Temperature PID (Proportion Integration Differentiation) control method and system of tea dryer

Abstract

The invention relates to the technical field of intelligent control, in particular to a temperature PID control method and system of a tea dryer. According to different temperature stages in the tea leaf drying process, the tea leaf drying process is divided into a plurality of drying stages; according to the monitoring data of each drying stage in the tea leaf drying process, obtaining an adjustment coefficient corresponding to each drying stage; and the proportional gain of the dryer temperature PID control system is adjusted through the adjusting coefficient, so that temperature control of the dryer temperature PID control system in each drying stage in the drying process is achieved. Different proportional gains are adjusted according to the dryer temperature PID control system in each drying stage, so that various monitoring data in each drying stage are accurately controlled, and the quality and yield of tea leaves are improved.

Description

Technical Field

[0001] The invention relates to the technical field of intelligent control, and in particular to a temperature PID control method and system for a tea drying machine. Background Art

[0002] Tea drying is a crucial step in tea processing, which directly affects the quality, flavor and storage stability of tea. In order to improve the drying efficiency and quality of tea, modern tea processing has gradually introduced automatic control technology, especially temperature control technology, to achieve a precise drying process. As a classic automatic control strategy, the temperature PID (proportional-integral-differential) control method 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 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 maintains and controls the temperature and humidity inside the dryer by adjusting the heating and dehumidification devices. During the response 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 in temperature regulation during the drying process. This control delay makes it difficult to achieve precise control of the tea drying process, which in turn affects the quality and yield of the tea. Summary of the invention

[0004] In order to solve the technical problem that the temperature PID control of the tea dryer in the prior art has a hysteresis phenomenon and is difficult to achieve accurate control, thereby 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. The technical scheme adopted is as follows: In a first aspect, the present invention provides a temperature PID control method for a tea dryer, the method comprising: dividing the tea drying process into a plurality of drying stages according to different temperature stages of the tea drying process; obtaining an adjustment coefficient corresponding to each drying stage according to monitoring data of each drying stage in the tea drying process; and adjusting the proportional gain of the dryer temperature PID control system by the adjustment coefficient to achieve temperature control of the dryer temperature PID control system in each drying stage during the drying process.

[0005] The present invention makes differential adjustments to the dryer temperature PID control system according to the different temperature stages in different tea drying processes. The drying process is divided into multiple drying stages according to different temperature stages, and then the various monitoring data of the dryer and tea leaves in each drying stage are analyzed to obtain the adjustment coefficient corresponding to each drying stage. The proportional gain of the dryer temperature PID control system is adjusted by the adjustment coefficient, thereby realizing the temperature control of the dryer temperature PID control system in each drying stage during the drying process. The core concept of the present invention is to set different proportional gains of the dryer temperature PID control system according to the temperature requirements of different drying stages, so as to achieve accurate control of various monitoring data in each drying stage.

[0006] Furthermore, based on the monitoring data of each drying stage during the tea drying process, the adjustment coefficient corresponding to each drying stage is obtained; specifically, the adjustment coefficient corresponding to the current drying stage is obtained based on the convection loss rate of the dryer temperature in the current drying stage.

[0007] Furthermore, the convection loss rate in the current drying stage is determined according to the dehumidification efficiency in the drying process of the current drying stage and the ratio between the temperature change inside the dryer and the temperature change outside the dryer in the current drying stage.

[0008] Furthermore, the moisture removal efficiency in the drying process of the current drying stage is determined according to the heat conversion rate in the drying process of the current drying stage and the average change rate of the humidity data in the current drying stage.

[0009] Furthermore, 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.

[0010] Furthermore, based on the correlation between the pressure change curve of 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 rate inside the dryer at two adjacent monitoring moments in the current drying stage, the heat conversion rate in the drying process in the current drying stage is determined.

[0011] Furthermore, the average pressure value generated by the tea leaves on the inside of the dryer drum in 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 a pressure change curve on the inner wall of the dryer drum in the current drying stage; wherein, the current drying stage includes several stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

[0012] Furthermore, according to the contact efficiency between tea leaves and hot air during the stirring process in the current stirring cycle and the deviation value of the drying temperature in the current stirring cycle, the stirring quality of the dryer in the current stirring cycle is obtained; according to the timing of the stirring cycle, the values ​​of the stirring quality of all stirring cycles in the current drying stage are fitted to obtain the fitting curve of the stirring quality of the dryer in the current drying stage; wherein, the current drying stage includes several stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

[0013] Furthermore, according to the standard deviation of the temperature monitoring data in the current stirring cycle and the average of the absolute values ​​of the temperature differences between the measured temperature and the ideal temperature at each moment in the current stirring cycle, the deviation value of the drying temperature in the current stirring cycle is obtained.

