CN115480478A - A DMC-PID-based process control method with constant speed and variable temperature - Google Patents

Abstract

The invention provides a constant-speed and variable-temperature process control method based on a DMC-PID technology. Aiming at the nonlinear characteristic of the heating furnace, based on the characteristic that the PID controller can improve the dynamic response of the controlled object, the PID controller is adopted in the control system secondary loop to reform the controlled object into a linear generalized object. And acquiring a system step response model based on the generalized object. Aiming at the problem of poor tracking performance in the control process, based on the characteristics of DMC algorithm advance predictability and optimal control, a DMC controller is adopted in a main loop to control a generalized linear object consisting of a PID controller and a heating furnace, static-error-free control is realized, the problem of slow system response in the initial stage of temperature rise control is solved, and the adjusting time is shortened. The invention can improve the tracking characteristic of the control process, effectively reduce the static error and improve the response speed of the system.

Description

A DMC-PID-based process control method with constant speed and variable temperature

technical field

The invention relates to a constant-speed variable-temperature process control method based on DMC-PID technology, which belongs to the field of process control.

Background technique

The heating process is stable without overshoot, which is of great significance to the precise control of the heating furnace temperature and temperature change rate. At present, the most commonly used algorithm and control unit for the temperature control of the heating furnace is the PID control module. PID control is simple in application and easy to implement, but it is difficult to tune the controller parameters, and the control effect on the controlled object with strong nonlinearity is not good. PID control has the problem of poor temperature tracking of the static difference between the measured value and the set value in the process of constant temperature rise control. The static difference between the measured value and the set value will affect the initial stage of the heating furnace in the heating process. And the response effect of the end stage, there is a problem of poor linearity of the heating curve in the initial stage, and there is a problem that the maximum temperature value required by the experiment cannot be reached in the end stage.

Contents of the invention

Aiming at the problems of poor tracking and poor control performance of the above-mentioned control method in the process of constant-speed heating of the heating furnace, the present invention proposes a DMC-PID control device for the process of constant-speed heating of the heating furnace.

The technical scheme that the present invention adopts for realizing the above object is: a kind of constant speed variable temperature process control method based on DMC-PID, the temperature of heating furnace is controlled by predictive control algorithm, comprises the following steps:

Combining the PID controller and the heating furnace into a generalized object to build a predictive controller;

Obtain the input setting value of the PID controller through the predictive controller;

The PID controller controls the temperature of the heating furnace according to the input set value and the measured actual temperature value.

The PID controller and the heating furnace are combined into a generalized object, and the PID parameters are adjusted by the critical proportionality method.

The construction of the predictive model includes the following steps:

Combining the PID controller and the heating furnace as a generalized object, the dynamic matrix of the predictive controller model A={a ₁ ,a ₂ ,…,a _N } is obtained by using the finite impact response test. The parameters completely describe the dynamic information of the heating furnace, a _i represents the i-th step response coefficient, i=1...N, N represents the model length, the model length is greater than the adjustment time of the controlled object heating furnace, and the measured lag time value t _d ; Set the linear temperature rise rate as v, formulate a linear temperature rise trajectory, maintain the set value at room temperature for a time greater than 2 times t _d , and then increase linearly at the rate v; complete the construction of the predictive controller.

Obtaining the input set value of the PID controller by the predictive controller comprises the following steps:

得到下一时刻输出预测值

According to the predictive controller, the temperature predictive control increment Δu _M (k) at the current moment k, and the initial output predictive value at the current moment

Get the output prediction value at the next moment

Measure the actual temperature output value y(k) at the same time, and make a difference between the two to obtain the prediction error e;

h为N维校正向量，取值均为1；

进行移向操作后得到下一时刻的初始输出预测值：

其中S为移项矩阵；The output prediction value is corrected by the prediction error, and the corrected output prediction value is

h is an N-dimensional correction vector, and the values are all 1;

After performing the moving operation, the initial output prediction value at the next moment is obtained:

Where S is the transposition matrix;

第一项为输出误差系数，是线性升温设定值与输出预测值的平方和；第二项为控制增量系数，是控制增量平方和；极小化输出误差系数和控制增量系数的两个性能指标，计算出最优控制增量

其中权系数构成的对角阵Q、R分别称为误差权矩阵和控制权矩阵；performance optimization function

The first item is the output error coefficient, which is the sum of the squares of the linear temperature rise set value and the output predicted value; the second item is the control increment coefficient, which is the sum of the squares of the control increment; the minimum output error coefficient and the control increment coefficient Two performance indicators to calculate the optimal control increment

Among them, the diagonal matrix Q and R composed of weight coefficients are respectively called error weight matrix and control weight matrix;

The actual control variable u ₁ (k+1)=u ₁ (k)+Δu _M (k+1) at the next moment is formed as the input setting value of the PID controller.

