JPS59153202A - Auto-tuning system of parameter of pid adjuster - Google Patents

Abstract

PURPOSE:To calculate the optimum parameter of a PID automatically on the basis of calculated characteristics by supposing that a controlled system is a system consisting of a secondary delay element and finding out the characteristics of the system by an original calculating means. CONSTITUTION:A PID adjuster 1 inputs the measured value PV(t) of a process variable of the controlled system, calculates the PID and applies the result to the controlled system as a manipulated variable MV3 to control the system. At that time, the PID adjuster 1 calculates the PID parameter and supposes that the controlled system is a system consisting of the secondary delay element and a signal generating circuit 8 outputs a step signal to the controlled system by a command from a command circuit 7. Consequently, a measured value PV(t) is obtained. A gain calculating circuit 17 calculates gain K, a multiplier 10 and integration circuits 11, 14 calculate integration values Z1, Z2 on the basis of a weight function from a function generating circuit 9 and a calculating circuit 15 finds out a natural period T and an attenuation factor tau. A PID parameter calculating circuit 16 calculates the optimum value of the PID parameters on the basis of said calculated results and then outputs the optimum value to a PID operation part 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a PID controller in filled pack control.More specifically, the present invention relates to a PID controller for filled pack control. I) Auto-tuning of PID controller parameters that allows the optimal differential time (D) for the controlled system to be automatically calculated and set within the controller without operator intervention. It is related to the method.

[Prior art and its problems]

Traditionally, tuning of controllers has been done by operators (on-site operators) through trial and error. In other words, the parameters of the controller are changed to "II" by the controller.
The method used was to roughly set the parameters in advance in a safe direction for the operation of the target (plant), and then the operator determined the optimal parameter values by trial and error while checking the adjustment results. This required a lot of manual labor and time. On the other hand, from the perspective of control theory, many methods have been proposed to calculate the optimal parameters for the controlled object.
In order to put it into practical use, there are many technical limitations such as complicated calculation formulas, a huge amount of calculation, and narrow application conditions. It had the disadvantage that it was not economical to apply it to the United States.

[Purpose of the invention]

The present invention has been conceived in view of the above-mentioned conventional technical circumstances, and therefore, an object of the present invention is to provide a system that does not require the operator's intervention and can be applied generally. It is an object of the present invention to provide an economically competitive auto-tuning method for parameters of a P'ID controller.

[Key points of the invention]

Now, the P, I, and D parameters of a controller are generally within a relatively wide range around a value that is considered to be the optimum value for the controlled object. It is known that if it is present, it will exhibit the same level of adjustment performance4. On the other hand, even if the characteristics of the controlled object in PID control are not obtained in an exact form, even if the characteristics of the controlled object are approximated by a simple approximation, for example, a transfer function using a second-order lag element, Generally, errors caused by approximation do not have a large effect on tuning (determination of optimal parameters). For these reasons, in this invention, the controlled object is assumed to be a system consisting of (second-order lag elements), its characteristics are determined by a unique calculation means, and based on the obtained characteristics, P, 1. The optimal parameters for D are automatically calculated.

[Example of invention]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing how devices are connected when implementing the present invention. This is exactly the same connection mode as when performing normal automatic control. In normal automatic control, the PID controller 1 takes in 4, which is the measured value pv(t) of the process variable in the controlled object 2, performs PID calculation on it, and uses the operation result as the manipulated variable MY. 3, in addition to the controlled object 2, a process variable is controlled, and the result appears as a measured value p v (t).

When performing auto-tuning according to the present invention,
The PID controller 1 outputs a predetermined signal as the manipulated variable 3, and as a result, the measured value pv(t) of the process variable obtained from the controlled object 2 is read into the controller 1, and the adjustment is performed. In total 1, the characteristics of the controlled object are determined by calculating the signals of both parties using a predetermined method, and the P, I,
Calculate the parameters of D. These arithmetic operations can be performed automatically by giving instructions to the microprocessor.

FIG. 2 is a block diagram showing one embodiment of the present invention (ie, the internal configuration of the PID controller 1). In the same figure, 5
8 is a step signal generation circuit, 9 is a Vi weight function W1(t) generation circuit, is a 1° multiplication circuit, 14 is an integration circuit, and 17 is a gain calculation circuit. circuit, 15 is a natural period, an attenuation coefficient calculation circuit, a 161 dPID parameter calculation circuit,
It is.

FIG. 3 is a waveform diagram showing signal waveforms of important parts in the circuit of FIG. 2 (or FIG. 4).

Next, the operation will be explained with reference to FIGS. 2 and 3.