[0014] In the second aspect, the present invention also provides a temperature PID control system for a tea dryer, the system comprising: a preprocessing module: used to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process; a 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; an adjustment module: used to adjust the proportional gain Kp of the dryer temperature PID control system through the adjustment coefficient, so as to realize the temperature control of the dryer temperature PID control system in each drying stage during the drying process.

[0015] The present invention has the following beneficial effects: The present invention divides the tea leaves into multiple drying stages according to different temperature requirements in the tea drying process, and then adjusts different proportional gains for the dryer temperature PID control system in each drying stage, thereby achieving accurate control of various monitoring data in each drying stage and improving the quality and yield of the tea leaves. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of a temperature PID control method for a tea drying machine provided by an embodiment of the present invention; Figure 2 Schematic diagram of an actual temperature curve and an ideal temperature curve in a single stirring cycle in one embodiment of the present invention; Figure 3 A schematic diagram of a stirring speed monitoring curve in a single stirring cycle in one embodiment of the present invention; Figure 4 It is a schematic diagram of a curve showing a pressure change on the inner wall of the drum in the current drying stage in one embodiment of the present invention; Figure 5 It is a schematic diagram of a moisture curve of a moisture outlet in the current drying stage in one embodiment of the present invention; Figure 6 A schematic diagram of a temperature PID control system for a tea drying machine provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the temperature PID control method and system of a tea drying machine proposed by the present invention, its specific implementation method, structure, features and effects are described in detail as follows in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

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

[0020] The following is a detailed description of the temperature PID control method and system of a tea drying machine provided by the present invention in conjunction with the accompanying drawings. Figure 1 , which shows a flow chart of a temperature PID control method for a tea drying machine provided by an embodiment of the present invention, the method comprising: First of all, according to the different temperature stages of the tea drying process, the tea drying process is divided into multiple drying stages. Based on different tea varieties, they have different temperature requirements during the drying process, which can generally be divided into the following three drying stages.

[0021] Initial drying stage: The water evaporates quickly, and the temperature can be appropriately increased (usually between 80℃ and 100℃) to avoid the tea surface from becoming "suffocating and damp"; Mid-drying stage: gradually lower the temperature (about 70℃-80℃), extend the drying time of the tea leaves, and ensure that the moisture content inside and outside the tea leaves is consistent; Sufficient drying stage: The temperature is further lowered (about 50℃-60℃) to ensure that the final moisture content of the tea leaves reaches 5%-6%.

[0022] Since the temperature requirements of each drying stage are different and the monitoring data collected in each drying stage are also different, the PID control of the temperature of the dryer is also different. Therefore, the embodiment of the present invention obtains the adjustment coefficient corresponding to each drying stage according to the monitoring data of each drying stage in the tea drying process.

[0023] Specifically, according to the convection loss rate of the temperature of the dryer in the current drying stage, the adjustment coefficient corresponding to the current drying stage is obtained. Taking the initial drying stage as an example, a detailed description is given below.

[0024] 1. One rotation of the dryer drum represents a stirring cycle, and the initial drying stage includes several stirring cycles. The pressure sensors installed at different positions on the inner wall of the dryer drum collect the pressure values ​​of the tea leaves on the inside of the dryer drum obtained by each pressure sensor in a single stirring cycle, and average the pressure values ​​of each pressure sensor in a single stirring cycle to obtain the average pressure value of the tea leaves on the inside of the dryer drum in 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 of the inner wall of the dryer drum in the initial drying stage.

[0025] 2. Taking a certain stirring cycle in the initial drying stage as an example, according to the standard deviation of the temperature monitoring data in the current stirring cycle and the average of the absolute value of the temperature difference between the measured temperature and the ideal temperature at each moment in the current stirring cycle, the deviation value of the drying temperature in 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 tea leaves and hot air during the stirring process in the current stirring cycle and the deviation value of the drying temperature in the current stirring cycle, the stirring quality of the dryer in the current stirring cycle is obtained. Then, according to the sequence of the stirring cycles, the stirring quality values ​​of all stirring cycles in the initial drying stage are fitted to obtain the fitting curve of the stirring quality of the dryer in the initial drying stage.

