A Temperature PID Control Method and System for a Tea Dryer

Abstract

The present invention relates to the field of intelligent control technology, and particularly relates to a temperature PID control method and system for a tea dryer. According to different temperature stages in the tea drying process, the present invention divides the tea drying process into multiple drying stages; according to the monitoring data of each drying stage in the tea drying process, the adjustment coefficients corresponding to each drying stage are obtained; the proportional gain of the temperature PID control system of the dryer is adjusted through the adjustment coefficients, so as to realize the temperature control of the temperature PID control system of the dryer in each drying stage during the drying process. The present invention adjusts different proportional gains for the temperature PID control system of the dryer in each drying stage, thereby achieving precise control of various monitoring data in each drying stage, and improving the quality and yield of tea.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent control, and particularly relates to a temperature PID control method and system for a tea dryer. Background Art

[0002] The drying of tea is a crucial link in the tea processing process, directly affecting the quality, flavor, and storage stability of tea. To improve the drying efficiency and quality of tea, modern tea processing has gradually introduced automated control technologies, especially temperature control technologies, to achieve precise drying processes. The temperature PID (Proportional-Integral-Derivative) control method, as a classic automatic control strategy, is widely used in the temperature control of tea dryers to improve the stability and consistency of the drying process.

[0003] Traditional tea drying methods mainly rely on natural sun drying or simple hot air drying, but these methods have problems such as uneven drying and unstable quality. During the tea drying process, the temperature control system usually adjusts the heating and moisture exhaust devices to maintain and control the temperature and humidity inside the dryer. During the response process of the temperature control system, due to the influence of various factors, the changes in temperature and humidity are not immediately reflected in the output of the temperature control system, resulting in a lag phenomenon in temperature regulation during the drying process. This regulation delay makes it difficult to achieve precise control in the tea drying process, thereby affecting the quality and yield of tea. Summary of the Invention

[0004] In order to solve the technical problem that there is a lag phenomenon in the temperature PID control of a tea dryer in the prior art, making it difficult to achieve precise control and thus affecting the quality and yield of tea, the purpose of the present invention is to provide a temperature PID control method and system for a tea dryer, and the specific technical solutions adopted are as follows:

[0005] In a first aspect, the present invention provides a temperature PID control method for a tea dryer, and the method includes: dividing the tea drying process into multiple drying stages according to different temperature stages of the tea drying process; obtaining the adjustment coefficients corresponding to each drying stage according to the monitoring data of each drying stage during the tea drying process; and adjusting the proportional gain of the temperature PID control system of the dryer through the adjustment coefficients to achieve temperature control of the temperature PID control system of the dryer in each drying stage during the drying process.

[0006] The present invention differentially adjusts the temperature PID control system of the dryer according to different temperature stages existing in the drying process of different teas. The drying process is divided into multiple drying stages based on different temperature stages, and then through the analysis of various monitoring data of the dryer and the tea in each drying stage, the adjustment coefficients corresponding to each drying stage are obtained. The proportional gain of the temperature PID control system of the dryer is adjusted by the adjustment coefficients, so as to realize the temperature control of the temperature PID control system of the dryer in each drying stage during the drying process. The core concept of the present invention is to separately set the proportional gain of the temperature PID control system of the dryer according to the temperature requirements of different drying stages, so as to achieve precise control of various monitoring data in each drying stage.

[0007] Further, according to the monitoring data of each drying stage in the tea drying process, the adjustment coefficients corresponding to each drying stage are obtained; specifically including: obtaining the adjustment coefficient corresponding to the current drying stage according to the convective loss rate of the dryer temperature in the current drying stage.

[0008] Further, according to the moisture discharge efficiency during the drying process of the current drying stage, and the ratio between the change amount of the internal temperature of the dryer and the change amount of the external temperature of the dryer in the current drying stage, the convective loss rate in the current drying stage is determined.