The PID controller controls the temperature of the heating furnace according to the input set value and measured actual temperature value, including the following steps:

The PID controller obtains the control quantity u ₂ of the heating mechanism according to the input setting value and the measured actual temperature value, so that the heating mechanism performs the heating operation of the heating furnace.

A DMC-PID-based constant-speed variable-temperature process control device includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement a DMC-based process control device when the computer program is executed. -PID constant speed variable temperature process control method.

A computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, a DMC-PID-based constant-speed variable-temperature process control method is realized.

The present invention has the following beneficial effects and advantages:

The PID controller is used in the sub-loop of the control system to improve the dynamic response characteristics of the controlled object and effectively improve the linearity of the controlled object. Through the step response test, it can be obtained that the generalized object composed of the PID controller and the heating furnace is a linear object. . Adopting DMC controller in the main circuit can realize the non-static control of the generalized linear object composed of PID controller and heating furnace. Finally, a feed-forward controller is introduced to improve the slow change of the control quantity in the initial stage through feed-forward compensation and reduce the adjustment time of the control system. The invention has the advantages of high control precision, good setting value tracking performance, lower initial effective temperature, and expanded effective temperature range.

Description of drawings

Figure 1 is a schematic diagram of the structure of the DMC-PID control device during the constant-speed heating process of the heating furnace;

Figure 2 is a schematic diagram of the DMC-PID control device during the constant-speed heating process of the heating furnace;

Fig. 3 is the structural diagram of the DMC-PID control method in the constant-speed heating process of the heating furnace;

Fig. 4 is a flow chart of the DMC-PID control method in the constant-speed heating process of the heating furnace.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, a control device for precisely controlling the temperature change rate of a heating furnace includes three parts: an input and output unit, an embedded DMC-PID control unit, and an execution unit.

The input and output unit includes a temperature sensor, an A/D conversion short circuit and anti-interference circuit, and a filter circuit. Thermal resistance, thermocouple and A/D conversion circuit are connected to convert various thermal resistance and thermocouple signals into voltage and current signals, and the output terminal of the A/D conversion circuit is connected to the anti-interference circuit to realize anti-surge and anti-series mode , anti-common mode, anti-cycle drop, anti-static, anti-group pulse, etc., the filter circuit transmits the pure digital signal to the DMC-PID control unit; the given control signal is output through the current after the embedded DMC-PID control unit calculates , Voltage pulse output, and relay output to the execution unit.

The execution unit includes a phase modulation control module for controlling the heating of the heating wire and a relay control module for controlling the cooling of liquid nitrogen. The phase modulation control module includes a main circuit thyristor and a phase shift control circuit, and the relay control module includes a relay and a solenoid valve. Through the phase modulation control module, the control quantity of the heating controller is converted into a voltage of 4-20mA/0-10mA/0-20mA current, and the voltage of the trigger circuit is adjusted for heating. By changing the heating power of the heating wire, the temperature can be adjusted. control effect.

The DMC-PID control unit includes an SPI interface, a filter, a DMC-PID control core algorithm controller, and a PWM module. Conventional parameters enter the control unit through the SPI interface, and enter the control algorithm core controller after being filtered by the filter. The DMC-PID algorithm in the chip is automatically completed, and manual control is used for process control startup, trial operation, or when the system is abnormal. , Manually adjust the valve position output until the abnormality is eliminated, and then switch to automatic control.

The DMC-PID control algorithm of the constant-speed heating process of the heating furnace adopts the cascade control method of the main loop DMC controller and the secondary loop PID controller.

The main circuit DMC controller is characterized in that its controlled object is a generalized object composed of a PID controller and a heating furnace, the controller input is a linear temperature rise set value _wp , that is, the temperature setting reference trajectory, and the output is a temperature prediction control Quantity u ₁ , using dynamic matrix predictive control algorithm. The controller includes a step response model for generalized objects, feedback correction, and roll optimization based on reference trajectories.

