Modification of Classical Two Loop Autopilot Design using PI Controller and Reduced Order Observer (DGO)

– A flight path rate demand modified two-loop lateral missile autopilot design methodology for a class of rear controlled guided missile, based on state feedback, output feedback, reduced order Das & Ghosal observer (DGO) and PI controller 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. An optimal pole placement has been done through an iterative method 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 modified two-loop autopilot has been significantly improved over the previous ones specially the flight path rate and body rate. 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. The system can now also cop up with the body rate demand and even the Maximum body rate demand is decreased to a great extent as compared to the classical two-loop design. Reduced order Das & Ghosal observer (DGO), using Generalized Matrix Inverse) 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––Two Loop Pitch Missile Autopilot, Non-minimum phase system, Flight path rate, Body Rate, Rate Gyro, Accelerometers, Luenberger Observer, Das & Ghosal Observer, Generalized Matrix Inverse, PI controller.