Research Of Intelligent PID Control Algorithm For Temperature Control System

The electric heater is a kind of heating facilities, which is widely used in the industrial processes and the labs. And the temperature control of it is a typical process control. However, electric heater is an object featuring in non-linearity, time variability, large time lag and asymmetry, regular PID controller can not obtain high control precision only if the control parameters are tuned accurately as well as system not to change sharply. But the two points can not be satisfied in a electric heater temperature control system, so an intelligent PID control algorithm based on synthesized strategy is brought forward to realize precise temperature control of electric heater.The first thing to do is to adopt recurrence least squares method based on open-loop control or estimated method based on performance indexes of close-loop response to compute the parameters of the first order plus time delay model of the system. Then, use PID parameter tuning rules of time domain to calculate the initial values of the control parameters according to the rough model. After that, in order to suit the process requirements, to overcome the influence of time variability of the system, and to guarantee the same control effects in the different temperature ranges, apply human-simulated intelligent PID control and single neuron PID control to change the control strategies on-line. The former one imitates human's experiences and adjusts the PID parameters according to the output mode, and the latter one changes the connection weights to modify the PID parameters through on-line study. In addition, the prediction PID control, overcomes the disadvantage that normal PID control computes only based on current error, it appends a prediction term to the controller so as to eliminate the bad influence of time delay.The above-mentioned method of electric heater temperature control based on synthesized strategy exerts the advantages of good robustness, high response speed and low overshoot of intelligent control, possesses dynamic tracing quality and stable status precision of PID controller, and realizes the self-tuning function of PID parameters. The algorithm is applied in the PLC temperature control instrument after being simplified and optimized, and the real-time test results have shown its good effect of temperature controlling, which get an overshoot less than 3% of the set value and a stable error in the range of±2℃. If the algorithm is optimized further, its applicability will be stronger and the temperature control instrument with it will be more efficient.