Dissertation > Industrial Technology > Machinery and Instrument Industry > Mechanical parts and gear > Control parts

The Design of Digital Control System and the Experimental Study of Flow Characteristics of EEV

Author DaiHuaLiang
Tutor YangQianMing
School Shandong University of Science and Technology
Course Mechanical and Electronic Engineering
Keywords electronic expansion valves modeling simulation PID algorithm PLC CAT system flow characteristics
Type Master's thesis
Year 2011
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Electronic expansion valves (EEV) are throttling components in refrigeration system. It can adjust the flow of refrigerants, throttle step-down, and control superheat in system. It has important academic and engineering significance of designing control law of flow and opening of electronic expansion valves reasonably and acquiring good run quality of heat pump air conditioning system by the way of studying flow output response characteristics of electronic expansion valves and the control characteristics of flow and open degree of electronic expansion valves in the round.Mathematical modeling of control system of electronic expansion valves is established based on discussing the characteristic of digital control of EEV in this paper, according of which simulation experimental platform of digital control of EEV and computer digital simulation analysis is carried out. The open degree and flow characteristics of control system of EEV are revealed. Steady-state response characteristics of the negative feedback control of flow of EEV and the influence of the steady-state output system with gap characteristics is obtained through the system simulation analysis. Simulation experiments show the rationality of mathematical model in this paper.Mathematical model control system with PID controller is established through introducing the PID control algorithm in control system of EEV and comparison and analysis of steady characteristics of the output is carried out with routine system. The results of the study show that PID control algorithm can shorten response time of system compared with routine system, and it can reduce the response volatility of system boots and suppress the overshoot phenomenon.In order to analyzing the flow characteristic of EEV, a test system of flow and open degree is established in this paper based on stepping motor by PLC controller, realizing the adjusting of digital controlling. The driving circuit of stepping-motor with the function of over-load protection and short-circuit protection is established; the accurate control characteristic of open degree of EEV is realized by the way of driving stepping motor directly and four-phase-eight-pat controlling pattern. Using FS4000 quality flow sensor, HITEK pressure transmitter and PT100 platinum resistance measure physical parameter of flow rate pressure and temperature variation of gas in pipeline respectively, and the acquisition circuit of voltage signal current signal circuit and the test circuit of PT100 resistance is designed measuring each physical parameter.The design of software of CAT experiment system contains PLC ladder-diagram program and the monitoring platform design of century star. PLC program gather testing data of sensor from the o4AD module and 04PT module, and control the speed and the direction of stepping motor and impulse output one by one with digital. Monitoring platform has a main interface of system which can real-time simulate the working site of electronic expansion valves, control and record the opening impulse number of electronic expansion valves, and display each physical parameter of system in time. Various kinds of test auxiliary interface are designed containing of data collecting, real-time curves, historical curve, etc, which can record and analyze the test data, enhancing the function of experiment of flow testing.Studying flow characteristics is put into effect compared with simulation and experiment in this paper in order to improve match characteristic of heat load of evaporator in the inverter air conditioner refrigeration system, realize the flow distribution of refrigerants in one with two refrigerant units, improve the performance of the refrigeration system, improve energy efficiency, reduce the energy consumption, and promote the refrigeration technology nonstop development and innovation. System has simultaneously monitoring and a control functions which has profound significance for the development of refrigeration system control technology.

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