A method for setting PID control parameters based on counteracting object factors

Abstract

The application discloses a PID control parameter setting method based on offset object factors, and relates to the technical field of automation control, aiming at solving the problem that the PID control parameters self-set for the controlled object approximating to a first-order pure lag object model are not ideal and need to be manually corrected according to experience. The method comprises the following steps: step one, the controlled object is equivalent to a second-order pure lag object model; step two, a DPID control algorithm is used for the controller; step three, the controlled object and the controller form a closed-loop control system; step four, the control parameters of the controller are set to overcome the defect that the system overshoot will be generated in the object transfer function, and then the object is simplified into a typical first-order pure lag transfer function; step five, a closed-loop system formed by the simplified controller and the controlled object; and step six, finally, the parameters of the elimination factor in step four are added to set the four control parameters of the controller.

Description

Technical Field

[0001] This invention relates to the field of automation control technology, specifically to a method for tuning PID control parameters based on a cancellation target factor. Background Technology

[0002] In the field of automation control, physical quantities such as temperature, flow rate, and liquid level all require target value control. The classic method is to apply PID control technology. In traditional automation control, the mathematical model of the controlled object is approximated as a first-order pure time-delay object model, with the following transfer function: Using an approximate first-order pure time-delay object model and the classic self-tuning PID parameter tuning method for control, the effect is always unsatisfactory, with varying degrees of defects such as system overshoot (commonly known as temperature overshoot) and excessively long transient process (commonly known as excessively long heating time). At this point, experienced engineers need to repeatedly modify the tuned PID control parameters to bring the control system to a state acceptable to the user.

[0003] In practical applications, we have found that the actual object model is often a high-order pure time-delay model, with the following transfer function: In practical applications, we also found that the response curves of higher-order pure time-delay models are very close to those of second-order pure time-delay object models. The transfer function of the second-order pure time-delay object model is as follows: In practical applications, we have also found that when Moreover, when When the step response occurs, a significant system overshoot will appear.

[0004] With the rapid development of control technology, the mathematical model identification technology of objects has become relatively mature. Controllers using microprocessor programming technology can easily identify the mathematical model of a second-order pure time-delay object. In response, we propose a PID control parameter tuning method based on the cancellation object factor. Summary of the Invention

[0005] The purpose of this invention is to provide a PID control parameter tuning method based on the offsetting object factor, so as to solve the problem mentioned in the background art that the self-tuned PID control parameters are not ideal when the controlled object is approximately a first-order pure time delay object model, and manual correction based on experience is required.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a PID control parameter tuning method based on the offsetting object factor, comprising the following steps: Step 1: The controlled object is equivalent to a second-order pure time-delay object model, and the object's transfer function is as follows: ; in This represents the gain of the controlled object. This represents the time constant of the first inertial element of the controlled object. Let represent the time constant of the second inertial element of the controlled object. For the convenience of the analysis and derivation in the following steps, we define . . Indicates the pure time delay of the controlled object; Step 2: The controller adopts a derivative-first DPID control algorithm, and the controller's transfer function is as follows: ; in This represents the proportional gain of the controller. This represents the derivative time of the controller's derivative-leader element (proportional-derivative element). This represents the integral time of the PID controller (proportional-integral-derivative). This represents the derivative time of the PID (proportional-integral-derivative) stage in the controller. Step 3: The controlled object and the controller constitute a closed-loop control system, and its closed-loop transfer function is: in This represents the measurement signal of the controller. Indicates the controller's setpoint; Step 4: To overcome the issues in object passing functions This can lead to system overshoot, so the controller parameters must be tuned first. ,Pick ,Right now After simplifying the numerator and denominator in the formula of step two, we get: exist The second inertial element has been eliminated. Given this model factor, the object has been simplified to a typical first-order pure time-delay transfer function: The controller has also been simplified to the transfer function of a typical PID controller: The simplified system block diagram consisting of the controller and the controlled object has the following closed-loop transfer function: ; Step 5: The simplified closed-loop system consisting of the controller and the controlled object is tuned using the classic PID parameter tuning method. , and Since the object model is a standard first-order pure time delay object, the tuned PID parameters are suitable for the control of this object model. Step 6: Finally, add the elimination steps from step 4. Factors Parameters, the entire controller , , , The tuning is achieved through four control parameters.

[0007] Preferably, in order to overcome the actual object passing function during object identification... Smaller than the recognition result, i.e. Greater than the actual When the system oscillations caused by this are adjusted using actual parameters, the following methods can be used: .

[0008] Preferably, to overcome the potential for large fluctuations in the controller output after two stages of proportional-derivative operations in practical applications, which could affect the actual control effect due to sudden disturbances, this method adds an output constraint judgment to the derivative-ahead stage during the discretization of the control algorithm. Specifically, when... hour, The discretization formula for the proportional-differential element is: ; in This represents the current output quantity during the discrete operation of the proportional-differential component. This indicates the deviation value currently sampled. This represents the deviation value from the previous sample. This indicates the control period, which is the time interval between two samplings.

