In this thesis, feedback controller designs are proposed for modern air-condition -ing systems which contain either single evaporator or multiple evaporators. For the single-evaporator air-conditioner, the feedback controller possesses a cascade structure for dealing with the fast and slow dynamics in the system. To determine appropriate control parameters, conditions that establish performance and stability are given. A dynamic compensator is also incorporated into the controller to reduce the performance degradation caused by the low-speed limit of the compressor. Experiments demonstrate that the proposed control system can simultaneously provide better regulation for the indoor temperature and improve the energy efficiency at steady state. For the multi-evaporator air-conditioner, a control strategy with flow-distribution capability is proposed to accommodate different thermal demands in different rooms. To determine appropriate control parameters, theorems regarding stability of the closed-loop system are also given. Experiments indicate that the proposed strategy can successfully regulate the indoor temperatures regardless that the reference settings for respective rooms are different and the settings are switched in the middle of the control process. Because the multi-evaporator air-conditioning machine can be operated in modes that only selected evaporator(s) is(are) turned on, when mode-switching is demanded, switching directly from one control strategy to another could lead to discomfort to the users. Therefore, the thesis also proposes a framework for the mode switching control of the multi-evaporator air-conditioning system. The framework is an integration of cascading control structure based on the flow distribution and a dynamic compensator. In the framework, only the controller that all the evaporators are on throughout the control process is used to provide the nominal performance, and the dynamic compensator can account for the influence when the mode switching operation occurs. Experiments also indicate that the proposed framework can provide satisfactory mode-switching performance.

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