CN115808872A - PID parameter self-tuning algorithm for temperature control - Google Patents

Abstract

The invention aims to provide a PID parameter self-tuning algorithm for temperature control, which can effectively avoid large overshoot, ensure the stability of temperature and has high tuning speed. The method comprises the steps of executing self-tuning when equipment starts temperature control, gradually changing the temperature in the controlled environment by recording the time of reaching the temperature limit value and the target temperature when the temperature is regulated at full power, executing output variable excitation to a temperature control module according to an excitation function after the target temperature is reached, then collecting the actual temperature limit value of the controlled environment and the time of returning to the temperature limit value after the target temperature is reached, and calculating PID control parameters according to the limit value of the actual temperature, the maximum excitation, the temperature limit value, t0, t1 and t2 and the control period TC of a controller and by combining a Ziegler-Nichols method. The invention is applied to the technical field of PID control.

Description

PID parameter self-tuning algorithm for temperature control

Technical Field

The invention is applied to the technical field of PID control, and particularly relates to a PID parameter self-tuning algorithm for temperature control.

Background

For products or places which are sensitive to the environmental temperature, in order to ensure that the products or articles in the places cannot be in the form or go bad due to the change of the temperature, the temperature of the places needs to be strictly controlled, such as places with strict temperature control requirements, such as a granary, a greenhouse and the like, and also such as a raw material melting and heat insulation structure in injection molding equipment. Most of the existing temperature control devices adopt a PID controller to automatically adjust the temperature basically so as to ensure that the temperature of a place is relatively constant.

The conventional temperature PID control parameters mainly comprise a step open loop self-setting method, a step closed loop self-setting method, a relay self-setting method and a relay feedback self-setting method.

The step open-loop self-setting method comprises the steps of applying steps to input and waiting until a steady state is reached (process variables are kept unchanged), supposing that a user can model any process into first-order lag and pure dead time, testing the dead time Td, the time constant T and the process gain K value of a controller by the step open-loop self-setting method, and multiplying the dead time Td, the time constant T and the process gain K value according to a formula of a heuristic method; for example, most PIDs use the Ziegler-Nichols method. The step closed loop self-setting method is similar to the step open loop method and reaches a steady state faster than the step open loop method. As shown in fig. 1, the relay self-tuning method is to determine information required for tuning a controller by using a set value relay experiment. The relay feedback self-tuning method is a variant of closed loop step test, but is more effective for a system with large time constant.

In the method, the open loop and relay algorithms are greatly overshot, and danger is possibly caused in high-temperature control occasions. Meanwhile, excitation can be suddenly cancelled (or reverse maximum excitation is applied) in setting of an open-loop and relay algorithm, so that noise is brought by sudden change of a system. In addition, the setting time of the relay algorithm is long, and at least two cycles are needed for stabilization.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a PID parameter self-tuning algorithm for temperature control, which can effectively avoid large overshoot, ensure the stability of temperature and has high tuning speed.

The technical scheme adopted by the invention is as follows: the invention comprises the following steps:

and step S1.Setting a target temperature T and a temperature threshold T _thr ；

S2, executing self-tuning;

s3, initializing the initial stage with the initialization time t of 0, and outputting the maximum excitation E by the equipment _Max The temperature control module is used for controlling the actual temperature A in the controlled environment to change to the target temperature T;

s4, when the actual temperature A reaches the temperature threshold T _thr Then, recording the current time as time t0;

s5, recording the current time as a moment T1 when the actual temperature A reaches the target temperature T;

s6, the equipment executes and outputs the variable excitation E to the temperature control module according to the excitation function so as to change the temperature in the controlled environment, and extreme value T of the actual temperature A after the moment T1 is collected _ext (ii) a The excitation function is

Wherein t is the current moment;

s7, when the actual temperature A returns to the temperature threshold T at the moment T0 _thr Then, recording the current time as a time t2;

s8, according to the extreme value T of the actual temperature _ext Maximum excitation E _Max Temperature threshold T _thr T0, t1, t2 and a control period TC, and a Ziegler-Nichols method is combined to calculate PID control parameters.