[0009] Further, according to the heat conversion rate during the drying process of the current drying stage, and the average change rate of the humidity data in the current drying stage, the moisture discharge efficiency during the drying process of the current drying stage is determined.

[0010] Further, the average change rate of the humidity data in the current drying stage is obtained by the ratio of the difference between the humidity data at the start time of the current drying stage and the humidity data at the end time of the current drying stage to the time period length of the current drying stage.

[0011] Further, according to the correlation between the pressure change curve received by the inner wall of the dryer drum in the current drying stage and the fitting curve of the stirring quality of the dryer in the current drying stage, and the average value of the pressure change rates at two adjacent monitoring times inside the dryer in the current drying stage, the heat conversion rate during the drying process of the current drying stage is determined.

[0012] Further, the average pressure value generated by the tea on the inside of the dryer drum within a single stirring cycle is obtained, and the average pressure values of each stirring cycle in the current drying stage are fitted in time sequence to obtain the pressure change curve received by the inner wall of the dryer drum in the current drying stage; wherein, the current drying stage includes several of the stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

[0013] Further, according to the contact efficiency between the tea leaves and the hot air during the stirring process of the current stirring cycle and the deviation value of the drying temperature within the current stirring cycle, the stirring quality of the dryer within the current stirring cycle is obtained; according to the time sequence of the stirring cycles, the values of the stirring quality of all the stirring cycles in the current drying stage are fitted to obtain the stirring quality fitting curve of the dryer in the current drying stage; wherein, the current drying stage includes a plurality of the stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

[0014] Further, according to the standard deviation of the temperature monitoring data within the current stirring cycle and the average value of the absolute values of the temperature differences between the measured temperatures and the ideal temperatures at each moment within the current stirring cycle, the deviation value of the drying temperature within the current stirring cycle is obtained.

[0015] In a second aspect, the present invention also provides a temperature PID control system for a tea dryer, and the system includes: a preprocessing module: configured to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process; a parameter acquisition module: configured to obtain the adjustment coefficients corresponding to each drying stage respectively according to the monitoring data of each drying stage during the tea drying process; an adjustment module: configured to adjust the proportional gain Kp of the temperature PID control system of the dryer through the adjustment coefficients so as to realize the temperature control of the temperature PID control system of the dryer in each drying stage during the drying process.

[0016] The present invention has the following beneficial effects:

[0017] According to different temperature requirements during the tea drying process, the present invention divides multiple drying stages, and then adjusts different proportional gains for the temperature PID control system of the dryer in each drying stage, so as to achieve precise control of various monitoring data in each drying stage and improve the quality and yield of the tea. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Schematic diagram of a temperature PID control method for a tea dryer provided by an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the actual temperature curve and the ideal temperature curve within a single stirring cycle in an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the stirring speed monitoring curve within a single stirring cycle in an embodiment of the present invention;

[0022] Figure 4 Schematic diagram of the pressure change curve on the inner wall of the drum during the current drying stage in an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the humidity curve at the moisture discharge port during the current drying stage in an embodiment of the present invention;

[0024] Figure 6 Schematic diagram of the temperature PID control system of a tea dryer provided in an embodiment of the present invention. Detailed implementation manners

[0025] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in combination with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features and effects of a temperature PID control method and system of a tea dryer proposed according to the present invention. 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.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs.

[0027] The following specifically describes the specific solutions of a temperature PID control method and system of a tea dryer provided by the present invention with reference to the accompanying drawings. Please refer to Figure 1 , which shows a flowchart of a temperature PID control method of a tea dryer provided in an embodiment of the present invention. The method includes:

[0028] First, according to different temperature stages in the tea drying process, the tea drying process is divided into multiple drying stages. Based on different tea varieties, different temperature requirements exist during the drying process. Generally, it can be divided into the following three drying stages.

