Application of plant inversion via output-redefinition to missile autopilot

Abstract

In this paper, nonlinear tracking control techniques developed for the control of nonlinear nonminimum systems have been applied to the autopilot design of a tail-controlled skid-to-turn(STT) missile system. The difficulties in the application of inversion-based control methods due to nonminimum phase characteristics are also discussed. To avoid the instability problems associated with unstable zero dynamics, plant inversion is applied with output-redefinition method. The output-redefinition method gives us an indirect way to apply the plant inversion controls to nonminimum phase plants by redefining the plant output such that the tracking control of the modified output ensures the asymptotic tracking of the original output. However, the robustness characteristics of the output-redefinition technique has not been well studied yet. The robustness problems of the output-redefinition method against uncertain aerodynamic coefficients of the missile are briefly investigated and an auxiliary robust control loop using classical proportional-integral error feedback controller is suggested to remedy the problems. The performance of the output-redefinition method compared with other pre-established plant inversion techniques is verified through numerical simulation.