JPH09190202A - Cascade controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reset winding up. SOLUTION: Thus cascade controller is provided with a primary control system 10 and a secondary control system 30. When the characteristic of the operation terminal 6 of the primary control system 10 is an inverse operation, a limit deviation signal output means 19 in which either upper/lower limit values or a change rate limit value or both values are set, whether operation signals being the outputs of PID (proportional integration differentiation) control operation means (12 and 13) in the primary control system 10 exceed the upper/lower limit values and the change rate limit value or not is judged and a limit deviation signal is outputted when they exceed them is provided for the primary control system 10. The secondary control system 30 is provided with integration control means (35, 43 and 44) discriminating the code of the limit deviation signal with that of speed-type I control operation output in the PID control operation means (32 and 33) of the secondary control system 30 and stopping the integration operation of the PID control operation means 32 and 33 in the secondary control system 30 when they are same codes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cascade control device used in control systems of various industries.

[0002]

2. Description of the Related Art PID (P: proportional, I: integral, D: derivative) regulators have been used since the history of process control began.
It is widely used in all industrial fields, and nowadays it is not possible without control systems in various industrial fields without a PID controller.

By the way, as one of the methods for improving the controllability of a process using this PID adjusting device, there is a cascade control device which is a combination of a plurality of PID adjusting devices. This cascade control device is configured such that the target value of one or more primary control systems is controlled by the output of another secondary control system. The reason for adopting such cascade control is as follows. By absorbing the disturbance with the primary control system,
It is to facilitate the control of the secondary control system and improve the overall controllability.

FIG. 5 is a block diagram of a conventional cascade control device applied to temperature control in a furnace. This cascade control device includes a furnace 2 equipped with a burner 1 for heating an object to be heated.
The furnace 1 is provided with a primary control system 3 and a secondary control system 4.

The primary control system 3 includes a fuel flow rate measuring means 5 for measuring the flow rate of fuel supplied to the burner 1, a fuel flow rate control valve 6 for adjusting the flow rate of fuel supplied to the burner 1.
The target value SV ₁ is compared with the fuel flow rate measurement signal PV ₁ of the fuel flow rate measuring means 5, PID adjustment calculation is executed so that the deviation becomes zero, and an operation signal MV ₁ is obtained and applied to the fuel flow rate adjustment valve 6. In addition, in the secondary control system 4, the in-reactor temperature measuring means 8 for measuring the in-reactor temperature and the in-reactor temperature measuring means 8 are provided. in the measured furnace deviation between the temperature measurement signal PV ₂ and furnace temperature target value SV ₂ executes a PID adjustment operation so that the zero outputs an operation signal MV _2, the target value of the primary control system 3 It is constituted by the secondary PID adjustment calculation means 9 for SV ₁ .

According to the cascade control device having such a configuration, first, as the primary control system 3, the primary PID adjusting means 7 is used and the fuel flow rate measuring signal P of the fuel flow rate measuring means 5 is obtained.
The PID adjustment calculation is executed so that V ₁ matches the target value SV _1, and the operation signal MV ₁ obtained by this calculation is applied to the fuel flow rate adjustment valve 6. On the other hand, in the secondary control system 4, the in-furnace temperature measurement signal PV ₂ of the in-furnace temperature measuring means 8 is sent to the in-furnace temperature target value SV ₂ by using the secondary PID adjustment calculating means 9.
PID adjustment calculation is performed so that the operation signal MV ₂ obtained by this calculation is the primary P of the primary control system 3.
The target value SV ₁ of the ID adjustment calculation means 7 is controlled so as to dominate.

Therefore, in such a cascade control device, even if the fuel pressure fluctuates, the effect of fuel pressure fluctuation is completely absorbed by the primary control system 3 within the range where the fuel flow rate can be controlled, and the secondary control system It is possible to prevent the effect of No. 4 on the temperature in the furnace.

However, in actual plant operation,
For example, when a so-called disturbance occurs in which the fuel pressure greatly changes, a case where the fuel flow rate reaches an uncontrollable region often occurs. When such a disturbance occurs, various problems occur in the conventional cascade control device having no information exchange between the primary control system 3 and the secondary control system 4.

This problem will be described with reference to FIG.
In the figure, letters in lowercase letters refer to conventional equipment (Fig. 5).
And the reference numeral with a dash in English lowercase means the characteristic of the device of the present invention described later.