[0029] Initial drying stage: The moisture evaporation speed is relatively fast, and the temperature can be appropriately increased (generally between 80°C and 100°C) to avoid "stuffiness and dampness" on the surface of the tea;

[0030] Middle drying stage: Gradually reduce the temperature (about 70°C - 80°C), extend the drying time of the tea, and ensure that the internal and external moisture is consistent;

[0031] Final drying stage: Further reduce the temperature (about 50°C - 60°C) to ensure that the final moisture content of the tea reaches 5% - 6%.

[0032] Since the temperature requirements for each drying stage are different, and the monitoring data collected in each drying stage are also different, the PID control of the dryer temperature needs to be different. Therefore, in the embodiments of the present invention, according to the monitoring data of each drying stage in the tea drying process, the adjustment coefficients corresponding to each drying stage are obtained.

[0033] Specifically, according to the convection loss rate of the dryer temperature in the current drying stage, the adjustment coefficient corresponding to the current drying stage is obtained. Taking the initial drying stage as an example, the following detailed description is given.

[0034] 1. One rotation of the dryer drum represents a stirring cycle, and the initial drying stage includes several stirring cycles. By pressure sensors arranged at different positions on the inner wall of the dryer drum, the pressure values of the tea on the inside of the dryer drum obtained by each pressure sensor within a single stirring cycle are collected, and the pressure values of each pressure sensor within a single stirring cycle are averaged to obtain the average pressure value of the tea on the inside of the dryer drum within a single stirring cycle. Then, the average pressure values of each stirring cycle in the initial drying stage are fitted in chronological order to obtain the pressure change curve on the inner wall of the dryer drum in the initial drying stage.

[0035] 2. Taking a certain stirring cycle in the initial drying stage as an example, according to the standard deviation of the temperature monitoring data within the current stirring cycle and the average value of the absolute values of the temperature differences between the measured temperature and the ideal temperature at each moment within the current stirring cycle, the deviation value of the drying temperature within the current stirring cycle is obtained. Taking a certain stirring cycle in the initial drying stage as an example, according to the contact efficiency between the tea and the hot air during the stirring process of the current stirring cycle and the deviation value of the drying temperature within the current stirring cycle, the stirring quality of the dryer within the current stirring cycle is obtained. Then, according to the time sequence of the stirring cycles, the values of the stirring quality of all stirring cycles in the initial drying stage are fitted to obtain the stirring quality fitting curve of the dryer in the initial drying stage.

[0036] 3. According to the correlation between the pressure change curve on the inner wall of the dryer drum in the initial drying stage obtained above and the stirring quality fitting curve of the dryer in the initial drying stage, and the average value of the pressure change rates at two adjacent monitoring moments inside the dryer in the initial drying stage, the heat conversion rate during the drying process in the initial drying stage is determined.

[0037] 4. By the ratio of the difference between the humidity data at the start time of the initial drying stage and the humidity data at the end time of the initial drying stage to the time length of the initial drying stage, the average change rate of the humidity data in the current drying stage is obtained. Then, according to the heat conversion rate during the drying process in the initial drying stage obtained in the above step 3 and the average change rate of the humidity data in the initial drying stage, the moisture discharge efficiency during the drying process in the initial drying stage is determined.

[0038] 5. Determine the convective loss rate in the initial drying stage based on the moisture removal efficiency during the drying process in the initial drying stage, as well as the ratio between the temperature change inside the dryer and the temperature change outside the dryer in the initial drying stage.

[0039] Finally, use (1 + convective loss rate) as the adjustment coefficient for the proportional gain, and adjust the proportional gain of the temperature PID control system of the dryer to achieve temperature control of the temperature PID control system of the dryer in the initial drying stage during the drying process.

[0040] For the other medium drying stage and full drying stage, the adjustment coefficients of the temperature PID control system of the dryer in their respective drying stages are also obtained based on the same analysis above, so as to achieve temperature control of the temperature PID control system of the dryer in each drying stage during the drying process. This will not be elaborated here.

