Digital Control Systems Design, Identification and Implementation电力—4 Design of Digital Controllers in the Presence of Random Disturbances.pdfVIP

4 Design of Digital Controllers in the Presence of Random Disturbances A large number of systems are subject to disturbances of a random nature. In the first p art of this chapter models suitable for the representation of these stochastic disturbances (the ARMAX models) will be presented and their properties analyzed . Three design methods will be presented: 1. minimum variance tracking and regulation (which minimizes the mean-square difference between the reference and the controlled variable) ; 2. the appr oximation of the minimum variance tracking and regulation by means of the pole placement (f or the case of systems with unstable zeros); 3. generalized minimum variance tracking and regulation. 4.1 Models for Random Disturbances 4.1.1 Description of the Disturbances First consider the basic deterministic disturbances, namely the Dirac pulse, the step and the ramp, represented in Figure 4. 1. Dirac step ramp pulse Figure 4.1. Main deterministic disturbances 169 170 Digital Control Systems 1 1 2 s s Disturbance Disturbance model model Figure 4.2. Deterministic disturbance models Note that the step and the ramp may be described as resulting from the passing of the Dirac pulse through a filter, as indicated in Figure 4.2. The corresponding filters are known as “disturbance models”. Any deterministic disturbance may be obtained by passing a Dirac pulse through a “disturbance model” (filter) having an app