Multivariable feedback design for regulating vapor compression cycles

This paper presents multivariable feedback control design for regulating a vapor compression cycle based on a lumped-parameter model. In particular, the conventional control strategy of SISO systems is studied based on the model and experimental tests, and compared to multivariable feedback control. It is shown that multivariable control of compressor speed and expansion valve opening has better performance than the existing SISO control method in regulating superheat and evaporating pressure. More importantly, with variable-speed compressor, electronic expansion, indoor and outdoor fans, evaporating and condensing pressures, the refrigerant superheat as well as subcool values can be simultaneously controlled to have the desired values such that desired COP can be maintained under different ambient conditions. It is expected that active multivariable feedback control will have wide applications in HVAC&R systems including air conditioners, heat pumps, and refrigerators etc. to achieve high performance and high energy-efficiency