Pool liquid level control method and system for the turbid circulating water system of a headless continuous casting and rolling production line

Abstract

The present application discloses a method and a system for controlling the water tank liquid level of a turbid circulating water system in a headless continuous casting and rolling production line, which relates to the technical field of automatic control. The method includes the following steps: obtaining the interval time T of liquid level change; adjusting the execution interval time Ti of the control process according to the interval time T of liquid level change; setting the liquid level, and constructing a fuzzy controller with the liquid level deviation e and the interval time T of liquid level change as output variables, wherein the liquid level deviation e = set liquid level - actual liquid level; adjusting the opening degree of the return water valve and the opening degree of the pump outlet valve through the fuzzy controller to realize the automatic control of the water tank liquid level. The method of the present invention realizes the automatic control of the water tank liquid level and improves the response speed of the system and the control accuracy of the water tank liquid level.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control, and more particularly to a method and system for controlling the water tank liquid level of a turbid circulating water system in a endless casting and rolling production line. Background Art

[0002] The turbid circulating water system of the endless casting and rolling production line includes a turbid circulating cold water tank, a swirl well water tank and a rare earth disk water tank. Due to the large lag in the liquid level control of these water tanks, large fluctuations in the inlet water flow rate, rapid rise and fall of the water tank liquid level when the rolling line operation mode changes, a large number of control objects in the liquid level control, high requirements for the liquid level control accuracy and safety, etc., it is impossible to obtain an accurate mathematical model of the system, and it is difficult to achieve precise automatic control of the water tank liquid level.

[0003] In the prior art, the fuzzy control algorithm can control according to the liquid level deviation and the liquid level change rate of the water tank, relying on the experience and intuitive judgment of the operator. However, due to the lag of the water tank liquid level, it is impossible to obtain an accurate liquid level change rate. The main reason is that a suitable sampling period cannot be found, resulting in the inability to respond in real time to the rapid change of the liquid level when controlling the liquid level, and causing the risk of accidents due to the sudden rise and fall of the liquid level; in addition, after a single control output, due to the lag of the system, a certain interval period must be set before the control output can be performed again, and it is very difficult to grasp the execution interval period. If it is too long, the risk brought by the rapid change of the liquid level cannot be responded to in time, and if it is too short, the requirements of the system lag cannot be met. Due to the above reasons, the application effect of the conventional fuzzy control algorithm is not ideal enough, and it can only control according to the liquid level deviation, and cannot avoid the risk brought by the sudden rise and fall of the liquid level, resulting in frequent overshoot of the liquid level control and poor liquid level stability.

[0004] Therefore, based on the deficiencies of the existing fuzzy control algorithm in the liquid level control of the turbid circulating water system water tank, the present invention provides an improved fuzzy control algorithm to improve the stability of the liquid level control. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for controlling the water tank liquid level of a turbid circulating water system in an endless casting and rolling production line, to realize the automatic control of the water tank liquid level, and to improve the response speed of the system and the control accuracy of the water tank liquid level.

[0006] To achieve the above purpose, the present invention discloses the following technical solutions:

[0007] On the one hand, the present invention provides a method for controlling the water tank liquid level of a turbid circulating water system in an endless casting and rolling production line, the method comprising the following steps:

[0008] Obtain the interval time T of the liquid level change;

[0009] Adjust the execution interval time Ti of the control process according to the interval time T of the liquid level change;

[0010] Set the liquid level, use the liquid level deviation e and the interval time T of the liquid level change as input variables, and construct a fuzzy controller. The output variable of the fuzzy controller is the increase or decrease value U of the return valve opening, where the liquid level deviation e = set liquid level - actual liquid level;

[0011] The fuzzy controller is used to adjust the opening of the return valve and the pump outlet valve to achieve automatic control of the water pool liquid level.

