What is doyle-stein observer?

Answer 1

Its an observer that is robust to variation in the input matrix B of the state space representation. An observer is a Doyle-Stein Observer when it satisfy:

K*inv(I+C*Phi*K)=B*inv(C*Phi*B)

Where Phi = inv(sI-A) and K is the observer gain.

If this conidtion is meet, the observed state is independent of B