[0026] 3. Based on the correlation between the pressure change curve on the inner wall of the dryer drum in the initial drying stage and the fitting curve of the stirring quality of the dryer in the initial drying stage, as well as the average value of the pressure change rate inside the dryer at two adjacent monitoring moments in the initial drying stage, the heat conversion rate in the drying process in the initial drying stage is determined.

[0027] 4. The average change rate of humidity data in the current drying stage is obtained by the difference between the humidity data at the beginning of the initial drying stage and the humidity data at the end of the initial drying stage and the ratio of the time period length of the initial drying stage. Then, the dehumidification efficiency in the initial drying stage is determined based on the heat conversion rate in the initial drying stage obtained in step 3 above and the average change rate of humidity data in the initial drying stage.

[0028] 5. Determine the convection loss rate in the initial drying stage based on the dehumidification efficiency during the drying process in the initial drying stage and the ratio between the temperature change inside the dryer and the temperature change outside the dryer in the initial drying stage.

[0029] Finally, using (1+convection loss rate) as the adjustment coefficient of the proportional gain, the proportional gain of the dryer temperature PID control system is adjusted to achieve temperature control of the dryer temperature PID control system in the initial drying stage during the drying process.

[0030] The other middle drying stage and full drying stage are also based on the same analysis as above to obtain the adjustment coefficient of the dryer temperature PID control system in each drying stage, so as to realize the temperature control of the dryer temperature PID control system in each drying stage during the drying process. No further details will be given here.

[0031] Due to the influence of various factors, the temperature and humidity changes of the temperature control system in the prior art are not immediately reflected in the output of the temperature control system, resulting in a lag in the temperature regulation during the tea drying process. This control delay makes it difficult to achieve precise control of the tea drying process. Therefore, this embodiment first divides the tea drying process into three stages, extracts the temperature deviation of the stirring device of the dryer during the stirring cycle in a single stage, and obtains the stirring quality of the stirring device according to the temperature deviation and the stirring state; observes the heat conversion during the drying process through the change in stirring quality and the stirring and tumbling state of the tea leaves, and then evaluates the moisture removal efficiency in the drying equipment according to the heat conversion rate, and finally analyzes the heat convection loss during the drying process according to the moisture removal efficiency and the temperature difference between the inside and outside of the drying equipment, and then timely optimizes the temperature PID control system, so as to timely respond to the heat loss generated by the system, so that the PID control system performs more stable and efficient in the working environment.

[0032] The dryer applicable to another method embodiment of the present invention is 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 dehumidification system, a transmission system, etc.

[0033] Its working principle is: 1. The wet material to be dried is fed into the feed port of the drum dryer through a feeding device (such as a conveyor belt or screw conveyor); 2. The interior 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 the motor. Due to the inclination angle and rotation of the drum, the material gradually moves from the feed end to the discharge end under the dual drive of gravity and the rotation force of the drum; 3. The hot air generated by the heat source (such as hot air furnace, steam system, gas furnace, etc.) is sent into the drum through the fan; 4. The water evaporated in the drum is mixed with the hot air in the form of water vapor and discharged through the dehumidification system (such as exhaust duct or fan); 5. After the tea leaves are dried with hot air in the drum, their moisture content gradually decreases to the level required by the process (usually 5%-6%, depending on the type of tea leaves).

[0034] The specific implementation process of the method in this embodiment is as follows: 1. Collect monitoring data during the tea drying process.

[0035] During the operation of the tea dryer, the main monitoring data include temperature, humidity, wind speed, heater status, tea surface temperature, dehumidification device status, etc. According to the design and working principle of the tea dryer, the sensor needs to be correctly installed in the appropriate position. For example, the humidity sensor is generally installed in the air circulation area and near the dehumidification port inside the dryer.

[0036] The data collected by the sensor needs to be processed by a data acquisition device (such as a data acquisition card, PLC controller or embedded computer). This process converts the sensor's analog signal into a digital signal for subsequent analysis and processing.

[0037] The data is transmitted to the central control system via wired or wireless means; the central control system then analyzes and processes the collected data and sends corresponding control instructions to the temperature PID control system.

[0038] 2. Screen and mark the drying stages of the tea leaves during drying.

[0039] According to different varieties of tea, different temperature stages are calibrated in the actual drying process, which can be divided into three stages: initial drying stage, middle drying stage and full drying stage. The division is the same as the aforementioned method embodiment and will not be repeated here.

