A constant pressure and constant liquid level control method for a glass utility water pump house

Abstract

A constant pressure and constant liquid level control method for a glass utility water pump house, belonging to the technical field of float glass manufacturing, solves the problem of how to design a constant pressure and constant liquid level control method with a short adjustment time and good dynamic performance; the pressure and liquid level signals of the water pump house fed back by an external transmitter are filtered for high-order harmonics in the signal after passing through an advanced low-pass filtering link, and then the differential judgment link is used to collect the pressure and liquid level data, find the difference and divide by the interval time to obtain the change rate, and finally the constant pressure and constant liquid level control signal of the water pump house is output through an improved incremental PID link; the advanced low-pass filtering link of the present invention eliminates high-order harmonics in the signal after signal acquisition, optimizing the input signal; the differential judgment link is added to dynamically balance and improve the execution efficiency of the change algorithm, greatly shortening the adjustment time; the improved incremental PID link dynamically adjusts the proportional gain to avoid generating an integral saturation area, making its dynamic performance better.

Description

Technical Field

[0001] The present invention belongs to the technical field of float glass manufacturing, and relates to a constant pressure and constant liquid level control method for a glass utility water pump house. Background Art

[0002] With the rapid development of the float glass industry, as the blood providing for the glass production line - utilities has become very important. Utilities include a water pump house, a gas station (air compressor station), and an oil station (gas station). Among them, the water pump house provides a circulating water system, which is mainly used for cooling instrument equipment. The gas station mainly provides compressed gas, which is mainly used as the power source for pneumatic equipment. The oil station (gas station) mainly provides heavy oil (natural gas), which mainly provides heat for the glass furnace. These are almost related to the reliability of the operation of all equipment and are also the basis of glass production. The control system of the water pump house is relatively complex. Among them, the stability of the water supply pressure is closely related to the quality of the glass. To ensure the stability of the water supply pressure, constant water supply pressure control is often required. In order to ensure the safe and reliable entry of the water in the hot water tank into the cooling tower, a constant liquid level control method is also required. This makes it necessary to include constant pressure control and constant liquid level control in the water pump house control system. The constant pressure control includes main line water supply constant pressure control and gas station water supply constant pressure control. The constant liquid level control is the constant liquid level control of the return water tank (hot water tank).

[0003] For the constant pressure control and constant liquid level control systems, because they themselves have a large number of inertial link characteristics, they all belong to the range of lag control. Simply put, when the controller outputs the result to the frequency converter, the output result needs to wait for a period of time to be truly fed back to the acquisition device, and there is a certain lag between the output and the result. The lag time of pressure and liquid level is relatively large. Such a control system is called a lag control system.

[0004] For hysteresis control, the existing technology mainly adopts position-type PID control. Position-type PID control requires precise control and adjustment algorithm refresh time for hysteresis systems. If the position-type PID refresh speed of the control system is too fast, much faster than the lag time of the system control link, this will cause the system to be at the maximum output for a long time. Even if a small data is changed, the entire system will be in an overshoot state. If the system is in an overshoot state for a long time, it will often cause the output link to have data that is too large or too low (even zero pressure may occur). Excessive water pressure will cause the output temperature to be too low, affecting the quality of the glass. At the same time, high pressure means higher power output, which will lead to energy waste. Too low pressure will cause the water temperature to rise as well, or the water flow will be cut off, which will damage equipment that requires water cooling. Such unstable output is very unfavorable for upstream glass production. However, if the refresh speed of the position PID of the control system is too slow, the adjustment time will be prolonged. The adjustment of the position PID relies on all the data remembered in the past, so it is easy to enter the integral saturation area. If it cannot be adjusted in time, the output result will remain at the wrong data for a long time, thereby affecting the efficiency of the operation. If the time is too long, then changing a smaller data will also cause oscillations of more than ten minutes before stabilizing at a result, which is a very unfavorable result. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to design a constant pressure and constant liquid level control method with short adjustment time and good dynamic performance for the large inertia link of pressure and liquid level signals in the water pump room of glass utility project.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] A constant pressure and level control method for a water pump room in a glass utility project includes an advanced low-pass filtering step, a differential judgment step, and an improved incremental PID step. The water pump room pressure and level signals fed back by an external transmitter are filtered for high-order harmonics through the advanced low-pass filtering step. The differential judgment step then collects the pressure and level data, calculates the difference, and divides the difference by the interval time to obtain the rate of change. Finally, the improved incremental PID step outputs the water pump room constant pressure and level control signal.