[0012] Preferably, in the above-mentioned pool liquid level control method, when the interval time T of the liquid level change is a positive number, it indicates that the pool liquid level is rising; when the interval time T of the liquid level change is a negative number, it indicates that the pool liquid level is falling. The smaller the absolute value of the interval time T of the liquid level change, the faster the rate of change of the pool liquid level; the larger the absolute value of the interval time T of the liquid level change, the slower the rate of change of the pool liquid level.

[0013] In the above-mentioned pool liquid level control method, the functional relationship between the execution interval time Ti of the control process and the interval time T of the liquid level change is as shown in formula (1):

[0014] Ti=(T-T1) / (T2-T1)×(Ti2-Ti1)+Ti1 (1)

[0015] Among them, T represents the interval time of liquid level change, T1 represents the shortest interval time of liquid level change, T2 represents the longest interval time of liquid level change, Ti1 represents the shortest execution interval time of the control process, and Ti2 represents the longest execution interval time of the control process.

[0016] In the above-mentioned water pool liquid level control method, the step of constructing a fuzzy controller further includes:

[0017] First, the liquid level deviation e and the interval time T of liquid level change are fuzzified;

[0018] Then, fuzzy reasoning is performed;

[0019] Next, the centroid method is used to perform defuzzification to obtain the output value U.

[0020] Preferably, in the above-mentioned pool liquid level control method, the output value U is a value for increasing or decreasing the opening of the return valve. A positive value of the output value U indicates an increase in the return valve opening, while a negative value indicates a decrease in the return valve opening. When the output value U is greater than 0, the return valve opening = the previous return valve opening + the output value U. When the output value U is less than 0, the pump outlet valve opening = the previous pump outlet valve opening - the output value U × f, where f = the return valve diameter² / the pump outlet valve diameter².

[0021] Another aspect of the present invention provides a water tank level control system for a turbid circulating water system of a headless continuous casting and rolling production line, the system comprising:

[0022] Liquid level change time module, used to obtain the interval time T of the liquid level change;

[0023] Control execution time module, used to adjust the execution interval time Ti of the control process according to the interval time T of the liquid level change;

[0024] Controller construction module, used to set the liquid level, take the liquid level deviation e and the interval time T of the liquid level change as input variables, and construct a fuzzy controller. The output variable of the fuzzy controller is the increase or decrease value U of the return water valve opening, where the liquid level deviation e = set liquid level - actual liquid level;

[0025] Automatic control module, used to adjust the return water valve opening and the pump outlet valve opening through the fuzzy controller to realize the automatic control of the water tank liquid level.

[0026] For the above-mentioned water tank liquid level control system, the functional relationship between the execution interval time Ti of the control process and the interval time T of the liquid level change is shown in Equation (1),

[0027] Ti = (T - T1) / (T2 - T1)×(Ti2 - Ti1) + Ti1 (1)

[0028] Wherein, T represents the interval time of the liquid level change, T1 represents the shortest interval time of the liquid level change, T2 represents the longest interval time of the liquid level change, Ti1 represents the shortest execution interval time of the control process, and Ti2 represents the longest execution interval time of the control process.

[0029] The effects provided in the invention content are only the effects of the embodiments, rather than all the effects of the invention. One of the technical solutions in the above technical solutions has the following advantages or beneficial effects:

[0030] In the embodiment of the present application, on the one hand, by using the interval time of the liquid level change instead of the conventional liquid level change rate, the problem of low accuracy caused by the inability to obtain an accurate sampling period for the liquid level change rate is solved; on the other hand, the execution interval time output by the system control can be dynamically adjusted according to the speed of the liquid level change, solving the problems of slow response and large hysteresis caused by the fixed execution period in the existing algorithms, and improving the liquid level control accuracy. In addition, by adjusting the return water valve and the pump outlet valve opening through the improved fuzzy control algorithm, the automatic control of the liquid level is realized, and the safety of the equipment operation is improved. Brief Description of the Drawings

[0031] The drawings here are incorporated into the description and form a part of the description, showing the embodiments in line with the present application, and are used together with the description to explain the principles of the present application.