According to the scheme, the function recorded in the step S6 is used as the excitation function, the excitation signal of the temperature control module can be adjusted in time, and further the situation that the actual temperature exceeds the set upper limit or lower limit due to the fact that the temperature is greatly overshot in the self-adjusting process is effectively restrained, and the fact that articles, raw materials and the like in a controlled scene cannot be damaged or deteriorated is guaranteed. Meanwhile, the excitation function can be adopted to complete parameter setting in a control period, so that the temperature is relatively constant in the setting process, and the temperature control effect is ensured. In addition, the method can also realize no mutation in the setting process, and is favorable for filtering and collecting disturbance when the actual temperature is collected.

Preferably, the temperature threshold T is _thr Including an upper temperature limit T _Max And a lower temperature limit T _min (ii) a When the demand of the controlled environment is a temperature rise, the temperature threshold T in step S4 _thr Is a lower limit of temperature T _min (ii) a When the demand of the controlled environment is cooling, the temperature threshold T in step S4 _thr Is the upper temperature limit T _Max 。

One preferable scheme is that the Ziegler-Nichols method in the step S8 is to calculate a limit gain KU and an oscillation period TU according to the obtained parameters, and to select calculation coefficients of a proportional parameter Kc, an integral action parameter Ti, and a differential action parameter Td according to a temperature change speed of a controlled environment; wherein the ultimate gain KU satisfies

Said oscillation period TU satisfying

。

Preferably, the variation of the excitation function according to the controlled scene and the hardware parameters of the device is

Wherein

,

…

The coefficients are calculated according to the controlled scene and the hardware parameters of the device.

Drawings

FIG. 1 is a working schematic diagram of a conventional relay self-tuning method;

FIG. 2 is a diagram of the variation of the excitation signal according to the first embodiment of the present invention;

fig. 3 is a graph showing the temperature change according to the first embodiment of the present invention.

Detailed Description

The first embodiment is as follows:

in this embodiment, the temperature control mode is temperature rise control, the temperature of the controlled scene is reduced along with the time change, the device includes a temperature sensor for detecting the real-time temperature a in the controlled environment and a heating device for increasing the temperature in the controlled environment, the heating device is controlled by a PID controller or a P controller or a PI controller for heating power, and the heating power is adjusted by adjusting the output excitation signal; and PID algorithm parameter adjustment is carried out through the PID parameter self-tuning algorithm, so that temperature fluctuation is smaller when constant temperature is executed.

As shown in fig. 2 and 3, the PID parameter self-tuning algorithm includes the following steps:

s1, determining the temperature requirement in the environment according to the physical properties or chemical properties of the controlled environment and the articles in the environment, and communicating with equipment through a computer to carry out target temperature T and upper temperature limit T _Max And a lower temperature limit T _min Setting (2);

s2, starting the PID controller to self-tune;

s3, initializing the time t to be 0 at the initial stage of self-tuning, and outputting the maximum excitation E by the equipment at the time _Max When the temperature control module is reached, the temperature control module heats the controlled environment at full power, so that the actual temperature A in the controlled environment is gradually increased;

s4, when the temperature sensor detects that the actual temperature A of the current time reaches the lower temperature limit T _min Then, the system records the current time as the time t0 and keeps the full-power temperature rise;

s5, when the temperature sensor detects that the actual temperature A of the current time reaches the target temperature T, the system records the current time as a moment T1, and stops full-power temperature rise and shifts to a variable temperature mode;

s6, in the temperature changing mode, the equipment executes and outputs the variable excitation E to the temperature control module according to the excitation function, so that the power of the temperature control module is gradually reduced, the temperature in the controlled environment is influenced by the waste heat of the temperature control module to keep the temperature rise for a short time and then is reduced, the actual temperature A temperature change after the time t1 is monitored in real time, and the maximum value A of the real-time temperature in the temperature changing process is obtained _Max ；

The excitation function is

Wherein t is the current moment;

s7, when the actual temperature A falls back to the lower temperature limit T _min Then, the system records the current time as the time t2;

s8, according to the maximum value A of the actual temperature _Max Maximum excitation E _Max Lower limit of temperature T _min T0, t1, t2 and the control period TC of the PID controller, and the PID control parameters are calculated by combining a Ziegler-Nichols method.

In this embodiment, the control period TC of the PID controller is determined according to the parameter table corresponding to the model of the selected PID controller, and is an inherent parameter of the selected PID controller.

The Ziegler-Nichols method in the step S8 is a method for setting a PID controller and exploring the control parameters of the PID controller. The tuning is performed by first setting the integral and differential gains to 0, then gradually increasing the proportional gain from zero until a limit gain KU is reached, at which time the controller output value oscillates at a constant value, and the limit gain KU and the oscillation period TU set the proportional, integral and differential gains in the following table according to different types.

