Control-oriented Modelling for Multivariable Control of Refrigerant Dynamics in Vapor Compression Systems

A multivariable MPC is developed on a VC system to control simultaneously the superheat and evaporator pressure. A nonlinear control-oriented model is implemented with 12 state variables and 2 inputs. The nonlinear model is linearized around a carefully selected steady state point so that MPC could be implemented to compute optimal expansion valve opening and compressor speed with measured feedbacks of superheat and evaporator pressure. The control-oriented model and MPC are implemented on Simulink using 4 interconnected subsystems namely, the VC system, the MPC system, the reference system and the environment. The coupling effects between superheat and evaporator pressure are considered. MPC performance was satisfactory in terms of disturbance rejection and reference tracking whilst considering the coupling effects between superheat and evaporator pressure.