[0032] Figure 1Schematic diagram of the method for controlling the water tank liquid level of the turbid circulating water system of the endless casting and rolling production line provided by an embodiment of the present application;

[0033] Figure 2 Analysis diagram of sampling the liquid level change rate at fixed time intervals;

[0034] Figure 3 Calculation and analysis diagram of the interval time T of the liquid level change;

[0035] Figure 4 Schematic diagram of the functional relationship between the system execution interval time Ti and the interval time T of the liquid level change;

[0036] Figure 5 Schematic diagram of the structure principle of the fuzzy controller constructed in this embodiment;

[0037] Figure 6 Membership function diagram of the liquid level deviation e;

[0038] Figure 7 Membership function diagram of the interval time T of the liquid level change;

[0039] Figure 8 Schematic diagram of the structure of the water tank liquid level control system of the turbid circulating water system of the endless casting and rolling production line provided by an embodiment of the present application. Detailed implementation manners

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0041] It should be noted that the references to "one embodiment", "embodiment", "exemplary embodiment", etc. in this specification mean that the described embodiment may include specific features, structures or characteristics, but not every embodiment must include these specific features, structures or characteristics. In addition, such expressions do not refer to the same embodiment. Further, when combining an embodiment to describe a specific feature, structure or characteristic, it is within the knowledge of those skilled in the art to combine such feature, structure or characteristic into other embodiments whether or not there is an explicit description.

[0042] In addition, in the specification and the subsequent claims, certain terms are used to refer to specific components or parts. Those with ordinary knowledge in the relevant field should understand that the manufacturer may use different nouns or terms to refer to the same component or part. The specification and the subsequent claims do not use the difference in names as a way to distinguish components or parts, but use the difference in functions of components or parts as the criterion for distinction. The terms "comprising" and "including" mentioned throughout the specification and the subsequent claims are open-ended terms and should therefore be interpreted as "including but not limited to". In addition, the term "connected" herein includes any direct and indirect electrical connection means. Indirect electrical connection means include connection through other devices.

[0043] Reference Figure 1 , Figure 1 FIG. shows a schematic flow chart of a method for controlling the water tank liquid level of a turbid circulating water system in a headless continuous casting and rolling production line provided by an embodiment of the present application. The method includes the following steps:

[0044] S10. Obtain the interval time T of the liquid level change;

[0045] In the method of this embodiment, the interval time T of the liquid level change is used instead of the conventional liquid level change rate.

[0046] In a specific implementation, the water tank liquid level detection generally uses 12-bit binary representation. If the liquid level range is 0 to 8 meters, then the liquid level detection accuracy = 8m / (2 12 ) = 0.01953 meters. Since the water tank liquid level is relatively large, the liquid level rise and fall generally increase or decrease in units of the liquid level detection accuracy. In practical applications, the shortest interval time of the liquid level change is 3s. If the liquid level rises and falls at the fastest speed, within 1 minute, the liquid level can change by 0.01953 meters × 60s ÷ 3s = 0.39 meters. And the start-up time of a water pump is 10s, and it takes 30s for the valve to open or close completely. Therefore, it is necessary to ensure that the fastest liquid level change can be detected, otherwise the liquid level is very easy to overshoot. However, if the liquid level change rate is calculated according to the time interval of the fastest change, the liquid level hardly changes most of the time, and even if it changes, the liquid level change rate cannot be correctly feedback.

[0047] Figure 2 FIG. is an analysis schematic diagram of sampling the liquid level change rate at a fixed interval time. As Figure 2As shown, the liquid level change rate D is calculated at fixed intervals of time T0. During the time period T3 - T4, the liquid level changes, but the actual time taken for the liquid level to change may be T2 - T4, that is, it has gone through 3 detection cycles. At the two ends of the interval time period T4 - T5, the liquid level decreases, but the actual liquid level is increasing at a higher speed, yet the control reaches the opposite conclusion. Therefore, the fixed interval time T0 cannot correctly reflect the actual liquid level change rate, and thus precise control of the liquid level cannot be achieved.

