Detection and diagnosis of model-plant mismatch in MIMO systems using plant-model ratio

The performance of any model-based controller depends on the quality of the model and hence on the model-plant mismatch (MPM). Model maintenance and correction is necessary to achieve desired performance. However, a complete re-identification of the model is usually a costly exercise. Therefore, it would be highly desirable to detect the precise location of the mismatch and update only those parts. The recently introduced plant-model ratio (PAIR) was Found to be effective in detecting and diagnosing MPM from closed loop operation data, for SISO systems. The PMR facilitates a unique identification of the source of mismatch - namely gain, dynamics and delay mismatches. However, direct application of PMR to MIMIC) systems is a challenge due to the presence of interactions between the various input-output channels. In this paper, the PMR approach is extended to MIMO control systems. It is assumed that the control loop is driven through broadband excitation in the set-points. The key Step pin the proposed methodology involves decoupling interactions using partial cross spectral density. The proposed methodology is able to detect the input-output channels with significant mismatch as well as identify the source of mismatch within these channels. The efficacy of this method is demonstrated through two simulation case studies. (c) 2016, IFAC (International Federation of Automatic. Control) Hosting, by Elsevier Ltd. All rights reserved.