Adaptive Fuzzy Control of Nonlinear Plant with Changing Dynamics
Vytautas Kaminskas, Raimundas Liutkevičius · 2002
This paper analyses the control of nonlinear plant with the changing dynamics. Adaptive controllers, based on fuzzy logics, are synthesized for the control of air pressure and water level. Their satisfactory efficiency is experimentally demonstrated under different working conditions. Fuzzy controllers are compared to conventional PI and PID controllers. Water level and air pressure control is a classical problem in control engineering. These problems are usually analyzed in literature in separate cases, mathematical models are defined for water level or air pressure systems, and digital control methods are investi- gated (Ogata, 1997; Driankov, 1998). In most cases simple control system conditions are assumed, such as natural water/air flow, not affected by additional forces. The control problem becomes more complex if water level and air pressure control are considered in one system. In such case the change of water level or air pressure set point, changes the dynamics of the whole system and this requires the adaptation of controller parameters. When water flows through pipes, the silt gathers on inner side decreasing its diameter and herewith the amount of flowing water. This feature changes the dynamics of the flow system and stipulates an adaptation of controller parameters. In this paper the effect of such phenomenon on control system is also analyzed. In this paper adaptive fuzzy controllers are introduced as an alternative for the water level and air pressure control. In the absence of sufficiently precise process mathemati- cal model and in the presence of non-linearity, fuzzy logic based control usually have an advantage over conventional PI or PID control (Ogata, 1997; Chen, 2001). The primary control problem, considered with this control system, is regulating both water level and air pressure at the specified set points. The secondary problem is that of decreasing vari- ations of manipulated variables, as these affect the useful life - time of physical devices, in this case water and air pumps.