CAD.Reference:4.5.1 - Keep a qualified loop and govern its commands

When an existing loop already tracks and rejects disturbances adequately, but abrupt or excessive commands violate constraints, command admission can be the remaining problem. Garone, Di Cairano and Kolmanovsky’s survey, §2.1 and §6.1 develops reference and command governors as additions before a stabilized loop. They modify commands using the current closed-loop state and predicted constraint admissibility, rather than merely applying a fixed low-pass filter.

For the basic held-command construction, use a model whose state includes the plant and controller. Obtain a set of state-command pairs from which holding the selected command satisfies the constraints at all claimed future instants. A scalar reference governor selects the largest admitted step along the line from the previous command toward the desired one; a command governor can optimize the command vector. The previous command supplies continuation only under the construction’s admissibility and initialization conditions. Scalar search is smaller, while the restricted search direction can sacrifice response.

This is a candidate within the control architecture question, not an opposing field. It can preserve a qualified lower controller and avoid introducing a reduced planning model. Compare its reference distortion, progress and computation with the required task. If filtering makes the requested arrival time unattainable, constraint satisfaction alone has not solved that task. If the lower controller, sensor or timing changes, its governor model and admissible sets must change with it.

Later constructions change different premises: observer-dependent domains in CAD.2–CAD.3, online cost adaptation in CAD.1, and inexact computation or controller switching in CAD.4. Use those developments only with their corresponding models and conditions.