Non-singular Terminal Sliding Mode Control Of Refrigeration System Based On Disturbance Observer

In the world,about thirty percent of social total energy consumption is building energy consumption in which sixty to seventy percent is air condition energy consumption.Thus,solving issues of energy saving and stable operation in air condition system is essential.Nowadays,most commercial air conditions are running on the basis of compression refrigeration system,and the selection of refrigeration unit is mainly based on maximum cooling and heating load.However,the system works in the partial load in most of time,so the efficiency is not ideal.In order to realize the energy saving effect,accurate temperature control and good disturbance rejection ability are both important.In view of this,the modeling of compression refrigeration system is studied,and a novel control method is proposed to realize stable,accurate and fast control performance.Meanwhile,it has good disturbance rejection ability.Firstly,the construction and mechanism of compression refrigeration system are studied.The steady-state lumped parameter method is used to describe compressor and electronic expansion valve on account of their small inertia and fast adjustment ability.While dynamic modeling method is used to describe evaporator and condenser because of their large inertia and slow adjustment ability.Then,according to laws of conservation of mass and energy,the refrigeration system model can be obtained by combining above parts together.The high-order model has problems such as complicated calculations,too many thermodynamics parameters and physical property parameters of refrigerant.Thus,with mild assumptions and simplifications of refrigerant parameters and heat exchange process,a fifth-order model of heat exchanger is proposed.After that,several experiments have been accomplished to identify unknown parameters in the model.The model shows high accuracy according to simulation and experiment results.Then,considering the fact that the refrigeration system is usually working in a wide range and susceptible to the disturbance,an extended disturbance observer is proposed to estimate the compound disturbance.The disturbance observer of evaporator is designed to estimate the disturbance and its derivative.Moreover,it canreduce the switching gain of controller when it is combined with sliding mode control.In order to solve the singularity problem of traditional terminal sliding mode control,a novel non-singular terminal sliding mode controller is proposed.The disturbance and its derivative are included in the surface by designing suitable sliding mode variables.The controlled variables are the derivatives of actual control inputs on the basis of second-order sliding mode system.Thus,the chattering problem can be alleviated because of the integration action.Finally,according to simulation results,the superiorities of disturbance observer and non-singular terminal sliding mode control method are verified.The control method has better dynamic performance and disturbance rejection ability.Meanwhile,it can eliminate chattering problem.