JPH07334204A - Digital pid controller - Google Patents

Abstract

PURPOSE:To operate a plant in a stable direction at all times. CONSTITUTION:Concerning the digital PID controller for executing digital PI control arithmetic operation corresponding to a controlled variable from a controlled system and the deviation of the controlled variable from a target value, executing digital D control arithmetic operation while using a control arithmetic cycle and differentiation time corresponding to the deviation or the controlled variable, synthesizing these operation metic outputs and impressing the result to the controlled system 8 as an operating signal, this device is provided with an instable area deciding means 12 for preventing the differentiation time from being updated when the differentiation time of an area to make control instable is set corresponding to the mutual relation of the control arithmetic cycle and the differentiation time and an alarming means 14 for outputting an alarm or a message not to update the differentiation time when this instable area deciding means 12 decides the differentiation time to be the instable area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital PID (P: proportional, I: integral, D: derivative) controller used in various process instrumentation control systems and the like, and more particularly to a function of setting a derivative time. The present invention relates to an improved digital PID controller.

[0002]

2. Description of the Related Art A PID control device has been widely used in all industrial fields since the history of control, and it is no longer possible for a control device in each industrial field to have a PID control device.

Conventionally, various control methods have been proposed,
In addition, with the transition of the times, the control calculation is shifting from the analog calculation method to the digital calculation method, but the throne of the PID control device is unlikely to change in the future.

The basic equations of PID control include a proportional operation (P operation) for performing an operation proportional to the deviation, an integral operation (I operation) for performing an operation proportional to the integral of the deviation, and an operation proportional to the derivative of the deviation. It is expressed by the sum of the differential action (D action) to be performed, and is expressed by the equation (1) when expressed in the form of a transfer function.

C (s) = MV (s) / E (s) = K _P {1+ (1 / T _I · s) + [(T _D · s) / (1 + η · T _D · s)]} ... (1) where C (s): transfer function of PID, MV (s): manipulated variable,
E (s): deviation, K _P : proportional gain, T _I : integration time, T
_D : differential time, s: Laplace operator, 1 / η: differential gain.

When this equation (1) is expressed as a velocity type digital arithmetic equation using data for each control arithmetic cycle Δt,
It becomes like the formula or the formula (5). _{△ MV n = K P {(} e n -e n-1) + (△ t / T I) e n + △ d n ... (2) MV n = MV n-1 + △ MV n ...... (3) _{△ d n = {T D /} (△ t + η · T D)} (e n -e n-1) - {△ t / (△ t + η · T D)} d n-1 ...... (4) d n = d _n-1 −Δd _n (5) In the above equation, MV _{n is} the operation amount at the present time, MV _{n-1 is} the operation amount at the time of the previous control calculation cycle, ΔMV _{n is} the operation amount from the previous time to the present time. Change amount, e _n : magnitude of deviation at the present time, e _n-1 : magnitude of deviation at the previous control calculation cycle,
d _{n is} the differential operation output at the present time, d _n-1 is the change in the differential operation up to the time of the previous control calculation cycle, Δd _n is the change in the differential operation output from the previous time to the present time.

FIG. 4 is a diagram showing a configuration of a conventional digital PID control device using the equations (2) to (5).
The controller directs the target value SV _n and the control amount PV _n the deviation computing means 51, after a deviation e _n performed here made (SV _n -PV _n) operation, the speed the deviation e _n It is applied to the proportional control means 52, the speed integral control means 53 and the speed differential control means 54. In the velocity type proportional control unit _{52 △ P n = (e n} -e n-1) becomes the calculated execution, the velocity type integral control means _{53 △ I n = (△ t} / T
_I) Perform e _n becomes operational, also velocity type derivative control unit 5
In 4, the calculation of the equation (4) is executed to obtain Δd _n, and the calculation results are added and synthesized by the addition means 55 and led to the proportional gain means 56.

