“…Further improvement of the PID controller is sought by applying advanced control designs (Ge et al, 2002;Hara et al, 2006;Wang et al, 2007;Goncalves et al, 2008). In order to design with robust control theory, the PID controller is expressed as a state feedback control law problem that can then be solved by using any full state feedback robust control synthesis, such as Guaranteed Cost Design using Quadratic Bound (Petersen et al, 2000), H ∞ synthesis (Green & Limebeer, 1995;Zhou & Doyle, 1998), Quadratic Dissipative Linear Systems (Yuliar et al, 1997) and so forth. The PID parameters selection by www.intechopen.com Robust Control, Theory and Applications 70 transforming into state feedback using linear quadratic method was first proposed by Williamson and Moore in (Williamson & Moore, 1971).…”