Comparison of open loop optimal control and closed loop optimal control of a fermentation process

Optimisation of a fed-batch fermentation process is usually done by using the calculus of variations to determine an optimal feed rate profile. This often results in a singular control problem and an open loop control structure. To overcome these problems, the closed loop optimal control is developed by dividing the optimisation problem into two parts. First, an optimal substrate concentration profile which has direct effect on the biochemical reactions in the fermentation process is derived. Then a controller is designed to track the obtained optimal profile. A biomass production process is used to compare the performance of the closed loop optimal control method and the open loop optimal feed rate control method. The results show a better performance of the closed loop optimal control than the open loop optimal feed rate profile. This is due to the feedback property of the closed loop optimal control method.