[0041] In the prior art, due to the influence of various factors, the changes in temperature and humidity are not immediately reflected in the output of the temperature control system, resulting in a lag phenomenon in the temperature adjustment during the tea drying process. This control delay makes it difficult to achieve precise control of the tea drying process. Therefore, in this embodiment, the tea drying process is first divided into three stages. The temperature deviation of the stirring device in the dryer within the stirring cycle in a single stage is extracted, and the stirring quality of the stirring device is obtained based on the temperature deviation and the stirring state. The heat conversion situation during the drying process is observed through the change in the stirring quality and the stirring and tumbling state of the tea. Then, the moisture removal efficiency in the drying equipment is evaluated based on the heat conversion rate. Finally, the heat convection loss situation during the drying process is analyzed based on the moisture removal efficiency and the temperature difference inside and outside the drying equipment, and then the temperature PID control system is optimized in a timely manner to respond to the heat loss situation generated by the system in a timely manner, making the PID control system perform more stably and efficiently in the working environment.

[0042] Another method embodiment of the present invention is applicable to a drum-type tea dryer, and its structure mainly includes: a drum, a heat source system, a stirring device, a feeding and discharging device, a fan and a moisture removal system, a transmission system, etc.

[0043] Its working principle is as follows:

[0044] 1. The wet material to be dried is fed into the feeding port of the drum-type dryer through a feeding device (such as a conveyor belt or a screw conveyor).

[0045] 2. The inside of the drum is designed as a slightly inclined cylinder (the inclination angle is usually 3° - 5°). The drum rotates slowly around the axis driven by an electric motor. Due to the inclination angle and rotation of the drum, the material moves gradually from the feeding end to the discharging end under the dual drive of gravity and the rotation force of the drum.

[0046] 3. Hot air generated by a heat source (such as a hot blast stove, steam system, gas furnace, etc.) is sent into the drum through a blower;

[0047] 4. The moisture evaporated in the drum is mixed in the hot air in the form of water vapor and discharged through a moisture exhaust system (such as an exhaust duct or a blower);

[0048] 5. After the tea leaves are dried by hot air in the drum, the moisture content gradually decreases to the level required by the process (usually 5%-6%, depending on the type of tea leaves).

[0049] The specific implementation process of the method in this embodiment is as follows:

[0050] 1. Collect monitoring data during the tea leaf drying process.

[0051] During the operation of the tea leaf dryer, the main monitoring data includes temperature, humidity, wind speed, heater status, tea leaf surface temperature, moisture exhaust device status, etc.; according to the design and working principle of the tea leaf dryer, the sensors need to be correctly installed in appropriate positions. For example, humidity sensors are generally installed near the air circulation area inside the dryer and the moisture exhaust outlet.

[0052] The data collected by the sensors needs to be processed by a data acquisition device (such as a data acquisition card, PLC controller or embedded computer). This process converts the analog signals of the sensors into data signals for subsequent analysis and processing.

[0053] The data is transmitted to the central control system by wired or wireless means; then the central control system analyzes and processes the collected data, and then sends corresponding control instructions to the temperature PID control system.

[0054] 2. Screen and mark the drying stages during the tea leaf drying process.

[0055] According to different varieties of tea leaves, different temperature stages can be calibrated during the actual drying process, which can be divided into three stages: the initial drying stage, the middle drying stage and the full drying stage. The division is the same as that in the foregoing method embodiment and will not be elaborated here.

[0056] 3. Extract the temperature deviation during the drying process.

[0057] The purpose of this step is to extract the temperature monitoring data during the drying process and analyze whether there is a deviation in the actual drying temperature. The temperature deviation will cause the temperature control system to fail to respond to the deviation in a timely manner.

[0058] Since the tea leaves entering the drum have a certain humidity and the humidity may be uneven, during the drying process in the dryer, some parts of the tea leaves receive more heat and some receive less heat; and if there is a deviation in the moisture exhaust efficiency, it will cause the moisture in some areas to not be exhausted in time, resulting in moisture accumulation and thus causing temperature deviation.