[0040] 3. Extract temperature deviation during drying process.

[0041] The purpose of this step is to extract the temperature monitoring data during the drying process and analyze whether the actual drying temperature deviates. Temperature deviation will cause the temperature control system to fail to respond to the deviation in a timely manner.

[0042] Since the tea leaves entering the drum have a certain humidity and the humidity may be uneven, during the drying process of the dryer, some parts of the tea leaves receive more heat and some parts receive less heat; and if there is a deviation in the dehumidification efficiency, the moisture in some areas cannot be removed in time, causing moisture accumulation, thus causing temperature deviation.

[0043] Take a single drying stage in the drying process as an example, such as the initial drying stage; obtain the monitoring data of a single stirring cycle (i.e. one rotation of the drum) in the initial drying stage through the sensor set in the tea dryer; obtain the ideal temperature change curve of the drying process of the dryer in advance, and mark the curve in a single stirring cycle in the initial drying stage of the drying process; obtain the temperature monitoring curve of the same time period in the actual monitoring process; a schematic diagram of the actual temperature curve and the ideal temperature curve in a single stirring cycle, such as Figure 2 shown.

[0044] The standard deviation of the temperature monitoring data during the stirring period is recorded as d; Then record the deviation value of the drying temperature in the time period: ; Where d represents the standard deviation of the temperature monitoring data during the stirring cycle; It represents the temperature monitoring value at the nth time point in this period of time; It represents the temperature data at the same time position in the ideal temperature curve; assuming that there are m time points in this period of time; Indicates the temperature monitoring value at the nth time point during this period of time Temperature data at the same time position as the ideal temperature curve The average of the absolute values ​​of the temperature differences at m time points, which reflects the average deviation between the actual temperature curve and the ideal temperature curve during the entire time period; The larger the product of is, the greater the temperature deviation is during the stirring cycle. The bigger.

[0045] A large temperature deviation indicates that the tea distribution in the current stirring cycle may be uneven. As the stirring cycle lengthens, is there heat accumulation inside the dryer or other factors that affect the response of the temperature control system? The following analysis is performed: 4. Observe the heat conversion of the dryer during the tea drying process.

[0046] During the drying process of tea leaves in a tumble dryer, the stirring state of the equipment has a certain influence on the heat loss in the dryer. That is, a poor stirring method will cause uneven distribution of tea leaves in the drum, affecting the maintenance of local temperature.

[0047] The tea leaves entering the dryer already have 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 leaves so that the degree of drying of the tea leaves is evenly distributed. However, if the temperature response during the stirring process is not timely or the moisture is discharged unevenly, the humidity gradient will increase or maintain a gradient state, which will further increase the oscillation of the temperature control system, and may further aggravate the response delay of the temperature control system.

[0048] The stirring speed monitoring data within a single stirring cycle is obtained; then the information entropy of the stirring speed monitoring curve within the period is calculated, and the entropy value is recorded as b, which is used as the contact efficiency between the tea leaves and the hot air during the stirring process; the stirring speed monitoring curve within a single stirring cycle is as follows Figure 3 shown.

[0049] Calculate the mixing quality of the tea dryer during the current mixing cycle: ; Among them, b represents the information entropy value of the stirring speed data in the current time period; It 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 leaves and the hot air is high; if unstable stirring behavior occurs, it means that the tea leaves are not effectively in contact with the hot air; The larger the value, the lower the contact efficiency between tea leaves and hot air and the greater the temperature difference during the stirring and drying process. The higher the possibility of uniform distribution of internal temperature, that is, the stirring quality is poor. The lower.

[0050] According to the order of the cycles, all the stirring quality D values ​​are fitted to obtain the stirring quality curve of the dryer in the current drying stage, which is recorded as P.

[0051] Under the premise of not affecting the drying process, pressure sensors are arranged at different positions on the inner wall of the tumbling dryer, and the pressure generated by the tea leaves on the inside of the dryer during the tumbling process in the current stirring cycle is obtained through the pressure sensors.

[0052] Generally speaking, tea leaves with a certain humidity have a certain weight compared to dry tea leaves. During the tumbling process, tea leaves with a certain weight pile up together. As the tumbling angle changes, the tea leaves in the drum slide from one position to the next, which will produce a certain pressure on the inner wall of the dryer.

