ABSTRACT
The models that are used in control systems design can be both continuous time and discrete-time and are nonlinear in their most general form. For com putational reasons these are typically linearized around their trajectory. The resulting linear time-varying systems can then subsequently be approximated by a time invariant one over a period of time where the model does not change too much. So we differentiate between six types of models that are used in this area. Notice that a discrete-time model will, e.g., result from using an ODE solver for the simulation of a corresponding continuous-time model. Moreover, we simplified the models by choosing explicit state equations, although the ideas presented in later sections generalize to a large extent to implicit state equations.