The proportional gain means 56 multiplies the additive combined output by the proportional gain K _P to obtain a velocity type ΔMV _n = K _P (ΔP _n + ΔI _n + Δd _n ) ... (6) The control signal is obtained and applied to the velocity-type / position-type signal converting means 57, where the equation (3) is calculated to convert into a position-type signal, and then applied to the controlled object 58. Then, the control amount PV _n of the controlled object 58 is detected by the control amount detecting means 59 and introduced into the deviation calculating means 51. Therefore, this control device controls so that the control amount PV _n detected by the control amount detecting means 59 becomes equal to the target value SV _n , that is, the deviation e _n = SV _n −PV _n becomes zero. .

Further, the differential time setting means for the speed-type differential control means 54 has a new differential time T set by the operator.
_The differential time setting means 60 for setting _D and the differential time T _D sent from the differential time setting means 60 are rewritten and updated, and the new differential time T _D ′ is supplied to the speed type differential control means 54.
And differential time memory means 61 for setting = T _D.

By the way, in the PID control calculation, the analog calculation is continuous, whereas in the digital calculation, discontinuous data is used to perform the PID calculation at regular time intervals. . As a result, PID
The control operation is easily affected by the discontinuous operation, but the most significant effect of the control operation is the differential control operation that handles a steep change.

Therefore, the differential control operation executes the operations of the expressions (4) and (5), and at this time, the differential operation output d _n is affected by the size of the control operation cycle Δt. This will be described with reference to FIG.

In FIG. 5, the differential time T _D = 2 sec, η =
0.1 a constant, is a diagram showing a differential operation output d _n when the control operation period △ t changed variously. The figure (a) shows the differential operation output d _n when the control calculation cycle is Δt = 0.01 sec, and the figure (b) shows the control calculation cycle Δt =
This is the differential operation output d _n when 0.05 sec, and the same figure (c) is the differential operation output d _n when the control calculation cycle is Δt = 0.1 sec. This is the differential operation output d _n when the calculation cycle is Δt = 0.2 sec. Further, FIG.
This is the differential operation output d _n when sec is set. 6 is shown in FIG.
It is the figure which piled up the operation output characteristic of (a), (b), (d), and (e).

Therefore, the following can be said from FIGS. 5 and 6. (B) The differential operation output is greatly affected by the size of the control calculation cycle Δt. (B) When the control calculation cycle Δt becomes large, the differential operation is influenced in a strong direction.

For example, in FIG. 5 (a), since the control operation cycle is very short, a differentiating operation output similar to the analog differentiating operation output is obtained, but as the control operation cycle increases, the differentiating operation output shows the original characteristic. , And the same figure (e)
When the control calculation period Δt becomes large as Δt = 0.5 sec, the differential operation output appears after 0.5 sec, and the original differential effect is obtained even though it should change continuously from 0 sec. Absent.

Further, in normal plant control,
It is often used in the range of differential time T _D = 0.5 to 10 sec, and in terms of capability, control calculation cycle Δt = 0.1 to 1 sec.
It can be said that it is mostly used between. The reason is that this type of plant instrumentation system is often a multi-loop having a large number of controllers, that is, digital PID control devices, and the control calculation cycle Δt cannot be reduced. As is clear from FIG. 5, this is unavoidable for use in the most susceptible area.

Therefore, FIG. 7 shows how the magnitude of the control calculation cycle Δt affects the controllability when a control loop is built using a digital PID controller.
Will be described with reference to. In FIG. 7, the transfer function of the controlled object 58 is G (s) = {1 / (1 + 5s)} e ^−2s , and
The optimum value of the PID parameter when Δt = 0.01 sec is K _P = 3.04, T _I = 3.24 sec, T _D = 0.8.
When 63sec and η = 0.1, Δt is 0.01sec
It shows the control response when changing from → 0.1sec → 0.4sec → 0.5sec → 1sec. △ t = 0.4sec
It is stable up to the vicinity, but becomes oscillating when Δt = 0.5 sec, and becomes completely divergent vibration when Δt = 1 sec, which is a dangerous state. That is, this case T _D / Δt
It can be seen that when = 0.863 sec /0.4 sec = greater than 2.16, it is stable, but when it is smaller than 2.13, it becomes oscillatory.

