ON-LINE PERFORMANCE MONITORING PROCEDURE FOR INTELLIGENT CONTROL

Abstract

In this study, several performance monitoring procedures using different techniques are presented to identify the maximum closed-loop log modulus, Lc,max. Lc,max is considered because it measures the robustness of control system and thereby can indicate the appropriateness of controller design with respect to the current process condition. In one approach, the monitoring procedures via several relay feedback experiments for on-line identification of Lc,max are derived. These methods require no a priori information of process conditions and can apply to multiloop control systems as well as full multivariable control systems. Furthermore, the accuracy of the identification method can be improved by inserting a fictitious transportation lag. The procedure is also tested against systems with noise and without noise. Simulation results show that the proposed method can be used in the identification of Lc,max with reasonable accuracy. In the other approach, FFT-based monitoring procedures for on-line identification of Lc,max are proposed. Two techniques are explored: one is decay exponential method and the other is decomposition method. Compared with the previous monitoring methods, both FFT-based methods have several advantages. First, the testing time is saved greatly since only one ideal relay experiment is involved. In addition, the frequency search range for identification of Lc,max is extended, whereas previous results are restricted to the third quadrant. All these features will make this FFT-based monitoring method very attractive in the intelligent control area.