Variable integral PID (Proportion Integration Differentiation) control algorithm for annealing furnace temperature

Abstract

The invention discloses a variable integral PID (Proportion Integration Differentiation) control algorithm for annealing furnace temperature, and belongs to the technical field of annealing furnace temperature control. An operator sets and inputs the furnace temperature, the PID controller adjusts the heat load of the burner according to the error between the actual furnace temperature and the set furnace temperature, and finally the furnace temperature is controlled; the calculation method of the PID controller comprises the steps that the difference between a current control signal and a previous control signal is used as input, a new control signal of a next time step is generated through superposition of control signals at the previous moment and the next moment, a coefficient alpha is introduced into a formula, the size of an integral coefficient of PID is modified in a self-adaptive mode through error changes of a furnace temperature control loop, and the temperature of the furnace is controlled. And changing the effect of the current integration link, and accumulating the increment delta u [n] as an output signal of the PID controller. Under the action of the introduced coefficient alpha, the furnace temperature is finely adjusted through controller output, the furnace temperature is effectively kept close to a set value, and the stability of furnace temperature control is further enhanced while the temperature rise of the annealing furnace is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of annealing furnace temperature control, in particular to a variable integral PID control algorithm for annealing furnace temperature. Background Art

[0002] Silicon steel is an important material with wide applications in the fields of electricity, electronics, communications, etc. In the process of manufacturing silicon steel, annealing is a crucial step. The performance of silicon steel depends largely on its microstructure and grain structure, and annealing can adjust these structures, thereby affecting the magnetic properties and mechanical properties of silicon steel. In the annealing process of silicon steel, furnace temperature control is very critical. The control of furnace temperature will directly affect the organization and performance of silicon steel. Therefore, optimizing furnace temperature control technology can improve the quality and efficiency of silicon steel production. Temperature control has the characteristics of nonlinearity, strong coupling, large inertia and large hysteresis, and is a relatively random process. The temperature control in the annealing furnace must comprehensively consider the impact of various factors on the control object. At the same time, different control methods are required for temperature control under different requirements. At present, the common temperature control method in China is PID control, and further optimization is partition PID control. This control method uses the difference interval between the annealing furnace temperature and the set furnace temperature to determine the size of the integral parameter. This a priori closed-loop adjustment requires engineers to rely on strong practical experience and has limitations as the annealing furnace working conditions change. Further optimization of the control algorithm is feasible and practical, so a more effective furnace temperature control method is needed to improve the performance of silicon steel annealing. Summary of the invention

[0003] The purpose of the present invention is to provide a variable integral PID control algorithm for the temperature of an annealing furnace, which can meet the temperature accuracy control requirements of cold-rolled silicon steel annealing and annealing, improve the performance of silicon steel after annealing, and further enhance the stability of furnace temperature control while ensuring the annealing furnace temperature rise, so as to solve the shortcomings of the prior art.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A variable integral PID control algorithm for the temperature of an annealing furnace. The operator first sets the furnace temperature and inputs it. The PID controller adjusts the burner heat load according to the error between the actual furnace temperature and the set furnace temperature, and finally realizes the control of the furnace temperature. The calculation method of the PID controller is as follows:

[0006] S1: Use the difference between the current and previous control signals as input, and generate a new control signal for the next time step by superimposing the control signals before and after. The calculation formula is as follows:

[0007]

[0008] Where: Δu[n] is an increment, e[n] is the deviation between the process variable and the set value, e[n-1] is the deviation between the process variable and the set value at the previous sampling moment, and e[n-2] is the deviation between the process variable and the set value at the previous sampling moment; T is the system sampling time; Kp is the proportional coefficient, Ti is the integral time, and Td is the differential time;

[0009] S2: Introduce coefficient α into formula (1) of S1, so that the furnace temperature control loop can adaptively modify the integral coefficient of PID through the change of error, and change the role of the current integral link. The expression of α is as follows:

[0010]

[0011] The calculation formula after introducing the coefficient α is as follows:

[0012]

[0013] S3: The output signal of the PID controller is obtained by summing Δu[n] in formula (2).

[0014] Furthermore, the coefficient α is used to weaken the integral when the error between the actual furnace temperature and the set furnace temperature is small, thereby reducing the influence of the integral on the PID controller during the steady-state process and maintaining the furnace temperature stable.

