Study On Sliding Mode Variable Structure Level Control System For Alumina Casting And Rolling Mill

The high speed aluminum sheet casting and rolling mill (HSASCRM) is the fourth generation, which can produce sheet with better structure, mechanics character and can improve the surface quality than normal coil sheet. So the R&D of HSASCRM, as well as casting and rolling crafts, was chosen to be the project of KTRDP in the 9th five-year plan by NDPC. During the process of high speed aluminum sheet casting and rolling, the sheet surface quality is chiefly determined by the control precision of the pre-tank liquid level and automation degree of the whole product line. So the level control system contributes much to the stability and quality of casting and rolling productIn present dissertation, the character of pre-tank level control system, such as strictly requirement for precision, great inertia and variable external disturbance which is hard to modeling, was analyzed. And PID control system was designed and implemented on the base of the control object modeling, which was considered to work well in most cases, after debugging, testing and running in the field, except some key drawbacks including weak robustness and lack of solution for the coagulation on the valve.So the sliding mode variable structure controller was discussed, which has strong robustness against the disturbance, and the chattering phenomenon inherited from VSC was taken advantage to regular valve vibration for the purpose of avoiding coagulation on it, while precision of level control can be almost unaffected. But for the reason of control limitation, especially the acceleration insufficiency, the continuous time quasi-sliding mode VSC for one class of controllable system, as the substitution of ideal sliding mode control system, which was impossible to implemented, was researched, including the three essentials, reaching condition in particular, and the chattering ex-pression was given. Furthermore, the effect to quasi-sliding mode motion and chatter-ing expression by extent disturbance was also analyzed. The theoretical reasoning and simulation results show that continuous time VSC system can be more robust than PID system, and chattering control an be partially decoupled with system dynamics.The discrete time VSC and chattering control was also be discussed. There are two implementations for discrete reaching law, both has obvious strongpoint and limi-tations. So the two was synthesized. Simulation results showed that the discrete VSC is easier to be implemented by computer control system, and go further in decoupling between chattering control and system dynamics, while the robustness is not so good as continuous time VSC.