Mu-synthesis of robust decentralised PI controllers

A new tuning method for robust decentralised PI controllers is given. The c ontroller tunings are obtained by minimising a robust performance criterion . The cost function to be minimised is derived from the standard mu-synthes is criterion and it takes into account the process uncertainty and the desi red performance. A constraint on the variations of the controller outputs c an also be added to the performance criterion. The two options, with and wi thout a constraint, respect the specifications in a minimal way to limit th e controller output variations obtained from the standard mu-synthesis crit erion. These two options and the standard mu-synthesis criterion are compar ed on an ill-conditioned two-input two-output (TITO) process example. The g eneralised step response for TITO processes is used to analyse the time beh aviour of closed-loop systems.