The problem of robust multiloop proportional-integral-derivative (PID) cont
roller tuning for multivariable processes is addressed in this paper. The p
roblem is formulated in the H-infinity control framework, and the controlle
r parameters are determined based on both user-specified performance and ro
bust stability. The PID settings are computed by solving a nonlinear optimi
zation problem with matrix inequality constraints, using a successive semid
efinite programming approach. The proposed method is illustrated by a simpl
e case study that investigates robust PID control of a distillation column.