[0048] Since the interval time T of the liquid level change is closely related to the liquid level change rate, the faster the liquid level changes, the shorter the interval time of the liquid level change, and vice versa. Therefore, the interval time of the liquid level change can be used to represent the liquid level change rate. Figure 3 The calculation and analysis diagram of the interval time T of the liquid level change is shown. Refer to Figure 3 As shown:

[0049] At time T2, the liquid level changes, that is, the liquid level remains at the same value from T1 to T2. Therefore, at time T2, the interval time of the liquid level change is T2 - T1;

[0050] From time T2 onwards, the liquid level may change at any time. Before the change occurs, the interval time has been T2 - T1 until T2'. At this time, the time interval clearly shows that the interval time exceeds that at time T2, and the interval time has been increasing until time T3 when the liquid level actually changes. Before the change, the interval time is the current time T - T2;

[0051] From T1 to T3, the liquid level is increasing all the time, and the interval time takes a positive sign;

[0052] Starting from time T3, the liquid level becomes decreasing, that is, the direction changes. At this time, the liquid level change value cannot be T3 - T2 anymore because from this moment on, the rising interval time of the previous moment cannot be used for the liquid level. At this time, we adopt a default value Ti with a negative sign to indicate a decrease. From time T3' onwards, Ti ≤ T - T3, and from this moment on, the interval time takes T - T3 until time T4;

[0053] Ti represents the default interval time when indicating the liquid level change direction;

[0054] From time T4 onwards, the interval time at this time takes -(T4 - T3) until the liquid level changes or T - T4 ≥ T4 - T3;

[0055] By time T6, the liquid level direction changes again, and at this time the default interval time Ti is taken.

[0056] The above method can be used to obtain the interval time T between liquid level changes, and indirectly express the liquid level change rate. A positive value indicates a rise in the liquid level, and a negative value indicates a fall in the liquid level. The smaller the absolute value of the interval time, the faster the liquid level change rate, and vice versa.

[0057] S20, adjusting the execution interval Ti of the control process according to the interval T of the liquid level change;

[0058] Due to the system's hysteresis, after controlling the pump and valve actions based on the liquid level deviation and the interval between liquid level changes, the system needs to delay for a period of time before the effect is manifested. How the output execution interval is controlled will affect the system's control effect. If the interval is too long, although the control output can achieve the effect of large hysteresis, it cannot avoid the liquid level loss caused by rapid liquid level changes. If the interval is too short, the hysteresis effect of the previous output cannot be fully reflected, causing the system to repeat the output and cause the system to overshoot.

[0059] As mentioned above, since the system uses the interval time of liquid level change instead of the conventional liquid level change rate, the system adjusts the execution interval time of the system according to the interval time of liquid level change. The relationship between the interval time of liquid level change T and the execution interval time Ti of the system is expressed by a linear function. The functional relationship is as follows: Figure 4 As shown, it can be expressed as follows:

[0060] Ti=(T-T1) / (T2-T1)×(Ti2-Ti1)+Ti1 (1)

[0061] Among them, T represents the interval time of liquid level change; T1 represents the shortest interval time of liquid level change, which can be 3s in practical applications; T2 represents the longest interval time of liquid level change, which can be 200s in practical applications; Ti1 represents the shortest execution interval time of the control process, which can be 30s in practical applications; Ti2 represents the longest execution interval time of the control process, which can be 120s in practical applications.

[0062] S30, setting the liquid level and constructing a fuzzy controller;

[0063] like Figure 5 As shown, a fuzzy controller is constructed with the liquid level deviation e and the interval time T of the liquid level change as input variables. The output variable of the fuzzy controller is the increase or decrease value U of the return valve opening, wherein the liquid level deviation e = set liquid level - actual liquid level.

