Method and system for controlling lower discharging centrifugal machine based on PLC (Programmable Logic Controller)

Abstract

The invention relates to the technical field of centrifugal machine control, in particular to a lower discharging centrifugal machine control method and system based on a PLC, and the method comprises the steps: obtaining a flow time sequence and a concentration time sequence of a material at a feeding valve in a feeding stage, and a power time sequence of a main motor of a centrifugal machine; obtaining a first characteristic value and a second characteristic value of the control moment by combining a correlation and an average trend of a flow time sequence and a concentration time sequence in a change trend in a time range corresponding to any control moment and a previous control moment, and a periodic fluctuation characteristic of a power time sequence; and a proportion parameter value is obtained by combining the first characteristic value and the second characteristic value, so that the rotating speed of a main motor of the lower discharging centrifugal machine is controlled at the corresponding control moment. The control effect on the main motor of the lower discharging centrifugal machine is improved, and therefore the filtering effect on materials is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of centrifuge control, in particular to a PLC-based control method and system for a bottom discharge centrifuge. BACKGROUND

[0002] A bottom discharge centrifuge is a centrifuge that separates solid and liquid by centrifugal force and discharges solid materials from the bottom of the equipment, and is mainly used for solid-liquid separation of a suspension containing solid particles. A PLC is a programmable logic controller and is widely used in full-automatic or semi-automatic control of centrifuges.

[0003] During operation of the bottom discharge centrifuge, the PLC control system is mainly used to control the start-stop, rotational speed, and running time of the centrifuge. The control accuracy of the PLC control system is the key to ensuring efficient and stable operation of the centrifuge, especially the control of the rotational speed of the rotating drum. However, the PLC control system itself has a certain time lag, and during the feeding stage of the bottom discharge centrifuge, the uneven load of the rotating drum caused by changes in the material at the feeding valve of the centrifuge and the instability of the power of the rotating drum motor will cause a relatively sharp lag change in the rotational speed of the rotating drum, thus exacerbating the actual error caused by the time lag, making it difficult to respond to changes in the rotational speed of the rotating drum when using the PLC control system to control the rotational speed of the rotating drum during the feeding stage of the centrifuge, thus reducing the control accuracy of the PLC control system when controlling the rotational speed of the rotating drum during the feeding stage of the centrifuge, thus easily causing frequent and sharp fluctuations in the rotational speed of the rotating drum, which not only exacerbates the uneven distribution of the material on the filter screen of the centrifuge, affecting the subsequent filtering effect of the centrifuge, but also easily causes the centrifuge to be difficult to run stably during the feeding stage, exacerbating the wear of the equipment and reducing the service life of the equipment. SUMMARY

[0004] The present application provides a PLC-based control method and system for a bottom discharge centrifuge to solve the existing problems.

[0005] The PLC-based control method and system for a bottom discharge centrifuge of the present application adopt the following technical solutions: One embodiment of the present application provides a PLC-based control method for a bottom discharge centrifuge, which comprises the following steps: obtaining the flow time sequence and concentration time sequence of the material at the feeding valve of the bottom discharge centrifuge during the feeding stage, and the power time sequence of the main motor of the centrifuge, and each data point in each sequence corresponds to a control time; obtaining a first characteristic value of the control time by combining the correlation between the flow time sequence and the concentration time sequence in the time range of the control time and the previous control time, and the average trend. acquire the second characteristic value of the control time by using the periodic fluctuation characteristics of the power time sequence in the time range corresponding to the control time and the previous control time; and acquire the proportional parameter value at the control time by combining the first characteristic value and the second characteristic value. control the rotating speed of the main motor of the lower discharge centrifuge at the corresponding control time by using the proportional parameter value.

[0006] Further, the first characteristic value of the control time is acquired by combining the correlation in the variation trend and the average trend between the flow time sequence and the concentration time sequence in the time range corresponding to the control time and the previous control time, and the specific method comprises the following steps: acquire the trend components of the flow time sequence and the concentration time sequence in the time range corresponding to the control time and the previous control time by using a time sequence decomposition algorithm, and obtain the trend variation characteristic value between the flow time sequence and the concentration time sequence according to the correlation between the trend components; perform linear fitting on the trend components of the flow time sequence and the concentration time sequence respectively, and obtain the first characteristic value of the control time by combining the average slope of the linear fitting results and the trend variation characteristic value, wherein the average slope and the trend variation characteristic value are positively correlated with the first characteristic value.