[0010] Now, when the fuel pressure is increased abruptly decreases in the illustrated Lee time, the primary PID adjusting means 7, the fuel flow rate PV ₁ is lowered as shown a, consistent fuel flow PV ₁ to the target value SV ₁ To do so, the operation signal MV ₁ is increased as shown in FIG. As a result, the operation signal MV ₁ reaches the upper limit value of 100%, but the fuel flow rate PV ₁ does not reach the target value SV ₁ as shown in FIG. Affects internal temperature. That is, the furnace temperature PV belonging to the secondary PID adjustment calculation means 4
₂ is kept lower than the target value temperature SV ₂ as shown in FIG. In the course of such a transition, in order to match the furnace temperature PV ₂ with the target value temperature SV ₂ , the secondary P
The operation signal MV ₂ which is the output of the ID adjustment calculation means 9 is gradually increased by the integration operation as shown by d, and the operation amount MV ₂ reaches a peak (100%), but only the integration operation is still performed. As it progresses, it will be in a so-called reset windup state.

After that, it is assumed that the fuel pressure has recovered at the time point B in the figure. At this time, the operation signal MV ₂ which is the output of the secondary PID adjustment calculation means 9 exceeds the upper limit value (100%) and reaches a peak as shown, so that the primary PID adjustment calculation means 7 , The operation signal MV
_The target value SV ₁ used by incorporating ₂ is also in a state of exceeding the upper limit value (100%) as shown in the figure e,
Along with this, the operation signal MV of the primary PID adjustment calculation means 7
₁ also exceeds the upper limit value as shown in FIG.

[0012] As a result, the fuel flow rate PV ₁ is increased to 100%, as shown in the drawing a, which furnace temperature as shown in the drawing c is increased with, as shown d when only the illustrated Ha time The operation signal MV ₂ begins to decrease, and the reset windup amount is cut off and settles to a normal value for a while. However, during this time, the furnace temperature PV ₂ greatly exceeds the target value SV ₂ and overshoot (overshoot) decreases.

[0013]

Therefore, as described above, in the conventional cascade control device, when a large disturbance is introduced into the primary control system 3, the control amount reaches a peak, and reset windup occurs during this period. However, in order to reset and wind up even after the disturbance disappears, the secondary control system 4
There is a problem in that the control amount PV ₂ of 1 above largely overshoots. (1) As a result, in general, when the control amount overshoots, for example, the quality of the product to be heated deteriorates, and some products to be heated must never be overshot. (2) In addition, when the disturbance is eliminated and the reset / windup portion is cut off, the excessive combustion period continues for a long time, which accelerates deterioration of related equipment such as the furnace and consumes unnecessary energy. It also causes pollution.

The present invention has been made in view of the above circumstances, and the output information of the primary control system is promptly taken in by the secondary control system, and the integration operation of the secondary control system is appropriately controlled to reset. -To provide a cascade control device that prevents windup.

[0015]

In order to solve the above problems, the invention according to claim 1 is directed to a cascade control in which a target value of a primary control system is controlled by an output of a secondary control system. In the apparatus, when the characteristic of the operating end of the primary control system is reverse operation, one or both of the upper / lower limit limit value and the change rate limit value are set in advance in the primary control system, A limit deviation signal output means is provided for judging whether or not the operation signal output from the PID adjustment calculation means of the control system exceeds the upper / lower limit limit value and the change rate limit value, and when it exceeds the limit deviation signal. The secondary control system determines the sign of the limit deviation signal and the speed type I adjustment operation output in the PID adjustment operation means of the secondary control system. Integral control for stopping the integral operation of the PID adjustment calculation means Stage is a cascade control device provided with a.

In the invention corresponding to claim 1, when the characteristics of the operating end of the primary control system are reverse operation, the output of the PID adjustment computing means of the primary control system is provided by taking the above means. When the operation signal exceeds a predetermined upper / lower limit value or the like, a limit deviation signal is sent to the secondary control system.

In this secondary control system, when the sign of the limit deviation signal of the primary control system and the output of the speed type I adjustment calculation of the secondary control system have the same sign, the integral operation of the secondary control system is the first order. It is judged that there is a direction to expand the operation signal which is the output of the control system, and 2
Since the integral operation of the secondary control system is stopped, the reset / windup of the secondary PID adjustment computing means can be prevented.

Next, in the invention corresponding to claim 2, when the characteristic of the operating end of the primary control system is reverse operation, the primary control system preliminarily determines which of the upper / lower limit limit value and the change rate limit value. Either or both of them are set, and the operation signal output from the PID adjustment calculation means of the primary control system is the upper / lower limit limit value,
An operation signal state output means for outputting a signal indicating whether or not the change rate limit value is exceeded is provided, and the secondary control system changes the operation signal from the output of the operation signal state output means to the upper / lower limit value or change. Sign of the signal when the rate limit value is not exceeded or when the operation signal exceeds the upper / lower limit values and the speed type I adjustment operation output in the PID adjustment operation means of the secondary control system Is a different sign, P of the secondary control system
It is a cascade control device provided with an integration control means for executing the integration operation of the ID adjustment calculation means.

