Controller configurations are crucial in a car's cruise control system because they manage speed over time to maintain a consistent pace regardless of road conditions, thereby meeting design goals. In traditional control systems, fixed-configuration design involves predetermined controller placement. System performance modifications are known as compensation.

Control-system compensation involves various configurations, most commonly series or cascade compensation, in which the controller aligns with the process. In series compensation, the controller is placed in series with the plant, modifying the system's dynamics to meet specific performance criteria. Feedback compensation, on the other hand, places the controller in the minor feedback path. This method allows fine-tuning of system behavior without directly affecting the primary feedback loop.

State-feedback control involves feeding back the state variables through constant real gains to generate the control signal. This method is effective for designing control systems with specific performance requirements. However, it can be costly or impractical for high-order systems due to the need for state variable measurements or estimations. The state-feedback control aims to place the closed-loop poles in desired locations, achieving improved transient and steady-state performance.

Other configurations include series-feedback compensation, which combines a series and feedback controller to leverage the benefits of both. Feedforward compensation places the feedforward controller in series with the closed-loop system, directly addressing the reference input to enhance performance.

In addition to the aforementioned configurations, the degrees of freedom in controller configurations significantly impact system performance. Series, feedback, and state feedback are one-degree-of-freedom (1DOF) controller configurations that face limitations in meeting specific performance criteria. These configurations can exhibit poor sensitivity to parameter variations or excessive overshoot in the step response. In contrast, two-degree-of-freedom (2DOF) configurations offer enhanced flexibility in achieving desired performance criteria. A 2DOF system allows independent tuning of the feedback and reference tracking paths, providing better control over system dynamics and robustness to parameter variations.

In summary, while 1DOF configurations are simpler and easier to implement, they may not always meet the stringent performance requirements of modern control systems. The flexibility of 2DOF configurations makes them a valuable tool in advanced control system design, particularly in applications like automotive cruise control, where precise performance and robustness are critical.