Enhanced predictive ratio control of interacting systems

Ratio control for two interacting processes is proposed with a PID feedforward design based on model predictive control (MPC) scheme. At each sampling instant, the MPC control action minimizes a state-dependent performance index associated with a PID-type state vector, thus yielding a PID-type control structure. Compared to the standard MPC formulations with separated single-variable control, such a control action allows one to take into account the non-uniformity of the two process outputs. After reformulating the MPC control law as a PID control law, we provide conditions for prediction horizon and weighting matrices so that the closed-loop control is asymptotically stable, and show the effectiveness of the approach with simulation and experiment results.

► Output ratio control of a TITO interacting system with different input delays.
► MPC is transformed into a feed-forward PID controller.
► The controller has variable gains initially, but fixed gains at steady stage.
► Stability condition is given.
► Practical tuning of weighting factors for ratio control purpose.