In the invention corresponding to claim 2, the PI is used in the primary control system by taking the above means.
A signal indicating whether or not the operation signal of the D adjustment calculation means exceeds a predetermined upper / lower limit value or the like is output and sent to the secondary control system.

This secondary control system, when the signal sent from the primary control system does not exceed the upper and lower limit values,
Alternatively, if the sign of the signal sent from the primary control system and the sign of the speed type I adjustment calculation output of the secondary control system are different, the secondary P
It is determined that there is no condition for causing the reset / windup of the ID adjusting means, and the integrating operation of the PID adjusting calculating means of the secondary control system is executed.

Next, the invention according to claim 3 is a cascade control device configured such that the target value of the primary control system is controlled by the output of the secondary control system. If the characteristic of is positive operation, one or both of the upper / lower limit limit value and the change rate limit value are set in advance in the primary control system, and this is the output of the PID adjustment computing means of the primary control system. A limit deviation signal output means is provided for judging whether or not the operation signal exceeds the upper / lower limit limit value and the change rate limit value, and outputs a limit deviation signal when the operation signal exceeds the limit value. An integral that determines the sign of the signal and the speed type I adjustment calculation output in the PID adjustment calculation means of the secondary control system, and stops the integration operation of the PID adjustment calculation means of the secondary control system when the sign is different. It is a cascade control device provided with control means.

The invention corresponding to claim 3 is claim 1
When the characteristics of the operating end of the primary control system are completely opposite to those of the invention corresponding to the above, the present invention has exactly the same operation as the invention corresponding to claim 1 except for the configuration and operation.

Further, in the invention according to claim 4, when the characteristic of the operating end of the primary control system is a positive operation, the primary control system preliminarily sets one of the upper / lower limit limit value and the change rate limit value. One or both of them are set, and the operation signal output from the PID adjustment computing means of the primary control system is the upper / lower limit limit value,
An operation signal state output means for outputting a signal indicating whether or not the change rate limit value is exceeded is provided, and the secondary control system changes the operation signal from the output of the operation signal state output means to the upper / lower limit value or change. Sign of the signal when the rate limit value is not exceeded or when the operation signal exceeds the upper / lower limit values and the speed type I adjustment operation output in the PID adjustment operation means of the secondary control system Are of the same sign, P of the secondary control system
It is a cascade control device provided with an integration control means for executing the integration operation of the ID adjustment calculation means.

The invention corresponding to claim 4 is also defined in claim 2.
When the characteristics of the operating end of the primary control system are completely opposite to those of the invention corresponding to the above, the same operation as that of the invention according to claim 2 is achieved except for the configuration and the operation by it.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a cascade control device according to claim 1. The same parts as those in the conventional device shown in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

The control system of this cascade control device comprises a primary PID control system 10 and a secondary PID control system 30. The primary PID control system 10 includes a deviation calculating means 11 for obtaining a deviation e _1n (= SV _1n −PV _1n ) between the target value signal SV _1n and the control amount PV _1n from the fuel flow rate measuring means 2, and the deviation e. Speed type (P + D) adjustment calculation is executed using _1n and Δ (P + D) _1n is output.
D) Adjustment calculation means 12, speed type I adjustment calculation means 13 that executes speed type I adjustment calculation using the deviation e _1n , and outputs _{ΔI 1n,} and output system of this speed type I adjustment calculation means 13 Switch means 14 provided in the
4 I adjustment calculation output ΔI _1n and the speed type (P + D) adjustment calculation means 12 adjustment calculation output Δ (P +
An adding means 15 for adding combines the D) _1n, signal conversion means 1 for converting the velocity-type PID controller output signal added synthesized by this adding means 15 into position type PID regulation output signal MV _1n
6, an upper / lower limit limiting means 17 for limiting the position type PID adjustment output signal MV _1n of the signal converting means 16 with upper / lower limit limiting values H / L, and a change rate limitation for the output of the upper / lower limit limiting means 17. Then, the change rate limiting means 18 for transmitting as the operation signal MV ′ _1n is provided.

Further, in the primary PID control system 10,
The position type PID of the signal converting means 16 is provided between the output side of the signal converting means 16 and the output side of the change rate limiting means 18.
The difference between the previous value MV _{1n-1 of the} adjustment output signal MV _{1n and} the previous value MV _1n-1 ′ of the output signal MV _1n ′ of the rate _-of- change limiting means 18, that is, the amount _exceeding the previous limit is calculated to obtain the secondary value. Control system 30
Limit deviation signal output means 19 for sending to the vehicle, the output of the limit deviation signal output means 19 and the speed type I adjustment calculation means 1
3 and the multiplication means 2 for multiplying the output of
The sign is discriminated from the output of 0, and when it is a positive sign, that is, when both are discriminated to be the same sign, it is judged that the deviation amount is further increased by the integral operation, and the switch means 14 is set to the off state to stop the integral operation. A code discriminating means 21 is provided.