[0007] Further, the specific acquisition method of the trend variation characteristic value comprises the following steps: extract the trend components of the flow time sequence and the concentration time sequence in the time range corresponding to the control time and the previous control time by using an STL time sequence decomposition algorithm, denoted as the first trend component and the second trend component, record the Pearson correlation coefficient between the first trend component and the second trend component as the trend variation characteristic value, and if the result of the Pearson correlation coefficient is less than 0, assign the trend variation characteristic value as 0.

[0008] Further, the specific acquisition method of the first characteristic value comprises the following steps: perform linear fitting on the first trend component and the second trend component respectively by using the least square method to obtain the first fitting straight line and the second fitting straight line, take the average slope of the first fitting straight line and the second fitting straight line as the input of a sigmoid function, map the value range of the average value to take the product between the output result of the sigmoid function and the trend variation characteristic value as the first characteristic value of the control time.

[0009] Further, the specific method for acquiring the second characteristic value of the control time by using the periodic fluctuation characteristics of the power time sequence in the time range corresponding to the control time and the previous control time, and acquiring the proportional parameter value at the control time by combining the first characteristic value and the second characteristic value comprises the following steps: The seasonal component of the power time series within the time range corresponding to any control moment and the previous control moment is obtained using the time series decomposition algorithm. The second eigenvalue of the control moment is obtained based on the absolute mean of all data points in the seasonal component. The upper limit and lower limit of the proportional parameter are preset, and the first eigenvalue and the second eigenvalue are combined with the upper limit and the lower limit of the proportional parameter to calculate the proportional parameter value at the control time.

[0010] Furthermore, the specific method for obtaining the second characteristic value at the control moment is: The seasonal component of the power time series is extracted using the STL time series decomposition algorithm, the mean of the absolute values ​​of all data points in the seasonal component is calculated, and the mean is used as the input of the sigmoid function to map the range of the mean to Within the range, the output result of the sigmoid function is recorded as the second eigenvalue of the control moment.

[0011] Furthermore, the specific method for obtaining the proportional parameter value at the control moment is: Obtain a numerical range formed by the upper and lower limits of the preset proportional parameter, which is recorded as the proportional parameter range value; obtain the average of the first eigenvalue and the second eigenvalue, which is recorded as the adjustment coefficient; round the product of the adjustment coefficient and the proportional parameter range value to obtain a compensation value, and add the lower limit of the proportional parameter and the compensation value to obtain a value as the proportional parameter value at the control moment.

[0012] Furthermore, the speed control of the main motor of the bottom discharge centrifuge at the corresponding control moment by using the proportional parameter value includes the following specific methods: The centrifuge drum speed signal of the lower discharge centrifuge in its feeding stage and the set value of the drum speed are used as the input of the PID control algorithm in the PLC control system, and the control time is set to The corresponding proportional parameter value is used as the PID control algorithm at the control moment and the value of the proportional parameter within the time period of the next control moment, and the output signal of the PID control algorithm is used as the control signal when the PLC control system controls the drum speed. The control signal is converted into a current signal by a D / A converter, and the inverter maps the current signal into a corresponding frequency to control the speed of the main motor of the centrifuge.

[0013] Furthermore, the specific method of obtaining the flow rate time series and concentration time series of the material at the feed valve of the lower discharge centrifuge during the feeding stage, as well as the power time series of the main motor of the centrifuge, includes: In the feeding stage of the lower discharge centrifuge, the flow data and concentration data of the material at the feeding valve of the centrifuge are collected by using a flow meter and a concentration meter respectively; the motor for controlling the rotating speed of the drum is referred to as a main motor, the power data of the main motor are collected by using a power meter, and the flow data, concentration data and power data are normalized by using linear normalization to obtain a flow time series, a concentration time series and a power time series.

[0014] The PLC-based lower discharge centrifuge control system comprises a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the PLC-based lower discharge centrifuge control method according to the computer program.

