The Application of Model-Based Observer Control to Bioreactors

The application of model-based observer (MBO) control to bioreactors is proposed. In this control strategy, a model is used to infer process information on-line. The model employed in this work was built within the modelling framework CELCYMUS and is used to predict cell age distribution on-line. A copy of the model is used as the process; the control strategy is thus applied to a simulated bioreactor. The MBO controller encompasses an algorithm to adapt the model and another to control the process. These algorithms are developed and tested separately; batch and repeated batch operation are considered. The model is successfully adapted except when manipulating parameters directly related to the model structure. Process control is achieved by manipulation of a process parameter with respect to cell age distribution; additionally using set point error leads to either the same or worse process perfon-nance. The above algorithms are subsequently integrated into an overall MBO control algorithm. In general, their interaction is minimal, although it results in successful adaptation for the parameters related to model structure. The MBO control algorithm developed is capable of enhancing process performance even when considering, separately or in combination, low sampling frequencies, presence of noise, presence of hidden mismatches, presence of human errors and a wide range of operational conditions. The objectives of this dissertation have been met. On-line prediction of cell age distribution has proven paramount in controlling a simulated bioreactor. In fact, it was concluded that it would be advantageous to control the process uniquely based on this information, disregarding set point error. The results obtained pre-empt success for the application of MBO control to bioreactors.

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