Consider a unity feedback control system with plant transfer function G(s) and controller transfer function Gc(s).
(a) If the phase margin and crossover frequency are adequate but you need to increase the error constant, which compensator would you use and how would you design it?
(b) If the phase margin and crossover frequency of a type-zero feedback system are adequate but you want to achieve zero-steady-state error to step inputs, which compensator would you use and why?
(c) If you want to increase the phase margin at a desired crossover frequency, which compensator would you use and how would you design it?