Furnace tube Heater heating control system based on PID (Proportion Integration Differentiation) control algorithm

Abstract

The invention relates to the technical field of furnace tube heating, in particular to a furnace tube Heater heating control system based on a PID (Proportion Integration Differentiation) control algorithm. The system comprises a temperature sensor used for collecting the temperature in the furnace tube in real time; the PID controller is used for receiving the temperature data of the temperature sensor, performing calculation according to the deviation between the set temperature and the actually measured temperature and outputting a control instruction; and the adjusting device is used for receiving a control instruction of the PID controller, adjusting the power of the heating element and realizing temperature control. According to the technical scheme, the fluctuation range of different temperature zones of the furnace body is + / -1 DEG C, and the temperature difference inside and outside the furnace body fluctuates by + / -0.1 DEG C; the precision and the stability of the heating control of the furnace tube Heater are obviously improved, and the temperature fluctuation is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of furnace tube heating, and in particular to a furnace tube heater heating control system based on a PID control algorithm. Background Art

[0002] In industrial production, furnace tube heaters are key equipment, and their heating efficiency and temperature control accuracy directly affect product quality, energy consumption and production safety. Traditional heating control systems mostly use simple switch control or basic temperature feedback control, which has problems such as slow impact speed, large overshoot, and large steady-state error, making it difficult to meet the needs of high-precision and high-efficiency heating.

[0003] At the same time, in the original heater control system, there are problems such as asynchronous temperature rise in multiple temperature zones, large temperature difference between inside and outside, and large temperature control fluctuations. The heating control of the furnace tube is the key to ensuring product quality and production efficiency. The traditional heating control method has the problems of slow response speed, high energy consumption and large temperature fluctuations.

[0004] Therefore, it is particularly important to develop a PID control system that can adjust the heating power in a timely manner, respond quickly to temperature changes, and reduce overshoot and steady-state errors. Summary of the invention

[0005] In view of the shortcomings of the heating control of furnace tube heaters in the prior art, the present invention aims to provide a furnace tube heater heating control system based on a PID control algorithm, which can significantly improve the heating efficiency, accurately control the heating temperature, reduce energy consumption, and improve product quality and production safety.

[0006] In the first aspect, the present invention provides a furnace tube heater heating control system based on a PID control algorithm, which adopts the following technical solution: A furnace tube heater heating control system based on PID control algorithm, comprising: Temperature sensor, used to collect the temperature inside the furnace tube in real time; PID controller, used to receive temperature data from the temperature sensor, calculate according to the deviation between the set temperature and the measured temperature, and output control instructions; The regulating device is used to receive the control instruction of the PID controller, adjust the power of the heating element, and realize temperature control.

[0007] Furthermore, the calculation is performed based on the deviation between the set temperature and the measured temperature, including the PID controller calculating the deviation signal based on the given signal and the feedback signal, and calculating the control quantity u based on proportional operation, integral operation and differential operation, thereby controlling the duty cycle D of the power tube.

[0008] Furthermore, the PID controller calculates a deviation signal according to a given signal and a feedback signal, including establishing a mathematical model of a position PID control algorithm based on a digital PID controller.

[0009] Furthermore, the control expression of the digital PID controller is: (7-1) Where, e(t) is the system deviation, e(t)=r(t)-c(t); is the proportionality coefficient; is the integration time constant; is the differential time constant.

[0010] Furthermore, the mathematical model of the position PID control algorithm is expressed as: ; Expand the expression and combine like terms to get: ; in: ; ; . Furthermore, the proportional operation includes calculating the error between the current temperature and the target temperature, directly adjusting the control amount according to the size of the deviation, and quickly responding to temperature changes.

[0011] Furthermore, the integral operation includes calculating the accumulation of the error according to the error obtained by the proportional operation to eliminate the steady-state error.

[0012] Furthermore, the differential operation includes predicting the deviation change trend according to the accumulation of errors, adjusting the control amount in advance, and reducing the overshoot.

[0013] Furthermore, the mathematical model of the position PID control algorithm is established based on the digital PID controller, including selecting PID controller parameters, including respectively determining the proportional coefficient Kp, the integral time constant Ti, the differential time constant Td, and the no-load and load joint regulation.

[0014] Furthermore, the regulating device controls the heater by controlling the length of the heating time within the cycle, wherein the heating state of the controller is set to 1, the non-heating state is set to 0, and a PWM square wave is formed, that is, the heating power is controlled by controlling the duty cycle of the PWM square wave through the control value.

