JPH0642161B2 - How to modify a feedforward model - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for automatically correcting a feedforward model in response to a change in a disturbance characteristic in a process control device that combines feedback control and feedforward control. It is a thing.

(Technical background of the invention) In process control, feedback control plays an important role, but this control method focuses only on the result, and performs correction control when the result does not match the target value. Therefore, there is no problem in the case of slow fluctuations, but even for sudden disturbances, the result will start to deviate from the target value and correction control will be performed, so the transient response to sudden changes such as load fluctuations and disturbances will be delayed. It has a big drawback. Therefore, the controllability is improved by measuring the disturbance and applying feed-forward control that compensates for the influence of the disturbance in advance before the influence of the disturbance appears in the control amount in combination with the feedback control. . Here, the disturbance refers to an external action that tries to change the state of the control system. In other words, when the control system is in the equilibrium state, that is, when the control deviation en (see FIG. 3) is in a stable state of zero, all of the external factors that change this state and generate the control deviation en Is called disturbance. Disturbances can range from very high to low. For example, it is assumed that a domestic gas water heater controls heating of water to a predetermined temperature. In this case, when the disturbances are listed in descending order of influence, the amount of hot water, the temperature of tap water, the environmental temperature of the gas water heater, the unit calorific value of the gas, the change in the water heater efficiency, and various measurement deviations.

FIG. 1 is a block diagram showing a basic system in which feedback control and feedforward control are combined. In the figure, the comparison unit 1 compares the target value with the control amount, inputs the deviation into the PID adjustment unit 2, performs adjustment calculation, and then guides it to the addition unit 3. On the other hand, the disturbance D influences the control X through the disturbance transfer path 7 having the transfer function GD. Therefore, in order to cancel and compensate for this effect, the disturbance compensation signal is added to the output signal of the adjusting section 2 by the adding section 3 via the feedforward model 8 having the transfer function GF, and this is added as the operation signal to be controlled. In addition to the above, the control quantity X is obtained by adding the output of the block 4 having the transfer function GP to be controlled and the influence of the disturbance (this addition is represented as being performed by the adding section 5).

Therefore, assuming that the output signal of the controller 2 is Y, X = (Y + D * GF) * GF + D * GD = Y * GP + D * (GD + GF * GP) ...
(1) From equation (1), no matter how much the disturbance D changes, the control amount X
GD + GF × GP = 0 must be satisfied in order not to affect Therefore, the transfer function GF of the feedforward model 8 is Need to be defined. GD and GP can generally be approximated by a composite of dead time and first-order lag.

Here, KP and KD are gain constants, TP and TD are time constants, and LP and LD are dead times. Therefore, the transfer function GF of the feedforward model 8 is Becomes In addition, when GP and GD have equal time, And becomes a simple formula. In practice, this simple formula is sufficient. As described above, conventionally, the coefficient KD of the transfer function GD for the disturbance of the controlled object is assumed to be constant, and the coefficient KF = KD / KP of the feedforward model is also assumed to be constant. However, in the actual process, this disturbance coefficient KD is not a constant value, and it is an indirect disturbance factor, a change in characteristics over time, a change in physical quantity inside and outside, a change in the amount of chemical components, a change in ambient temperature, and a disturbance element not measured. Due to the effect of, it changes greatly irregularly. Therefore, there is a problem that the effect of the feedforward control is lost, or conversely, it causes harm.

Especially recently, due to the diversification of raw materials and fuels used in processes, diversification of products, load changes accompanying changes in operating rates due to changes in the economic environment, and versatility, the flexibility of processes, and therefore the flexibility of compulsory devices, has been increased. There is a strong demand for higher abilities.

Hereinafter, the above points will be described in more detail by taking the heat conversion outlet temperature control as an example. In FIG. 2, the raw material 11 is led to the heat exchanger 14 through the pipe 12, where it is heated by steam and taken out. The outlet temperature T ₀ of the heat exchanger 14 is detected by the temperature detector 15 and put in the temperature controller 19, and adjustment calculation is performed so that the outlet temperature T ₀ becomes a predetermined value. on the other hand,
The raw material flow rate Fi is detected by the raw material flow rate detector 13, this is put into the feedforward model 21, the output thereof is added to the output of the controller 19 by the addition section 20, and the addition result is set in the steam flow controller 22. Given as a value. In the steam flow rate controller 22, the steam flow rate signal detected by the steam flow rate detector 17 is used as a feedback signal to perform adjustment calculation so as to be equal to the steam set value, and the output signal thereof is used to adjust the control valve 1
The opening degree of 8 is controlled. In this way, control is performed to keep the outlet temperature T ₀ of the heat exchanger 14 constant.