[0015] The technical scheme has the beneficial effects that: by combining the correlation between the flow time series and the concentration time series and their average trends, the variation law of the material can be better understood, and by using the periodic fluctuation characteristics of the power time series to extract the second feature value, the load condition of the main motor can be monitored in real time, the proportional parameter value in the PID control algorithm is dynamically adjusted, and the rotating speed of the main motor is adjusted according to the value, so that dynamic and real-time adjustment is realized, the centrifuge can maintain the best operating state under different operating conditions, the response speed of the PLC control system to the rotating speed of the main motor when the rotating drum load is unbalanced and the motor power is unstable due to the change of the centrifuge material can be improved, and the control accuracy of the PLC control system to the rotating speed of the centrifuge is improved, so that the rotating speed of the centrifuge in the feeding stage is prevented from fluctuating sharply frequently, and the stability and reliability of the system are further improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical scheme in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0017] Figure 1A flow chart of steps of the PLC-based lower unloading centrifuge control method of the present application; Figure 2 A flow chart of the first characteristic value analysis method of the control time according to an embodiment of the present application; Figure 3 A flow chart of the proportional parameter value analysis method of the control time according to an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purposes, the PLC-based lower unloading centrifuge control method and system according to the present application, its specific implementation, structure, features and effects are described in detail as follows in combination with the drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0020] The specific scheme of the PLC-based lower unloading centrifuge control method and system provided by the present application is specifically described below in combination with the drawings.

[0021] Please refer to Figure 1 , which shows a flow chart of steps of the PLC-based lower unloading centrifuge control method according to an embodiment of the present application. The method comprises the following steps: Step S001: Obtain the flow rate time sequence and concentration time sequence of the material at the feed valve of the lower unloading centrifuge during the feeding stage, and the power time sequence of the main motor of the centrifuge, and set a plurality of control times according to a preset time interval.

[0022] It should be noted that the scraper lower discharging automatic centrifuge controlled by the PLC control system is taken as an example in the embodiment of the application, and the embodiment of the application adds a PID control module in the control process of the drum rotating speed of the centrifuge in the feeding stage of the centrifuge in the PLC control system to relieve the time lag phenomenon existing in the PLC control system, and dynamically adjusts the proportional parameter in the PID control algorithm used in the PID control module to improve the response speed of the lag change of the drum rotating speed caused by the unbalanced load of the drum and the unstable motor power caused by the change of the material at the feeding valve in the feeding stage of the centrifuge, so as to avoid the frequent and sharp fluctuations of the drum rotating speed in the feeding stage of the centrifuge. The scraper lower discharging automatic centrifuge is collectively referred to as a lower discharging centrifuge hereinafter for subsequent description.

[0023] Specifically, in order to realize the lower discharging centrifuge control method based on PLC proposed in the embodiment, the flow time sequence, the concentration time sequence and the power time sequence need to be collected first, and the specific process is as follows: Firstly, in the data collection unit, the flow data and the concentration data of the material at the feeding valve of the centrifuge are collected by using the flow meter and the concentration meter respectively in the feeding stage of the lower discharging centrifuge, and the motor for controlling the drum rotating speed is referred to as the main motor, and the power data of the main motor is collected by using the power meter.

[0024] It should be noted that the sampling frequencies of the flow meter, the concentration meter and the power meter are all set to 10 Hz in the embodiment of the application, which can be set by itself according to the actual situation, and all the collected flow data, concentration data and power data are transmitted to the data processing unit.

[0025] Then, the flow data, the concentration data and the power data are normalized by using linear normalization to obtain the flow time sequence, the concentration time sequence and the power time sequence.

[0026] As an optional embodiment, the acquisition method of the flow time sequence, the concentration time sequence and the power time sequence includes that in the data processing unit, the embodiment of the application takes any one control moment in the PID control module as an example (not including the first control moment), the time interval between the adjacent two control moments is preset in the PID control module of the embodiment of the application, and the flow data, the concentration data and the power data at the control moment and the last control moment all the flow data, concentration data and power data collected in the time period, each kind of data is normalized by using Min-Max normalization method to reduce the influence of data dimension, and all the data points in each kind of normalized data are arranged in ascending order according to the sampling time corresponding to the data points, respectively, to obtain flow time series, concentration time series and power time series, wherein when the power data is normalized, the rated power value of the main motor of the lower discharge centrifuge is added to the normalization of the power data.

[0027] In addition, it should be noted that the control time and the time period of the last control time corresponding to the time range of the control time and the last control time mentioned in the subsequent embodiment of the present application.

[0028] Finally, according to the preset time interval, the time series is sampled at equal intervals to obtain several time points as the control time of the PLC control system.

[0029] It should be noted that the time interval between the control times in the embodiment of the present application is 2 seconds according to experience, and the time interval can be set by the implementer, and the embodiment of the present application is not specifically limited.

