Research Of Mould Level Control System

Mould level control is an important link in continuous casting process control, the stability and precision of mould level control is an essential part of production security and ensures the quality of casting billet. This thesis proposes an improvement on PID control scheme by brining fuzzy-predictive-PID compound control scheme, aiming at the poor anti-interference capability of traditional PID control scheme used in mould level control, and provides an in-depth analysis and research on the design of mould level controller. The main achievements are obtained as follows:(1) The model for the mould level control system is presented. Dynamic and static characteristic of each link of mould level control system has been analyzed and modeled by structural decomposition of mould level control system. These models have been simplified to highlight the essential features and to obtain the mathematical models of controlled device.(2) Design of mould level controller. A mould level cascade control system is designed, with slide gate nozzle displacement control circuit as inner loop and mould level control circuits as outside loop. Influence of nonlinear characteristics of slide gate nozzle and liquid steel’s level in tundish have been removed by a control scheme combined nonlinear compensation link, feedforward control strategy, self-tuning PID controller, fuzzy control strategy and predictive control strategy. Disturbance brought by the change of casting speed, unmodeled dynamics and sensor noise has been removed too.(3) The simulation and analysis of the results of mould level control system. The simulation results show that the two-loop PID achieves high steady state performance without disturbance, but shows obvious concussion after disturbance was applied. Fuzzy-PID compound controller has a fast response and a small steady-state error and an inevitable steady-state error, when casting speed disturbance was brought, there is a certain degree of volatility. Predictive-PID compound controller has a high anti-interference capability, but has a low respond speed. At preliminary stage, the liquid level fluctuates markedly because of the changes of initial model and parameter. Fuzzy-predictive-PID compound controller which combines these three controllers together, shows high steady state performance and dynamic performance without disturbance, and has a relatively good anti-interference capability. With analysis of said four control strategy, it’s revealed that mould level control based on fuzzy-predictive-PID compound control is a control method with high performance.