Bumpless switch between predictive functional control and a backup PI controller

Predictive controllers are used frequently with PI backup controllers. As the two algorithms (PI and predictive) are different a switch between them can cause big jumps. A bumpless switch is a very important issue. A smooth switch is desired to avoid any discontinuity in the manipulated and the controlled variables. A common strategy is to let run the backup controller in such a way that the calculated manipulated variable equals always to the manipulated variable of the active controller. This equivalence is ensured usually only in steady-state and the switch between the active and the backup controller is performed in steady-state. However operators do not wait always for steady-state. Therefore, a new algorithm was developed which allow a bumpless switch also during the transients.