Actuator saturation occurs when an actuator reaches a limit of its capabilities. These limits typically appear in the form of position or rate-of-change bounds. When actuator saturation occurs, the system's response to increasing controller gains becomes nonlinear and might be unacceptable.

A block diagram of a plant and controller is a graphical means to represent the structure of a controller design and its interaction with the plant. Each block represents a system component. Solid lines with arrows indicate the flow of signals between the components. In block diagrams of SISO systems, a solid line represents a single scalar signal. In MIMO systems, a line can represent multiple signals. Circles represent summing junctions, which combine their inputs by addition or subtraction depending on the + or - signs displayed next to each input.

Bode diagrams display the magnitude and phase of the open-loop frequency response of the combined plant and controller. The horizontal axis of both diagrams is frequency, displayed on a logarithmic scale. The magnitude diagram is displayed in units of decibels, and the phase diagram is in units of degrees. Together, the Bode diagrams represent the steady-state amplitude and phase of an output sine wave relative to an input sine wave at each frequency shown on the horizontal axes of the diagrams.

A continuous-time system has outputs with values defined at all points in time. Real-world plants are usually best represented as continuous-time systems. In other words, such systems...