The transfer function G of the feedforward model 22 in the above example
Consider F. First, the heat balance Q in the steady state of the process is obtained.

Where Fs is the steam weight flow rate, Hs is the latent heat of steam, Fi is the raw material weight, Gi is the specific heat of the raw material, Ta is the heat exchanger outlet temperature setting temperature, Ti is the heat exchanger inlet temperature of the raw material, and η is the heat exchanger efficiency. Is.

When the steam flow rate Fs, which is the manipulated variable, is calculated from the equation (5), Becomes From equation (6), the static characteristic compensation component GFS of the transfer function of the feedforward model 22 is And the transfer function GF of the feedforward model 22 loaded with the dynamic characteristic compensation is Becomes Here, TD is a time constant from the raw material flow rate detector 13 to the outlet temperature detector 15, and TP is a time constant from the setting of the vapor flow rate (output of the adding section 20) until this effect reaches the heat exchanger outlet temperature. .

In the above example, the feedforward control is performed with only the change in the raw material flow rate Fi as the disturbance. The coefficient KF is a constant, but in reality, the following factors are used: (i) change in raw material temperature (ii) change in heat exchange efficiency (iii) change in heat quantity of steam held (iv) change in ambient temperature (V) KF changes irregularly and largely due to changes in the specific heat of the raw material. Therefore, the effect of the feedforward control is not sufficiently exerted, the controllability at the time of changing the raw material flow rate is deteriorated, and the product quality is disturbed.

As described above, the conventional control method has a problem that the effect of the feedforward control is not exerted and, in some cases, it is an adverse effect, and the problem becomes more serious as the demand for process flexibility increases. It was supposed to be.

[Object of the Invention]

An object of the present invention is to provide an automatic correction method of a feedforward model, which can always maintain the feedforward compensation in an optimum state and improve the quality of process control.

[Outline of Invention]

The feedforward model correcting method of the present invention is configured by adding a feedforward control mechanism for suppressing the influence of disturbance in advance to a feedback control system.
In a process control device, a static characteristic including a calculation unit that calculates a static characteristic compensation component from the disturbance and a multiplication unit that multiplies an output from the calculation unit by a coefficient to generate a static characteristic compensation signal for canceling the influence of the disturbance Of the feedforward model,
In the correction method, at least one disturbance element is detected and given to the static characteristic feedforward model, and a signal based on the static characteristic compensation signal calculated by this model is used as the adjustment output signal of the feedback control system and the first output. A signal based on the signal obtained by the second addition unit is added by the second addition unit, and a signal based on the addition result and the dynamic characteristic compensation signal obtained from the static characteristic compensation signal are added. In addition, the control amount output from this controlled object is used as a feedback signal in the feedback control system, and the deviation discriminating unit determines whether the feedback signal and the control amount are initialized in a stable state with less disturbance. Of the static characteristic compensation signal and the calculated value of the static characteristic compensation signal, and a stable state with less disturbance is determined. The first addition, which is output from the subtraction unit, only when a coefficient change is determined to have been determined that the deviation between the static characteristic compensation signal and the signal corresponding to the signal based on the addition result from the first addition unit is greater than a predetermined value. A difference signal between the signal based on the output signal from the unit and the static characteristic compensation signal,
By applying to the feedforward model, the coefficient of the multiplication unit in the static characteristic compensation feedforward model is corrected so that the difference signal becomes substantially zero, and when the coefficient change is not necessary, the current value in the multiplication unit The coefficient is held so that the feedword control can be performed by the coefficient.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. In this embodiment, the adjustment output signal of the feedback control system is of the position type.

