Thermal equipment water temperature control method based on relaxation iteration PID (Proportion Integration Differentiation) algorithm

Abstract

The invention discloses a thermal equipment water temperature control method based on a relaxation iteration PID algorithm, and aims to solve the problems that overshoot is easy to occur when a set value suddenly changes, and integral saturation and noise sensitivity are easy to cause by integral item accumulated errors in traditional PID control. The method comprises the following steps: calculating a current error e (t) = Tset (t)-Tmeas (t); a relaxation factor is introduced to dynamically adjust PID output increment, and the relaxation factor is adjusted according to a set value change rate in a grading manner; the accumulative control quantity is limited within the duty ratio range of 0-100%; and when the error absolute value is greater than 2 DEG C, freezing an integral term to avoid overshoot. According to the method, overshoot is effectively suppressed by setting a relaxation factor, differential terms are improved to reduce noise interference, and integral terms are managed in a partitioned manner to improve stability. Compared with a traditional PID control method, the method has the advantages that overshoot can be effectively restrained, the adjusting time is shortened, and the method is suitable for an industrial control system.

Description

Technical Field

[0001] The present invention relates to the field of automatic control technology, and in particular to a water temperature control method for thermal equipment using a relaxation iterative PID algorithm. Background Art

[0002] PID algorithm control is widely used in industrial control systems. It uses the PID controller to calculate the error signal (the deviation between the set value and the actual value) in real time, and generates the control quantity based on the combined effect of the three links of proportion (p), integration (i), and differentiation (d), thereby driving the system output to quickly track the set value.

[0003] However, traditional PID control is prone to overshoot when the set value changes suddenly, causing system oscillation. For example, a sudden change in water temperature causes the actuator to start and stop frequently. The accumulated error in the integral term can easily lead to integral saturation, thereby reducing the stability of the control system. The differential term is sensitive to measurement noise and can easily aggravate the wear of the actuator.

[0004] In order to solve the above problems, the present invention proposes a water temperature control method for thermal equipment using a relaxed iterative PID algorithm. Summary of the Invention

[0005] The present invention aims to provide a method for controlling water temperature in thermal equipment using a relaxed iterative PID algorithm. This method addresses the problems of existing PID control algorithms, such as overshoot when the setpoint changes suddenly, low stability due to accumulated errors in the integral term, and increased wear of the actuator due to noise sensitivity in the differential term.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for controlling water temperature of thermal equipment using a relaxed iterative PID algorithm comprises the following steps:

[0008] S1. Calculate the current error e(t) = T set (t)-T meas (t), where Tset is the dynamic set temperature, T meas To measure temperature in real time;

[0009] S2, introduce relaxation factor α(t) to dynamically adjust the PID output increment:

[0010] Δu(t)=α(t)[K p ·(e(t)-e(t-1))+K i ·e(t)+K d ·(T meas (t-1))-2T meas (t-2)+T meas (t-3)]

[0011] where Kp is the proportional gain, K i is the integral gain, K d is the differential gain, α(t) changes according to the set value rate |dT set / dt|Adaptive adjustment:

[0012]

[0013] S3, cumulative control amount u(t) = u(t-1) + Δu(t), and limited to the duty cycle range of [0%, 100%];

[0014] S4. Manage the integral term in partitions and freeze the integral when |e(t)|>2℃ to avoid overshoot.

[0015] Furthermore, the method is applied to a constant temperature water circulation control system, whose hardware configuration is an STM32 controller, a PT100 temperature sensor, and a PWN speed-regulating water pump.

[0016] Furthermore, the method is applied to temperature control in the fields of industrial reactors, constant temperature water circulation systems, and domestic water heaters.

[0017] PID controllers are very simple and easy to use, so they can be very reliable and easy to use.In addition, the control circuit diagram of the control circuit diagram is very simple and easy to use. The control circuit diagram of the control circuit diagram is very simple and easy to use. The control circuit diagram of the control circuit diagram is very simple and easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the temperature regulation process using the method of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0020] Example

[0021] A method for controlling water temperature of thermal equipment using a relaxed iterative PID algorithm comprises the following steps:

[0022] S1. Calculate the current error e(t) = T set (t)-T meas (t), where Tset is the dynamic set temperature, T meas To measure temperature in real time;

[0023] S2, introduce relaxation factor α(t) to dynamically adjust the PID output increment:

[0024] Δu(t)=α(t)[K p ·(e(t)-e(t-1))+K i ·e(t)+K d ·(T meas (t-1))-2T meas (t-2)+T meas (t-3)]

[0025] where K p is the proportional gain, K i is the integral gain, K d is the differential gain, α(t) changes according to the set value rate |dT set / dt|Adaptive adjustment:

[0026]

[0027] S3, cumulative control amount u(t) = u(t-1) + Δu(t), and limited to the duty cycle range of [0%, 100%];

[0028] S4. Manage the integral term in partitions and freeze the integral when |e(t)|>2℃ to avoid overshoot.

[0029] The method of the present invention is now compared with the PID control algorithm of the prior art. The existing PID control algorithm is as follows:

[0030] The control output u(t) of the traditional PID is determined by the following formula:

[0031]

[0032] In the formula, K p is the proportional gain, which directly responds to the current error; K i is the integral gain, which will eliminate the steady-state error but may cause integral saturation; K d It is a differential gain that can suppress overshoot but is the most sensitive to noise.

