A fuzzy self-tuned PI controller for regulation of a nonlinear bioreac
tor is presented. The basic idea is to parameterize Ziegler-Nichols li
ke tuning formula by two parameters alpha and beta and then to use an
on-line fuzzy inference mechanism to tune the PI Controller parameters
k(epsilon) and tau(I). The fuzzy self-tuning method takes the process
output error as input and the tuning parameters alpha and beta as out
puts. Simulation studies on the nonlinear bioreactor model equations s
how that the present method is superior to that of fixed parameters co
nventional PI controller (based on transfer function) for both servo a
nd regulatory problems. The present fuzzy logic controller is robust t
o process parameters uncertainties and to changes in magnitude and dir
ection of the disturbances.