Fractional order PD control of an isotope separation columns cascade

Cryogenic isotope separation columns are unique equipments used to produce enriched substances in the isotope of interest for many industrial applications. The control of an isotope separation column is a difficult and challenging task, being a highly nonlinear plant with large time constants and time delays. A single column can enrich only to a low level of concentration, so column cascades are used for high purity final products. A cascade of three isotope separation columns due to the interdependencies between them represents an even more difficult process to control. Due to the fact that in prior studies fractional order controllers have been successfully implemented for a single isotope separation column, the present paper addresses the development of a control system for the isotope separation column cascade using fractional order PD controllers. As design parameters were imposed the phase margin, gain crossover frequency and robustness of process gain variations. The simulation results, evaluated using the nonlinear mathematical model of the process, including all process input effects, prove the efficiency of the method.