Problem 3 (25 pts): We consider the following process: y2(s)=2s+13u(s)y1(s)=8s+1y2(s)+2d(s) The measurement dynamics (for y1,y2 and d ) are all first-order with time constant 0.5. The objective is to use u to control y1 at the setpoint y1s. We consider three alternative control structures (subscript m denotes measurement): Control structure 1: Feedback only, u=c(s)(y15y1m), where c(s) is a PI controller. Control structure 2: Cascade control. Slave loop: u=c2(s)(y2sy2m), where c2(s) is a PI-controller. Master loop: y2s=c1(s)(y1sy1m) where c1(s) is a PI controller. Control structure 3: Feedforward control, u=cFF(s)dm. (a) Make block diagrams for the process and of the of the three structures. (b) Suggest settings for the four controllers (don't forget to include the measurement dynamics when tuning the controllers). (c) Which structure would you choose and why? Would you suggest using a PID controller instead of a PI for any of the three feedback controllers