[0015] Furthermore, the coefficient α is used to enhance the integral when the error between the actual furnace temperature and the set furnace temperature is large, so that the furnace temperature regulation responds quickly to the change of the set value and quickly adjusts the furnace temperature until the temperature stabilizes to the set furnace temperature.

[0016] Furthermore, the formula (2) after the coefficient α is introduced into S2 is equipped with a simulation model of furnace temperature control built by Simulink for verification.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The variable integral PID control algorithm for the temperature of an annealing furnace of the present invention optimizes the workload of the staff for adjusting different furnace temperature parameters. When the annealing furnace needs to be heated or cooled, the algorithm can respond quickly and output in time. When the furnace temperature is close to a steady state, under the effect of the introduced coefficient α, the controller output fine-tunes the furnace temperature, effectively maintaining the furnace temperature near the set value, with a small steady-state error. While ensuring the heating of the annealing furnace, the stability of the furnace temperature control is further enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a conventional PID control schematic diagram;

[0020] Figure 2 It is the furnace temperature control block diagram of the present invention;

[0021] Figure 3 It is a simulation model block diagram of furnace temperature control of the present invention;

[0022] Figure 4 This is a comparison diagram of conventional PID furnace temperature control and variable integral PID algorithm control in an embodiment of the present invention;

[0023] Figure 5 This is a comparison diagram of the relationship between the integral coefficient and α of the present invention;

[0024] Figure 6 It is the program design diagram of the present invention;

[0025] Figure 7 This is the variable integral PID program operation diagram of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 As shown in the figure, the conventional PID control principle consists of three links: proportional, integral, and differential, and finally outputs a control signal to act on the controlled object. The furnace temperature control block diagram of the silicon steel continuous annealing production line is shown in the figure. Figure 2 As shown in the figure, the process operator sets the furnace temperature and the PID controller adjusts the burner heat load according to the error between the actual furnace temperature and the set furnace temperature, and finally realizes the control of the furnace temperature. Among them, the temperature control of the annealing furnace is characterized by nonlinearity, strong coupling, large inertia and large hysteresis. Conventional PID has poor control effect on processes with long lag time. Incremental PID (proportional-integral-differential) is a PID control algorithm commonly used in industrial control systems to improve system performance; unlike standard PID control, which uses the error between the set value and the actual process value to determine the control signal, incremental PID uses the difference between the current and previous control signals as input. Its basic idea is to calculate the required control signal change to achieve the required process variable change.

[0028] Based on this, the embodiment of the present invention increases the temperature accuracy control requirements of cold-rolled silicon steel annealing and improves the performance of silicon steel after annealing. The present invention provides a variable integral PID control algorithm for the temperature of an annealing furnace. While ensuring the temperature rise of the annealing furnace, the stability of the furnace temperature control is further enhanced, which can help reduce the overshoot and undershoot that may occur in traditional PID control, especially in high dynamic processes. The specific calculation method is as follows:

[0029] S1: Use the difference between the current and previous control signals as input, and generate a new control signal for the next time step by superimposing the control signals before and after. The calculation formula is as follows:

[0030]

[0031] Where: Δu[n] is an increment, e[n] is the deviation between the process variable and the set value, e[n-1] is the deviation between the process variable and the set value at the previous sampling moment, and e[n-2] is the deviation between the process variable and the set value at the previous sampling moment; T is the system sampling time; Kp is the proportional coefficient, Ti is the integral time, and Td is the differential time;

[0032] S2: Introduce coefficient α into formula (1) of S1, so that the furnace temperature control loop can adaptively modify the integral coefficient of PID through the change of error, and change the role of the current integral link. The expression of α is as follows:

[0033]

[0034] The calculation formula after introducing the coefficient α is as follows:

[0035]

[0036] In this step, by introducing the coefficient α, the furnace temperature control loop can adaptively modify the size of the PID integral coefficient through the change of the error, changing the role of the current integral link. The role of this coefficient is divided into two aspects:

[0037] (1) When the error between the actual furnace temperature and the set furnace temperature is small, the integral effect is weakened to reduce the influence of the integral on the control system during the steady state process and keep the furnace temperature stable;

[0038] (2) When the error between the actual furnace temperature and the set furnace temperature is large, the integral effect is enhanced so that the furnace temperature regulation responds quickly to the change of the set value and quickly adjusts the furnace temperature until the temperature stabilizes to the set furnace temperature.

[0039] S3: The output signal of the PID controller is obtained by summing Δu[n] in formula (2).

