Active Disturbance Rejection Control Of Compression Refrigeration System

In public buildings,power consumption of the refrigeration system accounts for about 60% of the total power consumption.If the refrigeration system can operate stably and has a good ability to suppress disturbance,it is of great significance to reduce building energy consumption.Compression refrigeration system is a nonlinear system with time-varying disturbance,uncertainty and complex coupling relations,so its stability control is difficult.Since the active disturbance rejection controller(ADRC)has the advantage of not relying on the accurate model of the system and estimating the internal and external disturbance of the system in real time,it is introduced into the decoupling control of the compression refrigeration system in this paper.First of all,the working principle and characteristics of the refrigeration system are analyzed,including the influence of parameter variation on the cycle process and the internal coupling relationship.In addition,sixth-order nonlinear mechanism model of the refrigeration system is given,and its characteristics are briefly analyzed.Then,the structure and principle of ADRC are expounded,the function of each part of ADRC is analyzed in detail,and the advantages of the non-smooth feedback effect of nonlinear function in the controller are revealed.Secondly,the second-order delay model of the refrigeration system is identified by the experimental data.Based on the coupling characteristics of the model,static decoupling is applied to the refrigeration system,and the dynamic coupling part is compensated as the disturbance by the extended state observer.Considering the time-delay characteristic of the refrigeration system,third-order extended state observers are designed,and in order to use the initially large error signal to speed up the system output,the tracking differentiators are ignored.In the simulation experiment,it is verified that the ADRC decoupling control not only has the advantage in tracking and suppressing disturbance ability,but also has stronger robustness by comparing the control effect of the decoupling control with the Smith predictor and the internal model decoupling control.Finally,because the identification model of the refrigeration system can't fully reflect the operating characteristics of the refrigeration system in a large range of operating points,and the high-order nonlinear model of the refrigeration system is not conducive to design controller,the high-order model of the refrigeration system is simplified to fifth-order model.Based on the short convergence time of nonhomogeneous algorithm,an extended state observer with non-homogeneous finite time convergence is designed and the convergence property of the observer is proved by Lyapunov function.Furthermore,three single-loop improved active disturbance rejection controllers are designed for the fifth-order refrigeration system.The simulation results show that the improved active disturbance rejection controller has better disturbance rejection ability and faster convergence time,and has good robustness.It can achieve stable control of the refrigeration system.