[0033] The existing PID control has certain limitations and is prone to overshoot problems. The proportional term K p and the integral term K i When the set value suddenly changes, it is easy to cause output oscillation. For example, when the water temperature suddenly rises from 30℃ to 50℃, the PID may first rush to 55℃ and then fall back. The problem of integral saturation, long-term error accumulation will cause the integral term to be too large and the system to recover slowly. Noise sensitivity problem, the differential term K d Directly amplify the measurement noise, resulting in frequent start and stop of the actuator (such as a water pump).p , K i , K d It is a constant and cannot adaptively adjust to dynamic working conditions (dramatic changes in the set value).

[0034] 1. The present invention introduces a relaxation dynamic factor α(t), which is graded and adjusted according to the rate of change of the set value:

[0035] In the case of drastic changes in |dT set When / dt|≥0.5℃ / s: α(t)=1, the change of the controlled amount can be greatly suppressed.

[0036] In the gently changing |dT set When / dt|<0.5℃ / s: α(t)-0.05, it can be adjusted appropriately.

[0037] Through such a setting, the present invention can effectively suppress overshoot when the set value suddenly changes, and reduce the oscillation of the actuator, compared with the PID control algorithm in the prior art.

[0038] 2. Improvement of the differential term in the present invention: The differential term of the traditional PID control algorithm is based on the error difference (de(t) / dt), which is more sensitive to noise. The differential term in the present invention is calculated using the third-order difference of the measured temperature (K d ·(T meas (t-1))-2T meas (t-2)+T meas (t-3)). This multi-step differential calculation can smooth out noise and reduce the frequent movements of the actuator caused by noise.

[0039] 3. The present invention sets up partition management of integral items. The integral items of traditional PID control algorithms continuously accumulate errors, which easily leads to integral saturation. However, the control algorithm of the present invention sets a setting to freeze the integral when |e(t)|>2℃. This setting can disable the integral when there is a large error to avoid overclocking; restore the integral when the error is small to eliminate steady-state errors.

[0040] The method of the present invention was applied to a constant-temperature water circulation control system and compared with a traditional PID algorithm. The hardware in the constant-temperature water circulation control system includes an STM32 controller, a PT100 temperature sensor, and a PWM speed-regulating water pump. The internal PID algorithm parameters are Kp = -0.07, Ki = -0.001, and Kd = 0.1. α(t) is adjusted in stages based on the rate of change of the set value. The effectiveness of the method of the present invention was verified by varying the set temperature.

[0041] The results are as follows Figure 1As shown in Table 1, from 0 to 100 seconds, the initial setpoint was 43°C, and the measured temperature steadily decreased from 45°C with no overshoot. From 100 to 200 seconds, the setpoint suddenly increased to 46°C, and the temperature stabilized within 40 seconds, with an overshoot of less than 0.3°C. From 200 to 300 seconds, the setpoint suddenly dropped to 42°C, shortening the settling time to 35 seconds and achieving a steady-state error of ≤0.1°C. Compared to traditional PID control methods, this method reduces overshoot by 62% and shortens settling time by 28%.

[0042] Table 1 Performance comparison between the method of the present invention and the traditional PID control method

[0043]

[0044] In summary, the present invention solves the three major pain points of the traditional PID control algorithm in thermal control by improving the three aspects of setting dynamic relaxation factor, anti-noise differential and intelligent integral management. Overshoot suppression: softening the sudden change response through the dynamic relaxation factor α(t); setting the integral freezing mechanism to prevent saturation and improve stability; setting the third-order difference to replace the traditional differential term to increase robustness.

[0045] The above is only an embodiment of the present invention, and common knowledge such as the specific technical solutions or characteristics in the solution is not described in detail here. For those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for controlling water temperature of thermal equipment using a relaxed iterative PID algorithm, characterized in that: The following steps are involved: S1. Calculate the current error e(t) = T set (t)-T meas (t), where T set is the dynamic setting temperature, T meas To measure temperature in real time; S2, introduce relaxation factor α(t) to dynamically adjust the PID output increment: Δu(t)=α(t)[K p (e(t)-e(t-1))+K i e(t)+K d ·(T meas (t-1)) -2T meas (t-2)+T meas (t-3)] where K p is the proportional gain, K i is the integral gain, K d is the differential gain, α(t) changes according to the set value rate |dT set / dt|Adaptive adjustment: S3, cumulative control amount u(t) = u(t-1) + Δu(t), and limited to the duty cycle range of [0%, 100%]; S4. Manage the integral term in partitions and freeze the integral when |e(t)|>2℃ to avoid overshoot.

2. The method for controlling water temperature of thermal equipment using a relaxed iterative PID algorithm according to claim 1, characterized in that: This method is applied to a constant temperature water circulation control system, whose hardware configuration includes an STM32 controller, a PT100 temperature sensor, and a PWN speed-regulating water pump.

3. The method for controlling water temperature of thermal equipment using a relaxation iterative PID algorithm according to claim 1, characterized in that: This method is applied to temperature control in the fields of industrial reactors, constant temperature water circulation systems, and household water heaters.

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