[0053] During the drying process, as the drying time progresses, the moisture in the tea raw materials is evaporated, which leads to a relative decrease in the quality of the accumulated tea leaves. During the stirring process, the pressure of the tea leaves on the inner wall will be reduced.

[0054] That is, the desired state is that as the drying process proceeds, the water is evaporated, the tea leaves become dry, and the pressure change is in a continuous downward trend.

[0055] The average pressure value generated by the tea leaves on the inside of the drum during the stirring process in a single stirring cycle is obtained, and then the pressure change curve of the inner wall of the drum during the drying stage is fitted according to the above fitting method, which is recorded as Q; Figure 4 shown.

[0056] Then, the heat conversion rate of the tea dryer during the drying process is calculated by the stirring quality and the pressure change on the inner wall during the drying process:

[0057] Among them, P represents the fitting curve of the stirring quality as the stirring cycle proceeds; Q represents the pressure change curve inside the dryer during the drying stage; It represents the pressure value at the Nth moment during the internal pressure monitoring process; similarly, Indicates the pressure value at the N+1th moment; assuming that there are M monitoring moments in this stage; It represents the exponential function with the natural constant e as the base; It represents the average value of the pressure change rate inside the dryer at two adjacent monitoring moments during the current drying stage.

[0058] It means the correlation between stirring quality and pressure change as stirring proceeds. The correlation can be specifically expressed as P and The smaller the correlation value, the higher the correlation between the change in stirring quality and pressure; conversely, the lower the 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.

[0059] It represents the heat conversion rate of the 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 leaves 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.

[0060] 5. Heat conduction loss during the drying process of the tea dryer.

[0061] 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 generated by the heating equipment during the drying process. The more heat loss, the more it can be explained that there is a lag effect in the regulation of the temperature control system during the drying process; In an efficient tea dryer, high heat conversion rate helps improve moisture removal efficiency. The reason is that the heating source can heat the air and tea leaves more quickly, making it easier for moisture to evaporate. The rapidly evaporating 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 and cause temperature fluctuations.

[0062] The humidity monitoring data during the drying process is obtained by installing a humidity sensor at the dehumidification outlet of the dryer; the humidity curve of the dehumidification outlet is as follows: Figure 5 shown.

[0063] Then obtain the dehumidification efficiency during the drying process: ; in, It shows the initial humidity data of the humidity sensor; It indicates the humidity data at the last moment of the drying stage; Respectively represent the end time and start time of humidity monitoring data; Represents the heat conversion rate during the drying process; The larger the product of , the higher the heat conversion rate is, and the faster the moisture is discharged during the drying stage; that is, the higher the moisture removal efficiency during the drying process is.

[0064] If the dehumidification efficiency is low, water vapor cannot be discharged quickly, and moisture accumulates in the dryer, which may cause the temperature control system to work unstable, resulting in the heating system may need to work extra to maintain the set temperature, thereby increasing unnecessary heat energy consumption and generating greater heat loss.

[0065] In the current drying stage, the ambient temperature change data during this period is obtained near the outside of the dryer. Hot air is sent to the surface of the tea leaves to accelerate the evaporation of moisture. The air in the dryer flows after being heated and contacts the surface of the tea leaves, taking away the heat from the surface of the tea leaves. Part of the heat is transferred to the air through convection, and the air is then discharged from the system, resulting in heat loss.

[0066] In the monitoring curve of ambient temperature, there is a set of temperature differences between two adjacent time positions, recorded as Calculate the mean of all temperature differences to obtain the external temperature change, which is recorded as ; In the temperature monitoring curve inside the dryer within the same time, there is also a set of temperature differences at adjacent moments, recorded as , calculate the mean of all temperature differences, get the local temperature change, and record it as .

[0067] Calculate the convection loss rate of the dryer temperature during the current drying stage: ; in, It represents the moisture removal efficiency during the drying process; It represents the ratio between the internal temperature change and the external temperature change in the current drying stage. The larger the ratio, the greater the temperature difference between the inside and outside, that is, the greater the probability of convection loss. represents the hyperbolic tangent function, which plays the role of normalization of direct proportion; The larger the product of, the higher the convection loss rate during the drying process. Excessive convection loss may cause large temperature changes inside the dryer, affecting the stability and response speed of the temperature control system. The temperature control system may need to adjust the output of the heating equipment more frequently, resulting in excessive energy consumption.

[0068] 6. Optimize the temperature PID control system of the dryer.