In FIG. 3, as will be described later in detail, the output from the subtraction unit 43 is larger than a predetermined value, that is, the difference between the static characteristic compensation signal Dn and the signal A is larger than a predetermined value,
When the gain of the feedforward model 38 is adjusted and when the disturbance is in a stable state, that is, the deviation en, the output of the difference unit 51 and the output of the incomplete differentiator 42 are within a predetermined range. When contact 62a
Is closed to adjust the gain of the FF model 38, and at the same time, the contacts 62b and 62b 'are opened and FF control is not performed. If the disturbance is not in a stable state regardless of whether the output from the subtraction unit 43 is larger than a predetermined value, the contact 6
2a is opened, the contacts 62b and 62b 'are closed, FF control is executed, and the gain of the FF model 38 is not adjusted. That is,
In FIG. 3, paying attention to the fact that the FF control is not necessarily performed when the disturbance is stable, and when the disturbance is stable and it is necessary to adjust the gain of the FF model 38 (the subtraction unit 43 The FF control is stopped and the gain is adjusted only when the output is larger than a predetermined value.

The embodiment shown in FIG. 3 will be described in detail below.

The process variable PV obtained by measuring the controlled variable X is compared with the target value SV by the comparison unit 31, and the deviation en is adjusted by the adjustment unit 32.
Lead to. The adjusting unit 32 controls P (proportional), I (integral), D
An adjustment operation of any of (differential) operations or a combination is performed. The output signal 32a of the adjusting unit 32 is applied to the control target 36 as the operation signal M via the (first) adding unit 33 and the (second) adding unit 35. In this way, a feedback control system that feeds back and controls the control amount X is configured.

On the other hand, for feed-forward control, the disturbance signal D is input to the calculation unit 39, where the calculation for obtaining the static characteristic compensation amount is performed. The output of the calculation unit 39 is sent to the multiplication unit 40, multiplied by the coefficient in the multiplication unit 40, and the static characteristic compensation signal Dn is obtained.
Becomes In this way, the calculation unit 39 and the multiplication unit 40 form the static characteristic compensation feedforward model 38.

That is, if the formula (4) is transformed, Of these, the first term on the right side is the static characteristic compensation component, and the static characteristic compensation feedforward model 38 obtains this. On the other hand, the second term on the right side is the dynamic characteristic compensation component, It has been multiplied by. Therefore, the dynamic characteristic compensation component is obtained by inputting the output of the static characteristic compensation feedforward 38 to the incomplete differentiator 42, which will be described later, having the transfer function represented by the equation (10).

The static characteristic compensation signal Dn is a difference section 51 which constitutes a position-speed type signal converting section, and a static characteristic compensation component Dn at each sampling and a static characteristic compensation component Dn-1 at the previous sampling are obtained. The difference is obtained, that is, the static characteristic compensation component is converted into the velocity type in this way. Then, after that, the contact 6
It is given to the addition unit 33 via 2b, added with the adjustment output signal 32a in the addition unit 33, and then returned to the position form in the conversion unit 34 to become the signal A.

The static characteristic compensation component Dn also corresponds to the incomplete differentiator 42 and the contact 62.
The signal is added to the signal A in the adder 35 via b '.

On the other hand, the subtractor 43 obtains the difference between the signal A from the adder 33 and the static characteristic compensation component Dn, and this difference is given to the integrator 44 via the contact 62a, while the contact 62a is closed. The above difference is integrated by the integration unit 44, and the integrated value 44a is added to the multiplication unit 40. Then, the coefficient of the multiplication unit 40 is adjusted by the output from the integration unit 44 so that the output of the subtraction unit 43 becomes zero. That is, the process variable PV changes when the disturbance outside the detection target changes. Along with this, the deviation en changes, and the change appears as a change in the signal A. As a result, the output from the subtraction unit 43 changes, and the output is added to the multiplication unit 40 via the integration unit 44.
In the multiplication unit 40, the coefficient is changed by the output from the integration unit 44 so that the output from the subtraction unit 43 becomes zero. In this way, the feedforward model 38 is adjusted so that the signal A and the corrected static characteristic compensation amount Dn are matched.
Will be corrected.

In terms of conversion, as described above, for example, as shown in FIG. 5, it is described that the difference between the operation signal MV and the feedforward model output signal FF is controlled to be substantially zero. Will be described more appropriately with reference to FIGS. 5 to 7.