[0009] Preferably, in step one Indicates the gain of the object. Represents the second-order inertial element of the object. This represents the time constant of the first inertial element. The time constant of the second inertial element should be taken as the larger one during object identification. The small time constant is , Represents the pure time delay of the object.

[0010] Preferably, in step two Indicates the proportional gain of the controller. This represents the differential lead-ahead element of the controller. This represents the derivative time of the controller's derivative-ahead process, also known as the first derivative time. This indicates the PID control element of the controller. This represents the integral time of the controller. This represents the derivative time of the PID control loop in the controller, also known as the second derivative time.

[0011] Preferably, in step five, after eliminating the second inertial element factor of the object, the PID parameters are tuned using the 4:1 attenuation method, as shown in the following formula: .

[0012] Preferably, the Indicates the output of the current differential term. This indicates the current deviation value. This represents the deviation value from the previous control cycle. Represents the differential time. This indicates the control cycle of the controller.

[0013] Preferably, the The restriction is: when hour, .

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a PID control parameter tuning method that compensates for object factors. This method simplifies the tuning of PID control parameters and overcomes the problem of approximating second-order or higher-order pure time-delay objects with a first-order pure time-delay object model. It solves the problem that the self-tuned PID control parameters are not ideal and require manual correction based on experience. Attached Figure Description

[0015] Figure 1 This is a system block diagram of the controller and the second-order pure time-delay object of the present invention. Figure 2 The object of the present invention System block diagram after factor elimination; Figure 3 A comparison of the control response curves approximated by the object factor elimination method and the first-order pure time delay object model of the present invention. Figure 4 Comparison of the control response curves approximated by the object factor elimination method and the first-order pure time delay object model of the present invention (II); Figure 5 This is a flowchart of the PID control parameter tuning method of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0017] Please see Figure 1 , 2 5. An embodiment of the present invention provides a method for tuning PID control parameters based on a cancellation object factor, comprising the following steps: Step 1: The controlled object is equivalent to a second-order pure time-delay object model, and the object's transfer function is as follows: ; in This represents the gain of the controlled object. This represents the time constant of the first inertial element of the controlled object. Let represent the time constant of the second inertial element of the controlled object. For the convenience of the analysis and derivation in the following steps, we define . . Indicates the pure time delay of the controlled object; Step 2: The controller adopts a derivative-first DPID control algorithm, and the controller's transfer function is as follows: ; in This represents the proportional gain of the controller. This represents the derivative time of the controller's derivative-leader element (proportional-derivative element). This represents the integral time of the PID controller (proportional-integral-derivative). This represents the derivative time of the PID (proportional-integral-derivative) stage in the controller. Step 3: The controlled object and the controller constitute a closed-loop control system, and its closed-loop transfer function is: in This represents the measurement signal of the controller. Indicates the controller's setpoint; Step 4: To overcome the issues in object passing functions This can lead to system overshoot, so the controller parameters must be tuned first. ,Pick ,Right now After simplifying the numerator and denominator in the formula of step two, we get: exist The second inertial element has been eliminated. Given this model factor, the object has been simplified to a typical first-order pure time-delay transfer function: The controller has also been simplified to the transfer function of a typical PID controller: The simplified system block diagram consisting of the controller and the controlled object has the following closed-loop transfer function: ; Step 5: The simplified closed-loop system consisting of the controller and the controlled object is tuned using the classic PID parameter tuning method. , and Since the object model is a standard first-order pure time delay object, the tuned PID parameters are suitable for the control of this object model. Step 6: Finally, add the elimination steps from step 4. Factors Parameters, the entire controller , , , The tuning is achieved through four control parameters.

[0018] Furthermore, in order to overcome the actual object transfer function during object identification... Smaller than the recognition result, i.e. Greater than the actual When the system oscillations caused by this are adjusted using actual parameters, the following methods can be used: Through system simulation, The system overshoot is negligible at that time.

[0019] Furthermore, to overcome the potential for large fluctuations in the controller output after two stages of proportional-derivative operations in practical applications, which could affect the actual control performance, this method adds an output constraint judgment to the derivative-ahead stage during the discretization of the control algorithm. Specifically, when... hour, The discretization formula for the proportional-differential element is: ; in This represents the current output quantity during the discrete operation of the proportional-differential component. This indicates the deviation value currently sampled. This represents the deviation value from the previous sample. This indicates the control period, which is the time interval between two samplings.

[0020] Furthermore, in step one Indicates the gain of the object. Represents the second-order inertial element of the object. This represents the time constant of the first inertial element. The time constant of the second inertial element should be taken as the larger one during object identification. The small time constant is , Represents the pure time delay of the object.

