Load-bound Fuzzy Logic Control of an Industrial Nonlinear Plant

Most industrial plants have load dependent nonlinear characteristics. In the present research a Sugeno fuzzy logic controller (FLC) on the principle of parallel distributed compensation (PDC) is developed that considers the variance in the load and the plant nonlinearity. It consists of separate controllers for each boundary load and a PDC-based soft blender for their common control action as a function of the load. The controllers are designed for the boundary loads. First, PI PDC are developed to better compensate the plant nonlinearity based on, derived and validated from experimental data, Takagi-Sugeno-Kang (TSK) plant models. The PI PDC replicates the TSK plant model structure but with local PI controllers tuned with respect to the corresponding TSK local linear plant models. Second, PI controllers are designed based on the mean values of the TSK local plant models parameters. The suggested PDC load-bound controllers PI PDC and PI are applied for the control of level in a carbonisation column for soda ash production. The simulation investigations show that the PDC load-based PI PDC compensates best the system nonlinearity and improves its robustness to changes in the load compared to the PDC load-bound PI and the ordinary PDC and PI control systems designed for one load.