Research On Multi-Model Switching Control For Hydraulic Servo Position System Of Rolling Mill

Hydraulic servo system has been widely used in the domain of industry, national defense, spaceflight and so on due to its advantages of fast response speed and strong bearing ability. However, it should be noted that the hydraulic servo system has the inherent characteristic of time-variant parameters, uncertainty and nonlinearity, especially the parameter jumping under different working conditions, for example, jumping of elastic load force, elastic stiffness coefficient and the external load force of the hydraulic servo system from zero to a great value when the cylinder piston touches the rigid load which causes the change of system structure and affects the system performance. At the same time, control input saturation exists in the hydraulic-servo rolling mill system. So the multi-model switching control for hydraulic-servo mill rolling system is carried out to effectively solve the structure and parameter jump and control input saturation problem above-mentioned, which ensure the stability and dynamic static performance in various working conditions. So it is significantly meaningful to put the theory into practice and enrich the adaptive control theory by further study.Firstly, a mathematical model for rolling mill hydraulic servo system under different working conditions is established and model parameters are calculated and analyzed. In addition, a multi-model set is build up to deal with the structure and parameters jump problem of hydraulic-servo control system.Second, sliding mode variable structure control of multi-mode switching is proposed to handle the system structure and parameters jump. A switching control scheme is proposed for the whole system base on model optimal performance index, and the stability is analyzed for the switched system. Afterward, a simulation comparison with the conventional adaptive sliding mode control is given for verification. Third, a anti-saturation control strategy of multi-model switching with L₂ Gain is designed using (CLF) Common Lyapunov Function method to deal with the control input saturation, a local controller is designed using LMI to gain the global controller set. The changing of hydraulic cylinder pressure is considered as the switching rule which decides the switching among sub-model controllers. Simulation results demonstrate the effectiveness of the proposed method.Finally, the average dwell time method of anti-saturation multi-model switching control strategy is proposed for the mill hydraulic servo system to further reduce the conservativeness of the designed controllers. Simulation is given to demonstrate the effectiveness of the proposed method.