PLC变频器在制冷机组节能改造中的应用研究

发布时间：2018-04-22 00:37

本文选题：制冷机组 + 变频调速　；参考：《大连理工大学》2014年硕士论文

【摘要】：制冷机组是制冷系统的心脏,降低制冷机组能耗,提高制冷机组的自动化控制水平是制冷行业产品技术发展的方向和主题。目前,变频调速技术、计算机控制技术、电力电子技术等相关自动化技术在制冷行业中得到了大力的推广与应用,使得制冷系统在如下两个方面的到了质的飞跃： (1)提高制冷系统的能效水平,按照受控环境的温度波动情况制冷量可以按需供给,实现节能降耗。 (2)提高制冷系统的智能控制水平,使制冷系统逐步向计算机化,数字化以及可视化方向发展。本文将变频调速技术引入到制冷机组中,运用变频调速技术调节制冷系统的制冷量,满足精确的温度控制要求,提高制冷系统的能效水平。同时运用PLC工业控制器对制冷系统进行整体的控制与监控。本文通过对制冷机组控制现状的分析,指出制冷机组实现变频运转和自动控制的必要性。通过制冷理论、借助压焓图对制冷系统的各个部分的运转参数进行分析,得出制冷机组实现节能运行必须对制冷剂流量进行控制的结论。在机组控制方面,根据制冷剂的热力学性质特性,确定压缩机吸气压力为制冷机组的控制对象,通过压力传感器将吸气压力信号传递给PLC工业控制器,由PLC控制器进行模数转换、控制参数的比较之后输出4-20mA信号给变频器,由变频器来控制压缩机的转速以达到控制制冷剂流量的目的。通过T形图编程,PLC控制器不仅采集吸气压力信号,同时可以采集排气压力、吸气温度以及排气温度信号,同时通过对其他机组的保护信号的采集,可以对机组的运行状况进行实时监控,并在机组异常状况下发出警报信号同时记录机组的运行状况。为使制冷机组有更好的操控性,采取了触摸屏作为上位机,可以通过触摸屏设置机组运行参数,显示报警画面,记录机组运行曲线。完成了半封闭压缩机组控制系统的设计、安装、运转试验,结果表明变频调速技术能够通过调节压缩机的转速,在不同运转负荷情况下为制冷系统提供所需要的制冷量,使制冷机组在部分负荷下的能效比得到质的提高。整个控制系统的设计提高了制冷系统的控制水平,优化了系统的控制方法,提高了系统的控制精度,扩大了制冷机组在各个领域的应用范围,满足了日益多样的工艺要求。
[Abstract]:Refrigeration unit is the heart of refrigeration system. Reducing energy consumption of refrigeration unit and improving automation control level of refrigeration unit are the development direction and theme of refrigeration industry. At present, frequency conversion technology, computer control technology, power electronics technology and other related automation technology in the refrigeration industry has been vigorously promoted and applied, making the refrigeration system in the following two aspects of the qualitative leap: 1) improving the energy efficiency level of the refrigeration system, according to the temperature fluctuation of the controlled environment, the refrigerating capacity can be supplied according to the demand, and the energy saving and consumption reduction can be realized. 2) improving the level of intelligent control of refrigeration system, making the refrigeration system develop towards computerization, digitization and visualization. In this paper, the variable frequency speed regulation technology is introduced into the refrigeration unit, and the refrigeration capacity of the refrigeration system is adjusted by the frequency conversion speed regulation technology, which meets the precise temperature control requirements and improves the energy efficiency level of the refrigeration system. At the same time, the PLC industrial controller is used to control and monitor the refrigeration system as a whole. In this paper, the necessity of frequency conversion and automatic control of refrigeration unit is pointed out by analyzing the control status of refrigeration unit. Based on the refrigeration theory and the analysis of the operating parameters of each part of the refrigeration system with the help of the enthalpy diagram, it is concluded that the refrigerant flow must be controlled to realize the energy-saving operation of the refrigeration unit. In the aspect of unit control, according to the thermodynamic properties of refrigerant, the suction pressure of compressor is determined as the control object of refrigeration unit, and the suction pressure signal is transmitted to PLC industrial controller through pressure sensor. After the comparison of the control parameters, the PLC controller outputs the 4-20mA signal to the converter, and the frequency converter controls the speed of the compressor to achieve the purpose of controlling the refrigerant flow. The PLC controller can not only collect the inspiratory pressure signal, but also collect the exhaust pressure, suction temperature and exhaust temperature signal, at the same time, it can collect the protection signal of other units. The operation condition of the unit can be monitored in real time, and the alarm signal can be sent out under the abnormal condition of the unit to record the operation condition of the unit at the same time. In order to make the refrigeration unit have better control, the touch screen is adopted as the upper computer. The operating parameters of the unit can be set up by the touch screen, the alarm screen can be displayed and the running curve of the unit can be recorded. The design, installation and operation test of the semi-closed compressor unit control system have been completed. The results show that the frequency conversion speed regulation technology can provide the required refrigerating capacity for the refrigeration system under different operating loads by regulating the speed of the compressor. The energy efficiency ratio of refrigeration unit under partial load can be improved qualitatively. The design of the whole control system improves the control level of the refrigeration system, optimizes the control method of the system, improves the control precision of the system, expands the range of application of the refrigeration unit in various fields, and meets the increasingly diverse technological requirements.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657

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