Hybrid system modeling and model predictive control of a hot strip mill tension/looper system

This paper proposes a new looper control design method of a hot strip mill, where the strip tension and looper trajectories between the non-contact mode and the contact mode are simultaneously optimized. First, based on the model linearized around some equilibrium point in each mode, a discrete-time piecewise affine model, which is one of standard hybrid system models, is derived to describe the discontinuous dynamics of this system. Next, a model predictive control method for this model is proposed. The proposed method provides an exact solution to this control problem. However, it will not be easy to calculate an exact solution on-line via the usual personal computers. So an approximate solution method is also presented, where a solution can be obtained on line. Furthermore, the proposed method can be used to generate a feedforward control input, where optimality of trajectories between the non-contact mode and the contact mode is considered. This will be practically useful because it is executed via off line computation. Finally, numerical simulations show the effectiveness of the proposed method compared with the constant-torque based control.