21.1 INTRODUCTION

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There are a few terms to be defined,

identification - the process of determining a state space (or other) model of a process.

parameter identification - used to estimate model parameter values.

estimatior - this tries to determine state variable values given available data.

observer - a special type of estimator that uses available input and output data to estimate a system state given unknown initial conditions. This is simalar to running a system simulation in parallel with the real system.

compensator - a feedback control system designed to drive a system to an arbitrary input.

regulator - a feedback control system designed to drive a system to a given operating point. A special case of a compensator with a zero input.