[0064] First, the liquid level deviation e and the interval time T of liquid level change are fuzzified;

[0065] Liquid level deviation e = set liquid level - actual liquid level, the number of membership function language value variables is 5, such asFigure 6 As shown, they are NB (Negative Big), NS (Negative Small), ZO (Zero), PS (Positive Small), and PB (Positive Big) respectively. The membership functions adopted for each variable are all different.

[0066] The interval time T of the liquid level change is used to replace the conventional liquid level change rate. This parameter is crucial for the liquid level control accuracy. Therefore, the number of language value variables of the membership function is 7, such as Figure 7 As shown, they are NB (Negative Big), NM (Negative Medium), NS (Negative Small), ZO (Zero), PS (Positive Small), PM (Positive Medium), and PB (Positive Big) respectively. The membership functions adopted for each variable are all different.

[0067] Then, fuzzy inference is carried out;

[0068] The form of fuzzy inference is:

[0069] Premise: IF e is A and T is B

[0070] Conclusion: THEN output (U) = r ij

[0071] Among them, A is 5 fuzzy subsets on the domain U of the liquid level deviation e, and B is 7 fuzzy subsets on the domain of the interval time T of the liquid level change. The final knowledge base is presented in the form of the following table:

[0072]

[0073] Among them, the values of r11~r57 are summarized according to the experience of on-site operators and adjusted during practical debugging.

[0074] Next, defuzzification is carried out;

[0075] When implementing fuzzy control, many control rules are subjected to the above inference calculations, and then the control output is obtained by combining the inference results obtained from each calculation. In this embodiment, the defuzzification method adopts the centroid method, and finally the output value U is obtained. The output value U is the opening increase or decrease value of the control return water valve. A positive output value indicates an increase in the opening of the return water valve, and a negative output value indicates a decrease in the opening of the return water valve.

[0076] S40. Adjust the opening of the pump outlet valve and the return water valve through the fuzzy controller to achieve automatic control of the water tank liquid level;

[0077] Each pump has an automatic / manual switching function, and only the pumps in the automatic state can be selected for control. In the automatic state, the rules for adding or shutting down pumps can be selected by the user, including the rule for adding running pumps and the rule for shutting down running pumps. The system automatically finds the pump numbers that need to be added or stopped currently according to the current pump state and the selected rules, and uses them as the current controlled pumps to adjust the opening degree of the pump outlet valves.

[0078] The fuzzy control output value U is the value for increasing or decreasing the opening degree of the return water valve. If this value is positive, it means that the water outflow from the water tank needs to be reduced; otherwise, the water outflow needs to be increased. After the opening degree of the return water valve is adjusted to the limit, the opening degree of the pump outlet valve is then adjusted.

[0079] Since the pipe diameters of the return water valve and the pump outlet valve are not equal, when adjusting the opening degree of the pump outlet valve, the control output value U needs to be adjusted, that is, the value for controlling the opening degree of the pump outlet valve needs to be multiplied by the proportionality coefficient f on the basis of the output value U. The value of f is calculated through the following formula:

[0080] f = diameter of the return water valve 2 / diameter of the pump outlet valve 2 (2)

[0081] When the control output value U > 0:

[0082] Opening degree of the return water valve V = the previous control opening degree of the return water valve + U

[0083] When the opening degree of the return water valve V exceeds the maximum value (100%), the control opening degree of the return water valve is output according to the maximum value, indicating that the adjustment ability of the return water valve has reached the limit. If the water tank level continues to be low, the water output of the pump needs to be reduced. At this time, the system reduces the opening degree of the outlet valve of the stopped pump according to the pump number of the stopped pump currently, that is, the opening degree of the outlet valve of the stopped pump Vi = the previous control opening degree of the outlet valve of the stopped pump - U * f;

[0084] When the opening degree of the outlet valve of the stopped pump Vi < 30%, it is controlled at 30% opening degree. If it operates below this value, the opening degree of the pump outlet valve is too small, and the pump is in a state of being blocked for a long time;

[0085] If the opening degree of the outlet valve of the stopped pump Vi < 10%, it means that this pump can be shut down, and the system automatically shuts down this pump to reduce the operation of one pump.

