Saturation protection with pseudo control hedging: A control allocation perspective

In this paper, we derive a simple direct relationship between the pseudo control hedging signal and the pseudo control command, for a linear feedforward-feedback structure with a hedged linear reference model. The derivation indicates that, the hedging signal will slow down the pseudo control command with the low pass filtered hedging signal, given appropriately chosen bandwidths of the reference model and the error controller. Based on this observation, we propose a hedging structure with the saturation-induced algebraic control allocation error, which automatically triggers the protection, yet only when input saturations enter. In a steady state flight, the protection should exactly reduce the pseudo control command with the allocation error. Simulation results show that the hedged structure performs identically to the unhedged structure during nominal unsaturated operations, whereas the closed-loop performance with hedging shows a significant improvement, when input saturations are provoked due to harsh maneuvers and effector failures.