JPS6142284B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to process control, and particularly to a process control device (system) suitable for controlling a controlled object including dead time characteristics. In conventional process control, if there is a long dead time relative to the delay time constant of the process, control becomes difficult with a feedback control system using a normal PID controller as shown in FIG. For this reason, we have used Smith's control system (Figure 2), which has a minor loop around the main controller that has a model that simulates the process dynamic characteristics, as a controller, and a control system with the control calculation characteristics shown in Figure 3. equipment may be used. However, the symbols in these figures are as follows. G _p e ^-LPS : Transfer function representing the dynamic characteristics of the controlled process G _p : Process transfer function excluding dead time L _p : Process dead time S: Laplace operator G _c : Transfer function representing the characteristics of the control calculation unit G _cs : Transfer function of the main controller in Smith's controller G _p M : Transfer function of a model simulating the process characteristic G _p L _p M : Simulated value of process dead time G _ck : Main controller of the controller in Fig. 3 Transfer Function of Controller However, when using these control devices, if control parameters are determined with focus on controllability with respect to target value changes, controllability with respect to disturbances will deteriorate (recovery will be slow). On the other hand, if control parameters are determined with attention to controllability against disturbances, controllability deteriorates when the target value is changed (overshoot occurs and vibrations tend to occur). For this purpose, the following measures have been conventionally taken. (1) Decide control parameters by paying attention to either target value change or disturbance, and ignore deterioration in controllability in the other case. (2) By using the intermediate value between the optimal parameter value when changing the target value and the optimal parameter value for disturbance, it is not optimal for either changing the target value or for disturbance, but it achieves controllability that is a compromise between the two. . (3) Normally, control parameters are set so that optimal control can be obtained against disturbances, and when it becomes necessary to change the target value, set the parameters to be optimal for target value change control and change the target value. I do. After the process has settled to the new target value, the control parameter values for disturbance control are returned again. In this case, there are disadvantages in that the operation requires manpower, operation errors are likely to occur, and it is not possible to deal with disturbances when changing the target value. (4) It is equipped with two types of control calculation units, one for target value change control and one for disturbance control, or is equipped with two types of control parameter sets, and is normally controlled in disturbance control mode, and for target value change control. When the occurrence is detected, it automatically switches to the calculation section for target value change control,
A controller is used that switches to a calculation section for disturbance control when it is determined that the process has settled to a new target value. In this case, two types of calculation control units are required.
In addition, the bumpless switching and the automatic determination mechanism for the target value change control period are complicated and expensive. Also, as in the above-mentioned item (3), there was a drawback that it was impossible to deal with disturbances added during target value change control. Furthermore, when a PID controller is used in a normal control system as shown in FIG. 1, it is known how to determine and adjust the values of its control parameters (proportional gain; integral time; differential time). However, when a PID controller is used as the main controller of the Smith controller shown in Figure 2, the desirable values of the control parameters are different from those of the system shown in Figure 1, and the physical relationship between the parameter values and the response waveform of the control system is The correspondence between the two parameters was no longer clear, making parameter adjustment extremely difficult. An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a control system that can control a controlled object including dead time even when changing a target value.
Even when controlling against disturbances with a constant target value,
We are trying to obtain a process control device (system) that controls in the optimal mode. In addition, by simply setting the time constant of the waveform, which defines the control response waveform due to target value changes and disturbances, as an adjustment parameter, the controlled variable response waveform of the controlled process is automatically controlled to the desired shape.
The objective is to obtain a process control device (system) in which control parameters can be easily set and adjusted. An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a conceptual block diagram of an embodiment of the present invention. 11 is a target value input filter that inputs a target value signal; 12 is a deviation calculation circuit that compares the output of the target value input filter with the control amount of the controlled process 13 and outputs a deviation; and 14 calculates the control amount from the deviation signal. A control calculation unit calculates the manipulated variable for operating the controlled process to match the target value, 15 is an operating end that inputs the disturbance and the manipulated variable to operate the controlled process, and includes a deviation calculation circuit and a control calculation unit. This is a control device (system) having a configuration in which a target value input filter 11 of a transfer function _GF is added to a target value signal input part of a controller consisting of a controller. Here, the target value input filter 11 has a transfer function of first-order lag: 1/1+T _F1 S first-order lag + first-order lag lead: 1/1+T _F1 S・1+T
It has characteristics such as _F3 S/1+T _F2 S, and is realized by analog circuits and digital calculations. That is, in a control system using this control device (system), the transmission relationship of the control amount with respect to disturbance is G _p e ^{- LPS} /1 + G _c G _p e ^{- LPS} ...(1), and the control amount is controlled against disturbance with a constant target value. When the target value input section filter 11 is under control, the target value input section filter 11 is not dynamically involved in the control at all. Therefore, the transfer function G _c that defines the configuration and characteristics of the control calculation unit 14 can be arbitrarily determined so as to realize optimal control against disturbances. Next, when G _c is determined as described above, the transfer function of the control amount for changing the target value is G _F・G _C・G _p e ^-LPS /1+G _C G _p e ^-LP
S ...(2). Therefore, the target value input section filter 11
uses one whose characteristics (transfer function G _F ) are designed to optimize the response of this control system when changing the target value. As a result, this control device (system) operates in the optimal control mode even when changing the target value. Furthermore, in order to facilitate the parameter setting of the control calculation section 14 and the target value input section filter 11, an analog setting device such as a potentiometer, a pulse generator; a digital switch;
Keyboards; typewriters; digital setting devices such as CRT light pens. Alternatively, when signals corresponding to time constants are sent from an external host control device, etc., the response waveform time constant setting section 16 of a retainer, etc. that holds those signals and the control calculation are performed from the set time constants. A parameter calculation conversion section 17 is provided which converts the control parameters of the section 14 (e.g., proportional gain; integral time; differential time) into the filter time constant of the target value input section filter 11, and defines a response waveform to a target value change or disturbance. Once the time constant is set, the parameters of the arithmetic control section 14 and the target value input section filter 11 are automatically adjusted. Furthermore, if the process dynamic characteristics fluctuate and the control device (system) is desired to automatically deal with this fluctuation, the configuration shown in FIG. 6 can also be adopted. That is, in this case, a process dynamic characteristic identification section 18 is provided, and the process dynamic characteristic identification calculation is performed by inputting the state quantities of the process and the output of the control device. The process parameters (process gain process delay time constant; dead time, etc.) obtained as a result are received by the parameter calculation conversion unit 17 and the control calculation unit 14, and the process model parameters contained therein are automatically converted into the actual process state. It is now possible to match the The operation of the device of the present application having such a circuit configuration will be explained in detail with reference to the drawings. Assume that the dynamic characteristics of the controlled process are "first-order delay + dead time", that is, the transfer function can be approximated by equation (3) or this form. G _p e ^-LPS = K _p /1+T _p Se ^-LPS (3) where K _p is the process gain, T _p is the process delay time constant, and L _p is the process dead time. (S:
Laplace operator) This controlled object is controlled by a controller, for example, the Smith controller type controller _GC shown in Fig. 2, and the transfer function shown in equation ( ₄ ) is PID
When a controller or PID calculation unit is adopted, G _CS = K _S (1+1/T _SL S + T _SD S) ...(4) The control parameter is expressed by the following formula (T _D will be described later).