On the other hand, the secondary PID control system 30 obtains the deviation e _2n (= SV _2n -PV _2n ) between the furnace temperature measurement signal PV _2n of the furnace temperature measuring means 8 and the furnace temperature target value SV _2n. By using the deviation calculating means 31 and this deviation e _2n , the velocity type (P +
Speed D) running adjusting operation, run △ and (P + D) rate type that outputs a _2n (P + D) adjusting operation means 32, the velocity type I regulatory calculation using the deviation e _2n, and outputs the △ I _2n Type I adjustment calculation means 33 and this speed type I adjustment calculation means 33
Switch means 34, 3 serially provided in the output system of
5 and I coming through these switch means 34 and 35
Regulation computation output △ I _2n and the velocity type and (P + D) adjusting the calculated output △ (P + D) adding means 36 for adding combines the _2n adjustment calculation means 32, adds the synthesized velocity type PID regulation output from this adding means 36 Signal is position type PID control output signal M
V _2n signal converting means 37, position type PID adjustment output signal MV _2n of the signal converting means 37 is limited by upper and lower limit limiting values H and L, and upper and lower limit limiting means 38. Of the output of the control signal MV
A change rate limiting means 39 for transmitting as _2n 'is provided.

Further, in the secondary PID control system 30, it is provided between the output side of the signal converting means 37 and the output side of the change rate limiting means 39, and the position type P of the signal converting means 37 is provided.
The difference between the previous value MV _{2n-1 of the} ID adjustment output signal MV _{2n and} the previous value MV _2n-1 ′ of the output signal MV _2n ′ of the rate _-of- change limiting means 39, that is, the limit deviation for obtaining the amount exceeding the previous limit An amount acquisition means 40, a first multiplication means 41 for multiplying the output of the limit deviation amount acquisition means 40 and an output of the speed type I adjustment calculation means 33, and a code from the output of the first multiplication means 41 If the positive sign, that is, the both signs are the same sign, the switch means 34 is set to the off state to stop the integral operation, and the primary P and the primary P.
Second multiplication means 43 for taking in the output of the limit deviation signal output means 19 constituting the ID control system 10 and multiplying the output of the limit deviation signal output means 19 with the output of the speed type I adjustment calculation means 33, There is provided a second sign discriminating means 44 for discriminating the sign from the output of the second multiplying means 43 and setting the switch means 35 in the off state to stop the integrating operation of the secondary PID control system 30 when the sign is a positive sign. Has been.

Before explaining the operation of the cascade control device configured as described above, first, PID control in a continuous time system will be described. This PID
The basic control formula can be expressed by C (s) = K _P [1+ {1 / (T _I · s)} + {T _D · s / (1 + ηT _D · s)}] (1). However, K _P : proportional gain, T _I : integration time,
T _D: derivative time, s: Laplace operator, eta: a: (differential gain 1 / eta) derivative.

Therefore, when the above basic expression of PID control is converted into a digital speed type PID arithmetic expression, the following expression is obtained. _{△ MV n = K P {(} e n -e n-1) + (△ t / T I) · e n + △ d n} ...... (2) _{where, △ d n = d n-} 1 + [ _{{T D / (△ t +} ηT D)} · (e n -e n-1)] - a {△ t / (△ t + ηT D)} · d n-1 ...... (3), also, MV _n = MV _n-1 + ΔMV _n can be expressed by (4).

However, in the above equation, MV _n : current value of operation signal, ΔMV _n : change of operation signal, MV _n-1 : previous value of operation signal, e _n : current value of deviation, e _n-1 : Previous value of deviation, Δt: control cycle, Δd _n : speed type differential adjustment calculation output, d _n-1 : previous value of differential adjustment calculation output.

For the following description, the following equations can be defined from the equations (2) to (4). Velocity type (P + D) adjusting operation signal _{△ (P + D) n =} K P {(e n -e n-1) + △ d n} ...... (5) velocity type I (integral) adjusting operation signal △ I _n = K _{P (△ t / T I)} · e n ...... (6) below, relates to the operation of the cascade control system according to the present invention will be described on the assumption above each relation.