In FIG. 2, when the switch 6 is switched to the terminal cl side, the controller IVi and the process variable measured value p
v(t) is input, and the calculation unit 5 calculates P
Since it performs ID calculation and outputs the calculation result as the manipulated variable MV, its operation mode is in the adjustment mode. On the other hand, when the switch 6 is switched to the terminal C2 side, the operating mode is auto-tuning.
in mode.

The operation of the autotuning mode will be explained below.

Now, when a tuning start command is issued from the command circuit 7, the signal generation circuit 8 outputs the manipulated variable M as shown in FIG.
A step signal of height l, such as n, denoted as V, is applied to terminal 0.
It is input to the controlled object via the 2% switch 6.

It is assumed here that the controlled object is a system consisting of second-order delay elements. Generally, the transfer function G (s) of a secondary delay element (also referred to as a secondary imaging element) is expressed by the following equation (1).

Here, K is the gain, T is the natural period, S is the Laplace operator, and ζ is the damping coefficient.

The gain is k when the supporting step signal is applied to the controlled object,
If the steady-state value K of the measured value pv(1) of the process variable to be controlled is determined, this is the gain. The gain calculation circuit 17 in FIG. 2 calculates the gain of the controlled object in this way.

Once the gain K is found, in order to know the characteristics of the controlled object,
It is clear from Equation 11 above that it is only necessary to find the natural period T and the damping coefficient ζ.How to find these will be explained below.

Now, at the same time that the step signal generation circuit 8 outputs the step signal as the manipulated variable 3, the function generation circuit 9 generates a weighting function W4(t) (this is referred to as a first weighting function). The difference between the measured value pv(t) fed back from the controlled object and the previously determined gain (K - PV
(t) ), and add to it the first weighting function w1 (t) output from the weighting function w1 (t) generation circuit 9.
is multiplied by the multiplication circuit 10, and the multiplication result is further integrated by the integration circuit 11 to obtain the value z1.

Here, the first weighting function W1(t) and the value z1 are respectively expressed by the following equations.

−1 Wl (t) = e Tl ・・・・・・・
・・・・・・・・・・・・・・・・・・・・・(2) However,
T1 is a time constant, which is a parameter that determines the waveform of the weighting function Wl(t), i; b, h, weighting function W1
The waveform of (t) is shown in FIG.

zl-4″'w1(t) −(K=PV(month d t-
...(3) Also, the value z2, which is obtained by integrating the difference between the measured value pv(t) and the gain (K-PV(t)) by the integrating circuit 4, can be expressed by the following formula: 022=fo''' (K-PV(t))dt ---
・・・・・・・・・・・・・・・(4) At this time, the above (2)
) to (4), time constant T1 and Zl r 22
The formula for determining the natural period T and damping coefficient ζ of the controlled object is expressed as follows.

The characteristics of the process of a system consisting of second-order delay elements are uniquely determined by T, and the gain, so as described above, T
, ζ, K, and assuming that the process is a system consisting of second-order lag elements, the characteristics of the process are known, and from then on, P, I can be determined using known methods.
, D can be calculated.

Next, we will describe the known quantity Zl = 22, Tl and the unknown quantity T, and the process by which this relationship is derived as shown in equations (51 and (67) above.

Letting o be the time t at the start of tuning, the measured value pv(t) of the process is as follows. The formula for the integral value Z1 (formula (3) above) zl = ,4;'' (K-PV(t
)) When the above equations (2) and (7) are substituted into -Wl(t)dt and calculated, the following is obtained. Similarly, from equation (7) above, 2
2 is z2=4''(K-PV(t)) -dt=2K
Tζ ・・・・・・・・・・・・・・・
...(9). f8) above, formula (9) is T,
When this equation is solved, the above (51, ”(6)t) is obtained.

FIG. 4 is a block diagram showing another embodiment of the present invention.

The embodiment shown in the figure uses a second weighting function W2(i) generating circuit 12 in addition to the first weighting function W1(1) generating circuit 9, and these are connected as shown in the figure. This is an example.

In the same way as in the previous case, the equations for calculating the natural period T and the damping coefficient ζ from the integral results Zl and Z2 are written. Decide the weighting function using the same method as before.

−± Wl(t)−eTl ・・・・・・・・・・・・
・・・・・・・・・・・・(101h W2(t)=e 'r1 ・・・・・・・・・
・・・・・・・・・・・・・・・(Lll At this time,
The formula for determining T Tζ from zl, z2 and the time constant T1 in the above formula is as follows. Note that the weighting function W2 (
t) waveform is shown in FIG.