[0030] It should be noted that the Min-Max normalization method is a known technology, and the specific process will not be described again.

[0031] At this point, the flow time series, concentration time series and power time series are obtained by the above method.

[0032] Step S002: Obtain the first characteristic value of the control time by combining the correlation between the flow time series and the concentration time series in the time range corresponding to the control time and the last control time and the average trend in the change trend.

[0033] It should be noted that, in the feeding process of the lower discharge centrifuge, when the flow rate and concentration at the feeding valve of the centrifuge have the same change trend, such as increasing simultaneously, the amount of material entering the drum in a short time will increase, and the material on the filter screen side will be thrown to the filter screen side under the action of centrifugal force, which will increase the amount of material accumulation on the filter screen side, and further increase the load of the drum on the filter screen side, and vice versa. The change of the load of the drum usually causes the change of the motor torque of the drum, thereby causing the fluctuation of the speed of the motor, and further causing the fluctuation of the subsequent speed of the drum. Therefore, in order to improve the response speed of the speed of the drum to the lag change of the speed of the drum caused by the uneven load of the drum due to the change of the material at the feeding valve of the centrifuge in the PLC control system of the lower discharge centrifuge, the following processing is performed, such as Figure 2 Figure 1 shows a flowchart of the first characteristic value analysis method at the control time.

[0034] Specifically, the step of obtaining the first characteristic value at the control time in the embodiment of the application comprises: Step S201, obtaining the trend components of the flow time series and the concentration time series in the time range corresponding to any control time and the previous control time by using a time series decomposition algorithm, and obtaining the trend change characteristic value between the flow time series and the concentration time series according to the correlation between the trend components.

[0035] It should be noted that the preset time interval is the time interval between adjacent control times.

[0036] As an optional embodiment, the method for obtaining the trend change characteristic value is: in the data processing unit, the trend components of the flow time series and the concentration time series in the time range corresponding to any control time and the previous control time are extracted by using an STL time series decomposition algorithm, which are denoted as the first trend component and the second trend component. The Pearson correlation coefficient between the first trend component and the second trend component is denoted as the trend change characteristic value, and if the result of the Pearson correlation coefficient is less than 0, the trend change characteristic value is assigned as 0.

[0037] It should be noted that by extracting the trend components, the influence of the noise components introduced in the flow time series and the concentration time series on the subsequent evaluation of whether the flow time series and the concentration time series have the same change trend and the evaluation of their respective change amplitudes is reduced. In addition, in the embodiment of the application, the STL (Seasonal and Trend decomposition using Loess) time series decomposition algorithm is a known technology, and the specific process is not described again.

[0038] It needs to be further explained that the trend change characteristic value is used to evaluate whether the flow and the concentration at the feed valve of the lower discharge centrifuge have the same trend of change in the time period of the control moment t and its previous control moment, and the greater the trend change characteristic value is, the more the flow and the concentration have the same trend of change; in addition, when the result of the Pearson correlation coefficient is not greater than 0, the trend change characteristic value is assigned as 0, which is used to represent that the flow and the concentration do not have the same trend of change, wherein the calculation of the Pearson correlation coefficient is a known technology, and the specific process will not be described herein again, and the trend change characteristic value is between 0 and 1.

[0039] In step S202, the trend components of the flow time sequence and the concentration time sequence are respectively subjected to linear fitting, and the first characteristic value of the control moment is obtained by combining the mean value of the slopes of the linear fitting results and the trend change characteristic value, wherein the mean value of the slopes and the trend change characteristic value are positively correlated with the first characteristic value.

[0040] As a preferred embodiment, the specific acquisition method of the first characteristic value comprises: The first trend component and the second trend component are respectively subjected to linear fitting by using the least square method to obtain a first fitting straight line and a second fitting straight line, the mean value of the slopes corresponding to the first fitting straight line and the second fitting straight line is taken as the input of a sigmoid function, the value range of the mean value is mapped to The product between the output result of the sigmoid function and the trend change characteristic value is taken as the first characteristic value of the control moment.