[0086] When the control output value U < 0:

[0087] Opening degree of the outlet valve of the stopped pump Vi = the previous opening degree of the outlet valve of the stopped pump - U * f

[0088] When the opening degree of the outlet valve of the stopped pump > 100%, it is controlled at 100% opening degree, and this pump has been adjusted to the limit, and the opening degree of the return water valve needs to be adjusted;

[0089] Opening degree of the return water valve V = the previous opening degree of the return water valve - (Vi - 100%) / f

[0090] When the opening degree V of the return water valve is lower than the minimum value (0%), the control opening degree of the return water valve is output according to the minimum value, indicating that both the return water valve and the pump outlet valve have reached their limits. If the water level in the water tank continues to rise, the number of operating pumps needs to be increased to increase the water discharge flow rate. According to the selection rule for the newly added pump, the number of the newly added pump is found and the pump is started. After the pump is started, the directly controlled opening degree of the return water valve is set to the maximum value of 100%, and at the same time, the control value of the outlet valve of this pump is set to the minimum value of 30%.

[0091] The method of this embodiment adjusts the opening degrees of the return water valve and the pump outlet valve through an improved fuzzy control algorithm, thereby controlling the number of operating pumps and achieving automatic control of the water level. The water level control accuracy can be less than 0.2 meters. The automatic control of the water level in the water tank solves the problem of high labor intensity in manual control and greatly improves the safety of equipment operation.

[0092] It should be noted that for the method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the embodiments of this application are not limited by the described action sequences, because according to the embodiments of this application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily essential for the embodiments of this application.

[0093] Reference Figure 8 , Figure 8 shows a schematic structural diagram of a water tank liquid level control system for a turbid circulating water system of a endless casting and rolling production line provided by an embodiment of the present application. The system described below can be correspondingly referred to the method described above. The system 10 includes:

[0094] A liquid level change time module 11, configured to obtain the interval time T of the liquid level change;

[0095] A control execution time module 12, configured to adjust the execution interval time Ti of the control process according to the interval time T of the liquid level change;

[0096] A controller construction module 13, configured to set the liquid level, and construct a fuzzy controller with the liquid level deviation e and the interval time T of the liquid level change as input variables. The output variable of the fuzzy controller is the increment and decrement value U of the opening degree of the return water valve, where the liquid level deviation e = set liquid level - actual liquid level;

[0097] An automatic control module 14, configured to adjust the opening degrees of the return water valve and the pump outlet valve through the fuzzy controller to achieve automatic control of the water tank liquid level.

[0098] Specifically, in the above-mentioned pool liquid level control system, the functional relationship between the execution interval time Ti of the control process and the interval time T of the liquid level change is shown in Equation (1):

[0099] Ti = (T - T1) / (T2 - T1)×(Ti2 - Ti1) + Ti1 (1)

[0100] Wherein, T represents the interval time of the liquid level change, T1 represents the shortest interval time of the liquid level change, T2 represents the longest interval time of the liquid level change, Ti1 represents the shortest execution interval time of the control process, and Ti2 represents the longest execution interval time of the control process.

[0101] Regarding the functions realized by each unit of the pool liquid level control system and their combinations, as well as the achieved technical effects, reference can be made to the description of the corresponding parts of the above method embodiments, which will not be elaborated here.

[0102] Although the present application has been described in detail with general descriptions and specific embodiments above, on the basis of the present application, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present application fall within the scope of protection required by the present application.