The feature of the secondary loop PID controller is that the controlled object is a heating furnace, the controller inputs the temperature prediction control quantity u ₁ of the main loop, and outputs the heating mechanism control quantity u ₂ , and the algorithm adopts a proportional-integral-differential algorithm.

The steps of the DMC-PID control method in the constant-speed heating process of the heating furnace are as follows:

(1) Design the PID controller of the secondary loop, and adjust the parameters of the PID controller.

(2) The PID controller and the heating furnace in step (1) form a generalized object, and a step response test is performed on it to obtain the prediction model of the generalized object, as well as the lag time value t _d ; according to the lag time and the linear heating rate, formulate Linear temperature rise trajectory, that is, the linear temperature rise set value at each moment.

(3) According to the prediction model and the temperature prediction control variable u ₁ , calculate the output prediction value at the next moment, and measure the actual temperature output value at the current moment at the same time, and make the difference between the two to obtain the prediction error;

(4) Correct the output prediction value by the prediction error;

(5) Optimize performance indicators. The output error coefficient is the sum of the squares of the linear temperature rise set value and the output prediction value, and the control increment coefficient is the sum of the squares of the control increments. Minimize the two performance indicators of the output error coefficient and the control increment coefficient, calculate the optimal control increment, take the control increment at the current moment to form the actual control quantity, and use it as the input setting value of the PID controller;

(6) The control quantity u ₂ of the heating mechanism is calculated by the PID controller, and the heating mechanism performs the heating operation of the heating furnace;

(7) Steps (3) to (6) are repeated until the heating process ends.

The present invention takes a constant-speed temperature-rising process of a heating furnace based on a phase-modulating voltage regulation-controlled electric heating wire heating mechanism as an example. The specific implementation of the DMC-PID control method for the constant-speed heating process of the heating furnace is described, and other forms of controllers can be popularized according to the present invention.

The predictive control algorithm is an optimal control algorithm, which minimizes a performance index in each control cycle to obtain the optimal control law. The control quantity obtained by rolling optimization is to pursue the optimal solution under the condition of minimum set value and predicted value to a certain extent. Therefore, the predictive control algorithm can reduce the static difference between the set value and the output value, and realize the control without static difference. Therefore, the main controller is designed as a predictive controller to improve the tracking characteristics of the system. The parameter selection of the main controller DMC controller is carried out according to the device processor capability, the model time domain N=200, the prediction time domain P=200, and the control time domain M=100.

The implementation steps are as follows:

(1) Design the secondary loop PID controller. For the comprehensive nonlinear controlled object of the heating mechanism of the phase-modulating voltage regulator and the room temperature low convection temperature transfer model, it is firstly controlled by PID to form a generalized linear object. The critical proportionality method is used to tune the PID parameters for the controller.

(2) The PID controller and heating furnace in step (1) form a generalized object. The model vector A={a ₁ ,a ₂ ,…,a _N } is obtained by using the finite shock response test, and the selection of the sampling period conforms to Shannon’s theorem, which requires the prediction model parameters to describe the dynamic information of the controlled object as completely as possible, so N is taken as 200, the model step size is 0.25s, and the lag time value t _d is measured; set the linear heating rate as v, formulate a linear heating trajectory, and maintain the set value at room temperature for a time greater than 2 times t _d , and then increase linearly at the rate of v.

计算下一时刻输出预测值

(3) According to the prediction model, the temperature prediction control increment Δu _M (k) at the current time k, and the initial output prediction value at the current time

Calculate the output prediction value at the next moment

Measure the actual temperature output value y(k) at the same time, and make a difference between the two to obtain the prediction error e;

h为N维校正向量，取值均为1。

进行移向操作后得到下一时刻的初始输出预测值：

其中S为移项矩阵。(4) Correct the output prediction value by the prediction error, and the corrected output prediction value is

h is an N-dimensional correction vector, and its value is 1.

After performing the moving operation, the initial output prediction value at the next moment is obtained:

where S is the transposition matrix.