Now, the deviation calculating means 11 of the primary PID adjusting means 10 shown in FIG. 1 is a deviation e between the target value signal SV _1n and the fuel flow rate measuring signal (control amount) PV _1n of the fuel flow rate measuring means 2.
After obtaining _1n (= SV _1n −PV _1n ), this deviation e _1n is supplied to the speed type (P + D) adjustment calculation means 12 and the speed type I adjustment calculation means 13. Here, the speed type (P + D) adjustment calculation means 12 executes the PD adjustment calculation based on the deviation e _1n , and Δ (P + D) _1n = K _P {(e _1n −e _1n-1 ) + Δd _1n }. (7) The PD adjustment calculation output Δ (P + D) _1n is obtained, while the speed type I adjustment calculation means 13 executes the I adjustment calculation based on the deviation e _1n, and _{ΔI 1n} = K _P (Δ t / T _I ) · e _1n (8) Obtain the I adjustment calculation output ΔI _1n .

Then, the speed type (P + D) adjustment calculation means 1
The PD adjustment calculation output Δ (P + D) _{1n which} is the output of _{No. 2} is directly led to the adding means 15, while the I adjustment calculation output ΔI _1n which is the output of the speed type I adjustment calculation means 13 is integrated by the switch means 14. It is led to the addition means 15 via this, and using both outputs, the velocity type PID adjustment calculation output ΔMV _1n = Δ (P + D) _1n + processed _{ΔI 1n} (9) is executed, Velocity-type signal conversion means 1
6

The signal converting means 16 executes the calculation of MV _1n = MV _{1n -1} + ΔMV _1n (10) and outputs the speed type PID adjustment calculation output ΔMV _1n.
To the position type PID adjustment calculation output MV _1n . The position type PID adjustment calculation output MV _1n is used as the upper / lower limit limiting means 17.
And the final operation signal MV through the change rate limiting means 18.
_1n ′, which is applied to the fuel flow rate control valve 6.

At this time, the limit deviation signal output means 19 is
By using the previous value MV _1n-1 position type PID regulation computation output MV _1n and the final and 'previous value MV _1n-1 of the' operation signal MV _1n, limit deviation signal △ L _1n accordance with the following for (11) _-1
Ask for.

_{ΔL 1n-1} = MV _1n-1 −V _1n-1 ′ (11) Then, on the primary PID control system 10 side, the multiplication means 20 outputs the output ΔL _{1n of the} limit deviation signal output means 19. _-1 is multiplied by the velocity type I adjustment calculation output ΔI _1n to obtain a multiplication result of δ _1n = ΔL _1n-1 · ΔI _1n (12), and then this is introduced into the code discriminating means 21. To do. This sign discriminating means 21 is a switch means 1 when the sign of the multiplication result δ _1n by the multiplying means 20 is a different sign.
4 is left in the ON state to continue the integration operation, while
In the case of a plus sign, the switch means 14 is set to the off state and the integration operation is stopped.

Here, the significance of controlling the integration operation will be described. Considering now the case where the multiplication result δ _1n obtained from the above equation (12) is a positive sign, δ _1n = ΔL _1n−1 · ΔI _1n
> 0, and at least P
Since the ID adjustment calculation output is caught by the upper and lower limit values, the speed type I adjustment calculation is performed, and the speed type I adjustment calculation output is in the direction of expanding beyond the limit value, Under these conditions, the integral operation is stopped, while in the case of a negative sign, it is determined that the speed type I adjustment calculation output is acting in a direction to reduce the limit value over, and the switch means 14 is kept in the ON state. To continue the integration operation.

On the other hand, the multiplying means 41, the sign discriminating means 42, the switch means 34, etc. in the secondary PID control system 30 have substantially the same configuration and function as the primary PID control system 10, and the secondary PID Although the integral operation is controlled from the output state of the control system 30, the PID of the primary PID control system 10 is particularly controlled by the multiplication means 43, the code determination means 44 and the switch means 35 which are different from the primary PID control system 10.
Control calculation output, that is, the limit deviation signal output means 1 on the primary side
Limit deviation signal ΔL _1n-1 and secondary PI obtained from 9
After multiplying the speed type I adjustment operation output ΔI _{2n of the} D control system 30 to obtain a multiplication result δ _2n of δ _2n ′ = ΔL _1n−1 · ΔI _2n (13), the code discrimination means When the multiplication result δ _2n ′ is a positive sign at 44, the switch means 35 is set to the off state and the integration operation of the secondary PID control system 30 is stopped.

Here, the relationship of δ _2n ′ = ΔL _1n−1 · ΔI _2n > 0 means that the output of the primary PID control system 10 is caught at the limit value and the secondary PID control is performed. System 3
0 velocity type I regulatory operation output of △ I _2n is present and further secondary PID control system 30 velocity type I regulatory operation output △ I _2n of is in a direction to expand the limit value over a primary PID control system 10 Δ _2n ′ = ΔL _1n−1 · ΔI _2n > 0
Under these conditions, the integration operation of the secondary PID control system 30 is stopped.