Also in FIG. 5, as in FIG. 1, the disturbance D is added to the control target through the transfer path having the transfer function GD and affects the measured value PV (control amount X). The influence of this disturbance is removed by the combined control of the FB control and the FF control. That is, FIG. 5 shows the relationship between the FB component, the FF component and the operation signal MV when the FB (feedback) control is combined with the FF (feedforward) control. As can be seen from FIG. 5, the operation signal MV is a combined value of the FF component and the FB component as shown in the following equation.

MV = FF + FB (a) FIG. 6 is a diagram showing a basic concept for explaining how the feedforward model is automatically corrected. As can be seen from FIG. 6, the FF component is obtained from some of the added disturbances, and the measured value PV
The FF control is executed prior to appearing in the above, and the FF component cannot be obtained from other things, and the FB control is executed by appearing in the measured value PV. As a result of the one control, the measured value PV is set to the set value SV. That is, there are various disturbances. For example, in the case of the domestic gas water heater described above, there are various types such as the amount of hot water. However, in general, not all disturbances are incorporated to obtain FF control. Primarily for economic reasons, we have measured some of the major disturbances that have a high impact and not others. Information is obtained from the disturbance to be measured, and FF control is executed with the FF component based on the obtained information. On the other hand, even a disturbance outside the measurement target is added to the control target, affects the measurement value PV, and changes the measurement value PV. This measured value PV is fed back and subtracted from the set value SV to generate a deviation. That is, the disturbance outside the measurement target appears as the FB control output as a result. As a result, the operation signal MV becomes FF or F.
It is represented by the form B. In this case, if the gain of the FF control model is corrected so that the FB component becomes almost zero, the operation signal MV has only the FF component and only the control in advance. That is, the adaptive FF / FB control is performed. In the present invention, based on such an idea, the FF gain is automatically corrected so that the FB component becomes almost zero, and the adaptive FF / FB control is executed.

In FIG. 5, the FF control based on the disturbance may be performed without advance / delay in time, in some cases with advance in time, or in some cases with delay in time. That is, as can be seen from the equation (4) described in FIG. 1, the FF control model transfer function GF is the disturbance gain constant K
It is represented by D, controlled object gain KP, controlled object time constant TP, and disturbance time constant TD. As can be seen from the equation (4), there is no time advance / delay when TP = TD, and time advance compensation is performed when TD> TD, and TP
When <TD, time delay compensation is performed. In reality, there are overwhelmingly many cases of time advance compensation.

Further, as can be seen from FIG. 6, when the FF / FB control in which the FF control and the FB control are combined is ideally performed, MVFF ... (B), that is, the equation (b) is obtained. As can be seen from the equation (a), FB0 (c), that is, the operation signal is almost composed of the FF component, and a slight correction is performed in the FB control component. There is.

The above will be described in detail by taking the case of controlling heating of water to 40 ° C. in the domestic gas water heater described above as zero.

As described above, when the FF / FB control is ideally performed, the MVFF and FB0 are obtained, but the following two cases can be considered as the ideally performed. That is, generally, there are a plurality of factors that may act as a disturbance. For example, the amount of hot water,
These are the tap water temperature, the environmental temperature of the gas water heater, the unit calorific value of the gas, and the water heater efficiency. In the first ideal case,
A case will be described in which only one of these factors acts as a so-called disturbance, and the other factors are constant and do not act as a disturbance. For example, it is assumed that only the amount of hot water acts as a disturbance, and the tap water temperature, the environmental temperature of the gas water heater, the unit calorific value of the gas, the water heater efficiency, etc. are constant. In this case, measure only the amount of hot water,
Calculate how much gas flow is needed to bring the tap water to 40 ° C. If feedforward control is performed based on the calculation, the hot water temperature will be 40 ° C. At this time, the control deviation E becomes zero, and correction by feedback control becomes unnecessary,
After all, MV = FF. This is the first ideal case.

On the other hand, the second ideal case will be described in which all of the above factors act as disturbances. That is, all the factors such as the amount of hot water, the temperature of tap water, the environmental temperature of the gas water heater, the unit calorific value of the gas and the water heater efficiency are accurately measured, and the FF control amount is calculated based on the measurement result. Take control. As a result, the hot water temperature reaches the set value of 40 ° C., no matter which of the disturbances changes. Even in this case, the control deviation E becomes zero, correction by feedback control becomes unnecessary, FB = 0, and eventually MV = FF. This is the second ideal case.