[0017]

Therefore, although there is no problem in the analog PID control device as described above, in the digital PID control device, the differential operation is greatly affected by the size of the control calculation cycle Δt. The control response is greatly different.

As a result, in the conventional digital PID controller, the control response becomes oscillatory or divergent vibration depending on the set value of the differential time T _D in the relationship between the control calculation period Δt and the differential time T _D. The plant equipment may be damaged, the product quality may be deteriorated, or the plant may be stopped, and in the worst case, the plant may be exploded. It is certain that PL (product liability) will be pursued violently in the future, and such a situation must be absolutely prevented.

The present invention has been made in view of the above circumstances, and provides a digital PID control device for reliably preventing the setting of the differential time in the region where the control becomes unstable in the relation between the control calculation cycle and the differential time. The purpose is to

Another object of the present invention is to provide a digital PID control device which positively shifts to a stable region when the differential time is a region where control becomes unstable in the relation between the control calculation cycle and the differential time. To do.

Still another object of the present invention is to provide a digital PID control device for promptly informing the operator of the fact that the set differential time is involved in an unstable region and ensuring the safety of the instrumentation system. To provide.

[0022]

In order to solve the above problems, the invention according to claim 1 provides a digital PI for the deviation between a controlled variable from a controlled object and a target value of the controlled variable.
The control calculation is executed, and the digital D is calculated by using the control calculation cycle and the differential time with respect to the deviation or the control amount.
In a digital PID control device that executes control calculation, synthesizes these calculation outputs, and applies them as operation signals to the control target, control becomes unstable due to the mutual relationship between the control calculation cycle and the differential time. It is a digital PID control device provided with an unstable region determination means for preventing the differential time from being updated when the differential time of the region is set.

Next, in the invention according to claim 2, a digital PI control calculation is executed for the deviation between the controlled variable from the controlled object and the target value of the controlled variable, and the deviation or the controlled variable is calculated. On the other hand, in the digital PID control device for executing the digital D control calculation using the control calculation cycle and the differential time, synthesizing these calculation outputs and applying it as the operation signal to the control target, when the control calculation cycle is Δt. , O <T _D <nΔt (where n is a coefficient, usually n = 1 to 4), when the differential time T _D is set, only the differential time or all PID parameters are set. Is a digital PID control device provided with an unstable region determining means for preventing the updating of the PID.

Further, in the invention according to claim 3, a digital PI control calculation is executed for a deviation between a controlled variable from a controlled object and a target value of the controlled variable, and for the deviation or the controlled variable. In the digital PID control device that executes the digital D control calculation using the control calculation cycle and the differential time, synthesizes these calculation outputs, and applies as the operation signal to the control target, when the control calculation cycle Δt is set, O <T _D <nΔt (where n is a coefficient, usually n = 1 to 4), when the differential time T _D is set, T is the most stable region stored in advance.
_This is a digital PID control device provided with means for forcibly using the differential time T _D ′ with _D ′ = 0 for the digital D control calculation.

Further, in the invention corresponding to claim 4, when the newly set differential time is determined to be the differential time of the unstable region, the determination signal thereof is newly added to the requirements described in claims 1 to 3. In response to this, the digital PID control device is provided with an informing means for outputting an alarm or a message that the differential time is not updated.

[0026]

Therefore, according to the invention corresponding to claim 1, by taking the above-mentioned means, the unstable region determining means checks the unstable region or the stable region for the set differential time, and the unstable region is determined. When it is determined that the differential operation is executed, the previous differential time is used as it is without updating the set differential time.

In the invention corresponding to claim 2, when the control calculation cycle is Δt, the range is O <T _D <nΔt (where n is a coefficient, and usually n = 1 to 4). Derivative time of T _D
In this case, the unstable region determination means prohibits updating only the differential time or all of the PID parameters, and uses the previous differential time or PID parameter to ensure stable operation of the process. is there.

