JPH0713604A - Controller - Google Patents

Abstract

PURPOSE:To prevent the overshooting of a measured value of a controlled variable by deriving a differential value by a specific differential expression with regard to the controlled variable measured in a process, so that this value operates in the direction for decreasing the deviation of a target set value and the measured value. CONSTITUTION:By a differential arithmetic means 1, a differential value (p) is derived with regard to a controlled variable PV of a temperature, etc., measured in a process. In this case, a differential calculating expression is K1Xd(PV)/dt. k1 is a variable number being near '1', and used as a correction coefficient for deriving an effective set value. This value (p) is a value being proportional to a variation rate of a measured value at a measuring time, therefore, becomes a large value, when a variation of the measured value is large. This value (p) operates in the direction for decreasing the deviation between a target set value SV and a measured value PV. An effect for decreasing a control operation executed by decreasing this deviation can be compensated by a PID arithmetic operation. The largest effect to be taken notice of is the fact that the measured value PV approaches the target set value SV, this differential value (p) becomes small and is annihilated at the time when the former reaches SV.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is
The present invention relates to a controller used to control a process amount such as temperature and flow rate to a predetermined value, and particularly to a controller used to perform control while preventing overshoot.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing the adjustment calculation function of a PID controller. The adjustment calculation circuit 4 performs proportional, integral, and differential calculations (PID calculation) on the deviation between the value of the measured value PV, which is the control value of the process, and its target set value SV, so that the deviation becomes zero. Is output. It shows the main adjustment functions built into an industrial process controller or control computer.

In a batch process in which the charging of raw materials, the reaction, and the discharge of products are repeated in a relatively short time, such as the temperature control of a polymerization tank, the measured value does not overshoot and a predetermined value is reached in a short time after the process starts. Often required to reach temperature. In addition, the target set value is sometimes changed during steady operation, but it is required that this operation does not become a control disturbance. For such uses,
Various attempts have been made to improve the above PID controller.

[0004]

As one of the controllers for preventing overshoot, a PID control controller with a batch switch is used. In this operation, for example, when the temperature approaches the target set value, the switch is operated to change the operation amount. However, although it is a function that works effectively when the process is started up, it has no effect on preventing overshoot in the target setting value changing during steady operation or in the temperature cooling process. Further, there is no effect on the control when the control deviation is large at the start-up or the cooling process.

On the other hand, in order to prevent overshoot during steady operation, a PID having a variable set value filter function is provided.
A controller may be used. This action is effective only when the set value is changed. However, the effect cannot be expected when a large control deviation occurs, such as when the process is started or stopped. In addition to this, it is considered to use a controller applying fuzzy theory to prevent overshoot, but its construction requires many empirical factors and is not general.

Therefore, according to the present invention, when the batch process is started or stopped as described above, or when the target set value is changed during the operation of the continuous process, the measured value of the control amount overshoots. It is an object of the present invention to provide a controller that can obtain a stable control result against disturbances and the like, without doing so.

[0007]

According to the present invention, there is provided a differential operation means for performing a differential operation with a process amount such as pressure or temperature of a chemical process such as a reaction tank as an input and outputting the differential operation means from a target set value. First subtraction means for subtracting the output and outputting the effective set value, second subtraction means for subtracting and outputting the measured value from the output of the first subtraction means, and output of the second subtraction means as deviation inputs , And an adjustment calculation means for performing an adjustment calculation and outputting an operation amount for driving a control valve or the like.

[0008]

In the present invention, the differential value p is obtained for the controlled variable PV such as the temperature measured in the process by the differential operation means. This value p is a value proportional to the change rate of the measured value at the measurement time, and therefore takes a large value when the measured value change is large. This value p acts to reduce the deviation between the target set value SV and the measured value PV. However, the effect of reducing this deviation to reduce the adjusting operation can be compensated by the following PID operation operation. The most noticeable effect is the differential value p as the measured value PV approaches the target set value SV.
Is smaller and has reached SV, it has disappeared. Due to this effect, the measured value reaches the target set value without overshooting.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the adjustment calculation function of the present invention. First, the codes used will be described. SV represents a target set value. For example, it is a target value for adjustment of temperature or the like in the process (represented by the characteristic expression G (t)).

PV is an amount controlled in the process and is a measured value of a process amount such as temperature actually measured. SSV is an effective set value and is expressed by the following equation. SSV = target set value SV-coefficient K ₁ × differential value of measured value PV (p) Formula 1 DV represents a control deviation. The value is set as x and expressed by the following formula.

X = SSV-PV. Formula 2 MV is a manipulated variable. The value is represented by y. It is the amount of adjustment calculation performed on the value x of the control deviation DV. Reference numeral 1 denotes a differential operation means, which performs the operation of Expression 3 on the measured value PV and outputs the differential value (p).