[0008] The formula for the advanced low-pass filtering step is:

[0009]

[0010] Among them, y t is the result of the external transmitter feedback at the tth interruption, α and η are the filter coefficients, β is the filter gain value, is the intermediate value output after filtering at the tth interruption, is the intermediate value of the filtered output at the (t - 1)-th interruption, f t is the value of the filtered output at the t-th interruption, f t-1 is the value of the filtered output at the (t - 1)-th interruption;

[0011] The formula of the differential judgment link is:

[0012]

[0013] where t1 is the judgment time coefficient, λ is the judgment decision value, u t is the result of the incremental PID output at the t-th interruption, u t-1 is the result of the incremental PID output at the (t - 1)-th interruption, d t is the result of the differential judgment output at the t-th interruption, abs() is the absolute value operation;

[0014] The formula of the improved incremental PID link is:

[0015] err t = d t - d t-1

[0016]

[0017] u t = u t-1 + D(u t )

[0018]

[0019] where D(u t ) is the incremental value at the t-th interruption, k p is the proportionality coefficient, k i is the integral coefficient, k d is the differential coefficient, err t is the error value at the t-th interruption, err1 is the error value at the 1st interruption, err t-1 is the error value at the (t - 1)-th interruption, err t-2 is the error value at the (t - 2)-th interruption, d1 and d2 are the coefficients of the linear equation respectively, is the dynamic gain value, d t-1 is the result of the differential judgment output at the (t - 1)-th interruption.

[0020] The advantages of the present invention are:

[0021] The method of the present invention has three advantages: First, the advanced low-pass filtering link mainly eliminates the high-order harmonics in the filtered signal after signal acquisition and optimizes the input signal; Second, an additional differential judgment link is used to identify the final value after passing through the lag link after this calculation; It can dynamically balance and change the execution efficiency of the algorithm, greatly shortening the adjustment time; Third, compared with the position-type PID algorithm, the improved incremental PID algorithm has the following advantages: The advantage of incremental PID lies in adding a linear equation in terms of the proportional gain. The proportional link is the main link affecting the output result of the PID controller. Adding a linear equation allows for dynamically adjusting the proportional gain, resulting in better dynamic performance, less impact from misoperations, less impact during manual / automatic switching, facilitating disturbance-free switching, the formula not requiring accumulation, and avoiding the generation of an integral saturation region. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a structural block diagram of the constant pressure and constant liquid level control method for the glass utility water pump house according to an embodiment of the present invention;

[0023] Figure 2 is a flowchart of the constant pressure and constant liquid level control method for the glass utility water pump house according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0025] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0026] Embodiment 1

[0027] As Figure 1 and Figure 2 shown, a constant pressure and constant liquid level control method for a glass utility water pump house includes: an advanced low-pass filtering link, a differential judgment link, and an improved incremental PID link; The feedback water pump house pressure and liquid level signals pass through the advanced low-pass filtering link to filter out the high-order harmonics in the signal, and then through the differential judgment link, the pressure and liquid level data are collected, the difference is calculated and divided by the interval time to obtain the change rate, and finally, the water pump house pressure and liquid level control signals are output through the improved incremental PID link.

[0028] 1. Advanced low-pass filtering link

[0029] The formula for the advanced low-pass filtering section is as follows:

[0030]

[0031] where y t is the result feedback by the external transmitter at the t-th interruption, α and η are filtering coefficients, β is the filtering gain value, is the intermediate value output after filtering at the t-th interruption, is the intermediate value output after filtering at the (t - 1)-th interruption, f t is the value output after filtering at the t-th interruption, f t-1 is the value output after filtering at the (t - 1)-th interruption.

[0032] Since the phase of the constant pressure and constant liquid level control signal of the pump house is shifted when passing through the advanced low-pass filtering section, it will cause the total output data value to be slightly lower than the actual value. Therefore, a gain value needs to be provided for compensation. The size of the gain value needs to be judged in combination with on-site data. Generally, multiple samplings are taken at the same interval time, the difference between the two is obtained, and then the average value of the difference is taken to obtain the result.

[0033] 2. Differential judgment section

[0034] The formula for the differential judgment section is as follows:

[0035]

[0036] where t1 is the judgment time coefficient, λ is the judgment decision value, u t is the result of the incremental PID output at the t-th interruption, u t-1 is the result of the incremental PID output at the (t - 1)-th interruption, d t is the result of the differential judgment output at the t-th interruption, and abs() is the absolute value operation.