Further, in the invention corresponding to claim 3, when the control operation period is Δt, O <T _D <n · Δt (where n is a coefficient, usually n = 1 to 4) When the differential time T _{D in the} range is set, the differential time T _D ′ at which T _D ′ = 0, which is the most stable region, is forcibly set and used in the digital D control calculation.

Furthermore, in the invention according to claim 4, when it is determined that the set differential time is the differential time of the unstable region, the notification means does not update the differential time to the operator, that is, the differential time. It notifies the setting error of and realizes appropriate process operation.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the device of the present invention will be described below with reference to FIG. In the figure, reference numeral 1 denotes a deviation calculating means for obtaining a deviation between the target value SV _n and the control amount PV _n . The deviation e _n obtained by the deviation calculating means 1 is a speed proportional control means 2 and a speed integral control. It is introduced into the means 3 and the velocity type differential control means 4.

[0031] In the velocity type proportional control unit 2, using the size e _n-1 of size e _n and the previous control operation period time deviation of the current _{deviation, △ P n = e n -e} n- ₁ …… (7) is executed to obtain the proportional calculation output ΔP _n . Further, the velocity type integral control unit 3, control operation period △ t, based on the integral time T _I and deviation _{e n, △ T I = (} △ t / T I) perform a e _n ...... becomes (8) operation Then, the integral calculation output ΔT _I is obtained. Further, in the speed type differential control means 4, as shown in the equation (4), the differential time T _D , the control calculation cycle Δt, and the differential gain 1 /
eta, when the variation d _n-1 of the differential of the previous control operation period _{time, △ d n = {T D} / (△ t + η · T D)} (e n -e n-1) - {△ t / (Δt + η · T _D )} d _n-1 (9) is executed to obtain the differential operation output Δd _n .

[0032] Each operation output △ P _n obtained in these control means _{2~4, △ T I, △ d} n is introduced into the respective adding means 5, _{where, △ P n + △ T I} + △ d n .. (10) After calculating the addition combined value by performing the calculation, it is guided to the proportional gain means 6, and based on the addition combined value and the proportional gain K _P , ΔMV _n = K _P (ΔP _n + Δ T _I + Δd _n ) (11) The speed type control signal ΔMV _n is obtained by the following calculation. Then, the velocity type control signal ΔMV _n is introduced into the velocity type / position type signal converting means 7, and the position type signal is calculated by performing the following calculation: MV _n = MV _n-1 + ΔMV _n (12) The control target 8 is converted into the control target 8 and applied to the control target 8 to control the control target. Reference _numeral 9 is a control amount detecting means for obtaining the control amount PV _n .

By the way, the digital PID controller is
As described above, in the relationship between the control calculation cycle Δt and the differential time T _D , the differential value is greatly affected by the set value of the differential time, and there is a problem that the control response becomes oscillatory or divergent vibration.

In view of this, the apparatus of the present invention is provided with means for determining the unstable region and determining the unstable region and prohibiting the update of the differential time to be set by previously defining the unstable region and the stable region.

[0035] More specifically, the derivative time setting unit 10 for inputting set a new derivative time T _D, the derivative time T _D that is set by the differential time setting means 10 and updated and stored as a new derivative time T _D ' A differential time memory means 11 provided for the calculation of the speed type differential control means 4 is provided, and a control calculation cycle Δt used in the speed type differential control means 4 and a differential time T set by the differential time setting means 10. _D
And an unstable region determining means 12 for determining whether or not the differential time T _D set based on a predetermined determination condition is in an unstable region, and an unstable region determining means for normally making a non-conduction state. There is provided signal selecting means 13 for prohibiting updating of the differential time set by the differential time setting means 10 when it is determined by 12 that the differential time T _D is in the unstable region.

Furthermore, when the derivative time T _D in the unstable region determining means 12 is determined to be in the unstable region, Toka derivative time T _D to the operator outputs an alarm to the effect that in an unstable region, or An informing unit 14 is provided for displaying a message on a CRT or the like that the set differential time is in an unstable region.

