JPH0713607A - Controller - Google Patents

Abstract

PURPOSE:To execute a stable control by PID constants for making the most of merits of both of disturbance suppression and target value follow-up. CONSTITUTION:Based on a deviation E of a measured value PV from a control object 1 and a set value SV, a PID control means 2 outputs a manipulated variable MV. A PID selecting means 3 selects a target value follow-up type PID constants, when a target value (set value) is changed and when the deviation E is large, and selects a disturbance suppression type PID constants by a prescribed relation as the measured value approaches the target value, and sets it as PID parameters of the PID control means 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling a process amount such as a temperature of an electric furnace or other controlled object.

[0002]

2. Description of the Related Art P used in a PID control system
There are two types of ID parameters: target value tracking type and disturbance suppression type.
There are types. In so-called two-degree-of-freedom PID control, a target value filter is used to automatically change the control constant in response to a change in the target value, so that both types are compatible.

[0003]

However, when a considerably large disturbance is input, the recovery is fast, but overshoot and undershoot occur, and hunting tends to occur, which is not always sufficient.

In view of the above points, an object of the present invention is a control that enables stable control with a PID constant that takes advantage of both disturbance suppression and target value tracking from the relationship between the target value and the control amount. It is to provide a device.

[0005]

According to the present invention, a target value following type PID constant is used when the target value is changed or the deviation is large, and as the measured value approaches the target value, it is a disturbance suppressing type PID constant in a predetermined relationship. The control device is provided with PID selecting means and PID selecting means for performing a PID calculation on the deviation signal using the PID constant of the PID selecting means and outputting the manipulated variable to the controlled object.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural explanatory view showing an embodiment of the present invention. In the figure, 1 is an electric furnace or other controlled object, and its measured value (control amount) PV is a set value (target value) S
V and the deviation E (= SV-PV) are taken, PID control calculation is performed by the PID control means 2, and the manipulated variable MV is output to the controlled object 1 and controlled. Also, the measured value PV, the set value SV,
From the deviation E, the time constant T of the controlled object 1, the dead time L, etc., the PID constant is obtained by the PID selection (tuning) means,
Output to the PID control means 2. The above-mentioned control devices except the controlled object 1 are configured by a microcomputer or the like.

Next, the operation will be described with reference to FIG. Usually, there are a target value following type and a disturbance suppressing type as PID parameter constants, which are Kpo, Tio, Tdo, and Kpl, Ti1, Td1, respectively, and have the following values, for example.

Kpo = 0.6T / KL (K is a constant) (1) Tio = T (2) Tdo = 0.5L (3) Kpl = 1.2T / KL (4) Ti1 = 2L (5) Td1 = 0.42L (6) That is, as shown in FIG. 2, the proportional gain Kpn, the integration time Tin, and the differentiation time Tdn are determined by the coefficient, α, β, γ, (0 to 1) among the above two sets of parameters. , And takes an intermediate value as a control parameter. The selection of α, β, and γ is performed by the PID selecting means 3 when the target value is changed or when the deviation E is large, the target value following type PID constant Kpo,
Tio and Tdo. And the measured value PV is the target value SV
The PID constants Kpl, Ti1, and Tdo of the disturbance suppression type are changed in accordance with a predetermined relationship such as a first-order or an arbitrary function type as the value approaches. So that α, β,
If the coefficient of γ is determined from the deviation or the like, the optimum control is performed as shown in FIG.

Further, for example, as shown in FIG. 4, the PID selecting means 3 sets the coefficient of α, β, γ to 0 when the deviation E is sufficiently large, and sets it as a target value following type PID constant.
When is sufficiently small, the disturbance suppression type PID constant is set to 1 and
In between, an appropriate value may be set.

As described above, when the target value is changed, the target value following type parameter is used, and as the measured value PV approaches the target value SV, the target value following type is shifted to the disturbance suppressing type based on a predetermined relationship. . Then, at the time of stable control, it is completely switched to the disturbance suppression type. If a large disturbance is input and the deviation becomes large, the target value following type is restored, and the disturbance suppressing type is gradually switched again to perform high-speed and stable control.

Next, an example using fuzzy inference as the PID selecting means 3 will be described with reference to FIG.

Now, as an example of the fuzzy rule, the following 2
Consider one rule.

(1) If the deviation E is positive and large, the deviation change rate ΔE is negative, and the target value change C is small, the proportional band weighting coefficient α is small, the integration time weighting coefficient β is small, and the differential time is The weighting factor γ is small.

(2) If the deviation E is zero, the deviation change rate ΔE is zero, and the target value change C is small, the coefficients α, β,
γ is large.

Then, for example, the measured value PV and the set value SV
And the deviation E is +5, the deviation change rate ΔE = + 1, and the target value change is small. As shown in FIG. 5, in fuzzy operation,
The degree of each membership function is obtained, the degree of the small matched portion is obtained, and the degree of the coefficient of the contribution section is obtained from the results of these antecedent sections. The degrees of consequent conclusions for each rule are combined to obtain the center of gravity, which is used as the values of the coefficients α, β, and γ.

First, in rule (1), since the deviation E is 5 from each membership function, the degree W is 1 and the deviation change rate Δ
Since E is 1, the degree W is 0, and the target value change C is small, so the degree W is 1 and the minimum degree W of these is 0, so the coefficient α,
The degree W of β and γ is also 0 (see FIG. 5A).

Next, in rule (2), from each membership function, the deviation W is 0 because the deviation E is 5, the deviation change rate ΔE is 1, so the degree W is 0.6, and the target value change C is small, so the degree is W is 1, and the degree W of the coefficients α, β, and γ is 0.6 when these minimum degrees W = 0.6 (see FIG. 5B).

Since the degree W of these coefficients α, β and γ is 0.6, the center of gravity is lowered vertically toward the horizontal axis to obtain the coefficient 0.75.

Based on this coefficient α = β = γ = 0.75, P
Try to find the ID constant.

The example of the rule and the number of rules are not limited to the above, and the coefficients of α, β and γ may be optimal as long as they are the same.

[0021]

As described above, according to the present invention, the PID constant is determined by shifting from the target value following type PID constant to the disturbance suppression type PID constant.
The advantage of the constant is utilized, the response is quick, the overshoot and undershoot are small, and stable control to the target value becomes possible.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram showing an embodiment of the present invention.

FIG. 3 is an operation explanatory diagram showing an embodiment of the present invention.

FIG. 4 is an operation explanatory diagram showing an embodiment of the present invention.

FIG. 5 is an operation explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

 1 controlled object 2 PID control means 3 PID selection means

Claims (1)

[Claims] 1. A PID selecting means for setting a target value following type PID constant when the target value is changed or when the deviation is large, and a disturbance suppressing PID constant in a predetermined relationship as the measured value approaches the target value, and this PID selection. A PID control means for performing a PID calculation on the deviation signal using the PID constant of the means and outputting the manipulated variable to the controlled object.