However, as in the first and second ideal cases above,
It is extremely difficult to realize the FF / FB control sufficiently ideally due to various reasons such as economical efficiency and accuracy. That is, in reality, FF / FB control is not ideally performed, and it is necessary to assist FB control. That is, in reality, the FF control model is deviated, the equation (b) is not established, and the FB control component is generated. When the FB control component becomes large, the effect of FF control is attenuated. In order to prevent this, the FB control gain is corrected so that it becomes FB0.

FIG. 7 shows how the influence control characteristic of disturbance changes depending on the composition ratio of the FF component and the FB component in the operation signal MV. It can be seen that when FB = 100% and FF = 0%, that is, when only FB control is performed, the influence of the disturbance is large, but as the FF component approaches 100%, the influence of the disturbance decreases as the FF component approaches.

Therefore, in order to satisfy the equation (b), that is, the operation signal M
If the gain of the feedforward control model is modified so that the difference between the V and FF components becomes substantially zero, the FF / FB control will always be in the optimum state.

If the speed type PID formula is adopted, (c)
This is adopted because it is easier to use FB0 in the formula.

By doing so, as described above, even if the characteristic of the disturbance process changes economically, the optimum FF control effect can always be obtained.

The reason why the set value (SV) and the measured value (PV) match with each other as described above is as follows. As shown in FIG. 5, the FB control is a closed loop control that corrects the result of control. On the other hand, the FF control only predicts and outputs how much the operation signal should be changed in order to suppress the influence of the disturbance D according to the magnitude of the disturbance D, and outputs the open signal. -It is a loop control. Therefore, as described above, in the FF control, the gain of the FF control model is modified to only slightly change the relationship of the FF control output with respect to the disturbance D, and the original set value SV and the measured value PV are matched. There is no intervention in functional FB control. Therefore, the set value SV and the measured value PV are F
The effect of the B control results in agreement.

Further, the reason why the operation signal (MV) and the output signal (FF) of the feedforward model are made to coincide with each other in the stable state is as follows. That is, there is a disturbance
In the transient state where FB control is performed, FB is naturally
The control output is moving and cannot be FB. However, in the stable state, that is, in the state where the disturbance is constant and the FB control is not changed, if MV-FF ≠ 0 is not satisfied, it may be corrected so that MV-FF = 0, and the correct execution can be performed. For this reason, the changing transient state is avoided and correction is performed when the stable state is achieved.

The determination unit 54 closes the contact 62a to make a correction when the control system is in a stable state, and also makes contact with the contacts 62b, 62.
It is supposed to open b '. The determination as to whether or not the control system is in a stable state is performed as follows.

That is, first, the output signal of the subtractor 43 is set to the signal level detector 5
When the signal goes out of the predetermined range, the output of the level detector 55 is turned on and the timer 56 is entered. When a predetermined set time has elapsed from this time, the timer 5
The output signal of 6 is turned on. The output of the timer 56 is input to the logical product section 61.

On the other hand, the changing part of the static characteristic compensating part outputted from the converting part 51 is put into the signal level detecting part 57, and when it is within the predetermined range, the output signal of the detecting part 57 is turned on. The output signal of the incomplete differentiator 42 is the signal level detector 5
8 and the output signal of the incomplete differentiator 42 is within a predetermined range, the output signal of the detector 58 is turned on. Further, the deviation signal output from the comparison unit 31 is guided to the signal level detection unit 59, and when the deviation is within a predetermined range, the output signal of the detection unit 59 is turned on. The output signals of the detection units 57, 58 and 59 are guided to the logical integration 60. Therefore,
The output signal of the AND section 60 is turned on when the change of the disturbance is within a predetermined range, that is, when the change of the disturbance is small, and is added to the AND section 61.

