Modeling and control of hybrid vapor compression cycles

This thesis details the efforts made to develop nonlinear dynamic models, analysis techniques, and control schemes for hybrid vapor compression cycles. Hybrid vapor compression cycles come in many possible configurations, but they all combine the power producing components of a conventional cycle with a thermal energy storage unit to provide increased operational flexibility over the conventional unit. However, the gains associated with the increase in operational flexibility can only be achieved with the inclusion of appropriate control strategies to regulate and optionally optimize the energy flow throughout the hybrid system. This thesis makes contributions in improving a first principles modeling approach using the moving boundary method. It derives models for each component of a conventional system as well as a thermal energy storage unit designed to be used in a hybrid system configuration. These models are applied to simulate both a conventional and a hybrid system in open and closed loop configurations. The simulations showed that when the correct control strategy is applied, the hybrid system universally outperforms the conventional system in performance and energy efficiency in applications with rapid transient load profiles. Finally, analysis and optimization methods for hybrid system performance as well as thermal energy storage parameter selection are presented and applied to simulation data gathered from models developed in this thesis