The velocity-type differential control means 4 uses the deviation e _n
Although the differential calculation operation is performed based on the above, for example, a so-called measured value differential precedent type that directly takes in the control amount PV _n and performs the differential calculation operation may be used.

Next, the operation of setting the differential time, which is the main part of the device of the present invention, will be described. First, in the unstable region determination means 12, the control calculation cycle is Δt and the differential time is T _D.
Then, the unstable region is defined as 0 <T _D <n · Δt (13), and the stable region is defined as T _D = 0 or n · Δt ≦ T _D (14). Note that n in the equations (13) and (14) is n = 1 to 4 when calculated from various simulations.
Between The value of n varies depending on how much control fluctuation is allowed, but it is inevitable that the value of n has a certain width. However, preferably n =
If it is between 2 and 3, it exhibits an extremely excellent controllability.

Incidentally, in the example of FIG. 7, Δt = 0.4 sec
Since n = T _D /Δt=2.16, when the control calculation period Δt = 0.3 sec, the unstable region of the differential time T _D is expressed by the equation (4) as 0 < T _D <0.68 sec (15). Therefore, when the differential time T _D enters the region of the equation (15), the unstable region determination means 12 does not set the differential time T _D even if the differential time setting means 10 tries to set the differential time T _D.

The unstable region judging means 12 specifically takes in the control calculation cycle Δt used in the velocity type differential control means 4, and further, the differential time setting means 10 causes the differential time T _D.
Is received, for example, n = 1 to 4 based on the above equation (13).
Is used to determine whether or not the differential time T _D is in the unstable region, and when it is in the unstable region, the signal selecting means 13 is non-conducting When in the stable region, the signal selecting means 13 is conducting. To do.

That is, when the unstable region judging means 12 judges that the region is unstable, the signal selecting means 13 is kept in the non-conducting state, so that the differential time setting means 10
The differential time set by the above is prohibited and the differential time T _D ′ of the differential time memory means 11 is not updated.

On the other hand, by a conductive state signal selecting means 13 when it is determined that the stable region, derivative time T _D of the derivative time T derivative time based on the _D memory means 11 which are set from the derivative time setting means 10 ′ Is updated and the differential time provided to the speed type differential control means 4 is T _D ′ = T _D.

Although the differential time T _D can be freely set in the above embodiment, for example, 0 <T _D <nΔt (1 ≦ n ≦ 4) in the differential time memory means 11. When T _{D in the} unstable region is set, T _D ′ = 0 or T _D ′ = n · Δt is set in the speed type differential control means 11 as the differential time T _D ′ applied to the actual differential operation. Then
Unstable control can also be prohibited. Therefore, in this case, the differential time memory means 11 stores T _D ′ = 0 or T _D ′ = n · Δt which is a stable area in advance, and the differential time setting means 10 causes the differential time T to be an unstable area. _{When D} is set, it becomes a stable region T _D ′ = 0 or T _D ′
= NΔt is output, or T _D ′ = 0 or T _D ′ = n which is a stable region in the differential time memory means 11 in advance.
When Δt is stored and the unstable region determination means 12 determines that it is an unstable region, it becomes a stable region stored in the differential time memory means 11 as shown in FIG. 2, T _D ′ = 0 or T _D ′ The configuration may be such that = n · Δt is forcibly output. In particular, if T _D ′ = 0 is output at this time,
The differential action is completely ignored, and the state shifts to a stable state that is not affected by the differential action. In the case of this embodiment, the signal selecting means 13 may be omitted.

In the above embodiment, when it is determined that the set differential time is in the unstable region, the differential time is not updated. However, as shown in FIG. 3, for example, the proportional gain memory means 21, An integration time memory means 22,
In the case of a configuration in which the PID parameters can be freely set from the parameter setting means 23, the signal selecting means 13 may be kept in the non-conducting state and all the PID parameters may not be updated. The reason for adopting such a configuration is that the respective control parameters are greatly related to the controllability.

