Application Of Nonlinear Adaptive Control In Temperature Of Chinese Solar Greenhouses

At present,facility agriculture is developing rapidly and has become an important pillar industry of China’s national economy.As a typical representative of facility agriculture,solar greenhouse appropriately controls the internal environmental factors of greenhouse through regulation equipment to create a relatively independent and suitable microclimate environment,so as to overcome seasonal and regional differences and play a positive role in maintaining the long-term and stable supply of residents’ vegetable crops.Among various environmental factors related to crop growth,temperature has the most obvious impact on cash crops,especially in the northern region with extremely cold winter.Long-term low temperature is extremely unfavorable to the normal growth of vegetable crops.Therefore,how to realize the accurate control of temperature in northern solar greenhouse has become the difficulty of greenhouse research.The microclimate environment created by the greenhouse is actually a complex production process.The solar greenhouse has strong nonlinear characteristics,and various environmental factors outside the greenhouse will also interfere with the microclimate environment inside the greenhouse.In addition,the aging or distortion of the components of the solar greenhouse itself has the characteristics of parameter uncertainty.These difficulties make it difficult for the traditional control methods to obtain satisfactory control results.Therefore,the research on the temperature control method suitable for solar greenhouse in northern China has extremely important practical value and reference significance for solving the problem of crop demand in winter in northern China.According to the climate characteristics and actual agricultural production in northern China,this paper constructs the temperature dynamic model of northern solar greenhouse,and studies the control method for the established temperature dynamic model of northern solar greenhouse.This paper is based on the general project of NSFC "Research on intelligent optimal control method of greenhouse system"(Project No.:61673281).The specific innovative work of this paper is divided into the following three points:1)According to the climate characteristics of the northern region and the architectural characteristics of the northern solar greenhouse itself,a dynamic model of the northern solar greenhouse is constructed.According to the unique architectural characteristics of the northern solar greenhouse and the cold climate characteristics in northern winter,the heat exchange between the back wall and slope of the greenhouse and the internal air is constructed in the greenhouse temperature model.Considering the influence of greenhouse internal humidity on indoor temperature cannot be ignored,indoor humidity is added to the model as another state variable,and the factor of cold air infiltration is added to the actual data simulation shows that the greenhouse model is closer to the actual situation of the northern solar greenhouse,the model has high accuracy,can meet the actual needs,and provides a theoretical basis for the controller design.2)Aiming at the complex dynamic characteristics of nonlinear,multi disturbance and time-varying uncertainty of the constructed northern solar greenhouse system,a nonlinear adaptive control strategy based on RBF neural network is proposed in this paper.This paper combines linear adaptive controller,neural network nonlinear adaptive controller and switching mechanism to improve the dynamic performance of the system on the premise of ensuring the stability of the system.The parameters of the controller are determined based on the generalized minimum variance control law.RBF neural network is used to estimate the nonlinear term of solar greenhouse system.3)The above designed controller is verified by experiments to prove the feasibility and effectiveness of the control strategy.Firstly,the set point tracking experiment is carried out for the proposed control method.Secondly,in order to further verify the control performance of the controller in the actual greenhouse environment,the real weather data of a day in winter of the solar greenhouse are collected and substituted into the model for the control experiment,and the experimental curve of controlling the temperature of the solar greenhouse with the conventional PID method is added as a reference.Finally,the simulation experimental results are analyzed.The experimental results show that the proposed control strategy has fast response ability,the average error and standard error of control in the actual environment are significantly reduced compared with the conventional PID control method,showing a more ideal control effect,strong robustness and universality,and has important application value and reference significance for the future control research of Northern solar greenhouse.