In the low temperature chiller system electronic expansion application and improvement of the pneumatic valve

in the low temperature cold water machine, electronic expansion pneumatic valve in cooperation with compressor, condenser, evaporator plays a key role control system efficiency, its working state will determine actual refrigeration capacity and system control precision. But most often cold water machine is electronic expansion pneumatic valve or thermal expansion valve as a system of the throttle body, degree of superheat of compressor inlet is the main control. But due to the location in the configuration of this kind of design, it is electronic expansion pneumatic valve can not fully exert on the system accuracy control effect. In the working process of the system control can realize the optimization of cooling capacity output control system, but often in temperature close to the equipment, not fully displays the refrigerating capacity and output control system, ensure the precision of system. Although when using methods such as PID control precision is improved, but overall, the precision is still has great room to improve.
and electronic expansion the configuration and design of the pneumatic valve
in the low temperature chiller system electronic expansion pneumatic valve throttle body of general as a general compressor control degree of superheat, it usually configuration between the condenser evaporator export entrance, according to the degree of superheat of compressor inlet, adjust the opening size of real-time analysis judgment, to achieve the comparison of heat across optimization control, optimize the system cooling capacity output. But in precise control, due to the limitation of superheat, often can't play the best refrigeration output control ability, system temperature control precision is poor.
in this paper, on the basis of research on low temperature cold water machine, puts forward the electronic expansion as side vent valve, pneumatic valve connection compressor export to export condenser, and configure a thermal expansion pneumatic valve used to control independently regulate the degree of superheat, thus can realize, when temperature is close to set goals, can use the controller signal control, pneumatic valve to control the electronic expansion of opening a direct release of superheated steam compressor export, reduce the refrigeration output of system, can realize smoothly reach the set point temperature, and the precision is very high.
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electronic expansion of pneumatic valve control design electronic expansion by the pneumatic valve as a vent valve, it needs a special control strategy, need to be closed when temperature difference is bigger, the capacity to meet the system without interference, to realize the efficient work system, the temperature and set temperature deviation after reaching a certain range of the need to control the pneumatic valve has a certain opening, and with further reduce the temperature difference, the opening need to constantly change, make temperature can smooth reached set value, and there will be no overshoot or system in and out of the water temperature difference is bigger.
in this paper, using PID control strategy to control pneumatic valve opening, and in order to overcome the integral PID control overshoot phenomenon, this paper introduces the concept of fuzzy PID control, in different temperature difference rate of change of temperature difference, the controller of autonomous change PID parameters, is their control electronic system can be based on real-time state of pneumatic valve opening, the adjustment of the superheated steam input
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and experiment data analysis based on the above the system configuration and control design of the low temperature cold water machine system, as shown in figure for the low temperature cold water machine control effect, control accuracy can reach + / -. Degrees Celsius. From the practical effect is ideal to the expected effect, make the machine to further improve the control precision of low temperature cold water.