Design Of Nutrient Solution Adaptive Control System For Veranda Vegetable Machine

Nutrient solution is an important part of vegetable growth in soilless cultivation on veranda.Currently,the control technology of vegetable nutrient solution is relatively mature in large-scale agricultural fertilization system.It pays attention to the study of controlled objects（nutrient solution）,ignoring the effects and disturbances of external factors such as light intensity,temperature and humidity,CO₂ concentration and vegetable varieties and so on.As a result,the reference input can not be dynamically adjusted according to the changes of environment and vegetable growing days,and output is prone to overshoot,response time is unstable and is easily disturbed by external environmental factors and so on.It is often difficult to popularize and apply in small veranda vegetable machines for urban residents.To solve the above problems,this paper designs an adaptive nutrient solution control system for veranda vegetable machine,which consists of two subsystems:nutrient solution prediction and model reference EC（Electric Conductivity）and pH（Acidity and Alkalinity）adaptive decoupling control.The system can predict the best EC and pH value according to the parameters of temperature,humidity,light intensity and vegetable varieties,and realize the adaptive control of nutrient solution based on the prediction.The human-computer interaction interface of vegetable machine is designed to realize the functions of synchronous display of vegetable system parameters,voice broadcast and manual addition of nutrient solution.The main work of this paper is as follows:（1）Scheme design of nutrient solution control system.According to the structure characteristics and demand analysis of the veranda vegetable planter,the electrodes EC and pH sensors are selected to collect the parameters of nutrient solution,and DC peristaltic pump,stirring pump and circulating pump are used as the executing mechanism of the whole system.The environmental parameters of the veranda are collected by light intensity,temperature and humidity and CO₂ concentration sensors,and the nutrient solution is estimated on the cloud server.（2）Hardware design and test of nutrient solution control system.STM32 is chosen as the microcontroller of the veranda vegetable machine to design the interface circuits of peristaltic pump driver circuit,EC and pH amplifier circuit,and so on.Meanwhile,in order to improve the real-time data-processing,entertainment and human-computer interaction of vegetable machine,FreeRTOS embedded operating system and emWIN graphical interface library are transplanted to the microcontroller.Finally,the hardware test platform is built through integrated circuit design,which verifies the feasibility of communication,data acquisition and data display systems.（3）Design of vegetable nutrient solution prediction subsystem.On the basis of different regions,vegetable varieties and veranda environment,vegetable optimal nutrient solution EC and pH differ greatly and it is difficult to accurately predict manually,the improved Canopy-Kmeans clustering and SVM model algorithm are used to predict the set value of vegetable machine nutrient solution control system.The simulation validation of the experimental data sets of veranda vegetable machine shows that the maximum errors of EC and pH of nutrient solution were 4.17%and 3.80%respectively.（4）Design of model reference EC and pH decoupling adaptive control subsystem.Aiming at the problems of EC and pH coupling,veranda environment change and other external factors in nutrient solution control,such as fluctuation of nutrient solution mathematical model parameters,strong non-linearity and time-varying of the system in the process of mother liquor and water mixing,four mathematical models of mother liquor AB and EC,mother liquor C and pH and others were established by experiment and material conservation law,and the diagonal decoupling matrix of EC and pH was designed.According to the expected output such as the shortest response time（40s）and no overshoot of the process and others,the ideal reference model of the system is designed.The adaptive laws and control laws of EC and pH parameters of the system are designed respectively by using the model reference adaptive theory.Finally,the disturbance process of the system is studied when the external environment changes,and the following,robustness and output characteristics of the system are verified by simulation.The comprehensive experimental results show that the nutrient solution adaptive control system of the veranda vegetable machine can predict the optimum EC and pH of the vegetable machine according to the parameters such as region,vegetable species and veranda environment.It can reach a stable state in about 40 seconds.The EC control error is±0.1mS/cm,and the pH control error is±0.1,which is conducive to the scientific planting of vegetable on the veranda of the family.It has certain reference value for popularizing to medium and large scale soilless cultivation agricultural facilities.