Research And Simulation On Effect Of Czochralski Crystal Based On The Model Predictive Control

Czochralski is widely used in industrial production field, which is one of the method to grow out of uniform sharp and internal quality meeting the requirements of the single crystal. In the traditional production process, the one method is regulating the furnace temperature and the other method is regulating the pulling speed and heater temperature to track the target curves, in order to achieve the diameter growth of crystal. By simulating with traditional PID control and cascade PID control, we find that the control system show low control accuracy weak anti-interference capability, long settling time, poor robustness. Result that single crystal has defects, poor optical uniformity and failing in achieving the diameter growth of crystal.Consider that that traditional PID cannot effectively solve the control problem. In this paper, we do some research and simulation on effect of Czochralski crystal based on the model predictive control.(1) Firstly, pulling speed to equal diameter control unit is the main loop and temperature to equal diameter control unit is the secondary loop. Pulling speed-temperature PID cascade control with Smith Predictor control system improve the control quality, short settling time, good robustness and quiet anti-interference capability.(2) Secondly, An improved model predictive controller is proposed, which based on the expected response previously setting and implement reference trajectory move forward the respected trajectory step by step. Simulation results show that the improved DMC with PID control has better dynamic and tracking performance than the traditional predictive control and solve the conflicts between robustness and quick response.(3) Finally, consider that the control system with uncertain time-delay system, the control input bound and external disturbance, we combining model predictive control with robust control method. Robust model predictive control base on output feedback with PID control is presented which can not only guarantee the feasibility of control algorithm and the stability of closed-loop system, but also guarantee the impact of an uncertain external disturbance resulted in closed-loop system is restrained at a certain level of inhibition. Through simulation analysis, improved model predictive control and robust predictive control has a good effect, which improved stable and dynamic characteristics of the single crystal pulling system.