[Table] If the PID calculation characteristics are G _CS = K _S (1+1/T _ST S) (1+ T _SD S)...(
6) If

If the control parameters are set by calculation using [Table], the control amount response waveform will be as shown in FIG. 7 when a step-like disturbance is added to the process. In FIG. 7, the feedback control system cannot control the period when time t<2L _P due to process dead time, and the control amount response waveform during this period is uniquely determined by the process characteristics. Therefore, determine the desired exponential function waveform for the waveform after t>2L _P , and calculate the time constant T _D that defines that waveform as (5)
If the PID parameter value is calculated by substituting it into Equation or Equation (7), and the PID controller set to this value is used as a controller with the configuration shown in Figure 2, the transfer function of the controlled variable with respect to disturbance will be: G _p e ^-LPS /1+G _CS G _p e ^-LPS = (1-1+T _K2 S/1+T _D Se ^-LPS ) G _p e ^-LP
S ...(8) T _K2 = (1-e ^- L _P /T _P )・T _P +e ^- L _P /T _P・T _D
...(9) Thus, a response waveform with a damping characteristic as shown in FIG. 7 is realized in response to a step-like disturbance. Furthermore, G _PM (1
-e ^-LPMS ) is a process model calculation unit having characteristics obtained by subtracting process characteristics from process characteristics excluding dead time. That is, this control device (system) controls the controlled object against the disturbance in a response waveform mode designated as the most desirable for the step-like disturbance. In addition, when using the controller of the figure 3 type instead of the controller of the figure 2, the main control calculation unit (G _CK ) should have the characteristics of a first-order lag/lead filter.

[Table] 〓(11)

Claims (1)

[Scope of Claims] 1. Deviation calculation means for calculating the deviation between the target value and the controlled amount, and a transfer function that is set so that the response of the controlled amount to the disturbance has a desired damping characteristic. control calculation means for calculating a manipulated variable that makes the controlled variable match the target value by performing a control calculation; 1. A process control device comprising: a target value input filter means in which a transfer function to be adjusted is set. 2. The process control device according to claim 1, wherein the transfer function set in the target value input filter means has at least first-order lag characteristics. 3. The process control device according to claim 1, wherein the transfer function set in the target value input filter means has a first-order lag characteristic and a first-order lead-lag characteristic. 4. Controlling the deviation based on a deviation calculation means that calculates the deviation between the target value and the controlled amount, and a transfer function that can change the control parameter value so that the response of the controlled amount to the disturbance has a desired damping characteristic. control calculation means for calculating a manipulated variable that causes the controlled variable to match the target value by performing a calculation; a target value input filter means capable of changing a control parameter value for controlling the process; and a response of the controlled variable when the target value changes in a stepwise manner, and a response of the controlled variable in response to a stepwise change in the disturbance, based on characteristics of the process. A response waveform time constant setting means for setting response waveform time constants so as to match each other, and a function of changing control parameter values of the control calculation means and the target value input filter means based on the output of the response waveform time constant setting means. and a parameter calculation conversion means having a parameter calculation and conversion means, and by setting the response waveform time constant, the response of the control amount is automatically controlled to the response waveform specified respectively in response to the change in the target value and the disturbance. Characteristic process control equipment.