Claims

1. A method for controlling the water tank liquid level of the turbidity circulating water system in a headless continuous casting and rolling production line, characterized in that, It includes the following steps: Obtain the interval time T of the liquid level change; Adjust the execution interval time Ti of the control process according to the interval time T of the liquid level change; Set the liquid level. Taking the liquid level deviation e and the interval time T of the liquid level change as input variables, construct a fuzzy controller. The output variable of the fuzzy controller is the increment or decrement value U of the return water valve opening degree, where the liquid level deviation e = set liquid level - actual liquid level; Adjust the return water valve opening degree and the pump outlet valve opening degree through the fuzzy controller to achieve automatic control of the water tank liquid level.

2. The method for controlling the water level of a pool according to claim 1, wherein When the interval time T of the liquid level change is a positive number, it indicates that the water tank liquid level is rising; when the interval time T of the liquid level change is a negative number, it indicates that the water tank liquid level is falling.

3. The method for controlling the water level of the pool according to claim 2, wherein The smaller the absolute value of the interval time T of the liquid level change, the faster the liquid level change rate of the water tank; the larger the absolute value of the interval time T of the liquid level change, the slower the liquid level change rate of the water tank.

4. The method for controlling the water level of the pool according to claim 1, wherein, The functional relationship between the execution interval time Ti of the control process and the interval time T of the liquid level change is as shown in Equation (1), Ti = (T - T1) / (T2 - T1)×(Ti2 - Ti1) + Ti1 (1) Where, T represents the interval time of the liquid level change, T1 represents the shortest interval time of the liquid level change, T2 represents the longest interval time of the liquid level change, Ti1 represents the shortest execution interval time of the control process, and Ti2 represents the longest execution interval time of the control process.

5. The method for controlling the water level of a pool according to claim 1, characterized in that The steps of constructing the fuzzy controller further include: First, fuzzify the liquid level deviation e and the interval time T of the liquid level change; Then, perform fuzzy inference; Next, use the centroid method for defuzzification to obtain the output value U.

6. The method for controlling the water level of the pool according to claim 5, characterized in that, The output value U is the increment or decrement value of the opening degree of the return water valve. When the output value U is a positive number, it indicates increasing the opening degree of the return water valve. When the output value U is a negative number, it indicates decreasing the opening degree of the return water valve.

7. The pool liquid level control method according to claim 6, characterized in that When the output value U > 0, the return water valve opening degree = the previous return water valve opening degree + the output value U.

8. The pool liquid level control method according to claim 7, characterized in that When the output value U is less than 0, the opening degree of the pump outlet valve = the previous opening degree of the pump outlet valve - the output value U × f, where f = the diameter of the return water valve 2 / the diameter of the pump outlet valve 2 .

9. The water tank liquid level control system of the turbid circulating water system for the endless casting and rolling production line, characterized in that, The system includes: A liquid level change time module for obtaining the interval time T of the liquid level change; A control execution time module for adjusting the execution interval time Ti of the control process according to the interval time T of the liquid level change; A controller construction module for setting the liquid level, constructing a fuzzy controller with the liquid level deviation e and the interval time T of the liquid level change as input variables. The output variable of the fuzzy controller is the increment or decrement value U of the return water valve opening degree, where the liquid level deviation e = set liquid level - actual liquid level; An automatic control module for adjusting the return water valve opening degree and the pump outlet valve opening degree through the fuzzy controller to achieve automatic control of the water tank liquid level.

10. The water tank liquid level control system according to claim 9, characterized in that, The functional relationship between the execution interval time Ti of the control process and the interval time T of the liquid level change is as shown in Equation (1), Ti = (T - T1) / (T2 - T1)×(Ti2 - Ti1) + Ti1 (1) Where, T represents the interval time of the liquid level change, T1 represents the shortest interval time of the liquid level change, T2 represents the longest interval time of the liquid level change, Ti1 represents the shortest execution interval time of the control process, and Ti2 represents the longest execution interval time of the control process.

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