Feedback control systems are categorized in various ways based on their design, analysis, and signal types.

Linear feedback systems are theoretical models that simplify analysis and design. These systems operate under the principle that their output is directly proportional to their input within certain ranges. For instance, an amplifier in a control system behaves linearly as long as the input signal remains within a specific range. However, most physical systems exhibit inherent nonlinearity due to factors such as component saturation or friction. Nonlinearities can be intentionally incorporated to enhance performance; a notable example is the on-off controller in missile systems, which leverages nonlinearity to achieve rapid response times and improved control precision.

Time-invariant systems maintain constant parameters over time, ensuring consistent performance. An example is a motor control system where the winding resistance remains unchanged during operation. In contrast, time-varying systems have parameters that change over time, adapting to different operating conditions. A guided-missile control system exemplifies this, as the missile's mass decreases due to fuel consumption during flight, necessitating continuous adjustment of control parameters.

Continuous-data feedback control systems use signals that are functions of continuous time. These systems can be further divided into DC and AC control systems. DC control systems utilize unmodulated signals, while AC control systems employ modulated signals to reduce the effects of noise and disturbances. Discrete-data control systems, on the other hand, use signals in the form of pulse trains or digital codes. These systems are particularly advantageous in noisy environments, as digital signals are less susceptible to interference.

Each classification of feedback control systems offers distinct advantages and is suited to specific applications. Understanding these categories helps engineers design and implement effective control strategies, ensuring optimal performance and reliability across various technological domains.