[0037] In actual constant pressure and constant liquid level control, there is a lag relationship between the drive unit and the pressure and liquid level. That is, the data calculated by the CPU can be quickly sent to the frequency converter device through communication or analog quantity. This time is usually in milliseconds. However, it often takes a long time for the frequency converter to receive the signal and reach the frequency that the signal should output. Then, through the water supply of the pump to act on the pressure sensor or liquid level sensor part, it also takes a certain amount of time to finally obtain the feedback value under the action of this signal. Therefore, the CPU is very fast, while the execution and feedback mechanisms are very slow, which causes two problems. First, the rate mismatch leads to an incorrect relationship between the feedback result and the output, triggering system oscillation. Second, the adjustment time is lengthened, and the frequency converter is in an incorrect output for a long time, affecting normal production.

[0038] The differential judgment link obtains the change rate by collecting, taking the difference, and dividing by the interval time of the pressure and liquid level data in this time and the previous time. For example, given a pressure or liquid level, if there is no lag or it has reached equilibrium, then the change rate of the two collections and feedback is very small, and it can be considered that the current output has fully acted on the frequency converter. If there is a lag, the feedback pressure or liquid level will affect the slow change, and the change rate calculated from the data of the two collections will not be very small. It can be considered that the result of the previous data output is still in the action period. At this time, neither the feedback pressure nor the liquid level should be calculated. When the data is very small, that is, when it has fully acted on the frequency converter, the pressure and liquid level collected again can be calculated again to obtain a new output value, which can dynamically balance the execution efficiency of the algorithm and greatly shorten the adjustment time.

[0039] 3. Improved incremental PID link

[0040] The formula for the improved incremental PID link is as follows:

[0041] err t = d t - d t-1

[0042]

[0043] u t = u t-1 + D(u t )

[0044]

[0045] Among them, D(u t ) is the incremental value at the t-th interruption, k p is the proportionality coefficient, k i is the integral coefficient, k d is the differential coefficient, err t is the error value at the t-th interruption, err1 is the error value at the 1st interruption, err t-1 is the error value at the (t - 1)-th interruption, err t-2 is the error value at the (t - 2)-th interruption, d1 and d2 are the coefficients of the linear equation, is the dynamic gain value, d t-1 is the result of the differential judgment output at the (t - 1)-th interruption.

[0046] The advantage of the incremental PID is that a linear equation is added to the proportional gain. The proportional link is the main link affecting the output result of the PID controller. Adding a linear equation can dynamically adjust the proportional gain, making its dynamic performance better.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A constant pressure and constant liquid level control method for a glass utility water pump house, characterized in that, Including: An advanced low-pass filtering section, a differential judgment section, and an improved incremental PID section; the pressure and liquid level signals of the pump house fed back by an external transmitter are filtered for high-order harmonics in the signal after passing through the advanced low-pass filtering section, and then the differential judgment section is used to collect the pressure and liquid level data, find the difference and divide by the interval time to obtain the change rate, and finally the improved incremental PID section outputs the constant pressure and constant liquid level control signal of the pump house; The formula of the advanced low-pass filtering section is: where y t is the result feedback by the external transmitter at the t-th interruption, α and η are filtering coefficients, and β is the filtering gain value, is the intermediate value output after filtering at the t-th interruption, is the intermediate value output after filtering at the (t - 1)-th interruption, f t is the value output after filtering at the t-th interruption, f t-1 is the value output after filtering at the (t - 1)-th interruption; The formula of the differential judgment section is: Among them, t1 is the judgment time coefficient, λ is the judgment decision value, u t is the result of the incremental PID output at the t-th interruption, u t-1 is the result of the incremental PID output at the (t - 1)-th interruption, d t is the result of the differential judgment output at the t-th interruption, and abs() is the absolute value operation; The formula of the improved incremental PID section is: err t = d t -d t-1 u t = u t-1 + D(u t ) where D(u t ) is the t-th interruption increment value, k p is the proportionality coefficient, k i is the integral coefficient, k d is the differential coefficient, err t is the error value at the t-th interruption, err1 is the error value at the 1st interruption, err t-1 is the error value at the (t - 1)-th interruption, err t-2 is the error value at the (t - 2)-th interruption, d1 and d2 are the coefficients of the linear equation, is the dynamic gain value, d t-1 is the result of the differential judgment output at the (t - 1)-th interruption.

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