[0059] Taking a single drying stage during the drying process, such as the initial drying stage, as an example; the monitoring data during a single stirring cycle (i.e., when the drum rotates one week) in the initial drying stage is obtained through the sensors set in the tea dryer; the ideal temperature change curve during the drying process of the dryer is obtained in advance, and the curve during a single stirring cycle in the initial drying stage of the drying process is marked; by obtaining the temperature monitoring curve during the same time period in the actual monitoring process; the schematic diagram of the actual temperature curve and the ideal temperature curve during a single stirring cycle is as Figure 2 shown.

[0060] And denote the standard deviation of the temperature monitoring data during the stirring cycle as d;

[0061] Furthermore, record the deviation value of the drying temperature in the time period: ;

[0062] where d represents the standard deviation of the temperature monitoring data during this stirring cycle; represents the temperature monitoring value at the nth moment point in this time period; represents the temperature data at the same moment position in the ideal temperature curve; assume there are m moment points in this time period; represents the temperature monitoring value at the nth moment point in this time period and the temperature data at the same moment position in the ideal temperature curve the average value of the absolute values of the temperature differences at m moment points, this value reflects the average deviation degree between the actual temperature curve and the ideal temperature curve in the entire time period; the larger the product of, it means that the temperature deviation during this stirring cycle is larger, that is the larger.

[0063] A larger temperature deviation value can indicate that the distribution of tea leaves in the current stirring cycle may be uneven. Then, as the stirring cycle extends, whether there is heat accumulation inside the dryer or other factors affecting the response of the temperature control system, that is, the following analysis is carried out:

[0064] 4. Observe the heat conversion situation of the dryer during the tea drying process.

[0065] During the drying process of the tumbling tea dryer, since the stirring state of the equipment has a certain impact on the heat loss in the dryer, that is, if the stirring method is not good, it will lead to uneven distribution of tea in the drum and affect the maintenance of local temperature.

[0066] The tea entering the dryer itself has a certain humidity gradient. During the stirring and drying process of the dryer, it is expected that the adjustment of the temperature control system can reduce the gradient difference in the tea, making the drying degree distribution of the tea uniform. However, if the temperature response during the stirring process is not timely or the moisture discharge is uneven, it will lead to an increase in the humidity gradient or the maintenance of the gradient state, that is, further increase the oscillation of the temperature control system, and then may exacerbate the response delay of the temperature control system.

[0067] Obtain the stirring speed monitoring data within a single stirring cycle; then calculate the information entropy of the stirring speed monitoring curve during this period of time, and record the entropy value as b, which is used as the contact efficiency between the tea and the hot air during the stirring process; the stirring speed monitoring curve within a single stirring cycle is as Figure 3 shown.

[0068] Calculate the stirring quality of the tea dryer during the current stirring cycle: ;

[0069] Among them, b represents the information entropy value of the stirring speed data during the current period of time; represents the deviation value of the drying temperature in the e-th stirring cycle; the information entropy of the stirring speed can indicate whether the stirring state in the current stirring cycle is stable, that is, whether the contact efficiency between the tea and the hot air is high; if unstable stirring behavior occurs, it means that the tea does not effectively contact the hot air; The larger the value of, the lower the contact efficiency between the tea and the hot air during the stirring and drying process, and the larger the temperature difference, so the higher the possibility of uniform distribution of the internal temperature, that is, the stirring quality is lower.

[0070] According to the cycle order, fit all the stirring quality D values to obtain the stirring quality curve of the dryer during the current drying stage, denoted as P.

[0071] On the premise of not affecting the drying process, set pressure sensors at different positions on the inner wall of the tumbling dryer, and use the pressure sensors to obtain the pressure generated by the tea during the tumbling process on the inside of the dryer during the current stirring cycle.

[0072] Generally speaking, tea leaves with a certain humidity have a certain weight compared to dry tea leaves. During the tumbling process, the tea leaves with a certain weight accumulate together. As the tumbling angle changes, when the tea leaves in the drum slide from one position to the next, they will exert a certain pressure on the inner wall of the dryer.

