A Spatio-Temporal Fuzzy Logic Control System And Its Applications

A variety of industrial processes are inherently spatio-temporal systems or distributed parameter systems (DPS) where their states, controls, outputs and process parameters may vary temporally and spatially, such as many thermal, fluid flow and chemical reactor processes. The distributed parameter process is traditionally controlled with model-based methods, within which a precise mathematical model of the process is required. However, a precise mathematical model can not be obtained due to unknown uncertainty, nonlinearity and disturbances. When there are strong unknown uncertainties in the process, the performance will deteriorate. As an intelligent method, the fuzzy logic controller (FLC) is widely used in industrial processes due to its inherent robustness under unknown environment. Though some studies have been presented about application of type-1 FLCs to DPS control, however, these type-1 fuzzy approaches are not inherently designed for the spatially distributed dynamic process because of their two-dimensional (2D) nature. Thus, a new spatio-temporal fuzzy logic system (FLS) is proposed to control DPS. Without additional complexity, the spatio-temporal FLS can process spatial information by adding some sensors for measurement, which may reduce cost.The novelty of the spatio-temporal FLS mainly includes the following four parts:1) A spatio-temporal FLS is built.A novel application of type-2 FLS is presented by developing a spatio-temporal FLS to control a class of DPS. The key difference to the previous type-2 fuzzy system is that the secondary membership function describes a different physical variable - space domain. A spatio-temporal fuzzy set consists of a temporal (primary) membership function and a spatial (secondary) membership function. Since its secondary membership function is designed for the spatial domain, it has some different definitions and operations from the previous type-2 application. The type-reduction will become the spatial reduction before the traditional defuzzification. This spatio-temporal FLS is successfully applied to a catalytic reaction rod to demonstrate its effectiveness and potential to a wide range of engineering applications on modeling and control of DPS.2) A spatio-temporal FLC is designed. And its model is derived.A three domain FLC is proposed based on the spatial fuzzy set for the spatially distributed systems. An analytical mathematical model of the spatio-temporal FLC is derived using an extended graphic analytical method. The model of the spatio-temporal FLC is characteristic of a global sliding mode control techniques. A catalytic reactor is given to demonstrate the effectiveness of the spatio-temporal FLC and the proposed tuning method by comparing with other controller.3) An inherent saturation of the traditional FLC is revealed. And an efficient tuning method is proposed for fuzzy PID controller.An inherent saturation of the traditional FLC is revealed due to the finite fuzzy rules used. An equivalent structure and model of the fuzzy rule base is derived to show a saturation property. The bandwidth of the fuzzy PID control system can be adjusted by changing saturation parameter. An internal model control (IMC) based tuning method is proposed to auto-tune the fuzzy PID controller in this paper. The simulation and experiment results demonstrate these amazing effects of the inherent saturation, the proposed tuning method, and its influence to the robustness of fuzzy PID controller.4) A tuning method is proposed for spatio-temporal fuzzy PID controller.A spatio-temporal fuzzy PID controller and its tuning method are proposed to control a class of DPS. An analytical mathematical model of the 3D fuzzy PID controller is first obtained after simple derivation. Then, a spatial first-order plus delay time (FOPDT) model is proposed to tune the spatio-temporal fuzzy PID controller. An extension Nyquist principle is used to design parameter of the spatio-temporal fuzzy PID controller based on the FOPDT model. The stability of the fuzzy PID control system is analyzed using the Lyapunov stability theory. Finally, the simulation and experiment results demonstrate the effectiveness of the spatio-temporal fuzzy PID control and the proposed tuning method by comparing with other controller.