[0041] It needs to be explained that the first characteristic value is used to evaluate the change amplitude when the flow and the concentration at the feed valve of the lower discharge centrifuge have the same trend of change in the time period of the control moment t and its previous control moment, and the greater the first characteristic value is, the greater the change amplitude is, and then the proportional parameter of the PID control algorithm used in the subsequent PID control module should be greater, so as to improve the response speed of the drum of the subsequent centrifuge to the lag change of the drum speed caused by the unbalanced load of the drum due to the change of the material at the feed valve of the centrifuge. In the embodiment of the present application, the linear fitting algorithm is a linear fitting algorithm based on the least square method, wherein the linear fitting algorithm based on the least square method is a known technology, and the specific process will not be described herein again, and the trend characteristic value is between 0 and 1.

[0042] Up to now, the first characteristic value of the control moment is obtained by the above method.

[0043] Step S003: obtaining a second characteristic value of the control time by using the periodic fluctuation characteristics of the power time sequence in the time range corresponding to the control time and the previous control time; obtaining the proportional parameter value at the control time in combination with the first characteristic value and the second characteristic value.

[0044] It should be noted that during the feeding process of the lower discharge centrifuge, the power of the main motor (motor for controlling the rotation speed of the drum of the centrifuge) of the centrifuge directly affects the rotation speed of the drum, wherein the greater the power of the main motor, the greater the rotation speed of the drum, and vice versa, and the power of the main motor changes due to changes in the load of the main motor and the power voltage, current and other factors, so that when the motor power fluctuates, it is easy to cause subsequent fluctuations in the rotation speed of the drum. Therefore, when the PLC control system of the lower discharge centrifuge controls the rotation speed of the drum in the feeding stage, in order to improve the response speed of the rotation speed of the drum to the lag change in the rotation speed of the drum caused by the instability of the power of the drum motor of the centrifuge, the following processing is performed, such as Figure 3 The flow chart of the proportional parameter value analysis method at the control time is shown.

[0045] Specifically, the step of obtaining the proportional parameter value at the control time in the embodiment of the application comprises: Step S301: obtaining the seasonal component of the power time sequence in the time range corresponding to the control time and the previous control time by using a time series decomposition algorithm, and obtaining the second characteristic value of the control time according to the mean of the absolute values of all data points in the seasonal component.

[0046] As an optional embodiment, the method for obtaining the second characteristic value of the control time is: The seasonal component of the power time sequence is extracted by using the STL time series decomposition algorithm, the mean of the absolute values of all data points in the seasonal component is calculated, the mean is taken as the input of the sigmoid function, the value range of the mean is mapped to by the sigmoid function, and the output result of the sigmoid function is recorded as the second characteristic value of the control time.

[0047] It should be noted that the seasonal component of the power time sequence obtained in the embodiment of the application is used to represent the local data fluctuation of each data point in the power time sequence, and is used to reduce the influence of the noise component introduced in the power time sequence and the data change trend thereof on the subsequent evaluation of the data fluctuation of the power time sequence as a whole. In addition, the mean of the absolute values of all data points in the seasonal component is used to represent the data fluctuation degree of the power time sequence as a whole.

[0048] It is further needed to be explained that the second characteristic value is used to evaluate the data fluctuation degree of the power of the main motor of the lower discharge centrifuge in the time period of the control time t and its previous control time, the greater the second characteristic value is, the greater the fluctuation is, and then the proportional parameter of the PID control algorithm used in the subsequent PID control module should be greater, so as to improve the response speed of the drum of the subsequent centrifuge to the lag change of the drum speed caused by the instability of the drum motor of the centrifuge, wherein the STL time sequence decomposition algorithm is a known technology, and the specific process is not described in detail, and the numerical value of the second characteristic value is between 0 and 1.

[0049] In step S302, the upper limit and the lower limit of the proportional parameter are preset, and the proportional parameter value at the control time is calculated by combining the first characteristic value and the second characteristic value with the upper limit and the lower limit of the proportional parameter.

[0050] As a preferred embodiment, the method for obtaining the proportional parameter value is: obtaining the numerical range formed by the upper limit and the lower limit of the preset proportional parameter, denoted as the proportional parameter range value; obtaining the mean value of the first characteristic value and the second characteristic value, denoted as the adjustment coefficient; rounding the product of the adjustment coefficient and the proportional parameter range value to obtain a compensation value, and adding the compensation value to the lower limit of the proportional parameter to obtain the proportional parameter value at the control time.