The output of the logical product section 61 is used as a set signal for the memory 62. Therefore, a deviation more than a predetermined value continuously appears between the static characteristic compensation amount of the disturbance compensation and the operation signal (timer 56
Output) and when there is little change in the disturbance (when the AND section 60 outputs), the memory 62 is set by the output of the AND section 61. When set, the output of the memory 62 is turned on, its contact 62a becomes conductive, and its contacts 62b and 62b 'become non-conductive. As a result, the output (deviation) of the subtraction unit 43 is supplied to the integration unit 44 and integrated. The output of the integrator 44 is guided to the multiplier 40 and used to correct the coefficient of the disturbance compensation feedforward model. Meanwhile, during this period, the conversion unit (difference unit)
51, the supply of signals from the incomplete differentiator 42 to the adders 33 and 35 is blocked by the non-conductive contacts 62b and 62b ', and the feedforward control of disturbance is prohibited.

In this way, the coefficient of the feedforward model is automatically corrected, and when the deviation does not reach the predetermined value, the output signal of the signal level detection unit 55 is turned off, and at that moment, the timer 5
The output signal of 6 also turns off, and the output signal of the AND section 61 also turns off. On the other hand, the output of the signal inverting unit 63 is turned on, and when the set time of the timer 64 has elapsed, the output of the timer 64 is turned on and the memory 62 is reset. As a result, the contact 62a becomes non-conductive and the coefficient correction of the feedforward model (correction of the coefficient of the multiplication unit 40) is stopped. On the other hand, the contacts 62b and 62b 'are rendered conductive, and the feedforward control is restarted.

The feedforward model is automatically corrected as described above.

As described above, the contacts 62b and 62b 'are opened when the coefficient kn of the multiplication unit 40 is corrected, but the reason why the contacts 62b and 62b' are opened without being closed will be described below.

(a) If the coefficient kn is corrected while the contacts 62b and 62b 'are closed, the control will be disturbed as follows. That is, as the coefficient kn is modified, the output Dn (= k
n × D) changes, and accordingly, the output of the difference unit 51 and the output of the incomplete differentiation unit 42 change. When the output of the difference portion 51 changes, the change is caused by the contact 62b in the closed state,
The addition unit 33 and the conversion unit 34 reach the addition unit 35. Further, the change in the output of the incomplete differentiator 42 is also transmitted to the adder 35 via the contact 62b 'in the closed state. Thus, if the coefficient kn of the multiplication unit 40 is changed,
Although the control is in a stable state, the addition unit 35
The operation signal M, which is the output from, also changes. That is, if the coefficient kn of the multiplication unit 40 is changed, the control is disturbed even though the control is in the stable state.

(b) The adjustment of the coefficient kn of the multiplication unit 40 is performed by the subtraction unit 4
It is performed so that the output from 3 becomes zero. That is, the signal A output from the conversion unit 34 and the static characteristic compensation signal Dn (= kn × D) output from the multiplication unit 40 are A =
Dn * D) so that A = Dn.
In order to realize this, the output from the subtraction unit 43 is added to the multiplication unit 40 via the integration unit 44, the coefficient kn is changed, and the static characteristic compensation signal Dn is changed. At this time, the contact 62
When b is closed, the signal A is changed according to the change of the compensation signal Dn.
Also changes and A = Dn does not hold. On the other hand, if the contact 62b is opened, the compensation signal Dn can be changed while keeping the signal A as it is.
Therefore, if the contact 62b is opened, A = Dn can be set.

(c) Then, after the correction of the coefficient kn is completed, the contacts 62b, 6
When 2b 'is closed, the effect of the modification does not appear.

After that, when the disturbance D changes, the FF control is executed based on the new correction coefficient kn. For this reason,
The contacts 62b and 62b 'are opened at the time of correction.

In the above embodiment, the adjustment output signal 32a is of the speed type. However, in the case of the position type, the speed type / position type signal conversion unit 34 and the difference unit 51 of FIG. 3 are omitted and the output of the addition unit 33 is omitted. May be used as it is as the signal A, and the static characteristic compensation component Dn may be added as it is to the adding section 33 via the contact 62b.

Further, in the above embodiment, when the control deviation en, the change in proportional compensation and the amount in phase compensation are smaller than the respective predetermined values, it is assumed that the control system is in the stable control state with less disturbance, and the feedforward model is corrected at that time. However, as shown in FIG. 4, the output signal of the conversion unit 14 may be incompletely differentiated by the incomplete differentiation unit 35, and when it is smaller than a predetermined value, it may be corrected as if the control is in a stable state. .

