Fixed poles of H2 optimal control by measurement feedback

This paper is concerned with the flexibility in the closed loop pole location when solving the H2 optimal control problem (also called the H2 optimal disturbance attenuation prob­ lem) by proper measurement feedback. It is shown that there exists a precise and unique set of poles which is present in the closed loop system obtained by any measurement feedback solution of the H2 optimal control problem. These "H2 optimal fixed poles" are character­ ized in geometric as well as structural terms. A procedure to design Hi optimal controllers which simultaneously freely assign all the remaining poles, is also provided.