A nonlinear optimal control approach for the pulping process of paper mills

The mechanical pulping process is non-linear and multivariable. To solve the related control problem, the dynamic model of the pulping process undergoes first approximate linearization around a temporary operating point which is updated at each iteration of the control algorithm. The linearization process relies on first-order Taylor series expansion and on the computation of the Jacobian matrices of the state-space model of the pulping process. For the approximately linearized description of the pulping process, a stabilizing H-infinity feedback controller is designed. To compute the controller's feedback gains, an algebraic Riccati equation is solved at each time-step of the control method. The stability properties of the control scheme are proven through Lyapunov analysis.