P = K ₁ × d (PV) / dt Equation 3 The coefficient K ₁ is a variable number close to 1 unlike the gain K ₂ of the controller of Equation 6, and is treated as a correction coefficient for obtaining the effective set value SSV. 2 is a first subtraction means. Target set value SV
Then, the output (p) of the differential operation means 1 is subtracted from the output and output as the effective set value SSV.

SSV = SV-p Formula 4 3 is the second subtraction means. The measured value PV is subtracted from the effective set value SSV and output as the value x of the control deviation DV. x = SSV-PV = SV-p-PV Equation 54 is an adjustment calculation means. The value x of the deviation DV is input, the specified adjustment calculation is executed, and the manipulated variable MV is output. The value is represented by y. Normally, it outputs in response to an electric signal of 4-20 mA, and drives the operating end of a control valve or the like.

An example of the adjustment calculation formula is shown in formula 6. y = K ₂ {x + 1 / T _I · ∫xdt + T _D · dx / dt} Equation 6 The first term of the equation is the proportional equation (P), the second term is the integral equation (I), and the third term is the differential equation (D). Usually first
Use a combination of terms and others. K ₂ is the gain of the controller and takes a value of 100 × 1 / proportional band%.

T _I is the integration time. T _D is the derivative time. Reference numeral 5 represents a process having a characteristic expression G (t). This controller is characterized in that a differential operation means 1 and a first subtraction means 2 are added before the deviation input of the PID operation controller shown in FIG. 2 which is normally used.

The PID operation controller is similar to the form in which only the differential operation (D) in FIG. 2 is preceded, but the differential coefficient K ₁
Is a variable number close to 1 unlike the gain K ₂ of the controller of Expression 6, and is used as a correction coefficient for obtaining the effective set value.
By doing so, a specific operation is performed. Next, the operation is
It will be described based on.

The differential calculating means 1 obtains a differential value p with respect to the control amount PV such as temperature measured in the process.
The calculation formula is Formula 3. This value p is a value proportional to the change rate of the measured value at the measurement time, and therefore takes a large value when the measured value change is large. This value p acts to reduce the deviation between the target set value SV and the measured value PV, as shown in Expression 5. However, the effect of reducing the adjustment operation by reducing this deviation can be compensated by the next PID calculation operation. The most noticeable effect is that as the measured value PV approaches the target set value SV, the differential value p decreases and S
It means that when it reaches V, it disappears. Due to this effect, the measured value reaches the target set value without overshooting. This effect can be changed by the coefficient K ₁ .

FIG. 3 is a graph showing this operation. It can be seen that as the measured value (PV) approaches the target value (SV), the differential value (p) having the effect of reducing the set value disappears and overshoot is prevented. This operation is simulated by the process of the third-order delay characteristic shown in Expression 7.
However, there was no overshoot and good results were obtained.

G (s) = K _P × 1 / (1 + T ₁ s) × 1 / (1 + T ₂ s) × 1 / (1 + T ₃ s) × e ^−LS Operators Kp process gain of formula 7 s Laplace transform _1. 2 T 1 1-order delay time constant 20~30sec T _{2 2-order} delay time constant 0 to 30 seconds T ₃ 3-order delay time constant 0 to 30 seconds L dead time 10~20sec

[0020]

According to the present invention, the above control arithmetic circuit can be incorporated in an industrial controller, and can also be realized by performing software processing by a program. Since any of the methods makes a very stable operation, there is an excellent effect that a highly reliable controller for preventing overshoot can be easily constructed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an adjustment calculation function of the present invention.

FIG. 2 is a block diagram showing a control calculation function of a PID controller.

FIG. 3 is a conceptual diagram illustrating an adjustment calculation operation of the present invention.

[Explanation of symbols]

 DV control deviation, value is represented by x. The MV manipulated variable and value are represented by y. PV controlled variable value (measured value) SV target set value SSV effective set value G (t) process characteristic formula expressed in time function s Laplace operator G (s) process characteristic formula after Laplace conversion

Claims (1)

[Claims] 1. A differential operation means for performing a differential operation using a measured value signal (PV) from a process as an input, and a first subtraction means for subtracting an output of the differential operation means from a target set value and outputting an effective set value. A second subtraction means for subtracting the measured value from the output of the first subtraction means, and an adjustment calculation means for performing an adjustment calculation and outputting a manipulated variable using the output of the second subtraction means as a deviation input, The controller, wherein the differential operation means performs the following operation. The differential operation expression K ₁ × d (PV) / dt K ₁ is a variable number close to _{1 and} is used as a correction coefficient for obtaining the effective set value.