JPS59160205A - Sample value pid control device - Google Patents

Abstract

PURPOSE:To raise responsiveness and a suppressing property against a disturbance by injecting an identifying signal to a control system in the course of controlling a closed loop, identifying a dynamic characteristic of a process, and executing an auto-tuning to the control system having a response shape conforming to specifications. CONSTITUTION:In a process 1 in which a temperature, etc. of a chemical plant are controlled, a deviation between a sampled output y(t) and an output h(k) of a target value filter 4 is calculated by an operational amplifier 6, and this deviation e(k) executes a control through a deviation filter 7 and a PID operating part 8 so that the output signal y(t) of the process is made to coincide with a target value signal r(k) through a sample holding part 2. A pulse transfer function is identified by inputting an output u(k) of an adding part 10 and a sampled output y(k) to a pulse transfer function identifying part 11, and a control constant is obtained through an S transfer function operating part 12 and a control constant operating part 13 by its coefficient, a sample period tau, a response shape coefficient alpha of a control system, etc. In this regard, they are controlled by a deciding part 14 for ending of identification.

Description

[Detailed Description of the Invention] [Field to which the invention pertains] The present invention identifies dynamic characteristics of a process, and uses the identification results to automatically adjust control constants (auto-tuning) so as to satisfy specifications imposed on a control system. ) have the same function, 4
This invention relates to a PID control device.

Prior art and its problems] ゛ To realize the auto-tuning function, it is necessary to have a function to identify the dynamic characteristics of the controlled process by some method and a function to design the control system to satisfy the control specifications. . As for the identification method, there is a method in which the control device and the process to be controlled are separated and the process is performed under open-loop operation;
There is a method in which the control target process is controlled, that is, under closed-loop operation. Like petrochemical plants, numbers! In a complex process consisting of OO loops,
Keeping one control loop open for long periods of time to identify process dynamics is not only difficult because it upsets the balance of the entire plant, but also leads to a large number of defective products. This causes a large amount of energy loss. Therefore, it is desirable that the identification method be performed under closed loop operation from the viewpoint of economy, quality control, or safety.

As a sample value PID control device capable of performing auto-tuning of a control system during closed-loop control, a technique described in Japanese Patent Application Laid-Open No. 57-90704 is known. With this control device, even when the transfer function of the controlled object includes a zero point (which is the root of the numerator polynomial 20 of the transfer function) on the left half of the 8 regions, as is often seen in fluid transport processes, It was necessary to satisfy control specifications. Since the PID control unit itself uses series compensation, the control system after tuning has good responsiveness to changes in the target value, but it was also necessary to improve the ability to suppress disturbances. In other words, it is desirable for a process controller to have both good coordination and suppression properties.

[Purpose of the invention]

This invention identifies the dynamic characteristics of a controlled process whose transfer function has a zero point on the left half of the eight regions, and creates a control system that is highly responsive to changes in target values and excellent in suppressing disturbances. An object of the present invention is to provide a PID control device having a function of automatically adjusting constants (auto-tuning).

[Summary of the invention]

This invention calculates the deviation between a signal obtained by calculating a target value signal sampled in each sample control period using a target value filter and an output signal of a process sampled in each sample control period, and processes the deviation signal. filter and
A PID calculation unit that performs a PID calculation on the output signal of the deviation filter, an identification signal generation unit that generates an identification signal that is persistently exciting, and an addition unit that adds this identification signal and the output of the rabbit PID calculation unit. , the control target process is driven by the sample hold unit that holds the added signal and the output signal of the sample hold unit, that is, the operation signal of the control target process, and a control loop is constituted by the loop that becomes the output signal of the process, and further,
a pulse transfer function identification unit that identifies parameters of the pulse transfer function of the controlled process from the previously added signal, that is, the operation signal applied to the controlled process in each sample control period and the output signal of the process in each sample control period; Using the identified parameters of the pulse transfer function identification unit, calculate the poles and zero points of the 8 regions of the controlled object.
The PID of the PID calculation unit that governs the characteristics of the control system is determined from the transfer function calculation unit, the 8 transfer function parameters of the controlled object that are output from the 8 transfer function calculation units, the coefficients that specify the response shape of the control system, and the sample control period. Constant and Deviation Calculation Equipped with a control constant calculation unit that calculates constants of a deviation filter and a constant of a target value filter, and an identification completion determination unit that determines whether identification of a controlled process has been completed, closed-loop control is performed. While injecting an identification signal into the control system at every sample control period, the pulse transfer function of the controlled process is identified, and when the identification completion judgment section judges that the identification has been completed, the identification signal generation section starts generating the identification signal. This is a sample value PID control device that can tune the target value filter, deviation filter, and PID calculation unit to perform calculations using the constants calculated by the control constant calculation unit.

〔Effect of the invention〕

With the apparatus according to the present invention, the dynamic characteristics of the process can be identified during closed loop control, which is advantageous from an economical, quality control, and safety standpoint.

