Comparison of SISO and MIMO control techniques for a diagonally dominant vapor compression system

For vapor compression cycle (VCC) systems, it is important to meet multiple control objectives in order to satisfy system capacity and efficiency requirements. Moreover, in the HVAC industry, it is generally preferred to tune multiple single-input-single-output (SISO) control loops rather than a single multiple-input-multiple-output (MIMO) control loop. This paper shows that when using an appropriate choice of feedback variables, a decentralized control approach consisting of individual SISO control loops performs as well as a MIMO control approach. An identified system model is shown to be diagonally dominant when using a decoupling set of input-output pairings. A linear quadratic Gaussian (LQG) control design is compared to a decentralized SISO control design through experimental results. Both controllers produce comparable time-domain performance characteristics.