The design of a Sliding Mode Fuzzy Logic Controller (SMFLC) is considered for the control of the biomass in an unstable continuous bioreactor exhibiting output multiplicity. Bioreactors are characterized by high nonlinearities and are often subjected to parameter uncertainties and disturbances. The control of such processes is often difficult to achieve with traditional linear control techniques. A conventional Sliding Mode Controller (SMC) is first designed and integrated with fuzzy logic to achieve a SMFLC. The controllers are then compared by simulation. Set point step changes and external disturbances are considered in the study. The good performance of the SMFLC for the nonlinear system is demonstrated, especially for its ability to reject disturbances. Compared to the SMC, the SMFLC is faster and more robust, showing the best values of the performance indexes.
