A hybrid method based on evolutionary algorithms is developed in this study. Two additional operations, an acceleration operation and a migration operation, are embedded into the original version of differential evolution. These two operations are used for the improvement of the convergence speed without decreasing the diversity among the individuals. The acceleration operation is used to speed up convergence. However, the migration operation is used to increase the diversity among the individuals. The hybrid method is applied to estimate the parameters of the Monod model of a recombinant fermentation process. The model pro®les based on 50% variations of the initial concentrations of glucose can ®t the experimental observations satisfactorily.
IntroductionEstimation of kinetic parameters is always required for the development of bioreaction modeling. The mathematical estimation of model parameters is based on minimization of some quantity, which is a function of parameters to be estimated. If the model under consideration is linear, the estimation is generally an easy task. Linear regression or plot procedures are well known and do not pose any important problems of use for such models. There exists, however, no unique method for nonlinear models. Several approaches have been suggested to estimate kinetic parameters of nonlinear models.There has been widespread interest from the control community in applying evolutionary algorithms (EAs) to solve the problem of control system engineering [1]. EAs are a class of stochastic search and optimization methods that includes genetic algorithms [2], evolutionary programming [3], evolution strategies [4], genetic programming [5], and their variants [6]. These algorithms, based on the principles of natural biological evolution, have received considerable and increasing interest over the past decade. Compared to traditional search and optimization methods, such as calculus-based and enumerative strategies, the EAs are robust, global, and generally more straightforward to apply in situations where there is little or no a-priori knowledge about the process to be controlled. For the control engineer, EAs present opportunities to address some classes of problems that are not amenable to ef®cient solution by the application of conventional techniques. In recent years, EAs have been applied to a broad range of activities in control system engineering, including parametric optimization [7], robust control analysis [8], system identi®cation [9], and optimal control [10,11].Differential evolution (DE) developed by Stron and Price [6] is one of the most excellent EAs. DE turned out to be one of the best genetic algorithms for solving the real-valued test function suite of the ®rst International Contest on Evolutionary Computation, which was held in Nagoya, Japan, 1996. This method has proved to be a promising candidate to solve real-valued optimization problems. The computational algorithm of DE is very simple to understand and implement. Only a few parameters in this algorithm are re...