Study On Dynamic Characteristics And Control Strategy Of Small Frequency Conversion Air-Conditioning Systems

A dynamics model of small air conditioning system was proposed in the paper. The compressor model was based on the steady lumped parameter method, and the changes of flow type and heat transfer coefficient of the refrigerant in evaporator and condenser have been taken into account for the first time in the heat exchanger model. The electrical expansion valve model was based on the lumped parameter method. Calculation results indicate that the model is effective in simulating the dynamics characteristics of the small system.Self-defining function curving fitting method in Origin program was first used in the thermal properties calculation of the refrigerants. A simple and convenient method based on the Cleland equations was proposed to calculate thermal properties of refrigerants R410A and R407C, which are known as two main substitutes of R22. The calculating results were compared with the data from the literature and the errors were acceptable. Compared with other thermal properties calculation model, the method has greater computation speed. The calculation results with minor error indicated that this method is an effective method for studying the thermal propertied of the refrigerant substitutes.A new mathematical model to calculate the flow characteristic of the adiabatic capillary tube was proposed in the paper, which was aiming at solving the problems existing in the former models. The Stocker's basic model was modified with the consideration of various effects due to sub-cooling, area concentration, rolling diameter, and different equations for viscosity and friction factors. The new model not only can be used for R22, but also applied to the substitutes of R22, for example R410A and R407C. With those equations, the simulation results of the modified model are compared to those in literature, and the errors are within 10%. The flowing characteristic was also analyzed in the paper. In the calculating process, the iterated algorithm method was adopted to increasing the accuracy and velocity of the calculation.Simulation on the performance of adiabatic capillary tubes of the refrigerant R22, R407C and R410A was studied in the paper. According to the requirements of the simulation, a simple and convenient method based on the Cleland equations was proposed to calculate thermal properties of refrigerants R410A and R407C, which are known as two main substitutes of R22. The calculating results were compared with the data from the literature and the errors were acceptable.The PID, fuzzy and neural network control on evaporator superheat were studied and compared in the paper. Intelligent PID controller was proposed aiming at the problems existing in the PID controller. It can adjust the parameters on line to acquire the better controller results. In the fuzzy controller designing, the Gaussian function was selected as the membership function. The self-optimum method was adapted to optimize the fuzzy factor, and the minimum ITAE performance figure was used in inspecting the optimization performance. The genetic algorithms were introduced to optimize the fuzzy control rule to reduce the adverse effect of the useless control rule.A new fuzzy neural network controller based on the genetic algorithms was proposed in the paper, which combined the fuzzy control, neural network control and genetic algorithms. The control system based on the basic FNNC structure, and can be optimized through two ways. One way was off line optimization on the basis of genetic algorithms, the other way was on line optimization on the basis of BP. The purpose of off line optimization was optimize the structure and parameter of the FNNC, and the purpose of the on line optimization was utilizing the actual working parameters to further refine the controller rule to suit the actual control system, and enhancing the self-adapting ability. Geneticalgorithm is a kind of global optimization techniques that can be avoid the Back Propagation algorithm's shortcoming of getting into local solution. Simulation and application in the paper show that the scheme is effective and feasible. The intelligent method based on the neural network can be widely used in the refrigeration system through the comparison between the above methods. The foreground of the neural network intellectual technology application in the refrigeration system controlling is perfecting wide.