Therefore, according to the embodiment having the above-mentioned configuration, the operation output states in the primary and secondary PID control systems 10 and 30 are individually monitored, and the operation output states are preset to the upper and lower limit values. When the output of the speed type I adjustment operation of the self is in the direction of further expanding the limit deviation signal when the rate of change is exceeded, the integral operation of the self is stopped to prevent the expansion. As a result, it is possible to completely prevent the reset windup of the secondary PID control system 30 caused by the primary PID control system 10 being caught at the limit value and reaching its peak.
The controllability and safety of the cascade control device can be greatly improved.

The operating characteristics of the control device shown in FIG. 1 will be described with reference to FIG. As shown in FIG. 6, when the fuel pressure drops sharply at the time point a in the figure, the fuel flow rate PV ₁ of the primary PID control system 10 becomes a ′ in the figure.
Therefore, the operation signal is increased as indicated by b'in the figure in order to bring the PV ₁ into agreement with the target value SV ₁ . As a result, the operation signal MV ₁ is _{1 which} is the upper limit value.
Although it reaches 00%, the fuel flow rate PV due to the low fuel pressure
₁ changes to a low state without reaching the target value SV ₁ as shown in a ', and affects the temperature in the furnace. That is, the secondary PI
The in-furnace temperature PV ₂ belonging to the D adjustment calculation means 4 remains lower than the target temperature SV ₂ as shown in c '.

At this time, the regulation calculation output of the secondary PID control system 30 deviates from the limitation deviation signal output means 19 at the moment when the operation signal MV ₁ of the primary PID control system 10 reaches 100% of the upper limit value. Since the signal is sent to the secondary PID control system 30, this positive limit deviation signal and the secondary PID control system 3
Since the I adjustment calculation output of 0 has the same sign, the sign judging means 44 sets the switch means 35 to the off state, and the integration operation of the secondary PID control system 30 is stopped.
The operation signal MV ₂ becomes as shown in d'in the figure, and the so-called operation signal is reset / reset due to the progress of the integration operation while the peak value is reached.
Windup can be prevented.

Thereafter, when the fuel pressure is restored at the time point B in the figure, the operation signal of the primary PID control system 10 is 100%.
From the above state, first, the fuel flow rate PV ₁ increases as shown in a ', the furnace temperature rises accordingly, and the normal operation is stabilized by completely normal control. In this way, the furnace temperature PV ₂ quickly reaches the target value as shown by c ′ in the figure,
No overshoot occurs.

Next, FIG. 2 is a block diagram showing an embodiment of the cascade control device according to the present invention. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals and the detailed description thereof will be omitted, and hereinafter, different parts will be described particularly in comparison with FIG.

In this control device, instead of the limit deviation signal output means 19 in the primary PID control system 10, when the operation signal MV _1n does not exceed the upper / lower limit limit value or the change rate limit value, or the operation signal concerned. An operation signal state output means 22 for outputting any signal when MV _1n exceeds the upper and lower limit values is provided, and the output side of each of the multiplication means 41, 43 constituting the secondary PID control system 30 is provided. , The multiplication means 41, 43
When it is determined that the sign of the result of multiplication by N.sub.2 is negative or the result of multiplication is zero, sign determining means 46, 47 for outputting a switch-on signal and the speed type I adjustment calculating means 3 are provided.
The switch means 4 is provided on the output side of 3 serially corresponding to the respective code discriminating means 46 and 47, and receives the switch-on signal from the code discriminating means 46 and 47 and is set to the ON state.
8 and 49 are provided.

Next, the operation of the control device configured as described above will be described. When the output of the operation signal state output means 22 having the subtraction function which constitutes the primary PID adjustment means 10 is introduced into the multiplication means 43, the multiplication means 43
The output ΔL _{1n-1 of the} operation signal status output means 22 and the secondary PID
The speed type I adjustment calculation output ΔI _{2n of the} control system 30 is multiplied,
This multiplication output δ _2n ′ (= ΔL _1n−1 · ΔI _2n ) is guided to the code discriminating means 47. The sign discriminating means 47 outputs the multiplication output δ.
_{When 2n} 'is zero or a negative sign, a switch-on signal is output to set the switch means 49 to the on-state, and the secondary P
The integration operation of the ID control system 30 is executed.

The meaning of δ _2n ′ = ΔL _1n−1 · ΔI _2n ≦ 0 and the processing under such conditions will be described. (1) When δ _2n ′ = ΔL _1n−1 · ΔI _2n <0.

In this case, it means that ΔL _1n-1 and ΔI _2n have certain values and have different signs. ΔL _1n-1 having a certain value means that the operation signal which is the output of the primary PID control system 10 is caught at the limit value (upper / lower limit limit value or change rate limit value), and The fact that ΔI _2n has a certain value means that the speed type I adjustment calculation output of the secondary PID control system 30 exists, and that the signs of these two are different, This means that the speed type I adjustment calculation output of the secondary PID control system 30 is in the direction of eliminating the limit deviation of the operation signal which is the output of the primary PID control system 10.