[0073] During the drying process, as the drying time progresses, the moisture in the tea leaf raw materials is evaporated, which in turn causes the relative mass of the accumulated tea leaves to decrease. During the stirring process, the pressure exerted by the tea leaves on the inner wall will decrease.

[0074] That is, the desired state is that as the drying progresses, the moisture is evaporated, the tea leaves become dry, and the pressure change shows a continuous decreasing trend.

[0075] Obtain the average pressure value generated by the tea leaves on the inside of the drum during a single stirring cycle as the stirring process progresses, and then fit the pressure change curve on the inner wall of the drum during the drying stage according to the above fitting method, denoted as Q; as Figure 4 shown.

[0076] Furthermore, calculate the heat conversion rate of the tea leaf dryer during the drying process based on the stirring quality and the pressure change on the inner wall:

[0077]

[0078] Among them, P represents the fitting curve of the stirring quality as the stirring cycle progresses; Q represents the pressure change curve inside the dryer during this drying stage; represents the pressure value at the position of the Nth moment during the monitoring process of the internal pressure; similarly, represents the pressure value at the position of the (N + 1)th moment; assume that there are M monitoring moments in this stage; represents the exponential function with the natural constant e as the base; represents the average value of the pressure change rate between two adjacent monitoring moments inside the dryer during the current drying stage.

[0079] represents the correlation between the stirring quality and the pressure change as the stirring progresses. Specifically, this correlation can be the mean square error between P and The smaller the correlation value, the higher the correlation between the change in stirring quality and the pressure; conversely, it indicates a lower correlation, that is, during the stirring process, the moisture inside the tea leaves may not be effectively discharged, and the internal moisture may accumulate, further causing a response delay in the temperature control system.

[0080] It represents the heat conversion rate of the tea dryer during the tea drying process. The larger the product, the lower the heat conversion rate during the drying process, which means that the heat released by the heating source cannot be effectively transferred to the tea or the air. At this time, even if the temperature control system tries to adjust the heating power, the temperature change will be slow, resulting in a response delay.

[0081] 5. Heat conduction loss during the tea drying process of the tea dryer.

[0082] The purpose of this step is to observe and analyze the heat dissipation state and moisture removal efficiency during the tea drying process, so as to evaluate the heat loss of the heating equipment during the drying process. The more heat loss, the more it can indicate that there is a lag effect in the regulation of the temperature control system during the drying process;

[0083] In an efficient tea dryer, a high heat conversion rate helps to improve the moisture removal efficiency. The reason is that the heating source can heat the air and tea more quickly, making it easier for moisture to evaporate. The rapidly evaporated moisture needs to be taken away by the moisture removal system. Otherwise, the accumulated water vapor may affect the performance of the temperature control system, resulting in temperature fluctuations.

[0084] Obtain the humidity monitoring data during the drying process through the humidity sensor set at the moisture outlet of the dryer; the humidity curve at the moisture outlet is as Figure 5 shown.

[0085] Furthermore, obtain the moisture removal efficiency during the drying process: ;

[0086] Among them, represents the initial humidity data of the humidity sensor; represents the humidity data at the last moment during the drying stage; respectively represent the end moment and the start moment in the humidity monitoring data; represents the heat conversion rate during the drying process; The larger the product of, the higher the heat conversion rate, and the faster the speed of discharging moisture during the drying stage; that is, the higher the moisture removal efficiency during the drying process.

[0087] If the moisture removal efficiency is low, the water vapor cannot be discharged quickly, and the moisture accumulates in the dryer, which may make the operation of the temperature control system unstable, resulting in the heating system may need to work extra to maintain the set temperature, thereby increasing unnecessary heat energy consumption and generating a large amount of heat loss.