During identification, an identification signal is used, but the injection of the identification signal is automatically stopped when it is determined that the coefficients have converged, so disturbances in the process are kept to the minimum necessary.

In addition, it has tremendous benefits, such as being able to tune the control system to be stable even for processes that have a zero point, which was difficult to do in the past.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a PID control device according to the present invention.

The controlled object is a process (1) configured to control the temperature, flow rate, pressure, etc. of a chemical plant, and a sample hold section (2), a first sample holding section (2), which samples the target value r (t) at every sample control period τ. sampler, the target value signal r sampled by %VX or qt by the first sampler (3)
(k) (The following indicates discrete time, that is, 1 = 1 < τ.) A target value filter (4) that processes the process output y (1) with a sampling period τ A second sampler (5) samples each time, and a deviation calculator (6) calculates the difference between the sampled output y (k) and the output hr (k) of the target value filter (4). The output signal e of the deviation filter (7) and the difference filter (7) that calculate the deviation e (k) which is the output of the device (6)
.

(k) and the output U of the PID calculation unit (8). (k) and the identification signal v (k) which is the output signal of the identification signal generation section (9).
01 and the output U of the adder Q [present]) to the sample and hold unit (2), the target value signal r (t
A basic PID controller is constructed to match the output signal y (t) of the process to ). Furthermore, %LI(k
) and y [exist]) to identify the pulse transfer function of process (1). From τ, calculate the coefficients of the denominator polynomial and numerator polynomial of the transfer function of the 8 regions in process (1).
The transfer function calculation unit az and the coefficients of the numerator polynomial and denominator polynomial of the S transfer function which are the outputs of the S transfer function calculation unit (121), the response shape coefficient α of the control system, and the sample control period τ′ for actually performing the control operation are Input Pl, D calculation section (8), difference filter (control constant calculation section a3 that calculates control constants used in force and target value filter (4) and tuning start signal 8πk), and 8 transfer function calculation section (121 The tuning operation, that is, the operation of the identification signal generation section (9), the pulse transfer function identification section αυ, and the control constant calculation section 03).Next, each component of the apparatus of the present invention will be explained in more detail. First, for process (1) that has a stable zero point, the coefficients used in each calculation section of target value filter (4), deviation filter (7), and PID calculation section (8) are such that the control loop is stable. Closed-loop control is performed every sample control period τ with values set such that τ.

In response to the tuning start signal 8T(k), the identification signal completion determination section (14) outputs an identification start signal l8(k) to each calculation block. In response to this, the identification signal generator (9) generates a purging exciting [Per
siatently Exciting (P, B, ))
An M-sequence signal V (k), which is a typical signal, is generated every sample control period τ. Since v (k) is P, E, the signal u (k) added to the output uoOct of the PID calculation unit (8) by the addition unit Moe also becomes PJ. u (k) is P,
i! , so IEEF! Trans, on A
automatic Control, 1976+1
February.

Identity Condition
l'or Linear Multi-yarria
ble System Operating unde
r Feedback.

(837-840), by the theorem described in T, 86derstr5m et al., process (1) during closed-loop control.
The pulse transfer function of process (1) can be identified from the operation signal U(k) to and the output y(k) of the process.

Therefore, the pulse transfer function identification unit aυ starts identifying the coefficients of the pulse transfer function in process 11) using the identification start signal I8(k). The model of process (1) is given as the first equation.

ylk)t X'js y(k-i)= cod+u(
k-i) +, g(k+ + %θlε(k-i)+2
1.11. t l+-1・
...Equation 1: Expressing the vector θ consisting of the coefficients to be identified using the following equation, Contains! -(9,, nel ”, ”' l ’:; m 1 to I
``”” j ne, he,,,,,,,,8.,a)...
The identification method according to the second equation (here, T is transposed) and the extended least squares method calculated by the pulse transfer function identification unit αυ can be expressed by the following equations 3 to 5.

ε■=yfkl-9)klTθ(k-1)
...Deflection 4 formula% formula% χ(k)=β, (0,9<β<1)
...It is used by setting it to about 6 types for music. Also, ψ(k)
The vector is expressed as cp(kU”= (-y(k-+), =-,-y
(k−m) , u (k−1) , −・, u(k−
n).

ε(k-t),..., ε(k-m), t]
・Use the song ・Equation 7. The initial values of payout and P(6) are started using the following values.

Here, δ is a positive number of about 10" to 10', and ■ is a unit matrix. By executing a series of calculations from equations 3 to 5 every sample control period, the parameter θ to be identified is
is identified by the pulse transfer function identification unit aυ. Pulse transfer function Gp of process +1) using identified parameters
fzl is as shown in the following equation.

The S transfer function calculation section a is the identification coefficient al(1-1+2+...+rn)+I)l of the pulse transfer function identification section 0D.
(1-L2+...+n) is converted into a transfer function GpfS) format expressed by the following equation.

