Study On Fuzzy Fractional-order PID Control Of Temperature Difference Of Cooling Water In Central Air-conditioning System

With the raPID development of refrigeration technology and people's growing requirements for the living environment,central air-conditioning system has been widely used in more and more buildings.However,central air-conditioning systems provide us with benefits as well as problem of large energy consumption.When designing central air-conditioning system,we should take the building's maximum cooling load into consideration with the fact that the water flow in central air-conditioning system always keeps unchanged.The water system of a central air-conditioning system mainly consists of two parts: cold water system and cooling water system.In most buildings,traditional PID controller for temperature control is mostly used in cooling-water circulation.Traditional PID controllers are prone to make problems such as overshoot and oscillation.When the pipeline system changes,it is necessary to re-adjust the parameters of the PID controller,otherwise it will easily lead to a drop in control quality and waste of electricity.Based on the theory of fractional calculus and fuzzy control,this paper proposes a fuzzy controller fractional PID for the control of cooling water temperature difference.The software MATLAB is used for simulation experiment.The result of simulation experiment shows that this controller has good control quality and is valuable in practice.The main contents of this article are as follows:1.According to characteristics of the HVAC cooling water system,the input and output of cooling towers,cooling water pumps etc.are analyzed and their transfer functions are given.2.Based on the technical requirements of the central air-conditioning system for cooling water control as well as laws of fractional PID control and fuzzy control,a fuzzy fractional PID controller for cooling water and tuning method based on fuzzy rules are proposed.Besides,simulation experiment was done to prove the effectiveness of the controller.3.By means of simulation experiments,the traditional PID controller,fractional-order PID controller and the fuzzy fractional PID controller proposed in this paper are compared.Results of simulation experiments show that the fuzzy fractional PID controller presented in this paper has advantages over traditional PID controller and fractional-order PID controller in terms of overshoot,accuracy,adjustment time and other performance indicators.