Intelligent Controller Design Of VRV Central Air-Conditioning Based On Embedded System

VRV central air-conditioning is widely used in villas,shopping malls,small offices and other place,the multi-split air conditioning connects each evaporator of different rooms together through refrigerant pipe.When the room loads are changing,the stability characteristics of evaporator outlet’s superheat degree are affected directly.On the other hand,the evaporator superheat degree of VRV central air-conditioning system is one of the most important factors of affecting the energy efficiency ratio and safe operation.Therefore,it is great significance to study and realize the precise controlling of evaporator superheat degree in each room.To this end,the following works are done in this thesis:First of all,this thesis analyses the working principle of VRV central air-conditioning system and working characteristic of important link of heat exchanging of electronic expansion valve and evaporator,established the mathematical model of the electronic expansion valve and the evaporator superheat.The degree of superheat in the evaporator controlled by electronic expansion valve is nonlinear,uncertain and time-varying.This thesis designs a fuzzy PID controller with feedforward compensation,considers the degree of superheat and its difference value as input,through fuzzy reasoning setting PID controller parameters online,solves the problems of evaporator superheat degree controlling uncertainty,nonlinear and time-varying,realizes controlling precision to the room;Secondly,the coupling phenomenon of mutual influence is produced according to the change of room load,considering the change of total refrigerant flow outside of this room and its rate of change rate as input,the feedforward compensator is designed based on fuzzy control,the electronic expansion valve opening is fixed.This method reduces the interference of the other rooms’ load and working condition changes to this room effectively,and when the other rooms’ load are changing.In addition,the thesis also solve the problem that is difficult to control the coupling of different rooms in the multi-split central air conditioning system quickly and accurately;Then,the control method is verified by simulation,and the variation of operating condition and load in different rooms of VRV central air conditioning system are simulated.The results show that the degree of superheat control method is feasible and effective,and it can be used for adjusting the degree of superheat in coupling rooms accurately.Finally,the control method is realized by engineering,and the VRV degree of superheat controller based on STM32 is designed.The hardware circuit and PCB board are designed,and the degree of superheat fuzzy PID controller and the fuzzy feedforward compensation software are developed.Then,a part of experiments were carried out on VRV experimental platform,the experimental results show that the VRV degree of superheat controller based on STM32 operates stably,and the control algorithm achieves expected effect.This method can control the room degree of superheat accurately under complex interference and coupling,meet the actual control requirement of VRV central air conditioning,and guarantee the working efficiency of the central air-conditioning system effectively.