[0015] In summary, the present invention has the following beneficial technical effects: Through the above technical scheme, the present invention can achieve a fluctuation range of ±1°C in different temperature zones of the furnace body and a fluctuation of ±0.1°C in the temperature difference between the inside and outside of the furnace body.

[0016] Significantly improve the accuracy and stability of the heater control and reduce temperature fluctuations.

[0017] Improve heating efficiency, reduce energy consumption, save energy and reduce emissions.

[0018] Increase the adaptability and robustness of the system to adapt to heating requirements under different working conditions.

[0019] Improve production safety and product quality, and reduce production accidents and defective rates caused by improper temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a PID controller according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0022] Example 1 Reference Figure 1 , a furnace tube heater heating control system based on PID control algorithm of this embodiment includes: The temperature sensor collects the internal temperature of the furnace tube in real time and transmits the information to the PID controller; the PID controller outputs a control signal to the power regulation device through proportional, integral and differential operations based on the deviation between the set temperature and the measured temperature, thereby adjusting the power output of the heating element and achieving precise temperature control.

[0023] First, the PID control algorithm includes: Proportional (P): Directly adjust the control amount according to the deviation size and respond quickly to temperature changes.

[0024] Integration (I): Accumulated deviation. Eliminate system steady-state error and ensure temperature stability during long-term operation.

[0025] Differentiation (D): Predict the deviation change trend, adjust the control amount in advance, reduce overshoot, and improve the dynamic performance of the system.

[0026] Therefore, a PID controller consists of three parts: Proportional (P): Calculates the error between the current temperature and the target temperature.

[0027] Integration (I): Calculates the accumulation of errors to eliminate steady-state errors.

[0028] Derivative (D): predict future errors and reduce overshoot.

[0029] PID control algorithm logic: initialization: Set the target temperature and the initial temperature.

[0030] Initialize PID parameters (Kp, Ki, Kd).

[0031] Initialize the error, integral, and derivative values.

[0032] Loop Control: Read the current temperature.

[0033] Calculation error: error=target_temperature-current_temperature. Update integral: integral+error*dt (dt is the time interval).

[0034] Calculate the derivative: derivative = (error - previous_error) / dt.

[0035] Calculate PID output: output=Kp*error+Ki*interal+Kd*derivative.

[0036] Limit the output to the heater's power range (e.g. 0 to 100%).

[0037] Update the current temperature (simulated or read via a sensor).

[0038] Update the previous error: previous_error=error.

[0039] When the current temperature approaches the target temperature (within the set tolerance range), control stops.

[0040] PID controller principle: The PID controller in the system calculates the control quantity u based on the deviation signal obtained by subtracting the given signal from the feedback signal, thereby controlling the duty cycle D of the power tube. In automatic control systems, commonly used controllers include proportional-integral controllers (PI controllers), proportional-integral-differential controllers (PID controllers), and segmented approximation controllers. Newer controllers include fuzzy controllers and neural network controllers. This system uses the PID controller widely used in industrial process control. The controller that controls the deviation by proportion, integration, and differentiation is called a PID controller. The principle block diagram of the analog PID controller is shown below. Figure 1As shown, r(t) is the system given value, c(t) is the actual output, and u(t) is the control quantity. PID control solves the most basic problem to be solved by the white dynamic control theory, namely the stability, rapidity and accuracy of the system. By adjusting the parameters of PID, the load capacity and anti-interference ability of the system can be taken into account under the premise of system stability. At the same time, due to the introduction of the integral term in the PID controller, a zero integral point is added to the system, so that the steady-state error of the system step response is zero.

[0041] Figure 1 The control expression of the analog PID controller shown is: (7-1) In formula (7-1), e(t) is the system deviation, e(t)=r(t)-c(t); is the proportionality coefficient; is the integration time constant; is the differential time constant.

[0042] Formula (7-1) can also be written as: (7-2) In formula (7-2, is the proportionality coefficient; is the integration coefficient, = / ; is the differential coefficient, = ; The functions of each correction link in the PID controller are as follows: (1) The proportional link reflects the deviation signal e(t) of the control system in a timely and proportional manner. Once the deviation occurs, the controller immediately takes an adjustment action to reduce the deviation.

[0043] (2) The integral link is mainly used to eliminate static error and improve the system's error-free degree. The strength of the integral effect depends on the integral time constant. , T i The larger it is, the weaker the integral effect is, and vice versa.

[0044] (3) The differential link can reflect the changing trend of the deviation signal, that is, the rate of change of the deviation signal, and can introduce an effective early correction signal into the system before the deviation signal value becomes too large, thereby speeding up the system's action speed and reducing the adjustment time.

