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Research and Realization of Dual-loop Energy-saving Control Method of Refrigerator

Author: LiZhaoBo
Tutor: WuAiGuo
School: Tianjin University
Course: Control Science and Engineering
Keywords: Compressor variable frequency Minimum superheat Smithpredictor Model-free Air conditioning controller
CLC: TB651
Type: Master's thesis
Year: 2012
Downloads: 2
Quote: 0
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Abstract


Energy consumption of building accounts for about30%in the total social energyconsumption. Energy consumption of central air-conditioning system accounts for60%in the total energy consumption of building, thus energy-saving of refrigerationsystem takes an important part in the buildings’ energy-saving.Compressors of central air conditioning refrigeration systems often run in ratedfrequency and produce constant cooling capacity. However, the load of the system ischanging, which makes the system run on non-rated load for long time and produceexcess cooling capacity. Research on how to make the cooling capacity and loadmatch by control has great economic and social benefits.Firstly, the refrigeration system experimental platform is introduced. Thecharacteristics and coupling relationship of refrigeration system are analyzed. Thenhigh-order dynamic model simulation of refrigeration system is carried out. Thecomparison between simulation and experimental results show the model is correct.the strengths and weaknesses of several typical air-conditioning control methods aresummed up and analyzed. Dual-loop control method based on the constantevaporation temperature and the minimum stable superheat is proposed. Thenexperiment method of getting the minimum stable superheat is given. The experimentbased on this method is carried out and the result shows the energy-saving effect issignificant.Secondly, considering the requirements limit of model accuracy, improved Smithpredictive control is proposed. The result shows that improved Smith predictivecontrol has better control performance when time-delay parameter is mutative orexists a deviation. Then the Smith predictive control is introduced to multi-inputmulti-output system. Compared with PID, the simulation result of dual-looprefrigeration system with Smith predictive control method has better performance.Finally, the decoupling matrix eliminates coupling in the identification model,improving the system dynamic performance theoretically, but still has somerestrictions in application. At the same time, due to the complexity of dynamic modelof refrigeration system, the model-free control is introduced to refrigeration system.The design method of single-loop model-free control law is extended to multi-loop system and dual-loop model-free control law is given. Finally, the simulation resultsbased on dual-loop identification model of refrigeration system verify model-freecontrol.Finally, a central air-conditioning controller based on ARM (LM3S8970) isdesigned, including the schematic design and PCB design. The controller has10isolated digital input,10isolated digital output,16isolated analog inputs,8isolatedanalog outputs,2CAN, RS-232and Ethernet. Besides, the communication driver isdeveloped and the double-loop control program is written in C language. Thecontroller is used in the real refrigeration system platform and operates stably andreliably.

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CLC: > Industrial Technology > General industrial technology > Refrigeration Engineering > Refrigeration machinery and equipment > Refrigerator
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