Nonlinear Control of a Vapor Compression Cycle by Input-Output Linearisation

This paper proposes an input-output linearisation for the trajectory tracking control of a vapor compression cycle. For this purpose, a physical model-order reduction of an existing high-order system model is performed. Then, the design of a nonlinear feedback control structure exploiting an input-output linearisation is described, which involves the inversion of the system dynamics and the use of a reduced-order condenser submodel for the online reconstruction of unmeasurable states. An analysis of the stability of the internal dynamics is conducted. Here, a region of instability is identified that is dependent on the values of the external dynamics. The boundary of this region is calculated numerically and used for trajectory planning. Both the feedforward controller and the feedback controller are tested w.r.t. trajectory tracking on a high-order simulation model. The simulations show that the achieved performance of the feedforward controller validates the model-order reduction, whereas the feedback controller provides an accurate tracking even in the presence of unknown disturbances.