Research On Fuzzy Adaptive PID Control For The Temperature And Humidity System In Plant Factory

In recent years,plant factory has been widely valued by governments around the world and internationally renowned enterprises.Plant factory is an efficient production system to obtain plant products needed by human beings(in taste,nutrition,green,health,etc.)by utilizing intelligent automatic control technology according to agricultural crops' growth environment demand at minimum cost(including cost on space,time,material,water and electricity,economic cost,etc.).Plant growth cabinet,as a micro plant factory,can control plant growth environment factors including light,temperature,humidity,carbon dioxide concentration and nutrient solution through intelligent automatic control system in an airtight environment.Temperature and humidity control system in plant growth cabinet is a relatively complicated system.Temperature and humidity are important parameters in industrial production process.Since temperature and humidity control is a nonlinear time-varying,strongly-coupled and uncertain complex process,and it is difficult to establish accurate mathematical model,traditional PID control often fails to achieve satisfactory control effect.Aiming at solving above problems,this paper presents a design method for fuzzy adaptive PID controller,provides an effective way for modeling and controlling plant factory control system.The main contents include:Firstly,temperature and humidity control principle of plant growth cabinet was introduced briefly.Simplified mathematical models were established by step response curve method for four loops of heating rod-temperature,heating rod-humidity,humidifier-temperature and humidifier-humidity respectively.Secondly,PID control algorithm is simple and convenient,has fast adjusting speed but needs to establish accurate mathematical model,does not have good adaptability to model structure change;however,fuzzy control does not need to establish accurate mathematical model,has strong adaptability to parameter variation of the object to be controlled,and can obtain better control effect even when the structure of the object model to be controlled changes greatly.Then based on the two algorithms,fuzzy rules were used for self-tuning PID parameters,a design method for fuzzy adaptive PID controller was studied.Simulation comparison between system models was carried out.Simulation results verified that this control method could reduce overshoot,reduce oscillation and accelerate output response when compared with traditional PID control method,When subjected to random disturbance,the system has certain anti-jamming ability.Thirdly,as for strong coupling between temperature and humidity in plant factory,feed forward compensation decoupling method was adopted to decouple coupled loop of temperature and humidity control system.Thus coupling effect between heating rod-temperature and humidifier-humidity channel was removed.Finally,simulation model was built by MATLAB / Simulink.Simulation comparison verified the control effects of non-decoupled temperature and humidity PID control,decoupled temperature and humidity PID control,and decoupled fuzzy adaptive PID control.The fuzzy adaptive temperature and humidity PID control system designed in this paper can better control the object to be controlled and can remove coupling between temperature and humidity.It has advantages of fast response and high stability.