Two-degree-of-freedom design method of LQI servo systems: Use of frequency-dependent weighting matrices for sensitivity reduction

Missile attitude control via a hybrid LQG-LTR-LQI control scheme with optimum weight selection

“…In Huerta et al [25] a modified LQG as a servo controller has been proposed along with an integrator for guaranteed tracking performance. The concept can be considered as somewhat similar to the LQI scheme for the deterministic case [26]- [27]. The schematic diagram of classical state-feedback control to LQG regulator and finally LQG servo control as a hybridization of LQG and LQI is shown in Fig.…”

“…The tracking can be enforced by externally tuning the LQR weights using an optimization algorithm but the tracking cannot be guaranteed under parametric variation in the system matrices unless the controller contains a built-in proportional-integralderivative (PID) type scheme or its variants like a simple PI or at least an integral control [23]- [24]. To overcome the tracking problem in state-feedback control, the LQI scheme is proposed which considers the presence of an integrator in the forward path and acts as an output feedback controller beside the statefeedback controller implemented on either directly measured or observed states [25]- [27]. As a summary, the missile attitude control scheme must have a state-observer and state-feedback control (LQG), improved stability margin (LTR) and guaranteed tracking (LQI).…”