  This work is focused on optimal control of mechanical compression
refrigeration systems. A reduced-order state-space model based on the moving
boundary approach is proposed for the canonical cycle, which eases the
controller design. The optimal cycle (that satisfying the cooling demand while
maximizing efficiency) is defined by three variables, but only two inputs are
available, therefore the controllability of the proposed model is studied. It
is shown through optimization simulations how optimal cycles for a range of the
cooling demand turn out not to be achieved by keeping the degree of
superheating to a minimum. The Practical NMPC and a well-known
feedback-plus-feedforward strategy from the literature are compared in
simulation, both showing trouble in reaching the optimal cycle, which agrees
with the controllability study.