[0069] During the drying process, heat loss directly affects the control performance of the temperature control system, including its response speed and delay. By analyzing heat loss, the control delay performance of the temperature control system can be evaluated and provide an important reference for optimizing the system.

[0070] The greater the heat convection loss g during the drying process, the more serious the heat loss generated by the dryer during the drying process of the tea leaves. The more serious the heat loss, the higher the response delay of the temperature control system, which means that the temperature control system needs to make a stronger response.

[0071] Then, 1+g is used as the adjustment coefficient of the PID controller parameter (proportional gain Kp) of the tea dryer in the initial drying stage of tea leaves, and the adjusted proportional gain is used as the parameter of the temperature PID control system in the current stage, thereby improving the responsiveness of the temperature control system to the heat loss of the system.

[0072] 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: Initial drying stage: a higher response speed is required, and a larger Kp can be set; Mid-dry stage: Humidity regulation becomes the key, and Kp needs to be appropriately lowered to avoid over-regulation.

[0073] Fully dry stage: Entering the fine adjustment stage, Kp should be further reduced to ensure system stability.

[0074] In multi-stage, 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.

[0075] Based on the same inventive concept as the above method embodiment, the embodiment of the present invention also provides a temperature PID control system for a tea drying machine, such as Figure 6 As shown, including: Pretreatment module: used to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process; 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; Adjustment module: used to adjust the proportional gain Kp 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.

[0076] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0077] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A temperature PID control method for a tea drying machine, characterized in that: The method comprises: According to the different temperature stages of the tea drying process, the tea drying process is divided into multiple drying stages; According to the monitoring data of each drying stage in the tea drying process, the adjustment coefficient corresponding to each drying stage is obtained; The proportional gain of the dryer temperature PID control system is adjusted by adjusting the 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 drying machine according to claim 1, characterized in that: According to the monitoring data of each drying stage in the tea drying process, the adjustment coefficient corresponding to each drying stage is obtained; specifically including: According to the convection loss rate of the temperature of the dryer in the current drying stage, the adjustment coefficient corresponding to the current drying stage is obtained.

3. The temperature PID control method of the tea drying machine according to claim 2, characterized in that: The convection loss rate in the current drying stage is determined according to the dehumidification efficiency in the drying process in the current drying stage and the ratio between the temperature change inside the dryer and the temperature change outside the dryer in the current drying stage.

4. The temperature PID control method of the tea drying machine according to claim 3 is characterized in that: The moisture removal efficiency in the drying process of the current drying stage is determined according to the heat conversion rate in the drying process of the current drying stage and the average change rate of the humidity data in the current drying stage.

5. The temperature PID control method of the tea drying machine according to claim 3, characterized in that: 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.

6. The temperature PID control method of the tea drying machine according to claim 3, characterized in that: The heat conversion rate in the drying process of the current drying stage is determined based on the correlation between the pressure change curve on the inner wall of the dryer drum in the current drying stage and the fitting curve of the dryer stirring quality in the current drying stage, as well as the average value of the pressure change rate inside the dryer at two adjacent monitoring moments in the current drying stage.

7. The temperature PID control method of the tea drying machine according to claim 6, characterized in that: The average pressure value generated by the tea leaves on the inside of the dryer drum in 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 of the inner wall of the dryer drum in the current drying stage; The current drying stage includes a plurality of stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

8. The temperature PID control method of the tea drying machine according to claim 6, characterized in that: According to the contact efficiency between tea leaves and hot air during the stirring process of the current stirring cycle and the deviation value of the drying temperature in the current stirring cycle, the stirring quality of the dryer in the current stirring cycle is obtained; according to the time sequence of the stirring cycle, the stirring quality values ​​of all stirring cycles in the current drying stage are fitted to obtain the fitting curve of the stirring quality of the dryer in the current drying stage; The current drying stage includes a plurality of stirring cycles, and one stirring cycle represents one rotation of the dryer drum.

9. The temperature PID control method of the tea drying machine according to claim 8, characterized in that: The deviation value of the drying temperature in the current stirring cycle is obtained according to the standard deviation of the temperature monitoring data in the current stirring cycle and the average of the absolute values ​​of the temperature differences between the measured temperature and the ideal temperature at each moment in the current stirring cycle.

10. A temperature PID control system for a tea drying machine, characterized in that: The system comprises: Pretreatment module: used to divide the tea drying process into multiple drying stages according to different temperature stages of the tea drying process; 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; 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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