Decentralized Feedback Structures of a Vapor Compression Cycle System

In vapor compression cycle systems, it is desirable to effectively control the thermodynamic cycle by controlling the thermodynamic states of the refrigerant. By controlling the thermodynamic states with an inner loop, supervisory algorithms can manage critical functions and objectives such as maintaining superheat and maximizing the coefficient of performance. In practice, it is generally preferred to tune multiple single-input-single-output (SISO) control inner loops rather than a single multiple-input-multiple-output control inner loop. This paper presents a process by which a simplified feedback control structure, amenable to a decoupled SISO control loop design, may be identified. In particular, the many possible candidate input-output (I/O) pairs for decentralized control are sorted via a decoupling metric, called the relative gain array number. From a reduced set of promising candidate I/O pairs, engineering insight is applied to arrive at the most effective pairings successfully verified on an experimental air-conditioning-and-refrigeration test stand.