[0045] Computer control is a discrete sampling control. The digital PID controller is used in the computer control system, and equations (7-1) and (7-2) are both control expressions of analog PID controllers. Digital PID control can be achieved by approximating the integral and differential operations in the analog PID expression with numerical calculation methods. As long as the sampling period T is small enough, this approximation can be quite accurate.

[0046] Replace the differential term with the difference and the integral term with the rectangular sum. The control expression of the digital PID controller is as follows: (7-3) Similarly, formula (7-3) can also be written as: (7-4) in: = T / , .

[0047] The control algorithms of digital PID controllers can generally be divided into position PID control algorithms and incremental PID control algorithms. This system uses a position PID control algorithm, so the following will discuss how to establish a mathematical model of the position PID control algorithm.

[0048] From formula (7-4), the expression of PID regulation at the k-1th moment is: (7-5) Subtracting equation (7-4) from equation (7-5), we can get the expression of the position PID control algorithm: In order to make the expression simpler, the above formula can be expanded and similar terms can be combined to obtain: (7-6) in: .

[0049] Equation (7-6) is the mathematical model of the position PID controller used in this system.

[0050] When entering the PID adjustment subroutine, the deviation must first be calculated based on the system given value and the sampling value. In order to prevent the switch duty cycle D from being too large due to the excessive control quantity u(k) in the early stage of system operation, it is necessary to perform a certain limit processing on the e(k) substituted into the formula (7-6). Because the instantaneous excessive duty cycle may sometimes cause excessive current, resulting in damage to the switch. In addition, after the system enters the steady state, the deviation is very small. If the deviation fluctuates within a very small range, the controller will output a small control quantity after calculating such a small deviation. At this time, the output control value is within a very small range, constantly changing its direction, frequently moving, and vibrating, which is not conducive to the battery being charged. Therefore, when the control process enters this state, it enters an output allowable band e0 set by the system, that is, when the collected deviation |e(k)|e0, the control quantity is not changed, so that the charging and discharging process can proceed stably.

[0051] There are many methods for selecting PID controller parameters, such as trial and error, critical proportionality method, expanded critical proportionality method, etc. However, for PID control, parameter selection is always a very complicated task, and it requires constant adjustment to obtain a more satisfactory control effect. Based on experience, the steps for determining PID parameters are generally as follows: (1) Determine the proportionality coefficient Kp When determining the proportional coefficient Kp, first remove the integral and differential terms of PID, so that Ti-0, Td=0, making it a pure proportional regulation. The input is set to 60% to 70% of the maximum output allowed by the system, and the proportional coefficient Kp gradually increases from О until the system oscillates; conversely, the proportional coefficient Kp at this time gradually decreases until the system oscillation disappears. Record the proportional coefficient Kp at this time, and set the proportional coefficient Kp of PID to 60% to 70% of the current value.

[0052] (2) Determine the integral time constant Ti After the proportional coefficient Kp is determined, set a larger integral time constant Ti, then gradually reduce Ti until the system oscillates, and then conversely, gradually increase Ti until the system oscillation disappears. Record Ti at this time, and set the PID integral time constant Ti to 150% to 180% of the current value.

[0053] (3) Determine the differential time constant Td The differential time constant Td generally does not need to be set, and can be set to 0. At this time, PID regulation is converted to PI regulation. If it needs to be set, the method of determining Kp is the same, and 30% of its value when there is no oscillation is taken.

[0054] (4) System no-load and load joint debugging Fine-tune the PID parameters until the performance requirements are met.

[0055] The principle of PID temperature control algorithm is simply to adjust the temperature controller according to the difference between the measured temperature and the set temperature in a closed-loop system in order to finally reach a stable set temperature.

[0056] This is divided into three parts: measuring temperature, calculating control value, and controlling temperature.

[0057] Measuring temperature: The temperature measurement is relatively simple, and can usually be obtained by reading the data of the connected temperature measurement module through the port in the program. Of course, the actual measurement is usually a value such as voltage, not the actual temperature, but the relationship table between voltage and temperature is generally provided by the manufacturer, and those specific data can be fitted into an appropriate calculation formula, so that the voltage can be easily converted into an approximate temperature.

[0058] Calculate the control value: This is the most important part. It is calculated by the deviation between the actual temperature value measured and the temperature value set to be reached. The general practice is to directly use this absolute error value for calculation, but considering that the influence of this absolute error on temperature control is related to the actual set temperature, from the perspective of universality, I deliberately use relative error instead of absolute error, and increase it by 100 times for the convenience of calculation. In layman's terms, it is changed to the percentage error between the measured temperature and the set temperature. The specific relative error calculation is shown in formula 1.