・・・・・・・・・・・・(13 The characteristics of the process of the system consisting of second-order lag elements are uniquely determined by T, and the gain, so after Tjζ and K are determined, Under the condition that the process is assumed to be a system consisting of second-order lag elements, the process characteristics are known, and from now on, P, I,
The parameters of D can be calculated.

Next, a process will be described in which the relationship between the known quantity Z1 e z2 , 'rl and the unknown quantity T becomes as shown in the above equation 1121 (13).

When time t at the time of tuning start is set to 0, the measured value pv(t) of the process is as follows. By substituting the above αω and 04 formula into the integral value 2.0 formula % formula % ( , and calculating zl, we get
= fOa:'(K-pv( becomes month-w2(t)at. When formula (161, +t7) is solved as T, this equation, the above Q2, (Formula 13 is obtained.

〔Effect of the invention〕

According to this invention, the following effects can be expected.

■ The object to be controlled is expressed concisely, so the calculations can be performed with the capabilities of a microprocessor and are inexpensive.

■ Since the integral form of the measured value is used, even if the signal changes momentarily due to noise, etc., the integral value will not be greatly affected and the error will be small.

■ Since the step response is used only once, the time required to obtain the results is short b This invention can be applied to the following applications.

(2) By determining the characteristics of the controlled object once, storing it, and later determining the characteristics again and examining the differences, it can be used to diagnose abnormalities in the controlled object.

(2) Even when the parameters determined by the present invention are further finely adjusted by the operator's judgment, it is less troublesome than trial and error from the beginning.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the connection mode of the device when implementing the present invention, Fig. 2 is a block diagram showing an embodiment of the invention, and Fig. 3 is a block diagram showing the connection mode of the device when implementing the present invention. FIG. 4 is a waveform diagram showing signal waveforms of important parts. FIG. 4 is a block diagram of another embodiment of the present invention. Description of symbols 1... PID controller, 2... Controlled object, 3... Manipulated amount Wξ4... Measured value pv(t), 5... PID calculation unit, 6... Switch, 7... ...Tuning start command circuit, -8...Step signal generation circuit, 9...
・Weighting function Wl(t) generation circuit, 10.13... Multiplication circuit, 11.14... Integration circuit, 12... Weighting function W4(t) generation circuit, 15... Natural period, damping coefficient Calculation circuit, 16... PID parameter calculation circuit Agent Patent attorney Akio Namiki Patent attorney Kiyoshi Matsuzaki 11

Claims (1)

[Scope of Claims] 1) The control target of the PID controller is regarded as a controlled system consisting of second-order lag elements, and the natural period T and damping coefficient ζ of the second-order lag elements are determined by calculation from the step response. From T and ζ, the proportional band (P) is a parameter of the controller.
, an auto-tuning method for PID controller parameters that determines the optimum values of an integral time (I) and a differential time (D), which comprises step signal generation means, and when the step signal is applied to the controlled object. Step 6: Calculating the gain K from the measured value pv(t), and generating means for generating a first weighting function w1(t), which is an exponential function having a first time constant. and the measured value p from the gain K
v (value minus ri (K - pv(t) ) Kth
(D weighting function Wl(t) and integrating the multiplication result to obtain the first value Zl;
t))) to obtain a second value z2, and calculation means for calculating the natural period T and damping coefficient ζ of the controlled object from the first value z1 and the second value z2. And so,
The controller parameter (P
,I. D) is an auto-tuning method for PID controller parameters. 2) Regarding the controlled object of the PID controller as a controlled system consisting of second-order lag elements, calculate the second-order lag element G natural period T and damping coefficient ζ from the step response, and calculate the adjustment from T and ζ. Proportional band (P) which is a parameter of the meter
, an auto-tuning method for PID controller parameters that determines the optimum values of integral time (I) and differential time (D), which comprises a step signal generating means, and when the step signal is applied to the controlled object, the controlled object is means for calculating the gain K from the measured value pv(t) as a step response obtained from the step response, and means for generating a first weighting function Wl (t) consisting of an exponential function having a first time constant; means for generating a 29th weighting function W2(t) consisting of an exponential function having a 20th time constant having a specific relationship with the first time constant, and a measurement value pv(1) subtracted from the gain K; value (K-PV
(t)) by a weight function W1(t) and integrating the multiplication result to obtain a first value z1; Function *2 (
t ) and integrating the multiplication result to obtain a second value z2; and an operation for calculating the natural period T and damping coefficient ζ of the controlled object from the first value z1 and the second value z2. An auto-tuning system for PID controller parameters, characterized in that the controller parameters (P, , I, D) are determined from the natural period T and the damping coefficient ζ.