[0088] During the current drying stage, the ambient temperature change data during this time period is obtained near the outside of the dryer. Hot air is sent to the tea surface to accelerate water evaporation. The air inside the dryer is heated and flows, coming into contact with the tea surface and taking away the heat on the tea surface. Part of the heat is transferred to the air by convection, and the air is then discharged from the system, resulting in heat loss.

[0089] In the monitoring curve of the ambient temperature, there is a set of temperature differences at adjacent time positions, denoted as Calculate the mean of all temperature differences to obtain the external temperature change amount, denoted as ; In the temperature monitoring curve inside the dryer during the same time period, there is also a set of temperature differences at adjacent times, denoted as , calculate the mean of all temperature differences to obtain the internal temperature change amount, denoted as .

[0090] Calculate the convection loss rate of the dryer's temperature during the current drying stage: ;

[0091] Among them, represents the moisture discharge efficiency during the drying process; represents the ratio between the internal temperature change amount and the external temperature change amount during the current drying stage. The larger the ratio, it means the greater the temperature difference between the inside and outside, that is, the greater the probability of generating convection loss; represents the hyperbolic tangent function, which plays a role in positive proportional normalization; The larger the product of

[0092] 6. Optimize the temperature PID control system of the dryer.

[0093] During the drying process, heat loss directly affects the control performance of the temperature control system, including its response speed and delay degree. By analyzing heat loss, the control delay performance of the temperature control system can be evaluated, and it provides an important reference for optimizing the system.

[0094] The greater the heat convection loss g during the drying process, it can be considered that the heat loss situation generated by the dryer during the tea drying process is more serious. And the more serious the heat loss situation, it can explain that the response delay of the temperature control system is higher, that is, the temperature control system needs to make a stronger response.

[0095] Then, take 1 + g as the adjustment coefficient of the PID controller parameter (proportional gain Kp) of the tea dryer in the initial drying stage of tea, and use the adjusted proportional gain as the parameter of the temperature PID control system in the current stage, so as to improve the response ability of the temperature control system to the heat loss of the system.

[0096] When the dynamic characteristics of the system change significantly during operation, the fixed proportional gain Kp may not be able to maintain the best control effect; for example:

[0097] Initial drying stage: A higher response speed is required, and a larger Kp can be set;

[0098] Middle drying stage: Humidity adjustment becomes crucial, and Kp needs to be appropriately reduced to avoid overshoot.

[0099] Full drying stage: Enter the fine adjustment stage, and Kp should be further reduced to ensure system stability.

[0100] In multi-stage and multi-variable control scenarios such as tea drying, dynamically adjusting the proportional gain Kp can significantly improve the response speed and stability of the system, and avoid overshoot or oscillation.

[0101] Based on the same inventive concept as the above method embodiments, the embodiments of the present invention also provide a temperature PID control system for a tea dryer, as Figure 6 shown, including:

[0102] Pretreatment module: used to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process;

[0103] Parameter acquisition module: used to obtain the adjustment coefficient corresponding to each drying stage according to the monitoring data of each drying stage in the tea drying process;

[0104] Adjustment module: used to adjust the proportional gain Kp of the temperature PID control system of the dryer through the adjustment coefficient to achieve temperature control of the temperature PID control system of the dryer in each drying stage during the drying process.

[0105] It should be noted that: The above sequence of the embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. The processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multi-tasking and parallel processing are also possible or may be advantageous.

[0106] Each embodiment in this specification is described in a progressive manner. The same or similar parts between each embodiment can be referred to each other, and the key points of each embodiment are the differences from other embodiments.

