The Technical Research On Capacitive Sensing Defrost In Household Refrigerators

With the continuous advancement of human science and technology,household appliances are constantly becoming digital and intelligent in the wave of the technology,and together with other things to build a world of interconnected things.As one of the members,household refrigerators play a unique role in creating a healthier,more convenient and comfortable life for the people.The main function of the household refrigerator is food preservation,but during the operation of the refrigerator,the frost will gradually form on the surface of the evaporator,and the presence of the frost layer will affect the cooling performance of the system,so the defrosting control method is critical in the refrigerator.In this thesis,the development and research status of the defrost control method of the refrigerator in domestic and foreign markets are discussed comprehensively.Based on this,the capacitive sensing defrost control method is proposed,and the experimental test was conducted.The feasibility of the method was verified.Firstly,the basic principle of the cooling system of the household refrigerators and the reasons for the formation of the frost on the surface of the evaporator fins is explained,then this thesis introduces the design concept and control logic of the most widely used clock-based timing defrosting method in the industry,it is an indirect defrosting method.Indirect defrosting can not intuitively identify the frost status on the surface of the evaporator,during the operation,the phenomenon of defrosting not timely and frost-free defrosting often occurs,that means the cooling system executes a defrosting command when not necessary,resulting in a waste of energy.Secondly,the application of the capacitive sensing technology in life is introduced.Capacitive sensing is a low-power,low-cost and high-resolution non-contact sensing technology.The FDC2214 capacitance-to-digital converter developed by Texas Instruments is used in this thesis.A capacitance measuring system consisting of the metal surface of the evaporator and the sensor plate is eatablished.The defrosting is performed by detecting the capacitance value which is depend on the frosting state on the surface of the evaporator.The capacitive sensing defrosting logic is designed to avoid the occurrence of defrosting not timely and frost-free defrosting.The principle of the FDC2214 capacitance-to-digital converter is to derive the capacitance of the sensor by the resonant frequency of the LC oscillating circuit.Finally,the capacitive sensing defrost method was tested,and compared with the clock-based timing defrosting method under the same condition,the new method can save energy more effectively,the feasibility of the method was verified.The research of this thesis provides a new solution for the defrosting control method of the household refrigerator.The new method can more intelligently determine the timing of starting defrosting and achieve the purpose of defrosting on demand,which provides the theoretical basis and practical experience for the further research.