Design Of Automatic Control System For Enthalpy Difference Laboratory

The enthalpy difference laboratory is a laboratory to test the performance of air conditioning by simulating the working conditions of external environment manually.In our country,the accuracy and stability of enthalpy difference laboratory measurement variables are very high,which also puts forward higher requirements for the realization of enthalpy difference laboratory automatic control system.According to the requirements of GB/T 17758-2010 and GB/T 25128-2010: When the air conditioner carries out refrigeration and heating experiments,the maximum change range of dry bulb temperature is ±1.0?,the maximum change range of wet bulb temperature is ±0.5?.The enthalpy difference laboratory control has the characteristics of non-linearity,large coupling and large lag.It is difficult for conventional control algorithm to get good control effect.In this paper,fuzzy PID control and dynamic matrix control are adopted respectively for the temperature and air volume of enthalpy difference laboratory.The main research works of this paper are as follows:(1)The working principle and system structure of enthalpy difference laboratory are analyzed.According to the characteristics of the laboratory's relatively scattered and independent measurement points,the system architecture of the control system is designed by adopting the idea of distributed control system.Determine the various layers of the system,determine the signal and control point requirements of the instrument,and count the number of I/O points in the system.Determine the model and configuration of the PLC and module according to the principle of 20% margin.The system circuit diagram is drawn to complete the basic automation of enthalpy difference laboratory.(2)Through the analysis of the air measuring box and the field collected data,the existence of ripple in the data curve proves that there is disturbance in the field,which affects the detection of the unit under test.The inertia model of the system is established by using the field data,and the fitting curve error is compared.The second-order inertia model is chosen.According to the DMC control theory,a predictive controller based on the process model of air volume control in the air volume measuring box is designed.According to the continuous off-line simulation,the parameters are determined,and compared with the traditional PID control,the steady-state error of the system is significantly reduced,which shows that the control effect of predictive control is higher than that of traditional PID control.(3)According to the characteristics of enthalpy difference laboratory and the field situation,the temperature of laboratory is controlled by using fuzzy PID control algorithm.Using MATLAB to simulate,the steady-state performance and anti-interference of fuzzy PID control are better than traditional PID control,which verifies the feasibility of applying fuzzy PID control to temperature control.(4)Using Kingview and VB to develop the upper computer software of the system.Firstly,the OPC Server of Kingview is configured,and the OPC client based on VB is developed to realize data interaction between different platforms.The design of the host computer interface uses Kingview to form a good human-computer interaction interface.In addition,by running the software and observing the system operation status,the field operation effect diagram is obtained,which verifies the validity of the control software and meets the actual engineering needs.