Predictive control

Abstract

Constrained Predictive Control is radically different from other control approaches which are conventionally used, or might be used, for flight control. Not only is the design method rather different, but the implemented algorithm is quite different, because it works by repeatedly solving an optimisation problem on-line. As a straight replacement for those approaches, it is not currently competitive, primarily because of the computational load. Even when further advances in computing hardware bring the solution time down to acceptable levels, which they will surely do, the predictive control approach will give greater problems of certification than conventional controllers, because of the difficulty of analysing the controller behaviour.

On the other hand, predictive control offers some unique benefits: its very nonlinear behaviour when constraints are approached, and its ability to anticipate pilot commands, instead of merely reacting to errors propagating round the feedback loop.

We believe that predictive control is worth investigating further for use in flight control, if its unique benefits are exploited to obtain higher-level functionality, in addition to routine stability augmentation. This is discussed further in Chapter 25.