Further, the signal selecting means 13 is made non-conducting / conducting depending on the presence or absence of an unstable area. It is possible to have a configuration in which the differential time T _D is set to be conductive only when it is turned on and the differential time of the differential time memory means 11 is updated, and the unstable region determination means 12 and the signal selection means 13 have a hardware block configuration. But,
It can be easily processed by software. In addition, the present invention can be modified in various ways without departing from the scope of the invention.

[0046]

As described above, according to the present invention, in the relation between the control calculation cycle and the differential time, when the set differential time is in the unstable region in plant operation, the differential time is updated. By prohibiting, the plant can always be operated in a stable direction.

When the set differential time is in the unstable region in plant operation, the differential time is set positively in the stable region so that the plant is always operated on the stable and safe side. Can be made.

Further, when the set differential time is in an area where plant operation is unstable, updating of the differential time is prohibited, and the operator is informed of that fact. Therefore, the differential time is erroneously set again. Therefore, even an inexperienced operator can secure stable and safe plant operation while enhancing the learning effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a digital PID control device according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of a digital PID control device according to the present invention.

FIG. 3 is a block diagram showing another embodiment of the digital PID control device according to the present invention.

FIG. 4 is a block diagram showing a conventional digital PID control device.

FIG. 5 is a characteristic diagram of a differential operation output when the control calculation cycle is changed.

6 is a diagram in which a plurality of differential operation outputs shown in FIG. 5 are superimposed.

FIG. 7 is a control response diagram that changes according to the magnitude of a control calculation cycle.

[Explanation of symbols]

2 ... Velocity type proportional control means, 3 ... Velocity type integral control means, 4
... speed type differential control means, 5 ... addition means, 6 ... proportional gain means, 7 ... speed type / position type signal conversion means, 8 ... controlled object, 10 ... differential time setting means, 11 ... differential time memory means, 12 ... Unstable region determination means, 13 ... Signal selection means,
14 ... Notification means.

Claims (4)

[Claims] 1. A digital PI (P: proportional, I: relative to a deviation between a controlled variable from a controlled object and a target value of the controlled variable).
(Integration) control calculation is performed, and a digital D (D: derivative) control calculation is performed on the deviation or the control amount by using a control calculation cycle and a differential time, and these calculation outputs are combined to generate an operation signal. In the digital PID control device applied to the controlled object, when the differential time of the region where the control becomes unstable is set due to the mutual relationship between the control calculation cycle and the differential time, the differential time is not updated. A digital PID control device comprising an unstable region determining means for performing the above. 2. A digital PI (P: proportional, I: relative to a deviation between a controlled variable from a controlled object and a target value of the controlled variable).
(Integration) control calculation is performed, and a digital D (D: derivative) control calculation is performed on the deviation or the control amount by using a control calculation cycle and a differential time, and these calculation outputs are combined to generate an operation signal. In a digital PID controller applied to a controlled object, when the control calculation cycle is Δt, O <T _D <n · Δt (where n is a coefficient, and usually n
= 1 to 4) A digital PID control characterized in that an unstable region determining means is provided so as not to update only the differential time or all of the PID parameters when trying to set the differential time T _{D in the} range apparatus. 3. A digital PI (P: proportional, I: relative to a deviation between a controlled variable from a controlled object and a target value of the controlled variable).
(Integration) control calculation is performed, and a digital D (D: derivative) control calculation is performed on the deviation or the control amount by using a control calculation cycle and a differential time, and these calculation outputs are combined to generate an operation signal. in the digital PID controller to be applied to the control object, when said control operation period _{△ t, O <T D <} n · △ t ( where, n is a coefficient, usually n
= 1 to 4) when the differential time T _{D in the} range of T _D ′ = 0 is set, the differential time T _D becomes the most stable region stored in advance.
Digital PID control apparatus characterized in that a means used forcibly the digital D control operation of the _D '. 4. A digital PI according to claim 1.
In the D control device, when it is determined that the set differential time is the differential time of the unstable region, a notification unit is added to receive a determination signal and output an alarm or message that the differential time is not updated. A digital PID control device characterized by the above.