Modified Design of Three Loop Lateral Missile Autopilot based on LQR and Reduced Order Observer (DGO)

– A flight path rate demand modified three-loop lateral missile autopilot design methodology for a class of guided missile, based on state feedback, output feedback, reduced order Das & Ghosal observer (DGO) and Linear Quadratic Regulator (LQR), is proposed. The open loop undamped model of three-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 three-loop autopilot has been significantly improved over the previous ones. The flight path rate (as well as the lateral acceleration) has reached the commanded unit step input without compromising on its settling time thus it has been able to eliminate the steady state error. Performance (both transient and steady state) comparisons among the classical two loop design, three-loop design using frequency domain approach and the present one, are made. Reduced order Das & Ghosal observer is implemented successfully in this design. A program has been developed to find out 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. Keywords–– Three Loop Pitch Missile Autopilot , Non-minimum phase system, Angle of attack, Latex demand, Flight path rate demand loop, Rate Gyro, Accelerometers, Aerodynamic control, Luenberger Observer, Das & Ghosal Observer, Generalized Matrix Inverse, LQR, Ackermann.