Frequency weighted closed-loop order reduction in the control design configuration

This paper focuses on order reduction within a general control design configuration. The plant dynamics and the controller dynamics are written as a feedback loop in a frequency weighted interconnection. A straightforward extension of frequency weighted balanced reduction is explained that can be applied to the plant model and/or controller model in the control design configuration. A software tool is developed that helps the control engineer to find an acceptable trade-off between closed-loop performance and controller order, even for an extremely high-order plant. The user-interface of the tool supports the central engineer in evaluating the performance in the frequency domain, and provides additional frequency weights to be constructed `on screen´ in the form of piecewise quadratic functions. These functions define power spectra of the exogeneous signals of the control design configuration and are incorporated in the closed-loop balanced reduction algorithm in a very direct way. The ease of entering and adjusting frequency weighting functions facilitates the search for low-order controllers with minimal performance degradation