RST controller
The block diagram of a two degree of freedom RST controller is as follows:
where B/A is the plant model and R,S and T are the polynomials of q-1.
R(q-1) = r0+r1q-1+...+rnrq-nr
S(q-1) = 1+s1q-1+...+snsq-ns = 1+q-1S'(q-1)
T(q-1) = t0+t1q-1+...+tntq-nt
The control input u(t) is computed by:
u(t)=-S'(q-1)u(t)+T(q-1)r(t)-R(q-1)y(t)
The main advantage of this representation (RST form) is that all type of controllers can be represented by an RST controller. For example, a controller K=R/S in feedforward with unit feedback is equivalent of chossing T=R and a controller K=R/S in feedback is equivalent of chossing T=S and etc.
See: Closed loop identification module .
(file rst.htm)