Modification of classical two loop lateral missile autopilot design using reduced order observer (DGO) and LQR

A flight path rate demand modified two-loop lateral missile autopilot design methodology for a class of guided missile, based on state feedback, reduced order Das & Ghosal observer (DGO) and Linear Quadratic Regulator (LQR), is proposed. The open loop undamped model of two-loop autopilot has been stabilized by using pole placement and state feedback. The non-minimum phase feature of rear controlled missile airframes is analyzed. The LQR technique is adopted to ensure optimal pole placement such that the adverse effect of non-minimum phase property on the response of missile autopilot can be reduced considerably and also the system stability can be made better. The overall response of the two-loop autopilot has been significantly improved over the previous ones. Performance (both transient and steady state) comparisons among the classical two loop design, two-loop design using state feedback & Ackermann approach and the present one, are made. Reduced order Das & Ghosal observer (using Generalized Matrix Inverse) is implemented successfully in this design. A program has been developed to find out the appropriate state vector & control input weightage matrices which will give the optimal pole positions and feedback gains according to the desired time domain performance specifications. Finally a numerical example has been considered and the simulated results are discussed in details.