[0059] Error= (SetPoint-Curvalue)*100 / SetPoint Error refers to the relative error, SetPoint refers to the set temperature, and Curvalue refers to the current measured temperature.

[0060] The basic formula for calculating the control value also uses the common incremental PID algorithm, as shown in Formula 2: U(k)=kp*error(k)+ki error(j)+kd(error(k)-error(k-1)) Where u(k) refers to the control value required at time k, error(k) refers to the relative error at time k, kp is the proportional coefficient, ki is the integral coefficient, and kd is the differential coefficient. When the sampling period is constant, ki and kd in formula 2 have already taken the value of the sampling period into account.

[0061] Because when the entire PID control is started, ended, or greatly increased or decreased, the system output may have a large deviation in a short period of time, which will cause the integral accumulation of the PID operation, causing a large overshoot and oscillation of the system. Especially when the temperature changes slowly and has a pure lag link, if a simple PID control is used, when there is a large disturbance or a large change in the given value, a large deviation will occur. Therefore, referring to the practices of others, the proportional coefficient in Formula 3 was further adjusted, and a piecewise integral variation coefficient λ was added. The final formula is: u(k)=kp*error(k)+λ*ki error(j)+kd(error(k)-error(k-1)) The value of λ changes with the absolute value of the current relative error, and can basically be designed as a piecewise function. When the absolute value of the relative error is larger, that is, the measurement value deviates more from the set value, the influence of the integral coefficient is expected to be smaller, and λ is set smaller; on the contrary, when the absolute value of the relative error is smaller, that is, the measurement value is closer to the set value, the influence of the integral coefficient is expected to be greater, and λ is set larger. λ can be set according to formula 7-7. (7-7) Controlling Temperature: Generally speaking, temperature control is to control the electric heating elements of the temperature controller, such as heating wires and heating rods. In a simple control system, only two states can be controlled: heating or not heating. However, if heating or not heating is controlled only based on the calculated control value and the size of a certain threshold within a cycle, on the one hand, most of the calculated specific control values ​​lose their control significance and cannot play a role. On the other hand, more importantly, the inertial temperature error problem of the temperature controller's temperature control becomes more serious, and it is not easy to accurately stabilize the temperature.

[0062] Since controlling the temperature is to control the heating power, and the heating power is related to the heating time as well as the capacity of the heater itself, we can control the heater by controlling the length of the heating time within the cycle. If the heating state of the controller is regarded as 1 and the non-heating state is regarded as 0 to form a PWM square wave, then the control value can be used to control the duty cycle of the PWM to control the heating power.

[0063] The basic control program is implemented through the following code: double minval = 0; int times=int (1000*m_Samp1eTimes); if(controlva1>minval) { unsigned int th; unsigned int tl; double bili ; double limit=100; if(controlva1>1imit) bili=1; else bili=controlval / limit; th=(int) (times*bili); tl=(int)(times*(1-bili)); Heating(); / / Heating sleep(th); StopHeating(); / / Stop heating s1eep(t1); } else { StopHeating(); sleep(times); } Where minval is the minimum threshold value for a given control value to be heated, m_SampleTimes refers to the sampling period in seconds, and controlval is the control value calculated in the second part. As for the other threshold limit, 100 is selected considering that the current control value is obtained from the relative error percentage.

[0064] Program implementation: Considering the whole process of temperature control, you can consider adding two separate threads: one is responsible for communicating with the temperature measuring device and recording the current temperature in real time; the other is responsible for the whole process of temperature control. The main program is responsible for switching temperature control, setting temperature, interface, etc. Figure 1 A flow chart of the temperature control thread is given.

[0065] After the thread is suspended, it is awakened by the main program. After awakening, the thread will continue to execute the program after the suspension point.

[0066] Application of the algorithm: Another important step in the practical application of PID algorithm is to test and determine the PID parameters. The method I use is basically to first use the 4:1 attenuation curve method to obtain a basic proportional, integral, and differential parameter, and then adjust the three parameters based on experience according to the actual temperature change curve. The principle of adjustment is basically to adjust the proportional parameter if the curve climbs too fast or too slow and the curve oscillates frequently; adjust the differential parameter if overshoot; adjust the integral parameter if the curve fluctuation period is long or the recovery is slow.

[0067] This algorithm has been successfully applied to the temperature control programs of human pain detection systems and fused deposition modeling rapid prototyping control systems. The latter requires turning on three different temperature controllers, all of which achieve accurate temperature control, basically maintaining a range of only 0.5 degrees above or below, meeting application needs.