Therefore, under such a condition, by setting the switch means 49 to the ON state, the secondary PI is
The integral operation of the D control system 30 is executed, and as a result, the velocity type I
The adjustment calculation output ΔI _2n prevents the occurrence of reset windup. (2) When δ _2n ′ = ΔL _1n−1 · ΔI _2n = 0. (B) When ΔL _1n-1 = ΔI _2n = 0, reset windup does not occur because the speed type I adjustment calculation output ΔI _2n is zero, so the switch means 49 is turned on. And the integration operation of the secondary PID control system 30 is executed. (B) When ΔL _1n-1 ≠ 0 and ΔI _2n = 0,
As in (a) above, since the speed type I adjustment calculation output ΔI _2n is zero, reset windup does not occur, so the switch means 49 is set to the ON state.
The integration operation of the secondary PID control system 30 is executed. (C) When ΔL _1n-1 = 0 and ΔI _2n ≠ 0,
It means that the operation signal which is the output of the primary PID control system 10 is not caught by the limit value and that the speed type I adjustment calculation output ΔI _{2n of the} secondary PID control system 30 exists. Under this condition, since reset windup does not occur, the switch means 49 is set to the ON state,
The integration operation of the secondary PID control system 30 is executed.

In other words, this control device effectively utilizes the speed type I adjustment calculation output by taking in the information that the secondary PID control system 30 exceeds the limit of the primary PID control system 10, thereby effectively using the primary PID control calculation output. Completely eliminate the reset windup of the secondary PID control system 30 caused by the output of the control system 10 getting stuck at the limit value and reaching a peak.
It improves controllability and safety.

Further, FIG. 3 is a block diagram showing an embodiment of the cascade control device according to the present invention. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals, detailed description thereof will be omitted, and hereinafter, different parts will be described particularly in comparison with FIG.

The invention according to claim 1 is an invention corresponding to the one in which the characteristic of the fuel control valve 6 at the operating end has a reverse operation, that is, the control amount decreases when the operating signal increases. The invention according to claim 3 is an invention corresponding to the one in which the characteristic of the fuel control valve 6 as the operating end has a positive operation, that is, the characteristic that the control amount increases when the operation signal increases.

More specifically, on the output side of the multiplying means 20 constituting the primary PID control system 10, the sign discrimination for setting the switch means 14 to the off state when the sign of the multiplication output is negative contrary to FIG. A sign discriminating means for setting the switch means 35 to the off state when the sign of the multiplying output is negative on the output side of the multiplying means 43 constituting the secondary PID control system 30 and having the means 23. This is a configuration provided with 50.

In such a cascade control device, the same operation as that of FIG. 1 is performed except for the opposite sign discrimination of the corresponding means of FIG. That is, when the output of the multiplying means 20 is a negative sign, the sign determining means 23 stops the integration operation of the primary PID control system 10, and when the output of the multiplying means 43 is a negative sign, the sign determining means 50 is 2 The integration operation of the next PID control system 30 is stopped because the characteristics of the fuel control valve 6 are different as described above.

Further, FIG. 4 is a block diagram showing an embodiment of the cascade control device according to the present invention. Claim 2
The invention according to claim 3 corresponds to the invention in which the characteristic of the fuel control valve 6 at the operating end has a reverse operation, that is, the characteristic that the control amount decreases when the operating signal increases.
Another embodiment of the invention according to the invention is an invention corresponding to the one in which the characteristic of the fuel control valve 6 which is the operation end has the characteristic of a positive operation, that is, the control amount increases when the operation signal increases.

That is, in this embodiment of the cascade control device, an operation signal state output means 22 is provided as shown in FIG. 2 in place of the limit deviation signal output means 19 constituting the primary PID control system 10, and a multiplication means. A sign discriminating means 23 for setting the switch means 14 to the off state when the sign of the multiplication output is negative is provided on the output side of 20, while the multiplication output is provided on the output side of the multiplying means 43 constituting the secondary PID control system 30. Is a zero or its sign is a positive sign, the switch means 49 is set to the ON state, and the sign discriminating means 51 for executing the integration operation is provided. This control device performs exactly the same operation as that of FIG. 2 except that the sign discrimination opposite to that of FIG. 2 is performed, and therefore the description of the operation is omitted here.

[0059]

As described above, according to the present invention, it is possible to surely avoid overshoot and prevent deterioration of product quality and generation of defective products out of specification. Also,
When the disturbance is eliminated, the reset windup is eliminated, so the period of excessive combustion amount is shortened, deterioration of furnace related equipment can be reduced, wasteful energy consumption can be suppressed, and eventually pollution The cause of occurrence can also be reduced. Therefore, it can greatly contribute to full-scale flexible operation of the plant by a small number of people.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a cascade control device according to claim 1.

