Control of Nonlinear Nonminimum-Phase Processes

In this paper we show that a class of open-loop stable second order nonlinear processes with input multiplicity will always exhibit inverse response in a certain operating region. In contrast to linear predictive control, the minimum prediction horizon for stable control using nonlinear predictive control is dependent on the direction of setpoint change in the presence of inverse response and input multiplicity characteristics. Perfect control of nonlinear nonminimum-phase systems can be achieved under certain conditions. We show that the characteristics of the optimization problem solved in nonlinear predictive control depends on the prediction horizon. Using a longer prediction horizon results in a non-convex objective function.