Temperature Control Algorithm For Distributed Hysteresis Circulating Cooling Water System

In the field of ultra precision machning and measurement,strict requirements have been put forward to the working environment.The thermal pollution has become one of the key factors that restrict the improvement of manufacture and measurement accuracy.In these equipment,the circulating cooling water is used as the key heating element for heat exchange.Therefore,the temperature control accuracy of the circulating cooling water will directly affect the accuracy index of the instrument and equipment.The temperature control accuracy of the circulating cooling water largely depends on the index of the temperature control algorithm.But the circulating cooling water system has the characteristics of distribution and large time-delay,which makes the control performance of the system get worse.According to the characteristics of the above application requirements and the controlled object.The purpose of this thesis is to study the high-precision temperature control algorithm to solve the requirments of high precision,fast response,small overshoot and high stability for the circulating cooling water system in the field of ultra precision machning and measurement.The main contents of this paper are as follows:First,aiming at the problems of big distributed hysteresis in the circulating cooling water system,based on analysis of the principle and simulation of several advanced control algorithms for the large time-delay system proposed,complete the overall design of the circulating cooling water temperature control algorithm.The Smith predictive control algorithm and fuzzy PID algorithm are selected as temperature control aigorithms in the thesis.The program design of the algorithm is completed.Besides,the moving average filter subroutine is designed to solve the problem of the peak disturbance in the sampling process of the temperature sensor.Secondly,in order to solve the problem that Smith predictive control algorithm needs accurate system model,the model identification of the circulating cooling water system is carried out by combing theoretical analysis and experimental methods.The model of heating unit is obtained by mechanism modeling.The model of cooling unit is obtained by mechanism and least square identification.The model of the whole system is obtained by the bias based relay identification method.The parameter mismatch of the Smith predictor is analyzed and the parameters compensated.The accuracy and the compensation perfoamance of the predictor are improved.Thirdly,the design of the hardware circuit of the temperature controller is completed.The Smith predictive control algorithm and fuzzy PID control algorithm are embedded into the thermostat.Finally,the experimental platform of high precision circulating cooling water system is set up.The control index of Smith predictive algorithm and Fuzzy PID algorithm are tested.The results show that when the water flow rate is 16L/min and the experimental environmental temperatire is 25 ?,the Smith predictive control algorithm can achieve the regulation time of 73.2s and the temperature stability of ±0.017? with the control resolution of 0.015?.The Fuzzy PID algorithm can achieve the regulation time of 53.5s and the temperature stability of ±0.019? with the control resolution of 0.01?.The stability index is the same as that of the top industrial temperature controller SR23(± 0.015 ?)made in Japan under the same working condition,while the response speed index is obviously improved(SR23's adjustment time is 171s).