The synthesis of regulator logic using state-variable concepts

This is a tutorial paper. It was written for technically knowledgeable people who are not specialists in automatic control. It might also be of some use in university courses in automatic control. Linear feedback of the state variables for stationary linear plants permits choice of the gains to place poles (eigenvalues) of the controlled system in desired locations. Continuous estimates of the state variables can often be made from one or more measurements of the output using a filter of the same (or lower) order as the plant called "an observer": the poles of the observer can be placed arbitrarily through choice of the observer gains. Combining an observer with state-variable feedback yields a "compensator" design; the poles of the controlled system are the poles of the observer plus the poles of plant with state-variable feedback, which greatly simplifies the design problem.