The development of linear model of the present JET electromagnetic system has allowed the design of an optimized Plasma Shape Controller. Quite extreme plasma boundaries (elongation k=1.9 and triangularity <d> = 0.6) are shown to be controllable also in the presence of large variations of the values of poloidal beta (0.1<bp<0.6) and/or internal magnetic inductance (0.8<li<1.4). The developed model gives also an excellent simulation of the growth rate of the experimental vertical disruptions.