In addition, in this 8-transfer function calculation unit a2, the eigenvalue of the first O equation with a denominator=0 is the same as the eigenvalue of the ninth equation with a denominator=0 of z=
Further, through e, corresponding to 1 to l, the ninth
The zero point of Equation 10 is calculated so that the low frequency characteristics of the transfer functions converted into eight regions match each other according to Equation 10. Through these, the 8 low-frequency transfer functions Gp (sl) of process (1) are identified as shown in equation 10.
4) is the convergence of the coefficient correction error (+-1+2+-・+m)+(JmO,・-,m
t) ・+Determine from Equation 11.

The control constant calculation unit (13) calculates the PID calculation unit (
8), the coefficients of the deviation filter (7) and the target value filter (4) are identified by the fixed completion signal 5p(h) of the completion determination unit (I4).
Calculate by Note that upon completion of the identification, the generation of the identification signal in the identification signal generation section (9) and the calculation of the pulse transfer function identification section aυ are stopped.

Next, a reference model Gm (α, σ, s) that specifies the response specifications of the control system is determined based on the response shape coefficient α.

Here, σ is the time coefficient of the start-up of the control system, which is equal to -time measurement.

First, when △ is 12th modified using Z (time transition operator), the PID calculation unit (8) generates the following.

In addition, the transfer function of the deviation filter (7) is expressed by the following equation.Furthermore, the transfer function of the target value filter (4) is expressed as 4! When f is the sample system and the period τ is small, the transfer function from the target value r (t) to the process output y(t)J can be approximated as follows.

Here, the deviation filter coefficient Et(t-0+1+...
), the 16th equation becomes the 18th equation.

C0, C, so that the right side of this 18th equation matches the low frequency characteristics 1: of the reference model Gm (α, σ, S).

Calculate C2. With these, the nose part (8)
, the coefficients of the deviation filter (force) and the target value filter (4) are determined, and the control constant calculation unit 0 performs a series of calculations. Using the calculated coefficients, the target value filter (4) is calculated for each sample control period. 4) calculates the 15th formula, the deviation filter (7) calculates the 14th formula, and the PID calculation unit (8)
calculates Equation 13.

As described above, in detail 1-1, an identification signal is injected into the control system during closed-loop control, and the operation signal U(g)) and process output y are
The dynamic characteristics of the process are identified from (k), and based on the identification results, the control system is auto-tuned to have a response shape that meets the specifications. At this time, the zero point of the identified process is not forced into the denominator form, but is compensated by a deviation filter, and the transfer characteristic after compensation is matched to the reference model, so the zero point is Process 1: Stable control can be achieved even for processes that could not be designed due to

Next, FIG. 2 shows the results of applying the apparatus of the present invention to a process having a certain zero point. FIG. 2(a) shows the step response of the process output, and the identification result showed a large overshoot corresponding to the zero point. If we change it to the denominator form, we could not design it because there is a negative coefficient, but with this device, co""0.0737 + C+=4.40, C@"
"l 8.2, E6"' l + El = 50. In Figure 2, (b>) is the response of the process output y (t) when the target value is changed from O to l at time O.Even though the process has overshoot, it is effective control with damping. It can be seen that the system is connected to the system.

[Other embodiments of the invention]

In addition to this embodiment, the PID calculation unit (8) is operated next to the deviation calculation unit (6), and then the deviation filter (force function) is executed. (7
) The effect is the same even if the calculation includes the function.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a curve diagram showing the response as a result of tuning using the embodiment of the present invention. (1)...Process (2)...Sample hold 13), 15)...Sampler (4)...Target value filter (6)...Difference calculator (power...Difference filter (8)...PID calculation unit (9)...Identification signal generation unit On...Adder 0υ...Pulse transfer function identifier (L)...S transfer function calculation unit (13)...・Control constant calculation section αXu... Identification completion judgment section

Claims (1)

[Claims] An identification signal generation section that applies an identification signal that is a persistent exciting signal into a control loop controlled by the PID control calculation section in a device that includes a PID calculation section that controls a process to be controlled by sample values; , a deviation filter that calculates an operator on the target value signal, and a signal calculated by the deviation filter is introduced into a PID calculation section, and the identification signal generated by the identification signal generation section is outputted from the sample value PID control calculation section. a pulse that inputs an operation signal obtained by the addition and a process signal obtained by sampling the control amount of the process and identifies parameters of the process from these operation signals and the process signal; 8(
an S transfer function calculation section that calculates the coefficients of the transfer function in the region (Laplace operator); a control constant calculation section that calculates the coefficients calculated by the S transfer function calculation section; and a tuning start signal and outputs of the eight transfer functions. The sample value is characterized in that the sample value is configured such that the identification signal generation section and the definition completion determination section control the calculation operations of the pulse transfer function identification section and the control constant calculation section. P
ID control device.