State feedback using state estimates

Modern optimal control laws, whether state feedback or open-loop feedback in nature, almost invariably have the control commands based ultimately upon the state variables. In addition, state-space design methods such as pole placement are most easily done using full state feedback. The full state is rarely measured, however, so it is necessary for the engineer to modify the design. A very useful approach to doing this modification is to use state estimates in place of the state variables, with the estimates coming from an observer or Kalman filter. In this chapter we consider some implications of this approach.