Controlling the temperature of the controlled environment by the temperature control module through the excitation function to further obtain the parameters, and calculating a limit gain KU and an oscillation period TU through the parameters, wherein the limit gain KU meets the requirement of

Said oscillation period TU satisfying

。

As shown in table 1, the calculation coefficients of the proportional parameter Kc, the integral action parameter Ti, and the derivative action parameter Td are selected according to the temperature change speed of the controlled environment and the type of the controller.

For example, a calculation coefficient corresponding to the rapid performance is selected from the heating and melting scenes of the injection molding raw materials so as to meet the scene with rapid temperature change. And if the temperature of the granary is controlled and the like, in a scene with slow temperature change, the calculation coefficient corresponding to the normal performance or the slow performance is selected.

And calculating the values of the proportional parameter Kc, the integral action parameter Ti and the differential action parameter Td through the selected calculation coefficients, and outputting the values to the PID controller to execute the temperature control of the controlled environment so as to ensure that the temperature in the controlled environment is relatively constant.

Example two:

in this embodiment, the difference between this embodiment and the first embodiment is: the variation of the excitation function according to the controlled scene and the hardware parameters of the device is

Wherein

,

…

The coefficients are calculated according to the controlled scene and the hardware parameters of the device.

The speed of temperature change can be different because of hardware parameter difference in different temperature control modules and the controlled scene, in order to adapt to different temperature change speeds and adapt to the control cycle TC of different controllers, the change curve when the temperature falls back is adjusted through the deformation of the excitation function, and then the PID parameter which can satisfy the temperature stability of the corresponding scene is obtained.

While the embodiments of the present invention have been described in terms of practical embodiments, they are not to be construed as limiting the meaning of the present invention, and modifications of the embodiments and combinations with other embodiments will be apparent to those skilled in the art in light of the present description.

Claims (4)

1. A PID parameter self-tuning algorithm for temperature control is characterized by comprising the following steps:

s1, setting a target temperature T and a temperature threshold value T _thr ；

S2, executing self-tuning;

s3, initializing the initial stage with the initialization time t of 0, and outputting the maximum excitation E by the equipment _Max The temperature control module is used for controlling the actual temperature A in the controlled environment to change to the target temperature T;

s4, when the actual temperature A reaches a temperature threshold T _thr Then, recording the current time as a moment t0;

s5, recording the current time as a moment T1 when the actual temperature A reaches the target temperature T;

s6, the equipment outputs the variable excitation E to the temperature control module according to the excitation function execution to change the temperature in the controlled environment, and collects an extreme value T of the actual temperature A after the moment T1 _ext (ii) a The excitation function is

Wherein t is the current moment;

s7, when the actual temperature A returns to the temperature threshold T at the moment T0 _thr Then, recording the current time as a moment t2;

s8, according to the extreme value T of the actual temperature _ext Maximum excitation E _Max Temperature threshold T _thr T0, t1, t2 and a control period TC, and calculating PID control parameters by combining a Ziegler-Nichols method.

2. The PID parameter self-tuning algorithm for temperature control according to claim 1, wherein the temperature threshold T is _thr Including an upper temperature limit T _Max And a lower temperature limit T _min (ii) a When the demand of the controlled environment is a temperature rise, the temperature threshold T in step S4 _thr Is a lower temperature limit T _min (ii) a When the requirement of the controlled environment is temperature reduction, the temperature threshold T in the step S4 _thr Is the upper temperature limit T _Max 。

3. A method as claimed in claim 1The PID parameter self-tuning algorithm for temperature control is characterized in that the Ziegler-Nichols method in the step S8 is to calculate a limit gain KU and an oscillation period TU according to the obtained parameters, and to select the calculation coefficients of a proportional parameter Kc, an integral action parameter Ti and a differential action parameter Td according to the temperature change speed of the controlled environment; wherein the ultimate gain KU satisfies

Said oscillation period TU satisfying

。

4. The PID parameter self-tuning algorithm for temperature control according to claim 1, wherein the variation of the excitation function according to the controlled scene and the hardware parameter of the device is

Wherein

,

…

The coefficients are calculated according to the controlled scene and the hardware parameters of the device.

Images