11. APPLICATION OF DUAL CONTROLLERS TO THE SPEED CONTROL OF A THYRISTOR-DRIVEN DC-MOTOR

Abstract

Control engineers are often faced with the problem of insufficient control performance, such as large overshoots in the transient stages during the practical application of many digital adaptive controllers in real-time operation (Åström and Wittenmark, 1989; Filatov et al., 1994; Filatov et al., 1995; Filatov and Unbehauen, 1995a; Wittenmark, 1995). Large overshoots and oscillations of the system state can result in untimely wear and tear of the equipment. Moreover this leads to a general lack of acceptance of adaptive control. These shortcomings of adaptive control arise especially in cases of significant uncertainty of the plant parameters. These imperfections of adaptive controllers result from using the CE assumption, where the uncertainties of the estimated values are not taken into account and the parameter estimates are used as if they were the real values of the unknown parameters (Åström and Wittenmark, 1989). In dual controllers, however, the uncertainties of the estimates are taken into account, and the control system tries to track cautiously the reference signal and, at the same time, improves the estimation of the process parameters by optimal persistent excitation.