A Master of Science thesis in Mechatronics Engineering by Sayyed Hesam Pour Afzali entitled, "Modeling and Fuzzy Control of Modern Refrigeration System," submitted in June 2014. Thesis advisor is Dr. Ali A. Jhemi. Available are both soft and hard copies of the thesis.
Current typical refrigeration systems work with on-off controllers in each of their components and their expansion valves are regulated mechanically which is quite inefficient. This issue resides in the core design of the system which is based on the maximum possible load. This leads to high power consumption, low performance and an inability to precisely maintain the required temperature. In addition, this leads to a high number of on-off cycles and a high maintenance cost. Refrigeration cycles are highly dynamic and non-linear and moreover difficult to control. Due to this reason, this thesis focuses on a new control design that leads to precise temperature control. This design reduces power consumption and saves energy using fuzzy-PID controllers and variable speed drives. Different components such as compressors and heat exchangers are controlled and mechanical expansion valves are replaced with electronic units. The simplified model has been derived for refrigeration systems with vapor compression cycle, semi hermetic reciprocating compressor, direct expansion (DX) evaporator and air-cooled condenser. The refrigerant fluid used in the model is R-22. This model was validated and tested using experimental data acquired from a refrigeration system running in the field with the same proposed components. The onoff and fuzzy-PID controllers are simulated and the results are compared to demonstrate the efficiency and power-saving capability of the proposed system using a fuzzy-PID Controller.