第一项为输出误差系数，是线性升温设定值与输出预测值的平方和；第二项为控制增量系数，是控制增量平方和。极小化输出误差系数和控制增量系数的两个性能指标，计算出最优控制增量

其中权系数构成的对角阵Q、R分别称为误差权矩阵和控制权矩阵。(5)

The first item is the output error coefficient, which is the sum of the squares of the linear temperature rise set value and the output prediction value; the second item is the control increment coefficient, which is the sum of the squares of the control increment. Minimize the two performance indicators of the output error coefficient and the control increment coefficient, and calculate the optimal control increment

Among them, the diagonal matrix Q and R composed of weight coefficients are called error weight matrix and control weight matrix respectively.

Constitute the actual control quantity u ₁ (k+1)=u ₁ (k)+Δu _M (k+1) at the next moment as the input setting value of the PID controller;

(6) The control quantity u ₂ (k) of the heating mechanism is calculated by the PID controller, and the heating mechanism performs the heating operation of the heating furnace;

(7) Steps (3) to (6) are repeated until the heating process ends.

Claims (7)

1. A constant speed variable temperature process control method based on DMC-PID is characterized in that, the temperature of heating furnace is controlled by predictive control algorithm, comprising the following steps: Combining the PID controller and the heating furnace into a generalized object to build a predictive controller; Obtain the input setting value of the PID controller through the predictive controller; The PID controller controls the temperature of the heating furnace according to the input set value and the measured actual temperature value. 2. A kind of DMC-PID-based constant-speed temperature-variable process control method according to claim 1, characterized in that, said PID controller and heating furnace are formed into generalized objects, and the PID parameters are adjusted by critical proportionality method. 3. a kind of DMC-PID-based constant speed variable temperature process control method according to claim 1, is characterized in that: described construction predictive model comprises the following steps: Combining the PID controller and the heating furnace as a generalized object, the dynamic matrix of the predictive controller model A={a ₁ ,a ₂ ,…,a _N } is obtained by using the finite impact response test. The parameters completely describe the dynamic information of the heating furnace, a _i represents the i-th step response coefficient, i=1...N, N represents the model length, the model length is greater than the adjustment time of the controlled object heating furnace, and the measured lag time value t _d ; Set the linear temperature rise rate as v, formulate a linear temperature rise trajectory, maintain the set value at room temperature for a time greater than 2 times t _d , and then increase linearly at the rate v; complete the construction of the predictive controller. 4. a kind of DMC-PID-based constant speed variable temperature process control method according to claim 1, is characterized in that, described obtains the input setting value of PID controller by predictive controller, comprises the following steps: According to the predictive controller, the temperature predictive control increment Δu _M (k) at the current moment k, and the initial output predictive value at the current moment

Get the output prediction value at the next moment

Measure the actual temperature output value y(k) at the same time, and make a difference between the two to obtain the prediction error e;

The output prediction value is corrected by the prediction error, and the corrected output prediction value is

h is an N-dimensional correction vector, and the values are all 1;

After performing the moving operation, the initial output prediction value at the next moment is obtained:

Where S is the transposition matrix; performance optimization function

The first item is the output error coefficient, which is the sum of the squares of the linear temperature rise set value and the output predicted value; the second item is the control increment coefficient, which is the sum of the squares of the control increment; the minimum output error coefficient and the control increment coefficient Two performance indicators to calculate the optimal control increment

Among them, the diagonal matrix Q and R composed of weight coefficients are respectively called error weight matrix and control weight matrix; The actual control variable u ₁ (k+1)=u ₁ (k)+Δu _M (k+1) at the next moment is formed as the input setting value of the PID controller. 5. A kind of DMC-PID-based constant speed variable temperature process control method according to claim 1, characterized in that, said PID controller controls the heating furnace temperature according to the input set value and measured actual temperature value, comprising the following step: The PID controller obtains the control quantity u ₂ of the heating mechanism according to the input setting value and the measured actual temperature value, so that the heating mechanism performs the heating operation of the heating furnace. 6. A constant speed variable temperature process control device based on DMC-PID, characterized in that it includes a memory and a processor; the memory is used to store a computer program; the processor is used to execute the computer program when , to realize a kind of DMC-PID based constant speed variable temperature process control method as described in any one of claims 1-5. 7. A computer-readable storage medium, characterized in that, a computer program is stored on the storage medium, and when the computer program is executed by a processor, one of the methods described in any one of claims 1-5 is realized. A constant speed variable temperature process control method based on DMC-PID.

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