Antenna Position System and Robustness Analysis: A review

The performance of PID controllers is critically dependent on proper tuning, and while various classical techniques such as Ziegler–Nichols and Cohen–Coon result in acceptable performance during nominal conditions, they can produce inconsistent performance when subjected to any type of disturbance (e.g. environmental, noise, parameter variations, etc.) of the system or existences of uncertainty in their model. Also, traditional stability analysis tools (e.g., root locus and Bode plots) analyze the gain and phase of the controller independently, thus do not capture the simultaneous uncertainties associated with both control gain and phase. Most optimization-based tuning approaches primarily emphasize transient performance while failing to provide a comprehensive robustness assessment of the controlled system. The current literature is significantly lacking in terms of the comparative assessment of the various tuning methodologies for PID controllers based on purely time domain metrics, without any attempt at systematically evaluating the ability of the controller's tuning to withstand simultaneous variations in both gain and phase. Therefore, an overall unifying framework must be developed to provide both an assessment of the robustness of a given tuning methodology as well as comparing different tuning methodologies.