[0051] As an optional embodiment, the specific calculation method of the proportional parameter value w(t) is: In the formula, the proportional parameter value at the control time t is denoted as w(t); the adjustment coefficient at the control time t is denoted as a(t); , the upper limit and the lower limit of the preset proportional parameter are denoted as wmax and wmin respectively; is a rounding function. It is needed to be explained that the upper limit and the lower limit of the proportional parameter preset in the embodiment of the application are the upper limit and the lower limit of the proportional parameter in the PID control algorithm used in the subsequent PID control module, in addition, the upper limit wmax and the lower limit wmin are preset according to the experience method as 1 and 0.2.

[0052] It is needed to be explained that the upper limit and the lower limit of the proportional parameter preset in the embodiment of the application are the upper limit and the lower limit of the proportional parameter in the PID control algorithm used in the subsequent PID control module, in addition, the upper limit wmax and the lower limit wmin are preset according to the experience method as 1 and 0.2.

[0053] At this point, the proportional parameter value at the control time t is obtained by the above method.

[0054] In step S004, the rotational speed of the main motor of the lower discharge centrifuge is controlled by the proportional parameter value at the corresponding control time.

[0055] ​​​Specifically, the lower discharge centrifuge takes the drum rotation speed signal and the set value of the drum rotation speed in the feeding stage of the centrifuge as the input of the PID control algorithm in the PLC control system, and takes the control time point the corresponding proportional parameter value as the input of the PID control algorithm at the control time point and the value of the proportional parameter in the time period of the next control time point, and takes the output signal of the PID control algorithm as the control signal when the PLC control system controls the drum rotation speed, which is converted into a current signal by a D / A converter and is mapped into a corresponding frequency by an inverter to control the rotation speed of the main motor of the centrifuge, thereby realizing the control of the drum rotation speed of the centrifuge.

[0056] Through the above steps, the control of the lower discharge centrifuge is completed.

[0057] In another embodiment of the present application, a PLC-based lower discharge centrifuge control system is also provided, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements steps S001 to S004 of the PLC-based lower discharge centrifuge control method when executing the computer program.

[0058] By combining the correlation between the flow time series and the concentration time series, as well as their average trends, the variation law of the material can be better understood, and the periodic fluctuation characteristics of the power time series are used to extract the second feature value, which helps to monitor the load of the main motor in real time. By obtaining the proportional parameter value in real time and adjusting the rotation speed of the main motor according to the value, dynamic and real-time adjustment can be realized, so that the centrifuge can maintain the best operating state under different operating conditions, thereby further improving the stability and reliability of the system. This scheme combines multi-dimensional data of flow, concentration and power, extracts feature values at control time points using a calculation model, and realizes automatic intelligent control. This reduces human intervention and reduces operation risk, while also improving the intelligent level of the production process. Accurate speed control can ensure that the main motor provides appropriate power as needed, thereby effectively reducing unnecessary energy waste, optimizing the use efficiency of motor power, and effectively improving the control effect of the main motor of the lower discharge centrifuge, thereby improving the filtration effect of the material.

[0059] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. The control method of the bottom discharge centrifuge based on PLC is characterized in that: The method comprises the following steps: Obtain the flow rate time series and concentration time series of the material at the feed valve of the bottom discharge centrifuge during the feeding stage, as well as the power time series of the main motor of the centrifuge, and set a number of control moments according to preset time intervals; The first eigenvalue of the control moment is obtained by combining the correlation and average trend of the flow time series and concentration time series in the time range corresponding to any control moment and the previous control moment; Using the periodic fluctuation characteristics of the power time series within the time range corresponding to any control moment and the previous control moment, a second eigenvalue of the control moment is obtained; combining the first eigenvalue and the second eigenvalue to obtain the proportional parameter value at the control moment; The speed of the main motor of the bottom discharge centrifuge is controlled at the corresponding control moment through the proportional parameter value.

2. The PLC-based bottom discharge centrifuge control method according to claim 1, characterized in that: The first characteristic value at the control moment is obtained by combining the correlation and average trend of the flow time series and the concentration time series in the time range corresponding to any control moment and the previous control moment, including the specific method of: The time series decomposition algorithm is used to obtain the trend components of the flow time series and concentration time series within the time range corresponding to any control moment and the previous control moment. Based on the correlation between the trend components, the trend change characteristic values ​​between the flow time series and the concentration time series are obtained. Linear fitting is performed on the trend components of the flow time series and the concentration time series respectively. The first eigenvalue at the control moment is obtained by combining the slope mean and trend change eigenvalue of the linear fitting results. The slope mean and trend change eigenvalue are both positively correlated with the first eigenvalue.