[0068] Optimization strategy: An adaptive PID algorithm is introduced to adjust the PID parameters according to the actual situation during system operation to improve the adaptability and robustness of the system.

[0069] By combining fuzzy control theory or intelligent algorithms such as neural networks with PID control, the control accuracy and response speed of the system can be further improved.

[0070] Safety protection: Integrating over-temperature protection, short-circuit protection and other safety mechanisms ensures that the system automatically cuts off the heating source under abnormal conditions to ensure production safety.

[0071] PID algorithm control: PID controller design: The control system adopts an intelligent control algorithm, namely the PID control algorithm, which controls the execution state of the actuator through the algorithm result obtained by combining the ratio, differentiation and integration of the difference between the set temperature and the actual temperature, so that the control time, overshoot, lag reaction and final stability in the control system can be significantly improved. The system of the present invention has the advantages of simple overall structure, high temperature control accuracy, good real-time performance, stable and reliable functions, etc., and has wide application value.

[0072] PID control, also known as three-term control, is an algorithm that continuously adjusts the output to compensate for changes in the process variable according to a set of rules. It provides more stable control than on-off control, but requires setting parameters to match the characteristics of the controlled process. Algorithm implementation steps: 1. System initialization: set PID parameters, temperature setting value and sensor parameters.

[0073] 2. Temperature collection: The furnace tube temperature is collected through the temperature sensor and converted into a digital signal through the A / D converter.

[0074] The furnace tube temperature (PV) is collected in real time, compared with the target temperature (Sv) set by the user, and the deviation (Ek) is calculated.

[0075] According to the PID control algorithm formula (PWM=KpEk+KSk+Kd*Dk), calculate the output control quantity (PWM signal).

[0076] The PWM signal is output to the bidirectional thyristor controller to control the power of the heating resistor, thereby adjusting the temperature of the furnace tube.

[0077] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A furnace tube heater heating control system based on PID control algorithm, characterized in that: include: Temperature sensor, used to collect the temperature inside the furnace tube in real time; PID controller, used to receive temperature data from the temperature sensor, calculate according to the deviation between the set temperature and the measured temperature, and output control instructions; The regulating device is used to receive the control instruction of the PID controller, adjust the power of the heating element, and realize temperature control.

2. A furnace tube heater heating control system based on PID control algorithm according to claim 1, characterized in that: The calculation is performed based on the deviation between the set temperature and the measured temperature, including the PID controller calculating the deviation signal based on the given signal and the feedback signal, and calculating the control quantity u based on proportional operation, integral operation and differential operation, thereby controlling the duty cycle D of the power tube.

3. The furnace tube heater heating control system based on PID control algorithm according to claim 2 is characterized in that: The PID controller calculates a deviation signal according to a given signal and a feedback signal, including establishing a mathematical model of a position-type PID control algorithm based on a digital PID controller.

4. The furnace tube heater heating control system based on PID control algorithm according to claim 3 is characterized in that: The control expression of the digital PID controller is: (7-1) Where, e(t) is the system deviation, e(t)=r(t)-c(t); is the proportionality coefficient; is the integration time constant; is the differential time constant.

5. The furnace tube heater heating control system based on PID control algorithm according to claim 4 is characterized in that: The mathematical model of the position PID control algorithm is expressed as: ; Expand the expression and combine like terms to get: ； in: ; ； 。 6. The furnace tube heater heating control system based on PID control algorithm according to claim 5 is characterized in that: The proportional operation includes calculating the error between the current temperature and the target temperature, directly adjusting the control amount according to the size of the deviation, and quickly responding to temperature changes.

7. The furnace tube heater heating control system based on PID control algorithm according to claim 6 is characterized in that: The integral operation includes calculating the accumulation of the error according to the error obtained by the proportional operation to eliminate the steady-state error.

8. The furnace tube heater heating control system based on PID control algorithm according to claim 7, characterized in that: The differential operation includes predicting the deviation change trend according to the accumulation of errors, adjusting the control amount in advance, and reducing the overshoot.

9. The furnace tube heater heating control system based on PID control algorithm according to claim 8, characterized in that: The mathematical model of the position PID control algorithm is established based on the digital PID controller, including selecting PID controller parameters, including respectively determining the proportional coefficient Kp, the integral time constant Ti, the differential time constant Td, and the no-load and load joint adjustment.

10. The furnace tube heater heating control system based on PID control algorithm according to claim 9, characterized in that: The regulating device controls the heater by controlling the length of the heating time within the cycle, wherein the heating state of the controller is set to 1, the non-heating state is set to 0, and a PWM square wave is formed, that is, the heating power is controlled by controlling the duty cycle of the PWM square wave through the control value.

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