In each of the above embodiments, each component of the control system may be of an analog type, a digital type, may be formed of individual parts, or may be formed of a programmed computer. .

Further, in each of the above embodiments, not only the static characteristic compensation but also the dynamic characteristic compensation is performed by the feedforward control, but the present invention can be applied to the case where only the static characteristic compensation is performed. In this case, the incomplete differentiator 4 in FIG.
2, the addition unit 35 and the like may be removed.

Further, the bias may be modified instead of modifying the coefficient of the feedforward model.

ADVANTAGES OF THE INVENTION According to the present invention, a feedforward control mechanism is added to a feedback control system in a process control device, and a characteristic of a static characteristic compensation feedforward model in the feedforward control mechanism is corrected to adjust the feedback control system. A sum signal of an output signal and a signal based on the output signal from the model, an output signal from the model,
Since the difference is set to be substantially zero, the influence of the disturbance can be performed without the feedback control in the feedback control system. Further, in the present invention, since the correction of the feedforward model is performed in a stable state in which the disturbance is small, the fluctuation of the adjustment output signal from the feedback control system is small, and the rapid control is executed more correctly. can do.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional control device, FIG. 2 is a piping diagram showing a heat exchanger equipped with the conventional control device, and FIG. 3 is a control device used for carrying out a correction method according to the present invention. FIG. 4 is a block diagram showing the same, FIG. 4 is a block diagram showing a control device used for carrying out another embodiment of the present invention, and FIGS. 5 to 7 are a block diagram and a diagram for explaining the principle of the present invention. 12 ... Adjusting unit, 14 ... Velocity type signal-position type signal converting unit, 16 ... Control object, 19, 20 ... Computing unit, 21 ...
... Position type signal-speed type signal conversion unit, 22 ... Incomplete differentiation unit, 23 ... Subtraction unit, 24 ... Integration unit

Claims (3)

[Claims] 1. A static characteristic compensation from a disturbance for canceling the influence of the disturbance in a process control device, wherein a feedforward control mechanism for preventing the influence of the disturbance in advance is added to a feedback control system. A method for correcting a static characteristic feedforward model, which comprises a calculation section for calculating a minute and a multiplication section for multiplying an output from the calculation section by a coefficient to generate a static characteristic compensation signal, wherein at least an element that causes disturbance is One is detected and given to the static characteristic feedforward model, and a signal based on the static characteristic compensation signal calculated by this model is added to the adjustment output signal of the feedback control system by the first adding unit, and a signal based on the addition result is obtained. , A dynamic characteristic compensation signal obtained from the static characteristic compensation signal is added in a second adding section, and a signal based on the signal obtained in the second adding section is added to a control target. The control amount output from the control target is used as a feedback signal in the feedback control system, and the deviation determining unit determines whether the feedback signal and the control amount are the desired values by determining whether or not the system is in a stable state with less disturbance. Based on the deviation of the static characteristic compensation signal and the calculated value of the static characteristic compensation signal, is determined to be a stable state with less disturbance, and is based on the addition result from the static characteristic compensation signal and the first adding unit. A signal based on the output signal from the first addition unit and the static characteristic compensation signal output from the subtraction unit at that time when it is necessary to change the coefficient when it is determined that the deviation from the signal corresponding to the signal is larger than a predetermined value. And a multiplying unit in the static characteristic compensation feedforward model so that the difference signal becomes substantially zero. The method for correcting a feedforward model is characterized in that the coefficient is corrected, and the coefficient is held so as to perform the feedword control by the current coefficient in the multiplying unit when the coefficient is not required to be changed. 2. The method according to claim 1, wherein when the adjustment output signal of the feedback control system is a position type, the static characteristic compensation signal is directly added to the first adding section, and a feedback control system is provided. When the adjustment output signal of is a velocity type signal, the velocity type signal obtained by converting the static characteristic compensation signal to the velocity type signal is added to the first adding unit, and the output signal from the first adding unit is added to the position type signal. The method of adding the position-type signal converted to the above to the second adder and the subtractor. 3. The method according to claim 1, wherein the dynamic characteristic compensation signal is obtained by incompletely differentiating an output of the static characteristic compensation feedforward model.