3. The PLC-based bottom discharge centrifuge control method according to claim 2, characterized in that: The specific method for obtaining the trend change characteristic value is: The STL time series decomposition algorithm is used to extract the trend components of the flow time series and concentration time series within the time range corresponding to any control moment and the previous control moment, which are recorded as the first trend component and the second trend component. The Pearson correlation coefficient between the first trend component and the second trend component is recorded as the trend change characteristic value. If the result of the Pearson correlation coefficient is less than 0, the trend change characteristic value is assigned to 0.

4. The PLC-based bottom discharge centrifuge control method according to claim 3, characterized in that: The specific method for obtaining the first characteristic value is: The first trend component and the second trend component are fitted with a linear method using the least squares method to obtain a first fitting straight line and a second fitting straight line. The mean of the slopes corresponding to the first fitting straight line and the second fitting straight line is used as the input of the sigmoid function, and the range of the mean is mapped to Within the range, the product of the output result of the sigmoid function and the trend change eigenvalue is recorded as the first eigenvalue of the control moment.

5. The PLC-based bottom discharge centrifuge control method according to claim 1, characterized in that: The method of using the periodic fluctuation characteristics of the power time series within the time range corresponding to any control moment and the previous control moment to obtain the second characteristic value of the control moment; combining the first characteristic value and the second characteristic value to obtain the proportional parameter value at the control moment includes the following specific methods: The seasonal component of the power time series within the time range corresponding to any control moment and the previous control moment is obtained using the time series decomposition algorithm. The second eigenvalue of the control moment is obtained based on the absolute mean of all data points in the seasonal component. The upper limit and lower limit of the proportional parameter are preset, and the first eigenvalue and the second eigenvalue are combined with the upper limit and the lower limit of the proportional parameter to calculate the proportional parameter value at the control time.

6. The PLC-based bottom discharge centrifuge control method according to claim 5, characterized in that: The specific method for obtaining the second characteristic value at the control moment is: The STL time series decomposition algorithm is used to extract the seasonal component of the power time series within the time range corresponding to any control moment and the previous control moment, and the mean of the absolute values ​​of all data points in the seasonal component is calculated. The mean is used as the input of the sigmoid function to map the value range of the mean to Within the range, the output result of the sigmoid function is recorded as the second eigenvalue of the control moment.

7. The PLC-based bottom discharge centrifuge control method according to claim 5, characterized in that: The specific method for obtaining the proportional parameter value at the control moment is: Obtain a numerical range formed by the upper limit and lower limit of the preset proportional parameter, which is recorded as the proportional parameter range value; obtain the average of the first eigenvalue and the second eigenvalue, which is recorded as the adjustment coefficient; The product of the adjustment coefficient and the range value of the proportional parameter is rounded to obtain a compensation value, and the value obtained by adding the lower limit of the proportional parameter and the compensation value is used as the proportional parameter value at the control moment.

8. The PLC-based bottom discharge centrifuge control method according to claim 1, characterized in that: The speed control of the main motor of the bottom discharge centrifuge at the corresponding control time by using the proportional parameter value includes the following specific methods: The centrifuge drum speed signal of the lower discharge centrifuge in its feeding stage and the set value of the drum speed are used as the input of the PID control algorithm in the PLC control system, and the control time is set to The corresponding proportional parameter value is used as the PID control algorithm at the control moment and the value of the proportional parameter within the time period of the next control moment, and the output signal of the PID control algorithm is used as the control signal when the PLC control system controls the drum speed. The control signal is converted into a current signal by a D / A converter, and the inverter maps the current signal into a corresponding frequency to control the speed of the main motor of the centrifuge.

9. The PLC-based bottom discharge centrifuge control method according to claim 1, characterized in that: The specific method of obtaining the flow rate time series and concentration time series of the material at the feed valve of the lower discharge centrifuge during the feeding stage, as well as the power time series of the main motor of the centrifuge, includes: During the feeding stage of the bottom-discharging centrifuge, a flow meter and a concentration meter are used to collect flow data and concentration data of the material at the feed valve of the centrifuge, respectively. The motor that controls the drum speed is called the main motor, and a power meter is used to collect power data of the main motor. The flow data, concentration data, and power data are normalized using linear normalization to obtain flow time series, concentration time series, and power time series.

10. A PLC-based bottom discharge centrifuge control system comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the PLC-based bottom discharge centrifuge control method according to any one of claims 1 to 9 are implemented.

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