Claims

1. A temperature PID control method for a tea dryer, characterized in that, The method includes: Dividing the tea drying process into multiple drying stages according to different temperature stages of the tea drying process, where the multiple drying stages include an initial drying stage, a middle drying stage, and a full drying stage; Determining the moisture removal efficiency during the drying process of the current drying stage according to the heat conversion rate during the drying process of the current drying stage and the average change rate of the humidity data of the current drying stage. The current drying stage includes multiple stirring cycles, and one stirring cycle represents one rotation of the dryer drum. The heat conversion rate is determined according to the correlation between the pressure change curve on the inner wall of the dryer drum in the current drying stage and the stirring quality fitting curve of the dryer in the current drying stage, and the average value of the pressure change rates inside the dryer at two adjacent monitoring times in the current drying stage. The pressure change curve is obtained by fitting the average pressure values of each stirring cycle in the current drying stage in chronological order, and the stirring quality fitting curve is obtained by fitting the values of the stirring quality of multiple stirring cycles according to the time sequence of the multiple stirring cycles; Determining the convective loss rate in the current drying stage according to the moisture removal efficiency during the drying process of the current drying stage and the ratio between the temperature change amount inside the dryer and the temperature change amount outside the dryer in the current drying stage; The convective loss rate satisfies the following formula: ; where represents the convective loss rate, represents the moisture discharge efficiency during the drying process; represents the ratio between the internal temperature change and the external temperature change in the current drying stage, represents the hyperbolic tangent function; Obtaining the adjustment coefficient corresponding to the current drying stage according to the convective loss rate of the dryer temperature in the current drying stage; Adjusting the proportional gain of the dryer temperature PID control system through the adjustment coefficient to achieve temperature control of the dryer temperature PID control system in each drying stage during the drying process.

2. The temperature PID control method of the tea dryer according to claim 1, characterized in that, Obtaining the average change rate of the humidity data of the current drying stage by dividing the difference between the humidity data at the start time of the current drying stage and the humidity data at the end time of the current drying stage by the time period length of the current drying stage.

3. The temperature PID control method of the tea dryer according to claim 1, characterized in that Obtaining the stirring quality of the dryer during the current stirring cycle according to the contact efficiency between the tea and hot air during the stirring process of the current stirring cycle and the deviation value of the drying temperature during the current stirring cycle; fitting the values of the stirring quality of all stirring cycles in the current drying stage according to the time sequence of the stirring cycles to obtain the stirring quality fitting curve of the dryer in the current drying stage.

4. The temperature PID control method of the tea dryer according to claim 3, characterized in that, Obtaining the deviation value of the drying temperature during the current stirring cycle according to the standard deviation of the temperature monitoring data during the current stirring cycle and the average value of the absolute values of the temperature differences between the measured temperature and the ideal temperature at each moment during the current stirring cycle.

5. A temperature PID control system for a tea dryer, characterized in that, The system is used to implement the temperature PID control method of the tea dryer as described in Claim 1, and the system includes: A preprocessing module: used to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process, where the multiple drying stages include an initial drying stage, a middle drying stage, and a full drying stage; Parameter acquisition module: Determine the moisture discharge efficiency during the drying process of the current drying stage according to the heat conversion rate during the drying process of the current drying stage and the average change rate of the humidity data in the current drying stage. The current drying stage includes multiple stirring cycles, and one stirring cycle represents one rotation of the dryer drum. The heat conversion rate is determined according to the correlation between the pressure change curve on the inner wall of the dryer drum in the current drying stage and the stirring mass fitting curve of the dryer in the current drying stage, and the average value of the pressure change rates inside the dryer at two adjacent monitoring times in the current drying stage. The pressure change curve is obtained by fitting the average pressure values of each stirring cycle in the current drying stage in chronological order, and the stirring mass fitting curve is obtained by fitting the values of the stirring mass of multiple stirring cycles according to the time sequence of multiple stirring cycles; Moreover, determine the convective loss rate in the current drying stage according to the moisture discharge efficiency during the drying process of the current drying stage and the ratio between the temperature change amount inside the dryer and the temperature change amount outside the dryer in the current drying stage; Moreover, obtain the adjustment coefficient corresponding to the current drying stage according to the convective loss rate of the dryer temperature in the current drying stage; Adjustment module: Used to adjust the proportional gain of the dryer temperature PID control system through the adjustment coefficient to achieve temperature control of the dryer temperature PID control system in each drying stage during the drying process.

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