Study of a Simulation Tool To Determine Achievable Control Dynamics and Control Power Requirements With Perfect Tracking

ABSTRACT This paper contains a study of two methods for use in a genericnonlinear simulation tool that could be used to determine achievablecontrol dynamics and control power requirements while performingperfect tracking maneuvers over the entire flight envelope. The twomethods are NDI (nonlinear dynamic inversion) and the SOFFT(Stochastic Optimal Feedforward and Feedback Technology)feedforward control structure. Equivalent discrete and continuousSOFFT feedforward controllers have been developed. These equivalentforms clearly show that the closed-loop plant model loop is a plantinversion and is the same as the NDl formulation. The main difference isthat the NDl formulation has a closed-loop controller structure whereasSOFFT uses an open-loop command model. Continuous, discrete, andhybrid controller structures have been developed and integrated into theformulation. Linear simulation results show that seven differentconfigurations all give essentially the same response, with the NDIhybrid being slightly different. The SOFFT controller gave bettertracking performance compared to the NDI controller when a nonlinearsaturation element was added. Future plans include evaluation using anonlinear simulation.