Output feedback control

Abstract

Output feedback design methods are needed when the states are not available for feedback. There are many output feedback control design approaches. This chapter presents three design methods that have proven to be useful in developing output feedback flight control designs in aerospace applications. The first method is called projective control. This method is used to replicate the eigenstructure of a state feedback controller using static and/or dynamic output feedback. By selecting the dominant eigenvalues and associated eigenvectors from the state feedback design, the projective control retains those performance and robustness properties exhibited by that eigenstructure. For static output feedback, a partial eigenstructure can be retained equal to the number of feedback variables. For dynamic output feedback, a low-order compensator can be built that retains the entire state feedback eigenstructure. The second and third methods are based upon linear quadratic Gaussian with Loop Transfer Recovery (LQG/LTR). Both these methods use an optimal control state feedback control implemented with a full-order observer called a Kalman filter to estimate the states needed in the control law. These two variants of LQG/LTR have very different asymptotic properties for recovering frequency domain loop properties.