Cascaded Sliding-Mode Control of a Vapor Compression Cycle

This paper presents a cascaded control structure based on a sliding-mode controller for the trajectory tracking control of a vapor compression cycle. For this purpose, an existing high-order system model is split into a linear as well as a nonlinear subsystem and both are described by reduced-order models. The linear outer subsystem is controlled by an output feedback control in conjunction with a disturbance observer. The nonlinear subsystem, however, is controlled via a sliding-mode controller to address model uncertainty. The stability of the internal dynamics of the input-output linearisation, which serves as the basis of the sliding-mode controller, is ensured by input constraints w.r.t. the outer control-loop. The proposed control structure is tested on the full high-order simulation model and compared to a previously presented controller based on input-output linearisation. The comparison indicated a significant improvement of control performance as well as robustness concerning disturbances and model uncertainty.