[0040] In order to further better explain the present invention, the embodiment of the present invention is equipped with a simulation model of furnace temperature control built by Simulink in formula (2) after the coefficient α is introduced for verification. Specifically, Simulink is a visual simulation tool of MATLAB, which provides an integrated environment for system modeling, simulation and comprehensive analysis. In Simulink, users can select appropriate modules and connect them through simple and intuitive mouse operations to construct complex simulation models. Simulink has wide adaptability and can be used for various system modeling. Its structure and process are clear, presented in the form of block diagrams, and the simulation is fine.

[0041] like Figure 3 As shown: This model can realize the temperature rise simulation under the control of variable integral PID algorithm and conventional PID algorithm, and output the corresponding temperature rise curve.

[0042] Simulation conditions: The furnace temperature is set to 760℃. The two algorithms use the same initial PID parameters. The variable integral PID algorithm introduces the coefficient α in the integral term. The simulation results are shown in Figure 2. Figure 4 shown.

[0043] The role of the introduced coefficient α is further explained by combining the changing curve of the integral coefficient and α in the variable integral PID algorithm:

[0044] Depend on Figure 5 It can be seen that in the dynamic response process of furnace temperature control, the coefficient α is close to 1, and has almost no effect on the integral after multiplying it with the integral coefficient, which ensures the rapidity of heating. After the furnace temperature reaches a steady state, the coefficient α fluctuates around 0.2. At this time, α has a weakening effect on the integral, thereby ensuring the stability of the furnace temperature after reaching a steady state.

[0045] In actual application, the furnace temperature is set by the process operator during the silicon steel annealing process, that is, the furnace temperature during the silicon steel annealing process must reach the set furnace temperature to ensure the performance of the silicon steel after annealing. When the furnace temperature is adjusted, the thermocouple installed on the top of the annealing furnace detects the actual furnace temperature and sends this signal to the PLC controller. The PLC controller controls the ignition and flameout of the burner according to the established PID program. Specifically, the variable integral PID algorithm is written into the PLC controller through the Botu software, such as Figure 6-7 shown.

[0046] In summary, the variable integral PID control algorithm for the annealing furnace temperature provided by the present invention ensures the dynamic characteristics of the PID algorithm in the furnace temperature adjustment process, and at the same time, after the furnace temperature reaches a steady state, the algorithm can fine-tune the furnace temperature, always making the furnace temperature stable near the set value, thus meeting the process requirements for the furnace temperature very well.

[0047] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A variable integral PID control algorithm for the temperature of an annealing furnace. The operator first sets the furnace temperature and inputs it. The PID controller adjusts the burner heat load according to the error between the actual furnace temperature and the set furnace temperature, and finally realizes the control of the furnace temperature. It is characterized by: The calculation method of PID controller is as follows: S1: Use the difference between the current and previous control signals as input, and generate a new control signal for the next time step by superimposing the control signals before and after. The calculation formula is as follows: Where: Δu[n] is an increment, e[n] is the deviation between the process variable and the set value, e[n-1] is the deviation between the process variable and the set value at the previous sampling moment, and e[n-2] is the deviation between the process variable and the set value at the previous sampling moment; T is the system sampling time; Kp is the proportional coefficient, Ti is the integral time, and Td is the differential time; S2: Introduce coefficient α into formula (1) of S1, so that the furnace temperature control loop can adaptively modify the integral coefficient of PID through the change of error, and change the role of the current integral link. The expression of α is as follows: The calculation formula after introducing the coefficient α is as follows: S3: The output signal of the PID controller is obtained by adding Δu[n] in formula (2).

2. A variable integral PID control algorithm for annealing furnace temperature as claimed in claim 1, characterized in that: The coefficient α is used to weaken the integral when the error between the actual furnace temperature and the set furnace temperature is small, reducing the impact of the integral on the PID controller during the steady state process to keep the furnace temperature stable.

3. The variable integral PID control algorithm for the temperature of an annealing furnace as claimed in claim 1, characterized in that: The coefficient α is used to enhance the integral when the error between the actual furnace temperature and the set furnace temperature is large, so that the furnace temperature regulation responds quickly to the change of the set value and quickly adjusts the furnace temperature until the temperature stabilizes to the set furnace temperature.

4. The variable integral PID control algorithm for the temperature of an annealing furnace as claimed in claim 1, characterized in that: Formula (2) after the coefficient α is introduced into S2 is verified by a simulation model of furnace temperature control built by Simulink.

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