching law calculating means controls the output to the saturation output side outside a preset area near the switching line, and to the sliding mode control output side within the area. A controller using sliding mode control characterized by switching output.