[0021] Furthermore, in step two... Indicates the proportional gain of the controller. This represents the differential lead-ahead element of the controller. This represents the derivative time of the controller's derivative-ahead process, also known as the first derivative time. This indicates the PID control element of the controller. This represents the integral time of the controller. This represents the derivative time of the PID control loop in the controller, also known as the second derivative time.

[0022] Furthermore, in step five, after eliminating the second inertial element factor of the object, the PID parameters are tuned using the 4:1 attenuation method, as shown in the following formula: .

[0023] Furthermore, the aforementioned This indicates the output of the current differential term. This indicates the current deviation value. This represents the deviation value from the previous control cycle. Represents the differential time. This indicates the control cycle of the controller.

[0024] Furthermore, the aforementioned The constraint is: at that time, .

[0025] like Figure 2 As shown, when At this time, it is a typical control system consisting of a PID controller and a first-order pure time delay object.

[0026] like Figure 3 As shown, the mathematical model of the object represented by the solid line is: The mathematical model for the DPID controller is as follows: The temperature control system, with an ambient temperature of 22.8℃ and a setpoint of 200℃, has the following PID parameters: Second ℃ Second Second.

[0027] The dashed line represents the following: The mathematical model of the above object is approximately: The mathematical model of the PID controller is as follows: The temperature control system, with an ambient temperature of 23.3℃ and a setpoint of 200℃, has the following PID parameters: Second Second.

[0028] Comparing the two control response curves, the DPID parameters tuned using the object factor elimination method exhibit excellent phase control performance, achieving a relatively short transient response (nearly zero deviation at 20 minutes) and virtually no overshoot. In contrast, the PID control approximated by a first-order pure time-delay object model suffers from 20.8°C overshoot and a transient response as long as 35 minutes. The advantages of both are evident.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for tuning PID control parameters based on a cancellation target factor, characterized in that: Includes the following steps: Step 1: The controlled object is equivalent to a second-order pure time-delay object model, and the object's transfer function is as follows: ； in This represents the gain of the controlled object. This represents the time constant of the first inertial element of the controlled object. Let represent the time constant of the second inertial element of the controlled object. For the convenience of the analysis and derivation in the following steps, Indicates the pure time delay of the controlled object; Step 2: The controller adopts a derivative-first DPID control algorithm, and the controller's transfer function is as follows: ； in This represents the proportional gain of the controller. This represents the derivative time of the differential advance element of the controller. This represents the integral time of the PID controller. This represents the derivative time of the PID controller. Step 3: The controlled object and the controller constitute a closed-loop control system, and its closed-loop transfer function is: in This represents the measurement signal of the controller. Indicates the controller's setpoint; Step 4: To overcome the issues in object passing functions This can lead to system overshoot, so the controller parameters must be tuned first. ,Pick ,Right now After simplifying the numerator and denominator in the formula of step two, we get: exist The second inertial element has been eliminated. Given this model factor, the object has been simplified to a typical first-order pure time-delay transfer function: The controller has also been simplified to the transfer function of a typical PID controller: The simplified system block diagram consisting of the controller and the controlled object has the following closed-loop transfer function: ； Step 5: The simplified closed-loop system consisting of the controller and the controlled object is tuned using the classic PID parameter tuning method. , and Since the object model is a standard first-order pure time delay object, the tuned PID parameters are suitable for the control of this object model. Step 6: Finally, add the elimination steps from step 4. Factors Parameters, the entire controller , , , The tuning is achieved through four control parameters.

2. The PID control parameter tuning method based on the offsetting object factor according to claim 1, characterized in that: To overcome the actual object passing function during object identification... Smaller than the recognition result, i.e. Greater than the actual When the system oscillations caused by this are adjusted using actual parameters, the following methods can be used: .

3. The PID control parameter tuning method based on the offsetting object factor according to claim 1, characterized in that: To overcome sudden disturbances encountered in practical applications, and to address the potential for significant output fluctuations after two stages of proportional-derivative operations that could affect the actual control performance, an output constraint judgment for the derivative-ahead stage is added to the discretized control algorithm. Specifically, when… hour, The discretization formula for the proportional-differential element is: ; in This represents the current output quantity during the discrete operation of the proportional-differential component. This indicates the deviation value currently sampled. This represents the deviation value from the previous sample. This indicates the control period, which is the time interval between two samplings.

4. The PID control parameter tuning method based on the offsetting object factor according to claim 1, characterized in that: The For representing the second-order inertial element of an object, a large time constant should be chosen during object identification. The small time constant is .

5. The PID control parameter tuning method based on the offsetting object factor according to claim 1, characterized in that: The This represents the differential lead-ahead element of the controller. This indicates PID control of the controller.

6. The PID control parameter tuning method based on the offsetting object factor according to claim 1, characterized in that: In step five, after eliminating the second inertial element factor of the object, the PID parameters are tuned using the 4:1 attenuation method, as shown in the following formula: .

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