Robust Control of a High-Purity Distillation Column Using μ-Synthesis

Distillation control is a challenging undertaking given the inherent nonlinearity of the process, severe coupling present for dual-composition control and the sensitivity of disturbances. Among various distillation operations, management of the high-purity column poses a difficult control situation due to a number of characteristics of these systems, including strong directionality, ill-conditioning and strongly nonlinear behaviour. In this paper, a diagonal PID controller is designed and analysed for ahigh-purity distillation column by computing the structured singular value μ introduced by Doyle (1982). For this purpose, a structured uncertainty model has been developed which describes the dynamics of the column for the entire operating range. The achievable manageable performance is also defined in terms of the Hf-norm of the weighted sensitivity function.