FIG. 2 is a configuration diagram showing an embodiment of a cascade control device according to claim 2;

FIG. 3 is a configuration diagram showing an embodiment of a cascade control device according to claim 3;

FIG. 4 is a configuration diagram showing an embodiment of a cascade control device according to claim 4;

FIG. 5 is a diagram showing a configuration of a conventional cascade control device.

FIG. 6 is a comparison diagram of characteristics of the conventional device and the device of the present invention.

[Explanation of symbols]

2 ... Furnace, 10 ... Primary PID control system, 12 ... Velocity type (P +
D) Adjustment calculation means, 13 ... Speed type I adjustment calculation means, 14
... switch means, 16 ... signal conversion means, 17 ... upper / lower limit limiting means, 18 ... change rate limiting means, 19 ... limit deviation signal output means, 20 ... multiplying means 21, 23 ... sign discriminating means,
22 ... Operation signal status output means, 30 ... Secondary PID control system, 32 ... Speed type (P + D) adjustment calculation means, 33 ... Speed type I adjustment calculation means, 34, 35 ... Switch means, 37 ...
Signal converting means, 38 ... Upper and lower limit limiting means, 39 ... Change rate limiting means, 43 ... Multiplying means, 44, 47, 51 ... Sign discriminating means, 48, 49 ... Switching means.

Claims (4)

[Claims] 1. A cascade control device configured so that a target value of a primary control system is controlled by an output of a secondary control system, wherein when the characteristic of an operating end of the primary control system is reverse operation, In the secondary control system, one or both of the upper and lower limit limit values and the rate of change limit value are set in advance, and the operation signal output from the PID adjustment calculation means of the primary control system is the upper and lower limit limit values, Judge whether the rate of change limit has been exceeded,
A limit deviation signal output means for outputting a limit deviation signal when exceeding is provided, and the secondary control system outputs the limit deviation signal and the speed type I adjustment calculation output in the PID adjustment calculation means of the secondary control system. The sign is determined, and when the sign is the same, the PID of the secondary control system
A cascade control device comprising an integration control means for stopping the integration operation of the adjustment calculation means. 2. A cascade control device configured such that the target value of the primary control system is controlled by the output of the secondary control system, wherein when the characteristic of the operating end of the primary control system is reverse operation, In the secondary control system, one or both of the upper and lower limit limit values and the rate of change limit value are set in advance, and the operation signal output from the PID adjustment calculation means of the primary control system is the upper and lower limit limit values, An operation signal state output means for outputting a signal indicating whether or not the change rate limit value is exceeded is provided, and the secondary control system changes the operation signal from the output of the operation signal state output means to the upper / lower limit values. When the rate limit value is not exceeded, or when the operation signal exceeds the upper / lower limit values and the PI of the secondary control system
Integral control means is provided for executing the integral operation of the PID adjustment calculation means of the secondary control system when the sign of the speed type I adjustment calculation output in the D adjustment calculation means has a different sign. Cascade controller. 3. A cascade control device configured such that the target value of the primary control system is controlled by the output of the secondary control system, wherein when the characteristic of the operating end of the primary control system is normal operation, In the secondary control system, one or both of the upper and lower limit limit values and the rate of change limit value are set in advance, and the operation signal output from the PID adjustment calculation means of the primary control system is the upper and lower limit limit values, Judge whether the rate of change limit has been exceeded,
A limit deviation signal output means for outputting a limit deviation signal when exceeding is provided, and the secondary control system outputs the limit deviation signal and the speed type I adjustment calculation output in the PID adjustment calculation means of the secondary control system. The sign is determined, and when the sign is different, the PID of the secondary control system
A cascade control device comprising an integration control means for stopping the integration operation of the adjustment calculation means. 4. A cascade control device configured such that the target value of the primary control system is controlled by the output of the secondary control system, wherein when the characteristic of the operating end of the primary control system is positive operation, In the secondary control system, one or both of the upper and lower limit limit values and the rate of change limit value are set in advance, and the operation signal output from the PID adjustment calculation means of the primary control system is the upper and lower limit limit values, An operation signal state output means for outputting a signal indicating whether or not the change rate limit value is exceeded is provided, and the secondary control system changes the operation signal from the output of the operation signal state output means to the upper / lower limit values. When the rate limit value is not exceeded, or when the operation signal exceeds the upper / lower limit values and the PI of the secondary control system
Integral control means for executing the integral operation of the PID adjustment calculation means of the secondary control system when the sign of the speed type I adjustment calculation output in the D adjustment calculation means is the same sign. Cascade controller.