Research On Temperature Control System For Large-scale Hydraulic Source

In this paper, Temperature control system is designed for hydraulic source in large hydraulic testing bench. The accuracy of temperature control can reach the grade B (±2℃) of the national standard (GB/T 7935-2005). The design of temperature control system for hydraulic source include three parts: the design of temperature control device, the design of temperature control algorithm and the design of PLC control system.Cooling components selection and design of the cooling line are two parts in the design of Temperature control device. Plate heat exchanger is selected for cooling components. The type and number of plate for heat exchanger are determined by calculating the maximum heating power of hydraulic system in the different conditions,thus the ability of the cooling system is ensured; The flow ratio of Cooling water is adjusted by three-way valve continuously. By adjusting the three-way valve spool position, temperature control system can regulate the flow of water through the heat exchanger, which will change the heat transfer capability of heat exchanger. Thus the purpose of temperature control is achieved.On temperature control algorithm design, the temperature control system of hydraulic source is a nonlinear, time-varying and Large-lag system. PID control algorithm is sensitive to time-varying parameters of the system, it depends on sysytem model. The steady-state accuracy of fuzzy control is not ideal. In order to avoid the shortcomings of them, self-tuning parameters fuzzy PID control algorithm is uesd. By online Fuzzy Reasoning, three PID parameters are adjusted. This will ensure the system to have more excelent performence in responsiveness, stability and accuracy. System with PID algorithm and parameters self-tuning is disigned and analyzed with computer aided.In terms of PLC control system design, S7-SCL language is used for writing temperature programs. Moreover, a GUI is designed by configuration software to implement system debugging. Ultimately realizing the temperature control program based on PID algorithm and parameters self-tuning on PLC platform.In the certainty experiment of this hydraulic source temperature control system with all kinds of power and flow, some results are found as followings:1. It's very important to choose the proper initial parameters in PID control method, including K_P0, K_I0 and K_D0. Neither choosing the parameter that will make system oscillated and divergent. Meanwhile it's proper to imprehensively consider the selecting of scaling factor. As to their application in actual system, these parameters are repeatedly adjusted in field test to ensure the most proper values for the best system performance. 2. The dimension of fuzzy logical rules is better to be appropriate while realizing program algorithm with PLC controller or the operating will be slowed down and the real-time performance badly affected.3. Fuzzy control is greatly dependent on human experience. The development of tuning rules is established on repeatedly test of system performance and these parameters, especially the scaling factor, should be optimized in this progress.4. It's a key question to improve the system anti-interference ability during the process of PLC-controlled system design, which will affect temperature controlled performance greatly. Moreover, the differential link is especially sensitive to the interference. So some measures should be taken to reduce the interference for the purpose of avoiding system oscillating.