Multivariable Control of Vapor Compression Cycles: Coordination of Compressor and Expansion Valve

Abstract

This paper discusses a control design for regulating vapor compression cycles based on multivariable feedback techniques. The performance of conventional controllers based on independent SISO loops has been limited, due to the strong cross-couplings inherent among the SISO loops. An LQG compensator with integrators is proposed to replace the SISO feedback design. A lumped-parameter model proposed by the authors in (He et al., 1995) has proved to be effective in describing the cycle dynamics in the vicinity of an operating point. For designing a MIMO LQG compensator, a reduced order model is proposed such that the dimension of the compensator is maintained reasonably low. The experimental results show that the performance of the MIMO LGQ is superior to the SISO design. The robustness of the LQG compensator based on the reduced-order model is also discussed.